Autoregulatory properties of dorsal raphe 5-HT neurons: Possible role of electrotonic coupling and 5-HT1D receptors in the rat brain

• Published in: Synapse (New York, N.Y.) Vol. 22; no. 1; pp. 54 - 62
• Main Authors: Piñeyro, Graciela, de Montigny, Claude, Weiss, Michel, Blier, Pierre
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01.01.1996
• Subjects: 5-HT1D receptors; Action Potentials - drug effects; Action Potentials - physiology; Animals; Dendrites - drug effects; Dendrites - physiology; dorsal raphe; Electric Stimulation; Electrophysiology; electrotonic coupling; Extracellular Space - drug effects; Extracellular Space - physiology; gap junctions; Indoles - pharmacology; Male; Mianserin - pharmacology; Piperazines - pharmacology; Propranolol - pharmacology; Raphe Nuclei - cytology; Raphe Nuclei - drug effects; Raphe Nuclei - physiology; Rats; Rats, Sprague-Dawley; Receptors, Serotonin - drug effects; Receptors, Serotonin - physiology; release; serotonin; Serotonin - physiology; Serotonin Antagonists - pharmacology; Serotonin Receptor Agonists - pharmacology; somatodendritic; Synapses - drug effects; Synapses - physiology
• ISSN: 0887-4476; 1098-2396
• DOI: 10.1002/(SICI)1098-2396(199601)22:1<54::AID-SYN6>3.0.CO;2-H

In the present study, the hypothesis that somatodendritic availability of 5‐hydroxytryptamine (5‐HT) could be regulated independently of the firing activity of dorsal raphe 5‐HT neurons was tested. The 5‐HT pathway was electrically stimulated at the level of the ventromedial tegmentum and the ensuing action potentials, recorded in the dorsal raphe, met all criteria for antidromic invasion of 5‐HT neurons. The latency of antidromic spikes was current‐dependent and the changes in latency were of quantal nature. This observation suggests an electrotonic coupling between 5‐HT neurons. Stimulation of the ventromedial tegmentum also induced a decrease in the probability of firing of 5‐HT neurons. This reduction in 5‐HT neuron firing activity is a 5‐HT‐mediated response, due to an increased bioavailability of the neurotransmitter in the biophase of somatodendritic 5‐HT1A autoreceptors. The intravenous administration of the 5‐HT1 agonists TFMPP and RU 24969 reduced the duration of suppression of firing induced by the 5‐HT‐pathway stimulation, without altering the spontaneous firing rate of 5‐HT neurons. The effect of TFMPP and RU 24969 on duration of suppression was blocked by (±)mianserin, a drug with high affinity for the rat 5‐HT1D, but not 5‐HT1B, receptors. On the other hand, (−)propranolol, a mixed 5‐HT antagonist also blocked the effect of TFMPP. However, the selective 5‐HT1A antagonist (+)WAY 100135 did not alter the effect of TFMPP. These results, in keeping with previous anatomical studies, suggest the existence of electrotonic coupling of 5‐HT neurons and indicate that 5‐HT release in the rat dorsal raphe nucleus may be controlled independently of firing‐regulating 5‐HT1A autoreceptors. They also suggest that 5‐HT1D receptors may play a role in this regulatory function of 5‐HT neurons. © 1996 Wiley‐Liss, Inc.