The role of GABA(A) and GABA(B) receptors in the control of GnRH release in anestrous ewes.

The paper reviews data concerning the involvement of GABA(A) and GABA(B) receptors in the control of GnRH secretion in anestrous ewes. Generally, GABA influences the GnRH release through GABA(A) and GABA(B) receptors located on perikaria of the GnRH neurons in the preoptic area (MPOA) or through the influence on beta-endorphinergic and catecholaminergic systems activity in MPOA and in ventromedial-infundibular region of the hypothalamus (VEN/NI). Stimulation of GABA(A) receptors in VEN/NI and MPOA attenuates GnRH release, while activation of GABA(B) receptors in MPOA decreases GnRH secretion, and in VEN/NI increases concentration of GnRH. The different neural mechanisms could be involved in this process: direct ligand action on the GABA(A) and GABA(B) receptors located on GnRH cells and axon terminals or indirect effect through the changes in the beta-endorphinergic and catecholaminergic systems activity in these structures of the brain.