Nanne E. van de Poll

Behavioral differences between male and female wistar rats on DRL schedules: Effect of stimuli promoting collateral activities☆

Female rats are more active than males in open-field procedures. They also make fewer unreinforced responses than males on schedules which maintain low rates of responding (differential reinforcement of low rate responding, DRL). The addition of objects to promote collateral activities facilitates the acquisition of efficient DRL behavior. It was hypothesized that differences in activity levels might underlie the observed sex differences in DRL learning. If females are more likely than males to engage in activities other than lever pressing, the addition of objects to the experimental environment should not as much influence the behavior of females than that of males. Male and female rats were exposed to a DRL 15 sec or a DRL 30 sec schedule, either with or without objects to promote collateral activities. General activity was tested twice in an open-field procedure. Females showed higher activity levels than males in the open-field. They also acquired a DRL task more efficiently than males. The addition of objects facilitated the acquisition of efficient DRL performance in males, but not in females. The results of the present experiments, therefore, suggest that differences in general activity between male and female rats may underlie sex differences in some experimental paradigms.

Behavioural changes following lesions of the orbital prefrontal cortex in male rats.

Abstract Bilateral lesions were made, confined to the orbitofrontal part of the prefrontal cortex (OF) of male WEZOB rats at 3 different ages (30, 45 and 60 days) and behavioural changes were studied in adulthood. In a test situation for intermale aggression OF-lesioned animals showed a higher level of aggression than their control-operated opponents. Such changes were not witnessed in encounters with male rats of the less aggressive Wistar strain which emphasizes the importance of the choice of the opponents in tests for agonistic behaviour. OF lesioning did not interfere with male sexual behaviour. When tested in an open field, activity scores of OF-lesioned animals exceeded those of the control group. OF lesioning resulted in a slight but significant long-term weight reduction, 2–3 months following surgery, in comparison with the control group. However, a severe reduction in food intake (aphagia), immediately after the operation, was not observed. Increase in both aggression and locomotor activity was seen in all 3 age groups, and data do not support the hypothesis that sparing of function had occurred in the 30-day operates, as compared with the 60-day operates. However, the duration of allogrooming bouts per approach in the social agonistic situation did show a pattern depending on the lesion momentum: prepubertal OF lesions resulting in less frequent approaches and grooming bouts of longer duration. These findings are explained in terms of perseverative tendencies following OF lesions.

The effect of a choice alternative on sex differences in passive avoidance behavior

Abstract A modified standard passive avoidance conditioning procedure was used to investigate whether or not “inferior” passive avoidance behavior of female Wistar rats could be attributed to memory deficits. Male and female Wistar rats were first adapted to two standard passive avoidance conditioning compartments, which were clearly different from one another. Both compartments were accessible from the same illuminated platform. Three learning trials in one compartment were alternated with three trials in the other compartment and unavoidable shock was presented on the last (6th) learning trial in one of the compartments. One hour after shock presentation, subjects were again placed on the platform. Significantly more females than males reentered one of the compartments. Of the subjects which reentered, significantly more females and males than would have been expected by chance, entered the compartment in which shock had not been presented. The data are interpreted to show that sexual dimorphism in passive avoidance behavior should not be attributed to differences in memory capacities of male and female rats. Therefore, it remains to be determined which variables associated with hormonal or genetic background of the subjects and which requirements of the experimental task, are responsible for the occurrence of the observed difference.

Delayed spatial response alternation: Effects of delay-interval duration and lesions of the medial prefrontal cortex on response accuracy of male and female Wistar rats ☆

A delayed spatial response alternation procedure was used to assess behavioural differences between male and female Wistar rats, assumed to involve memory functioning. In Expt. I, subjects were required to alternate responses between two levers in an operant environment. The delay between response opportunities was varied between 1, 3, 7.5 and 15 s in different experimental conditions. Incorrect responses produced a time-out from experimental contingencies for the duration of the currently active delay interval. Response accuracy decreased for males as well as females as the duration of the delay interval was increased. Performance improved as subjects were exposed to the different delay interval durations during consecutive trials. Sex differences in behavioural accuracy were not observed. In Expt. II, some subjects who participated in Expt. I received lesions of the medial prefrontal cortex, while others were control-operated. When re-exposed to the 1 and 7.5 s delay conditions of the first experiment, lesioned subjects at first behaved less accurately than control-operated subjects. Accuracy, however, improved after prolonged exposure to the experimental conditions. Sex differences in behaviour after surgery could not be observed.

Absence of behavioral differences between male and female rats in different radial-maze procedures ☆

Male and female Wistar rats were exposed to different radial-maze procedures to determine whether or not behavioral differences would be observed. They were allowed free access to all arms of the maze in the first experimental condition, while they were confined between choices to the central platform for 1 and 15 sec during the second and third experimental conditions. In addition, separate, experimentally naive groups of males and females were exposed to the 15 sec confinement procedure. Female and male Wistar rats required an equal number of choices and equal amounts of time to successfully complete visits to eight different arms in all experimental conditions, whether they were experienced or not. Performance improved as training progressed. The results of the present experiments suggest that the previously observed behavioral differences between the sexes in different complex maze procedures, may not be a function of differences in visuospatial abilities, but of activity differences, which interact with the behavioral requirements of different experimental procedures.

Behavioral consequences of agonistic experience in rats: sex differences and the effects of testosterone.

The effects of winning or losing on subsequent aggressive behavior in male and female rats were studied. By using three strains of rats with different levels of aggression, a procedure was developed to create winners and losers. Subsequently, winners were tested against losers. Behavioral analysis of all tests enabled a thorough study of these processes and of their consequences. The results indicate that significant and relatively permanent behavioral changes are induced in intact and castrated, testosterone-treated males but not in females. The results suggest that behavioral inhibition is a specific characteristic of the males agonistic behavioral repertoire.

The influence of Estrogen, Testosterone and Progesterone on partner preference, receptivity and proceptivity

The influence of Estradiol benzoate (EB), Testosterone propionate (TP) and Progesterone (P) on the females partner preference for sexually active males was investigated and compared to levels of receptive and proceptive behaviors observed in a tethered male test situation. Doses of EB (1 micrograms), TP (500 micrograms) and P were selected on the basis of previous investigations indicating that female rats treated with these dosages will show comparable levels of lordosis behavior. The results indicate that TP stimulates partner preference for sexually active males over estrous females in ovariectomized female rats. Females treated with EB tended to prefer the company of sexually active males more than Oil-treated females and less and TP-treated females. However, preference behavior of EB-treated females was not significantly different from that of Oil- or TP-treated females. Additional treatment with P (100 micrograms) did not influence partner preference of Oil-, EB- or TP-treated females. In the tethered male tests, P stimulated proceptivity of EB- or TP-treated females and receptivity of EB-treated females. Significant differences in proceptive and receptive behaviors between EB- or TP-treated were not found. Although facilitation of receptive and in particular, proceptive behaviors were found to be generally accompanied by an increased partner preference for males, it is concluded that gonadal hormones are differentially affecting aspects of female rat sexuality: Relative to the activation of receptive behavior, TP was found to be more effective (than EB) to increase preference for a male; P (given to EB- or TP-treated females) was found to stimulate receptive and proceptive behaviors considerably, while being ineffective to stimulate preference for a male.

Sex differences in passive avoidance behavior of rats: Sex-dependent susceptibility to shock-induced behavioral depression

Male and female Wistar rats were trained in a standard passive avoidance task. One-half of the subjects was shocked (S) upon entering a dark compartment, the other half was not (NS). One hour after S and NS experience subjects were tested. During testing different behavioral elements were observed in order to elucidate the variables which might be responsible for the observation of sex differences in passive avoidance behavior (Experiment Ia). In addition, separate groups of NS and S male and female rats were used to establish effects of sex and shock presentation on locomotor activity (Experiment Ib). One hour after S and NS experience within a passive avoidance procedure these subjects were tested for open field ambulation. Results of both experiments indicated that shock-stress reduces locomotor activity of male and female rats, but to a lesser extent in female rats. Sex differences in behavioral responses to aversive stimuli may thus be a consequence of a sex-dependent susceptability to stress-induced behavioral depression.

Sexual behavior and sexual orientation of the female rat after hormonal treatment during various stages of development

The amount of circulating sex steroids during Postnatal Days 30-90 was varied in normally developed and in androgenized female rats. The influence of these manipulations on sexual behavior and sexual orientation was investigated. Normally developed or neonatally androgenized females were ovariectomized and implanted with estradiol through Postnatal Days 30-90 or sham-implanted. The remaining subjects were left intact during that period. The hormonal condition during Postnatal Days 30-90 significantly affected the behavior of normally developed females, but affected the behavior of neonatally androgenized females only to minor extent. Estrogen implants in normally developed females enhanced masculine sexual responses and induced a female-directed sexual orientation. Feminine sexual responses were unaffected by this treatment. Sham-implanted, normally developed females showed a male-directed sexual orientation and fewer masculine sexual responses than subjects which were left intact during Postnatal Days 30-90. Neonatal androgen treatment in general resulted in elevated levels of masculine Neonatal androgen treatment in general resulted in elevated levels of masculine sexual responses, inhibited feminine sexual behavior, and facilitated a female-directed sexual orientation.Abstract The amount of circulating sex steroids during Postnatal Days 30–90 was varied in normally developed and in androgenized female rats. The influence of these manipulations on sexual behavior and sexual orientation was investigated. Normally developed or neonatally androgenized females were ovariectomized and implanted with estradiol through Postnatal Days 30–90 or sham-implanted. The remaining subjects were left intact during that period. The hormonal condition during Postnatal Days 30–90 significantly affected the behavior of normally developed females, but affected the behavior of neonatally androgenized females only to minor extent. Estrogen implants in normally developed females enhanced masculine sexual responses and induced a female-directed sexual orientation. Feminine sexual responses were unaffected by this treatment. Sham-implanted, normally developed females showed a male-directed sexual orientation and fewer masculine sexual responses than subjects which were left intact during Postnatal Days 30–90. Neonatal androgen treatment in general resulted in elevated levels of masculine sexual responses, inhibited feminine sexual behavior, and facilitated a female-directed sexual orientation.

The behavior of male and female Wistar rats pressing a lever for food is not affected by sex differences in food motivation.

Abstract Male rats both eat more and weigh more than females. Differences in food intake and body weight result, at least partly, from differences in gonadal hormone secretions. The present experiments were designed to investigate whether sex differences in food motivation might contribute to the behavioral differences observed when food-deprived male and female rats are exposed to appetitively motivated operant learning tasks. Male and female Wistar rats were exposed to different progressive ratio schedules of reinforcement which have been shown to generate reliable indices of ‘motivational’ conditions. In progressive ratio schedules, subjects are required to make a systematically increasing number of responses for each successive reinforcer, until the requirement becomes so large that the subjects stop responding. Expt. Ia was designed to investigate whether or not food-deprived males would be more motivated than food-deprived females to obtain food. Expt. Ib investigated whether gonadectomy might differentially affect food motivation of male and female rats exposed to a progressive ratio schedule of reinforcement. Motivational differences between males and females were not observed. Males and females obtained an equal number of reinforcers, while differences in the total number of responses and response rate were not observed. Gonadectomy did not affect the total number of responses in the final completed ratio. The results of the present experiments do therefore not support the hypothesis that sex differences in food motivation might underlie sex differences in behavior when food-deprived male and female rats are exposed to operant schedules of positive reinforcement.