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Melatonin sees the light: blocking GABA‐ergic transmission in the paraventricular nucleus induces daytime secretion of melatonin
Author(s) -
Kalsbeek Andries,
Garidou MarieLaure,
Palm Inge F.,
Van Der Vliet Jan,
Simonneaux Valérie,
Pévet Paul,
Buijs Ruud M.
Publication year - 2000
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.2000.00202.x
Subject(s) - melatonin , suprachiasmatic nucleus , medicine , endocrinology , circadian rhythm , light effects on circadian rhythm , hypothalamus , vasopressin , biology , pineal gland , inhibitory postsynaptic potential , endogeny , chemistry
Despite a pronounced inhibitory effect of light on pineal melatonin synthesis, usually the daily melatonin rhythm is not a passive response to the surrounding world. In mammals, and almost every other vertebrate species studied so far, the melatonin rhythm is coupled to an endogenous pacemaker, i.e. a circadian clock. In mammals the principal circadian pacemaker is located in the suprachiasmatic nuclei (SCN), a bilateral cluster of neurons in the anterior hypothalamus. In the present paper we show in the rat that bilateral abolition of γ‐aminobutyric acid (GABA), but not vasopressin, neurotransmission in an SCN target area, i.e. the paraventricular nucleus of the hypothalamus, during (subjective) daytime results in increased pineal melatonin levels. The fact that complete removal of the SCN results in a pronounced increase of daytime pineal mRNA levels for arylalkylamine N‐acetyltransferase (AA‐NAT), i.e. the rate‐limiting enzyme of melatonin synthesis, further substantiates the existence of a major inhibitory SCN output controlling the circadian melatonin rhythm.