Melatonin modulation of presynaptic nicotinic acetylcholine receptors located on short noradrenergic neurons of the rat vas deferens: a pharmacological characterization
Braz. j. med. biol. res
;
32(8): 999-1006, Aug. 1999.
Artigo
em Inglês
| LILACS
| ID: lil-238969
ABSTRACT
Melatonin, the pineal hormone produced during the dark phase of the light-dark cycle, modulates neuronal acetylcholine receptors located presynaptically on nerve terminals of the rat vas deferens. Recently we showed the presence of high affinity nicotine-binding sites during the light phase, and low and high affinity binding sites during the dark phase. The appearance of the low affinity binding sites was due to the nocturnal melatonin surge and could be mimicked by exposure to melatonin in vitro. The aim of the present research was to identify the receptor subtypes responsible for the functional response during the light and the dark phase. The rank order of potency of agonists was dimethylphenylpiperazinium (DMPP) = cytisine > nicotine > carbachol and DMPP = nicotine = cytisine > carbachol, during the light and dark phase, respectively, due to an increase in apparent affinity for nicotine. Mecamylamine similarly blocked the DMPP response during the light and the dark phase, while the response to nicotine was more efficiently blocked during the light phase. In contrast, methyllycaconitine inhibited the nicotine-induced response only at 2100 h. Since = 7 nicotinic acetylcholine receptors (nAChRs) have low affinity for nicotine in binding assays, we suggest that a mixed population composed of alpha 3 Beta 4 - plus alpha7-bearing nAChR subtypes is present at night. This plasticity in receptor subtypes is probably driven by melatonin since nicotine-induced contraction in organs from animals sacrificed at 1500 h and incubated with melatonin (100 pg/ml, 4 h) is not totally blocked by mecamylamine. Thus melatonin, by acting directly on the short adrenergic neurons that innervate the rat vas deferens, induces the appearance of the low affinity binding site, probably an alpha nAChR subtype
Texto completo:
DisponíveL
Índice:
LILACS (Américas)
Assunto principal:
Ducto Deferente
/
Receptores Nicotínicos
/
Antagonistas Nicotínicos
/
Agonistas Nicotínicos
/
Melatonina
/
Neurônios
Limite:
Animais
Idioma:
Inglês
Revista:
Braz. j. med. biol. res
Assunto da revista:
Biologia
/
Medicina
Ano de publicação:
1999
Tipo de documento:
Artigo
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