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Three‐photon microscopy shows that somatic release can be a quantitatively significant component of serotonergic neurotransmission in the mammalian brain
Author(s) -
Kaushalya S.K.,
Desai R.,
Arumugam S.,
Ghosh H.,
Balaji J.,
Maiti S.
Publication year - 2008
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.21794
Subject(s) - serotonergic , serotonin , dorsal raphe nucleus , vesicle , raphe nuclei , monoaminergic , neurotransmission , soma , synaptic vesicle , biophysics , chemistry , neuroscience , raphe , monoamine neurotransmitter , biology , biochemistry , receptor , membrane
Abstract Recent experiments on monoaminergic neurons have shown that neurotransmission can originate from somatic release. However, little is known about the quantity of monoamine available to be released through this extrasynaptic pathway or about the intracellular dynamics that mediate such release. Using three‐photon microscopy, we directly imaged serotonin autofluorescence and investigated the total serotonin content, release competence, and release kinetics of somatic serotonergic vesicles in the dorsal raphe neurons of the rat. We found that the somata of primary cultured neurons contain a large number of serotonin‐filled vesicles arranged in a perinuclear fashion. A similar distribution is also observed in fresh tissue slice preparations obtained from the rat dorsal raphe. We estimate that the soma of a cultured neuron on an average contains about 9 fmoles of serotonin in about 450 vesicles (or vesicle clusters) of ≤370 nm average diameter. A substantial fraction (>30%) of this serotonin is released with a time scale of several minutes by K + ‐induced depolarization or by para‐chloroamphetamine treatment. The amount of releasable serotonin stored in the somatic vesicles is comparable to the total serotonin content of all the synaptic vesicles in a raphe neuron, indicating that somatic release can potentially play a major role in serotonergic neurotransmission in the mammalian brain. © 2008 Wiley‐Liss, Inc.