Electrical stimulation of dorsal and ventral striatum differentially alters the copulatory behavior of male rats.

Sexual behavior is a natural reward that activates striatal dopaminergic (DA) circuits, and dopamine exerts a facilitative influence on copulation. Electrical stimulation of the striatum has been shown to be rewarding, but its effect on male sexual behavior display has not been established. The objective of the present work was to assess the effects of low- and high-frequency electrical stimulation of the dorsal and ventral striatum on male rat sexual behavior expression. To this aim, copulatory activity of sexually experienced male rats was recorded during electrical stimulation of the nucleus accumbens (NAcc) or caudate-putamen (CP), at each stimulation frequency, before and after sexual exhaustion. Results showed that electrical stimulation of the NAcc at both frequencies increased the number of ejaculations that male rats were able to show in a 30-min period. By contrast, stimulation delivered to the CP inhibited sexual behavior by slowing its display. Each effect was more pronounced at low than at high stimulation frequencies. In the same rats, once sexually exhausted, electrical stimulation of these brain areas did not reverse the sexual behavior inhibition that characterizes the sexual exhaustion state. It is concluded that dorsal and ventral striatal DA brain regions exert opposite influences on copulatory behavior expression of sexually experienced male rats. Also, that the facilitative effect of NAcc electrical stimulation on sexual activity, with the stimulation parameters used, cannot surmount the sexual behavior inhibition resulting from copulation to satiation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the medial preoptic area interfere with the display of a conditioned place preference for vaginocervical stimulation in rats.

The present study examined the effect of ibotenic acid lesions of the medial preoptic area (mPOA) on the expression of a conditioned place preference (CPP) for vaginocervical stimulation. Rats with bilateral lesions of the mPOA failed to display the CPP for vaginocervical stimulation shown by rats with sham or incomplete lesions. These findings provide additional support for the role of the mPOA in the neural circuitry underlying the reinforcing effects of female sexual behavior and raise the possibility that the altered pattern of approach and withdrawal behavior observed following lesions of the mPOA may be attributable in part to a diminution of the reinforcing effects of vaginocervical stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopamine release in the medial preoptic area is related to hormonal action and sexual motivation.

To help elucidate how general the role of dopamine (DA) release in the medial preoptic area (mPOA) is for the activation of male sexual behavior in vertebrates, we recently developed an in vivo microdialysis procedure in the mPOA of Japanese quail. Using these techniques in the present experiment, the temporal pattern of DA release in relation to the precopulatory exposure to a female and to the expression of both appetitive and consummatory aspects of male sexual behavior was investigated. Extracellular samples from the mPOA of adult sexually experienced male quail were collected every 6 min before, while viewing, while in physical contact with, and after exposure to a female. In the absence of a precopulatory rise in DA, males failed to copulate when the barrier separating them from the female was removed. In contrast, males that showed a substantial increase in mPOA DA during precopulatory interactions behind the barrier, copulated with females after its removal. However, there was no difference in DA during periods when the quail were copulating as compared to when the female was present but the males were not copulating. In addition, we show that precopulatory DA predicts future DA levels and copulatory behavior frequency. Furthermore, the size of the cloacal gland, an accurate indicator of testosterone action, is positively correlated with precopulatory DA. Taken together, these results provide further support for the hypothesis that DA action in the mPOA is specifically linked to sexual motivation as compared to copulatory behavior per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Properties and sex-specific differences of GABAA receptors in neurons expressing gamma1 subunit mRNA in the preoptic area of the rat

Gamma-aminobutyric acid type A (GABAA) receptors expressed within the medial preoptic area (mPOA) are known to play a critical role in regulating sexual and neuroendocrine functions. In the rat brain, high levels of expression of the gamma1 subunit mRNA of the GABAA receptor are restricted to a limited number of regions that mediate sexual behaviors, including the mPOA. The biophysical and pharmacological profiles of native gamma1-containing receptors in neurons are unknown. Here, we have characterized the properties of GABAA receptor-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) and currents elicited by fast perfusion of GABA to isolated mPOA neurons of juvenile male and female rats. No significant sex-specific differences were evident in the mean peak amplitude, distribution of event amplitudes, kinetics of current decay, or the frequency of sIPSCs. The profile of modulation of sIPSCs by diazepam, beta-CCM and zolpidem, allosteric modulators that act at the benzodiazepine (BZ) site of the GABAA receptor, support the assertion that mPOA neurons of both sexes express functional gamma1-containing receptors. The ability of zolpidem to modulate both sIPSC amplitude and currents elicited by rapid perfusion of GABA to mPOA neurons differed significantly between the sexes. Zolpidem reversibly induced negative modulation of currents in mPOA neurons isolated from male rats, but had no effect in mPOA neurons from female rats. Concentration-response analysis of responses in neurons acutely isolated from male rats indicated an IC50 of 58 nM with maximal decreases of approximately 50% of control peak current amplitude. In situ hybridization analysis demonstrated that levels of the gamma1 subunit mRNA are significantly higher in mPOA neurons from male than female rats. No significant sex-specific differences were detected in the levels of alpha1, alpha2, or alpha5 mRNAs. These results suggest that native gamma1-containing receptors are expressed in primary neurons of the mPOA and that sex-specific differences in the expression of this subunit may contribute to sexual dimorphism in GABAA receptor modulation by compounds acting at the BZ site.     

Effect of lesion location within the medial preoptic-anterior hypothalamic continuum on maternal and male sexual behaviors in female rats.

Lesions of the medial preoptic-anterior hypothalamic continuum (MPOA-AH) disrupt both maternal behavior and male sexual behavior in the rat. To test the hypothesis that the 2 behaviors involve different neural systems in the MPOA-AH, small bilateral lesions were made in different anterior-posterior locations in the MPOA-AH of 41 maternal-sensitized Charles River female rats treated with testosterone propionate (.5 mg/day, sc), and the effects of these lesions on maternal and male sexual behaviors were assessed. Lesions centering in the MPOA disrupted maternal behavior (pup retrieval, nest building, and nursing), with anterior MPOA lesions being more effective (on pup retrieval and nest building) than posterior MPOA lesions. Lesions centering in the AH had little or no effect on maternal behavior. By contrast, male sexual behavior (mounting) was strongly disrupted by lesions in either the MPOA or the AH, with lesions in the rostral AH being most effective. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Forebrain sites of estradiol-17!b action on sexual behavior and aggression in female Syrian hamsters.

The effects of intracranial implants of estradiol in the ventromedial hypothalamus (VMH), the anterior hypothalamus (AH), or the medial amygdala (AMG) on aggression, sexual behavior, and serum estradiol were examined in female Syrian hamsters. Estradiol implants in the VMH, followed by systemic progesterone, stimulated sexual behavior and inhibited aggression. Estradiol implants in other intracranial sites activated sexual behavior but did not reliably inhibit aggression. Intracranially implanted and systemically treated animals had equivalent peripheral estradiol concentrations at sacrifice. Results suggest that (1) the VMH is an important neural site for estradiol actions on sexual and aggressive behavior, (2) the caudal AH and AMG may also be sites of estradiol action on sexual behavior, and (3) intracranial implants may only be effective given systemic estradiol exposure or the concurrent stimulation of multiple brain areas. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is sexual motivational state linked to dopamine release in the medial preoptic area?

The medial preoptic area (mPOA) is a key site for the dopaminergic enhancement of male sexual behavior. Dopamine release increases in the rat mPOA with mating, supporting the critical stimulatory role played by preoptic dopamine on male sexual behavior. However, it has been questioned whether dopamine is specifically related to the occurrence of male sexual behavior and not simply involved in general arousal. To address this question, we asked whether dopamine release in the mPOA is linked to the production of male sexual behavior in Japanese quail (Coturnix japonica), a species that exhibits a much shorter temporal pattern of copulation than rats and does not have an intromittent organ, resulting in a very different topography of their sexual response. Extracellular samples from the mPOA of adult sexually experienced male quail were collected every 6 min before, during, and after exposure to a female using in vivo microdialysis and analyzed using high-performance liquid chromatography with electrochemical detection. Extracellular dopamine significantly increased in the presence of a female and returned to baseline after removal of the female. However, quail that failed to copulate did not display this increased release. These findings indicate that it is not solely the presence of a female that drives dopamine release in males, but how a male responds to her. Furthermore, in quail that copulated, dopamine release did not change in samples collected during periods of no copulation. Together, these findings support the hypothesis that dopamine action in the mPOA is specifically linked to sexual motivation and not only to copulatory behavior or physical arousal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Different receptor mechanisms mediate the effects of endotoxin and interleukin-1 on female sexual behavior

Activation of the immune system by lipopolysaccharide (LPS) produces physiological, neuroendocrine and behavioral effects, some of which are mediated by cytokine production. We have previously shown that the cytokine interleukin-1 (IL-1) inhibits sexual behavior in female, but not male rats, while producing a comparable suppression of locomotion in both sexes. The present study examined the effects of LPS on sexual behavior and locomotion of male and female rats, and the involvement of IL-1 receptors in mediating the effects of IL-1 and LPS on females' behavior. Peripheral (i.p.) administration of LPS (50 or 250 microg/kg) significantly decreased sexual behavior in females, up to 6 h after administration, while it had no effect on male sexual behavior. However, locomotor activity, measured in the open-field test, was similarly reduced by LPS in both males and females. Pretreatment with the IL-1 receptor antagonist (IL-1ra) either i.p. (10 mg/kg) or intracerebroventricularly (i.c.v.) (50 microg/rat) did not prevent the inhibition of female sexual behavior and locomotion induced by either i.p. (50 microg/kg) or i.c.v. (200 or 400 ng/rat) administration of LPS, respectively. However, identical doses of IL-1ra significantly reversed the effects of IL-1beta, administered either i.p. (5 microg/kg) or i.c.v. (50 ng/rat), respectively. These results demonstrate that both LPS and IL-1beta produce marked inhibition of sexual behavior in female, but not in male rats. However, IL-1 receptors are not required for the effects of LPS on sexual behavior in female rats.     

Hypophysectomy facilitates sexual behavior in female rats

Lordosis was elecited in 49% of 87 hormonally untreated, hypophysectomized-ovariectomized (hypox-ovx) female rats in response to palpation of the flanks and perineum (vaginal stimulation was not applied). By contrast, only 12% of 113 hormonally untreated ovariectomized (ovx) rats showed lordosis in response to such stimulation. Subsequently, hypox-ovx and ovx-only rats were given daily injections of 1 mug/kg estradiol benzoate (EB) and tested for sexual receptivity with males. Teh estrogen-treated hypox-ovx females became sexually receptive significantly earlier, and exhibited higher lordosis quotients and more soliciting behavior, than the estrogen-treated ovx-only rats. The increased sexual responsiveness in the hypox-ovx rats could be due to increased LRH activity. To test this, we treated hypox-ovx rats with dihydrotestosterone propionate (DHT-P), which suppresses plasma LH levels but is relatively ineffective in inducing sexual receptivity, and found a significant depression of lordosis responsiveness. These experiments suggest that hypox-ovx females show a heightened responsiveness to hormonal and/or sensory factors that induce a lordosis response, possibly because of increased LRH activity.     

Effects of paced mating and intromissive stimulation on feminine sexual behavior and estrus termination in the cycling rat.

The effects of differential mating stimulation on sexual behavior and estrus length were examined in cycling rats that could or could not self-regulate, or pace, the timing of sexual contact. Female rats (Rattus norvegicus) received 30 paced, 30 nonpaced, or 15 nonpaced followed by 15 paced intromissions during mating tests. Decreases in sexual responsiveness were seen during the 2nd half of testing; pacing was associated with greater inter-intromission intervals, decreased proceptivity, and increased rejection behavior at this time. Female rats pacing during the 2nd test half behaved similarly, regardless of prior treatment, showing that the number rather than the timing of prior intromissions affected subsequent behavior. However, estrus length was decreased by prior paced mating. These data suggest that changes in sexual responsivity occur throughout estrus and that the nature of these changes is differentially dependent on the type of mating stimulation received. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopamine release in the medial preoptic area of female rats in response to hormonal manipulation and sexual activity.

Dopamine (DA) is responsive to hormonal manipulations and has been implicated in the regulation of female rat sexual behavior. In the present studies, extracellular DA levels were assessed in the medial preoptic area (MPOA) of ovariectomized female rats in response to exogenous ovarian hormones and during sexual activity. In female rats primed with a low dose of estradiol benzoate (2 μg), but not with a higher dose (20 μg), a 500-μg progesterone injection increased extracellular DA and facilitated copulatory behavior. Extracellular DA levels in the MPOA were further augmented during sexual interactions with a male rat in a nonpacing copulatory chamber by either perineal or vaginal stimulation. However, in a pacing chamber, DA efflux did not increase, although the metabolites rose significantly during copulation. Together, these findings suggest that extracellular DA in the MPOA responds to the hormonal state of the female rat and may contribute to her expression of sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Long-lasting effects of neonatal stimulation on the behavior of rats.

The present study aimed to analyze the effects of neonatal stimulation on species-specific behaviors (defensive reactions to a predator and social interactions) in adult male and female rats. Handling and an unpredictable sequence of aversive stimuli were applied to male and female pups from the 1st to the 10th day after delivery; behavioral inhibition, aggression, and sexual behavior were evaluated in adulthood. Results showed that either neonatal handling or aversive stimulation decreased behavioral inhibition in a novel and potentially harmful situation (open field with a predator) in both male and female rats and increased maternal aggressive behavior. Sexual behavior in both males and females decreased, which could affect reproductive capability. The results could cast doubts on the generalization of beneficial effects of neonatal stimulation on the behavior of adult rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relation of Fos-IR expression in the pelvic ganglion to sexual behavior in laboratory rats.

The pelvic ganglion (PG) provides both sympathetic and parasympathetic innervation to the genitalia and other pelvic structures. To determine whether neuronal activity of the PG, as detected by Fos-like immunoreactivity (Fos-IR), is related to sexual stimulation, male and female rats were tested under a variety of conditions. In males, Fos-IR expression in the PG was positively correlated with the amount of both genital and noncontact stimulation. In females, only ejaculation preceded by multiple intromissions induced a significant increase in Fos-IR; multiple intromissions or ejaculation preceded by only 0–1 intromission did not affect Fos-IR. Additional experiments comparing Fos-IR expression, in which some females were allowed to pace their sexual contact and others were not, revealed that ejaculation duration was the key factor in the induction of Fos-IR in female rats. Because the conditions under which Fos-IR expression occurred in females are identical to those required for sperm transport, we suggest that, in the female, sperm transport is regulated in part by autonomic outflow from the PG after copulation. These relations between sexual behavior and measures of PG activity are consistent with the idea that the sexually dimorphic organization of the peripheral nervous system plays a major role in mediating the gender-specific outcome of copulation: ejaculation in the male and sperm transport in the female. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal and cortical activity during sexual behavior in the female rat.

Studied hippocampal and cortical activity during sexual behavior in 6 female albino van Leeuwenhoek-Huis R-strain rats. Hippocampal theta appeared during S's soliciting behavior. High-frequency theta accompanying the male's pursuit slowed when the male mounted the female and then increased in frequency during the brief continuation of lordosis following mounts without vaginal penetration. During prolonged lordosis after intromissions and ejaculations, slow theta continued. No changes in cortical frequencies were observed during mounts, intromissions, or ejaculations. During immobility (standing, sitting, and lying down), hippocampal activity became slow and irregular. High-amplitude hippocampal and, eventually, cortical spindles developed during immobility as sexual exhaustion was approached. Immobility and its accompanying EEG spindling are interpreted as indicative of a sexual satiety or inhibitory process. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implications of immediate-early gene induction in the brain following sexual stimulation of female and male rodents

Induction of immediate-early genes (IEGs), such as c-fos, has been widely used to mark the activation of brain regions following different types of sexual stimulation and behavior. A relatively common set of hormone-concentrating basal forebrain and midbrain structures in female and male rodents is activated by copulatory stimulation, in particular, stimulation of sensory nerves that innervate the penis or vagina/cervix, olfactory or pheromonal stimuli, and conditioned sexual incentives. These regions include the preoptic area, lateral septum, bed nucleus of the stria terminalis, paraventricular hypothalamus, ventromedial hypothalamus, medial amygdala, ventral premammillary nuclei, ventral tegmentum, central tegmental field, mesencephalic central gray, and peripeduncular nuclei. Regions that do not contain classic intracellular steroid receptors, such as the ventral and dorsal striatum or cortex, are also activated. IEGs have also been colocalized with cytoplasmic proteins like GnRH and oxytocin, and have been used in conjunction with retrograde tracers to reveal functional pathways associated with different sexual behaviors. Steroid hormones can also alter the ability of sexual stimulation to induce IEGs. Despite the many similarities, some differences in IEG induction between sexes have also been found. We review these findings and raise the question of what IEG induction in the brain actually means for sexual behavior, that is, whether it indicates the perception of sexual stimulation, commands for motor output, or the stimulation of a future behavioral or neuroendocrine event related to the consequences of sexual stimulation. To understand the role of a particular activated region, the behavioral or neuroendocrine effects of lesions, electrical stimulation, drug or hormone infusions, must also be known.     

Sensory modulation of the medial preoptic area neuronal activity by dorsal penile nerve stimulation in rats

The study was aimed at finding out the influence exerted by the genital afferents on the medial preoptic area (mPOA), which plays a pivotal role in the regulation of male sex behavior. To fulfil this objective, the effects of stimulation of the dorsal penile nerve (DPN) on the activity of 82 mPOA neurons were studied. The base line firing rates of the mPOA neurons, studied by extracellular recording, ranged between 0.5 and 38.5 Hz (mean 7.18 +/- 7.91). The stimulation of the DPN (20 Hz, 0.4 msec. 70 microA) influenced 79.69% of the neurons studied. Though increased firing was the predominant influence produced (50%), decreased firing was also seen in a few (29.69%). The excited and inhibited neurons were randomly distributed within the mPOA. Neurons located in the lateral and posterior hypothalamus were not affected by the DPN stimulation. The stimulation parameters used in this study did not produce any change in the systemic arterial pressure and heart rate. The results provide electrophysiological evidence of afferent inputs from the male sex organ to the mPOA, which is an important area controlling male sex behavior.     

Effects of repeated testing on sexual behavior of the female rat.

Investigated effects of stimulation during repeated testing, using 24 female Sprague-Dawley rats in which intromission was prevented by a vaginal mask. Ss were ovariectomized and administered 1 mg of estradiol benzoate (EB) daily for 10 days (Exp I) or 5 mg of EB for 2 days (Exp II). Behavioral indices included lordosis quotient (a measure of sexual receptivity) and rejection quotient (a measure of social rejection of the male). Intensity and duration of lordosis gave additional measures. In Exp I hourly testing increased lordosis quotient and duration, especially in Ss receiving EB for 5 days; no effects of daily testing were shown. Exp II compared the behavior of Ss that were either handled hourly and tested hourly with the male rat or only handled hourly to the behavior of Ss that were tested and handled only once. Repeated testing and/or handling facilitated sexual responsiveness, while Ss that received neither treatment were sluggish in their social response to the male rat when they were tested, and were not sexually receptive. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential rates of exhaustion and recovery of several parameters of male rat sexual behavior.

Studied sexual exhaustion of 12 sexually experienced Long-Evans male rats with respect to several copulatory measures. The ejaculatory latency, intercouplatory interval, and intromission frequency demonstrated a U-shaped curve, exhibiting high values for the initial ejaculatory series, falling to a minimum at an intermediate ejaculatory series, and again increasing at exhaustion. The absolute refractory period of the postejaculatory interval (measured at vocalization termination) increased linearly, whereas the relative refractory period (the remaining portion of the postejaculatory interval) was a positively accelerating function. Partial recovery tests demonstrate that the preejaculatory measures and absolute refractory period substantially returned to baseline values by Day 6, while the relative refractory period was still extended. The significance of these data to the theoretical modeling of sexual behavior is discussed. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pain sensitivity and individual differences in self-reported sexual behavior.

The relationship between sexual behavior and pain sensitivity was assessed in 27 heterosexual men and 20 heterosexual women. Sexual behavior measures included sexual motivation and ratings of subjective sexual arousal to and enjoyment of an auditory stimulus. Pain sensitivity measures were pain threshold and pain tolerance in a cold pressor task. Participants were tested after exposure to a neutral or a sexual audio stimulus. Exposure to the sexual stimulus increased pain sensitivity in women but not in men. However, sexual behavior measures were correlated with pain threshold for both men and women. Specifically, higher pain thresholds were associated with weaker sexual motivation, lower enjoyment potential for sexual interaction, and increased inhibition during intercourse. These results are consistent with findings in laboratory animals, suggesting that differences in sexual behavior may reflect differences in responsiveness to a variety of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Testosterone has rewarding affective properties in male rats: Implications for the biological basis of sexual motivation.

Evidence from mammalian species, including humans, suggests that testosterone (TST) enhances motivational aspects of sexual behavior, although the mechanism by which TST exerts this effect is unknown. The hypothesis that increases in plasma TST have rewarding affective properties was examined. Acute elevations of plasma TST were induced in intact male rats by systemic administration of a recently developed testosterone-hydroxypropyl-β-cyclodextrin inclusion complex that mimics pulsatile release of the hormone. In a conditioned-place-preference paradigm, rats displayed a preference for an environment previously paired with TST administration (800 μg/kg and 1,200 μg/kg) as opposed to an environment paired with saline administration, indicating that TST has rewarding affective properties. The findings suggest that TST may enhance motivational aspects of mammalian sexual behavior by facilitating acquisition or expression of learned associations between environmental stimuli and sexual activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)