Kisspeptin neurones in the posterodorsal medial amygdala modulate sexual partner preference and anxiety in male mice

Abstract

The posterodorsal medial amygdala (MePD) is a neural site in the limbic brain involved in regulating emotional and sexual behaviours. There is, however, limited information available on the specific neuronal cell type in the MePD functionally mediating these behaviours in rodents. The recent discovery of a significant kisspeptin neurone population in the MePD has raised interest in the possible role of kisspeptin and its cognate receptor in sexual behaviour. The present study therefore tested the hypothesis that the MePD kisspeptin neurone population is involved in regulating attraction towards opposite sex conspecifics, sexual behaviour, social interaction and the anxiety response by selectively stimulating these neurones using the novel pharmacosynthetic DREADDs (designer receptors exclusively activated by designer drugs) technique. Adult male Kiss-Cre mice received bilateral stereotaxic injections of a stimulatory DREADD viral construct (AAV-hSyn-DIO-hM₃ D(Gq)-mCherry) targeted to the MePD, with subsequent activation by i.p. injection of clozapine-N-oxide (CNO). Socio-sexual behaviours were assessed in a counter-balanced fashion after i.p. injection of either saline or CNO (5 mg kg^-1 ). Selective activation of MePD kisspeptin neurones by CNO significantly increased the time spent by male mice in investigating an oestrous female, as well as the duration of social interaction. Additionally, after CNO injection, the mice appeared less anxious, as indicated by a longer exploratory time in the open arms of the elevated plus maze. However, levels of copulatory behaviour were comparable between CNO and saline-treated controls. These data indicate that DREADD-induced activation of MePD kisspeptin neurones enhances both sexual partner preference in males and social interaction and also decreases anxiety, suggesting a key role played by MePD kisspeptin in sexual motivation and social behaviour.

Keywords: amygdala; anxiety; kisspeptin; mice; partner preference; sexual behaviour.

Figure 1

Expression of posterodorsal medial amygdala (MePD) kisspeptin neurones with hM3Dq‐mCherry in Kiss‐Cre mice. Coronal section shows red mCherry fluorescence positive neurones (blue line) in the MePD but not in the arcuate nucleus (ARC) (A) and the white arrow indicates the injection site of AAV‐hSyn‐DIO‐hM ₃D(Gq)‐mCherry into the MePD of Kiss‐Cre mice in the same section (B). Higher‐power view shows the MePD kisspeptin neurones tagged with mCherry (red fluorescence), which indicates hM3Dq receptor expressing kisspeptin neurones (C). The absence of red fluorescence in the anteroventral periventricular nucleus (AVPV) (blue dotted line) (D) and arcuate nucleus (ARC) (yellow dotted line) (E) shows the specificity of the viral contruct to MePD kisspeptin neurones. Schematic representation27 of MePD and its spatial relationship with the optic tract (blue dotted line) (F). ME, median eminence; OT, optic tract; 3V, third ventricle

Figure 2

Effect of clozapine‐N‐oxide (CNO) on sexual partner preference. CNO (5 mg kg^‐1; i.p.) resulted in a significant increase in the time spent investigating oestrous females compared to males, whereas, with vehicle (saline), there was only a tendency for increased investigation of oestrous female (A). The partner preference score for oestrous female was significantly increased following treament with CNO compared to vehicle (B). The overall investigatory time with both male and female conspecifics was significantly greater with CNO (C). Genital grooming episodes were not significantly differerent with or without CNO (D). *P < .05 vs vehicle, ^# P < .05 vs female in response to CNO (n = 9). The results are the mean ± SEM

Figure 3

Effect of clozapine‐N‐oxide (CNO) on anxiety and social interaction. CNO (5 mg kg^‐1; i.p.) significantly increased the time spent in the open arms of the elevated plus maze (EPM) (A) and the number of entries into the EPM open arms (B), resulting in a significant reduction in the anxiety index (C). Time spent in social interaction with juvenile conspecific significantly increased following CNO administration compared to vehicle (D). *P < .05 vs vehicle (n = 9). The results are the mean ± SEM