Intracranial cycloheximide: effects on maternal behavior in the postparturient rat

Cycloheximide (Cyclo), 100μg/gml saline infused bilaterally into the preoptic area (POA) of female rats on the fourth day postpartum, significantly suppressed maternal behavior for a period of some 72 hr. At the same time, females subjected to infusions of Cyclo in the caudate nucleus, as well as those receiving as s.c. injection of the drug, continued to show high levels of maternal behavior. Since, in addition, estrogen-progesterone induced lordosis was unaffected by POA infusion when the infusion occurred 24 hr after estrogen administration, the view was advanced that (a) maternal behavior was selectively suppressed, (b) the suppression was produced through biochemical rather than through cytotoxic action, and (c) continuing protein synthesis, particularly in the POA, is essential for the maintenance of such nurtural responses as nursing, nest building, licking, and retrieving.     

Increased homocysteine levels associated with sex and stress in the learned helplessness model of depression

Elevated levels of homocysteine (Hcy) have been associated with major depressive (MD) illness. As human females show a higher predisposition towards depression, this study examined how Hcy levels in rats are affected by sex and estrous cycle in the learned helplessness (LH) model of depression. Male and female rats in either estrus or diestrus were subjected to LH, with intervals of 4 days between the two stress tests and between tests and sacrifice, in order to accommodate the female estrous cycle. No differences were found in LH behavior between males and females at either estrous phase. Control Hcy levels were significantly lower in females than in males (-36%, P<.001), with no further differences between estrous and diestrus phases in females. Stress exposure increased plasma Hcy by approximately 26% in females, both in estrus and diestrus, but not in males. However, when behavioral responses to stress were considered, no association was found between increased Hcy levels and propensity to develop helpless behavior. Therefore, while male rats have higher basal Hcy levels than females, females appear to be more vulnerable than males to stress-induced elevations in Hcy, although this did not correlate with behavioral responses to stress. Neither was this vulnerability influenced by estrous phase. These results imply that both stress and sex should be considered as risk factors for increased plasma Hcy.     

Effects of chronic and acute ethanol treatment during prenatal and early postnatal ages on testosterone levels and sexual behaviors in rats

This study was prompted by previous findings that prenatal ethanol exposure may interfere with the differentiation of the sexual behavior in rats. Ethanol (6 g/kg) administered daily from day 15 postconception, resulted in elevated testosterone (T) levels on Day 18 in male and female fetuses. No alterations of sexual behavior in the ethanol-treated male offspring were seen under these conditions. However, in ethanol-treated female offspring the onset of regular estrous cycling was significantly delayed. Acute treatment with doses of ethanol, 2, 4 or 6 g/kg, was ineffective in influencing plasma T levels of the fetuses. Acute treatment with 3 g/kg ethanol did not prevent the rise of T levels normally occurring immediately after birth. In adulthood, but not at prepubertal age (Day 30), treatment of male rats with 2 g/kg ethanol caused a depression of plasma T levels. Possible mechanisms affected by ethanol exposure and influencing on the fetal development were discussed.     

Sex behavior of male and female Wistar rats affected by the serotonin agonist 8-OH-DPAT.

Four experiments were carried out to test the stimulatory effects of 8-OH-DPAT on various aspects of "masculine" sexual behavior of male and female rats and on the sexual attractivity of male rats. In Experiment 1 8-OH-DPAT (0.2 mg/kg) stimulated ejaculation frequency in middle-aged (approx. 15 months old) males, both sexually inactive and active subjects. There was a coinciding decrease in total number of mounts, intromissions, intromissions to first ejaculation and latency to first ejaculation. In Experiment 2 the effects of two doses (0.2 and 0.4 mg/kg) 8-OH-DPAT on the first ejaculation cycle were investigated. Especially, the higher dose made a high percentage (45-55%) of males to ejaculate "prematurely," i.e., at the first or second intromission. Latency to ejaculation decreased. With the higher dose, 25-35% of the males ejaculated extravaginally. In Experiment 3 8-OH-DPAT did not make males more attractive for an estrous female than saline-treated males, as judged by the time spent in their vicinity. However, estrous females received much more ejaculations from the tethered 8-OH-DPAT males, with the lowest latencies to first ejaculation, than from the saline-treated males. In Experiment 4 8-OH-DPAT stimulated mounting behavior in female rats only when they were long-term treated with testosterone. In that condition also shortest latencies to first mount were found with 8-OH-DPAT treatment.     

Estrous cycle and sex differences in performance on anxiety tasks coincide with increases in hippocampal progesterone and 3alpha,5alpha-THP

Sex differences and estrous cycle variations in anxiolytic-like behaviors and progestin concentrations were examined. Proestrous (n=22), estrous (n=19), diestrous (n=20), and male (n=18) Long-Evans rats were tested in horizontal crossing, open field, elevated plus-maze, emergence, holeboard, social interaction, tailflick, pawlick, and defensive burying tasks. Concentrations of plasma and hippocampal progesterone and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) were measured by radioimmunoassay in behaviorally tested (proestrus n=11, estrus n=8, diestrus n=9, male n=7) and yoked non-tested rats (proestrus n=11, estrus n=8, diestrus n=10, male n=8). Proestrous females exhibited more anxiolytic-like behavior than all other groups on the elevated plus-maze, social interaction, and defensive burying tasks. Proestrous females had significantly shorter latencies to emerge from a cylinder than did estrous and diestrous females, but not males. Proestrous and estrous females entered significantly more peripheral and total squares in a brightly-lit open field than did males. While proestrous females had a tendency to make more beam breaks than did males in the horizontal crossing task, there were no differences between groups on the holeboard task. There was a tendency for proestrous females to have longer tailflick latencies than diestrous and male rats; however, on the pawlick task there were no differences among the groups. Plasma and central progesterone and 3alpha,5alpha-THP of tested and non-tested rats were not different. Proestrous females had significantly higher plasma and hippocampal progesterone and 3alpha,5alpha-THP levels than all other groups. These data demonstrate that proestrous increases in anxiolytic-like behavior coincide with elevated circulating and hippocampal progestin concentrations.     

5alpha-reductase 2 inhibition impairs brain defeminization of male rats: reproductive aspects

The present study was carried out to determine whether 5alpha-reductase 2 (5alpha-R2) metabolic pathway plays a key role in brain sexual differentiation. The inhibition of 5alpha-R2 by finasteride (20 mg/kg/day) from gestational day 19 to postnatal day 5 has long-term effects on sexual behavior and reproductive physiology detected only in adult life. Sexual maturation assessed by timing of preputial separation was unchanged. Finasteride-treated males were able to mate with untreated females which became pregnant but exhibited increased rate of pre-implantation loss. The subfertility observed was probably due to abnormally shaped sperm, since the sperm number was not altered. While plasma testosterone was enhanced, LH levels were not changed. The copulatory potential was not affected and all finasteride-treated rats presented male sexual behavior. Despite this, 53% of them showed homosexual behavior when pretreated with estradiol, suggesting an incomplete brain defeminization. These results indicate that 5alpha-R2 acts in brain sexual differentiation of male rats. Moreover, we suggest that 5alpha-R2 not only produces essential metabolites that act together with estradiol in brain sexual differentiation but also protects the brain from the damaging effects of estradiol excess.     

The effect of neuroleptic drugs on serum testosterone level in the male rat

The effects of systemically administered haloperidol (haldol) and N-ethoxycarbonyl-2-ethoxy-1,2, dihydroquinoline (EEDQ) on serum testosterone level were studied in Sprague-Dawley adult male rats. Animals were injected intraperitoneally with either 0.1, 5 and 10 mg/kg of haldol or 0.5 and 5 mg/kg of EEDQ. Animals were sacrificed at 15, 60 min, 12, 24 or 48 hr after drug treatment and blood was collected for subsequent testosterone analysis. Results obtained indicate that 10 mg/kg of haldol significantly (P less than 0.01) suppressed serum testosterone levels both at 1 and 24 hr post drug treatment. EEDQ treatment significantly (P less than 0.01) suppressed serum testosterone levels only when administered at the higher dose of 5 mg/kg. This effect was observed as long as 12 hr after drug treatment. These results suggest that high doses of haldol and EEDQ can suppress serum testosterone levels in the male rat. The sexual dysfunction associated with neuroleptic drugs may be partially due to the effects of the drugs on serum testosterone levels.     

Perinatal or adult exposure to cannabinoids alters male reproductive functions in mice

Oral administration of THC or CBN at a dose of 50 mg/kg body weight to pregnant and lactating female mice results in long-term effects on their male offspring, including: body weight regulation, pituitary-gonadal function, responsivity to exteroceptive stimuli from conspecifics and copulatory activity. Effects of perinatal exposure to cannabinoids on the male reproductive system did not become evident until after weaning (21 days of age). Male mice exposed to THC had reduced testes weight and elevated plasma LH levels during and after sexual maturation. In contrast, CBN-exposed males had reduced levels of testosterone (T) and LH during the prepubertal period and normal levels of these hormones after sexual maturation, although plasma FSH levels appeared reduced. In prepubertal males, production of androgen-dependent urinary pheromones, as assessed by uterine weight gain in cohabitant immature females, was not differentially affected by perinatal cannabinoid exposure. However, the pattern of body weight gain in the maturing males, the weights of the accessory reproductive organs and pituitary LH release were affected by the interaction of perinatal drug exposure and housing with an immature female. Plasma levels of T were elevated in all prepubertal males housed with an immature female for one week, whether or not the animals were previously exposed to cannabinoids. Copulatory behavior was reduced in adult males exposed to either THC or CBN during the perinatal period of sexual differentiation. Chronic treatment of adult males with 50 mg THC/kg body weight for 3 weeks increased testes weight and decresed the weights of the seminal vesicles. However, these effects were no longer evident after 7 weeks of THC treatment. The levels of copulatory activity displayed by the THC-exposed males were reduced after both 2.5 and 6 weeks of treatment. In contrast, oral administration of 50 mg/kg cannabinol for 3 weeks decreased testes and seminal vesicle weights and plasma T and LH levels. In addition, 2.5 weeks after the onset of CBN treatment, copulatory behavior was significantly suppressed. These findings indicate that both psychoactive and non-psychoactive constituents of mariuana affect pituitary-gonadal function in adult mice, and that the development of the male reproductive system is significantly altered in animals exposured to cannabinoids during critical periods of sexual differentiation. Moreover, some of the observed effects on male reproductive function and androgen-dependent behaviors may be secondary to alterations in the endocrine system produced by non-psychoactive and psychoactive components of marihuana.     

Reproductive and sexual behavior changes in male rats exposed perinatally to picrotoxin

Previous studies in rats suggested that picrotoxin, a GABA_A receptor antagonist, may cause long-term changes in male reproductive physiology and behavior in rats exposed during prenatal and postnatal periods. The present study has further examined this phenomenon. Wistar rat dams were dosed subcutaneously with 0.75 mg/kg picrotoxin in saline, or vehicle alone, during the perinatal period (day 19 of gestation, immediately after parturition, and once a day during the first 5 days of lactation). Birth weight and sexual maturation of pups were unchanged; however, plasma testosterone levels and sexual behavior was altered in male offspring. Although fertile, these males showed altered mating behavior in terms of a decrease in the mean number of mounts during a 30-min observation period with normal females. Some showed homosexual behavior when castrated and pretreated with exogenous estrogen. These findings suggest that perinatal exposure to picrotoxin alters sexual dimorphism in the developing rat brain, manifesting as altered reproductive performance and sexual behavior of males.     

Effects of anabolic androgenic steroids and social subjugation on behavior and neurochemistry in male rats

Early abuse and anabolic androgenic steroids (AAS) both increase aggression. We assessed the behavioral and neurochemical consequences of AAS, alone or in combination with social subjugation (SS), an animal model of child abuse. On P26, gonadally intact male rats began SS consisting of daily pairings with an adult male for 2 weeks followed by daily injections of the AAS, testosterone on P40. As adults, males were tested for sexual and aggressive behaviors towards females in various hormonal conditions and inter-male aggression in a neutral setting using home or opponent bedding. Neurotransmitter levels were assessed using HPLC. Results showed that AAS males displayed significantly more mounts toward sexually receptive, vaginally obstructed females (OBS) and displayed significantly more threats towards ovariectomized females. SS males mounted OBS females significantly less and were not aggressive toward females. The role of olfactory cues in a neutral setting did not affect aggression regardless of treatment. AAS significantly increased brainstem DOPAC and NE. SS decreased 5HIAA, DA, DOPAC, and NE in brainstem. 5HIAA was significantly increased in the prefrontal cortex of all experimental groups. We conclude that AAS and SS differentially affect behavior towards females as well as neurotransmitter levels.     

Alteration of behavioral sex differentiation by exposure to estrogenic compounds during a critical neonatal period: effects of zearalenone, methoxychlor, and estradiol in hamsters

The present study was designed to determine if neonatal exposure to the estrogenic mycotoxin zearalenone or the weakly estrogenic pesticide methoxychlor could masculinize and/or defeminize the behavior of female hamsters. Neonatal hamsters were given a single sc injection of either zearalenone (1 mg/pup), methoxychlor (1 mg/pup), 17 beta-estradiol (E2) (40 micrograms/pup), or the vehicle 2 days after birth. After puberty, behavioral estrous cyclicity was measured. The females were then ovariectomized, treated with the male hormone testosterone, and tested for their ability to mount a receptive female (a behavior not normally displayed by female hamsters). Females treated neonatally with estradiol or zearalenone were masculinized but not defeminized, an effect consistent with perinatal exposure to low doses of sex hormones. Females in these two treatment groups displayed normal 4-day behavioral estrous cycles, but following ovariectomy and testosterone treatment they mounted a sexually receptive female at a frequency comparable to the males. Methoxychlor-treated females did not differ from controls. The mounting behavior of similarly treated males was unaffected by any of the chemicals. However, males receiving estradiol treatment had smaller testes, seminal vesicles, and cauda epididymides and 57% had epididymal cysts. These results demonstrate that a single exposure to a weakly estrogenic chemical like zearalenone during a critical developmental period can cause the brain to differentiate in a manner inconsistent with the female's genetic sex. This enables the female to respond to the activational influence of testosterone as an adult and readily mount a sexually receptive female. The failure of methoxychlor to alter reproductive development in the current study may be due to an inability of the neonatal hamster to convert methoxychlor to estrogenic metabolites.     

Methoxychlor given in the periimplantation period blocks sexual arousal in male mice

To determine whether pesticide methoxychlor (MXC) alters sexual arousal in male offspring, pregnant ICR mice remained untreated or received daily subcutaneous injections (s.c.) of olive oil, 33.0 mg/kg bw purified (95%) MXC, or 0.33 mg/kg bw estradiol-173 in vehicle on Days 5 to 7 of pregnancy. Live births were recorded in all groups except the estradiol group. At 4 months, untreated or olive oil-treated male offspring exhibited normal sexual arousal. When placed near a plastic partition with an estrus female behind it, these males spent significantly more time near the partition than near a vacant half of the cage and exhibited a sharp increase in plasma testosterone. MXC-exposed males showed no sexual arousal, spent much less time near the partition with an estrus female, and exhibited significantly lower plasma testosterone levels. Exposure to purified MXC close to implantation alters the function of the hypothalamic-pituitary-testicular axis and compromises male sexual behavior in offspring.     

Role of testosterone in gamma-glutamyltranspeptidase-dependent renal methylmercury uptake in mice.

To elucidate the mechanisms responsible for sex and age differences in renal methylmercury uptake, effects of castration and testosterone treatment on mercury content and activity of renal gamma-glutamyltranspeptidase (gamma-GTP), which supposedly plays an important role in renal mercury uptake, were investigated in mice. Between 2 and 8 weeks of age, renal methylmercury uptake in male mice determined 4 hr after injection of a nontoxic dose of methylmercuric chloride (MMC, 1 mumol/kg, sc) increased about fivefold. At 4 weeks of age, a significant sex difference in renal mercury uptake first appeared. Renal mercury content in 4-week-old male mice was twofold higher than that of females and increased with age, but remained constant in females. Small but significant (p less than 0.05) differences in mercury content in other tissues were observed, which could not account for the marked sex- and age-related differences in renal mercury concentrations. Renal gamma-GTP activity gradually increased in males with maturation, and a sexual dimorphism of renal gamma-GTP was apparent after the fourth week. Seven days after castration of 4-week-old male mice, both renal mercury content and gamma-GTP activity were decreased to the levels in females. Activity of gamma-GTP was subsequently elevated to control male levels by sc injection of testosterone (5 mg/kg/day x 7 days). In female mice, both renal mercury content and gamma-GTP activity were increased to the level of males by testosterone treatment (5 mg/kg/day x 14 days). Thus, the renal mercury content was closely correlated with changes in renal gamma-GTP activity. These results suggest that sex and age differences in renal methylmercury accumulation may be due to a difference in renal gamma-GTP activity controlled at least in part by testosterone.     

Effects of chlordiazepoxide,oxazepam, chlorpromazine,andd-Amphetamine on sexual responses in male and female hamsters

The acute effects on sexual behavior of oxazepam (16–64 mg/kg), chlordiazepoxide (8–64 mg/kg), chlorpromazine (2–8 mg/kg), andd-amphetamine (0.8–3.2 mg/kg) were examined in intact male and female golden hamsters (Mesocricetus auratus). Intraperitoneal injections were given 45 min before the first behavioral test. In 10-min tests lordosis was observed in estrous females both before and after copulation, and mounts, intromissions, and ejaculations were observed in males. Dose-response related decrements in male sexual behavior were observed following chlorpromazine and chlordiazepoxide. All dose levels of oxazepam depressed male sexual behavior. The highest dose of chlordiazepoxide and oxazepam attenuated the onset of female sexual behavior, and all dose levels reduced postcopulatory lordosis durations. Amphetamine did not interrupt either male or female sexual behavior, and chlorpromazine disrupted male but not female behavior.     

Effect of early pre- and postnatal acquired malnutrition on development and sexual behavior in the rat

In this paper we attempt to elucidate the effects on the rat offspring of undernourishment during pregnancy and lactation on the following parameters were examined: weight at birth and its evolution over a three-month period, sexual behavior of adult males, vaginal opening and sexual cycle of females, blood sugar, blood proteins, hematocrit, natremia, potassemia, body weight and weight of testicles, seminal vesicles and adrenal glands in males 5 months of age. Our results indicate highly significant decreases in body weight in experimental animals over a period of three months. Vaginal opening in experimental females is significantly delayed and their estrous cycle is shortened. Male sexual behavior shows decreases in neuromotor activity and prolongation of the refractory period in experimental male animals. Of the parameters monitored at 5 months of age, only blood sugar levels were significant decreased in experimental male rats. In view of these results, it can be concluded that in utero and lactation period malnutrition affects fundamental parameters of both development and reproductive function in the offspring.     

Reproductive effects in male and female rats of neonatal exposure to genistein

Sprague-Dawley rats were administered genistein orally at doses of 12.5, 25, 50, or 100 mg/kg on postnatal days 1 through 5 to examine its effects on reproductive function after puberty. In addition, preputial separation and vaginal opening as endpoints of sexual maturation, estrous cycling, sperm count, serum testosterone concentration, and histopathologic changes of reproductive organs of male and female rats were examined. Body weights of male and female rats exposed to genistein at any dose level examined were lower than those of controls. Timing of preputial separation in males and timing of vaginal opening were not affected by genistein treatment. The number of females showing estrous cycle irregularities was increased by genistein treatment. The fertility of female rats exposed neonatally to genistein at 100 mg/kg was disrupted, while neonatal exposure to genistein did not affect male fertility. Neither sperm counts nor serum testosterone concentration were changed by neonatal exposure to genistein. Female rats exposed neonatally to genistein at 100 mg/kg showed histopathologic changes in the ovaries and uterus, while male rats showed no histopathologic alterations in the gonads. The results of this study indicate that early neonatal exposure to genistein caused dysfunction of postpubertal reproductive performance as well as abnormal development of gonads in female but not in male rats.     

Sex differences and regulatory mechanism of epidermal growth factor receptor in the rat liver

The number of epidermal growth factor (EGF) receptor in rat hepatic membranes was about 2-hold higher in adult male than in adult female rats. Castration of adult males slightly decreased the EGF receptor number. Castration of neonatal males decreased the number of EGF receptors when they reached sexual maturity. This decrease was restored by the combination of neonatal and pubertal treatments with testosterone. Hypophysectomy caused a marked decrease in the number of EGF receptors in the male animals, and this decrease was not restored by either testosterone or triiodothyronine administration. Continuous administration of human growth hormone (hGH) with an osmotic minipump to normal males reduced the EGF receptor number. In contrast, intermittent administration of hGH twice a day (every 12 hr) to hypophysectomized males and/or normal females significantly increased the EGF receptor number. These results indicate that the number of EGF receptors in rat hepatic membranes is regulated by the secretory rhythm of GH in the pituitary, which may be "imprinted" by neonatal androgen.     

Clinical and reproductive effects of Clophen A50 (PCB) administered during gestation on pregnant guinea pigs and their offspring

Female and male guinea pigs exposed to polychlorinated biphenyls (PCBs) in utero and via mother's milk showed growth retardation and signs of delayed onset of sexual maturation. In female young exposed to PCBs first vaginal opening occurred at a significantly older age and was of shorter duration compared with control females. The age at the first ovulation did not differ significantly between PCB-exposed females and control females. Male young exposed to PCBs had significantly lower absolute and relative testis weights at 3 months of age compared with control males. No differences in plasma testosterone concentrations were observed.     

Enhanced social interactions in rats following chronic, centrally infused oxytocin.

Most studies investigating the behavioral effects of centrally administered oxytocin (OT) have been confined to single acute injections followed by brief behavioral observations lasting up to 90 min. The present study examines the behavioral effects of chronic, centrally administered OT in male rats observed continuously for prolonged periods of time. Either artificial cerebrospinal fluid or OT was centrally infused (via osmotic minipump) to gonadally intact male rats. Behavioral observations were made on males paired with either ovariectomized or estrous females during a 6-h time period. Most striking was the observation that durations of physical contact were doubled in pairs containing OT-infused males, even in the absence of sexual interactions. Also, OT-infused males showed significantly higher levels of anogenital sniffing of females and autogrooming; however, sexual interactions were unaffected by chronic OT. Chronic OT had no effect on body temperature, analgesia, or exploratory behavior in an open field. These findings suggest that chronic OT in male rats has behavioral effects that may significantly enhance adult social (nonsexual) interactions, possibly through alterations in olfactory and somatosensory information processing.     

Gonadal hormone modulation of the behavioral effects of Delta9-tetrahydrocannabinol in male and female rats

Female rats are more sensitive than males to many behavioral effects of cannabinoids. The purpose of the present study was to determine if sex differences in the antinociceptive and motoric effects of Delta(9)-tetrahydrocannabinol (THC) are due to activational effects of gonadal steroid hormones. THC-induced antinociception (tail withdrawal, paw pressure tests) and motoric effects (horizontal locomotion, catalepsy) were compared in male and female gonadectomized rats that were chronically treated with hormone (testosterone in males, estradiol in females) vs. those that were gonadectomized and had no hormone replacement. THC's effects were also compared between gonadally intact females tested during vaginal estrus vs. diestrus. THC (5 and 10 mg/kg i.p.) produced very similar antinociceptive effects in no-hormone vs. testosterone-treated males, but significantly less locomotor suppression in testosterone-treated males than those with no hormone replacement. In gonadectomized females, estradiol enhanced THC's antinociceptive but not motoric effects. In gonadally intact, cycling females, 5 mg/kg THC produced slightly to significantly greater behavioral effects in estrous than in diestrous females. These results suggest that sex differences in THC-induced behavioral effects in the adult rat can be attributed to activational effects of testosterone in males and/or estradiol in females.