Androgen receptor blockade in the MPOA or VMN: effects on male sociosexual behaviors

Previously, our laboratory has shown that androgen receptors in the medial preoptic area (MPOA) and ventromedial nucleus (VMN) are necessary for copulation in male rats. The present study examined whether these receptors are required for other sociosexual behaviors. In Experiment 1, different regions of the VMN were implanted with the antiandrogen hydroxyflutamide (OHF). We found that implants located in anterodorsal portions of the VMN were more effective at inhibiting the restoration of copulation than implants in the posteroventral VMN. In Experiment 2, a second set of male rats was pretested for copulation and other sociosexual behaviors and was castrated. Experimental animals then received Silastic capsules filled with testosterone (T) plus intracranial (IC) implants filled with OHF to selectively block androgen receptors in either the MPOA or VMN. We found that androgen receptor blockade in the MPOA inhibited the restoration of copulation but had no effect on other sociosexual behaviors. OHF directed at the VMN inhibited the restoration of copulation and 50-kHz vocalizations but had no effect on scent marking. Two tests were used to assay sexual motivation: partner preference and conditioned place preference (CPP). Both methods revealed impairments in sexual motivation in the VMN group but not in animals receiving OHF in the MPOA. Taken together, these data suggest that androgen receptors in the MPOA are essential for copulatory performance, while androgen receptors in the VMN are important for copulation, sexual motivation, and androgen-dependent vocalizations.     

Antennae sense heat stress to inhibit mating and promote escaping in Drosophila females

Environmental stress is a major factor that affects courtship behavior and evolutionary fitness. Although mature virgin females of Drosophila melanogaster usually accept a courting male to mate, they may not mate under stressful conditions. Above the temperature optimal for mating (20–25?°C), copulation success of D. melanogaster declines with increasing temperature although we observed vigorous courtship attempts by males, and no copulation takes place at temperatures over 36?°C. We attempted to identify the sensory pathway for detecting heat threat that drives a female to escape rather than to engage in mating that detects hot temperature and suppresses courtship behavior. We found that the artificial activation of warmth-sensitive neurons (‘hot cells’) in the antennal arista of females completely abrogates female copulation success even at permissive temperatures below 32?°C. Moreover, mutational loss of the GR28b.d thermoreceptor protein caused females to copulate even at 36?°C. These results indicate that antennal hot cells provide the input channel for detecting the high ambient temperature in the control of virgin female mating under stressful conditions.     

Chemosignals and hormones in the neural control of mammalian sexual behavior

Males and females of most mammalian species depend on chemosignals to find, attract and evaluate mates and, in most cases, these appetitive sexual behaviors are strongly modulated by activational and organizational effects of sex steroids. The neural circuit underlying chemosensory-mediated pre- and peri-copulatory behavior involves the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), medial preoptic area (MPOA) and ventromedial hypothalamus (VMH), each area being subdivided into interconnected chemoreceptive and hormone-sensitive zones. For males, MA–BNST connections mediate chemoinvestigation whereas the MA–MPOA pathway regulates copulatory initiation. For females, MA–MPOA/BNST connections also control aspects of precopulatory behavior whereas MA–VMH projections control both precopulatory and copulatory behavior. Significant gaps in understanding remain, including the role of VMH in male behavior and MPOA in female appetitive behavior, the function of cortical amygdala, the underlying chemical architecture of this circuit and sex differences in hormonal and neurochemical regulation of precopulatory behavior.     

Ventral midbrain involvement in copulatory behavior of the male rat

Stimulation bound copulation was obtained from a ventral midbrain extension of the hypothalamic medial forebrain bundle. Electrical stimulation at this site accelerated the achievement of ejaculation and the resumption of copulation after ejaculation. Sexual activity was temporarily depressed immediately after stimulation. The results are discussed in terms of a preoptic medial forebrain bundle ventral midbrain system influencing copulation in the male rat.     

Dopamine receptors in the ventral tegmental area affect motor, but not motivational or reflexive, components of copulation in male rats

Microinjection of apomorphine into the ventral tegmental area (VTA) of male rats was previously shown to delay the onset of copulation and slow its rate, presumably by stimulating impulse-regulating autoreceptors on cell bodies of the A10 mesocorticolimbic dopamine tract. Such stimulation would be expected to slow the firing rate of these neurons and, thereby, to impair locomotion and/or motivational processes. The present experiments tested whether the delayed onset and slowed rate of copulation were related to deficits in motor performance, sexual motivation, and/or genital reflexes. In X-maze tests the speed of running to all 4 goal boxes was slowed; however, the percentage of trials on which the male chose the female's goal box was not decreased. Examination of videotaped copulation tests revealed that the male showed fewer complete copulatory behaviors (mounts, intromissions, and ejaculations), but more misdirected or incomplete copulatory attempts after apomorphine in the VTA. There were also fewer scores of active, as opposed to inactive, behaviors, and the onset and rate of copulation were slowed. The total number of female directed behaviors was not different in apomorphine tests, compared to vehicle. Finally, tests of ex copula genital reflexes revealed no significant effects of apomorphine in the VTA on erections, penile movements, or seminal emissions. These data suggest a role of the VTA in the motor aspects and/or sensorimotor integration of copulation. Sexual motivation and ex copula genital reflexes appeared to be unaffected by apomorphine in the VTA.     

Amphetamine pretreatment facilitates appetitive sexual behaviors in the female rat

Rationale

Intermittent treatment of rats with psychomotor stimulants induces behavioral sensitization to their motor-stimulating effects. This sensitization involves an increase in mesolimbic and nigrostriatal dopamine release, and in male rats, facilitates sexual behavior.

Objectives

The aim of this study is to investigate the effect of repeated injections of d-amphetamine on appetitive and consummatory sexual behaviors in female rats.

Materials and methods

Sexually experienced or naïve females were injected with either d-amphetamine (1 mg/kg, i.p.) or saline every other day for three injections each. After each amphetamine injection, females were placed either in a bilevel testing chamber or in their home cages. After saline injections, females were placed in bilevel chambers. Following a 3-week washout period, females were tested for sexual behavior in bilevel chambers in a drug-free state.

Results

Amphetamine pre-exposure facilitated the display of solicitations, hops and darts, and female–male mounting (FMM), regardless of whether the drug was paired with the testing environment.

Conclusion

Intermittent amphetamine pretreatment that induces behavioral sensitization facilitates appetitive sexual behaviors in female rats, as has been shown previously in male rats. This suggests that the physiological substrates that modulate sensitized responses to psychomotor stimulants also mediate sensitized appetitive responses to sexual cues, including solicitation, hops and darts, and FMM. As in male rats, this facilitation was a direct consequence of amphetamine sensitization and not due to conditioned associations between drug and test environment.

     

Copulatory behavior is controlled by the sexually dimorphic nucleus of the quail POA

The medial preoptic nucleus (POM) of the quail preoptic area is sexually dimorphic and testosterone sensitive. Stereotaxic implantation of needles filled with crystalline testosterone demonstrated that the POM is a critical site of steroid action in the control of copulatory behavior. Only implants located in the POM reliably restored the behavior in castrated birds. Implants around the nucleus weakly activated the behavior; those which were distant by more than 200 microns were totally inactive. Electrolytic lesions confirmed the role of the POM in the control of copulatory behavior. The percentage of the POM which was lesioned was highly correlated to the behavioral deficit while the absolute size of the lesion was not. Electrolytic lesions in or around POM also significantly decreased the volume of the nucleus suggesting that the afferents and efferents of the nucleus are required for its full development. The total volume of the POM was correlated with the sexual behavior of the birds. The morphological changes in POM observed following exposure to testosterone probably represent the signature of the behavioral effects of the steroid. The sexually dimorphic testosterone-sensitive POM is therefore an excellent animal model to study the brain-steroid interactions which mediate the activation of male reproductive behavior.     

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 pheremonal 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.     

Copulation-induced abbreviation of estrus in the female guinea pig: Block by clonidine

In the female guinea pig, copulation produces a rapid inhibition of subsequent sexual receptivity. Injection of the alpha adrenergic agonist clonidine before mating blocked the early inhibitory effects of coital stimulation, while the serotonergic antagonist methysergide, and the dopaminergic antagonist pimozide were without effect. The effects of clonidine were prevented by pretreatment with the alpha adrenergic antagonist yohimbine. These results suggest that an adrenergic system is involved in the copulation-induced inhibition of receptivity and provide further evidence that such a system has an important facilitative role in the control of female sexual behavior in the guinea pig.     

Mating induces pupillary dilatation in female rats: role of pelvic nerve

In the present study, we demonstrate that natural or artificial vaginal stimulation exerts a powerful effect on autonomic activity, as measured by pupillary diameter. Pupillary diameter was recorded approximately 3-5 sec after copulatory mounts, intromissions, ejaculations or experimenter delivered stimulation. The pupil was magnified 43X and its diameter was measured directly from a calibrated video screen. Mating tests were performed on 13 female rats which received at least one complete ejaculatory series. Compared to the premount (baseline) value (1.01 mm), mean pupillary diameters were significantly greater during (a) mounts without intromissions (1.20 mm; 20% increase), (b) mounts with intromissions (1.34 mm; 33% increase), or (c) ejaculation (1.49 mm; 48% increase). Mean pupillary diameter during the post-ejaculatory interval (0.95 mm; 6% decrease) did not differ significantly from the premount baseline. Since the mean pupillary diameter at the last intromission before ejaculation was significantly larger (by 18%) than the diameter at the first intromission, repeated intromissions may generate a gradually increasing net sympathetic response reaching a peak at ejaculation. In order to identify the adequate stimuli for increasing pupillary diameter, we applied external genital stimulation (flank-perineal palpation), internal genital stimulation (probing the vaginal cervix with a glass rod), or both combined. Vaginal stimulation alone produced near-maximal pupillary dilatation; external genital stimulation was less effective, and combined internal and external genital stimulation was more effective. Thus, vaginal afferent activity is an adequate stimulus to produce pupillary dilatation. Furthermore, bilateral pelvic neurectomy markedly attenuated the effect of vaginal stimulation on dilating the pupil. Since pupillary diameter is at least partly a function of autonomic tone, this "bioassay" indicates that genital stimulation may produce a net sympathetic activating effect.