Transition from precopulatory to copulatory behaviour in male rats with lesions in medial preoptic area: dependence on precopulatory pattern of female

In the present study, both the precopulatory behaviour and the copulatory readiness of male rats following the bilateral medial preoptic area lesions was compared with their intact states. In behavioural testing, the intensity of female precopulatory behaviour was used as an experimental variable. The results showed that the natural threshold of copulatory readiness of males was increased in the lesioned state, the animals were more dependent on the soliciting patterns of the female. However, all the males exhibited conspicuous precopulatory behaviour towards the stimulus females used. Apparently, further brain structures participate in the regulation of sexual behaviour of males, above all, in activation or maintenance of precopulatory activity.     

Effects of neonatal septal lesions on reproductive behavior of male and female rats

The purpose of this study was to examine the effects of neonatally placed septal lesions (SL) in male, female, and androgenized female rats on reproductive behavior. Animals were castrated as adults and tested for both feminine and masculine sexual behavior. After treatment with estradiol benzoate (EB) alone (2 μg daily for 3 days), only the females with SL which had not been given testosterone propionate (TP) neonatally showed a facilitation of lordosis behavior. Following EB (2 μg for 3 days) plus 0.5 mg progesterone (P), both the lesioned and the sham-operated female groups showed an increase in the display of lordosis in either hormonal condition. All animals were given a pretest for masculine sexual behavior and tested on Days 4, 7, 11, and 15 of daily TP treatment (150 μg/day). There was no effect of the neonatally placed SL on masculine sexual behavior in female rats or in female rats androgenized with 30 μg TP. However, lesioned females treated neonatally with 1 mg TP showed a marginal enhancement of masculine sexual behavior. Male rats given SL neonatally showed a marked enhancement of masculine sexual behavior compared to that of controls. These results suggest that, depending on the neonatal hormone environment, SL selectively increase behavioral sensitivity to hormones. Although neonatally lesioned females show behavioral responses similar to females given SL as adults, male rats given SL neonatally are unique in that they show enhanced masculine sexual behavior whereas males lesioned as adults do not.     

Effects of ventromedial nucleus lesions on estradiol induced ovulation in the rat

Small bilateral stereotaxic lesions were made in the hypothalamic ventromedial nucleus (SVMN) to determine: (i) whether estrogen would restore early receptivity in unreceptive SVMN lesioned female rats and (ii) whether SVMN lesions would suppress estrogen induced ovulation in the rat. SVMN lesions were shown to completely suppress spontaneous early receptivity and seriously impair estrous receptivity in 5-day cyclic female Wistar rats. A loss of early receptivity in response to 10 μg estradiol benzoate (EB) was also observed in SVMN lesioned females, in comparison to unoperated, sham VMN and dorsomedial nucleus (DMN) lesioned animals. Isolated SVMN lesioned females exhibited a weak ovulatory response to 10 μg EB, but, where shown to be unreceptive prior to estrogen injection, they never ovulated. On the contrary, ovulation occured in about 50% of cases in isolated unoperated and in sham VMN and DMN lesioned females following estrogen administration. The mechanisms whereby EB brought about precocious ovulation in 5-day cyclic female rats were therefore concluded to be dependent on VMN functional integrity and thereby on the degree of early sexual receptivity in the rat.     

Male-like sexual behaviour of female rats with unilateral lesions in the hypothalamic ventromedial nuclear region.

In castrated female rats treated with androgen or oestrogen a significant decrease of female sexual behaviour assocated with a significant increase of male sexual behaviour was induced by unilateral lesions of the hypothalamic ventromedial nucleus.     

Reinforcing stimulation of the postero-lateral hypothalamus and mating behaviour in the rat.

Male rats implanted with chronic electrodes into the postero-lateral hypothalamic site were tested for self-stimulation behaviour. Rats exhibiting steady self-stimulation behaviour were observed during mating tests with an oestrus female. During these tests the hypothalamus of male rats was stimulated. Results show that no stimulus-bound sexual behaviour was observed. Nevertheless, correlations were found between the rewarding value of the cerebral stimulation and the specific sexual components of mating behaviour. These results are interpreted with the hypothesis of a balancing effect between the reward elicited by direct stimulation of the brain and reward acquired by the presence of an oestrus female.     

The effect of medial preoptic area lesions on sexually stimulated hormone release in the male rat

Male rats were subjected to bilateral electrolytic lesions in the medial preoptic area (mPOA). These lesions disrupted sexual behavior without affecting basal levels of luteinizing hormone (LH), prolactin (PRL), or testosterone (T). During exposure to an estrous female, intact and sham-operated rats mated; these rats showed elevations in LH, PRL, and T levels. Lesioned rats, which did not mate, showed elevations in LH but not PRL or T levels. These results demonstrate that the mPOA is not required for sexually stimulated LH release. The failure of lesioned rats to release PRL and T may be secondary to their failure to mate. Alternatively, the mPOA may participate in sexually stimulated PRL release, while T release may depend on prior elevations in both LH and PRL levels. LH release may be related to arousal, and PRL release to consummation, providing a hormonal analogy for the dual mechanism theory of sexual behavior.     

Reproductive function and sexual behaviour in female rats exposed to immobilization stress or ACTH injections during gestation

Pregnant primiparous rats were exposed to low immobilization stress or ACTH injections (one unit) throughout pregnancy. We measured the following parameters in the female offsprings: puberty (vaginal opening and first oestrous), oestrous cycle and sexual behaviour. Compared to the controls, female sexual receptivity measured by means of lordosis and the lordosis quotient (LQ) increased in both the experimental groups, but the puberty parameters of the offspring did not alter.     

Precopulatory behaviour of male rats: developmental aspects and dependence on female's solicitation

Sexual communication between sex partners can involve just one sensory modality or a combination, depending upon such factors as species, habitat, and context. Ethological aspects of sexual communication has been widely documented in rodents. In rats, sexual communication between male and female varies according to the production of signals by a female that signal receptivity, proceptivity, and attractivity. However, in the laboratory experiment, such approach is often neglected. In the present study, two types of stimulus female--Lordotic and Darting--were used with the aim to examine developmental changes in precopulatory behaviour of males. Besides the dependence of the male's precopulatory repertoire on the strength of proceptive stimuli emitted by the female was studied. Male rats ranging from 30 to 175 days of age were observed under the dyadic interaction. It was found: (a) Precopulatory behaviour of the 30-day-old males was not clear-cut, the males devoted more time to social investigation of adult (Darting) female. (b) All the 40-day-old males exhibited precopulatory behaviour in the range of the repertoire displayed by adult animals. (c) Precopulatory activity of juvenile (45-day-old) as well as of adult (90-day-old) males exposed to Lordotic female was significantly lower as compared with that exhibited by males toward Darting female. (d) Copulatory readiness of males increased with the age, in fact, all animals aged from 75-135 day were able to pass from the precopulatory into the copulatory phase of sexual interaction. (e) Although the 175-day-old males exhibited pronounced precopulatory activity, they did not initiate copulations. The implications of each of these findings are discussed from the point of view of both the developmental aspects and the stimulus-response relationships. To sum up, the development of normal flow of sexual behaviour of male rats proceeds simultaneously with the development of physiological and morphological parameters. The appearance of precopulatory behaviour is less dependent on the internal (hormonal) readiness than copulatory behaviour. The connection of both phases, i.e. precopulatory and copulatory, is terminated at about Day 75, and is the key moment of sexual interaction from the point of view of reproductive success. In fact, a successful course of sexual interaction is codetermined by the intensity of behavioural stimuli and/or by the completeness of proceptive patterns provided by the female partner. It is clear that the reproductive process cannot be completed without some degree of communication. The deterioration of sexual interaction found in males aged 175 day seems to be the consequence of their absolute heterosexual abstinence.(ABSTRACT TRUNCATED AT 400 WORDS)     

Sexual behaviour of male rats rehabilitated after early protein-calorie malnutrition.

The effect of early protein-calorie malnutrition (from birth to the age of 55 days) followed by nutritional rehabilitation (from the 58th day) on sexual behaviour was studied in male rats aged about 125 days. The sexual stimulation conditions on the part of the oestrus female were made as optimal as possible and were fully controlled. About half the malnourished males displayed precopulatory and copulatory behaviour, while in the control group these values were almost 100%. When malnourished males copulated, their copulatory performance did not differ very greatly from that of the well-nourished controls. The other experimental males displayed no signs of sexual behaviour during the testing period. Exposure of the males to the scent of a female in the latter's absence greatly stimulated their interest in the odour (sniffing the floor of the experimental box) in both the control and the malnourished animals which afterwards copulated. The results indicate that the sexual behaviour of males subjected to protein-calorie deficiency in early ontogenesis is at the very least delayed, if not completely suppressed.     

Maturation of sexual behavior in laboratory male mice: a role of genotype

Sexual behaviour and testosterone output in response to a receptive female were investigated in male mice of three inbred strains BALB/cLac, CBA/Lac and PT at puberty (45 days of age) and in adulthood (90 days of age). The animals were exposed for 10 min to a receptive female separated by a plastic grill, which would not allow contact between male and female. Male and female behaviour was recorded by measuring the time the male or female spent at the grill and the number of approaches to it (sexual motivation). The grill was then removed and the number of mounts and chemoinvestigatory behavior towards a female (nasal and anogenital sniffing) was recorded for each male. An increase in serum concentration and testicular content of testosterone was used as an endocrine index of the sensitivity to female pheromones. It has been shown the significant genotype and developmental effects on sexual behaviour and the hormonal response to sexual stimuli. The pubertal BALB/cLac males were characterised by the adult pattern of sexual motivation, chemoinvestigatory behaviour and the evident testosterone respond to a female. Males of the strain PT showed the lowest sexual motivation, chemoinvestigatory behavior towards a receptive female and no testosterone responses at both ages. This is a very different situation with the CBA/Lac's who showed the developmental increase in the sexual motivation, sniffing behaviour and the endocrine reflex, and the highest level of sexual behaviour but the moderate testosterone respond to a female at adulthood. The data obtained suggest genotype related asynchrony in maturation of the olfactory system, pituitary-gonadal axis and neural circuits of sexual behavior, and their independent genetic control. So, the set of mice strains investigated represents a useful tool for genetic and endocrine study of sexual behavior and the chemosensory control of testicular steroidogenesis.     

Effect of synthetic LH-RH and hypothalamic extracts on RNA synthesis by rat pituitaries in vitro (author's transl)]

Incorporation of 14C-Uridine in pituitary RNA from adults or prepuberal female rats in vitro, incubated with synthetic LH-RH or hypothalamic extracts, was studied in this work. RNA synthesis was not increased by any of the assayed stimuli in adult female rat pituitaries. The 14C-Uridine incorporation in pituitary prepuberal female rats increased in presence of synthetic LH-RH or adult female hypothalamic extracts, but not in presence of prepuberal female hypothalamic extracts. The differences found in the in vitro behaviour between pituitaries from prepuberal and adult female rats, and between their respective hypothalamic extracts, are attributables to the evolution of these organs along the sexual maturing process.     

The effect of ablation in the n. medianus raphe on the aggressive and sexual behavior of white rats]

A study was made of a change in the aggressive and sexual behaviour of albino rats under the influence of ablation of the n. medianus raphe whose serotonin-containing units send ascending projections to the forebrain. Ablation of the nucleus produced a drop in the serotonin level in the forebrain, and aggressiveness to mice, which was much more pronounced in the male than in the female animals. Intraspecial aggressiveness between animals of the same sex and the sexual behaviour of the male rats did not change. It has been assumed that n. medianus raphe exerts an inhibitory influence on the manifestation of aggression of the "predatory" animal.     

Role of the medial preoptic area in sexual behaviour of the male rat: a study using repeated cycloheximide infusions

The effect of cycloheximide (CHX), an inhibitor of proteosynthesis, on sexual behaviour was studied in adult male rats in which it was infused into the medial preoptic area of the hypothalamus (MPOA). Sexual interaction took place under control and modification of the precopulatory behaviour of the female. Among the various bilaterally infused amounts of CHX--20 micrograms in 1 microliter, 40 micrograms in 1 microliter, 80 micrograms in 2 microliters--the effect of the largest dose corresponded to a hypothetical state of copulatory readiness of the males; 2 h after administration the males were not capable of initiating copulatory behaviour with a passively receptive female, but did so successfully with a highly soliciting female. The dependence of copulatory readiness of the males on the precopulatory behaviour of the females was confirmed repeatedly after this dose of CHX. At the same time, the precopulatory activity of the males towards a passively receptive female was unimpaired. The effect of CHX was reversible; 48 h after infusion the males displayed high copulatory readiness. Only half the males (n = 7) given bilateral infusions of 80 micrograms CHX fulfilled criterion of copulatory performance. Histological control demonstrated that the MPOA was affected bilaterally by CHX infusion in 10 males out of 14. The results are discussed from the aspect of participation of the MPOA in the regulation of male sexual behaviour. The method allows changes in sexual behaviour to be studied in the same individual in a chronic experiment.     

Medullo adrenal response to lesion of anterodorsal thalamic nuclei in rats

Anterodorsal thalamic nuclei (ADTN) exert an inhibitory influence on hypophyso-adrenal system (HAS) in rats. With the purpose of evaluating if ADTN are also involved in the control of medullo adrenal activity, experiments were conducted on female rats with bilateral lesion of these nuclei. Thirty days after lesion, plasma epinephrine (E) concentration in lesioned rats was higher than that in sham-lesioned control group (P < 0.02). Meanwhile, adrenal E content was significantly lower in lesioned animals than that found in the control group (P < 0.005). Plasma norepinephrine (NE) values in lesioned rats were not significantly different from those in the control ones, however, there was a significant decrease in adrenal NE when compared to the control one (P < 0.02). Basal values of plasma ACTH and plasma and adrenal corticosterone (C) were signicantly higher than those in sham lesioned rats (P < 0.05; P < 0. 001; P < 0.001 respectively). These findings demonstrate that the ADTN in rats are involved in the regulation of both cortico and medullo adrenal activity.     

Sexual and maternal behaviour at the postpartum oestrus: The role of experience in time-sharing

The postpartum sexual and maternal behaviour of Norway rats (Rattus norvegicus) was observed in a seminatural habitat. Behavioural decision-making by the female was examined by disrupting the nest and newborn offspring during mating. In experiment 1, multiparous females responded to nest disruption with an increase in maternal behaviour that was largely restricted to the post-ejaculatory intervals. The temporal and frequency measures of copulation were largely unaffected, implicating behavioural time-sharing. In experiment 2, following nest disruption primiparous females did not switch efficiently between maternal and sexual behaviour, showed poor retrieval of pups, and returned to the nest during ejaculatory series. They did not display the characteristics of behavioural time-sharing, indicating that previous experience may play a role in the ability to time-share.     

Sniffing behaviour, copulatory readiness, copulatory performance and reproductive morphology of adult male rats weaned prematurely

Sexual behaviour of adult male rats weaned prematurely--on day 15 after birth--and of males weaned at the optimal age--on day 28--was compared at two life periods: at the age of 90 days and when the males were one year old. Sexual behaviour was evaluated by means of three characteristics: a) sniffing behaviour, b) copulatory readiness, c) copulatory performance. The differences in sniffing behaviour between prematurely and normally weaned males were assessed in terms of their responsiveness to sccents of unrelated adult males or oestrous females and from the point of view of both housing conditions after weaning and the animals' sexual experience. No differences were found in copulatory readiness as well as in copulatory performance between the two groups of males tested in their interaction with a female exhibiting complete precopulatory pattern. The morphological examination revealed no differences in the weight of reproductive organs and in spermatozoa development. We conclude that the sexual behaviour as well as reproductive organs of male rats are very resistant to early separation of pups from the mother which contrasts with some earlier findings.     

Effects of septal lesions on the lordotic behavior of weanling male and female rats

Twenty-four-day-old weanling male and female rats were either lesioned in the septal area, gonadectomized, lesioned and gonadectomized, or not treated. Tests for lordotic behavior were carried out at 27 and 28 days of age after priming with estradiol alone and with estradiol plus progesterone. A second set of tests for lordotic behavior was carried out at 47 and 48 days of age. In the interim period, some of the animals were given chronic estrogen treatment. In tests given at 27 days of age, septal lesions facilitated lordotic responding after estrogen priming; no differences were observed between male and female animals. At 47 and 48 days of age, however, unless male rats had been exposed to chronic estrogens following septal lesioning, no facilitation of estrogen-induced lordotic behavior occurred. In addition, it was found that female rats gonadectomized at 24 days of age and given no exposure to estrogens between the tests at 27 and 28 days and those at 47 and 48 days of age showed reduced sensitivity to estrogens, as compared to normal or estrogen-treated females, whether lesioned or not.     

Age- and Sex-Dependent Laterality of Rat Hippocampal Cholinergic System in Relation to Animal Models of Neurodevelopmental and Neurodegenerative Disorders

Studies suggest age- and sex-dependent structural and functional patterns of human cerebral lateralization underlie hemisphere specialization and its alterations in schizophrenia. Recent works report sexual dimorphism of neurons in the hippocampal formation and specialization of hemispheres in rats. Our experiments indicate for the first time functional lateralization of the high-affinity choline uptake (HACU) system directly associated with a synthesis of acetylcholine in the hippocampus of Wistar rats. The markedly increased HACU activity was found in the left compared to the right hippocampus of adult male but not female animals. Lineweaver-Burk plot analysis revealed a statistically significant increase of Vmax in the left hippocampus of 14-day-old when compared to 7-day-old males. It appears that laterality of HACU occurs during late postnatal maturation, and its degree is markedly enhanced after puberty and attenuated during aging. Quinolinic acid (QUIN), an endogenous agonist of N-methyl-D-aspartate type glutamate receptors, was used in this study to evaluate the neurodevelopmental hypothesis of schizophrenia. It is known that elevated levels of QUIN accompany viral infections, increasing the risk of developing schizophrenia. Bilateral intracerebroventricular application of QUIN (250 nmoles/ventricle) to pups aged 12 days significantly impaired the cholinergic hippocampal system of adolescent male and female rats and reversed lateralization of male HACU. Morphological analysis indicated marked changes in brain lesion sizes (extensive 24 h and moderate 38 days after the operation). Asymmetry of lesions was observed in the majority of cases, but the left hemisphere was not generally more vulnerable to QUIN effects than the right side. Moreover, no lateral differences were found between lesioned hippocampi in the specific binding of [3H]hemicholinium-3 (10%-15% loss of binding sites when compared to sham-operated animals). In summary, our results indicate a symmetrical drop in the number of choline carriers of lesioned male rats but a asymmetrical decrease in the activity of remaing carriers, suggesting defects in processes of sexual brain differentiation, leading under normal conditions to the higher activity of carriers in the left hippocampus. The data demonstrate viral infection-mediated alterations in normal patterns of brain asymmetry and are discussed in relation to animal models of neurodevelopmental and neurodegenerative diseases.     

Administration of an oxytocin receptor antagonist attenuates sexual motivation in male rats

In male rats, oxytocin impacts both sexual arousal and certain types of consummatory sexual behaviors. However, the role of oxytocin in the motivational aspects of sexual behavior has received limited attention. Given the role that oxytocin signaling plays in consummatory sexual behaviors, it was hypothesized that pharmacological attenuation of oxytocin signaling would reduce sexual motivation in male rats. Sexually experienced Long-Evans male rats were administered either an oxytocin receptor antagonist (L368,899 hydrochloride; 1 mg/kg) or vehicle control into the intraperitoneal cavity 40 min prior to placement into the center chamber of a three-chambered arena designed to assess sexual motivation. During the 20-minute test, a sexually experienced stimulus male rat and a sexually receptive stimulus female rat were separately confined to smaller chambers that were attached to the larger end chambers of the arena. However, physical contact between test and stimulus rats was prevented by perforated dividers. Immediately following the sexual motivation test, test male rats were placed with a sexually receptive female to examine consummatory sexual behaviors. Although both drug and vehicle treated rats exhibited a preference for the female, treatment with an oxytocin receptor antagonist decreased the amount of time spent with the female. There were no differences between drug and vehicle treated rats in either general activity, exploratory behaviors, the amount of time spent near the stimulus male rat, or consummatory sexual behaviors. Extending previous findings, these results indicate that oxytocin receptors are involved in sexual motivation in male rats.     

Plasma corticosterone level of rats after bilateral lesion of the globus pallidus and elimination of the sex-dependence of the body weight loss following pallidal lesion by bilateral adrenalectomy

Plasma corticosterone (CST) level and body weight were studied in male and female rats after bilateral pallidal lesion (GPL). The effect of high dose of glycocorticoids on body weight of food and water deprived, non-lesioned rats was also studied since high CST levels due to the stress caused by the aphagia and adipsia could be anticipated. Weight changes in lesioned-adrenalectomized animals were in investigated as well. A weight loss, higher in males than females, developed after the pallidal lesion and the CST level was higher in lesioned females than in lesioned males. This sex-difference was present in non-lesioned, food and water deprived animals as well. The weight loss was higher in lesioned males than in food and water deprived male/female controls. Adrenalectomy eliminated weight loss differences between the sexes after lesion, by reducing the weight loss in males. CST administration reduced body weight loss in food and water deprived males but not in familes, and cortisol facilitated it in both sexes.