Neurotensin excitation of serotonergic neurons in the rat nucleus raphe magnus: ionic and molecular mechanisms

To understand the cellular and molecular mechanisms by which neurotensin (N T) induces an analgesic effect in the nucleus raphe magnus (NRM), whole-cel l patch-clamp recordings were performed to investigate the electrophysiolog ical effects of NT on acutely dissociated NRM neurons. Two subtypes of neur ons, primary serotonergic and secondary non-serotonergic cells, were identi fied from acutely isolated NRM neurons. During current-clamp recordings, NT depolarized NRM serotonergic neurons and evoked action potentials. Voltage -clamp recordings showed that NT excited serotonergic neurons by enhancing a voltage-insensitive and non-selective cationic conductance, Both SR48692, a selective antagonist of subtype 1 neurotensin receptor (NTR-1), and SR 1 42948A, a non-selective antagonist of NTR-1 and subtype 2 neurotensin recep tor (NTR-2), failed to prevent neurotensin from exciting NRM serotonergic n eurons. NT-evoked cationic current was inhibited by the intracellular admin istration of GDP-P-S. NT failed to induce cationic currents after dialyzing serotonergic neurons with the anti-G(alphaq/11) antibody. Cellular Ca2+ im aging study using fura-2 showed that NT induced the calcium release from th e intracellular store. NT-evoked current was blocked after the internal per fusion of heparin, an IP3 receptor antagonist, or BAPTA, a fast Ca2+ chelat or. It is concluded that neurotensin enhancement of the cationic conductanc e of NRM serotonergic neurons is mediated by a novel subtype of neurotensin receptors. The coupling mechanism via G(alphaq/11) proteins is likely to i nvolve the generation of IP3, and subsequent IP3-evoked Ca2+ release from i ntracellular stores results in activating the non-selective cationic conduc tance. (C) 2001 Elsevier Science Ltd. All rights reserved.