DIFFERENTIAL REGULATION OF ADENYLATE-CYCLASE ACTIVITY IN RAT VENTRAL AND DORSAL HIPPOCAMPUS BY RAT GALANIN

Pat galanin inhibits basal as well as forskolin-stimulated adenylate c yclase 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 hippocam pus (IC50 = 1.1 nM) compared to the dorsal hippocampus (IC50 = 270 nM) , The maximal inhibition of basal and forskolin-stimulated adenylate c yclase activity in both ventral and dorsal hippocampus in the presence of 10 mu M rat galanin is 34-45%. The analysis of the binding data ob tained with I-125-labelled Tyr(26)-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 difference s between the ventral and dorsal hippocampus have been noted by Hedlun d et al. (Eur. J. Pharmacol., 224 (1992) 203-205). This study yields f urther confirmation for the existence of different galanin receptor su btypes or for differential coupling of galanin receptors to the adenyl ate cyclase in the dorsal versus ventral hippohampus.