LH-RH in the mesencephalic central grey can potentiate lordosis reflex of female rats

Abstract

The lordosis reflex, which characterises female reproductive behaviour in rodents, can be potentiated in oestrogen-primed ovariectomised female rats by electrical stimulation of the ventromedial nucleus of the hypothalamus (VMN). Subsequent demonstration of an immediate and large facilitation of the lordosis reflex from the mesencephalic central grey (CG) prompted us to speculate that the VMN may exert an oestrogen-dependent tonic bias on the mesencephalic circuitry for lordosis via its heavy descending projections. Moreover, we considered that luteinising hormone-releasing hormone (LH-RH) could be involved in this system. LH-RH can potentiate lordosis when given systemically to oestrogen-primed ovariectomised rats, and neurotropic effects of this peptide have been shown by microiontophoresis. Also, some axons in the CG have been stained with antiserum to LH-RH. The present study examined a possible role of LH-RH in the CG in the regulation of the lordosis reflex of oestrogen-primed ovariectomised female rats. Infusion of exogenous LH-RH in the CG had an immediate facilitative effect on the lordosis reflex, whereas passive immunisation against endogenous LH-RH by anti-LH-RH gamma-globulin diminished the reflex.