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Autoregulatory properties of dorsal raphe 5‐HT neurons: Possible role of electrotonic coupling and 5‐HT 1D receptors in the rat brain
Author(s) -
Piñeyro Graciela,
de Montigny Claude,
Weiss Michel,
Blier Pierre
Publication year - 1996
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/(sici)1098-2396(199601)22:1<54::aid-syn6>3.0.co;2-h
Subject(s) - antidromic , dorsal raphe nucleus , neuroscience , tegmentum , stimulation , chemistry , raphe nuclei , autoreceptor , serotonin , receptor , midbrain , psychology , serotonergic , central nervous system , biochemistry
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‐HT 1A autoreceptors. The intravenous administration of the 5‐HT 1 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‐HT 1D , but not 5‐HT 1B , receptors. On the other hand, (−)propranolol, a mixed 5‐HT antagonist also blocked the effect of TFMPP. However, the selective 5‐HT 1A 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‐HT 1A autoreceptors. They also suggest that 5‐HT 1D receptors may play a role in this regulatory function of 5‐HT neurons. © 1996 Wiley‐Liss, Inc.