Prenatal !b-endorphin can modulate some aspects of sexual differentiation in rats

[CHANGES IN THE BRAIN TESTOSTERONE METABOLISM AND SEXUAL BEHAVIOR IN MALE RATS PRENATALLY EXPOSED TO METHYLDOPA AND STRESS]

The changes of aromatase and 5α-reductase activities were studied in preoptic area (POA) and medial basal hypothalamus of 10-days-old and sexual behavior in 3-month-old male offsprings of rats exposed daily to noradrenaline antagonist methyldopa (400 mg/kg per os) 30 minutes prior to 1-hour immobilization during the last week of pregnancy (from 15th to 21st day). Prenatal stress caused aromatase activity lowering in the POA of developing brain and feminization (appearance of lordosis) and demasculinization of sexual behavior (prolongation of latent periods to the first mounting and first intromission as well as of the first ejaculation and postejaculation refractory period) in young male offspring. Oral methyldopa used prior to pregnant females stressing prevented early effect of prenatal stress on aromatase activity in the POA and normalized the male sexual behavior in young male rats by shortening both latent period to the first ejaculation and postejaculation refractory period, and an increase of numbers of ejaculation. The data obtained indicate that brain noradrenergic system plays significant role in the mechanisms of metabolic- and behavioral disturbances developing in male rats exposed to prenatal stress.

Maternal and early life stress effects on immune function: relevance to immunotoxicology

Stress is triggered by a variety of unexpected environmental stimuli, such as aggressive behavior, fear, forced physical activity, sudden environmental changes, social isolation or pathological conditions. Stressful experiences during very early life (particularly, maternal stress during fetal ontogeny) can permanently alter the responsiveness of the nervous system, an effect called programming or imprinting. Programming affects the hypothalamic-pituitary-adrenocortical (HPA) axis, brain neurotransmitter systems, sympathetic nervous system (SNS), and the cognitive abilities of the offspring, which can alter neural regulation of immune function. Prenatal or early life stress may contribute to the maladaptive immune responses to stress that occur later in life. This review focuses on the effect of maternal and early life stress on immune function in the offspring across life span. It highlights potential mechanisms by which prenatal stress impacts immune functions over life span. The literature discussed in this review suggests that psychosocial stress during pre- and early postnatal life may increase the vulnerability of infants to the effects of immunotoxicants or immune-mediated diseases, with long-term consequences. Neural-immune interactions may provide an indirect route through which immunotoxicants affect the developing immune system. A developmental approach to understanding how immunotoxicants interact with maternal and early life stress-induced changes in immunity is needed, because as the body changes physiologically across life span so do the effects of stress and immunotoxicants. In early and late life, the immune system is more vulnerable to the effects of stress. Stress can mimic the effects of aging and exacerbate age-related changes in immune function. This is important because immune dysregulation in the elderly is more frequently and seriously associated with clinical impairment and death. Aging, exposure to teratogens, and psychological stress interact to increase vulnerability and put the elderly at the greatest risk for disease.

Foster mother care but not prenatal morphine exposure enhances cocaine self-administration in young adult male and female rats

The present study was designed to investigate cocaine self-administration in adult male and female rats exposed prenatally to morphine. Pregnant dams were injected two times a day with either saline, analgesic doses of morphine or no drug at all (controls) on gestation Days 11-18. One day after birth, litters were cross-fostered such that control dams were paired with one another and their litters were crossed; saline- and morphine-treated dams were paired and half of each saline litter was crossed with half of each morphine litter. Thus, each mother (control, saline, and morphine) raised half of her own and half of the adopted litter. At the age of 60 days, males and females were trained first to lever press for sucrose pellets and then for cocaine. Once the lever-pressing behavior was learned and baseline level of this activity was established, animals received a cocaine (.5 mg/kg per infusion) reward for each correct response on the active lever during the next 9-day session. The data demonstrate that adult control, saline- and morphine-exposed male rats self-administer cocaine at a similar rate independent of their prenatal treatment. Adult female rats self-administer cocaine at a higher rate than male rats. Further, saline- and morphine-exposed females in diestrus self-administer more than females in proestrus phase of the estrous cycle, while control females show no such differences. In addition, fostering induces increase in cocaine self-administration in all groups of male rats regardless of prenatal drug exposure. In females, the only fostering-induced increase is in prenatally saline-exposed female rats raised by morphine-treated foster mother. Thus, our results suggest that the prenatal drug exposure does not induce changes in lever-pressing behavior for cocaine reward in adult male and female rats, but it sensitizes the animals to postnatal stimuli such as gonadal hormones and/or rearing conditions that result in increased drug self-administration.

Maternal adrenal hormone secretion mediates behavioural alterations induced by prenatal stress in male and female rats

Prenatal stress in rats has been shown to impair the regulation of the hypothalamic pituitary adrenal (HPA) axis and predispose to anxiogenic and depressive-like behaviour. In a previous study, abolition of excess corticosterone (COR) release during stress by maternal adrenalectomy prevented the dysregulation of the HPA axis. In the present study, we determined whether excess maternal COR is also responsible for the alterations in offspring behaviour. Pregnant Wistar rats were adrenalectomized or sham-operated on day 11 of gestation and subjected once daily to mild restraint for 30 min on days 14-21 of gestation. An undisturbed group of pregnant females served as controls. All experiments were performed in male and female offspring. Pup weight and anogenital distance of males were measured after birth; anxiogenic behaviour was assessed in the elevated plus maze (EPM) at the age of 5 weeks and spatial memory in the Morris water maze in littermates at 3-4 months. Prenatally stressed (PS) males did not show a reduction in anogenital distance, and their increase in anxiogenic behaviour in the EPM was less than that in PS females. On the other hand, impairment of spatial learning was only seen in PS males. Both the anxiogenic behaviour of PS males and females and the learning deficit in males were completely abolished by adrenalectomy. These data show that excess stress-induced COR can alter the programming of the foetal brain and predispose it to alterations in behaviour that are gender specific.

Sexual motivation is demasculinized, but not feminized, in prenatally stressed male rats

Sexual motivation and copulation in male rats are associated with dopamine release in the nucleus accumbens. Demasculinized copulatory behavior has been demonstrated in prenatally stressed adult male rats. We have previously reported that approximately 80% of prenatally stressed male rats do not exhibit copulation and that no significant changes in nucleus accumbens dopamine release are seen during exposure to estrous females. In the present study, we investigated whether prenatal stress affects sexual motivation in these animals as adults. Pregnant Wistar rats were subjected to immobilization stress for two hours daily from day 15-19 of gestation. The prenatally stressed male offspring at the age of 3 months were allowed contact with receptive female rats for a 30 min period per week for 10 weeks; then, between the age of 5 and 6 months, their sexual motivation and copulatory activity were measured. Sexual motivation was measured in terms of sexual partner preference. The number of visits and the duration of each visit to an estrous female (stimulus female) or to a sexually active male rat (stimulus male) were recorded. Compared with control males, prenatally stressed male rats showed a significantly lower number of visits and a shorter duration of each visit to stimulus females. Prenatally stressed males showed no preference for male or female stimulus rats in terms of the number of visits and the duration of each visit, whereas control rats showed a significantly higher number of visits and duration of visits to female stimulus rats than male stimulus rats. A significant decrease in copulatory activity was observed in the prenatally stressed male offspring compared with control male rats, with most of the prenatally stressed males failing to show copulation. In vivo microdialysis experiments were performed on the nucleus accumbens with concurrent observation of sexual behavior. The prenatally stressed rats that did not exhibit copulation showed no significant changes in nucleus accumbens dopamine release during exposure to a stimulus male behind a wire-mesh barrier and the amount of dopamine release remained at the basal levels during actual physical contact. These results, combined with those of our previous report, indicate that sexual motivation in prenatally stressed male rats is demasculinized, but not feminized.

Naloxone treatment prevents prenatal stress effects on peritoneal macrophage activity in mice offspring

The present study analyzed the effects of maternal stress (PS) and/or naloxone treatment on the activity of peritoneal macrophage in male and female Swiss mice offspring. Pregnant female rats received a daily footshock (0.2 mA) and/or a naloxone injection from gestational day 15 to 19. Experiments were performed on postnatal day 30 on male and female pups. The following results were obtained in male offspring: (1) PS decreased both the index and the percentage of phagocytosis, this decrement being reversed by naloxone treatment, and (2) naloxone alone decreased the percentage of phagocytosis. The following results were obtained in female offspring: (1) PS decreased spontaneous and phorbol myristate acetate-induced macrophage oxidative burst, this decrement being reversed by naloxone pretreatment, and (2) PS decreased both the index and percentage of the phagocytosis, this effect was prevented by naloxone treatment. These data are discussed focussing on a putative neuroimmune interaction involving opioidergic systems during the ontogeny of the central nervous and immune systems.

Effects of prenatal stress on stress-induced changes in behavior and macrophage activity of mice

The present study analyzed the effects of maternal stress on behavior and macrophage activity of mice. Pregnant mice received a daily footshock (0.2 mA) from gestational days 15 (GD15) to 19. Experiments were performed on male offspring, challenged or not with another footshock (0.2 mA) on postnatal day 30 (PND30) or 60. The following results were obtained for maternal stress: (1) increment in locomotor activity of juvenile but not of adult mice observed in both open-field and plus-maze; (2) increment in rearing frequency of juvenile but not of adult mice observed in the open-field; (3) decrement in macrophage spreading of adult but not of juvenile mice; (4) abolishment of postnatal footshock effects in both macrophage spreading on PND30 and macrophage nitric oxide (NO) production on PND60; (5) reversion of postnatal footshock effects on H(2)O(2) spontaneous and PMA-induced release by macrophage on PND30; (6) modification of postnatal stress effects on macrophage phagocytosis on PND60. These changes were unrelated to differences in gestational parameters and did not reflect altered maternal-pup interactions or nutritional factors. The observed data provide experimental evidence that maternal stress alters behavior, and macrophage activity at the same time and in the same litter. These data were discussed in the light of possible neuroimmune interactions that involve catecholaminergic pathways.

Prenatal opiate exposure: long-term CNS consequences in the stress system of the offspring

Our data show that prenatal morphine exposure induces long-term alterations in adult brain and behavior in both male and female rats, and these alterations are sex-specific. It is also evident that the alterations are not restricted to a single brain site or to a single neurotransmitter or neuromodulator. Moreover, there are long-term alterations in both the norepinephrine (NE) and opioid systems in several brain regions involved in stress responses and in the maintenance of homeostatic balance between the external environment, the brain and the rest of the body. Thus, this short paper reviews the prenatal morphine exposure data and highlights gaps in stress response to drug vulnerability/predisposition as an adult.

Effects of maternal stress on anxiety levels, macrophage activity, and Ehrlich tumor growth

The present study analyzed the effects of maternal stress on behavior and immune function of mice. Pregnant mice received a daily footshock (0.4 mA) from gestational day 15 (GD 15) to GD 19. Experiments were performed on male offspring aged 2 months. The following results were obtained for offspring from dams stressed during pregnancy: (1) decreased locomotor activity observed in the open-field central zone; (2) decreased number of entries into the open arms of the plus-maze and decreased time spent in the exploration of these arms; (3) decreased macrophage spreading and phagocytosis, but no changes in macrophage NO(2)(-) production; (4) increased growth of both the ascitic and solid forms of Ehrlich tumor. These changes were unrelated to differences in gestational parameters and did not reflect altered maternal-pup interactions or nutritional factors. The observed data provide experimental evidence that maternal stress alters stress/anxiety levels, macrophage activity and Ehrlich tumor growth at the same time and in the same litter. The data were discussed in the light of possible neuroendocrine-immune system interactions.

Prenatal morphine exposure induces age- and sex-dependent changes in seizure susceptibility

1. Prenatal exposure to morphine induces long-term alterations in seizure susceptibility, which are age-, sex-, and seizure model-specific. 2. Adult male and female rats exposed prenatally to morphine show decreased susceptibility to GABA-regulated seizures. 3. Prenatally morphine-exposed, adult male rats are more sensitive to excitatory amino acid receptor-mediated seizures than control males, control females, or morphine-exposed females.

Short- and long-term consequences of corticotropin-releasing factor in early development

Corticotropin-releasing factor (CRF) mediates various stress-related responses in adult animals. Little is known about the effects of CRF during early development. Young mammals often vocalize when isolated in novel surroundings. Heightened levels of CRF inhibit vocalizing in isolated rat and guinea pig pups. Still lower levels of CRF may facilitate or permit vocalizing in rat pups. In guinea pigs, CRF appears to move pups from an initial active, to a subsequent passive, stage of behavioral responsiveness. CRF activity prior to birth can also affect the young. Exposing pregnant female rats to stressors during the last trimester of pregnancy alters the morphological and behavioral development of the offspring. Effects of gestational stress can be mimicked by injecting pregnant females with CRF during the last trimester. CRF appears to mediate both short- and long-term responses to stressors during developmental in rodents.

Stress during pregnancy alters the offspring hypothalamic, pituitary, adrenal, and testicular response to isolation on the day of weaning

Subjecting pregnant female rats to situations that activate the hypothalamic-pituitary-adrenal (HPA) axis can have long-term effects on the development of the offspring. Restraint under bright lights is a common method of stressing pregnant females that results in consistent behavioral changes in the offspring. We investigated the effects of gestationally administered restraint, bright lights, and heat on the HPA axis response of 21-day-old offspring following exposure to isolation in a novel environment or under resting conditions. Corticotropin-releasing factor titers in the hypothalamus were unaffected following isolation. Nonetheless, adrenocorticotropin hormone (ACTH) was found to be lower in the gestationally stressed offspring prior to or following the isolation period. Corticosterone was attenuated in gestationally stressed offspring following the postnatal stressor and there was also a tendency for the gestationally stressed females to have lower concentrations of aldosterone. Plasmatic testosterone levels were higher in the gestationally stressed males following the period of isolation. The present data suggest that the HPA axis of the offspring is differentially affected by the gestational stress procedure, that is, it is attenuated at the level of the pituitary and adrenal, but not at the level of the hypothalamus. These data have implications for behavioral differences observed in gestationally stressed animals.

Changes in the hormonal concentrations of pregnant rats and their fetuses following multiple exposures to a stressor during the third trimester

Human and animal studies indicate that stress during pregnancy can exert long-term effects on the development of the offspring, effects that appear to be mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis. In this experiment changes in levels of a variety of HPA and other hormones in both pregnant rats and their fetuses were investigated. Trunk blood was collected from pregnant females and fetuses following repeated 45-min presentations of restraint, bright lights, and heat during the third trimester. In addition, testes were harvested from the male fetuses. Hormone concentrations were determined by radioimmunoassay. Pregnant females had elevated titers of plasma corticosterone, aldosterone, and ACTH for approximately 15 min following termination of the stressor. No differences were found for beta-endorphin or prolactin. Fetuses showed a pattern of changes in plasma corticosterone and aldosterone that was similar to that of pregnant females, but no effect was observed for fetal ACTH titers. These results are consistent with a role of the HPA axis in the effects of gestational stress. Testicular levels of CRF on gestational day 21 were lower in fetuses of stressed females than in those of nonstressed females. The reduced levels of testicular CRF suggest that CRF may be involved in the altered pattern of sexual differentiation of males stressed during gestation.

Effects of prenatal morphine exposure on rat heterotypical sexual behavior

Prenatal exposure to morphine inhibits ovarian steroid-dependent lordosis behavior in female rats, and enhances certain components of male sexual behavior in male rats. In the present study, the effects of mid to late gestational morphine exposure on male sexual behavior in females and on female sexual behavior in males were examined in adult offspring. Gonadectomized male rats were injected at weekly intervals with 30 or 60 microg estradiol benzoate and 1.0 mg progesterone and tested for female sexual behavior with stimulus males on 2 consecutive weekly tests. Ovariohysterectomized (OVX) females were injected with 500 microg testosterone propionate (TP) daily for 15 days and tested for male sexual behavior with stimulus females on the last day of TP injection and 1 week later, after TP withdrawal. Prenatal morphine exposure increased the expression of male sexual behaviors in female rats, but it did not increase lordosis behavior in male rats. Thus, exposure to morphine during gestation alters male and female sexual behavior in young adult animals. Because prenatal morphine exposure both defeminized and masculinized adult sexual behavior in female rats, it is possible that female brain development is more vulnerable to prenatal insult such as opiate exposure.

Fetal alcohol exposure blocks full masculinization of the dorsolateral nucleus in rat spinal cord

Male rats prenatally exposed to a combination of stress and ethanol show severely impaired ejaculatory patterns. This study examined two sexually dimorphic nuclei in the lumbar spinal cord implicated in the control of male copulatory reflexes in rats whose mothers were exposed to alcohol, to stress, or to both treatments during pregnancy. Alcohol exposure led to a marked decrease (22%) in the number of motor neurons in the dorsolateral nucleus (DLN) of the adult male offspring, but no significant change in cell count was detectable in the sexually dimorphic nucleus of the bulbocavernosus (SNB). The combination of alcohol and stress did not enhance the effect on the DLN above that produced by alcohol alone. Somal sizes in the DLN and SNB were not altered by any of the treatment conditions. Alcohol exposure probably leads to incomplete masculinization of the DLN in male rats by decreasing testicular steroidogenesis during the fetal stage(s) when sexual differentiation is ongoing in that CNS structure.

The distribution of radiolabeled corticotropin-releasing factor in pregnant rats: an investigation of placental transfer to the fetuses

Stress during gestation can have serious consequences on the development of the fetus. Many of these effects appear to be mediated by hormones of the hypothalamic-pituitary-adrenal (HPA) axis. Corticotropin-releasing factor (CRF), released by the hypothalamus during times of stress serves to activate release of pituitary hormones and is also present in low levels in rat plasma. Moreover, the uterus contains significant quantities of CRF at implantation sites, probably from local sources. Therefore, the possibility exists that CRF may cross the placenta and activate the fetal HPA axis. However, the ability of CRF to cross the placenta has not been demonstrated. In the present study, pregnant rats were administered radiolabeled CRF intraperitoneally, and the distribution of the labeled product was determined in the fetuses and various maternal organs. High levels of activity were observed in the pregnant female's uterus, adrenals, heart and the placentae, but only background levels of activity were detected in the maternal brain. Very low levels of activity were observed in the fetuses, indicating that the transfer of CRF across the placenta is greatly restricted. These findings suggest that maternal CRF has little or no direct effect on the developing fetus during gestational stress.

Effects of prenatal morphine and cocaine exposure on spinal sexual reflexes in male and female rats

Previous studies demonstrated that in utero exposure to morphine or cocaine differentially alters adult sexual behaviors, which are dependent on circulating gonadal hormones in male and female rats. In the present study, the effects of in utero morphine and cocaine exposure on the urethrogenital reflex were examined. The urethrogenital reflex is thought to be a hormone-independent spinal sexual reflex in both males and females. This reflex is tonically inhibited by supraspinal neurons but can be consistently evoked by urethral stimulation in the spinally transected animals. Prenatal morphine or cocaine exposure did not remove the supraspinal inhibition of the urethrogenital reflex in spinally intact male or female rats. In spinally transected animals, the urethrogenital reflex was qualitatively similar in all groups. However, morphine-exposed males required a stronger stimulus to elicit the urethrogenital reflex but once elicited, the frequency of the urethrogenital reflex was significantly higher compared to either controls or cocaine-exposed males. In contrast, in female rats, neither prenatal morphine nor cocaine exposure had any effect on the urethrogenital reflex. Thus, the urethrogenital reflex appears to be differentially affected by prenatal exposure to morphine in males and females.

Stress during pregnancy alters rat offspring morphology and ultrasonic vocalizations

Stress during pregnancy, or prenatal stress, is known to alter offspring behavior, morphology and physiology. We found that a heat, light and restraint stressor applied during the third trimester of pregnancy: 1) decreased the weight gain of adult female rats during pregnancy; 2) reduced the weight of pups, as well as the anogenital distance of male offspring, at birth; and 3) increased the number of ultrasonic vocalizations emitted by pups during isolation in a novel environment on Postnatal Day 14. These results closely approximate those we previously observed after peripheral administration of corticotropin-releasing factor to pregnant females during the third trimester. Together, the studies strongly suggest a role for corticotropin-releasing factor and/or other hormones of the hypothalamic-pituitary-adrenal system in mediating some of the effects of gestational stress.

Opioid receptor blockade during prenatal life modifies postnatal behavioral development

The ontogeny of physical characteristics, spontaneous motor, and sensorimotor behaviors of preweaning rats, as well as ambulation and emotionality at weaning (day 21) were studied in rats exposed to 50 mg/kg naltrexone (NTX) or saline (controls) daily throughout gestation by maternal administration; all animals were cross-fostered to untreated mothers at birth. Morphine challenge tests and nociceptive measures revealed that this dosage of opioid antagonist blocked opioid receptors for 24 h. At birth and weaning, animals in the NTX group weighed 12 and 20%, respectively, more than control offspring. The age at which a specific physical characteristic, spontaneous motor behavior, or reflex initially appeared and the age at which 100% of the animals demonstrated a particular characteristic/behavior often were accelerated in animals prenatally exposed to NTX. The frequency of ambulation was subnormal in the NTX group, and the frequency and/or incidence of rearing, grooming, wet-dog shakes, and defecation were reduced from normal levels in these opioid antagonist-exposed rats. These results imply that interactions of endogenous opioid systems during embryogenesis are determinants of somatic, physical, and behavioral development in postnatal life.

Prenatal naltrexone facilitates male sexual behavior in the rat

The involvement of endogenous opiates in the differentiation of sexual behavior was tested by exposing rat fetuses to continuous naltrexone during the last 9 days of gestation. Time-mated female rats received oral naltrexone, 40 mg/kg/day, via their drinking water, from gestational day 13 until parturition. Early motor development, measured by swimming ability in 7-, 9-, and 11-day-old offspring of the treated dams, was unaffected by prenatal naltrexone. Adult male offspring were given three tests of male sexual behavior, then castrated, primed with ovarian hormones, and given two tests of feminine receptivity (lordosis quotient). Prenatal naltrexone facilitated masculine behavior and suppressed feminine receptivity: latencies to first mount and to ejaculation were shorter, mount rate was higher, and lordosis quotient was lower in naltrexone-treated rats, compared with control animals. These findings implicate endogenous opiates in prenatal organization of sex-specific behavioral dispositions.

CRF administered to pregnant rats alters offspring behavior and morphology

Pregnant rats injected with 20 micrograms of corticotropin-releasing factor (CRF) from day 14 through 21 gained less weight during gestation than did saline-injected controls. The offspring of CRF-injected females differed from the offspring of control females in several ways: males and females weighed less during the first 2 weeks of life, males had shorter anogenital distances at birth, and males and females emitted more ultrasonic vocalizations during isolation in tests at 6 and 14 days of age. These effects are similar to those that have been observed following exposure of pregnant females to stressors, and provide support for the notion that CRF and/or CRF activation of the hypothalamic-pituitary-adrenal axis mediate effects of gestational stress.

Prenatal dexamethasone or stress but not ACTH or corticosterone alter sexual behavior in male rats

Prenatal maternal stress in rats and mice can demasculinize and feminize the sexual behavior of adult male offspring. Causal mechanisms are unknown, but one attractive hypothesis is that stress activation of maternal adrenal glucocorticoid secretion is the responsible agent. To test this hypothesis, pregnant rats were exposed to a variety of substances which enhance glucocorticoid actions. These included ACTH (20 IU of a gel preparation, SC once daily), corticosterone (CORT; 7 mg/kg SC in oil, three times daily), or dexamethasone (DEX; 0.1 mg/kg, SC once daily). Controls included noninjected dams and a positive stress control group (restraint under bright lights three times daily). All treatments reduced maternal weight gain, DEX most potently. No treatment altered litter size, stillbirths, or sex ratio, but DEX reduced weight at birth, an effect still seen at postnatal day 85. DEX, CORT, and stress reduced male adrenal weight at birth, while DEX and CORT altered sexual differentiation as measured by anogenital distance. Stress impaired adult male sexual performance but not the lordosis quotient following exposure of animals to stud males. DEX affected both measures. No other treatment had any significant effect on sexual behavior. No treatment altered plasma LH levels, either basal or in response to an estrogen challenge in adult gonadectomized males. In adulthood there was no treatment effect on stress reactivity, measured behaviorally or by plasma glucocorticoids. Correlational analysis revealed that weight gain during pregnancy was the single best predictor of subsequent sexual performance. It is concluded that prenatal dexamethasone exposure demasculinizes and feminizes male offspring.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

Ontogeny of Leu-enkephalin and beta-endorphin innervation of the preoptic area in male and female rats

The distribution of endogenous opioid peptide-containing fibers in the medial preoptic area of developing male and female rats was examined using immunohistochemical methods. In particular, the ontogeny of leucine-enkephalin (leu-enk) and beta-endorphin (beta-endo) innervation was studied using antisera directed against these compounds. The distribution of Leu-enk and beta-endo differed at each age examined from birth to postnatal day 12 (P12). Furthermore, the patterns of fiber innervation differed across development. Leu-enk-like immunoreactivity was initially densest in the lateral preoptic region of both sexes, ultimately expanding into the medial preoptic region to become densest in the lateral portion of the medial preoptic nucleus by P12. This latter pattern was observed only in males, however, as females continued to exhibit diffuse medial preoptic Leu-enk-like immunoreactivity at P12. In contrast, the distribution and developmental pattern of beta-endo-like immunoreactivity was similar in both sexes; diffuse staining was observed in the medial preoptic region at birth, later becoming dense only in the periventricular and parastrial nuclei. The time course of development of Leu-enk and beta-endo innervation of the medial preoptic area suggests that the sexually dimorphic expression of opioid immunoreactivity occurs after preoptic neurons appear in their sexually dimorphic configuration. Therefore, although the development of opioid-containing pathways could be influenced by the perinatal gonadal steroid hormone environment, medial preoptic Leu-enk and beta-endo innervation might not contribute directly to the sexually dimorphic neuronal organization of the preoptic area.

Prenatal flutamide alters sexually dimorphic nuclei in the spinal cord of male rats

The effects of prenatal exposure to the antiandrogen flutamide on two sexually dimorphic nuclei of the lumbar spinal cord, the dorsolateral nucleus (DLN) and the spinal nucleus of the bulbocavernosus (SNB), were investigated. Rat dams were given daily injections of 5 mg flutamide or vehicle alone from day 11 through 21 of pregnancy. The spinal cords and perineal morphology of their male and female offspring were examined in adulthood. Flutamide reduced the number of SNB and DLN neurons, reduced the somal and nuclear area of SNB neurons, and reduced the weight of the perineal muscles in males. Flutamide produced no effect in females. No sexual dimorphism was found in the mean somal area of DLN neurons, but a sexual dimorphism was found in the distribution of somal areas in our samples; females had proportionately more large neurons than males. Flutamide-treated males also had proportionately more large neurons than control males but fewer than females. A sexual dimorphism was found in the nuclear areas of DLN neurons but flutamide did not influence this trait.