Selective up-regulation of neuropeptide synthesis by blocking the neuronal activity: galanin expression in septohippocampal neurons.

Neuronal activity regulates expression of phenotype-specific genes, including galanin, which coexists with choline acetyltransferase in septal and basal forebrain neurons. Transections of the fornix and the diagonal band alter galanin expression in septohippocampal neurons attributed to a deficit in target-derived trophic factors. The present study demonstrates that tetrodotoxin-induced blockade of neuronal activity fully mimicked the effect of axotomy (transection of the septohippocampal fibers) in the neurons of the nucleus of the diagonal band, and caused a dramatic, although temporary, up-regulation of galanin immunoreactivity and galanin mRNA without significant alteration in choline acetyltransferase expression. This finding suggests that in the septohippocampal cholinergic system perturbance of electrical activity alone can lead to temporary up-regulation of galanin expression, previously attributed exclusively to a "lesion effect."