Optical neurophysiology based on animal models.
Optical neurophysiology based on animal models.
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基于动物模型的光学神经生理学。
DOI：
10.1109/memb.2007.384091
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Gratton,Gabriele
中科院分区：
文献类型：
--
作者：
Sable,JeffreyJ;Rector,DavidM;Gratton,Gabriele
These studies demonstrated the sequential elicitation of brainstem and cortical evoked responses through electrical stimulation of the vagus nerve bundle. Cellular swelling in vivo can lead to profound changes in optical properties of the tissue and may be their principal biophysical mechanism. Total brain volume is composed roughly of 30–40% neurons, 40–50% glial cells, and 15–25% extracellular space [20]–[21]. In cerebral cortical slices, cellular swelling was observed during anoxia and membrane depolarization [22]. Such swelling reduces the extracellular spaces [23]–[24], and affects neural and glial function. Since activation can decrease the extracellular fraction by 67%[25], a reduction in extracellular space increases the excitability of neurons by increasing the proximity of pre-and postsynaptic structures [26]. These profound dynamics in cellular pressure and volume underscore the physical mechanisms that might lead to optical changes in the tissue, possibly due to dilution of intracellular components or a change in refractive index. Since the cellular membrane normally has invaginations, cellular swelling pressure can be relieved by stretching the cell’s membrane, causing changes in light scattering and birefringence. Neurotransmitter-filled vesicles tend to accumulate at the axon terminal, thus forming a high concentration of scattering particles in a localized region. Fusion of the vesicles through activation-induced exocytosis could spread the scattering particles across a larger area. The presence of a complex cytoskeleton within the axoplasm of the neuron creates additional sources of scatteredlight changes. Microtubules exist in all parts of the neuron and are responsible for creating the shape and structure of the cell membrane. Recent birefringence studies of microtubules show that a significant portion of light rotation can be attributed to bundled microtubules [27]. Since neurons contain an extensive network of microtubules, a large fraction of light-scattering changes may arise from structural alterations in the microtubule lattice. Microtubule formations are particularly dense within dendrites [28].At least some of the scattered-light changes can occur from direct effects of the gel-like axoplasm that composes the inner layers of the cell [29]. The axoplasm consists of a polymerbased hydrogel that expands with water during activation. As the hydrogel expands, its refractive index and scattering properties change. Through use of artificial hydrogels, Tasaki showed that the propagation of the action potential could be accompanied by a sequence of mechanical events that move along the length of the nerve.
