Biomedical Engineering Reference
In-Depth Information
(a)
Excitation
λ
(nm)
1.0
760±2
780±2
800±2
820±2
840±2
860±2
880±2
0.8
0.6
0.4
0.2
0.0
370
380
390
400 410
Wavelength (nm)
420
430
440
450
(b)
λ
ex
= 774 nm
λ
ex
= 830 nm
350
400
450
500
550
600
650
Wavelength (nm)
FIgurE 7.5
Emission spectra from microtubules and other subcellular structures. (a) Normalized emission
intensities from the mossy fibers of a rat hippocampal slice. The emission spectra always center at half of the excita-
tion wavelength and are stronger for short wavelengths. The mean normalized SHG intensity excited with constant
excitation power at different wavelengths is plotted with dots and error bars. (Reprinted from Dombeck, D. A.
et al., 2003. Uniform polarity microtubule assemblies imaged in native brain tissue by second harmonic genera-
tion microscopy.
Proceedings of the National Academy of Sciences of the United States of America
, 100, 7081-7086.
Copyright 2003, with permission from the National Academy of Sciences, USA.) (b) The emission spectra obtained
from a senile plaque in a brain slice of an Alzheimer's disease mouse model. The molecular origin of this SHG
signal is not known. When the excitation wavelength was changed from 774 to 830 nm, the SHG-related spectra
shifted accordingly, distinguishing the SHG signal from the broadband autofluorescence. (Reprinted from Kwan,
A. C. et al., 2009. Optical visualization of Alzheimer's pathology via multiphoton-excited intrinsic fluorescence
and second harmonic generation.
Optics Express
, 17, 3679-3689. Copyright 2009, with permission from the Optical
Society of America.)
7.2 Application 1: Mapping the Distribution of Polarized
Microtubule Bundles in native Brain tissues
Many proteins and messenger RNAs are synthesized in the cell body and are then actively transported
to other compartments. Neuron is an extreme example with many distal sites along the long axon and
branching dendrites. Cargoes are carried by molecular motors, such as kinesin and dynein, which move
along microtubules with preference toward the plus- or minus-end direction. As a result, the polarity of
microtubule bundles within axons and dendrites has implications for sorting cargo traffic and limiting
the speed and throughput of transport.
