GABA Signaling in the Posterodorsal Medial Amygdala Mediates Stress-induced Suppression of LH Pulsatility in Female Mice

Abstract

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.

NK3R signalling in the posterodorsal medial amygdala is involved in stress‐induced suppression of pulsatile LH secretion in female mice

“…The discovery that activation of MePD kiss1 neurons increases the frequency of the GnRH pulse generator raised the hypothesis for the involvement of intranuclear GABA‐GABA disinhibitory interactions, typical of limbic pallidal structures, such as the MePD. Moreover, the MePD sends functional GABAergic projections to the ARC, 66 providing a possible route via which MePD kiss1 neurons modulate the activity of the GnRH pulse generator. Neuropharmacological studies aiming to untangle this functional neural circuitry in the MePD have demonstrated that GABA and glutamate neurotransmission within this region is necessary for kiss1 neurons to exert their upstream control over the GnRH pulse generator 38 .…”

Neuronal Network Dynamics in the Posterodorsal Amygdala: Shaping Reproductive Hormone Pulsatility

“…On the other hand, an ‘instructive’ component, i.e. GABA projections, provides a unique contribution that is imperative for the inhibitory effect of the MePD on reproductive function ( McIntyre et al, 2022 ). Balanced feed-forward excitation and feed-forward inhibition ensures that the overall excitability of the KNDy network is robust to the elevated excitatory input, permitting GABAergic projections to exert ‘inhibitory brake’, thus maintaining the LH IPI to prestimulation levels.…”

“…On the other hand, an 'instructive' component, i.e. GABA projections, provides a unique contribution that is imperative for the inhibitory effect of the MePD on reproductive function(McIntyre et al, 2022).…”

A Neuronal Circuit for Stress-induced Reproductive Suppression

“…Two recent Endocrinology papers from the O’Byrne lab ( 1 , 2 ) advance and elaborate the role of GABAergic and urocortin-3 neurons in the posterodorsal subnucleus of the medial amygdala (MePD) in mediating acute psychological stress-induced suppression of luteinizing hormone (LH) pulses, possibly via their projection to the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator. This group has already laid much of the groundwork to show that the MePD modulates pulsatile LH secretion ( 3 ) as well as pubertal timing.…”

“…Others have provided evidence for direct projections from the amygdala to the kisspeptin neurons located in the arcuate nucleus (eg, 4 ), which are considered to be the hypothalamic GnRH/LH pulse generator. In the first of the 2 featured O’Byrne papers ( 1 ), McIntyre and colleagues show that MePD GABAergic neurons mediate stress-induced suppression of LH pulses in female mice. Two different experimental psychosocial stressors were used to reinforce their findings: restraint and exposure to the odor of 2,5-dihydro-2,4,5-trimethylthiazoline (a single molecule constituent of fox urine).…”