Differential regulation of adenylate cyclase activity in rat ventral and dorsal hippocampus by rat galanin.

Rat galanin inhibits basal as well as forskolin-stimulated adenylate cyclase activity in rat ventral and dorsal hippocampus. The inhibition of adenylate cyclase activity, both basal and forskolin-stimulated, is characterised by IC50 values being 250-fold lower in ventral hippocampus (IC50 = 1.1 nM) compared to the dorsal hippocampus (IC50 = 270 nM). The maximal inhibition of basal and forskolin-stimulated adenylate cyclase activity in both ventral and dorsal hippocampus in the presence of 10 microM rat galanin is 34-45%. The analysis of the binding data obtained with 125I-labelled Tyr26-porcine galanin as a tracer reveals similar binding constants for rat galanin in both ventral and dorsal hippocampus with 4.8-fold higher concentration of galanin receptors in the ventral hippocampus. Putative galanin receptor subtype differences between the ventral and dorsal hippocampus have been noted by Hedlund et al. (Eur. J. Pharmacol., 224 (1992) 203-205). This study yields further confirmation for the existence of different galanin receptor subtypes or for differential coupling of galanin receptors to the adenylate cyclase in the dorsal versus ventral hippohampus.