Functional interactions between anteroventral periventricular kisspeptin neurons and gonadotropin-releasing hormone neurons in female mice.

In vitro electrophysiological study using optogenetics in acutely prepared mouse brain slices

“To determine if estradiol or ovarian cycle stage modulate functional connectivity in this circuit, anteroventral‐periventricular (AVPV) area kisspeptin neurons were photostimulated while recording firing and/or evoked synaptic currents from preoptic area GnRH neurons in acutely‐prepared mouse brain slices.”

Adult female GnRH-GFP and Kiss-Cre transgenic mice

“Adult female (80–185 days) GnRH‐green fluorescent protein (GFP), kisspeptin Cre recombinase (Kiss‐Cre); Kiss1‐hrGFP, and Kiss‐Cre;GnRH‐GFP mice were used for these studies.”

Variable number of mice and GnRH neurons per experimental group, totaling 200 cells across all groups

“Thirteen cells across all the groups studied (total 200 cells) had an increase in firing rate of >1 Hz within 5 s of stimulus onset that was atypical for the firing pattern of that cell”

Experiments involved viral injection followed by 3-6 weeks recovery, with ovariectomy performed 2 days to 6 weeks prior to recording

“Brain slices were prepared 3–5 weeks (Experiments 1–3) or 6 weeks (Experiment 4) after viral injection.”

Photostimulation induced a sustained, frequency-dependent increase in GnRH neuron firing rate that was blunted in 1-week ovariectomized mice

“Photostimulation induced a sustained, frequency‐dependent increase in GnRH neuron firing rate. This neuromodulatory‐typical response was not different in diestrous versus proestrous mice but was blunted in 1‐week OVX mice, suggesting ovarian steroids are needed for maintenance.”

Monosynaptic connectivity between AVPV kisspeptin and GnRH neurons was low and consistently GABAergic across hormonal states

“Monosynaptic connectivity was similarly low among hormonal states and consistently GABAergic.”

Fast-synaptic transmission was associated with greater increases in firing rate only during proestrus

“Fast‐synaptic transmission was, however, associated with greater increases in firing rate, but only during proestrus, indicating GnRH neuron responsiveness to AVPV kisspeptin neuron activation is dependent on both hormone milieu and synaptic connectivity.”

Low incidence of detected synapses and low signal-to-noise ratio in some recordings limited statistical power for certain interactions

“The observation that a firing response was not always associated with detection of synaptic transmission motivated us to increase the rigor of our design to determine if this was an artifact of our experimental conditions. Specifically, the low percentage of GnRH neurons exhibiting either a change in firing rate or evoked PSCs raised three primary concerns about our approach of using whole‐cell recordings with physiologic chloride concentration.”