LATERALITY OF THE GONADOTROPIN-RELEASING-HORMONE PULSE-GENERATOR IN THE RAT - INTERACTION OF NEURONS LOCATED IN BOTH PREOPTIC AREAS AS A BASIC FEATURE

Though the pivotal importance of pulsatile gonadotrophin releasing hormone (GnRH) release from the hypothalamus for sufficient luteinizing hormone (LH) secretion is well recognized, the mechanisms causing GnRH pulses are still largely unknown. In the rat, the GnRH neurons are concentrated in the preoptic area, which is a bilateral structure of the anterior hypothalamus. This distribution into two distinct brain areas raises the question of whether the GnRH neurons in both preoptic areas are simultaneously or alternatively active and whether an interaction between both areas is required to generate GnRH pulses. We addressed these questions by unilateral manipulations of the activity of GnRH neurons using either electrical lesion or local infusion of gamma-aminobutyric acid (GABA), a neurotransmitter known to inhibit LH release via a hypothalamic action. Acute lesion of one preoptic area caused complete cessation Of pulsatile LH release which was restored after 48 h. An acute inhibition of LH release was also observed after unilateral preoptic application of GABA. It is concluded that an interaction of both preoptic areas is mandatory for GnRH pulse generation. However, we suggest that the pacemaker function is not intrinsic to GnRH nor GABA neurons but the cross-talk between these neurons within and.between both preoptic areas results in episodic GnRH release.