Seventy-five nonkiller male rats were divided into two groups, 38 animals receiving 3 mg/kg reserpine and the other 37 receiving saline. Fifty percent of the reserpine-treated animals showed mouse killing, whereas none of the other animals did so. Mouse-kill responses were already exhibited within 32 h after treatment, while the animals were still heavily sedated.

The role of sex hormones in sexuality and mood across the menstrual cycle was investigated. Twenty-one normal healthy women were followed for one menstrual cycle. Blood samples were taken frequently, and analyzed for estradiol, progesterone, testosterone, androstenedione, dehydroepiandrosterone sulfate, cortisol, and sex hormone-binding globulin. A diary concerning sexual interest and behavior, and different moods, was completed daily. Although the sample was not large, a clear effect of menstrual cycle phase on levels of testosterone and the free testosterone index was demonstrated. In a preliminary screening interview, 11 of the 21 women had reported that they suffered from premenstrual complaints (PC), the other 10 had reported no complaints in the premenstrual phase (NPC). Significant differences between the two groups were established in estradiol and the estradiol–progesterone ratio, with the NPC group having higher levels of both endocrine parameters across different menstrual samples. Psychologically, a cycle effect on tension and sexual interest was demonstrated. The NPC group reported a peak in sexual interest in the premenstrual phase, whereas the PC group reported a peak in the ovulatory phase. There was a difference between the two groups in feelings of fatigue but not in other moods across the menstrual cycle. The study provides further evidence of the importance of androgen levels in women's sexuality and shows again that the relationship between menstrual cycle phase and sexuality is much clearer than between phase and mood.

The present experiment was designed to study whether or not prior exposure to inescapable shock is accompanied by sex-dependent changes in pituitary and central levels of immunoreactive beta-endorphin, which is proposed to play an important role in opioid analgesia induced by aversive stimulation. Further, the effects of brief reexposure (5 min) to the chamber where inescapable shock was experienced earlier, were established in both sexes. Elevated levels of beta-endorphin were found 24 hours after inescapable shock, in the anterior pituitary of males and in the midbrain periaqueductal gray of both males and females. Reexposure to the experimental chamber only affected beta-endorphin levels if shock had been experienced in this chamber. Reexposure after inescapable shock reduced beta-endorphin content of the arcuate nucleus of males and beta-endorphin content of the periaqueductal gray of males and females. The present results are related to previous findings of sensitization and conditioning of analgesic reactions. The sex differences found in the present experiment are discussed with respect to sex-dependent behavioral consequences of inescapable shock.

Preexposure to unsignaled food presentation retards the subsequent acquisition of stimulus-directed responding in autoshaping procedures. We hypothesized that this effect might be a direct function of the extent to which subjects engage in food-tray directed behavior during preexposure. To investigate this notion, unsignaled food presentation was made contingent upon high levels of food-tray directed behavior during preexposure for one group of subjects. For another group of subjects, food presentation during preexposure was contingent upon the occurrence of behavior other than food-tray directed activities. The subjects were then exposed to an autoshaping procedure, in which response-independent food presentations were preceded by the insertion of a response lever into the experimental chamber. Both male and female rats were exposed to these experimental procedures. The subjects that had engaged in high levels of food-tray directed behavior during preexposure exhibited low levels of stimulus-directed behavior during autoshaping, and vice versa. Sex differences were also observed. Males showed more stimulus-directed responding during autoshaping than did females, with no differential effects of preexposure experience.

The present experiment was designed to investigate the effect of stimulus presentations during the delay interval of an operant delayed spatial response alternation procedure on the response accuracy of male and female Wistar rats. Subjects were exposed to three different delay intervals (5, 10, and 20 sec) during each experimental session. Response accuracy decreased for both males and females as the duration of the delay interval increased. Performance improved over sessions for both sexes. The presentation of stimuli during the delay interval differentially affected the behavior of males and females. Performance of males decreased at all delay intervals when stimuli were presented, whereas no differences in the response accuracy of females were observed.

The present experiments investigated sex differences in the effects of d-amphetamine on schedule-controlled behavior. Male and female Wistar rats were exposed to either a differential reinforcement of low rate 15 s schedule, or a differential reinforcement of high rate 0.75 s schedule and challenged with different doses of d-amphetamine (0.2, 0.4, 0.8, 1.6 and 3.2 mg/kg). d-Amphetamine in low to moderate doses increased low response rates. High doses of d-amphetamine decreased low and high response rates in both males and females. The response rate increasing effects of d-amphetamine on low baseline rates were significantly higher for females than for males. Sex differences for high baseline rates were not observed. The results of these experiments show not only that hormonal and neurochemical variables influence the effects of d-amphetamine administration on schedule-controlled behavior, but also that environmental contingencies maintaining the behavior can modify these effects.

Male and female Wistar rats were treated with different doses of vasopressin (0.05, 0.25, 1.25, 3.75 and 6.25 μg/kg) after responding had stabilized on either a differential reinforcement of low rate 15 s (DRL 15 s) or a differential reinforcement of high rate 0.75 s (DRH 0.75 s) schedule of reinforcement. Low to moderate doses of vasopressin did not affect response rates, response efficiency or the number of reinforcers obtained during vasopressin sessions on both the DRL and DRH schedules. Administration of 6.25 μg/kg vasopressin reduced low response rates and the number of reinforcers obtained during vasopressin sessions, but increased response efficiency. High response rates and response efficiency were reduced after administration of 3.75 and 6.25 μg/kg vasopressin, while the number of reinforcers obtained during vasopressin sessions was reduced at 6.25 μg/kg. Sex differences in the effects of vasopressin were not observed on either schedule.

Sex, age and shock-intensity were studied in a step-through passive avoidance test. In adult rats (140 days) males showed more inhibition of a previously punished approach response. No sex differences were observed in young adult animals (60 days). In prepuberal animals (30 days), on the other hand, it was the females which showed more response inhibition. In prepuberty females showed far more response inhibition than in adulthood. Even when using 1.6 mA as a reinforcer, only 17% of the adult females showed inhibition after punishment of the entering response.

Publisher Summary This chapter discusses the sexual differentiation of behavior in rat. The concept of psychosexual differentiation essentially refers to two intertwined research approaches to sex-related behavior, one originating from studies demonstrating sex differences in various behavior patterns between male and female animals, the other founded in the study of ontogenetic processes in which morphological differentiation has an impact upon the adult male-female differences in behavior. The process of sexual differentiation has genetic, morphological, neuroendocrine and behavioral aspects.The normal ontogenetic development of an individual into masculine or feminine direction is basically dependent upon the individual's genotype. The relation between masculine and feminine sexual behavior can be adequately studied in male rats in which both masculine and feminine behavior can be investigated. Sex-linked differences in non-sexual behavior patterns are well known in many species and concern many different classes of behavior—for example, eating and drinking behavior, general activity, emotional behaviors, avoidance conditioning, parental activities, aggressive behaviors and many others. A comparative approach concerning sex differences in non-sexual behavior has challenging prospects because of the existence of several psychiatric disorders that have incidence ratios strongly in favor of one or the other sex.

Self-stimulation and sexual behavior of male rats with electrodes implanted in the medial preoptic area were studied in an experiment in which the animals were castrated and subsequently treated with testosterone propionate. The rewarding effect of an electrical stimulus in this area proved to depend upon the presense of testosterone. The results of this study provide additional evidence for the importance of the medial preoptic area in the motivational aspects of male sexual behavior.