EXCITATORY AMINO-ACIDS AS MODULATORS OF GONADOTROPIN-SECRETION

The effects of quinolinic acid (QUIN) and quisqualate (QA) on the secr etion of GnRH from MBH and LH and FSH from AP of 50 day old male rats have been evaluated by means of an ''in vitro'' perifusion technique. QUIN (100 mu M) is able to increase GnRH secretion with an action medi ated by an NMDA receptor type, as shown by the inhibitory effect exert ed by both a competitive (AP-5) and a non-competitive (MK-801) specifi c antagonist. QA ''per se'' at the concentrations tested(1-100 mu M) d oes not modify GnRH and gonadotropin secretion, but in the presence of a specific KA/QA receptor antagonist (DNQX) exerts a stimulatory effe ct at both levels. This observation might indicate that of the two QA receptor subtypes (ionotropic and metabotropic), this agonist binds to the metabotropic one with very low affinity: thus it is likely that a higher dose is required in order to have any effect on gonadotropin s ecretion. However, in the presence of DNQX, which binds to the ionotro pic receptor, all the available QA can bind to the metabotropic one an d can exert its action at MBH AP levels.