Galanin differentially regulates acetylcholine release in ventral and dorsal hippocampus: a microdialysis study in awake rat

Abstract

The purpose of the present study was to investigate, by use of in vivo microdialysis technique, the regulatory role of galanin on acetylcholine (ACh) release in the CA1, CA3, and dentate gyrus (DG) subregions of rat dorsal and ventral hippocampus. In the ventral hippocampus, local infusions of galanin (1.5 nmol) into CA1, and CA3, but not DG (3 nmol), decreased basal ACh release to 58.6% and 68.4%, respectively. In addition, local infusion of galanin (1.5 nmol) into the ventral DG, and CA3 areas decreased basal ACh levels in the CA1 to 51.2% and 84%, respectively. This observation implies that the effects of galanin are unlikely to be mediated via galanin autoreceptors on the cholinergic terminals, but rather via mechanisms involving galanin internalization and modulation of hippocampo-septo-hippocampal loops, attenuation of the excitability of the principal cells, or indirect modulation by galanin-containing vasopressin terminals to the ventral and/or dorsal hippocampus. In the dorsal hippocampus, galanin infusion (1.5 nmol) into the CA1 region increased ACh release to 128.2% of the control levels, but infusions of galanin had no effects in the CA3 and DG. In all cases, the ACh levels returned to basal values within 100 min after the galanin infusion. It is concluded that the attenuating effects of galanin on ACh release in the ventral hippocampus and increase in ACh release in the dorsal hippocampus are in line and support the current view on molecular and functional distinction between the ventral hippocampus being involved preferentially in motivational and emotional behavior, whereas the dorsal hippocampus is primarily implicated in cognitive processes of learning and memory.