Hypothalamic Expression of Estrogen Receptor Isoforms Underlies Estradiol Control of Luteinizing Hormone in Female Rats.

Luteinizing hormone (LH) secretion during the ovarian cycle is governed by fluctuations in circulating estradiol (E2) that oppositely regulate kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) of the hypothalamus. However, how these effects are orchestrated to achieve fertility is unknown. Here, we have tested the hypothesis that AVPV and ARC neurons have different sensitivities to E2 to coordinate changes in LH secretion. Cycling and ovariectomized rats with low and high E2 levels were used. As an index of E2 responsiveness, progesterone receptor (PR) was expressed only in the AVPV of rats with high E2, showing the preovulatory LH surge. On the other hand, kisspeptin neurons in the ARC responded to low E2 levels sufficient to suppress LH release. Notably, the Esr1/Esr2 ratio of gene expression was higher in the ARC than AVPV, regardless of E2 levels. Accordingly, the selective pharmacological activation of estrogen receptor α (ERα) required lower doses to induce PR in the ARC. The activation of ERß, in turn, amplified E2-induced PR expression in the AVPV and the LH surge. Thus, ARC and AVPV neurons are differently responsive to E2. Lower E2 levels activate ERα in the ARC, whereas ERß potentiates the E2 positive feedback in the AVPV, which appears related to the differential Esr1/Esr2 ratio in these 2 brain areas. Our findings provide evidence that the distinct expression of ER isoforms in the AVPV and ARC plays a key role in the control of periodic secretion of LH required for fertility in females.

Sex- and age-dependent differences in the hormone and drinking responses to water deprivation.

Maintenance of the volume and osmolality of body fluids is important, and the adaptive responses recruited to protect against osmotic stress are crucial for survival. The objective of this work was to compare the responses that occur in aging male and female rats during water deprivation. For this purpose, groups of male and female Wistar rats aged 3 mo (adults) or 18 mo (old) were submitted to water deprivation (WD) for 48 h. The water and sodium (0.15 M NaCl) intake, plasma concentrations of oxytocin (OT), arginine vasopressin (AVP), corticosterone (CORT), atrial natriuretic peptide (ANP), and angiotensin II (ANG II) were determined in hydrated and water-deprived animals. In response to WD, old male and female rats drank less water and saline than adults, and both adult and old females drank more water and saline than respective males. Dehydrated old animals displayed lower ANG II plasma concentration and CORT response compared with the respective normohydrated rats. Dehydrated adult males had higher plasma ANP and AVP as well as lower CORT concentrations than dehydrated adult females. Moreover, plasma OT and CORT levels of old female rats were higher than those in the dehydrated old male rats. Relative expression of ANG II type 1 receptor mRNA was decreased in the subfornical organ of adult and old male rats as well as adult female rats in response to WD. In conclusion, the study elucidated the effect of sex and age on responses induced by WD, altering the degree of dehydration induced by 48 h of WD.

α-Estrogen and Progesterone Receptors Modulate Kisspeptin Effects on Prolactin: Role in Estradiol-Induced Prolactin Surge in Female Rats.

Kisspeptin (Kp) regulates prolactin (PRL) in an estradiol-dependent manner. We investigated the interaction between ovarian steroid receptors and Kp in the control of PRL secretion. Intracerebroventricular injections of Kp-10 or Kp-234 were performed in ovariectomized (OVX) rats under different hormonal treatments. Kp-10 increased PRL release and decreased 3,4-dihydroxyphenylacetic acid levels in the median eminence (ME) of OVX rats treated with estradiol (OVX+E), which was prevented by tamoxifen. Whereas these effects of Kp-10 were absent in OVX rats, they were replicated in OVX rats treated with selective agonist of estrogen receptor (ER)α, propylpyrazole triol, but not of ERß, diarylpropionitrile. Furthermore, the Kp-10-induced increase in PRL was two times higher in OVX+E rats also treated with progesterone (OVX+EP), which was associated with a reduced expression of both tyrosine hydroxylase (TH) and Ser40-phosphorylated TH in the ME. Kp-10 also reduced dopamine levels in the ME of OVX+EP rats, an effect blocked by the progesterone receptor (PR) antagonist RU486. We also determined the effect of Kp antagonism with Kp-234 on the estradiol-induced surges of PRL and luteinizing hormone (LH), using tail-tip blood sampling combined with ultrasensitive enzyme-linked immunosorbent assay. Kp-234 impaired the early phase of the PRL surge and prevented the LH surge in OVX+E rats. Thus, we provide evidence that Kp stimulation of PRL release requires ERα and is potentiated by progesterone via PR activation. Moreover, alongside its essential role in the LH surge, Kp seems to play a role in the peak phase of the estradiol-induced PRL surge.

Effects of early and late neonatal bromocriptine treatment on hypothalamic neuropeptides, dopaminergic reward system and behavior of adult rats.

In humans, bromocriptine (BRO) is used as a treatment for many disorders, such as prolactinomas, even during pregnancy and lactation. Previously we demonstrated that maternal BRO treatment at the end of lactation programs offspring for obesity and several endocrine dysfunctions. Here, we studied the long-term effects of direct BRO injection in neonatal Wistar rats on their dopaminergic pathway, anxiety-like behavior and locomotor activity at adulthood. Male pups were either s.c. injected with BRO (0.1µg/once daily) from postnatal day (PN) 1 to 10 or from PN11 to 20. Controls were injected with methanol-saline. Body mass, food intake, neuropeptides, dopamine pathway parameters, anxiety-like behavior and locomotor activity were analyzed. The dopamine pathway was analyzed in the ventral tegmental area (VTA), nucleus accumbens (NAc) and dorsal striatum (DS) at PN180. PN1-10 BRO-treated animals had normal body mass and adiposity but lower food intake and plasma prolactin (PRL). This group had higher POMC in the arcuate nucleus (ARC), higher tyrosine hydroxylase (TH) in the VTA, higher dopa decarboxylase (DDc), higher D2R and µu-opioid receptor in the NAc. Concerning behavior in elevated plus maze (EPM), BRO-treated animals displayed more anxiety-like behaviors. PN11-20 BRO-treated showed normal body mass and adiposity but higher food intake and plasma PRL. This group had lower POMC in the ARC, lower TH in the VTA and lower DAT in the NAc. BRO-treated animals showed less anxiety-like behaviors in the EPM. Thus, neonatal BRO injection, depending on the time of treatment, leads to different long-term dysfunctions in the dopaminergic reward system, food intake behavior and anxiety levels, findings that could be partially due to PRL and POMC changes.

The impact of maternal consumption of cafeteria diet on reproductive function in the offspring.

Maternal obesity is a risk factor for the development of metabolic syndrome and childhood obesity, and early overnutrition seems to induce the development of pathologies in adulthood, including insulin resistance, cardiovascular diseases, type 2 diabetes mellitus, and a higher BMI. In addition, it is known that obesity can negatively affect fertility and reproductive function in men. The objective of this work was to investigate the impact of maternal obesity induced by the consumption of cafeteria diet on metabolic, endocrine and reproductive outcomes in the male offspring. Body weight, abdominal fat content and concentrations of insulin, leptin, glucose and total cholesterol were analyzed in dams. The same parameters were evaluated in pups when in adulthood, in addition to the analysis of sexual behavior, followed by measurement of plasma luteinizing hormone, follicle-stimulating hormone, testosterone, and prolactin. Maternal consumption of cafeteria diet affected reproductive hormone regulation in the offspring and such modifications were reflected on sexual performance. Also, these modifications were independent of time and of the reproductive period during which dams consumed the diet. Our results indicate, for the first time, that maternal nutrition may have a deep impact on the reproductive function of the adult male offspring.

Prolactin regulates kisspeptin neurons in the arcuate nucleus to suppress LH secretion in female rats.

Prolactin (PRL) is known to suppress LH secretion. Kisspeptin neurons regulate LH secretion and express PRL receptors. We investigated whether PRL acts on kisspeptin neurons to suppress LH secretion in lactating (Lac) and virgin rats. Lac rats displayed high PRL secretion and reduced plasma LH and kisspeptin immunoreactivity in the arcuate nucleus (ARC). Bromocriptine-induced PRL blockade significantly increased ARC kisspeptin and plasma LH levels in Lac rats but did not restore them to the levels of non-Lac rats. Bromocriptine effects were prevented by the coadministration of ovine PRL (oPRL). Virgin ovariectomized (OVX) rats treated with either systemic or intracerebroventricular oPRL displayed reduction of kisspeptin expression in the ARC and plasma LH levels, and these effects were comparable with those of estradiol treatment in OVX rats. Conversely, estradiol-treated OVX rats displayed increased kisspeptin immunoreactivity in the anteroventral periventricular nucleus, whereas oPRL had no effect in this brain area. The expression of phosphorylated signal transducer and activator of transcription 5 was used to determine whether kisspeptin neurons in the ARC were responsive to PRL. Accordingly, intracerebroventricular oPRL induced expression of phosphorylated signal transducer and activator of transcription 5 in the great majority of ARC kisspeptin neurons in virgin and Lac rats. We provide here evidence that PRL acts on ARC neurons to inhibit kisspeptin expression in female rats. During lactation, PRL contributes to the inhibition of ARC kisspeptin. In OVX rats, high PRL levels suppress kisspeptin expression and reduce LH release. These findings suggest a pathway through which hyperprolactinemia may inhibit LH secretion and thereby cause infertility.

Reproductive dysfunction in female rats with renovascular hypertension.

BACKGROUND: Hypertension is a major public health epidemic that is highly associated with sexual dysfunction in both men and women. Despite its high prevalence, clinical and animal literature on the underlying mechanisms of sexual dysfunction in hypertensive women is remarkably limited. METHODS: Using a well-established rodent model of renovascular hypertension-the 2-kidney, 1-clip (2K1C) Goldblatt model-we investigated possible reproductive deficits in female rats. We evaluated several aspects of reproductive function in hypertensive female rats: estrous cycle, sexual behavior, ovulation, and plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol at proestrus afternoon. RESULTS: Clipping of the left renal artery resulted in dramatic elevations in systolic blood pressure and heart rate. Renovascular hypertension was associated with a delay for reestablishing estrous cyclicity (50% of 2K1C rats failed to resume cycling by 15 days after surgery). In rats that resumed cycling, 2K1C female rats showed a decrease in sexual behavior, evidenced by a decreased lordosis quotient and a reduction in ovulation, as demonstrated by a decreased number of oocytes. Moreover, plasma levels of LH on the proestrus afternoon were reduced in hypertensive female rats, but no changes in estradiol or FSH were observed. CONCLUSIONS: Our results demonstrate that renovascular hypertension induces an overall decrease in reproductive function in female rats. Most important, our results indicate that the animal model of renovascular hypertension could be used as a relevant tool to understand better the pathophysiological mechanisms involved in the reproductive deficits in women with renovascular hypertension.

Release of norepinephrine in the preoptic area activates anteroventral periventricular nucleus neurons and stimulates the surge of luteinizing hormone.

The role of norepinephrine (NE) in regulation of LH is still controversial. We investigated the role played by NE in the positive feedback of estradiol and progesterone. Ovarian-steroid control over NE release in the preoptic area (POA) was determined using microdialysis. Compared with ovariectomized (OVX) rats, estradiol-treated OVX (OVX+E) rats displayed lower release of NE in the morning but increased release coincident with the afternoon surge of LH. OVX rats treated with estradiol and progesterone (OVX+EP) exhibited markedly greater NE release than OVX+E rats, and amplification of the LH surge. The effect of NE on LH secretion was confirmed using reverse microdialysis. The LH surge and c-Fos expression in anteroventral periventricular nucleus neurons were significantly increased in OVX+E rats dialyzed with 100 nm NE in the POA. After Fluoro-Gold injection in the POA, c-Fos expression in Fluoro-Gold/tyrosine hydroxylase-immunoreactive neurons increased during the afternoon in the A2 of both OVX+E and OVX+EP rats, in the locus coeruleus (LC) of OVX+EP rats, but was unchanged in the A1. The selective lesion of LC terminals, by intracerebroventricular N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, reduced the surge of LH in OVX+EP but not in OVX+E rats. Thus, estradiol and progesterone activate A2 and LC neurons, respectively, and this is associated with the increased release of NE in the POA and the magnitude of the LH surge. NE stimulates LH secretion, at least in part, through activation of anteroventral periventricular neurons. These findings contribute to elucidation of the role played by NE during the positive feedback of ovarian steroids.

Pre-and post-puberty physiological plasma oxytocin concentrations in male domestic cats (Felis silvestris catus) / Concentrações fisiológicas plasmáticas de ocitocina pré e pós-puberal em gatos machos (Felis silvestris catus)

The hormone oxytocin is released by the neuropituitary gland through stimulation of the neurons of the supraoptic and paraventricular nuclei of the hypothalamus. In order to determine the physiological concentrations of this hormone in domestic cats, blood samples were collected from 15 male animals (Felis silvestris catus) during the pre- and post-puberty periods (at four and eight months of age, respectively). Oxytocin determination was accomplished by radioimmunoassay. The average oxytocin concentrations measured in the pre- and post-puberty periods were 2.54±0.24 (μg/dL) and 2.53±0.28 (μg/dL), respectively, and there were no statistical differences between these measurements. Because there are few literature on the analysis of this hormone, especially in the case of male Felis silvestris catus, more studies on the influence of oxytocin on the physiology and reproduction of this species should be conducted under maintenance and situations of stress (such as transportation), and other routine events.

A ocitocina é um hormônio secretado pela neurohipófise através da estimulação dos neurônios dos núcleos supraópticos e paraventriculares do hipotálamo. Com o intuito de determinar as concentrações fisiológicas de ocitocina em gatos domésticos foram coletadas amostras de sangue de 15 animais (Felis silvestris catus) machos, nos períodos pré e pós puberdade (quarto e oitavo mês de vida), sendo utilizada a técnica de radioimunoensaio para tal determinação. Na primeira dosagem a concentração média foi de 2,54±0,24 (μg/dL), e na segunda 2,53±0,28 (μg/dL), não sendo encontrada diferenças significativas entre as médias analisadas. Devido a escassez de trabalhos analisando este hormônio, especialmente para machos desta espécie, sugere-se mais estudos abordando a influência deste hormônio na fisiologia e reprodução destes animais, tanto em condições de manutenção, condições de estresse, como no transporte e outras situações de rotina na vida destes animais.

Risk assessment behaviors associated with corticosterone trigger the defense reaction to social isolation in rats: role of the anterior cingulate cortex.

The extent to which the hypothalamic-pituitary-adrenal axis is activated by short-term and long-term consequences of stress is still open to investigation. This study aimed to determine (i) the correlation between plasma corticosterone and exploratory behavior exhibited by rats subjected to the elevated plus maze (EPM) following different periods of social isolation, (ii) the effects of the corticosterone synthesis blocker, metyrapone, on the behavioral consequences of isolation, and (iii) whether corticosterone produces its effects through an action on the anterior cingulate cortex, area 1 (Cg1). Rats were subjected to 30-min, 2-h, 24-h, or 7-day isolation periods before EPM exposure and plasma corticosterone assessments. Isolation for longer periods of time produced greater anxiogenic-like effects on the EPM. However, stretched attend posture (SAP) and plasma corticosterone concentrations were increased significantly after 30 min of isolation. Among all of the behavioral categories measured in the EPM, only SAP positively correlated with plasma corticosterone. Metyrapone injected prior to the 24 h isolation period reversed the anxiogenic effects of isolation. Moreover, corticosterone injected into the Cg1 produced a selective increase in SAP. These findings indicate that risk assessment behavior induced by the action of corticosterone on Cg1 neurons initiates a cascade of defensive responses during exposure to stressors.

Early onset of obesity induces reproductive deficits in female rats.

The incidence of obesity is increasing rapidly all over the world and results in numerous health detriments, including disruptions in reproduction. However, the mechanisms by which excess body fat interferes with reproductive functions are still not fully understood. After weaning, female rats were treated with a cafeteria diet or a chow diet (control group). Biometric and metabolic parameters were evaluated in adulthood. Reproductive parameters, including estradiol, progesterone, LH and prolactin during the proestrus afternoon, sexual behavior, ovulation rates and histological analysis of ovaries were also evaluated. Cafeteria diet was able to induce obesity in female rats by increasing body and fat pad weight, which resulted in increased levels of triglycerides, total cholesterol, LDL and induced insulin resistance. The cafeteria diet also negatively affected female reproduction by reducing the number of oocytes and preantral follicles, as well as the thickness of the follicular layer. Obese females did not show preovulatory progesterone and LH surges, though plasma estradiol and prolactin showed preovulatory surges similar to control rats. Nevertheless, sexual receptiveness was not altered by cafeteria diet. Taken together, our results suggest that the cafeteria diet administered from weaning age was able to induce obesity and reduce the reproductive capability in adult female rats, indicating that this obesity model can be used to better understand the mechanisms underlying reproductive dysfunction in obese subjects.

Cortisol influence on testicular testosterone secretion in domestic cat: an in vitro study / Ação do cortisol sobre a secreção de testosterona em testículos de gato doméstico: um estudo in vitro

The aim of the present experiment was to investigate the effect of corticosteroids (exogen) on in vitro testosterone secretion after stress by transportation (40 minutes). Feline testes (Felis silvestris catus) were incubated in the following media: TCM 199; TCM 199 + hCG 10_7M; TCM 199 + hydrocortisone 10_7M, or TCM 199 + hCG + hydrocortisone. The animals (n=21) were allocated into three groups: (S) that arrived at 3 h prior to surgery, (A) that remained in the laboratory for 36 h before being submitted to surgical procedure, and (C) that were also allowed to remain for 36 hours in the laboratory before the surgical procedure, but whose testes had been incubated with hydrocortisone prior to incubation in the referred media. The results showed that group S secreted higher levels of testosterone, regardless of the culture media. It is noteworthy that the suppressing action of hydrocortisone sodium succinate led to a reduction in the testosterone concentration, despite the presence of hCG.

O objetivo deste trabalho foi investigar o efeito da hidrocortisona sobre a secreção de testosterona após cultivo in vitro dos testículos, em distintas situações de estresse (transporte) de gatos domésticos (Felis silvestris catus). Testículos foram incubados nos seguintes meios de cultura: TCM 199; TCM 199 + hCG 10_7M; TCM 199 + hydrocortisona 10_7M e TCM 199 + hCG + hidrocortisona. Os animais (n=21) foram alocados em 3 sub-grupos: (S) animal admitido 3 horas antes da orquiectomia, (A) animais orquiectomizados após 36 horas de permanência no biotério e (C) animais que permaneceram por 36 horas no biotério antes da cirurgia e que tiveram seus testículos pré-incubados em hidrocortisona. Os resultados demonstraram que o grupo S secretou maiores valores de testosterona em todas as condições estudadas. É válido mencionar que a supressão promovida pela hidrocortisona também promoveu redução na concentração de testosterona no meio TCM 199, a despeito da presença de hCG.

Kisspeptin regulates prolactin release through hypothalamic dopaminergic neurons.

Prolactin (PRL) is tonically inhibited by dopamine (DA) released from neurons in the arcuate and periventricular nuclei. Kisspeptin plays a pivotal role in LH regulation. In rodents, kisspeptin neurons are found mostly in the anteroventral periventricular and arcuate nuclei, but the physiology of arcuate kisspeptin neurons is not completely understood. We investigated the role of kisspeptin in the control of hypothalamic DA and pituitary PRL secretion in adult rats. Intracerebroventricular kisspeptin-10 (Kp-10) elicited PRL release in a dose-dependent manner in estradiol (E2)-treated ovariectomized rats (OVX+E2), whereas no effect was found in oil-treated ovariectomized rats (OVX). Kp-10 increased PRL release in males and proestrous but not diestrous females. Associated with the increase in PRL release, intracerebroventricular Kp-10 reduced Fos-related antigen expression in tyrosine hydroxylase-immunoreactive (ir) neurons of arcuate and periventricular nuclei in OVX+E2 rats, with no effect in OVX rats. Kp-10 also decreased 3,4-dihydroxyphenylacetic acid concentration and 3,4-dihydroxyphenylacetic acid-DA ratio in the median eminence but not striatum in OVX+E2 rats. Double-label immunofluorescence combined with confocal microscopy revealed kisspeptin-ir fibers in close apposition to and in contact with tyrosine hydroxylase-ir perikarya in the arcuate. In addition, Kp-10 was not found to alter PRL release from anterior pituitary cell cultures regardless of E2 treatment. We provide herein evidence that kisspeptin regulates PRL release through inhibition of hypothalamic dopaminergic neurons, and that this mechanism is E2 dependent in females. These findings suggest a new role for central kisspeptin with possible implications for reproductive physiology.

The ventral premammillary nucleus links fasting-induced changes in leptin levels and coordinated luteinizing hormone secretion.

Physiological conditions of low leptin levels like those observed during negative energy balance are usually characterized by the suppression of luteinizing hormone (LH) secretion and fertility. Leptin administration restores LH levels and reproductive function. Leptin action on LH secretion is thought to be mediated by the brain. However, the neuronal population that mediates this effect is still undefined. The hypothalamic ventral premammillary nucleus (PMV) neurons express a dense concentration of leptin receptors and project to brain areas related to reproductive control. Therefore, we hypothesized that the PMV is well located to mediate leptin action on LH secretion. To test our hypothesis, we performed bilateral excitotoxic lesions of the PMV in adult female rats. PMV-lesioned animals displayed a clear disruption of the estrous cycle, remaining in anestrus for 15-20 d. After apparent recovery of cyclicity, animals perfused in the afternoon of proestrus showed decreased Fos immunoreactivity in the anteroventral periventricular nucleus and in gonadotropin releasing hormone neurons. PMV-lesioned animals also displayed decreased estrogen and LH secretion on proestrus. Lesions caused no changes in mean food intake and body weight up to 7 weeks after surgery. We further tested the ability of leptin to induce LH secretion in PMV-lesioned fasted animals. We found that complete lesions of the PMV precluded leptin stimulation of LH secretion on fasting. Our findings demonstrate that the PMV is a key site linking changing levels of leptin and coordinated control of reproduction.

Plasma hormonal profiles and dendritic spine density and morphology in the hippocampal CA1 stratum radiatum, evidenced by light microscopy, of virgin and postpartum female rats.

Successful reproduction requires that changes in plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), oxytocin (OT), estrogen (E(2)) and progesterone (P(4)) occur together with the display of maternal behaviors. Ovarian steroids and environmental stimuli can affect the dendritic spines in the rat hippocampus. Here, studying Wistar rats, it is described: (a) the sequential and concomitant changes in the hormonal profile of females at postpartum days (PP) 4, 8, 12, 16, 20 and 24, comparing to estrous cycle referential values; (b) the dendritic spine density in the stratum radiatum of CA1 (CA1-SR) Golgi-impregnated neurons in virgin females across the estrous cycle and in multiparous age-matched ones; and (c) the proportion of different types of spines in the CA1-SR of virgin and postpartum females, both in diestrus. Plasma levels of gonadotrophins and ovarian hormones remained low along PP while LH increased and PRL decreased near the end of the lactating period. The lowest dendritic spine density was found in virgin females in estrus when compared to diestrus and proestrus phases or to postpartum females in diestrus (p<0.03). Other comparisons among groups were not statistically significant (p>0.4). There were no differences in the proportions of the different spine types in nulliparous and postpartum females (p>0.2). Results suggest that medium layer CA1-SR spines undergo rapid modifications in Wistar females across the estrous cycle (not quite comparable to Sprague-Dawley data or to hormonal substitutive therapy following ovariectomy), but persistent effects of motherhood on dendritic spine density and morphology were not found in this area.

Trypanosoma cruzi: plasma corticosterone after repetitive stress during the acute phase of infection.

An increased level of plasma corticosterone is one manifestation of severe environmental or physiologic stress. The stress response mediated by the hypothalamic-pituitary-adrenal axis is already known to suppress immunoglobulin production and to impair immune function, but there are few studies relating stress and plasma corticosterone to the outcome of Trypanosoma cruzi infection. In this study, male Wistar rats were infected with the Y strain of T. cruzi and then subjected to repetitive stress by exposure to ether vapor for 1min twice a day during the acute phase of infection. Stressed animals showed decreased lytic antibody activity and lowered levels of peritoneal macrophages. Despite an increase in the weight of the spleen, histological analyses demonstrated tissue alterations, the presence of amastigote nests, and a complete absence of activated lymphoid follicles. These results suggest that stress-induced increases in plasma corticosterone can suppress the immune response and worsen tissue injury during the acute phase of T. cruzi infection.

Prolactin secretory surge during estrus coincides with increased dopamine activity in the hypothalamus and preoptic area and is not altered by ovariectomy on proestrus.

Prolactin (PRL) secretory surges have been reported on the afternoons of both proestrus and estrous in cycling rats. As neuroendocrine regulation of estrous PRL surge is poorly understood, the present study aimed to investigate the involvement of hypothalamic dopamine and serotonin as well as of plasma ovarian steroids in this hormonal surge generation. For that, we determined the concentrations of dopamine, serotonin and their respective metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindole-3-acetic acid (5-HIAA) in the mediobasal hypothalamus (MBH) and medial preoptic area (MPOA) throughout the day of estrus and correlated them with plasma PRL levels. In a second study, we evaluated the effect of ovariectomy on the morning of proestrus on PRL surges of both proestrus and estrus. Dopamine turnover, as determined by DOPAC/dopamine ratio, increased in both the MBH and MPOA coinciding with the afternoon PRL surge on estrus. In contrast, both the concentration and turnover (5-HIAA/serotonin) of serotonin within these areas were unaltered during estrus. In addition, ovariectomy reduced plasma estradiol and progesterone levels but did not alter the PRL surges on proestrus and estrus. Considering that dopamine is the main inhibitor of PRL release and that PRL auto-regulates its secretion through a short-loop feedback mechanism, our present results suggest that PRL may suppress its own secretion during the estrus surge through the activation of the dopaminergic neurons in the MBH and MPOA. In addition, the PRL surge on estrus seems do not depend on either the activity of hypothalamic serotonin or the increased secretion of ovarian steroids on proestrus.

Alterations in the central vasopressin and oxytocin axis after lesion of a brain osmotic sensory region.

The anteroventral region of the third ventricle (AV3V) is critical in mediating osmotic sensitivity. AV3V lesions increase plasma osmolality and block osmotic-induced vasopressin (VP) and oxytocin (OT) secretion. The aim was to evaluate the effects of AV3V lesions on neurosecretion under control/water replete conditions and after 48 h dehydration. The focus was on central peptidergic changes with measurement of OT and VP content in the hypothalamic paraventricular (PVN) and supraoptic (OT) regions and the posterior pituitary. AV3V-lesioned rats exhibited an elevated plasma osmolality and higher OT content in SON and PVN. There was an increase in VP content in PVN, but no change in SON. As predicted, the plasma peptide response to dehydration was absent in lesioned animals. However, dehydration produced depletion in posterior pituitary VP in lesioned animals with no change in OT. No changes in nuclear VP and OT levels were seen after dehydration. These results demonstrate that AV3V lesions alter the VP and OT neurosecretory system, seen as a blockade of osmotic-induced release and an increase in basal nuclear peptide content. The data indicate that interruption of the osmotic sensory system affects the central neurosecretory axis, resulting in a backup in content and likely changes in synthesis and processing.

Effects of neonatal handling on the behavior and prolactin stress response in male and female rats at various ages and estrous cycle phases of females.

Neonatal handling induces behavioral and hormonal changes, characterized by reduced fear in novel environments, and lesser elevation and faster return to basal levels of plasma corticosterone, prolactin and adrenaline, in response to stressors in adulthood. The present study aimed to analyze the effects of neonatal handling from Days 1 to 10 postnatal on prolactin response to ether stress in male and female rats at three life periods: neonatal, peripubertal and adulthood. Moreover, adult females were tested in two different phases of the estrous cycle, i.e., diestrus and estrus. In another set of experiments, the behavior of peripubertal and adult males and females in estrus and diestrus was analyzed in the elevated plus maze test. Pups were either handled for 1 min (handled group) or left undisturbed (nonhandled group) during the first 10 days after delivery. In adults, in the handled females in diestrus, stress induced a lesser increase in plasma prolactin compared with nonhandled ones, as in males. However, in estrus, handled females showed no difference in the prolactin response to stress. In the elevated plus maze, handled females in diestrus, but not in estrus, showed higher locomotor activity compared with nonhandled ones. Peripubertal male and female rats handled during the neonatal period showed no difference in behavior in the elevated plus maze compared with nonhandled animals. Early-life stimulation can induce long-lasting behavioral and stress-related hormonal changes, but they are not stable throughout life and phases of the estrous cycle.

Atrial natriuretic peptide mediates oxytocin secretion induced by osmotic stimulus.

Atrial natriuretic peptide (ANP), first discovered in the heart, has been also detected in various brain regions involved in the control of cardiovascular function and water and sodium balance. The anteroventral region of the third ventricle (AV3V) and the subfornical organ (SFO) have ANP-immunoreactive projections towards the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Extracellular fluid (ECF) hyperosmolality stimulates the secretion of oxytocin (OT) which induces ANP release by the atrium. On the other hand, passive immunoneutralization of ANP reduces OT secretion in response to ECF hypertonicity. Previous studies have shown the co-localization of ANP and OT in PVN and SON neurons and in the periventricular region, as well as the presence of ANPergic and oxytocinergic neurons in the median eminence. The aim of the present study was to investigate the OT and ANP content in the SON and PVN of the hypothalamus and in the posterior pituitary (PP) after an osmotic stimulus that induces OT secretion. The results showed that intracerebroventricular microinjection of normal rabbit serum (NRS) or of ANP antiserum followed or not by an intraperitoneal injection of isotonic saline did not alter OT secretion or OT content in the PVN, SON, and PP; passive ANP immunoneutralization reduced the basal content of ANP in the PVN, SON, and PP of animals in a situation of isotonicity; the ANP antiserum inhibited the increase of OT secretion and content of OT and ANP in the PVN, SON and PP induced by the osmotic stimulus. Thus, the increase in plasma OT and oxytocinergic neurons of the hypothalamus-posterior pituitary system in response to hypertonicity depends on the action of endogenous ANP, i.e., ECF hypertonicity must activate ANPergic neurons which directly or indirectly stimulate OT release.