The activation of metabotropic glutamate receptors differentially affects GABA and alpha-melanocyte stimulating hormone release from the hypothalamus and the posterior pituitary of male rats.

The aim of the present study was to investigate the effect of metabotropic glutamate receptor (mGluR) activation on gamma-aminobutyric acid (GABA) and alpha-melanocyte stimulating hormone (alpha-MSH) release from hypothalamic fragments and posterior pituitaries. The actions of a number of subtype-selective mGluR agonists were monitored. A group I mGluR agonist, (S)-3-hydroxyphenylglycine (3-HPG; 0.5 mM), decreased K+-induced hypothalamic GABA release. (RS)-1-Aminoindan-1,5-dicarboxylic acid (AIDA), a specific group I mGluR antagonist (0.2 mM), blocked the effect of 3-HPG. (2S, 1'S, 2'S)-2-(Carboxycyclopropyl) glycine (L-CCG-I) and L-serine-O-phosphate (L-SOP; 0.01-1 mM), agonists of group II and III mGluRs, respectively, did not modify hypothalamic evoked GABA release. Group I mGluR activation decreased, whereas group III increased and group II induced no changes in GABA release from the posterior pituitary. 3-HPG (1 mM) and L-CCG-I (0.1 mM) decreased, whereas L-SOP (0.01-0.1 mM) did not change alpha-MSH release from hypothalamic fragments. No agonists of the three mGluR groups modified alpha-MSH release from the posterior pituitary. These results indicate that activation of mGluRs differentially affects GABA and alpha-MSH release from the hypothalamus and the posterior pituitary.