Selectively bred male rat lines differ in naïve and experienced sexual behavior

Effects of early life adversity on male reproductive behavior and the medial preoptic area transcriptome

Early life adversity can alter reproductive development in humans, changing the timing of pubertal onset and sexual activity. One common form of early adversity is limited access to resources. This adversity can be modeled in rats using the limited bedding/nesting model (LBN), in which dams and pups are placed in a low resource environment from pups' postnatal days 2-9. Our laboratory previously found that adult male rats raised in LBN conditions have elevated levels of plasma estradiol compared to control males. In females, LBN had no effect on plasma hormone levels, pubertal timing, or estrous cycle duration. Estradiol mediates male reproductive behaviors. Thus, here we compared reproductive behaviors in adult males exposed to LBN vs. control housing. LBN males acquired the suite of reproductive behaviors (mounts, intromissions, and ejaculations) more quickly than their control counterparts over 3 weeks of testing. However, there was no effect of LBN in males on puberty onset or masculinization of certain brain regions, suggesting LBN effects on estradiol and reproductive behaviors manifest after puberty. In male and female rats, we next used RNA sequencing to characterize LBN-induced transcriptional changes in the medial preoptic area (mPOA), which underlies male reproductive behaviors. LBN produced sex-specific alterations in gene expression, with many transcripts showing changes in opposite directions. Numerous transcripts altered by LBN in males are regulated by estradiol, linking hormonal changes to molecular changes in the mPOA. Pathway analysis revealed that LBN induced changes in neurosignaling and immune signaling in males and females, respectively. Collectively, these studies reveal novel neurobiological mechanisms by which early life adversity can alter reproductive strategies.

Revisiting medial preoptic area plasticity induced in male mice by sexual experience

Sexual experience in male rodents, induced by a first exposure to a receptive female, improves efficiency of following copulations. In mice, the mechanisms supporting this improvement are poorly understood. We characterized molecular modifications of the mouse hypothalamic medial preoptic area (mPOA), the main integrative structure for male sexual behaviour, after a single mating event. This paradigm induced long-lasting behavioural improvements and mPOA morphological changes, evidenced by dendritic spine maturation and an increase in the acetylated and tri-methylated forms of histone H3. Ejaculation affected testosterone, progesterone and corticosterone levels in both naive and experienced mice, but sexual experience did not modify basal plasma or hypothalamic levels of steroids. In contrast to studies carried out in rats, no changes were observed, either in the nitrergic system, or in sex steroid receptor levels. However, levels of glutamate- and calcium-associated proteins, including PSD-95, calbindin and the GluN1 subunit of the NMDA receptor, were increased in sexually experienced male mice. The Iba-1 microglial marker was up-regulated in these animals suggesting multicellular interactions induced within the mPOA by sexual experience. In conclusion, plasticity mechanisms induced by sexual experience differ between rat and mouse, even if in both cases they converge to potentiation of the mPOA network.

Differential organization of male copulatory patterns in high- and low-yawning-frequency sublines versus outbred Sprague-Dawley rats

The temporal organization of masculine sexual behavior in rats is highly stereotyped; involving a sequence of mounts, intromissions and ejaculations. Sexual behavior has been described in exogamic and genetically manipulated rodent species. In this work, we compare the male sexual behavior of outbred Sprague-Dawley (SD) to those of rats inbred for high (HY)- and low (LY)- spontaneous yawning frequency. In the first experiment, the percentage of inexperienced rats' ejaculatory behavior is significantly lower in the HY and LY respect to Sprague-Dawley rats. The latency to ejaculate for inexperienced HY was shorter than the LY and SD rats. In the second experiment, we examined the differences between inbred sublines and Sprague-Dawley rats once the subjects had become sexually experienced after four copulatory sessions. HY rats still have slower proportion of ejaculators respect to LY and SD rats. Additionally, postejaculatory latencies were longer for HY rats, with longer intercopulatory intervals and higher number of copulatory bouts that delayed ejaculation. Both sublines show lower copulatory efficiency respect to SD rats. In conclusion, both sublines show alterations in the temporal organization of sexual motor pattern that are due at least partially to strong inbreeding process to select them.

Sexual experience affects reproductive behavior and preoptic androgen receptors in male mice

Reproductive behavior in male rodents is made up of anticipatory and consummatory elements which are regulated in the brain by sensory systems, reward circuits and hormone signaling. Gonadal steroids play a key role in the regulation of male sexual behavior via steroid receptors in the hypothalamus and preoptic area. Typical patterns of male reproductive behavior have been characterized, however these are not fixed but are modulated by adult experience. We assessed the effects of repeated sexual experience on male reproductive behavior of C57BL/6 mice; including measures of olfactory investigation of females, mounting, intromission and ejaculation. The effects of sexual experience on the number of cells expressing either androgen receptor (AR) or estrogen receptor alpha (ERα) in the primary brain nuclei regulating male sexual behavior was also measured. Sexually experienced male mice engaged in less sniffing of females before initiating sexual behavior and exhibited shorter latencies to mount and intromit, increased frequency of intromission, and increased duration of intromission relative to mounting. No changes in numbers of ERα-positive cells were observed, however sexually experienced males had increased numbers of AR-positive cells in the medial preoptic area (MPOA); the primary regulatory nucleus for male sexual behavior. These results indicate that sexual experience results in a qualitative change in male reproductive behavior in mice that is associated with increased testosterone sensitivity in the MPOA and that this nucleus may play a key integrative role in mediating the effects of sexual experience on male behavior.

The association of testosterone, sleep, and sexual function in men and women

Testosterone has been the focus of several investigations and review studies in males, but few have addressed its effects on sleep and sexual function, despite evidence of its androgenic effects on circadian activity in both sexes. Studies have been conducted to understand how sleeping increases (and how waking decreases) testosterone levels and how this rhythm can be related to sexual function. This review addresses the inter-relationships among testosterone, sexual function and sleep, including sleep-disordered breathing in both sexes, specifically its effects related to sleep deprivation. In addition, hormonal changes in testosterone that occur in the gonadal and adrenal axis with obstructive sleep apnea and other conditions of chronic sleep deprivation, and which consequently affect sexual life, have also been explored. Nevertheless, hormone-associated sleep disruptions occur across a lifetime, particularly in women. The association between endogenous testosterone and sex, sleep and sleep disturbances is discussed, including the results of clinical trials as well as animal model studies. Evidence of possible pathophysiological mechanisms underlying this relationship is also described. Unraveling the associations of sex steroid hormone concentrations with sleep and sexual function may have clinical implications, as sleep loss reduces testosterone levels in males, and low sex steroid hormone concentrations have been associated with sexual dysfunction.

Differences in sexual behaviour in male and female rodents: role of serotonin

Serotonin plays an important role in both male and female sexual behaviour. In general, reduction of 5-HT function facilitates, whereas enhancement inhibits sexual behaviour. Most fundamental research on the involvement of 5-HT in sex has been performed in rats. Selective serotonin reuptake inhibitors (SSRIs) have comparable effects on male and female sexual behaviour in rats; they inhibit it but only after chronic administration. Activation of the 5-HT(1A) receptor facilitates sexual behaviour in male rats but inhibits sexual behaviour in female rats, suggesting a differential role for 5-HT(1A) receptors in male and female rats. Research on sexual behaviour in rats with null mutations in the serotonin transporter (SERT) indicated also a differential role for 5-HT(1A) receptors in male and female sexual behaviour. Evidence exists that different pools of 5-HT(1A) receptors have differential roles in various parts of the cascade of sexual events occurring during sexual interactions. Roles for other 5-HT receptors are less well defined although 5-HT(1B), 5-HT(2A/B) and 5-HT(7) receptors seem to be involved. Identification of putative differential or comparable roles in female and male sexual activities requires more research.

Activation of lumbosacral 5-HT2C receptors induces bursts of rhythmic activity in sympathetic nerves to the vas deferens in male rats

1. We previously demonstrated that p-chloroamphetamine (PCA) intravenously (i.v.) evokes a specific patterned bursting response in the vas deferens nerve (VDN) of anaesthetised male rats that is associated with contraction of the vas deferens, and ejaculation and contraction of the bulbospongiosus muscles. The present study used selective 5-HT agonists to induce similar rhythmic bursting responses in the VDN in order to reveal the 5-HT receptor subtypes involved. 2. The 5-HT(2C) receptor agonist (1.0 mg kg(-1) Ro600175 i.v.) evoked the characteristic bursting pattern responses in the VDN. The 5-HT(1A) receptor agonist (1.0 mg kg(-1) 8-OH-DPAT i.v.) failed to elicit any responses. However, 8-OH-DPAT coadministered in combination with Ro600175 induced a potentiation of the responses. 3. Responses were also evoked in rats with a mid-thoracic spinalisation, with a more predictable response being observed following the combination of agonists. This suggests an action of both agonists in the lumbosacral spinal cord. 4. Responses were blocked by 0.5 mg kg(-1) SB206553 i.v. (5-HT(2B/C) receptor antagonist) or 0.5 mg kg(-1) WAY100635 i.v. (5-HT(1A) receptor antagonist), but not 0.1 or 1.0 mg kg(-1) SB269970 i.v. (5-HT(7) receptor antagonist). 5. We suggest that activation of 5-HT(2C) and 5-HT(1A) receptor subtypes synergistically elicits contraction of the vas deferens through the activation of sympathetic preganglionic neurones in the spinal cord. 6. These data support the idea of a proejaculatory action of 5-HT(2C) receptors in the lumbosacral spinal cord, suggesting a descending 5-HT excitatory pathway in addition to a 5-HT inhibitory pathway. An excitatory action of 8-OH-DPAT at lumbosacral sites is also evident.

Do similar neural systems subserve aggressive and sexual behaviour in male rats? Insights from c-Fos and pharmacological studies

It is a common belief that male aggressive and sexual behaviour share many of the underlying neurobiological, neurological, pharmacological and neuroendocrine mechanisms. Therefore, we studied brain activation patterns in male rat after performance of aggressive and sexual behaviour and compared serotonergic pharmacology in the same paradigms to delineate possible similarities and differences. Patterns of Fos-immunoreactivity induced by aggressive and sexual encounters of Wild-type male Brown Norway rats were studied to localise the commonly activated (functionally shared) parts of the circuitry, and the specific (functionally different) parts of the neuronal circuitry. Some brain areas (caudal medial preoptic area and medial amygdala) were commonly activated, but other areas (e.g. posterodorsal parts of the medial amygdala, rostral preoptic and premammillary hypothalamus) showed remarkably specific differences in neural activation. 5-HT(1A) receptor agonists inhibit aggressive, but stimulate male sexual behaviour, whereas 5-HT(1B) receptor agonists inhibit both types of behaviour. Selective serotonin reuptake inhibitors share comparable inhibitory effects in aggression and sexual behaviour, although only at relatively high doses. We propose that separate hard-wired neural systems exist in the brain for aggressive and sexual behaviours, modulated via hierarchically 'higher-level' brain areas that are involved in the integration (gating) of the behavioural outcome of an organism.

Differential effects of simultaneous or sequential administration of paroxetine and WAY-100,635 on ejaculatory behavior

Clinical treatment of depression or anxiety with selective serotonin reuptake inhibitors (SSRIs) often results in delayed ejaculation or anorgasmia. Co-treatment with subtype-selective serotonin receptor antagonists may alter the timing of onset of action and potentiate or reduce sexual side effects. Sexual behavior in male Sprague-Dawley rats was examined after acute administration of the SSRI, paroxetine and the serotonin1A antagonist, WAY-100,635. Acute administration of paroxetine alone did not alter male ejaculatory behavior. However, administration of paroxetine plus WAY-100,635 resulted in a significant delay in mounting behavior and increased the time to ejaculation. Simultaneous administration of paroxetine and WAY-100,635 produced a greater delay in initiation of mounting behavior and ejaculation compared to sequential administration of paroxetine followed by WAY-100,635. The differential effect on sexual behavior or addition of specific serotonin receptor antagonists may be relevant for clinical treatment therapies of premature ejaculation.