Chronic estradiol-17ß exposure suppresses hypothalamic norepinephrine release and the steroid-induced luteinizing hormone surge: role of nitration of tyrosine hydroxylase.

Chronic exposure to estrogens is known to produce a variety of deleterious effects in women including breast and ovarian cancer and anovulation. In female rats, exposure to low levels of estradiol-17ß (E2) decreases hypothalamic norepinephrine (NE) to suppress luteinizing hormone (LH) secretion and cause failure of ovulation. We hypothesized that E2 exposure most likely decreases NE release in the medial preoptic area (MPA) of the hypothalamus to produce this effect and that this may be due to E2-induced inflammatory changes in noradrenergic nuclei leading to nitration of an enzyme involved in NE synthesis. To test this, female Sprague Dawley rats were sham implanted or implanted with slow release E2 pellets (20ng/day) for 30, 60 or 90 days (E30, E60 and E90 respectively). At the end of the treatment period, the rats were implanted with a push-pull cannula in the MPA, ovariectomized and steroid primied to induce a LH surge and subjected to push-pull perfusion. Perfusates were analyzed for NE levels using HPLC-EC. Blood samples collected simultaneously were analyzed for LH levels. We measured interleukin-1ß (IL-1ß) and nitrate levels in brainstem noradrenergic nuclei that innervate the MPA. In control animals, there was a marked increase in NE levels in response to steroid priming at 1600h that was reduced in the E30 group, and completely abolished after 60 and 90 days of E2 exposure. LH profiles were similar to NE release profiles in control and E2-treated animals. We found that IL-1ß levels increased in all three (A1, A2 and A6) noradrenergic nuclei with chronic E2 exposure, while nitrate levels increased only in the A6 region. There was an increase in the nitration of the NE synthesizing enzyme in the MPA in this group as well probably contributing to reduced NE synthesis. This could be a possible mechanism by which chronic E2 exposure decreases NE levels in the MPA to suppress the LH surge.

Chronic estradiol exposure induces oxidative stress in the hypothalamus to decrease hypothalamic dopamine and cause hyperprolactinemia.

Estrogens are known to cause hyperprolactinemia, most probably by acting on the tuberoinfundibular dopaminergic (TIDA) system of the hypothalamus. Dopamine (DA) produced by TIDA neurons directly inhibits prolactin secretion and, therefore, to stimulate prolactin secretion, estrogens inhibit TIDA neurons to decrease DA production. However, the mechanism by which estrogen produces this effect is not clear. In the present study, we used a paradigm involving chronic exposure to low levels of estradiol-17ß (E(2)) to mimic prolonged exposures to environmental and endogenous estrogens. We hypothesized that chronic exposure to low levels of E(2) induces oxidative stress in the arcuate nucleus (AN) of the hypothalamus that contains TIDA neurons and causes nitration of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of DA. This results in a significant decrease in DA and consequently, hyperprolactinemia. To investigate this, adult, intact female cycling rats were implanted with slow-release E(2) pellets (20 ng/day) for 30, 60, or 90 days and were compared with old (16-18 mo old) constant estrous (OCE) rats. Chronic E(2) exposure significantly increased the expression of glial fibrillary acidic protein and the concentrations of interleukin-1ß (IL-1ß) and nitrate in the AN that contains perikarya of TIDA neurons and increased nitration of TH in the median eminence (ME) that contains the terminals. These levels were comparable to those seen in OCE rats. We observed a significant decrease in DA concentrations in the ME and hyperprolactinemia in an exposure-dependent manner similar to that seen in OCE rats. It was concluded that chronic exposure to low levels of E(2) evokes oxidative stress in the AN to inhibit TIDA neuronal function, most probably leading to hyperprolactinemia.

Progesterone decreases cortical and sub-cortical edema in young and aged ovariectomized rats with brain injury.

PURPOSE: Traumatic brain injury (TBI) -induced brain edema can be reduced by acute progesterone (PROG) treatment in young adult males and females, and in aged males. To extend these findings we tested these hypotheses: 1. Acute PROG treatment post-TBI will reduce cortical edema in aged females as much as in young adults. 2. TBI will induce edema in sub-cortical structures (SCS): the thalamus (TH), hypothalamus (HT), brain stem (BS) and anterior pituitary (AP). 3. Acute, systemic PROG treatment post-TBI will reduce edema in SCS. METHODS: Young adult (n = 42) and aged (n = 40), bilaterally ovariectomized rats were given medial frontal cortical (MFC) contusion injury, treated with PROG (16 mg/kg body weight) or vehicle at 1, 6 and 24 hours post-injury and killed at 6, 24 and 48 hours post-injury. Their brains were removed and the target areas isolated and measured for water content. RESULTS: TBI induced cortical and delayed sub-cortical edema. Acute PROG treatment decreased this edema. At 6 hours post-TBI serum PROG levels were substantially elevated in both young and aged, PROG-treated, groups, but were higher in the latter. CONCLUSION: Acute PROG treatment post-TBI could prove an effective intervention to prevent or attenuate systemic, post-injury cortical and sub-cortical edema in young and aged females.

Traumatic brain injury causes long-term reduction in serum growth hormone and persistent astrocytosis in the cortico-hypothalamo-pituitary axis of adult male rats.

UNLABELLED: In humans, traumatic brain injury (TBI) causes pathological changes in the hypothalamus (HT) and the pituitary. One consequence of TBI is hypopituitarism, with deficiency of single or multiple hormones of the anterior pituitary (AP), including growth hormone (GH). At present no animal model of TBI with ensuing hypopituitarism has been demonstrated. The main objective of this study was to investigate whether cortical contusion injury (CCI) could induce long-term reduction of serum GH in rats. We also tested the hypothesis that TBI to the medial frontal cortex (MFC) would induce inflammatory changes in the HT and AP. METHODS: Nine young adult male rats were given sham surgery (n = 4) or controlled impact contusions (n = 5) of the MFC. Two months post-injury they were killed, trunk blood collected and their brains and AP harvested. GH was measured in serum and AP using ELISA and Western blot respectively. Interleukin-1beta (IL-1beta) and glial fibrillary acidic protein (GFAP) were measured in the cortex (Cx), HT, and AP by Western blot. RESULTS: Lesion rats had significantly (p < 0.05) lower levels of GH in the AP and serum, unaltered serum IGF-1, and significantly (p < 0.05) higher levels of IL-1beta in the Cx and HT and GFAP in the Cx, HT, and AP compared to that of shams. CONCLUSION: CCI leads to a long-term depletion of serum GH in male rats. This chronic change in GH post-TBI is probably the result of systemic and persistent inflammatory changes observed at the level of HT and AP, the mechanism of which is not yet known.

Effects of central and systemic administration of leptin on neurotransmitter concentrations in specific areas of the hypothalamus.

Leptin, a hormone produced by adipocytes, has been shown to affect a number of central functions, such as regulation of the hypothalamo-pituitary-adrenal axis, feeding, and body weight regulation. Because hypothalamic monoamines are intricately involved in the regulation of these functions, we hypothesized that leptin may produce its effects by altering the activity of these neurotransmitters. To test this hypothesis, male rats received peripheral (0, 100, or 500 microg ip), or central (0 or 5 microg icv) injections of leptin. The animals were killed 5 h later, and their brains were removed, frozen, and sectioned. Serum was collected to measure leptin and corticosterone by RIA. The paraventricular nucleus (PVN), arcuate nucleus (AN), ventromedial hypothalamus (VMH), dorsomedial dorsal nucleus (DMD), median eminence (ME), and medial preoptic area (MPA) were obtained using Palkovits' microdissection technique, and monoamine concentrations in these areas were determined using HPLC-EC. Intraperitoneal administration of leptin increased serum leptin concentrations in a dose-dependent manner (P < 0.05). Both intraperitoneal and intracerebroventricular administration of leptin decreased serum corticosterone significantly (P < 0.05). Norepinephrine (NE) concentration decreased significantly in the PVN, AN, and VMH after both intraperitoneal and intracerebroventricular administration of leptin (P < 0.05). NE concentrations decreased significantly in the DMN after intracerebroventricular administration of leptin (P < 0.05). Leptin treatment (both ip and icv) decreased dopamine concentrations significantly in the PVN. Serotonin (5-HT) concentration decreased significantly in the PVN after both intraperitoneal and intracerebroventricular injections of leptin and decreased in the VMH only with intracerebroventricular treatment of leptin. Leptin did not affect any of the monoamines in the ME and MPA. These results indicate that both central and systemic administration of leptin can affect hypothalamic monoamines in a region-specific manner, which, in turn, could mediate many of leptin's central and neuroendocrine effects.

Neuroendocrine effects of perfluorooctane sulfonate in rats.

Perfluorooctane sulfonate (PFOS) is a degradation product of sulfonyl-based fluorochemicals that are used extensively in industrial and household applications. Humans and wildlife are exposed to this class of compounds from several sources. Toxicity tests in rodents have raised concerns about potential developmental, reproductive, and systemic effects of PFOS. However, the effect of PFOS on the neuroendocrine system has not been investigated thus far. In this study, adult female rats were injected intraperitoneally with 0, 1, or 10 mg PFOS/kg body weight (BW) for 2 weeks. Food and water intake, BW, and estrous cycles were monitored daily. At the end of treatment, PFOS levels in tissues were measured by high-performance liquid chromatography (HPLC) interfaced with electrospray mass spectrometry. Changes in brain monoamines were measured by HPLC with electrochemical detection, and serum corticosterone and leptin were monitored using radioimmunoassay. Treatment with PFOS produced a dose-dependent accumulation of this chemical in various body tissues, including the brain. PFOS exposure decreased food intake and BW in a dose-dependent manner. Treatment with PFOS affected estrous cyclicity and increased serum corticosterone levels while decreasing serum leptin concentrations. PFOS treatment also increased norepinephrine concentrations in the paraventricular nucleus of the hypothalamus. These results indicate that exposure to PFOS can affect the neuroendocrine system in rats.

Diabetes-induced neuroendocrine changes in rats: role of brain monoamines, insulin and leptin.

Diabetes is characterized by hyperphagia, polydypsia and activation of the HPA axis. However, the mechanisms by which diabetes produces these effects are not clear. This study was conducted to examine the effects of diabetes on the neuroendocrine system and to see if treatment with insulin and/or leptin is capable of reversing these effects. Streptozotocin-induced diabetic adult male rats were subjected to the following treatments: vehicle, insulin (2 U/day, s.c.), leptin (100 microg/kg BW) or leptin+insulin every day for 2 weeks. Food intake, water intake, and body weight were monitored daily. We measured changes in monoamine concentrations in discrete nuclei of the hypothalamus at the end of treatment. Diabetes produced a marked increase in food intake and water intake and this effect was completely reversed by insulin treatment and partially reversed by leptin treatment (P<0.05). Diabetes caused an increase in norepinephrine (NE) concentrations in the paraventricular nucleus with a concurrent increase in serum corticosterone. Treatment with insulin and leptin completely reversed these effects. Induction of diabetes also increased the concentrations of NE, dopamine and serotonin in the arcuate nucleus and NE concentrations in the lateral hypothalamus, ventromedial hypothalamus (VMH) and suprachiasmatic nucleus (P<0.05). Although insulin treatment was capable of reversing all these changes, leptin treatment was unable to decrease diabetes-induced increase in NE concentrations in the VMH. These data provide evidence that hypothalamic monoamines could mediate the neuroendocrine effects of diabetes and that insulin and leptin act as important signals in this process.