Ovarian hormones influence odor stimulated flank marking behavior in the hamster (Mesocricetus auratus)

The effect of ovarian hormones on the frequency of female flank marking in response to the odors of male hamsters was examined. The amount of flank marking differed significantly (p less than 0.01) among the days of the estrous cycle, with the lowest levels of flank marking occurring on estrus. Ovariectomy (OVX) eliminated the 4 day rhythm, and significantly (p less than 0.01) reduced the total amount of flank marking. Implantation of Silastic capsules containing estradiol benzoate (EB) in OVX hamsters increased flank marking by approximately two-fold when compared to hamsters implanted with blank Silastic capsules. In a second series of experiments, OVX hamsters given EB flank marked significantly (p less than 0.01) more than those with blank capsules. Subcutaneous injection of progesterone (P) into OVX-EB treated hamsters 6 hr prior to testing significantly reduced flank marking when compared to OVX-EB treated hamsters given oil. No differences were observed in flank marking between groups of OVX hamsters with blank capsules and injected with P or oil. In summary, these data indicate that the four day rhythm of odor stimulated flank marking in intact female hamsters may be the result of the 4 day fluctuations of estrogen and progesterone that occur during the estrous cycle.     

Individual differences in estradiol-induced behaviors and in neural 3H-estradiol uptake in rats

The effects of estradiol benzoate (EB) treatment on food intake, running wheel activity, and sexual receptivity were measured in a group of 14 ovariectomized rats. Rats were then injected with ³H-estradiol-17β, and uptake of radioactivity was determined in whole homogenates and cell nuclear fractions of cerebral cortex, preoptic area, hypothalamus, and pituitary gland. During EB treatment the heaviest rats tended to show the greatest anorexia and weight loss, consistent with the hypothesized weight-regulating actions of estradiol. In contrast, the activity increases and weight losses induced by EB were unrelated. The 3 behavioral responses to EB (anorexia, increased activity, and estrous behavior) were completely independent of one another, suggesting that estradiol acts on separate neural substrates to alter these 3 behaviors. Large amounts of radioactivity were taken up by cell nuclei, with pituitary uptake highest, followed by preoptic area and hypothalamus (which did not differ) and cerebral cortex. However, a greater proportion of the total tissue radioactivity was found in cell nuclei in hypothalamus and prooptic area than in pituitary. Finally, none of the behavioral responses to EB displayed a significant correlation with any of the indices of brain or pituitary ³H-estradiol uptake.     

Sexual and olfactory preference in noncopulating male rats

In some species including rats, mice, gerbils, and rams, apparently normal males fail to copulate when repeatedly tested with receptive females. These animals are called "noncopulators (NC)," and the cause of this behavioral deficit is unknown. It has been shown that NC rats do not have hormonal alterations or deficits in the mechanisms that control penile function. The present study was designed to examine (Experiment 1) whether NC male rats prefer receptive females to sexually active males. In addition, the olfactory preference for bedding soiled from estrous or for anestrous bedding was investigated. These tests were performed in NC and copulating (C) male rats when the subjects were intact, gonadectomized (GDX), or GDX and treated with high doses of testosterone propionate (TP). Our results demonstrate that NC rats do not display sexual behavior even after high TP treatment. While C male rats have a clear preference for receptive females as opposed to a sexually active male, NC rats do not. In all hormonal conditions, the preference shown by NC rats for estrous bedding was significantly reduced in comparison to that seen in C rats. TP treatment in NC rats did not modify either partner or odor preference. In Experiment 2, we evaluated if NC rats are feminized and if it could be easier to induce feminine-like behavior by hormone treatment with estradiol benzoate (EB) or with EB plus progesterone (P) (EB+P). Odor preference for estrous or male bedding under these hormonal conditions was also compared. No differences between NC and C rats were found in feminine sexual behavior. In the olfactory test, we found that NC rats prefer odors from receptive females as opposed to male odors, but this preference is reduced compared to that of C rats. Males treated with EB or EB+P show no preference for female odors. These results demonstrate that treatment with EB or EB+P does not increase feminine sexual behavior in NC rats.     

Effect of progesterone on the estrous activity cycle of the rat

Two, 3 or 4 Silastic capsules of progesterone were implanted sc for 24–35 days, removed for a 12–14 day interval and re-implanted into the same adult female rats from which they were taken. A control group received cholesterol capsules. For approximately 4–10 days, Silastic capsules of progesterone suppressed estrous activity cycles. Thereafter, amplitude of running increased progressively and definite periodicities re-emerged. Following a 12 day recovery period, the same capsules were re-implanted and activity was again suppressed. During the first implantation, the number of estrous cycles with greater than 4-day periods significantly increased. Progesterone was also found to delay the daily onset of activity in relation to the light/dark cycle (phase angle difference). Phase angle difference prior to the first implantation was negatively correlated with the rate of recovery. The data support the conclusion that progesterone affects parameters of estrous activity by antagonizing the actions of estrogen and suggest that animals may make internal adjustments to high titers of progesterone.     

Intrahypothalamic implants of noradrenergic antagonists disrupt lordosis behavior in female rats

There is considerable experimental evidence that hormonal activation of lordosis in female rats involves norepinephrine (NE) neurotransmission. However, no clear picture has emerged regarding either: 1) the neural sites at which NE influences lordosis, or 2) the NE receptor subtype(s) mediating NE effects on lordosis. To address these two issues, the behavioral effects of antagonists with relative specificity for alpha 1, alpha 2, or beta adrenergic receptors were examined. Drugs were administered via bilateral crystalline implants directly into the ventromedial nucleus of the hypothalamus (VMN) or medial preoptic area (MPOA) of ovariectomized female rats primed for 48 hr with 3 micrograms of estradiol benzoate (EB) and given 200 micrograms of progesterone (P) 3.5-4 hr before testing. When applied to the VMN 1 hr before the P injection, the alpha 1 receptor antagonist prazosin reduced lordosis behavior in 86% of animals but in only 10% of rats when applied to the MPOA. However, prazosin did not inhibit lordosis when implanted into the VMN just prior to EB administration. Yohimbine, an alpha 2 receptor antagonist with low affinity for alpha 1 receptors, also suppressed lordosis in 41% of animals with VMN implants and in 37% of rats with MPOA implants. By contrast, the alpha 2 antagonist idazoxan, which has little activity at alpha 1 receptors, did not significantly affect estrous responding when implanted into either the VMN or MPOA. VMN implants of the beta receptor antagonists propranolol and pindolol reduced lordosis behavior in 50% and 86% of rats, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of estrogen upon feeding inhibition produced by intragastric glucose loads

Two studies were performed to determine if estrogen could potentiate the inhibitory effects of glucose on feeding behavior. In the first experiment, ovariectomized rats were injected with either 6 μg of estradiol benzoate (EB) or with sesame oil, and two days later were given 5 ml intragastric loads of either 40% glucose or 13.5% urea by gavage. Gavage was performed after a 12-hr fast, during the light period. Food intake (FI) was measured at hourly intervals, starting 2 hr after gavage and reaccess to food as well as daily throughout the experiment. In a second experiment, rats received a similar treatment, except that gavage was performed in an unfasted condition, during the dark period. It was found that (1) a 12-hr fast abolishes anorexic effects of EB, but leaves the inhibitory effects of glucose intact, (2) EB does not potentiate short-term effects of glucose, and (3) EB enhances delayed (22 hr after gavage) effects of glucose upon feeding. These findings are consistent with the hypothesis that EB modified the long-term control of feeding behavior, probably at the level of the ventromedial hypothalamus.     

Induction of ovulation in the pregnant hamster

Pregnant hamsters consistently ovulated when injected with 20 IU of human chorionic gonadotropin (HCG). The induced ovulation rate from days 4–8 of pregnancy was comparable to that observed during the estrous cycle; however, starting at day 10, a marked increase occurred, culminating in a peak of 35 ova at day 12. Animals injected with HCG on day 16, the day before delivery, ovulated an average of 14.5 ova, although spontaneous postpartum ovulation does not occur in the hamster. The number of ovulations induced by HCG correlated with the varying number of antral follicles present during different stages of pregnancy. Unilaterally ovariectomized pregnant hamsters did not show a compensatory increase in induced ovulation rate in the remaining ovary. The induction of ovulation on days 4 or 10 of pregnancy did not interfere with embryonic development nor influence the time of parturition. Following parturition, the primary and induced corpora lutea regressed synchronously.     

Copulation-illness associations in male rats: lithium chloride dose and delay manipulations

Male rats that receive an injection of lithium chloride (LiCl) after each pairing with an estrous female gradually decrease their copulatory behaviors. In the present experiments we demonstrated that a 6.0 mEq/kg (0.3 M, 20 ml/kg) dose of LiCl injected after trials spaced twice weekly at 3-4-day intervals induced more rapid acquisition of copulation-illness associations than a 3.0 mEq/kg (0.15 M, 20 ml/kg) dose. Contingent 0.3 M saline or noncontingent 0.3 M LiCl injections did not affect copulatory behaviors. The location of the male rat (home cage or test chamber) during a portion of the aversive state induced by LiCl did not influence rate of acquisition. Copulation-illness associations, once established, were retained over a 60-day interval. Comparable decrements in copulatory behaviors were evident when LiCl was injected at 1-, 5-, or 15-min intervals after pairings with estrous females when the males were detained in the test chambers during the delay intervals; decrements were not observed when the interval was increased to 30 or 60 min. An electric shock analog to the aversive state induced by LiCl did not induce decrements in copulatory behaviors. It was suggested that odor-illness associations may, in part, account for the decrements in copulatory behaviors in this paradigm.     

Dietary self-selection in intact, ovariectomized, and estradiol-treated female rats

The effects of estrogenic stimulation on diet selection were examined in intact, estrous cycling rats, ovariectomized (OVX) rats, and OVX rats given estradiol benzoate (EB) hormone replacement therapy. In Experiment 1, OVX was associated with the nearly exclusive choice of the more calorically dense diet of a pair of diets varying in the concentration of one of the three basic macronutrients (i.e., fat, carbohydrate, and protein), an effect that was decreased by EB administration. In the second experiment, dietary self-selection was examined in intact, estrous cycling rats given access to an isocaloric diet triplet of fat, carbohydrate (CHO), and protein. Total caloric intake and body weight did not vary across the estrous cycle. However, diet selection did vary. Fat intake increased; CHO and, to a lesser extent, protein intake decreased during estrus. An opposite diet selection occurred during diestrus. In Experiment 3, OVX resulted in progressive increases in CHO and protein intake, with a concurrent decrease in fat consumption. The EB treatment partially reversed this diet selection profile (Experiment 4). These results were confirmed by diet pairs with both naturally occurring and experimentally produced estrogenic stimulation (Experiments 5 and 6). These data are consistent with the findings of previous research demonstrating estrogenic reduction in CHO intake with standard high-CHO commercial diets. In addition, an increase in fat intake during estrogenic stimulation was found.     

The anorectic effect of fenfluramine is increased by estradiol treatment in ovariectomized rats

The emergence of sex- and estrous cycle-related differences in the anorectic effect of fenfluramine, a serotonin (5-HT) agonist, prompted us to investigate whether these behavioral changes are mediated by estradiol. Rats were ovariectomized and housed in cages that permitted the analysis of feeding and locomotor activity via an automated, computerized system. Using a within-subjects design, we investigated the effects of 1 mg/kg d-fenfluramine and saline vehicle on food intake and wheel running in ovariectomized rats following estradiol benzoate (EB) and oil vehicle treatment. A cyclic regimen of EB treatment was used to mimic the changes in endogenous estradiol secretion over the rat's 4-day estrous cycle. The decrease in food intake following fenfluramine treatment was greater in EB-treated rats, relative to oil-treated rats. Fenfluramine also produced a small but significant decrease in wheel running in ovariectomized rats that was not modulated by EB treatment. Thus, EB's ability to increase the anorectic effect of this dose of fenfluramine appears behaviorally specific. Although the inhibition of food intake by fenfluramine is largely attributed to its ability to increase synaptic levels of 5-HT, additional research involving selective 5-HT receptor agonists and antagonists is necessary to determine whether estradiol interacts with the endogenous 5-HT system to control food intake in the female rat.     

Effect of reproductive state on circadian periodicity in the rat

The circadian activity rhythms of adult female rats maintained under a light-dark cycle of 14 hr light, 10 hr dark (LD 14:10) or constant dim illumination (dim LL) were recorded during their 4 or 5 day estrous activity cycles and when they were pseudopregnant. In LD 14:10 both the phase angle difference (ψ), which defines the temporal relationship between the onsets of activity and darkness, and the period (τ) of locomotor activity differed significantly among the days of the 4 and 5 day estrous cycle. Activity-time (α) varied reliably only over the days of the 5 day estrous cycle. The period of the free-running activity rhythm in dim LL also differed significantly among the days of the estrous cycle. In both LD and dim LL the most positive ψ, shortest τ and longest α were observed on the day of estrus. Pseudopregnancy diminished the amplitude and altered the daily pattern of the estrous activity rhythm. We conclude that the periodicity of circadian activity systematically varies as a function of the stage of the estrous cycle and in a manner that cannot be solely explained by corresponding alterations in endogenous estrogen.     

Development of running activity in maturing rats: dependence upon prior androgen exposure and ovarian function.

Female Sprague-Dawley derived rats were given either 1 mg testosterone propionate or an oil vehicle at 2 days of age. At weaning age half of each group were ovariectomized and at puberty the rats were placed in Wahmann activity wheels. In all groups there was a rise in running activity during the first 10 days after vaginal opening. This rise continued progressively in intact, ovulatory rats but did not continue in either persistent estrous or ovariectomized females. Beginning at 85 days of age running activity began to decline in all groups except the ovulatory females. This regression was protected against to some extent by ovariectomy in the androgen-treated females. It can be concluded that the ovaries are not required for either the initiation of running activity or the later decline seen in mature rats but that the gradually increasing running seen in intact rats is directly related to ovarian function.     

The role of estrogen and progesterone in the control of preputial gland sex attractant odors in the female rat

Sexually experienced male rats were used to test the attractiveness of body odors of female rats. The attractiveness of these odors varied with the estrous cycle. Odors from female rats in proestrus were the most attractive to male rats and those from female rats during the darkness hours of diestrus the least attractive. The preputial glands appeared to be the source of these odors for the male rats showed no preference for the odors of proestrous female rats that had been preputialectomized. Administration of 1 μg estrdiol benzoate (EB) for 5 days increased the attractiveness of body odors of ovariectomized rats. A higher dose of EB (5 μg) had the same effect when administered for 1 or 5 days although the increase that occurred after 3 days was not significant. A single dose of progesterone (P) (500 μg) on the other hand, decreased the attractiveness of ovariectomized female odors although no change was seen after 3 days of treatment. A single injection of P also decreased the attractiveness of odors of ovariectomized females that had received EB for 3 days. However, P failed to decrease the attractiveness of odors in ovariectomized females after preputialectomy. We conclude that the preputial glands are an important source of sex attractant odors in the female rat and that the changes in the release of these odors that occur throughout the estrous cycle and pregnancy are controlled by ovarian steroids. While estrogen acts to stimulate the production and release of these odors P appears to inhibit their release.     

Body temperature and temperature gradients: changes during the estrous cycle and in response to ovarian steroids

Rectal temperature, body weight, and vaginal membrane condition were monitored in female guinea pigs in order to determine the pattern and magnitude of changes in these variables across the estrous cycle and as a result of treatment with ovarian hormones. A thermistor probe was used to measure rectal temperatures at depths of 4 and 8 cm and to determine the temperature gradient between these two sites. Data collected across the estrous cycles of 18 intact females were aligned by day of vaginal membrane rupture, the estimated time of ovulation. Compared to measurements during the midluteal phase of the estrous cycle, rectal temperatures increased significantly one to three days prior to vaginal membrane rupture. In addition, a significant periovular decline was observed in the temperature gradient and in body weight. Treatment of ovariectomized females with 3 micrograms estradiol benzoate for 3 days (EB) followed by a single injection of 0.4 mg progesterone on the 4th day (P) led to biphasic changes in temperature. Compared to a control group which received injections of 0.2 ml corn oil vehicle for 4 consecutive days (OIL), EB significantly increased rectal temperature measured at the depth of 4 cm, but had no significant effect on measurements taken at a depth of 8 cm. The temperature difference between these two sites also decreased significantly. Rectal temperatures at both 4 cm and 8 cm sites dropped significantly following injection of progesterone. Ovarian hormones therefore have significant effects on body temperature of guinea pigs, effects which, in combination with other evidence, lead us to suggest that some of the observed temperature variations may be related to estrogen-induced changes in peripheral vasodilation or other mechanisms of heat loss.     

Splitting of wheelrunning rhythms by castrated or steroid treated male and female hamsters

Male and female hamsters, with or without gonadal hormones, were housed in constant light (LL) while wheel running rhythms were recorded. Estradiol benzoate (EB) in Silastic capsules reduced rhythm desynchronies, such as splitting, in ovariectomized animals compared to blank implanted controls. In males, there were no significant effects of testosterone or EB in Silastic implants, castration or sham operation on incidence of rhythm desynchronies. Males generated split rhythms which differed from females in clarity and the angle at which the limbs of the splitting rhythms diverged. Other differences were (a) greater activity onset variability for castrated females with relatively little onset variability for other groups and (b) more running time by EB treated males than any other group. Splitting for all animals occurred with an average latency in LL of 55±3 days; the period stabilized in 12±1 days and was 0.2 hr shorter in length. The two limbs of the split rhythm were a mean 181±5° apart. Induction of splitting by LL is critically discussed with special reference to the two oscillator model of hamster activity and existing evidence for more than two oscillations in wheelrunning activity.     

Formalin-induced nociceptive behavior and c-Fos expression in middle-aged female rats

The impact of the estrous cycle on the nociceptive response in middle-aged female rats was assessed using the formalin test and c-Fos immunoreactivity as a marker of neural activation. Young (2-month-old) and middle-aged (11-month-old) rats were examined, dividing the middle-aged rats into two groups based on their estrous cycle: regular 4-day estrous cycle and irregular estrous cycle. The right hind paw was subcutaneously injected with 50 μl of 2% formalin or saline as a control. Behavioral changes were observed for 1 h. Cycling rats were used during proestrus. Middle-aged female rats had a significantly higher score for nociceptive behavior compared to young rats, irrespective of estrous cyclicity, which suggests that aging, not the ability to maintain estrous cyclicity, causes hypersensitivity to the formalin injection. Immunohistochemical analysis found that the brain response to formalin injection was also more sensitive in middle-aged rats than young rats; a significant increase in the number of c-Fos immunoreactive cells was found in the ventral portion of the lateral septum of middle-aged rats injected with formalin compared to young and middle-aged rats injected with saline, irrespective of estrous cyclicity. Based on these results, we conclude that the sensitivity to painful stimuli in middle-aged female rats, which are in a neuroendocrine state similar to pre- and peri-menopausal women, is associated with age and not affected by reproductive ability.     

Sex differences in the basal firing rate and the responsiveness to opioid peptides of rat hippocampal neurons.

The basal firing rate and the responsiveness to dynorphin and leu-enkephalin of the neurons in the pyramidal cell layer of the hippocampus were studied in intact male, castrated male, castrated female, and castrated female rats injected s.c. with 20 micrograms estradiol benzoate (EB) for 3 days. Most of the neurons studied had low spontaneous firing rate (less than 5 Hz) and burst-like activity in all the groups. The basal firing rates in castrated males and females were not different from those in intact males and castrated females treated with EB, respectively. However, neurons in intact and castrated males had significantly higher firing rates than those in castrated females with and without EB treatment, respectively. When effective, both iontophoretically applied dynorphin and leu-enkephalin evoked predominantly excitatory responses. Either castration of males or EB treatment to castrated females did not affect the neuronal responsiveness to these peptides. On the other hand, the responsiveness of neurons to leu-enkephalin, but not to dynorphin, was significantly different between castrated male and female rats. These results suggest that sex steroids do not affect the basal firing rate as well as the responsiveness to opioid peptides of the pyramidal cells in the hippocampus in adult animals. However, sex differences in the basal firing rate and in the responsiveness to leu-enkephalin might account for the differences in hippocampal functions between male and female rats.     

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 female's 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.     

Hormonal substrate of estrous odor preference in beagles

The biological substrate and functional role played by vaginal secretions in the mediation of sociosexual behavior in the beagle was assessed. The effect of the presence of androgen during development and/or in adulthood on the display of a behavioral preference for estrous vaginal secretions was measured. Six groups of adult, purebred beagles were tested for the display of preference behavior. Treatment and constitution of the several groups were as follows: females whose mothers were injected with testosterone propionate (TP) for 10 days during the second trimester; females implanted with a testosterone pellet 1–3 days postpartum; females whose mothers were injected with TP during pregnancy and who also received a testosterone pellet 1–3 days postpartum; females ovariohysterectomized in adulthood but given no androgen treatment during development; males castrated in adulthood; and, untreated gonadally-intact males. All animals except the intact males were tested first without and then with additional TP treatment during testing. During tests conducted prior to treatment with exogenous TP during testing, only intact and castrated males showed a significant preference for estrous vaginal secretions. After treatment with TP castrated males showed a greater preference for the estrous secretions. In addition, during the TP tests females treated with androgen before and females exposed to androgen before and after birth also displayed significant preference for estrous vaginal secretions. It is concluded that the display of estrous odor preference is a sexually dimorphic behavior pattern which depends jointly upon developmental and concurrent androgenic stimulation for its expression.     

Neonatal organization of adult partner preference behavior in male rats

Male rats were castrated or sham castrated shortly after birth. Castrated males were then injected every other day on days 0-10 with testosterone propionate (TP, 0.5 mg), dihydrotestosterone propionate (DHTP, 0.5 mg) or the oil vehicle (0.05 ml); sham-castrated males received oil injections. In adulthood, when substituted with DHT, DHT + E2, or T (silastic implants), sexual partner preference was measured in an automated open field (AOF), in which wire mesh prevented sexual interaction with incentives, and in a 3-compartment box (3-CB), in which sexual interaction with tethered incentives was possible. Choices were an estrous female and a nonestrous female or an estrous female and a sexually active male. In adulthood, following long-term treatment with DHT or DHT + E2, the males did not show any partner preference when sexual interaction with incentives was prevented. Following sexual experience with an estrous female these males preferred the estrous over the nonestrous female, although this change could also be due to long-term hormone treatment. In the 3-CB, a clearcut preference emerged for the estrous female over the nonestrous conspecific, although the neonatally DHTP- or oil-treated males scored lower than the neonatally TP-treated or control males. Six weeks after removal of the hormone implants, when tested in the 3-CB (estrous female vs. active male), the males showed no partner preference. Unexpectedly the control males showed a low preference for the active male. Three weeks T-treatment made all males show a preference for the estrous female (in 3-CB).(ABSTRACT TRUNCATED AT 250 WORDS)