Olfactory bulb removal and response suppression in rats

Following either olfactory bulb damage or control surgery, Sprague-Dawley rats were trained on a VI 30-sec reinforcement schedule until their response rate stabilized and then placed on one of three schedules to assess response suppression ability: omission training, extinction, or DRL. Animals with OB damage responded at higher rates than controls during VI training and performed less efficiently on all measures of response suppression ability. The results were compared with performance by animals with septal damage from a previous study.     

Olfactory cues and accessory olfactory bulb lesion: effects on sexual behavior in the cyclic female rat

The influence of olfactory cues and accessory olfactory bulb (AOB) lesion on female sexual behavior was studied in virgin female Wistar rats. In Experiment 1, it appeared that distance or contact exposure to male urine soiled bedding for 8 hours before testing increased sexual receptivity, i.e., the number of receptive females at 18:00-19:00 on proestrus. In Experiment 2, we observed that sexual receptivity at 18:00-19:00 on proestrus was not affected by AOB lesion as compared to sham-operated females. In Experiment 3 the effects of both AOB lesion and olfactory cues were analyzed. Sexual receptivity at 18:00-19:00 on proestrus did not significantly differ in sham-operated and accessory olfactory bulbectomized females both exposed to the odor of male urine. Regarding lordosis quotient in the three experiments, no significant difference was observed. Mechanisms whereby olfactory cues and/or AOB lesion modified female sexual behavior on proestrus in virgin female rats were discussed in the light of previous and present observations.     

Olfactory bulb removal: influences on the aggressive behaviors of male mice

Bilateral removal of the olfactory bulbs of castrated male mice completely prevented the arousal of aggressiveness by exogenous administration of androgen. Unilateralally bulbectomized mice showed fighting comparable to that shown by sham-operated control mice. It was concluded that earlier demonstrations of the abolition of intermale aggressive behavior in mice following olfactory bulb removal could not be attributed to impairment in pituitary-gonadal function. Although in this experiment bulbectomy completely prevented the androgenic arousal of intermale aggression, bulbectomy did not affect the display of aggressive behavior in a competition for food situation.     

Naltrexone effects on male sexual behavior, corticosterone, and testosterone in stressed male rats

Chronic physical or psychological stress disrupts male reproductive function. Studies in our laboratory have shown that stress by immersion in cold water (ICW) and by electrical foot shocks (EFS) has inhibitory effects on male sexual behavior; these effects do not seem to be mediated by an increase in corticosterone, nor by a decrease in testosterone. On the other hand, it is known that endogenous opioids are released in the brain in response to these same stressors; consequently, they could be participating in the impairment of sexual behavior, as well as in the changes in corticosterone and testosterone caused by stress. The aim of this study was to analyze the effects of the opioid antagonist naltrexone (NTX) on male sexual behavior, corticosterone, and testosterone in both stressed sexually experienced and naive male rats. Sexually experienced adult male rats were assigned to one of the following groups (n = 10 each): 1) control group, males without sexual evaluation; 2) control group, rats injected ip with saline, non-stressed; 3) control group, rats injected with NTX (3 mg/kg) non-stressed; 4) rats injected ip with saline, and stressed by EFS; 5) rats injected ip with NTX (1.5 mg/kg) and stressed by EFS; 6) rats injected ip with saline and stressed by ICW; 7) rats injected ip with NTX (1.5 mg/kg) and stressed by ICW; 8) rats injected ip with NTX (3 mg/kg) and stressed by ICW. Naive males were assigned to the same control groups but only stressed by ICW and the NTX dose used was 3 mg/kg. Injections were given 30 min before stress sessions. Stress was applied on 20 consecutive days. Male sexual behavior was assessed 15 min after EFS or 30 min after ICW, on days 1, 4, 8, 12, 15, and 20. Trunk blood was collected at the end of the experiments on day 20 of stress. Corticosterone and testosterone were evaluated by HPLC.Mount, intromission and ejaculation latencies were longer in control saline naive males compared to control saline sexually experienced males on the first day. NTX administration to control naive males caused a decrease in mount, intromission, and ejaculation latencies, as well as an increase in ejaculatory frequency/30 min, compared to control-saline only on day 1. Stressed naive males showed higher mount, intromission and ejaculation latencies, compared to control and stressed sexually experienced males, as well as comparable increase in corticosterone and decrease in testosterone plasma levels. NTX administration before exposure to stress prevented the modifications caused by stress in sexual parameters. Sexual behavior in control sexually-active males injected with saline or NTX was not modified. Saline stressed males showed the previously reported alterations in sexual behavior, as well as an increase in corticosterone and a decrease in testosterone plasma levels. Stressed males injected with NTX before exposure to stress showed no alterations in male sexual behavior. NTX in control non-stressed males did not modify corticosterone plasma levels, but did cause a significant increase in plasma testosterone. The increase in corticosterone and the decrease in testosterone due to stress, were attenuated with the opioid antagonist, both in naive and sexually experienced males. Prevention of ICW stress effects was more effective with higher doses of NTX (3 mg/kg). These data suggest that endogenous opioids could be participating in the effects caused by stress on male sexual behavior, corticosterone, and testosterone.     

Stress and sexual behavior in male rats

The relationship between sexual behavior and stress in male rats was investigated. Stress induction by psychophysical immobilization fo 3 hours along three days caused significant alterations of the different parameters which make up the sexual behavior of male rats. An extension of the stressing situation from 3 to 6 hours under the same experimental conditions produced very similar sexual disturbances. Our experimental results suggest that effects of acute stress on sexuality may be independent of time.     

Olfactory control of the sexual behavior of male and female mice

Bilateral removal of the olfactory bulbs virtually eliminates sexual behavior in male and female mice. In the studies reported here, mice were rendered anosmic by intranasal application of a zinc sulfate solution. Peripherally induced anosmia did not affect the sexual behavior of male mice. Peripherally induced anosmia attenuated the hormone induced display of sexual receptivity in female mice, but peripherally anosmic females were significantly more receptive than bulbectomized females. This finding suggests that (1) pheromonal factors may be involved in the full arousal of sexual receptiveness in female mice, but (2) that the effect of bulbectomy upon sexual receptivity in female mice cannot be attributed solely to the surgical production of anosmia. The general failure of peripherally induced anosmia to mimic the effects of olfactory bulb removal upon the display of sexual behavior in male and female mice suggests that the olfactory bulbs are importantly involved in the control of sexual behavior in some manner not related to sense of smell.     

Effects of olfactory bulb removal and flank shock on copulation in male rats

Sexually experienced male rats received bilateral olfactory bulbectomy (BOB, N=9), unilateral olfactory bulbectomy (UOB, N=7) or a sham operation (Sham, N=8). Copulation was severely disrupted in BOB males, whereas only minimal effects on copulation were observed in UOB males. Penile reflexes were not affected by either operation. Intermittent flank shock stimulated copulation in 5/6 BOB males. The BOB males that ejaculated had longer intromission latencies and longer postejaculatory intromission intervals than did Sham males receiving a similar schedule of shocks. Even so, all BOB males that ejaculated with flank shock also resumed copulation and ejaculated a second time without further shocks. Three BOB males that ejaculated with flank shock were tested the following week without shock, and none of these males copulated. These results strengthen previous conclusions that the olfactory bulbs are critical for the initiation and maintenance of sexual arousal in male rats.     

Simultaneous and successive olfactory bulb removal: influences on the mating behavior of male mice

Simultaneous olfactory bulb removal abolished mating behavior in sexually experienced male mice. In contrast to simultaneous bulbectomy, removal of both olfactory bulbs in two operations separated by an interval of 30 days had no effect on the mating behavior of male mice. In successively bulbectomized males, the occurrence or nonocurrence of the opportunity for mating behavior in the interval between the removal of each bulb had no influence on the degree to which mating behavior was spared. It was concluded that the abolition of mating behavior produced by simultaneously removing both olfactory bulbs in male mice is not a consequence of a sensory deficit, but is due to the destruction of tissues directly involved in the mediation of sexual behavior.     

Yohimbine and naloxone: effects on male rat sexual behavior.

We evaluated the effects of yohimbine (2 mg/kg) and naloxone (5 mg/kg), separately and in combination, on copulatory behavior in male rats. In Experiment 1, yohimbine evinced decrements in intromission frequency, ejaculation latency, and copulatory efficiency, whereas naloxone administration was followed by an increased ejaculation latency, and the combination of yohimbine plus naloxone was without effect. In Experiment 2, yohimbine evinced decreases in intromission frequency, ejaculation latency, copulatory efficiency in the first, but not subsequent, copulatory series, as well as a decreased latency to sexual exhaustion. Further, treatment with yohimbine alone, naloxone alone, or yohimbine plus naloxone was followed by a reduction in the number of ejaculation prior to sexual exhaustion. Thus, at the doses tested, no synergistic effects were observed for the combination of yohimbine plus naloxone.     

Endomorphin-1, effects on male sexual behavior

We examined the effect of endomorphin-1 (EM-1), an endogenous opioid peptide that binds selectively to the μ receptor, on male copulatory behavior in sexually vigorous Wistar rats. In the first experiment, four doses of EM-1 (1, 10, 50, and 100 μM) injected intracerebroventricularly produced a marked increase in ejaculation latency and interintromission interval and reduced the number of ejaculations during the test. In experiment 2 the effects of EM-1 were completely blocked by pretreatment with naloxone (5 mg/kg) 30 min prior to intracerebroventricular injection of EM-1 (100 μM). Collectively these results indicate that the activation of μ receptors by EM-1 modifies parameters associated with ejaculation (increases ejaculation latency and reduces the number of ejaculations) confirming that opioids are released during sexual behavior.     

Effects of vasopressin on female sexual behavior in male rats

Intracerebroventricular (i.c.v.) injection of an Arg-vasopressin (AVP) antagonist did not stimulate female sexual behavior in adult castrated male rats treated with ovarian hormone but stimulated this behavior in male rats which were castrated on the day of birth. It is suggested that neonatal androgen stimulation in the male rat offsets the influence of AVP on female sexual behavior in the adult.     

The effects of prenatal psychological stress on the sexual behavior and reactivity of male rats

Male offspring of prenatally stressed rats showed low levels of copulatory behavior during a series of brief tests with estrous females but successfully impregnated female cagemates during long term tests of breeding effectiveness. Sexual performance on the short term tests was inversely related to open field activity with the offspring of prenatally handled mothers exhibiting more sexual behavior and less open field activity. These results support the notion that prenatal stress influences both the sexual behavior and emotional reactivity of male offspring. Deficits observed during short term tests of breeding effectiveness appear to be reversible under optimal conditions.     

Relation of autogrooming to sexual behavior in male rats

Grooming and penile reflexes were studied in male rats that were restrained in supine position with the penile sheath retracted or were free to copulate with sexually receptive females. In Experiment 1 there was a reliable concordance in supine males between the tendency to groom and the tendency to display penile reflexes. In Experiment 2 we analyzed the sequential organization of grooming and genital events in supine tests. It was assumed that many or most episodes of ventral grooming would have been genital grooming had access to the genitalia not been prevented by restraint. Paw grooming tended to precede clusters of penile responses, whereas ventral grooming started after the onset of erections. Experiment 3 was an exploration of grooming in the context of copulation, rather than supine restraint. Males groomed their genitalia immediately after all intromissions and after all mounts that ended mount bouts. The duration of grooming was not affected by whether or not intromission occurred. Finally, in Experiment 4 we observed genital and nongenital grooming and recorded electromyographic (EMG) activity from the striated bulbospongiosus muscle (mBS) of the penis in freely moving rats. Consistently, mBS activity led to genital grooming with a short latency, whereas nongenital grooming rarely led to genital grooming, and EMG activity was not associated with nongenital grooming nor did it tend to follow after genital grooming was initiated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short-term endogenous hyperprolactinaemia and sexual behavior of male rats

Sexual behavior of male rats was studied in a short-term endogenous hyperprolactinaemic condition. Hyperprolactinaemia was induced by grafting two pituitary glands under the kidney capsule. Five days after operation homografted animals, as compared to the sham operated, displayed an enhancement of several parameters of copulatory behavior. In particular, significant reductions in the mount and intromission latencies were observed. The stimulation of sexual behavior of male rats by short-term hyperprolactinaemia might be due to an enhancement of dopaminergic transmission in specific brain areas by prolactin (PRL).     

Prostaglandin E2 accelerates sexual behavior in male rats

Sexual behavior in male rats is accompanied by an increase in body temperature of 18 degrees C. It has been suggested that this increase may be, at least in part, a febrile response mediated by the endogenous central release of prostaglandins of the E series (PGE). This putative release of PGE could also affect the expression of sexual behavior, a possibility that was tested in the present experiment. PGE2 was infused into the cerebral aqueduct and sexual behavior and hypothalamic temperature were monitored. PGE2 infusion raised hypothalamic temperature and decreased the postejaculatory interval and ejaculation latency. The exact cause of this acceleration of sexual behavior cannot as yet be determined.     

Tail pinch induces sexual behavior in olfactory bulbectomized male rats

Adult male Long-Evans rats were subjected to bilateral olfactory bulbectomy, sham surgery or no treatment. Of 34 bulbectomized rats, 24 failed to ejaculate on either of 2 tests with a primed ovariectomized female. All control animals exhibited normal sexual behavior, and 10 bulbectomized animals ejaculated at least once during the 2 tests. Later histological examination revealed a relationship between size of lesion and extent of behavioral deficits. After a third test, 16 nonejaculatory animals were subjected to a tail pinch (TP) procedure, immediately followed by a fourth test. The remaining 8 nonejaculatory animals were tested similarly, but without tail pinch. Ten of the 16 tail pinch animals showed complete sexual behavior on the first test, while 2 additional animals began to copulate after a second TP procedure 4 days later. Only 1 of the 8 animals not receiving TP ejaculated on these tests. Thus, TP applied shortly before sexual behavior tests can induce copulation in some males whose behavior had been disrupted by olfactory bulbectomy.     

Chemoinvestigatory and sexual behavior of male guinea pigs following vomeronasal organ removal

The vomeronasal organs of male guinea pigs were removed (VNX; n=10) or males experienced sham surgery (Sham; n=10). Subsequently a battery of chemosensory tests of investigatory responsiveness to conspecific urine was conducted. Additionally, male subjects were paired with female conspecifics for short and long periods and social and sexual behaviors were monitored. VNX males exhibited a depression in urine investigation and this depression became more profound following repeated testing and/or the passage of time. By 6.3 months following surgery, investigatory responsiveness to urine was practically eliminated. Maintenance of responsiveness to urine odors may require reinforcing input through the accessory olfactory system. In contrast to these effects on responsiveness to odors, VNX and Sham males were indistinguishable in their social and sexual behavior. These data indicate that male guinea pigs without a VNO: (1) Exhibit a depression of investigation of urine odors which is time dependent and which may involve an extinction-like process; (2) continue to discriminate classes of urine (e.g., urine from male vs urine from female conspecifics); and (3) exhibit normal sexual behavior. The vomeronasal organ in the male domestic guinea pig is apparently critical for the maintenance of normal responsiveness to sex odors but, in its absence, other sensory systems are capable of maintaining normal sexual behavior under conditions of laboratory testing.