Effects of ibotenic acid lesions of the nucleus accumbens on paced mating behavior in the female rat.

The present study investigated the role of the nucleus accumbens (NAcc) in paced mating behavior in female rats. A sexually receptive female rat will approach and withdraw from a sexually active male, thereby controlling the timing of the receipt of sexual stimulation (e.g., mounts, intromissions, ejaculations). In this study, ibotenic acid lesions in the NAcc core increased the likelihood that a female rat would withdraw from a male rat after a mount but did not affect contact return latency or sexual receptivity. lbotenic acid lesions in the NAcc shell did not affect paced mating behavior or sexual receptivity. The results suggest that the NAcc core plays a role in suppressing withdrawal behavior in response to less intense mating stimulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Female sexual responses in male cats facilitated by olfactory bulbectomy and medial preoptic/anterior hypothalamic lesions.

Using 23 sexually active male cats, the authors performed bilateral lesions of the medial preoptic/anterior hypothalamic area and olfactory bulbectomies, with the order of operations balanced. In all Ss, male sexual behavior was virtually eliminated by the combined operations. Increased levels of female proceptive behavior were seen after either type of lesion alone, and combined operations resulted in increased levels of receptivity. Results support the concept that there exists, within the brains of male animals, the neural basis for the display of female as well as male sexual responses and that certain brain operations may potentiate the display of female responses. However, it does not appear that the reduction of male behavior is necessarily coupled with an increase in female behavior, since no correlation was seen between the degree of enhancement of female behavior and the decrement in male behavior. (21 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)     

The medial and lateral cell groups of the sexually dimorphic area of the gerbil hypothalamus are essential for male sex behavior and act via separate pathways

Male reptiles, birds and mammals do not copulate if the medial preoptic area (MPOA) is destroyed but the MPOA cell groups necessary for male sexual behavior were not known. Here, two cell groups essential for copulation are identified in the sexually dimorphic area (SDA) of the gerbil (Meriones unguiculatus) MPOA. Bilateral cell-body lesions of either the medial or lateral SDA eliminated mating in sexually experienced male gerbils given testosterone. Nearby MPOA lesions did not. The medial and lateral SDA affect sex behavior via separate pathways since lesioning the medial SDA on one side of the brain and the lateral SDA on the other did not stop sexual behavior.     

Polyandrous females discriminate against previous mates

In most animal species, particularly those in which females engage in polyandry, mate choice is a sequential process in which a female must choose to mate or not to mate with each male encountered. Although a number of theoretical and empirical investigations have examined the effects of sequential mate choice on the operation of sexual selection, how females respond to solicitation by previous mates has received little attention. Here, we report the results of a study carried out on the polyandrous pseudoscorpion, Cordylochernes scorpioides, that assessed the sexual receptivity of once-mated females presented after a lapse of 1.5 hr or 48 hr with either their first mate or a different male. Females exhibited a high level of receptivity to new males, irrespective of intermating interval. By contrast, time between matings exerted a strong effect on female receptivity to previous mates. After a lapse of 48 hr, females did not differ significantly in their receptivity toward previous mates and different males, whereas at 1.5 hr after first mating, females were almost invariably unreceptive to males from whom they had previously accepted sperm. This result could not be attributed to male size or mating experience or to male sexual receptivity. Indeed, males were as willing to transfer sperm to a previous mate as they were to a new female. This difference between males and females in their propensity to remate with the same individual may reflect a conflict between the sexes, with males seeking to minimize postcopulatory sexual selection and females actively keeping open the opportunity for sperm competition and female choice of sperm by discriminating against previous mates.     

Exposure to constant photoperiod alters serum prolactin concentrations and behavioral response to estradiol in the ovariectomized goat

The effects of constant photoperiod on serum prolactin concentrations and sexual behavior of ovariectomized goats was investigated. Fourteen ovariectomized goats were divided into groups of seven goats each and placed in photoperiod-controlled rooms with either 8L:16D or 16L:8D. All goats received six estradiol (E2) treatments in a Latin square design. Following each treatment six 1-h observation periods were conducted. Blood was collected before E2 treatment and at each observation period for prolactin quantification. During the observation periods measures of attractivity, proceptivity, and receptivity were recorded. Goats exposed to 8L:16D displayed sexual behavior in response to doses of E2 lower than those required by goats exposed to 16L:8D. Prolactin concentrations were higher in goats exposed to 16L:8D than in those exposed to 8L:16D. It was concluded that photoperiod affects prolactin concentrations and behavioral sensitivity to E2 in goats. The effect of continued exposure to constant photoperiod on these variables was then investigated. The goats were held in constant photoperiod for 211 d and behavior tests as described for Exp. 1 were repeated. Scores for attractivity, proceptivity, and receptivity did not differ between the two groups after 211 d of exposure to constant photoperiod. Prolactin concentrations did not differ in this study between the two groups. It was concluded that after chronic exposure to 8L:16D ovariectomized goats become refractory to the stimulatory effects of short photoperiod.     

Connections between the pontine central gray and the ventromedial hypothalamus are essential for lordosis in female rats.

Lesions and knife cuts were used to study central gray (CG) and ventromedial hypothalamic (VMH) mediation of sexual receptivity in female rats. Lesions of the midbrain–pontine CG eliminated lordosis in female rats. Bilateral sagittal knife cuts that bracketed the rostral pontine CG also eliminated lordosis, and an experiment with the retrograde tracer Fluoro-Gold confirmed the effectiveness of these cuts in severing the lateral connections linking the VMH and the CG. Finally, females with a unilateral hypothalamic cut combined with a contralateral CG transection almost never showed lordosis. Each cut, at a different level for each side of the brain, transected axons linking the VMH and the CG. The demonstration that this combination eliminated lordosis provides new evidence that the lateral connections between the VMH and the CG are essential for the display of sexual receptivity in female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual selection, receiver biases, and the evolution of sex differences

REVIEW Recent approaches to analyzing the evolution of female mating preferences emphasize how historical influences on female receiver systems can bias the evolution of male traits that females find attractive. These studies combine animal behavior, sensory biology, phylogenetics, and artificial neural network models. They attempt to understand why specific phenotypes involved in sexual selection have evolved, rather than merely determining whether such traits and preferences are adaptive. It is now clear that traits and preferences often do not coevolve via genetic correlations, that female mating preferences for a given male trait are influenced by adaptations and constraints outside of the context of female responses to that particular trait, and that receiver biases can explain much of the diversity in male signaling phenotypes. It also appears that an understanding of historical effects will prove valuable in investigating why neural and cognitive systems respond to sensory stimuli as they do.     

Roles of gonadotropins and releasing hormones in hypothalamic control of lordotic behavior in ovariectomized, estrogen-primed rats.

Intrahypothalamic effects of gonadotropins (luteinizing hormone and follicle-stimulating hormone, LH and FSH, respectively), thyrotropin-releasing hormone (TRH), and luteinizing-hormone-releasing hormone (LRH) on lordotic behavior were evaluated in 63 Wistar ovariectomized (OVX) rats maintained at different receptivity levels. Under low receptivity, in which LRH has been shown to enhance mating behavior, medial preoptic area (MPOA) infusions of LH caused significant depressions in the lordotic response, whereas LH infusions into arcuate ventromedial area (ARC-VM) had no significant effect. FSH infusions into either area did not alter the response. In Exp II, in which OVX Ss were primed with higher doses of estrone to maintain high preinfusion receptivity, MPOA or ARC-VM infusions of either LH or TRH depressed lordotic behavior significantly, whereas neither LRH nor FSH inhibited the response. Exp III evaluated the effects of LH, FSH, and TRH on LRH-facilitated mating behavior with 50 Sprague-Dawley male rats. Infusions of LRH into either MPOA or ARC-VM significantly enhanced mating behavior, whereas addition of TRH or LH to the LRH infusates abolished this response. The antagonistic effects of LH and TRH on LRH-facilitated mating were correlated with previous observations of antagonistic effects on hypothalamic unit activity and monoamine metabolism. The antagonistic interrelation between LRH and LH may represent a mechanism for activation and coordination of sexual receptivity with ovulation. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of novelty on the reproductive behavior of male Japanese quail (Coturnix coturnix japonica).

In Exp I, 8 sexually deprived male Japanese quail were exposed to 1 of 7 female Japanese quail until they satisfied a 20-min sexual satiation criterion. The female was then replaced with a novel female or was allowed to remain in the test cage undisturbed. Introduction of the novel female did not reinvigorate sexual behavior above levels observed when the female was allowed to remain undisturbed. In Exp II, with 9 males and 15 females, males that were not sexually deprived were tested in the presence of 2 females. During experimental tests, 1 of the females was novel and the other was familiar. During control tests, both of the females were familiar. The presence of a novel female increased overall levels of male sexual behavior and also increased the number of males engaged in reproductive behavior. However, the enhanced sexual behavior was not differentially directed toward the novel or familiar female. Implications of these findings for the mating system of Japanese quail and for studies of the role of novelty in sexual behavior are discussed. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences among ovariectomized female rhesus macaques in the display of sexual behavior without and with estradiol treatment.

Ovariectomized, estrogen-primed, adult female rhesus macaques were preselected for the display of high (HLP) and low (LLP) levels of sexual performance. Eight sexually vigorous adult males were selected as partners. For 13 consecutive days each month, females received 0, 2.5, 5.0, and 10.0 μg of estradiol benzoate (EB) and were tested on Days 12 and 13 of injection. Blood samples were taken before and on the last day of each of the four injection series, and serum levels of estradiol, progesterone, and testosterone were determined with a radioimmunoassay. The HLP females (n?=?5) displayed higher levels of receptivity and proceptivity and received more mounts, intromissions, and ejaculations when tested without EB treatment than LLP females (n?=?5) did when they were tested with 10.0 μg of EB. Female receptivity, proceptivity, and attractiveness cannot be explained by estrogen action alone. The effectiveness of estrogen is limited by the somatic characteristics of the individual on which it acts. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The antidepressant, nefazodone, attenuates corticosterone-induced increases in 5-HT2A receptor-mediated behaviors in the female rat

The effects of chronic corticosterone administration on sexual behavior and on wet-dog shakes, a 5-HT2A mediated behavior, were investigated in the female rat. In addition, effects of the antidepressant nefazodone, a selective 5-HT2A receptor antagonist, both alone and in combination with corticosterone were examined. Testing was conducted in ovariectomized animals primed with estrogen and progesterone. Corticosterone was found to significantly increase sexual receptivity, sexual proceptivity and wet dog shakes. While nefazodone alone had no significant effects, it completely attenuated the corticosterone-induced increases in both sexual behavior and wet dog shakes. This suggests that corticosterone influences sexual behavior and wet dog shakes via a 5-HT2A receptor mechanism.     

Decrease in food intake following cortical spreading depression in static obese rats with ventromedial hypothalamic lesions.

Subjected 19 male and 23 female rats with ventromedial hypothalamic (VMH) lesions or with sham lesions to cortical spreading depression (CSD) 150 days after lesioning. Lesioned Ss showed a significantly lower food intake (as percentage of intake before CSD) than sham-lesioned Ss in the 14 days after CSD, but water intake did not differ between lesioned and sham-lesioned Ss. Both groups showed a slight decline in body weight, but lesioned Ss lost significantly more weight than sham-lesioned Ss. After 14 days, body weight, food intake, and water intake had returned to pre-CSD levels in both groups. Findings indicate that Ss with VMH damage are more sensitive to the effects of CSD than are normals and suggest that CSD acts to increase the activity of the VMH and to inhibit food intake, and this increase in activity is prolonged in VMH-lesioned Ss. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preoptic and subthalamic connections with the caudal brainstem are important for copulation in the male rat.

Bilateral lesions of either the medial preoptic area/anterior hypothalamus (MPAH) or a subthalamic region that includes the caudal zona incerta eliminate copulation in male rats. Pathways connecting the MPAH and subthalamus with the caudal brainstem may help regulate sexual behavior. Exp 1 showed that bilateral coronal transections of the pontine tegmentum reduce mating and that the combination of a unilateral tegmental cut with a contralateral excitotoxin lesion of either the MPAH (Exp 2) or subthalamus (Exp 3) virtually eliminates copulation. Asymmetric bilateral damage appears to eliminate mating through a bilateral effect common to the transection and the lesion: the destruction of connections linking the MPAH and subthalamus with the caudal brainstem. These results indicate that preoptic and subthalamic connections with the caudal brainstem are important for copulation in the male rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age and sex differences in behaviors mediated by the ventromedial hypothalamus.

Studied 28 male and 28 female Wistar rats. Circadian rhythm, emotionality, and taste responsiveness (except for responsiveness to quinine adulteration) were found to shift, in 1 or both sexes, toward a pattern suggesting decreased ventromedial hypothalamic (VMH) functioning with increasing age. A post hoc analysis of the configuration of positive and negative results suggests that, for those behaviors known to show both immediate and sustained effects of VMH lesion, male Ss showed a marked trend toward the lesioned pattern of behavior with increasing age, whereas females showed weaker or nonexistent age trends in the same behaviors. For those behaviors that changed only during the static, obese phase, or for which data are controversial as to whether changes took place as a result of the VMH lesion at all, this age and sex pattern did not emerge. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortisol facilitates induction of sexual behavior in the female musk shrew (Suncus murinus).

The role of cortisol in sexual behavior in the female musk shrew (Suncus murinus) was examined. High levels of cortisol were associated with sexual receptivity, as indicated by species-typical tail-wagging behavior, during brief (15-min) mating tests. When cortisol production was blocked by metyrapone, an 11-β-hydroxylase inhibitor, females exhibited reduced sexual behavior relative to controls, an effect that was reversed with acute cortisol replacement. These results indicate that cortisol facilitates, rather than inhibits, sexual behavior in this species and expands the comparative understanding of hypothalamic–pituitary–adrenal (HPA) effects on reproduction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of pre- and postpubertal social experience on sexual and social behavior in male and female brown lemmings (Lemmus sibiricus).

In 3 studies, male and female brown lemmings were either isolated at weaning (18 days) or then housed with siblings for another 10 days before being isolated. Before testing for sexual behavior at the age of 75–103 days, half of each group of males received a series of exposures to estrous females and half of each group of females was housed with a stud male. The results of mating tests indicate that whereas prior sexual experience facilitated subsequent copulatory behavior in both sexes, prepubertal interactions subsequently facilitated contact social and sexual behavior in males but did not increase the behavioral scores of females, who engaged in high levels of sexual behavior regardless of prepubertal experience. The effect of prior copulatory activity on male sexual performance could not be attributed to increasing age (i.e., maturational processes) because the behavior of males tested once but at different ages did not differ appreciably. Prepubertal social interaction appeared to predispose males to benefit from sexual experience later in life. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hyperinsulinemia in rats with ventromedial hypothalamic lesions: Role of hyperphagia.

Examined the relation of hyperinsulinemia to hyperphagia in 18 female hooded Long-Evans rats with lesions of the ventromedial hypothalamus (VMH). Plasma insulin and glucose levels were assayed after a 4-hr fast and 17 min after the initiation of a meal (6 ml of sweetened milk in 7 min) in 8 other Ss with sham lesions, VMH Ss maintained at preoperative body weight by food restriction, and VMH Ss fed ad lib. Both VMH groups displayed basal and postabsorptive hyperinsulinemia compared with the sham-operated group, but insulin levels were greatest under the ad lib feeding condition. It is suggested that VMH hyperinsulinemia is due both to a primary effect of the lesion and to hyperphagia and that marked obesity can result in the absence of basal hyperinsulinemia as a result of hyperphagia with consequent postabsorptive hyperinsulinemia. (14 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Projection of the sexually dimorphic area of the gerbil hypothalamus to the retrorubral field is essential for male sexual behavior: Role of A8 and other cells.

To determine if the sexually dimorphic area (SDA) of the gerbil hypothalamus affects male sexual behavior through its projections to the retrorubral field (RRF) or ventrolateral periaqueductal gray (PAGvl), these pathways were lesioned asymmetrically. Unilateral radio frequency lesions of the lateral SDA (LSDA), the major source of the pathways, impaired mating when combined with contralateral RRF, but not PAGvl, lesions. N-methyl-{d}-aspartate (NMDA) lesions of the medial SDA, LSDA, and the area between them (the total pathway source) eliminated mating when combined with contralateral, but not ipsilateral, NMDA lesions of the RRF. To determine if A8 cells contributed to these effects, males received NMDA in the SDA and NMDA or 6-hydroxydopamine in the contralateral RRF. When combined with large SDA lesions, A8 lesions impaired but did not eliminate mating. Thus the SDA–RRF pathway, but not an SDA-A8 pathway, is essential for sexual behavior in male gerbils. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)