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Abstract
An ultrastructural analysis of post-embedding glutamate immunocytochemistry within
the neural lobe of the pituitary was used to explore the possible role of glutamate
within the magnocellular neuroendocrine cells. Relative densities of a colloidal gold
marker associated with various cellular and subcellular compartments of the neural
lobe were quantified by computer analysis of electron micrographs. Robust glutamate
immunoreactivity was observed in both pituicytes (cytoplasm, mitochondria and nucleus)
and neurosecretory endings. Within the neurosecretory endings, glutamate staining
was specifically localized to the microvesicles with no overlap into the neurosecretory
granule population. Stimulation of the vasopressin/oxytocin neurosecretory system
by water deprivation increased glutamate content in pituicytes and mitochondria within
neurosecretory endings but had little influence on microvesicle glutamate content.
The results are consistent with the existence of multiple functional pools of immunoreactive
glutamate in both pituicytes and neurosecretory endings. Microvesicles within the
neurosecretory endings exhibit many properties of secretory vesicles, appear to be
functionally independent of the neurosecretory granules, and have sufficient glutamate
immunoreactivity to suggest that this amino acid may be compartmentalized for release
in the neural lobe.