Gonadal hormones and sex differences in nonreproductive behaviors in rodents: organizational and activational influences

Failure of dexamethasone to influence sex differences in acquisition of discriminated lever press avoidance

Discriminated lever press avoidance was used to test the hypothesis that higher plasma levels of pituitary-adrenocortical hormones in female rats can be held responsible for the superior active avoidance of female as compared to male rats. Male and female rats were administered dexamethasone (500 microg/kg body weight) during 4 days of avoidance acquisition and 1 additional day of extinction. This treatment resulted in a strong suppression of the pituitary-adrenocortical activity in both sexes. The corticosterone plasma level was very low, the adrenal weight was significantly reduced, but the pituitary weight was not affected. In other words, animals treated with dexamethasone were exposed to the lever press avoidance situation without a reactive pituitary-adrenocortical system. Under these conditions, sex differences in behavior were not affected and, therefore, the hypothesis that sex differences in pituitary-adrenocortical hormone levels contribute to sex differences in active avoidance, was not confirmed.

The involvement of gonads and gonadal steroids in the regulation of food intake, body weight and adiposity in the white Leghorn cock

The effects of long-term injections of testosterone propionate (TP), diethylstilbestrol (DES) and TP+DES simultaneously to castrated and sham-operated White Leghorn cocks on feeding, weight gain, obesity, blood lipids and weight of various glands were studied. DES induced marked adiposity while TP reduced carcass fat content. Injections of TP+DES induced only moderate obesity. The responses of the castrated cocks to TP or DES were not always parallel to those of the sham-operated ones. In sham-operated cocks, TP induced permanent hypophagia and emaciation while in castrated cocks, although alleviating adiposity, it did not reduce the rate of weight gain and induced only a transient hypophagia. DES induced permanent hyperphagia and accelerated weight gain in sham-operated cocks while in those castrated, it induced only transient hyperphagia which later on changed into hypophagia. Although the latter cocks did not gain more weight than those castrated with no steroids supplementation, they were much more obese and had a fat content similar to that of the sham-operated ones treated with DES. The castration was found to alleviate the depressing effect of TP on adenohypophyseal and thyroidal weights. The results may suggest: (1) In the White Leghorn cocks, DES increases lipogenesis and food intake while TP results in the contrary. (2) Castration should not be considered as a lack of gonadal steroids only.

Aromatization: important for testosterone's developmental influences on the neurocircuits mediating cervically stimulated prolactin secretion in the female rat

Adult female rats treated neonatally with testosterone or estrogen fail to respond to cervical stimulation with episodic prolactin release. The developmental action of testosterone is inhibited by co-administration of 1,4,6-androstatriene-3,17-dione at a dose sufficient to inhibit the testosterone-induced rise in estrogen receptors in limbic brain cell nuclei. These data suggest the importance of aromatization for testosterone action.

Effects of ovariectomy, estrogen treatment and CI-628 on food intake and body weight in female rats treated neonatally with gonadal hormones

Body weights and skeletal growth of female rats treated neonatally with low doses of testosterone propionate (TP) or estradiol benzoate (FB) were greater than oil-treated controls. After ovariectomy at 75 days of age EB-treated animals gained less weight than did the oil-treated controls and TP-treated rats which were comparable in weight gain. Neonatal treatment with TP or EB produced decreased sensitivity to the anorexic and weight-limiting effects of estrogen treatment after ovariectomy. However, all groups were equally sensitive to the anorexic effects of a single dose of CI-628. The possible mechanisms by which neonatal treatments with gonadal hormones influence food intake and body weight regulation are discussed.

Aromatization of testosterone to estrogen varies between strains of mice

The nuclear uptake and retention of [3H]testosterone or one of its metabolites and the aromatization of testosterone to estrogen were examined in the Swiss--Webster mouse. Castrated male mice were injected with 0.2 micrograms of either [1 alpha, 2 alpha-3H(N)]testosterone or [1 beta, 2 beta-3H(N)]testosterone per 100 g of body weight and killed one and one-half hours later. The brains were removed and processed for autoradiography. A nuclear localization of testosterone or one of its metabolites was found in the nucleus (n) interstitialis striae terminalis, n. preopticus medialis, n. premamillaris ventralis and n. amygdaloideus medialis in animals injected with [1 alpha, 2 alpha-3H(N)]testosterone. In animals injected with [1 beta, 2 beta-3H(N)]testosterone a nuclear localization was found in only n. interstitialis striae terminalis, n. premamillaris ventralis and n. amygdaloideus medialis. The results suggest testosterone is aromatized to estrogen in n. preopticus medialis ventralis in the Swiss--Webster mouse. Together with previous data, these data suggest (1) the uptake and retention of testosterone or one of its androgenic metabolites and the aromatization of testosterone to estrogen varies between strains of mice and (2) there are two separate uptake and retention systems (receptors?) for testosterone and dihydrotestosterone in the brain in all animals studied thus far with autoradiographic techniques.

Contiguity to males in utero affects avoidance responding in adult female mice

Female mice that had been situated in utero between two female fetuses displayed higher levels of active avoidance responding in adult life than females that had been located between two male fetuses and males for whom uterine position was without effect. Uterine position, therefore, influences acquired as well as species-typical behaviors.

Progestin-induced changes in play behaviour of the prepubertal rat

The effects of neonatal exposure to medroxyprogesterone acetate on later play behaviour was studied. The experiments reported here indicate that animals of both sexes exposed to the hormone neonatally show lower levels of rough-and-tumble play in the prepubertal period. The effect is primarily one on play initiation: the organisation of play behaviour once initiated is not significantly affected, and the effect on play does not seem to be secondary to effects on some other behaviour. Several hypotheses are considered that might account for these findings.

Genotype modulates testosterone-dependent activity and reactivity in male mice

Adult castration significantly reduced the homecage locomotor activity of both inbred C57BL/6J and DBA/2J and outbred Rockland-Swiss (R-S) male mice. Castrated C57BL animals exhibited greater reductions in this behavior than did the other genotypes. Locomotor activity in a novel environment (reactivity) was also reduced by castration but only for inbred males. In both test situations, postcastration reductions in ambulation were prevented by implants of testosterone (T)-containing Silastic capsules. Thus, testicular hormones promote activity and reactivity in the male mouse in a genotype-dependent fashion.

Organisational effects of neonatal and pubertal testosterone on sexually differentiated behaviours in the open-field and head-dip apparatus

On days 1 and 4 after birth rats were injected with 100 μg of testosterone propionate (TP) or vehicle, and at 35 days of age they were injected intramuscularly with 400 μg of testosterone oenanthate (TO), a long acting androgen, or the vehicle. There were four groups (oil-oil, TP-oil, oil-TO, TP-TO), each group subdivided by sex. Females treated with testosterone neonatally or at puberty were masculinised or defeminised on adult open-field behaviours, being less active and rearing less than oil-oil females; the oil-TO group also defaecated significantly more than controls. The TP-TO female group was indistinguishable from the oil-TO group. In a second experiment, sex differences were found in head-dipping behaviour as well as in activity and rearing. Females treated with TP or TO reared less and defaecated more than controls, and TP also decreased activity, but neither hormone treatment affected head-dipping behaviour. There is thus a peripubertal as well as a neonatal period when testosterone can act organisationally to masculinise or defeminise female rats. Potentiation between effects of neonatal and pubertal androgens was found on female body weights. TO alone had no effect, but TP-TO females were significantly heavier than controls at 90 days of age and by 130 days of age the TP-oil group was also heavier than controls.

Sex differences and estrous cycle dependent variation in rotational behavior elicited by electrical stimulation of the mesostriatal dopamine system

In this study electrical stimulation-induced rotational behavior was used as a behavioral index of mesostriatal dopamine (DA) activity to investigate gender and hormonal influences on the DA system. In female rats we found estrous cycle related variations in electrical stimulation-induced rotational behavior. A constant electrical stimulus produced significantly more turning on the day of estrus, than it did 24 h later, on diestrus 1. Gonadectomy attenuated contraversive rotational behavior in female, but not male rats. In contrast, ovariectomy had no effect on the ipsiversive rotational behavior produced by stimulation of the reticular formation. This evidence supports the idea that endogenous changes in gonadal hormone levels influence the functional activity of the mesostriatal DA system in a sexually dimorphic manner.

Selective breeding for sensitivity to DFP: generalization of effects beyond criterion variables

The degree of generalization to the effects of DFP, an organophosphate anticholinesterase, was studied in two lines of Sprague-Dawley derived rats selectively bred for varying sensitivities to DFP. In the S13, S14, S15, and S16 generations the Flinders S-line of rats were still more sensitive to the effects of DFP on the criterion variables upon which selection was based: core body temperature, body weight and a simple operant response for water reward. The flinders S-line were also more sensitive to the effects of DFP on locomotor activity, FR5 responding for a water reward, and analgesia, indicating some degree of generalization. However, diarrhea, a symptom of peripheral effects of DFP, occurred at a similar incidence in the two lines, although males of both lines had higher incidences than the females. Neither of the two lines was affected by DFP for variables in which aversive (i.e. shock) motivation was used: The number of discriminative escape responses and the escape times were similar. These findings indicate that while the effects of DFP do generalize beyond the criterion variables upon which selection was based, the generalization is relatively specific. The data are consistent with the hypothesis that the changes in sensitivity have arisen because of changes in the functioning of a central cholinergic system(s).

Effects of sex steroids on the development of the vomeronasal organ in the rat

In the present report the effects of postnatal (on day 1 after birth) male castration and female androgenization on vomeronasal organ (VO) development were studied. Control males showed greater values than females in VO volume and neurosensorial epithelium, while the opposite was true with respect to nuclear size. Postnatal treatments abolished these differences. It is suggested that the VO development is influenced by sexual hormones during at least a postnatal period as it occurs for several structures of the central nervous system connected with the VO.

Sex differences in alpha-adrenergic receptors in the rat brain

[3H]Dihydroergocryptine ([3H]DHE) binding to several brain regions was studied in male and female rats, the latter in two different endocrinological states (estrous and diestrous-1). males showed higher [3H]DHE binding than females in hypothalamus, hippocampus and olfactory bulb, while females showed higher levels than males in spinal cord and visual cortex. In addition, intra-sex (that is, estrous versus diestrous-1) differences were detected in the cervico-thoracic spinal cord and cerebellum. Diestrous females presented higher values in both regions.

Testosterone affects food intake and body weight of weanling male rats

The effects of testosterone propionate (TP) on food intake and body weight were investigated using castrated prepubertal male rats. Regardless of dose (1 mg, 0.2 mg or 0.1 mg), daily injections of TP increased body weight gain and food intake during the prepubertal period (from 22 to 40 days to age). Considering previous results, the present observations suggest that in the male rat sensitivity to the effects of gonadal hormones on feeding develops earlier than in females.

Is testosterone metabolized to estrogen in the forebrain of the Rockland-Swiss mouse?

The nuclear uptake and retention of [3H]testosterone or one of its metabolites was examined in the Rockland-Swiss (R-S) mouse. Castrated male and female mice were injected with 0.2 microgram of testosterone [1,2,6,7-3H(N)] per 100 g body weight and killed 1.5 h later. The brains were removed and processed for autoradiography. A nuclear localization of [3H]testosterone or one of its metabolites was found in the nucleus (n.) interstitialis striae terminalis and the n. amygdaloideus medialis. This localization is very different from that reported in another strain of mouse after the injection of [3H]dihydrotestosterone. Together with previous reports, these data suggest: (1) that aromatization of T to E2 in the forebrain of the R-S mouse is of minimal consequence; (2) there may be differences in uptake of T or its metabolites in different strains of mice; and (3) different androgens may exhibit unique patterns of nuclear uptake and retention.

Facilitation of active avoidance responding following chronic haloperidol treatment in rats

Rats were chronically treated with once-daily injections of either haloperidol or vehicle for 21 days. When spontaneous locomotor activity or acquisition of active avoidance in a two-way shuttle box were measured 48 h after the cessation of chronic treatment, the haloperidol-treated animals were significantly more active and performed significantly more avoidance responses. These findings suggest that the increased dopamine receptors that have been reported following chronic haloperidol treatment may have functional relevance.

Persistence of attention to a novel conspecific: some developmental variables in laboratory rats

Persistence of social attention by male and female laboratory rats was examined following exposure to novel conspecifics. In experiment I we compared performance of castrate female controls. Testosterone significantly prolonged mean social investigation time. Castrate females treated with a 10-day regimen of testosterone propionate to that of intact males and castrate females treated with a relatively high dosage of testosterone failed to differ from intact males. In Experiment II we compared neonatally androgenized female castrates with castrate male and castrate female controls. Postnatal exposure to testosterone increased sensitivity of females to exogenous testosterone in maturity as measured by persistence of social investigation. In Experiment III we compared investigation time of intact and castrate males and females at 10-day intervals from 40 to 80 days of age. Intact males investigated novel conspecifics significantly longer than other groups, with longest investigation times at 60 and 70 days of age. In Experiment IV we compared investigation times of 30-day, 60-day, and 200-day-old males. Sixty-day-old males investigated significantly longer than 30-day-old or 200-day-old groups, which failed to differ from each other. The combined results demonstrate a gender and age-related effect of testosterone on persistence of social investigation.

Sex differences in drug-induced rotation in two strains of rats

Female Fischer and Sprague-Dawley rats rotate significantly more in response to D-amphetamine sulfate (1 mg/kg, i.p.) than their male littermates. Although Sprague-Dawley males rotate more than females when injected with apomorphine hydrochloride (10 mg/kg, i.p.), Fischer males and females respond similarly to this drug. The sexually dimorphic behavioral response to amphetamine appears to be due to differences in brain sensitivity to this drug, and may relate to reports of sex-related differences in nigrostriatal dopaminergic activity.

Effects of gonadectomy and exogenous gonadal steroids on sex differences in open field behaviour of adult rats

Two experiments were carried out to investigate the contribution of gonadal hormones to the expression of sex differences in open field behaviour of adult female and male rats. In the first experiment rats were gonadectomized or sham-operated in adulthood and tested in the open field 1, 2, 3, 4, 5 or 6 weeks later (3 min/rat on 3 consecutive days during the light period of the day). It was found that following gonadectomy the well known sex difference in ambulation and rearing behaviour (females more than males), as well as in defaecation (females less than males) remained. Ovariectomy caused a decrease in ambulation and rearing, with an increase in defaecation, whereas castration had no significant effect on ambulation and rearing, but also increased defaecation. Also an overall increase in ambulation and rearing was found: animals tested 5 and 6 weeks following the operation were significantly more active than animals tested at 1-4 weeks after the operation. In the second experiment female and male rats were gonadectomized and 7 weeks later they received a silastic implant containing testosterone (T), dihydrotestosterone (DHT), oestradiol (E2), DHT plus E2, or nothing (control condition). Four weeks after the implantation the animals were tested in the open field (3 min/rat on 3 consecutive days). An overall sex difference was found for ambulation (females more than males) and for defaecation (females less than males). The only effect of hormone administration was found in DHT-treated animals: lowest ambulation and highest defaecation compared to other hormone and control animals. No differences were found between the T, E2, DHT plus E2, and control animals. From these data it was concluded that endogenous gonadal steroids seem to play a minor role in the expression of sex differences in adult open field behaviour in the rat.

Neural gonadal steroid actions

Neurons sensitive to gonadal steroids are located strategically within neural circuits that mediate behaviors broadly related to the reproductive process. Some neuronal events and properties are regulated by these hormones. Variability in the occurrence and distribution of particular neural hormonal sensitivities across species may be related to variations in the hormonal requirements for sexual differentiation and for activation of reproductive behaviors.

Sexual differentiation of the central nervous system

Sexual differentiation of reproductive and behavior patterns is largely effected by hormones produced by the gonads. In many higher vertebrates, an integral part of this process is the induction of permanent and essentially irreversible sex differences in central nervous function, in response to gonadal hormones secreted early in development.

Sex differences in amphetamine-elicited rotational behavior and the lateralization of striatal dopamine in rats

Sex differences are described in both a lateralized behavior (amphetamine-elicited rotation) and in the lateralization of striatal dopamine (DA) content. Amphetamine (AMPH) elicited significantly more partial turns, total rotations and lateralized (net) rotations in female, than in male rats. The two sexes also differed in their pattern of net rotations over time. In females, but not males, the striatum containing higher DA levels after amphetamine was consistently found to be contralateral to the dominant direction of rotation observed in the first 5 min interval after AMPH. No relationship was found between rotational behavior and medial frontal cortex DA or norepinephrine. The results are discussed in reference to cerebral lateralization in humans, and to possible sex differences in the modulatory effects of gonadal steroid hormones on striatal function.