The stimulation of GABA(B) receptors increases serotonin release in the rat suprachiasmatic area.
The action of ?-aminobutyric acid (GABA) and related compounds on the spontaneous release of newly synthesized [(3)H]5-hydroxytryptamine ([(3)H]5-HT) was studied in the suprachiasmatic area (SCA) using a superfusion system. GABA (10 ?M) increased [(3)H]5-HT release from SCA by up to 190%. Bicuculline or picrotoxin (10 ?M) failed to inhibit the stimulatory effect of GABA. Muscimol (10 ?M), a GABA(A) agonist, was ineffective, however ?-p-chlorophenyl GABA, R(?)baclofen, enhanced over 200% the release of the indoleamine; this latter effect was stereospecific. RS baclofen was twice less potent than the R(?)isomer in increasing the [(3)H]5-HT release. S(+)baclofen failed to affect the release of the indoleamine, whereas it attenuated the effect of its enantiomer. The effect of R(?)baclofen was Ca(2+) dependent and was abolished by tetrodotoxin (TTX). Taken together these results suggest that in the SCA, [(3)H]5-HT release is facilitated by the stimulation of GABA(B) receptors. The possible localization of these receptors is discussed in the light of morphological data recently reported by Bosler et al. (1985) and results obtained after TTX application.
François-Bellan
A M
AM
INSERM-U6 and CNRS-UA634, 280, Bd Sainte-Marguerite, 13009 Marseille, France.
Hery
M
M
Barrit
M C
MC
Faudon
M
M
Hery
F
F