Serotonin-induced reduction of the calcium-dependent plateau in frog dorsal root ganglion cells is blocked by serotonergic agents acting at 5-hydroxytryptamine1A sites

W Marszalec, RS Scroggs and EG Anderson

Department of Pharmacology, University of Illinois Medical College, Chicago.

Intracellular recordings from the dorsal root ganglion cells of adult frogs in the presence of tetraethylammonium display action potentials with a prominent calcium-dependent plateau. These action potentials can be altered by serotonergic agents in one of two ways. The superfusion of 5-HT (0.1-1 microM) usually produces a dose-dependent reduction of the action potential duration, whereas 8-hydroxy dipropylaminotetralin (8-OH-DPAT) (10-50 microM) produces a dose-dependent increase in duration. A series of 5-HT antagonists were tested for their ability to block either the 5-HT or the 8-OH-DPAT effect. The antagonists were chosen for their reported selectivity in distinguishing receptors of the 5-HT1A, 5-HT2 and 5-HT3 subtypes. The antagonists' action on 5-HT narrowing [blockade by methiothepin, spiperone and spiroxitrine, but not by ketanserin or 3-tropyl-indole-3-carboxylate (ICS 205-930)] suggests that this response is mediated by 5-HT1A receptors. The widening effect produced by 8-OH-DPAT (a putative 5-HT1A agonist) was not blocked by any antagonist tested. At lower concentrations (0.1-2.5 microM) 8-OH-DPAT exhibited no agonist actions, but antagonized the 5- HT-induced narrowing. These results suggest the 5-HT receptors mediating 5-HT action potential narrowing in these cells are of the 5- HT1A subtype, but that they differ from the 5-HT1A receptors described in other tissues in which 8-OH-DPAT is an agonist or a partial agonist.

Volume 247, Issue 2, pp. 399-404, 11/01/1988
Copyright © 1988 by American Society for Pharmacology and Experimental Therapeutics