Effects of the intraventricular administration of 5,7-dihydroxytryptamine on FSH, LH and prolactin secretion in neonatally estrogenized male rats

The role of the serotoninergic system in the control of LH, FSH and prolactin secretion was analyzed in control and neonatally estrogenized male rats. Animals injected s.c. with 500 micrograms of estradiol benzoate (EB) on day 1 of life, or their corresponding sham-treated controls, were divided on day 75 into the following groups: (1) orchidectomized; (2) injected intraventricularly with 5,7-dihydroxytryptamine (5,7-DHT); (3) orchidectomized and treated with 5,7-DHT, and (4) sham operated. 15 days later, the animals were decapitated and their FHS, LH and prolactin plasma values measured by specific RIA systems. After the treatment with 5,7-DHT, control animals showed a decline in basal prolactin levels but no modification in basal LH and FSH values. After castration, 5,7-DHT-treated animals showed a reduced LH increase and a more marked prolactin decrease. In neonatal estrogen-treated animals, the 5,7-DHT injection did not change FSH, LH or prolactin levels but did partially or completely abolish the post-castration rise in FSH and LH levels, respectively. These data seem to indicate that neonatal estrogenization induced a modification of the serotoninergic role in the control of LH, FSH and prolactin.     

Manipulation of neonatal gonadal steroid milieu and leptin secretion in later life in male and female rats

The mechanism underlying the gender-based difference in circulating leptin levels (females>males) is still uncertain, because the difference persists even after adjustment for fat mass and sex steroid concentrations. In this study, we tested the possibility that the neonatal sex steroid milieu, which is critical for the sexual differentiation of the brain, may permanently affect leptin secretion in rats of both sexes. Male rats were neonatally castrated (NC), and females were neonatally androgenized (NA) by testosterone (T). Two subsets of the NC males were given T on postnatal day 1 or 29. Appropriate controls for all these groups were prepared. The animals were sacrificed on postnatal day 57, and at this age, the percent body fat was similar among all the male and female groups. NC males had a two-fold, significantly higher level of leptin than intact males. This hyperleptinemia induced by NC was prevented by T when it was given neonatally, but not on the day 29. By contrast, NA for females was without effect on leptin titers in later life. These results suggest that neonatal T in male rats may, at least in part, mediate the sex-related difference in leptin secretion that becomes apparent in later life. However, as intact females still had significantly higher leptin titers than NC males, it is very likely that additional factors may also be responsible for the sexually dimorphic leptin secretion in rats.     

Maternal Deprivation Exacerbates the Response to a High Fat Diet in a Sexually Dimorphic Manner

Maternal deprivation (MD) during neonatal life has diverse long-term effects, including affectation of metabolism. Indeed, MD for 24 hours during the neonatal period reduces body weight throughout life when the animals are maintained on a normal diet. However, little information is available regarding how this early stress affects the response to increased metabolic challenges during postnatal life. We hypothesized that MD modifies the response to a high fat diet (HFD) and that this response differs between males and females. To address this question, both male and female Wistar rats were maternally deprived for 24 hours starting on the morning of postnatal day (PND) 9. Upon weaning on PND22 half of each group received a control diet (CD) and the other half HFD. MD rats of both sexes had significantly reduced accumulated food intake and weight gain compared to controls when raised on the CD. In contrast, when maintained on a HFD energy intake and weight gain did not differ between control and MD rats of either sex. However, high fat intake induced hyperleptinemia in MD rats as early as PND35, but not until PND85 in control males and control females did not become hyperleptinemic on the HFD even at PND102. High fat intake stimulated hypothalamic inflammatory markers in both male and female rats that had been exposed to MD, but not in controls. Reduced insulin sensitivity was observed only in MD males on the HFD. These results indicate that MD modifies the metabolic response to HFD intake, with this response being different between males and females. Thus, the development of obesity and secondary complications in response to high fat intake depends on numerous factors.     

A decrease in thymus-mediated immune responses as a result of treatment of neonatal rats with glutamate

We investigated whether administration of monosodium l-glutamate (MSG) to neonatal rats would disrupt immune responses in intact and orchidectomized adult male rats. Neonatal male rats were treated with saline or MSG which causes severe endocrine abnormalities. Half of each group of animals were orchidectomized as adults and killed one week later along with intact rats. MSG treatment resulted in suppressed serum LH levels in intact rats. Thymus weight and spleen cellularity in intact animals were not affected by MSG treatment, but thymus weight increased within one week after orchidectomy in both saline- and MSG-treated groups. In intact rats, lymphocyte stimulation by the T cell specific mitogens (concanavalin A or phytohemagglutinin) or the B cell specific mitogen (lipopolysaccharide) was unaffected by prior treatment with MSG. However, MSG treatment blocked the decrease attributable to orchidectomy in concanavalin A and phytohemagglutinin stimulation of lymphocyte blastogenesis. The results suggest that administration of MSG to neonatal male rats can alter some immune responses in the adult animal.     

Modulation of the binding characteristics of hypothalamic mu opioid receptors in rats by gonadal steroids.

Recent evidence suggests that the effects of the opioids on gonadotropin release may depend on the endocrine status existing in the experimental animal. In the brain, the effects of the opioids are exerted through the interaction with different classes of opioid receptors (mu, delta, kappa, etc.). Among these, the mu receptors appear to be particularly relevant to the control of gonadotropin secretion. Different groups of experiments have been performed in the rat in order to analyze whether changes of circulating levels of sex steroids may have an impact on the binding characteristics of hypothalamic mu opioid receptors, as evaluated by a receptor binding assay performed on plasma membrane preparations, using [3H]dihydromorphine as a mu ligand. In a first series of experiments, it has been observed that the ontogenesis of hypothalamic mu opioid receptors is different in male and in female rats: the concentration of mu sites, similar in animals of the two sexes at 16 days of age, increases in females, but not in males, between day 16 and day 26 of life. This sexual difference persists in 60-day old animals, when the brain is fully mature. It has also been observed that the pattern of maturation of hypothalamic mu receptors can be reversed by neonatal castration of males and by neonatal testosterone treatment of females. In a second series of experiments, it has been shown that in the hypothalamus of regularly cycling female rats the concentration of mu receptors varies during the different phases of the estrous cycle. In particular, a rather high density of mu sites during diestrus day 2 and the morning of the day of proestrus was found; this is followed by a progressive decline during the afternoon of the day of proestrus and the day of estrus, with a minimum value of the concentration of mu receptors being recorded in the first day of diestrus. These fluctuations seem to be linked to the physiological changes of serum levels of ovarian steroids: in fact, in a third series of experiments, it has been found that the positive feedback effect on LH release, exerted by the treatment of ovariectomized female rats with estrogens plus progesterone, is accompanied by a significant decrease of the concentration of hypothalamic mu opioid receptors; treatments with estrogens alone, able to induce a negative feedback effect on LH secretion, are not associated with modifications of hypothalamic mu receptors. These data seem to indicate that hypothalamic mu receptors may be involved in the positive but not in the negative feedback control of LH secretion.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hydrophobic surface properties of myosin in solution as studied by partition in aqueous two-phase systems: effects of ionic strength,pH and temperature

Summary The effect of gonadectomy (at the 10th day of life) and treatment with sexual steroids (during the first month) upon development of alpha-amylase activity in rat parotid gland has been studied.Alpha-amylase specific activity of parotid glands from 20-day-old orchidectomized rats and from 25-day-old ovariectomized animals was significantly higher than that of intact male and female rats of the same age respectively. Spayed males treated with testosterone (10 g/day on the 13th, 15th, and 17th day) and ovariectomized rats treated with oestradiol (2.5 g/day from the 16th to the 22nd day) showed values of enzymic activity similar to those of normal animals.Results indicate that oestradiol and testosterone have an inhibitory effect upon the increase of alpha-amylase activity in parotid gland during a very defined period of development.Career investigators of Consejo Nacional de Investigaciones Cientificas y Técnicas.     

Effects of male sex hormones on specific uptake and release of 3H-serotonin in the rat hypothalamus in vitro]

With the use of "isotopic method" a study was made of the main parameters of functional activity of serotoninergic elements of hypothalamus--the specific uptake and release of 5-OT. The animals used were sexually mature rats castrated on the first postnatal day. In sexually mature intact males the specific uptake of 3H-5-OT by serotoninergic structures of the anterior hypothalamus was significantly lower than in females. Castration of animals on the first day of life resulted in the increase of specific 5-OT uptake in sexually mature males up to that observed in females. There were no differences between the sexes in the rate of spontaneous release of 5-OT. However, response to K(+)-depolarization in the anterior hypothalamus of intact males was significantly lower than that in females. In the hypothalamus of males castrated neonatally the amplitude of the response to the effect of the depolarizing agent was increase up to the level observed in females. By the results obtained it is indicated that elimination of the effect of male hormones on the first postnatal day results in the increase of 5-OT uptake and release in the hypothalamus of sexually mature rat males.     

Aflatoxin B1 induced hepatocarcinogenesis in neonatal rats.

Role of cell replication on aflatoxin B1 (AFB1) induced hepatocarcinogenesis was investigated in neonatal rats showing persistence of cell replication in the liver for 21 days of post natal life. Adult (8-10 weeks old) rats displaying no hepatocytic proliferation served as controls. Three doses of AFB1 were administered to both the groups at intervals of 48 hr with the doses starting on 10th day of age in the neonatal group. Appearance of phenotypically altered preneoplastic hepatocytes was quantitated in both the groups. A significantly higher incidence of preneoplastic foci was recorded in neonatal rats as compared to adult animals. The results suggest that presence of cell replication in neonatal rats at the time of AFB1 administration enhances the process of hepatocarcinogenesis.     

An experimental study of anti-amnestic activity of piracetam in orchidectomized rats]

The decrease of learning ability by 50% as assessed by passive avoidance test and the increase 28% of microviscosity of synaptosomal membranes from brain cortex were observed in rats in a month after orchidectomy as compared with that of intact or sham--operated animals. The treatment of orchidectomized rats with piracetam either by single application or in the course of 10 days applications in the daily dose of 250 mg/kg intraperitoneally failed to improve learning ability of animals in passive avoidance test and to produce a normalizing effect on the structure of membrane lipid matrix. The testosterone content in blood of orchidectomized rats was 10 times lower as compared with control and was not affected by treatment with piracetam.     

Neonatal infection produces significant changes in immune function with no associated learning deficits in juvenile rats

The current experiments examined the impact of early‐life immune activation and a subsequent mild immune challenge with lipopolysaccharide (LPS; 25µg/kg) on hippocampal‐dependent learning, proinflammatory cytokine expression in the brain, and peripheral immune function in juvenile male and female rats at P24, an age when hippocampal‐dependent learning and memory first emerges. Our results indicate that neonatal infection did not produce learning deficits in the hippocampal‐dependent context pre‐exposure facilitation effect paradigm in juvenile males and females, contrary to what has been observed in adults. Neonatal infection produced an increase in baseline IL‐1β expression in the hippocampus (HP) and medial prefrontal cortex (mPFC) of juvenile rats. Furthermore, neonatally infected rats showed exaggerated IL‐1β expression in the HP following LPS treatment as juveniles; and juvenile females, but not males, showed exaggerated IL‐1β expression in the mPFC following LPS treatment. Neonatal infection attenuated the production of IL‐6 expression following LPS treatment in both the brain and the spleen, and neonatal infection decreased the numbers of circulating white blood cells in juvenile males and females, an effect that was further exacerbated by subsequent LPS treatment. Together, our data indicate that the consequences of neonatal infection are detectable even early in juvenile development, though we found no concomitant hippocampal‐dependent learning deficits at this young age. These findings underscore the need to consider age and associated on‐going neurodevelopmental processes as important factors contributing to the emergence of cognitive and behavioral disorders linked to early‐life immune activation. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1221–1236, 2017     

Hypothalamic receptors of sex hormones in the mechanism of the sexual differentiation of the brain in rats

Studies have been made on the content of receptors of estradiol (E2) and testosterone (T) in cytoplasmic and nuclear fractions of the hypothalamus of male and female rats during neonatal development, as well as in adult females after androgenization in neonatal period and adult males castrated within 3 days of postnatal life. It was shown that both E2 and T are present in the blood serum of male and female newborn rats. In female hypothalamus, only E2 receptors were found, whereas in males both types of receptors were revealed, their content being higher than in females. In adult animals subjected to changes in the level of sex hormones in the blood during early neonatal period, changes in concentration of the receptors in the hypothalamic centres of regulation of tonic and cyclic secretion of gonadotropins were found. The data obtained presumably reveal the role of receptors of sex hormones in sex differentiation of the brain.     

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein in the rat

Sex-related differences in the hepatobiliary transport of phenolsulfonphthalein (PSP) were investigated in male and female Wistar rats. Maximal biliary excretion of unconjugated PSP was significantly higher in females while the excretion of the conjugated dye and liver UDP-glucuronosyltransferase activity toward PSP were higher in male animals. Orchidectomy decreased enzyme activity and excretion of the conjugate, whereas ovariectomy produced the opposite effect. Both in gonadectomized males and females maximal biliary excretion of the unconjugated dye was significantly reduced. Testosterone treatment increased the excretion of both conjugated and unconjugated PSP and transferase activity in orchidectomized males. Combined treatment of gonadectomized females with estradiol plus progesterone led to excretions of both conjugated and unconjugated PSP and UDP-glucoronosyltransferase activities similar to those found in control rats. These data indicate the existence of sex-related differences in the conjugation and biliary excretion of PSP in the rat and its modulation by sex hormones.     

Aromatization: Important for sexual differentiation of the neonatal rat brain

This paper examines the hypothesis that testosterone (T) produces its differ-entiative effect on the neonatal rat brain after undergoing conversion in situ to estradiol-17β (E₂). We examined the abilities of an aromatizing enzyme inhibitor, (1,4,6-androstatriene-3,17-dione) (ATD), and an anti-estrogen, CI628, to inhibit sexual differentiation. Male and female rats were treated during the first few days of postnatal life with ATD or CI628, and females were treated on the following day with T in Silastic capsules or its propionate (TP) in oil. ATD and ATD+T females were normal with respect to time of vaginal opening, ovarian weight, ability to demonstrate an LH surge, and lordosis behavior. T and TP females were masculinized with respect to all these measures. CI628 and CI628+TP females had impaired ovarian function and intermediate lordosis quotients (LQs) compared to controls, though they were higher in both measures than T females. ATD males demonstrated high LQs in response to estradiol benzoate (EB) + progesterone, comparable to those of control females. CI628 males had intermediate LQs, which were significantly higher than those of control males. These results indicate that ATD can substantially protect the neonatal rat brain from the differentiative effects of exogenous or endogenous T, probably by blocking aromatization. CI628 affords only partial protection against T and produces a weak differentiative effect due to its own weak estrogenicity. Thus, aromatization of T in newborn rat brains appears to be essential if sexual differentiation is to occur.     

Possible interaction of the adrenal-gonadal systems on brain catecholamines of adult male rats

Studies from this laboratory showed that gonadectomy (GDX) alters biogenic amines concentrations in diencephalon during the first 40 days. While the GDX females maintain the differences at day 60, the differences are eliminated in males at that time. In the present work, we have studied in three cerebral regions the adrenal involvement in the mechanism responsible for this normalization of catecholamine concentration in long-term castrated adult male rats. A hypersecretion of adrenal steroids seems to compensate for the lack of gonadal effect when the orchidectomized rats reach adulthood only for diencephalic dopamine.     

Early androgen treatment and male and female sexual behavior in mice

To investigate the role of neonatal androgen stimulation in the development of the potential for masculine and feminine sexual behavior in the mouse, different groups of mice were hormonally manipulated early in life. One group of female mice was administered testosterone propionate (TP) within 24 hr of birth; a second group of females was given a control injection of oil on the day of birth; a third group of females received an injection of TP on the 10th day after birth. A group of males received a control injection of oil on the day of birth. All mice were gonadectomized at about 30 days of age. At 60 days of age, mice were injected with estrogen and progesterone and tested for sexual receptivity; several weeks later all mice were injected with TP and tested for male sexual behavior. Female behavior: Females given oil at birth and females given TP on the 10th day after birth showed high levels of sexual receptivity as adults following estrogen-progesterone treatment. Females given TP on the day of birth, and male mice, rarely exhibited lordosis following estrogen-progesterone treatment. Male behavior: Most mice, regardless of genetic sex or neonatal treatment, mounted in adulthood following administration of exogenous androgen. There was little difference in mounting frequency between groups, suggesting that exogenous or endogenous androgen stimulation of the neonatal mouse does not facilitate adult mounting behavior. These data for the mouse are in essential agreement with existing data for the rat, and indicate that sexual behavioral differentiation induced by androgen stimulation in infancy is best characterized as an inhibition of the potential to display feminine sexual behavior in adulthood.     

Sexual differentiation of the steroid feedback mechanism regulating follicle-stimulating hormone secretion in the Syrian hamster

The ability of gonadal steroid hormones to influence tonic follicle-stimulating hormone (FSH) secretion was investigated in Syrian hamsters. In Experiment 1, males were castrated as adults, and administered testosterone in 20-, 30-, 40-, and 50-mm silastic capsules (s.c.) at 67, 74, 81, and 88 days, respectively. Circulating FSH was reduced by testosterone in a dose-dependent manner. A similar FSH response to testosterone in adulthood was evident in neonatally androgenized hamsters given testosterone proprionate (TP) on Days 0 and 1 of life. By contrast, the absence of gonadal androgens during the neonatal period (females ovariectomized at 60 days of age and males orchidectomized at birth) resulted in only a partial suppression of circulating FSH by even the highest dose of testosterone during adulthood. Treatment with estradiol benzoate at birth failed to produce a masculine response to androgen in adulthood. In Experiment 2, using a similar protocol, the nonaromatizable androgen, dihydrotestosterone, produced a dose-dependent suppression in serum FSH in males castrated in adulthood (30-, 60-, 90-mm capsules). However, dihydrotestosterone failed to alter the hypersecretion of FSH produced by orchidectomy at birth in males or in females ovariectomized at 60 days of age and treated neonatally with either vehicle or TP. In Experiment 3, treatment with estradiol (10-, 20-, 30-mm capsules) decreased serum FSH in gonadectomized hamsters in a dose-dependent manner; males and females treated neonatally with TP were more responsive to estradiol as adults compared to neonatally orchidectomized males or females treated with vehicle at birth.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanisms by which neonatal testosterone exposure mediates sex differences in impulsivity in prepubertal rats

Neonatal testosterone, either acting directly or through its conversion to estradiol, can exert organizational effects on the brain and behavior. The goal of the current study was to examine sex differences and determine the role of neonatal testosterone on prefrontal cortex-dependent impulsive choice behavior in prepubertal rats. Male and female prepubertal rats were tested on the delay-based impulsive choice task. Impulsive choice was defined as choosing an immediate small food reward over a delayed large reward. In a first experiment to examine sex differences, males made significantly more impulsive choices than did females. In a second experiment to examine the organizational effects of testosterone, females treated with neonatal testosterone made significantly more impulsive choices than did control females and their performance was indistinguishable from that of control males. In a third experiment to determine if the effect of testosterone on performance is due to the actions of androgens or estrogens through its conversion to estradiol, males treated neonatally with the aromatase inhibitor formestane, which blocks the conversion of testosterone to estradiol, females treated neonatally with the non-aromatizable androgen dihydrotestosterone, and females treated neonatally with estradiol made significantly more impulsive choices than did control females and their performance was indistinguishable from that of control males. Results indicate that male pubertal rats display increased impulsive choice behavior as compared to females, that this sex difference results from organizing actions of testosterone during the neonatal period, and that this effect can result from both androgenic and estrogenic actions.     

Two-year chronic bioassay study of rats exposed to a 1.6 GHz radiofrequency signal

The purpose of this study was to determine whether long-term exposure to a 1.6 GHz radiofrequency (RF) field would affect the incidence of cancer in Fischer 344 rats. Thirty-six timed-pregnant rats were randomly assigned to each of three treatment groups: two groups exposed to a far-field RF Iridium signal and a third group that was sham exposed. Exposures were chosen such that the brain SAR in the fetuses was 0.16 W/kg. Whole-body far-field exposures were initiated at 19 days of gestation and continued at 2 h/day, 7 days/week for dams and pups after parturition until weaning (approximately 23 days old). The offspring (700) of these dams were selected, 90 males and 90 females for each near-field treatment group, with SAR levels in the brain calculated to be as follows: (1) 1.6 W/kg, (2) 0.16 W/kg and (3) near-field sham controls, with an additional 80 males and 80 females as shelf controls. Confining, head-first, near-field exposures of 2 h/day, 5 days/week were initiated when the offspring were 36 +/- 1 days old and continued until the rats were 2 years old. No statistically significant differences were observed among treatment groups for number of live pups/litter, survival index, and weaning weights, nor were there differences in clinical signs or neoplastic lesions among the treatment groups. The percentages of animals surviving at the end of the near-field exposure were not different among the male groups. In females a significant decrease in survival time was observed for the cage control group.     

Role of aromatization in sexual differentiation: Effects of prenatal ATD treatment and neonatal castration

Pregnant female rats were administered either the aromatization inhibitor ATD (1,4,6-androstatriene-3,17-dione) or propylene glycol from Days 10 to 21 of gestation. On the day of birth one-half of the offspring from each group were gonadectomized. The remaining offspring were gonadectomized 35 days after birth. When adult the animals were given eight weekly mating tests following treatment with 2 or 8 μg of estradiol benzoate (EB) and 25 or 200 μg of progesterone (P). The probability of lordotic behavior as well as the frequency of ear-wiggle and hop and dart responses was measured. Prenatal ATD treatment resulted in a slight increase in lordotic behavior in the males. Lordotic potential was greatly facilitated by castration at birth. ATD treatment also increased the frequency of proceptive behaviors in males and combined ATD treatment and neonatal castration produced a dramatic increase in these behaviors. Prenatal ATD treatment and neonatal ovariectomy had only modest effects on the display of receptive and proceptive behaviors in females. Two weeks after the last test for female mating behaviors, the animals received daily injections of 200 μg of testosterone propionate. Four weekly tests for male-typical responses were given starting 1 week after the first injection. Prenatal ATD treatment did not markedly affect masculine behavior in the males. Castration at birth eliminated the ejaculatory response and reduced the frequency of mounting and intromission behavior. Prenatal ATD treatment and ovariectomy at birth had no appreciable effects on the display of male-typical behaviors in the females. Testosterone-stimulated masculine behavior of the female was similar to that of the male castrated at birth.     

Testosterone propionate treatment of an XY gonadal dysgenetic chacma baboon

Behavioral studies of an XY gonadal dysgenetic chacma baboon prior to and during testosterone propionate treatment were carried out. The orchidectomized dysgenetic individual, two intact males, a castrate male, and two ovariectomized females were pair-tested with a group of eight ovariectomized stimulus females prior to and during their treatment with estradiol benzoate. Three test series were carried out. One series occurred prior to any treatment of the agonadal focal subject animals. During this series it was only the intact males who showed behavior change during their testing with the estrogen treated females. A second test series occurred after a month of daily testosterone propionate injections (1 mg/kg/day) had been given to the four agonadal subjects. During this test series the castrate male ejaculated once with one of the estrogen-treated females. All of the treated subjects showed increases in their frequency of yawning. Upon completion of this test series the androgen dosage was increased (2 mg/kg/day) and 2 weeks later a third test series was carried out. During this series the castrate male ejaculated with five of his eight estrogen-treated partners. The yawning of all the treated subjects continued. As had been the case in the second series the XY gonadal dysgenetic individual continued to behave as did the ovariectomized females. None of these animals showed any increase in any measure of male sexual behavior. This study establishes the fact that a genetic male primate deprived of in utero exposure to testicular hormones will go on to develop as a normal genetic female and will fail to exhibit increased levels of male sexual behavior during androgen treatment.