Abstract
Based on early immunocytochemical findings, galanin (GAL) was postulated to function as an inhibitory cotransmitter in rat cholinergic memory pathways. However, recent studies indicate that in the basal state GAL is not widely expressed by forebrain cholinergic neurons in rats. Inhibition of cholinergic transmission by cosecreted GAL may be enhanced under certain conditions, because GAL gene expression in the cholinergic basal forebrain is significantly increased prior to puberty and following nerve growth factor treatment. Other sources of GAL in rat septohippocampus that could interact with cholinergic pathways include noradrenergic neurons in the locus ceruleus and vasopressinergic neurons in the bed nucleus of the stria terminalis (BST) and medial amygdala (Me). GAL is extensively colocalized within these steroid-sensitive cell groups where its expression is upregulated by gonadal hormones. GAL, acting via the GALR1 receptor subtype, does not appear to directly regulate the activity of cholinergic neurons, but it may regulate the release of vasopressin and GAL into septohippocampus from BST/Me neurons.
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