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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 5 — Mar. 2, 2009
  • pp: 3679–3689
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Optical visualization of Alzheimer’s pathology via multiphoton-excited intrinsic fluorescence and second harmonic generation

Alex C. Kwan, Karen Duff, Gunnar K. Gouras, and Watt W. Webb  »View Author Affiliations


Optics Express, Vol. 17, Issue 5, pp. 3679-3689 (2009)
http://dx.doi.org/10.1364/OE.17.003679


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Abstract

Intrinsic optical emissions, such as autofluorescence and second harmonic generation (SHG), are potentially useful for functional fluorescence imaging and biomedical disease diagnosis for neurodegenerative diseases such as Alzheimer’s disease (AD). Here, using multiphoton and SHG microscopy, we identified sources of intrinsic emissions in ex vivo, acute brain slices from AD transgenic mouse models. We observed autofluorescence and SHG at senile plaques as well as characterized their emission spectra. The utility of intrinsic emissions was demonstrated by imaging senile plaque autofluorescence in conjunction with SHG from microtubule arrays to assess the polarity of microtubules near pathological lesions. Our results suggest that tissues from AD transgenic models contain distinct intrinsic emissions, which can provide valuable information about the disease mechanisms.

© 2009 Optical Society of America

1. Introduction

Alzheimer’s disease (AD) is a prevalent neurodegenerative disease for which there is no known cure. Patients usually suffer from dementia, along with other behavioral changes, so examinations on memory and cognitive abilities are standard tests for diagnosing AD. However, confirming the initial diagnosis of the actual cause of dementia is often difficult. Definitive confirmation is possible with post-mortem autopsy, where histology on brain tissues reveals senile plaques and neurofibrillary tangles (NFT), the two hallmark pathological lesions in AD. As a result, there are strong incentives to develop reliable methods for early diagnosis of AD. To address this need, new approaches are being developed. Positron emission tomography (PET) imaging of Pittsburgh Compound-B has been shown to bind amyloid-beta deposits in human patients in vivo [1

1. M. D. Ikonomovic, W. E. Klunk, E. E. Abrahamson, C. A. Mathis, J. C. Price, N. D. Tsopelas, B. J. Lopresti, S. Ziolko, W. Bi, W. R. Paljug, M. L. Debnath, C. E. Hope, B. A. Isanski, R. L. Hamilton, and S. T. DeKosky, “Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer’s disease,” Brain 131, 1630–1645 (2008). [CrossRef] [PubMed]

]. Optical imaging with amyloid-beta deposit-specific near-infrared optical probes is being developed and has generated some successes in transgenic mouse models [2

2. M. Hintersteiner, A. Enz, P. Frey, A. L. Jaton, W. Kinzy, R. Kneuer, U. Neumann, M. Rudin, M. Staufenbiel, M. Stoeckli, K. H. Wiederhold, and H. U. Gremlich, “In vivo detection of amyloid-beta deposits by near-infrared imaging using an oxazine-derivative probe,” Nat. Biotechnol. 23, 577–583 (2005). [CrossRef] [PubMed]

]. These new imaging approaches use exogenous compounds that can selectively label pathological lesions and therefore enhance signal-to-noise. Alternatively, endogenous optical signals may also provide contrast between AD and normal tissues. For example, one recent study [3

3. E. B. Hanlon, L. T. Perelman, E. I. Vitkin, F. A. Greco, A. C. McKee, and N. W. Kowall, “Scattering differentiates Alzheimer disease in vitro,” Opt. Lett. 33, 624–626 (2008). [CrossRef] [PubMed]

] reports that transmission and reflectance spectra in near-infrared region from unstained in vitro tissue slab samples may be useful in distinguishing AD from normal tissues, although the molecular origin of this observation was not specified. Interpreting this type of studies is difficult due to a lack of information about intrinsic emissions from AD tissues, which has only been recently investigated in detail in normal tissues [4

4. W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T. Hyman, and W. W. Webb, “Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation,” Proc. Natl. Acad. Sci. 100, 7075–7080 (2003). [CrossRef] [PubMed]

].

It is generally known that brain tissues contain various endogenous proteins that can generate autofluorescence and/or second harmonic emissions. It is possible that these endogenous optical signals can provide contrast between normal and AD tissues. Moreover, if applied to AD tissues, intrinsic emissions may provide functional information that is useful in understanding the disease mechanisms. For example, fluorescence from NAD(P)H, an electron carrier that is crucial in metabolic pathways, has been used to investigate the dynamics of functional brain energy metabolism [5

5. K. A. Kasischke, H. D. Vishwasrao, P. J. Fisher, W. R. Zipfel, and W. W. Webb, “Neural activity triggers neuronal oxidative metabolism followed by astrocytic glycolysis,” Science 305, 99–103 (2004). [CrossRef] [PubMed]

, 6

6. H. D. Vishwasrao, A. A. Heikal, K. A. Kasischke, and W. W. Webb, “Conformational dependence of intracellular NADH on metabolic state revealed by associated fluorescence anisotropy,” J. Biol. Chem. 280, 25119–25126 (2005). [CrossRef] [PubMed]

]. Second harmonic generation (SHG) emitted from microtubules has been used to map the distribution of polarized microtubule arrays in acute brain tissues from mice of various ages [7

7. D. A. Dombeck, K. A. Kasischke, H. D. Vishwasrao, M. Ingelsson, B. T. Hyman, and W. W. Webb, “Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy,” Proc. Natl. Acad. Sci. 100, 7081–7086 (2003). [CrossRef] [PubMed]

, 8

8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

].

2. Materials and methods

2.1. Multiphoton and second harmonic microscope

Imaging was performed on a custom-built multiphoton microscope based on a commercial laser beam scanning unit (Bio-Rad MRC 1024) and an inverted microscope (Olympus, IX-70). Trains of laser pulses at 80MHz and ~100fs duration were generated by a mode-locked Ti:Sapphire laser (Spectra-Physics Tsunami), which was pumped by a 5W diode laser (Spectra-Physics Millennia). Intensity and polarization were controlled by a Pockels cell (Conoptics 350-50) and a Berek compensator (New Focus 5540). The beam was focused onto the sample by an Olympus UApo/340 20X/NA 0.7 water immersion objective, which also collected the epi-fluorescence. The transmitted SHG was collected by an Olympus XLUMPlanFl 20X/NA 0.95 dipping objective. The average power after the objective was ~70–130mW. For imaging, samples were excited at 774nm and signals were detected with bi-alkali photomultiplier tubes (Hamamatsu HC125-02). SHG was collected behind a focusing lens, an IR-blocking short-pass dichroic and a narrowband emission filter, centered at 387nm (Semrock FF720 and FF01-387/11). Autofluorescence was collected from 400-550nm behind a blue glass filter (Chroma BGG22).

Emission spectra were obtained using a liquid nitrogen-cooled CCD spectrometer (Jobin Yvon Spex270M). The spectrometer was coupled to the microscope via an optical fiber replacing the usual bi-alkali photomultiplier in the transmission-direction. To collect one spectrum, a small square area ~50μm wide was continuously scanned at high zoom for 10 seconds. To reduce photodamage, excitation wavelength was set at 830nm and average power was reduced to ~25mW. Dark counts were subtracted by acquiring a blank spectrum with shutter closed. The spectrometer was calibrated with collagen SHG spectra collected from a rat tendon sample.

2.2. Tissue preparation

Acute brain slices were prepared from 12 mice, including one with APP Swedish mutation [14

14. K. Hsiao, P. Chapman, S. Nilsen, C. Eckman, Y. Harigaya, S. Younkin, F. Yang, and G. Cole, “Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice,” Science 274, 99–102 (1996). [CrossRef] [PubMed]

] (obtained from G. K. Gouras), two with APPSwe/PS1 double mutations [15

15. D. R. Borchelt, T. Ratovitski, J. van Lare, M. K. Lee, V. Gonzales, N. A. Jenkins, N. G. Copeland, D. L. Price, and S. S. Sisodia, “Accelerated amyloid deposition in the brains of transgenic mice coexpressing mutant presenilin 1 and amyloid precursor proteins,” Neuron 19, 939–945 (1997). [CrossRef] [PubMed]

] (ordered from Jackson Laboratory), two with APPSwe/TauJNPL3 double mutations [16

16. J. Lewis, D. W. Dickson, W. L. Lin, L. Chisholm, A. Corral, G. Jones, S. H. Yen, N. Sahara, L. Skipper, D. Yager, C. Eckman, J. Hardy, M. Hutton, and E. McGowan, “Enhanced neurofibrillary degeneration in transgenic mice expressing mutant tau and APP,” Science 293, 1487–1491 (2001). [CrossRef] [PubMed]

] (obtained from K. Duff), and three with APPSwe/PS1/Tau triple mutations [17

17. S. Oddo, A. Caccamo, J. D. Shepherd, M. P. Murphy, T. E. Golde, R. Kayed, R. Metherate, M. P. Mattson, Y. Akbari, and F. M. LaFerla, “Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction,” Neuron 39, 409–421 (2003). [CrossRef] [PubMed]

] (obtained from G. K. Gouras), and four wild-type mice. All mice were at least 1-year old. All preparations were performed in accordance with Cornell University animal use regulations (IACUC protocol 00-46-03).

To prepare acute slices, we removed the brain following CO2 euthanasia. Immediately, the brain was dipped in iced artificial cerebrospinal fluid (ACSF) composed of (in mM): NaCl, 120; KCl, 2.5; NaH2PO4, 1; MgSO4, 1.3, NaHCO3, 25; D-glucose, 10; CaCl2, 2.5, that was saturated with 95% O2 and 5% CO2. Transverse hippocampal slices 300–400μm thick were cut using a vibratome (Campden Instruments). Slices were then incubated in oxygenated ACSF at 35°C for 1 hour. During imaging, slices were held under nylon grid anchors in a flow chamber (Warner Instruments) and perfused with oxygenated ACSF at room temperature.

3. Results

3.1. Autofluorescence and SHG in acute brain slices of AD mouse models

Acute hippocampal slices from transgenic AD mouse models show a distinct pattern of autofluorescence and SHG emissions (Fig. 1). Four sources of emissions can be identified by morphology: senile plaques, lipofuscins, microtubules, and blood vessels. Senile plaques appear as spherical objects with diameter ~30–70μm that emit a diffuse autofluorescence. Lipofuscin is small, bright, and densely packed along the pyramidal cell layers. Microtubules are only visible in the SHG channel and are most visible in regions adjacent to the cell layers [7

7. D. A. Dombeck, K. A. Kasischke, H. D. Vishwasrao, M. Ingelsson, B. T. Hyman, and W. W. Webb, “Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy,” Proc. Natl. Acad. Sci. 100, 7081–7086 (2003). [CrossRef] [PubMed]

, 8

8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

]. Blood vessels are sparse and tend to branch with Y-shaped junctions [8

8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

]. When comparing AD mouse models to wild-type mice, autofluorescence from senile plaques is unique to the transgenic models.

Fig. 1. Autofluorescence and second harmonic emissions from acute hippocampal brain slice of transgenic Alzheimer’s disease mouse models. (a) Autofluorescence, (b) second harmonic emissions, (c) and their overlay of the hippocampus of a 17-month old APPSwe/TauJNPL3 mouse. Senile plaques emit autofluorescence (white arrows) that were morphologically distinct from other sources of intrinsic emissions and were missing from wild-type animals, as shown in (d). Each panel is a mosaic of z-projections of a 50μm thick image stack acquired in 10μm steps. Multiphoton excitation wavelength = 774nm, circular polarization.

To confirm the identity of the intrinsically fluorescent structures that morphologically resemble senile plaques, after imaging we fixed the brain slices and stained with plaque-specific dyes Thioflavin-S or BTA-1. Figure 2 compares unstained and stained plaque-burdened regions to show that the autofluorescence originates from senile plaques. Interestingly, a small amount of SHG emission was also seen to be generated by senile plaques.

Fig. 2. Senile plaques emit autofluorescence and second harmonic signal. (a) Autofluorescence and (b) second harmonic emissions detected in the entorhinal cortex in acute slices of a 22-month old APPSwe/TauJNPL3 mouse. (c) Overlay of (a) and (b) shows the same large, round structures (appears as yellow in the overlay) emit both the autofluorescence and second harmonic signals, which were then identified to be senile plaques when (d) this brain slice was subsequently fixed and stained with the plaque-specific dye Thioflavin-S. The small, bright specks were lipofuscins, which did not generate second harmonic emission. (e–h) Autofluorescence and second harmonic signal, of unknown molecular origin, were also detected near a blood vessel that was affected by cerebral amyloid angiopathy. Signal could be emitted from a source similar to that in senile plaque or from collagen. Each panel is a z-projection of a 40–60μm thick image stack acquired in 3 or 4μm steps. Multiphoton excitation wavelength = 774nm, circular polarization.

The number density of intrinsically fluorescent senile plaques is highly variable between different mice, possibly due to the variable stages of disease progression. All mice showed substantial numbers of intrinsically fluorescent senile plaques in the entorhinal cortex and a lesser amount in the neocortex. Senile plaques tend to be sparse or absent in area CA1 in the hippocampus, although a fair number of plaques could be seen in an 18-month-old APPSwe2756/PS1 mouse that was probably in an advanced disease state.

We tested whether our preparation methods could affect the quality of autofluorescence. Senile plaque autofluorescence was seen in slices that were imaged immediately following dissection, i.e. without the 1-hour incubation period. Moreover, the autofluorescence persists after overnight fixation in formaldehyde.

Lipofuscins appeared as small, bright specks in all areas of the brain, but were especially numerous along the CA1 and CA3 layers in the hippocampus. We compared the number density of lipofuscins between transgenic and wild-type mice at similar ages, but found no statistically significant differences (data not shown), which agrees with a published study [19

19. L. M. Drach, J. Bohl, and H. H. Goebel, “The lipofuscin content of nerve cells of the inferior olivary nucleus in Alzheimer’s disease,” Dementia 5, 234–239 (1994). [PubMed]

]. Finally, our group has previously reported [3

3. E. B. Hanlon, L. T. Perelman, E. I. Vitkin, F. A. Greco, A. C. McKee, and N. W. Kowall, “Scattering differentiates Alzheimer disease in vitro,” Opt. Lett. 33, 624–626 (2008). [CrossRef] [PubMed]

] that NFTs in human AD brain tissues are intrinsically fluorescent, but we have not been able to find such examples in our APPSwe/PS1/Tau transgenic models that have been reported to contain NFTs [17

17. S. Oddo, A. Caccamo, J. D. Shepherd, M. P. Murphy, T. E. Golde, R. Kayed, R. Metherate, M. P. Mattson, Y. Akbari, and F. M. LaFerla, “Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction,” Neuron 39, 409–421 (2003). [CrossRef] [PubMed]

]. The lack of autofluorescence here does not necessarily imply a negative result: the mice examined in this work could be at relatively early stages of disease, or they may lack particular tangle pathologies when compared to human tissues. These ideas are addressed in detail in the Discussions section.

3.2. Emission spectrum of autofluorescence from individual senile plaques

Fig. 3. Typical emission spectra of senile plaque autofluorescence. (a) The emission spectra of a senile plaque (red trace) and of an adjacent plaque-free region (blue trace) were measured 50μm beneath the surface of an acute slice from an 18-month-old APPSwe mouse. A typical emission spectrum of the senile plaque autofluorescence, excited at 830nm, peaked at ~520nm and showed detectable SHG emissions at 415nm. After acquiring the spectra, this brain slice was fixed and stained with Thioflavin-S. Emission spectrum of one Thioflavin-S-stained senile plaque, obtained at ~10 times less power and 10 times less acquisition time as the autofluorescence, is shown (black trace, normalized) for comparison. (b) The region in the neocortex of the acute slice where the spectra (red and blue boxes) were taken for (a). (c) The emission spectra for four different conditions recorded from the same mouse: i) emission spectrum at senile plaque, excited at 774nm; ii) emission spectrum at a different senile plaque, excited at 774nm, but with quick acquisition to reduce photodamage; iii) emission spectrum at another senile plaque, excited at 830nm; iv) emission spectrum at a plaque-less location, dominated by autofluorescence, presumably from lipofuscin because of the high emission wavelength. Second harmonic peak in iv) is exaggerated because emission intensity was re-scaled. The actual recorded second harmonic peak was weak, see panel (a), and it may be extraneous signal generated when the spectrometer gratings diffract the intense excitation beam. Arrows indicate the locations of the peak emission wavelengths for the autofluorescence.

In an adjacent region with no plaque, the detected emission is significantly weaker and seems to contain multiple broad peaks. It is likely that lipofuscins contribute to emissions at higher wavelengths and possibly NAD(P)H or flavins contribute to emissions below 500nm (Cf. [4

4. W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T. Hyman, and W. W. Webb, “Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation,” Proc. Natl. Acad. Sci. 100, 7075–7080 (2003). [CrossRef] [PubMed]

]). Comparing the spectra obtained at senile plaques and from adjacent regions showed that autofluorescence can be distinguished from the background by the emission spectrum. We also obtained the emission spectra of senile plaques that were stained with Thioflavin-S following formaldehyde fixation. The Thioflavin-S fluorescence has a relatively narrow spectrum that peaked at ~480nm, which is distinct from the autofluorescence emission obtained from unstained brain slices. Thioflavin-S fluorescence in stained brain slices was significantly brighter than the autofluorescence in unstained brain slices. There was significant difference between the peak emission wavelength and spectral shape of the emissions recorded at plaques from Thioflavin-S-stained and unstained brain slices. This difference confirms that the autofluorescence in unstained brain slices is not fluorescence resulting from Thioflavin-S contamination.

3.3. Functional imaging of intrinsic emissions in AD mouse models

To demonstrate the utility of intrinsic emissions, we imaged SHG emissions from polarized microtubules and autofluorescence from senile plaques to investigate whether the polarity or the morphology of microtubule arrays are affected in AD mouse models. Tau, a microtubule-associated protein, has been implicated as a possible cause for neurodegeneration [20

20. C. Ballatore, V. M. Lee, and J. Q. Trojanowski, “Tau-mediated neurodegeneration in Alzheimer’s disease and related disorders,” Nat. Rev. Neurosci. 8, 663–672 (2007). [CrossRef] [PubMed]

]. Electron microscopy studies have shown that tau can accumulate in postsynaptic locations [21

21. R. H. Takahashi, T. A. Milner, F. Li, E. E. Nam, M. A. Edgar, H. Yamaguchi, M. F. Beal, H. Xu, P. Greengard, and G. K. Gouras, “Intraneuronal Alzheimer abeta42 accumulates in multivesicular bodies and is associated with synaptic pathology,” Am. J. Pathol. 161, 1869–1879 (2002). [CrossRef] [PubMed]

, 22

22. R. H. Takahashi, E. Capetillo-Zarate, M. T. Lin, T. A. Milner, and G. K. Gouras, “Co-occurrence of Alzheimer’s disease beta-amyloid and tau pathologies at synapses,” Neurobiol. Aging, in press (2008).

], and therefore can possibly affect microtubule organization in the dendrites. In neuronal culture models of AD, manipulation of tau expressions or mutations show that microtubules can be depolymerized [23

23. B. Li, M. O. Chohan, I. Grundke-Iqbal, and K. Iqbal, “Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau,” Acta Neuropathol. 113, 501–511 (2007). [CrossRef] [PubMed]

, 24

24. L. Qiang, W. Yu, A. Andreadis, M. Luo, and P. W. Baas, “Tau protects microtubules in the axon from severing by katanin,” J. Neurosci. 26, 3120–3129 (2006). [CrossRef] [PubMed]

], or be forming a star-shaped aster array after reversing polarity [25

25. O. A. Shemesh, H. Erez, I Ginzburg, and M. E. Spira, “Tau-induced traffic jam reflect organelles accumulation at points of microtubule polar mismatching,” Traffic 9, 458–471 (2008). [CrossRef] [PubMed]

]. Such modifications to the microtubule arrays as formation of a star-shaped structure should drastically alter morphology and be directly observable by our imaging technique because SHG emission is a good qualitative indicator of the polarity and number density of microtubules in single neurites [7

7. D. A. Dombeck, K. A. Kasischke, H. D. Vishwasrao, M. Ingelsson, B. T. Hyman, and W. W. Webb, “Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy,” Proc. Natl. Acad. Sci. 100, 7081–7086 (2003). [CrossRef] [PubMed]

, 8

8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

].

Fig. 4. Length and number density of polarized microtubule arrays in area CA1 in Alzheimer’s disease mouse models. (a) Typical autofluorescence (red) and second harmonic emissions (green) in area CA1 from an acute slice of a 21-month-old APPSwe/PS1 mouse. This image is a z-projection of an 18μm thick image stack acquired in 3μm steps. Multiphoton excitation wavelength = 774nm, linear polarization. (b) The length and number density of polarized microtubules in area CA1 of Alzheimer’s disease mouse models (solid dots) and of wild-type mice studied that were over 1 year old (hollow dots). The dotted lines show the trend based on data from a larger set of wild-type mice from our previous study [8].

We initially tested whether it is possible to observe SHG emissions from microtubules near senile plaques stained with Thioflavin-S or BTA-1. We found that even a small amount of plaque-specific dye would emit too much fluorescence, and therefore obscures intrinsic emissions. Therefore, in all of the following imaging experiments, we chose to use unstained brain slices. In unstained acute slices, we were able to image simultaneously intrinsic emissions from polarized microtubules in apical dendrites in area CA1 and senile plaques (Fig. 4). We measured the length and number density of polarized microtubules in this region, using a previously described procedure [8

8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

]. We found that the length of polarized microtubule arrays is 77±13μm (n=6 transgenic AD models) versus 89±9μm (n=4 wild-types) and the number density is 0.053±0.010μm-2 versus 0.062±0.011μm-2. These differences are not statistically significant, although our sample size is small. Interestingly, the three mice that showed the shortest microtubule arrays were the mice with the triple APPSwe2756/PS1/Tau mutations. However, those same mice were also older than most of the mice examined and there were only data from one wild-type littermate of similar age.

Fig. 5. Polarized microtubules in apical dendrites near a senile plaque. A series of images shows second harmonic emissions from polarized microtubules of apical dendrites (green) near an autofluorescent senile plaque (red). The z value denotes the distance to the slice surface. The senile plaque was located in the area CA1 in the hippocampus in an acute slice from a 17-month old APPSwe/TauJNPL3 mouse. Multiphoton excitation wavelength = 774nm, circular polarization.

When focusing on a single senile plaque, we can resolve the polarized microtubule arrays within individual apical dendrites of CA1 pyramidal neurons (Fig. 5). There have previously been studies [26–29

26. T. L. Spires, M. Meyer-Leuhmann, E. A. Stern, P. J. McLean, J. Skoch, P. T. Nguyen, B. J. Bacskai, and B. T. Hyman, “Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy,” J. Neurosci. 25, 7278–7287 (2005). [CrossRef] [PubMed]

] on the morphology of axons and dendrites near a senile plaque. Reported abnormal features in neurite morphology include loss of dendritic spines [26–28

26. T. L. Spires, M. Meyer-Leuhmann, E. A. Stern, P. J. McLean, J. Skoch, P. T. Nguyen, B. J. Bacskai, and B. T. Hyman, “Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy,” J. Neurosci. 25, 7278–7287 (2005). [CrossRef] [PubMed]

], shaft atrophy [28

28. J. Grutzendler, K. Helmin, J. Tsai, and W. B. Gan, “Various dendritic abnormalities are associated with fibrillar amyloid deposits in Alzheimer’s disease,” Ann. N. Y. Acad. Sci. 1097, 30–39 (2007). [CrossRef] [PubMed]

], varicosity and sprouting [27

27. J. Tsai, J. Grutzendler, K. Duff, and W. B. Gan, “Fibrillar amyloid deposition leads to local synaptic abnormalities and breakage of neuronal brances,” Nat. Neurosci. 7, 1181–1183 (2004). [CrossRef] [PubMed]

, 28

28. J. Grutzendler, K. Helmin, J. Tsai, and W. B. Gan, “Various dendritic abnormalities are associated with fibrillar amyloid deposits in Alzheimer’s disease,” Ann. N. Y. Acad. Sci. 1097, 30–39 (2007). [CrossRef] [PubMed]

]. Axons and dendrites seem to be affected differently such that axons frequently have varicosities, which are not seen as often in dendrites [28

28. J. Grutzendler, K. Helmin, J. Tsai, and W. B. Gan, “Various dendritic abnormalities are associated with fibrillar amyloid deposits in Alzheimer’s disease,” Ann. N. Y. Acad. Sci. 1097, 30–39 (2007). [CrossRef] [PubMed]

]. Moreover, there have been conflicting observations as to whether the length and diameter of dendrite shafts are affected [27

27. J. Tsai, J. Grutzendler, K. Duff, and W. B. Gan, “Fibrillar amyloid deposition leads to local synaptic abnormalities and breakage of neuronal brances,” Nat. Neurosci. 7, 1181–1183 (2004). [CrossRef] [PubMed]

, 29

29. A. Alpár, U. Ueberham, M. K. Brückner, G. Seeger, T. Arendt, and U. Gärtner, “Different dendrite and dendritic spine alterations in basal and apical arbors in mutant human amyloid precursor protein transgenic mice,” Brain Res. 1099, 189–198 (2006). [CrossRef] [PubMed]

]. One common theme is that the amount of abnormal features tends to increase dramatically within a ~15μm-diameter region around the senile plaque [26

26. T. L. Spires, M. Meyer-Leuhmann, E. A. Stern, P. J. McLean, J. Skoch, P. T. Nguyen, B. J. Bacskai, and B. T. Hyman, “Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy,” J. Neurosci. 25, 7278–7287 (2005). [CrossRef] [PubMed]

, 27

27. J. Tsai, J. Grutzendler, K. Duff, and W. B. Gan, “Fibrillar amyloid deposition leads to local synaptic abnormalities and breakage of neuronal brances,” Nat. Neurosci. 7, 1181–1183 (2004). [CrossRef] [PubMed]

].

4. Discussion

We have shown that autofluorescence and SHG emissions can be excited and imaged by multiphoton microscopy in acute brain slices of transgenic AD mouse models. More specifically, we confirmed that senile plaques exhibit autofluorescence with a distinct emission spectrum and also weakly generate SHG. This autofluorescence was seen in all four of the transgenic mouse models examined; therefore suggesting this type of intrinsic emission is a general property. This ability to identify senile plaques by their autofluorescence enables an array of possible functional studies using other intrinsic emissions, which we demonstrated by imaging SHG from dendritic microtubule arrays near senile plaques.

Although not demonstrated here, it may be possible to use autofluorescence as a diagnostic tool for in vivo studies in transgenic mouse models. Our study shows that autofluorescence from senile plaques is weak but clearly detectable and has a characteristic multiphoton-excited emission spectrum. One possible diagnostic method deep within the brain is to use gradient-index (GRIN) lenses [34

34. M. J. Levene, D. A. Dombeck, K. A. Kasischke, R. P. Molloy, and W. W. Webb, “In vivo multiphoton microscopy of deep brain tissue,” J. Neurophysiol. 91, 1908–1912 (2004). [CrossRef]

, 35

35. J. C. Jung and M. J. Schnitzer, “Multiphoton endoscopy,” Opt. Lett. 28, 902–904 (2003). [CrossRef] [PubMed]

] or optical fiber bundles [36

36. W. Göbel, J. N. Kerr, A Nimmerjahn, and F. Helmchen, “Miniaturized two-photon microscope based on a flexible coherent fiber and a gradient-index lens objective,” Opt. Lett. 29, 2521–2523 (2004). [CrossRef] [PubMed]

] to excite and collect autofluorescence from a small volume within the brain. Imaging may not be required, since spectral information will be the key for distinguishing AD versus normal tissues.

In our imaging-only results, senile plaques and lipofuscin have broad emission spectra so we distinguish them by morphology. In terms of size, senile plaques have diameters ~10 times larger than lipofuscin. This size difference can be clearly resolved in multiphoton microscopy images, which have submicron spatial resolution within scattering tissues. In some cases, lipofuscin can “clump” together to form larger structures. However, in those cases, multiphoton microscopy images can still clearly resolve individual, smaller-diameter lipofuscins (see Fig. 4(a) in [4

4. W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T. Hyman, and W. W. Webb, “Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation,” Proc. Natl. Acad. Sci. 100, 7075–7080 (2003). [CrossRef] [PubMed]

]). On the other hand, it is unlikely to find small, nascent plaques. Plaques grow quickly in vivo within 1-3 days to their full size [30

30. R. H. Christie, B. J. Bacskai, W. R. Zipfel, R. M. Williams, S. T. Kajdasz, W. W. Webb, and B. T. Hyman, “Growth arrest of individual senile plaques in a model of Alzheimer’s disease observed by in vivo multiphoton microscopy,” J. Neurosci. 21, 858–864 (2001). [PubMed]

, 37

37. M. Meyer-Luehmann, T. L. Spires-Jones, C. Prada, M. Garcia-Alloza, A. de Calignon, A. Rozkalne, J. Koenigsknecht-Talboo, D. M. Holtzman, B. J. Bacskai, and B. T. Hyman, “Rapid appearance and local toxicity of amyloid-beta plaques in a mouse model of Alzheimer’s disease,” Nature 451, 720–724 (2008). [CrossRef] [PubMed]

]. Therefore, finding nascent plaques is a rare occurrence even in animal models with significant plaque load [37

37. M. Meyer-Luehmann, T. L. Spires-Jones, C. Prada, M. Garcia-Alloza, A. de Calignon, A. Rozkalne, J. Koenigsknecht-Talboo, D. M. Holtzman, B. J. Bacskai, and B. T. Hyman, “Rapid appearance and local toxicity of amyloid-beta plaques in a mouse model of Alzheimer’s disease,” Nature 451, 720–724 (2008). [CrossRef] [PubMed]

]. Although morphology may be a good correlate, identification of senile plaques versus other autofluorescent materials would be more accurate if spectral information were obtained.

Intrinsic emissions such as autofluorescence and SHG are useful indicators for detecting the presence of pathological lesions. Changes in the intensity and spectrum of intrinsic emissions have previously been studied as possible diagnosis methods for tumors [39

39. C. Zhu, T. M. Breslin, J. Harter, and N. Ramanujam, “Model based and empirical spectral analysis for the diagnosis of breast cancer,” Opt. Express 16, 14961–14978 (2008). [CrossRef] [PubMed]

] or skin pathology [40

40. J. A. Palero, H. S. de Bruijn, A. van der Ploeg-van den Heuvel, H. J. C. M. Sterenborg, and H. C. Gerritsen, “In vivo nonlinear spectral imaging in mouse skin,” Opt. Express 14, 4395–4402 (2006). [CrossRef] [PubMed]

], and can potentially also be useful for neurodegenerative diseases. Here we have demonstrated that intrinsic emissions, particularly that of senile plaques, can be detected from relatively thick, native tissues. Furthermore, the senile plaque emission spectrum is distinct from the background to possibly further enhance detection sensitivity. We anticipate that this work will be useful for interpreting future studies that aim to use endogenous optical signals as a diagnostic tool or as functional fluorescent indicators.

Acknowledgments

We would like to thank Huizhong Xu for help on the spectrometer, Valerie Anderson for amyloid fibrils and Mark Williams for editorial assistance. This research was supported by NIH grant 9-P41-EB001976 for A.C.K. and W.W.W., by NIH grant 1-R21-AG026650 for W.W.W., and by the Nanobiotechnology Center (NBTC), an STC Program of the National Science Foundation under Agreement No. ECS-9876771 for A.C.K.

References and links

1.

M. D. Ikonomovic, W. E. Klunk, E. E. Abrahamson, C. A. Mathis, J. C. Price, N. D. Tsopelas, B. J. Lopresti, S. Ziolko, W. Bi, W. R. Paljug, M. L. Debnath, C. E. Hope, B. A. Isanski, R. L. Hamilton, and S. T. DeKosky, “Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer’s disease,” Brain 131, 1630–1645 (2008). [CrossRef] [PubMed]

2.

M. Hintersteiner, A. Enz, P. Frey, A. L. Jaton, W. Kinzy, R. Kneuer, U. Neumann, M. Rudin, M. Staufenbiel, M. Stoeckli, K. H. Wiederhold, and H. U. Gremlich, “In vivo detection of amyloid-beta deposits by near-infrared imaging using an oxazine-derivative probe,” Nat. Biotechnol. 23, 577–583 (2005). [CrossRef] [PubMed]

3.

E. B. Hanlon, L. T. Perelman, E. I. Vitkin, F. A. Greco, A. C. McKee, and N. W. Kowall, “Scattering differentiates Alzheimer disease in vitro,” Opt. Lett. 33, 624–626 (2008). [CrossRef] [PubMed]

4.

W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T. Hyman, and W. W. Webb, “Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation,” Proc. Natl. Acad. Sci. 100, 7075–7080 (2003). [CrossRef] [PubMed]

5.

K. A. Kasischke, H. D. Vishwasrao, P. J. Fisher, W. R. Zipfel, and W. W. Webb, “Neural activity triggers neuronal oxidative metabolism followed by astrocytic glycolysis,” Science 305, 99–103 (2004). [CrossRef] [PubMed]

6.

H. D. Vishwasrao, A. A. Heikal, K. A. Kasischke, and W. W. Webb, “Conformational dependence of intracellular NADH on metabolic state revealed by associated fluorescence anisotropy,” J. Biol. Chem. 280, 25119–25126 (2005). [CrossRef] [PubMed]

7.

D. A. Dombeck, K. A. Kasischke, H. D. Vishwasrao, M. Ingelsson, B. T. Hyman, and W. W. Webb, “Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy,” Proc. Natl. Acad. Sci. 100, 7081–7086 (2003). [CrossRef] [PubMed]

8.

A. C. Kwan, D. A. Dombeck, and W. W. Webb, “Polarized microtubule arrays in apical dendrites and axons,” Proc. Natl. Acad. Sci. 105, 11370–11375 (2008). [CrossRef] [PubMed]

9.

J. H. Dowson, “A sensitive method for demonstration of senile plaques in the dementing brain,” Histopathology 5, 305–310. (1981). [CrossRef] [PubMed]

10.

D. R. Thal, E. Ghebremedhin, C. Haass, and C. Schultz, “UV light-induced autofluorescence of full-length abeta-protein deposits in the human brain,” Clin. Neuropathol. 21, 35–40 (2002). [PubMed]

11.

M. Diez, J. Koistinaho, K. Kahn, D. Games, and T. Hökfelt, “Neuropeptides in hippocampus and cortex in transgenic mice overexpressing V717F beta-amyloid precursor protein - initial observations,” Neuroscience 100, 259–286. (2003). [CrossRef]

12.

W. Denk, J. H. Strickler, and W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248, 73–76 (1990). [CrossRef] [PubMed]

13.

W. R. Zipfel, R. M. Williams, and W. W. Webb, “Nonlinear magic: multiphoton microscopy in the biosciences,” Nat. Biotechnol. 21, 1369–1377 (2003). [CrossRef] [PubMed]

14.

K. Hsiao, P. Chapman, S. Nilsen, C. Eckman, Y. Harigaya, S. Younkin, F. Yang, and G. Cole, “Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice,” Science 274, 99–102 (1996). [CrossRef] [PubMed]

15.

D. R. Borchelt, T. Ratovitski, J. van Lare, M. K. Lee, V. Gonzales, N. A. Jenkins, N. G. Copeland, D. L. Price, and S. S. Sisodia, “Accelerated amyloid deposition in the brains of transgenic mice coexpressing mutant presenilin 1 and amyloid precursor proteins,” Neuron 19, 939–945 (1997). [CrossRef] [PubMed]

16.

J. Lewis, D. W. Dickson, W. L. Lin, L. Chisholm, A. Corral, G. Jones, S. H. Yen, N. Sahara, L. Skipper, D. Yager, C. Eckman, J. Hardy, M. Hutton, and E. McGowan, “Enhanced neurofibrillary degeneration in transgenic mice expressing mutant tau and APP,” Science 293, 1487–1491 (2001). [CrossRef] [PubMed]

17.

S. Oddo, A. Caccamo, J. D. Shepherd, M. P. Murphy, T. E. Golde, R. Kayed, R. Metherate, M. P. Mattson, Y. Akbari, and F. M. LaFerla, “Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction,” Neuron 39, 409–421 (2003). [CrossRef] [PubMed]

18.

B. Sakmann and G. Stuart, “Patch-pipette recordings from the soma, dendrites and, and axon of neurons in brain slices,” in Single-Channel Recording, 2nd ed., B. Sakmann and E. Neher, eds. (Plenum, 1983), pp. 199–211.

19.

L. M. Drach, J. Bohl, and H. H. Goebel, “The lipofuscin content of nerve cells of the inferior olivary nucleus in Alzheimer’s disease,” Dementia 5, 234–239 (1994). [PubMed]

20.

C. Ballatore, V. M. Lee, and J. Q. Trojanowski, “Tau-mediated neurodegeneration in Alzheimer’s disease and related disorders,” Nat. Rev. Neurosci. 8, 663–672 (2007). [CrossRef] [PubMed]

21.

R. H. Takahashi, T. A. Milner, F. Li, E. E. Nam, M. A. Edgar, H. Yamaguchi, M. F. Beal, H. Xu, P. Greengard, and G. K. Gouras, “Intraneuronal Alzheimer abeta42 accumulates in multivesicular bodies and is associated with synaptic pathology,” Am. J. Pathol. 161, 1869–1879 (2002). [CrossRef] [PubMed]

22.

R. H. Takahashi, E. Capetillo-Zarate, M. T. Lin, T. A. Milner, and G. K. Gouras, “Co-occurrence of Alzheimer’s disease beta-amyloid and tau pathologies at synapses,” Neurobiol. Aging, in press (2008).

23.

B. Li, M. O. Chohan, I. Grundke-Iqbal, and K. Iqbal, “Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau,” Acta Neuropathol. 113, 501–511 (2007). [CrossRef] [PubMed]

24.

L. Qiang, W. Yu, A. Andreadis, M. Luo, and P. W. Baas, “Tau protects microtubules in the axon from severing by katanin,” J. Neurosci. 26, 3120–3129 (2006). [CrossRef] [PubMed]

25.

O. A. Shemesh, H. Erez, I Ginzburg, and M. E. Spira, “Tau-induced traffic jam reflect organelles accumulation at points of microtubule polar mismatching,” Traffic 9, 458–471 (2008). [CrossRef] [PubMed]

26.

T. L. Spires, M. Meyer-Leuhmann, E. A. Stern, P. J. McLean, J. Skoch, P. T. Nguyen, B. J. Bacskai, and B. T. Hyman, “Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy,” J. Neurosci. 25, 7278–7287 (2005). [CrossRef] [PubMed]

27.

J. Tsai, J. Grutzendler, K. Duff, and W. B. Gan, “Fibrillar amyloid deposition leads to local synaptic abnormalities and breakage of neuronal brances,” Nat. Neurosci. 7, 1181–1183 (2004). [CrossRef] [PubMed]

28.

J. Grutzendler, K. Helmin, J. Tsai, and W. B. Gan, “Various dendritic abnormalities are associated with fibrillar amyloid deposits in Alzheimer’s disease,” Ann. N. Y. Acad. Sci. 1097, 30–39 (2007). [CrossRef] [PubMed]

29.

A. Alpár, U. Ueberham, M. K. Brückner, G. Seeger, T. Arendt, and U. Gärtner, “Different dendrite and dendritic spine alterations in basal and apical arbors in mutant human amyloid precursor protein transgenic mice,” Brain Res. 1099, 189–198 (2006). [CrossRef] [PubMed]

30.

R. H. Christie, B. J. Bacskai, W. R. Zipfel, R. M. Williams, S. T. Kajdasz, W. W. Webb, and B. T. Hyman, “Growth arrest of individual senile plaques in a model of Alzheimer’s disease observed by in vivo multiphoton microscopy,” J. Neurosci. 21, 858–864 (2001). [PubMed]

31.

G. Eichhoff, M. A. Busche, and O. Garaschuk, “In vivo calcium imaging of the aging and diseased brain,” Eur. J. Nucl. Med. Mol. Imaging 35, S99–S106 (2008). [CrossRef] [PubMed]

32.

T. Takano, X. Han, R. Deane, B. Zlokovic, and M. Nedergaard, “Two-photon imaging of astrocytic Ca2+ signaling and the microvasculature in experimental mice models of Alzheimer’s disease,” Ann. N.Y. Acad. Sci. 1097, 40–50 (2007). [CrossRef] [PubMed]

33.

B. J. Bacskai, S. T. Kajdasz, R. H. Christie, C. Carter, D. Games, P. Seubert, D. Schenk, and B. T. Hyman, “Imaging of amyloid-beta deposits in brains of living mice permits direct observation of clearance of plaques with immunotherapy,” Nat. Med. 7, 369–372 (2001). [CrossRef] [PubMed]

34.

M. J. Levene, D. A. Dombeck, K. A. Kasischke, R. P. Molloy, and W. W. Webb, “In vivo multiphoton microscopy of deep brain tissue,” J. Neurophysiol. 91, 1908–1912 (2004). [CrossRef]

35.

J. C. Jung and M. J. Schnitzer, “Multiphoton endoscopy,” Opt. Lett. 28, 902–904 (2003). [CrossRef] [PubMed]

36.

W. Göbel, J. N. Kerr, A Nimmerjahn, and F. Helmchen, “Miniaturized two-photon microscope based on a flexible coherent fiber and a gradient-index lens objective,” Opt. Lett. 29, 2521–2523 (2004). [CrossRef] [PubMed]

37.

M. Meyer-Luehmann, T. L. Spires-Jones, C. Prada, M. Garcia-Alloza, A. de Calignon, A. Rozkalne, J. Koenigsknecht-Talboo, D. M. Holtzman, B. J. Bacskai, and B. T. Hyman, “Rapid appearance and local toxicity of amyloid-beta plaques in a mouse model of Alzheimer’s disease,” Nature 451, 720–724 (2008). [CrossRef] [PubMed]

38.

C. S. Atwood, R. N. Martins, M. A. Smith, and G. Perry, “Senile plaque composition and posttranslational modification of amyloid-beta peptide and associated proteins,” Peptides 23, 1343–1350 (2002). [CrossRef] [PubMed]

39.

C. Zhu, T. M. Breslin, J. Harter, and N. Ramanujam, “Model based and empirical spectral analysis for the diagnosis of breast cancer,” Opt. Express 16, 14961–14978 (2008). [CrossRef] [PubMed]

40.

J. A. Palero, H. S. de Bruijn, A. van der Ploeg-van den Heuvel, H. J. C. M. Sterenborg, and H. C. Gerritsen, “In vivo nonlinear spectral imaging in mouse skin,” Opt. Express 14, 4395–4402 (2006). [CrossRef] [PubMed]

OCIS Codes
(170.0110) Medical optics and biotechnology : Imaging systems
(170.2520) Medical optics and biotechnology : Fluorescence microscopy
(170.3880) Medical optics and biotechnology : Medical and biological imaging
(170.6510) Medical optics and biotechnology : Spectroscopy, tissue diagnostics
(170.6930) Medical optics and biotechnology : Tissue

ToC Category:
Medical Optics and Biotechnology

History
Original Manuscript: October 21, 2008
Revised Manuscript: November 11, 2008
Manuscript Accepted: December 7, 2008
Published: February 24, 2009

Virtual Issues
Vol. 4, Iss. 5 Virtual Journal for Biomedical Optics

Citation
Alex C. Kwan, Karen Duff, Gunnar K. Gouras, and Watt W. Webb, "Optical visualization of Alzheimer’s pathology via multiphoton-excited intrinsic fluorescence and second harmonic generation," Opt. Express 17, 3679-3689 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-5-3679


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References

  1. M. D. Ikonomovic, W. E. Klunk, E. E. Abrahamson, C. A. Mathis, J. C. Price, N. D. Tsopelas, B. J. Lopresti, S. Ziolko, W. Bi, W. R. Paljug, M. L. Debnath, C. E. Hope, B. A. Isanski, R. L. Hamilton, and S. T. DeKosky, "Post-mortem correlates of in vivo PiB-PET amyloid imaging in a typical case of Alzheimer’s disease," Brain 131, 1630-1645 (2008). [CrossRef] [PubMed]
  2. M. Hintersteiner, A. Enz, P. Frey, A. L. Jaton, W. Kinzy, R. Kneuer, U. Neumann, M. Rudin, M. Staufenbiel, M. Stoeckli, K. H. Wiederhold, and H. U. Gremlich, "In vivo detection of amyloid-beta deposits by near-infrared imaging using an oxazine-derivative probe," Nat. Biotechnol. 23, 577-583 (2005). [CrossRef] [PubMed]
  3. E. B. Hanlon, L. T. Perelman, E. I. Vitkin, F. A. Greco, A. C. McKee, and N. W. Kowall, "Scattering differentiates Alzheimer disease in vitro," Opt. Lett. 33, 624-626 (2008). [CrossRef] [PubMed]
  4. W. R. Zipfel, R. M. Williams, R. Christie, A. Y. Nikitin, B. T. Hyman, and W. W. Webb, "Live tissue intrinsic emission microscopy using multiphoton-excited native fluorescence and second harmonic generation," Proc. Natl. Acad. Sci. 100, 7075-7080 (2003). [CrossRef] [PubMed]
  5. K. A. Kasischke, H. D. Vishwasrao, P. J. Fisher, W. R. Zipfel, and W. W. Webb, "Neural activity triggers neuronal oxidative metabolism followed by astrocytic glycolysis," Science 305, 99-103 (2004). [CrossRef] [PubMed]
  6. H. D. Vishwasrao, A. A. Heikal, K. A. Kasischke, and W. W. Webb, "Conformational dependence of intracellular NADH on metabolic state revealed by associated fluorescence anisotropy," J. Biol. Chem. 280, 25119-25126 (2005). [CrossRef] [PubMed]
  7. D. A. Dombeck, K. A. Kasischke, H. D. Vishwasrao, M. Ingelsson, B. T. Hyman, and W. W. Webb, "Uniform polarity microtubule assemblies imaged in native brain tissue by second-harmonic generation microscopy," Proc. Natl. Acad. Sci. 100, 7081-7086 (2003). [CrossRef] [PubMed]
  8. A. C. Kwan, D. A. Dombeck, and W. W. Webb, "Polarized microtubule arrays in apical dendrites and axons," Proc. Natl. Acad. Sci. 105, 11370-11375 (2008). [CrossRef] [PubMed]
  9. J. H. Dowson, "A sensitive method for demonstration of senile plaques in the dementing brain," Histopathology 5, 305-310. (1981). [CrossRef] [PubMed]
  10. D. R. Thal, E. Ghebremedhin, C. Haass, and C. Schultz, "UV light-induced autofluorescence of full-length abeta-protein deposits in the human brain," Clin. Neuropathol. 21, 35-40 (2002). [PubMed]
  11. M. Diez, J. Koistinaho, K. Kahn, D. Games, and T. Hökfelt, "Neuropeptides in hippocampus and cortex in transgenic mice overexpressing V717F beta-amyloid precursor protein - initial observations," Neuroscience 100, 259-286. (2003). [CrossRef]
  12. W. Denk, J. H. Strickler, and W. W. Webb, "Two-photon laser scanning fluorescence microscopy," Science 248, 73-76 (1990). [CrossRef] [PubMed]
  13. W. R. Zipfel, R. M. Williams, and W. W. Webb, "Nonlinear magic: multiphoton microscopy in the biosciences," Nat. Biotechnol. 21, 1369-1377 (2003). [CrossRef] [PubMed]
  14. K. Hsiao, P. Chapman, S. Nilsen, C. Eckman, Y. Harigaya, S. Younkin, F. Yang, and G. Cole, "Correlative memory deficits, Abeta elevation, and amyloid plaques in transgenic mice," Science 274, 99-102 (1996). [CrossRef] [PubMed]
  15. D. R. Borchelt, T. Ratovitski, J. van Lare, M. K. Lee, V. Gonzales, N. A. Jenkins, N. G. Copeland, D. L. Price, and S. S. Sisodia, "Accelerated amyloid deposition in the brains of transgenic mice coexpressing mutant presenilin 1 and amyloid precursor proteins," Neuron 19, 939-945 (1997). [CrossRef] [PubMed]
  16. J. Lewis, D. W. Dickson, W. L. Lin, L. Chisholm, A. Corral, G. Jones, S. H. Yen, N. Sahara, L. Skipper, D. Yager, C. Eckman, J. Hardy, M. Hutton, and E. McGowan, "Enhanced neurofibrillary degeneration in transgenic mice expressing mutant tau and APP," Science 293, 1487-1491 (2001). [CrossRef] [PubMed]
  17. S. Oddo, A. Caccamo, J. D. Shepherd, M. P. Murphy, T. E. Golde, R. Kayed, R. Metherate, M. P. Mattson, Y. Akbari, and F. M. LaFerla, "Triple-transgenic model of Alzheimer’s disease with plaques and tangles: intracellular Abeta and synaptic dysfunction," Neuron 39, 409-421 (2003). [CrossRef] [PubMed]
  18. B. Sakmann and G. Stuart, "Patch-pipette recordings from the soma, dendrites and, and axon of neurons in brain slices," in Single-Channel Recording, 2nd ed., B. Sakmann and E. Neher, eds. (Plenum, 1983), pp. 199-211.
  19. L. M. Drach, J. Bohl, and H. H. Goebel, "The lipofuscin content of nerve cells of the inferior olivary nucleus in Alzheimer’s disease," Dementia 5, 234-239 (1994). [PubMed]
  20. C. Ballatore, V. M. Lee, and J. Q. Trojanowski, "Tau-mediated neurodegeneration in Alzheimer’s disease and related disorders," Nat. Rev. Neurosci. 8, 663-672 (2007). [CrossRef] [PubMed]
  21. R. H. Takahashi, T. A. Milner, F. Li, E. E. Nam, M. A. Edgar, H. Yamaguchi, M. F. Beal, H. Xu, P. Greengard, and G. K. Gouras, "Intraneuronal Alzheimer abeta42 accumulates in multivesicular bodies and is associated with synaptic pathology," Am. J. Pathol. 161, 1869-1879 (2002). [CrossRef] [PubMed]
  22. R. H. Takahashi, E. Capetillo-Zarate, M. T. Lin, T. A. Milner, and G. K. Gouras, "Co-occurrence of Alzheimer’s disease beta-amyloid and tau pathologies at synapses," Neurobiol. Aging, in press (2008).
  23. B. Li, M. O. Chohan, I. Grundke-Iqbal, K. Iqbal, "Disruption of microtubule network by Alzheimer abnormally hyperphosphorylated tau," Acta Neuropathol. 113, 501-511 (2007). [CrossRef] [PubMed]
  24. L. Qiang, W. Yu, A. Andreadis, M. Luo, and P. W. Baas, "Tau protects microtubules in the axon from severing by katanin," J. Neurosci. 26, 3120-3129 (2006). [CrossRef] [PubMed]
  25. O. A. Shemesh, H. Erez, I Ginzburg, and M. E. Spira, "Tau-induced traffic jam reflect organelles accumulation at points of microtubule polar mismatching," Traffic 9, 458-471 (2008). [CrossRef] [PubMed]
  26. T. L. Spires, M. Meyer-Leuhmann, E. A. Stern, P. J. McLean, J. Skoch, P. T. Nguyen, B. J. Bacskai, B. T. Hyman, "Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy," J. Neurosci. 25, 7278-7287 (2005). [CrossRef] [PubMed]
  27. J. Tsai, J. Grutzendler, K. Duff, and W. B. Gan, "Fibrillar amyloid deposition leads to local synaptic abnormalities and breakage of neuronal brances," Nat. Neurosci. 7, 1181-1183 (2004). [CrossRef] [PubMed]
  28. J. Grutzendler, K. Helmin, J. Tsai, and W. B. Gan, "Various dendritic abnormalities are associated with fibrillar amyloid deposits in Alzheimer’s disease," Ann. N. Y. Acad. Sci. 1097, 30-39 (2007). [CrossRef] [PubMed]
  29. A. Alpár, U. Ueberham, M. K. Brückner, G. Seeger, T. Arendt, and U. Gärtner, "Different dendrite and dendritic spine alterations in basal and apical arbors in mutant human amyloid precursor protein transgenic mice," Brain Res. 1099, 189-198 (2006). [CrossRef] [PubMed]
  30. R. H. Christie, B. J. Bacskai, W. R. Zipfel, R. M. Williams, S. T. Kajdasz, W. W. Webb, and B. T. Hyman, "Growth arrest of individual senile plaques in a model of Alzheimer’s disease observed by in vivo multiphoton microscopy," J. Neurosci. 21, 858-864 (2001). [PubMed]
  31. G. Eichhoff, M. A. Busche, and O. Garaschuk, "In vivo calcium imaging of the aging and diseased brain," Eur. J. Nucl. Med. Mol. Imaging 35, S99-S106 (2008). [CrossRef] [PubMed]
  32. T. Takano, X. Han, R. Deane, B. Zlokovic, and M. Nedergaard, "Two-photon imaging of astrocytic Ca2+ signaling and the microvasculature in experimental mice models of Alzheimer’s disease," Ann. N.Y. Acad. Sci. 1097, 40-50 (2007). [CrossRef] [PubMed]
  33. B. J. Bacskai, S. T. Kajdasz, R. H. Christie, C. Carter, D. Games, P. Seubert, D. Schenk, and B. T. Hyman, "Imaging of amyloid-beta deposits in brains of living mice permits direct observation of clearance of plaques with immunotherapy," Nat. Med. 7, 369-372 (2001). [CrossRef] [PubMed]
  34. M. J. Levene, D. A. Dombeck, K. A. Kasischke, R. P. Molloy, and W. W. Webb, "In vivo multiphoton microscopy of deep brain tissue," J. Neurophysiol. 91, 1908-1912 (2004). [CrossRef]
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