GABA signaling in the posterodorsal medial amygdala mediates stress-induced suppression of LH pulsatility in female mice.

Psychological stress is linked to infertility by suppressing the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. The posterodorsal subnucleus of the medial amygdala (MePD) is an upstream regulator of GnRH pulse generator activity and displays increased neuronal activation during psychological stress. The MePD is primarily a GABAergic nucleus with a strong GABAergic projection to hypothalamic reproductive centres, however, their functional significance has not been determined. We hypothesis that MePD GABAergic signalling mediates psychological stress-induced suppression of pulsatile luteinising hormone (LH) secretion. We selectively inhibited MePD GABA neurones during psychological stress in ovariectomised (OVX) Vgat-cre-tdTomato mice, to determine the effect on stress-induced suppression of pulsatile LH secretion. MePD GABA neurones were virally infected with inhibitory hM4DGi-DREADDs to selectively inhibit MePD GABA neurones. Furthermore, we optogenetically stimulated potential MePD GABAergic projection terminals in the hypothalamic arcuate nucleus (ARC) and determined the effect on pulsatile LH secretion. MePD GABA neurones in OVX female Vgat-cre-tdTomato mice were virally infected to express channelrhodopsin-2 and MePD GABAergic terminals in the ARC were selectively stimulated by blue light via an optic fibre implanted in the ARC. DREADD-mediated inhibition of MePD GABA neurones blocked predator odour and restraint stress-induced suppression of LH pulse frequency. Furthermore, sustained optogenetic stimulation at 10 and 20 Hz of MePD GABAergic terminals in the ARC suppressed pulsatile LH secretion. These results show for the first time that GABAergic signalling in the MePD mediates psychological stress-induced suppression of pulsatile LH secretion and suggest a functionally significant MePD GABAergic projection to the hypothalamic GnRH pulse generator.