Brain circuits activated by female sexual behavior evaluated by manganese enhanced magnetic resonance imaging

Kisspeptin participates in the positive reward state induced by paced mating and modulates sexual receptivity and paced mating behavior in female rats

Kisspeptin (Kp), a potent regulator of the hypothalamic-pituitary-gonad axis, was recently shown to be involved in partner preference and sexual receptivity in females. Interestingly, Kp and its receptor (Kiss1r) are expressed in brain regions involved in the reward and motivation of reinforcing behaviors. Therefore, in the present study, we designed 3 experiments to determine the participation of Kp in female sexual behavior and the positive affective (PA) reward state induced by paced mating (PM). In all experiments, we used sexually naïve ovariectomized Wistar female rats primed with estradiol benzoate (EB, 2.5 μg/rat) 48 h before behavioral tests. In experiment 1 (n = 9), we tested the effect of Kp on PM. We demonstrated that Kp-10 (14 nmol) induced similar levels of receptivity to treatment with EB + progesterone and facilitated PM by reducing the return latency after intromissions. In experiment 2 (n = 8), we evaluated the effect of p234 penetratin, a Kiss1r antagonist, on PM. The administration of p234 in doses of 7.5 nmol and 15 nmol reduced the mean lordosis intensity and increased mount and intromission return latencies. Finally, in Experiment 3, we tested the capacity of Kp to induce a PA state or the antagonist to block the reward state induced by PM. Kp-10 (7 and 14 nmol) induced a clear conditioned place preference. This reward state and that produced by PM were blocked by p234 (15 nmol). Our findings underscore the critical role of Kp in modulating female sexual behavior and the PA state associated with PM, highlighting its potential to enhance sexual motivation.

Identification of neural circuits controlling male sexual behavior and sexual motivation by manganese-enhanced magnetic resonance imaging

Introduction

Different techniques have been used to identify the brain regions that control sexual motivation and sexual behavior. However, the influence of sexual experience on the activation of these brain regions in the same subject is unknown. Using manganese-enhanced magnetic resonance imaging (MEMRI), we analyzed the activation of brain regions in the sexual incentive motivation (SIM) and the partner preference PP (tests) on weeks 1, 5, and 10 in male rats tested for 10 weeks. AIM. In experiment 1, we analyzed the possible toxic effects of 16 mg/kg of MnCl2 on male sexual behavior, running wheel, and motor execution. In experiment 2, subjects were tested for SIM and PP using MEMRI.

Methods

In both experiments, a dose of 16 mg/kg (s.c) of chloride manganese (MnCl2) was administered 24 h before subjects were tested and placed immediately thereafter in a 7-Tesla Bruker scanner.

Results

In experiment 1, the dose of 16 mg/kg of MnCl2 did not induce behavioral alterations that could interfere with interpreting the imaging data. In experiment 2, we found a clear preference for the female in both the SIM and PP tests. We found a higher signal intensity in the olfactory bulb (OB) in week 1 of the SIM test compared to the control group. We also found increased signal intensity in the socio-sexual behavior and mesolimbic reward circuits in the SIM test in week 1. In the PP test, we found a higher signal intensity in the ventral tegmental area (VTA) in week 10 compared to the control group. In the same test, we found increased signal intensity in the socio-sexual and mesolimbic reward circuits in week 5 compared to the control group. Cohen's d analysis of the whole brain revealed that as the subjects gained sexual experience we observed a higher brain activation in the OB in the SIM group. The PP group showed higher brain activation in the cortex and subcortical structures as they acquired sexual experience.

Discussion

As the subjects gain sexual experience, more structures of the reward and socio-sexual circuits are recruited, resulting in different, and large brain activations.

Being friendly: paced mating for the study of physiological, behavioral, and neuroplastic changes induced by sexual behavior in females

Paced mating in rats is an experimental condition that allows the evaluation of sexual behavior in a way that closely resembles what occurs in seminatural and natural conditions enabling the female to control the rate of the sexual interaction. In conventional non-paced mating tests, females cannot escape from male approaches, which may lead to an unrewarding overstimulation. Paced mating is an alternative laboratory procedure that improves animal welfare and has a higher ethological relevance. The use of this procedure contributed to the identification of physiological and behavioral factors that favor reproduction. Paced mating includes motivational and behavioral components differentiating quantitative and qualitative characteristics that are critical for the induction of the rewarding properties of mating. These positive consequences ensure that the behavior will be repeated, favoring the species' survival. Sexual reward is an immediate consequence of paced mating, mediated mainly by the endogenous opioid system. Paced mating also induces long-lasting neuroplastic changes, including gene expression, synthesis of proteins, and neurogenesis in sex-relevant brain areas. The interest in paced mating is growing since the complexity of its elements and consequences at different levels in a laboratory setting resembles what occurs in natural conditions. In this review, we analyze the classic studies and recent publications demonstrating the advantages of using paced mating to evaluate different aspects of sexual behavior in females.