GnRH pulse generator frequency is modulated by kisspeptin and GABA‐glutamate interactions in the posterodorsal medial amygdala in female mice

Abstract

Kisspeptin neurons in the arcuate nucleus of the hypothalamus generate gonadotrophinreleasing hormone (GnRH) pulses, and act as critical initiators of functional gonadotrophin secretion and reproductive competency. However, kisspeptin in other brain regions, most notably the posterodorsal subnucleus of the medial amygdala (MePD), plays a significant modulatory role over the hypothalamic kisspeptin population; our recent studies using optogenetics have shown that low-frequency light stimulation of MePD kisspeptin results in increased luteinsing hormone pulse frequency. Nonetheless, the neurochemical pathways that underpin this regulatory function remain unknown. To study this, we have utilised an optofluid technology, precisely combining optogenetic stimulation with intranuclear pharmacological receptor antagonism, to investigate the neurotransmission involved in this circuitry. We have shown experimentally and verified using a mathematical model that functional neurotransmission of both GABA and glutamate is a requirement for effective modulation of the GnRH pulse generator by amygdala kisspeptin neurons.

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

“…Additionally, the activation of a glutamatergic projection from the MePD to the ARC was predicted to result in silencing of the KNDy network due to excessive activation, as the GnRH pulse generator is highly sensitive to incoming stimuli. 38 This interpretation is in line with mathematical modelling of the ultradian oscillation of the ARC KNDy network, which is known to work on a bifurcation system that is terminated as an upper threshold of basal neuronal activity is reached. 8,10 Basal activity within the ARC KNDy network may reflect endogenous activity or mimic inputs that the network can receive externally from other brain regions, such as the MePD.…”

“…This enhanced stimulatory input from the MePD increases ARC KNDy network excitability resulting in the transition from a pulsatile to a quiescent dynamic state of the GnRH pulse generator in the absence of gonadal steroids. 10,38 In our model, exposure to psychosocial stress is proposed to activate NK3R signalling in the MePD, exerting a similar effect on the activity of the GnRH pulse generator as senktide administration in the MePD (see Figure 4A,D,G).…”

“…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 These experimental observations led to the development of a mathematical model to verify the hypothetical mechanism that low-frequency activation of MePD kiss1 neurons may provide a direct stimulatory signal to downstream GABA interneurons, which, in turn, suppress inhibitory GABAergic projections from the MePD to ARC KNDy neurons resulting in an increase in GnRH pulse generator activity. Additionally, the activation of a glutamatergic projection from the MePD to the ARC was predicted to result in silencing of the KNDy network due to excessive activation, as the GnRH pulse generator is highly sensitive to incoming stimuli.…”

“…We have already extended a previously published mathematical model of the ARC KNDy neuronal population incorporating inputs from the MePD neural circuitry comprised of kiss1, GABA and glutamate signalling. 8,10,38 In the current study, we build upon this…”

The molecular phenotype of kisspeptin neurons in the medial amygdala of female mice

“…Because kisspeptin can potently stimulate GnRH neurons (10,11) and the MeA projects both directly and indirectly to the POA where GnRH neurons reside (45)(46)(47)(48), it remains possible that MeA Kiss1 neurons participate in the regulation of the reproductive axis by acting directly or indirectly on GnRH neurons. Some recent optogenetic and chemogenetic mouse studies have begun to address this possibility (39,(49)(50)(51), but this is still currently not well understood. Thus, at present, the various functional roles of MeA kisspeptin neurons remain unknown, in part due to our limited understanding of the detailed phenotype of those specific kisspeptin neurons.…”