Prenatal exposure to bisphenol A and/or diethylhexyl phthalate alters stress responses in rat offspring in a sex- and dose-dependent manner

Background: Prenatal exposures to endocrine disrupting chemicals (EDCs) are correlated with adverse behavioral outcomes, but the effects of combinations of these chemicals are unclear. The aim of this study was to determine the dose-dependent effects of prenatal exposure to EDCs on male and female behavior. Methods: Pregnant Sprague-Dawley rats were orally dosed with vehicle, bisphenol A (BPA) (5 μg/kg body weight (BW)/day), low-dose (LD) diethylhexyl phthalate (DEHP) (5 μg/kg BW/day), high-dose (HD) DEHP (7.5 mg/kg BW/day), a combination of BPA and LD-DEHP (B + D (LD)), or a combination of BPA and HD-DEHP (B + D (HD)) on gestational days 6-21. Adult offspring were subjected to the Open Field Test (OFT), Elevated Plus Maze (EPM), and Shock Probe Defensive Burying test (SPDB) in adulthood. Body, adrenal gland, and pituitary gland weights were collected at sacrifice. Corticosterone (CORT) was measured in the serum. Results: Female EDC-exposed offspring showed anxiolytic effects in the OFT, while male offspring were unaffected. DEHP (HD) male offspring demonstrated a feminization of behavior in the EPM. Most EDC-exposed male offspring buried less in the SPDB, while their female counterparts showed reduced shock reactivity, indicating sex-specific maladaptive alterations in defensive behaviors. Additionally, DEHP (LD) males and females and B + D (LD) females displayed increased immobility in this test. DEHP (LD) alone and in combination with BPA led to lower adrenal gland weights, but only in male offspring. Finally, females treated with a mixture of B + D (HD) had elevated CORT levels. Conclusion: Prenatal exposure to BPA, DEHP, or a mixture of the two, affects behavior, CORT levels, and adrenal gland weights in a sex- and dose-dependent manner.

Role of cytokines and reactive oxygen species in brain aging

Aging is a complex process that produces profound effects on the brain. Although a number of external factors can promote the initiation and progression of brain aging, peripheral and central changes in the immune cells with time, also play an important role. Immunosenescence, which is an age-associated decline in immune function and Inflammaging, a low-grade inflammatory state in the aging brain contribute to an elevation in cytokine and reactive oxygen species production. In this review, we focus on the pro-inflammatory state that is established in the brain as a consequence of these two phenomena and the resulting detrimental changes in brain structure, function and repair that lead to a decline in central and neuroendocrine function.

Evaluation of the Central Effects of Systemic Lentiviral-Mediated Leptin Delivery in Streptozotocin-Induced Diabetic Rats

Type 1 diabetes (T1D) is characterized by hyperphagia, hyperglycemia and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We have reported previously that daily leptin injections help to alleviate these symptoms. Therefore, we hypothesized that leptin gene therapy could help to normalize the neuroendocrine dysfunction seen in T1D. Adult male Sprague Dawley rats were injected i.v. with a lentiviral vector containing the leptin gene or green fluorescent protein. Ten days later, they were injected with the vehicle or streptozotocin (STZ). HPA function was assessed by measuring norepinephrine (NE) levels in the paraventricular nucleus (PVN) and serum corticosterone (CS). Treatment with the leptin lentiviral vector (Lepvv) increased leptin and insulin levels in non-diabetic rats, but not in diabetic animals. There was a significant reduction in blood glucose levels in diabetic rats due to Lepvv treatment. Both NE levels in the PVN and serum CS were reduced in diabetic rats treated with Lepvv. Results from this study provide evidence that leptin gene therapy in STZ-induced diabetic rats was able to partially normalize some of the neuroendocrine abnormalities, but studies with higher doses of the Lepvv are needed to develop this into a viable option for treating T1D.

Prenatal exposure to bisphenols affects pregnancy outcomes and offspring development in rats

The objective of this study was to evaluate the effects of gestational exposure to low doses of bisphenol A (BPA), bisphenol S (BPS), and bisphenol F (BPF) on pregnancy outcomes and offspring development. Pregnant Sprague-Dawley rats were orally dosed with vehicle, 5 μg/kg body weight (BW)/day of BPA, BPS and BPF, or 1 μg/kg BW/day of BPF on gestational days 6-21. Pregnancy and gestational outcomes, including number of abortions and stillbirths, were monitored. Male and female offspring were subjected to morphometry at birth, followed by pre- and post-weaning body weights, post-weaning food and water intakes, and adult organ weights. Ovarian follicular counts were also obtained from adult female offspring. We observed spontaneous abortions in over 80% of dams exposed to 5 μg/kg of BPF. BPA exposure increased Graafian follicles in female offspring, while BPS and BPF exposure decreased the number of corpora lutea, suggesting reduced ovulation rates. Moreover, BPA exposure increased male kidney and prostate gland weights, BPF decreased epididymal adipose tissue weights, and BPS had modest effects on male abdominal adipose tissue weights. Prenatal BPS exposure reduced anogenital distance (AGD) in male offspring, suggesting possible feminization, whereas both BPS and BPA induced oxidative stress in the testes. These results indicate that prenatal exposure to BPF affects pregnancy outcomes, BPS alters male AGD, and all three bisphenols alter certain organ weights in male offspring and ovarian function in female offspring. Altogether, it appears that prenatal exposure to BPA or its analogues can induce reproductive toxicity even at low doses.

Oleic acid stimulates monoamine efflux through PPAR-α: Differential effects in diet-induced obesity

Obesity continues to be a growing health concern around the world, and elevated levels of free fatty acids as a result of high-fat intake might play a role in neuroendocrine alterations leading to obesity. However, it is unclear how fatty acids affect neuroendocrine functions and energy metabolism. Since hypothalamic monoamines play a crucial role in regulating neuroendocrine functions relating to energy balance, we investigated the direct effects of oleic acid on hypothalamic monoamines and hypothesized that oleic acid would activate peroxisome proliferator-activated receptor alpha (PPAR-α), a nuclear transcription factor involved with fatty acid metabolism, to affect monoamines. We also hypothesized that this response would be subdued in diet-induced obesity (DIO). To test these hypotheses, hypothalami from Sprague Dawley and DIO rats were incubated with 0 (Control), 0.00132 mM, 0.132 mM, 1.32 mM oleic acid, 50 μM MK 886 (a selective PPAR- α antagonist), or oleic acid + MK 886 in Krebs Ringers Henseleit (KRH) solution. HPLC-EC was used to measure monoamine levels in perfusates. Oleic acid produced a significant increase in norepinephrine, dopamine, and serotonin levels in a dose-dependent manner, and incubation with MK886 blocked these effects. The effect of oleic acid on hypothalamic monoamines was attenuated in DIO rats. These findings suggest that PPARα probably plays an essential role in fatty acid sensing in the hypothalamus, by affecting monoamine efflux and DIO rats are resistant to the effects of oleic acid.

SAT-717 Region-Specific Effects of the Exposome on Brain Monoamine Levels in Female Rats

Prenatal programming with endocrine disrupting chemicals (EDCs), in particular the ubiquitous plasticizers bisphenol A (BPA) and di(2-ethylhexyl) phthalate (DEHP), can induce long-lasting behavioral changes in rats. Additionally, changes in estrogen are correlated with the development of mood disorders in women; however, the underlying neurobiological mechanisms are unclear. This study was conducted to determine the cumulative effects of prenatal exposure to EDCs followed by chronic estradiol treatment in adult female rats on monoamine levels in the prefrontal cortex (PFC) and hippocampus (HC). Dams were orally administered saline (control; 10 µL/kg), BPA (B; 5 µg/kg), DEHP (D; 7.5 mg/kg) or a combination of BPA+DEHP (B+D) during days 6 through 21 of pregnancy. Adult female offspring were sham-implanted or implanted with pellets that release 17β-estradiol (E2) for 90 days (20 ng/day; Innovative Research America). The offspring then underwent a battery of behavioral tests at the end of treatment. Brains collected from the offspring were sectioned and the PFC and HC were microdissected and analyzed for levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT), using High-Performance Liquid Chromatography (HPLC). Significant reductions in monoamine levels were observed in the PFC while NE and 5-HT levels were markedly reduced in the HC after prenatal exposure to D or BD. BPA’s effects on monoamines were comparatively modest. E2 exposure increased DA but decreased 5-HT levels in the PFC of control animals. Prenatal exposure to EDCs made the offspring non-responsive to E2. The marked reduction in monoamine levels could have implications for learning and memory.

SAT-719 Prenatal Exposure to Bisphenol A, S and F Increases Blood Pressure in Female Rats

Cardiovascular diseases are the leading causes of mortality among men and women. With the new blood pressure guidelines from the American Heart Association, almost half of the United States population has hypertension (45.6%). The reasons for this high prevalence of hypertension in our population could be several, but the effect of emerging contaminants are overlooked and understudied. Bisphenol-A (BPA) is a widely used plasticizing agent that contaminates the environment. Most humans are exposed to BPA on a daily basis and urine levels of this endocrine disrupting chemical (EDC) are positively correlated with hypertension. The FDA banned the use of BPA in baby bottles in 2012, however, it is still being used in food containers and plastics. Currently, several BPA analogs such as bisphenol-S (BPS) and bisphenol-F (BPF) are used to replace BPA in the plastic industry. But their physiological effects are not clear. In order to study the effects of these EDCs on the development of hypertension, we exposed pregnant Sprague Dawley (SD) rats to saline, 5 µg/Kg BW of BPA, BPS or 1µg/kg BW of BPF. The offspring were allowed to reach adulthood before implantation with a radiotelemeter (Data Sciences International; HD-S10) in the femoral artery for undisturbed monitoring of systolic, diastolic and mean arterial blood pressure and heart rate. Recordings were measured once a week for 11 weeks over 24 hours to establish day and night readings. Night-time systolic BP was significantly elevated in BPA, BPF and BPS exposed rats compared to control. During the day, systolic BP was significantly higher in the BPA group compared to control. Diastolic BP was elevated in the BPS and BPF groups. Heart rate was elevated the most in the BPS group. These results indicate that prenatal exposure to low levels of BPA analogs has a profound effect on hypertension.

Chronic estrogen affects TIDA neurons through IL-1β and NO: effects of aging

Women are chronically exposed to estrogens through oral contraceptives, hormone replacement therapy or environmental estrogens. We hypothesized that chronic exposure to low levels of estradiol-17β (E2) can induce inflammatory and degenerative changes in the tuberoinfundibular dopaminergic (TIDA) system leading to reduced dopamine synthesis and hyperprolactinemia. Young (Y; 3–4 months) and middle-aged (MA; 10–12 months) Sprague-Dawley rats that were intact or ovariectomized (OVX) were either sham-implanted or implanted with a slow-release E2 pellet (20 ng E2/day for 90 days). To get mechanistic insight, adult 3- to 4-month-old WT, inducible nitric oxide synthase (iNOS) and IL-1 receptor (IL-1R) knockout (KO) mice were subjected to a similar treatment. Hypothalamic areas corresponding to the TIDA system were analyzed. E2 treatment increased IL-1β protein and nitrate levels in the arcuate nucleus of intact animals (Y and MA). Nitration of tyrosine hydroxylase in the median eminence increased with E2 treatment in both intact and OVX animals. There was no additional effect of age. This was accompanied by a reduction in dopamine levels and an increase in prolactin in intact animals. E2 treatment increased nitrate and reduced dopamine levels in the hypothalamus and increased serum prolactin in WT mice. In contrast, the effect of E2 on nitrate levels was blocked in IL-1R KO mice and the effect on dopamine and prolactin were blocked in iNOS KO animals. Taken together, these results show that chronic exposure to low levels of E2 decreases TIDA activity through a cytokine-nitric oxide-mediated pathway leading to hyperprolactinemia and that aging could promote these degenerative changes.

Chronic estradiol exposure - harmful effects on behavior, cardiovascular and reproductive functions

Estradiol (E2) is a female hormone that is produced largely by the ovaries, but also by the adrenal glands, fat and liver. It is present in the circulation of both males and females. Many studies in the literature have described how E2 is beneficial to the body in terms of preventing bone loss, affording protection in ischemia reperfusion injury, relieving symptoms of menopause, maintaining vaginal health and helping with ovarian failure or hypogonadism. Beneficial effects on the brain have been reported to include protection against memory loss, neuronal degeneration, changes in cognition, mood and behavior. However, the effects of E2 exposure on the neuroendocrine system have not been understood completely. This is because differences in doses, preparation and duration of exposure have produced variable results ranging from beneficial, to no change, or to detrimental. Studies in our lab over the last few years have shown that chronic exposures to low levels of E2 in young rats can produce specific effects on the neuroendocrine system. We have observed that these exposures can induce reproductive senescence, hypertension, anxiety-like behavior and cause degenerative changes in specific neuronal populations leading to hyperprolactinemia. The purpose of the review is to present evidence from the literature for these effects and to discuss the underlying molecular mechanisms.

Chronic exposure to low doses of estradiol-17ß increases blood pressure in young female rats: A possible role for central Endothelin-1

Previously, we demonstrated that chronic exposure to low levels of estradiol-17β (E2) increases mean arterial pressure (MAP) in young female Sprague-Dawley (SD) rats, however, the underlying mechanisms are unclear. Since endothelin-1 (ET-1) is implicated in blood pressure (BP) regulation, we hypothesized that E2’s effects on MAP are mediated through central ET-1. To test this, young female SD rats were either sham implanted or implanted s.c. with slow-release E2 pellets (20 ng/day for 90 days). BP was monitored by telemetry. After 75 days of E2 exposure, ET_A antagonist or vehicle was administered i.c.v. After 90 days of E2 exposure, rats were sacrificed, and the paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM) were microdissected for gene expression and protein analysis of ET-1 and its receptors. E2 exposure increased MAP after pellet implantation. Gene expression of ET-1 and ET_A but not ET_B receptors were upregulated in the PVN and RVLM of E2 treated animals. Further, the protein levels of ET_A receptor were also increased in the PVN of E2 treated animals. However, i.c.v. infusion of the ET_A antagonist did not completely block the increase in blood pressure. Our results suggest that increases in central ET-1 activity could possibly play a role in chronic E2-induced increase in BP but further studies are needed to completely understand the contribution of ET-1 in this phenomenon.

Differential effects of prenatal stress on metabolic programming in diet-induced obese and dietary-resistant rats

Stress during pregnancy is a known contributing factor for the development of obesity in the offspring. Since maternal obesity is on the rise, we wanted to identify the effects of prenatal stress in the offspring of diet-induced obese (DIO) rats and compare them with the offspring of dietary-resistant (DR) rats. We hypothesized that prenatal stress would make both DIO and DR offspring susceptible to obesity, but the effect would be more pronounced in DIO rats. Pregnant DIO and DR rats were divided into two groups: nonstressed controls (control) and prenatal stress (subjected to restraint stress, three times/day from days 14 to 21 of gestation). After recording birth weight and weaning weight, male offspring were weaned onto a chow diet for 9 wk and shifted to a high-fat (HF) diet for 1 wk. At the end of the 10th wk the animals were euthanized, and visceral adipose mass, blood glucose, serum insulin, and C-peptide levels were measured. Prenatal stress resulted in hyperinsulinemia and higher C-peptide levels without altering caloric intake, body weight gain, or fat mass in the DIO offspring after 1 wk of HF intake, but not in DR offspring. To determine the mechanism underlying the hyperinsulinemia, we measured the levels of CEACAM1 that are responsible for insulin clearance. CEACAM1 levels in the liver were reduced in prenatally stressed DIO offspring after the HF challenge, suggesting that preexisting genetic predisposition in combination with prenatal stress increases the risk for obesity in adulthood, especially when offspring are fed a HF diet.

Chronic exposures to low levels of estradiol and their effects on the ovaries and reproductive hormones: Comparison with aging

Aging in female rats is characterized by a state called "constant estrous" in which rats are unable to ovulate, have polycystic ovaries and moderately elevated estrogen levels. We hypothesized that chronic exposure of young animals to low levels of E2 can produce reproductive changes similar to that seen in aging animals. Adult female rats were sham-implanted (control) or implanted with slow-release E2 (20 ng/day) pellets for 30, 60, or 90 days. Old constant estrous (OCE) rats were used for comparison. Estrous cyclicity was monitored periodically. At the end of treatment, animals were sacrificed, trunk blood was collected for hormone measurements and ovaries for immunohistochemistry. Young animals became acyclic with increasing duration of E2 exposure while OCE rats were in a state of acyclicity. Ovaries became increasingly more cystic with E2 exposure, and were comparable to OCE rats; however, there was a marked reduction in interstitial tissue with exogenous E2 treatment. Exogenous E2 also decreased Mullerian inhibiting substance expression, increased infiltration of macrophages without much impact on apoptosis in the ovaries. Serum testosterone levels decreased in E2-treated young animals, while it increased significantly in OCE rats. There was a marked reduction in LH but not FSH levels with E2 exposure in both young and old animals. These results indicate that even very low doses of E2 are capable of inducing aging-like changes in young animals.

Chronic estradiol-17β exposure increases superoxide production in the rostral ventrolateral medulla and causes hypertension: reversal by resveratrol

Women are exposed to estrogen in several forms, such as oral contraceptive pills and hormone replacement therapy. Although estrogen was believed to be cardioprotective, lately, its beneficial effects are being questioned. Recent studies indicate that oxidative stress in the rostral ventrolateral medulla (RVLM) may play a role in the development of hypertension. Therefore, we hypothesized that chronic exposure to low levels of estradiol-17β (E(2)) leads to hypertension in adult-cycling female Sprague Dawley (SD) rats potentially through generation of superoxide in the RVLM. To test this hypothesis, young adult (3 or 4 mo old) female SD rats were either sham-implanted or implanted (subcutaneously) with slow-release E(2) pellets (20 ng/day) for 90 days. A group of control and E(2)-treated animals were fed lab chow or chow containing resveratrol (0.84 g/kg of chow), an antioxidant. Rats were implanted with telemeters to continuously monitor blood pressure (BP) and heart rate (HR). At the end of treatment, the RVLM was isolated for measurements of superoxide. E(2) treatment significantly increased mean arterial pressure (mmHg) and HR (beats/min) compared with sham rats (119.6 ± 0.8 vs. 105.1 ± 0.7 mmHg and 371.7 ± 1.5 vs. 354.4 ± 1.3 beats/min, respectively; P < 0.0001). Diastolic and systolic BP were significantly increased in E(2)-treated rats compared with control animals. Superoxide levels in the RVLM increased significantly in the E(2)-treated group (0.833 ± 0.11 nmol/min·mg) compared with control (0.532 ± 0.04 nmol/min·mg; P < 0.05). Treatment with resveratrol reversed the E(2)-induced increases in BP and superoxide levels in the RVLM. In conclusion, these findings support the hypothesis that chronic exposure to low levels of E(2) induces hypertension and increases superoxide levels in the RVLM and that this effect can be reversed by resveratrol treatment.

Developmental programming: impact of excess prenatal testosterone on intrauterine fetal endocrine milieu and growth in sheep

Prenatal testosterone excess in sheep leads to reproductive and metabolic disruptions that mimic those seen in women with polycystic ovary syndrome. Comparison of prenatal testosterone-treated sheep with prenatal dihydrotestosterone-treated sheep suggests facilitation of defects by androgenic as well as androgen-independent effects of testosterone. We hypothesized that the disruptive impact of prenatal testosterone on adult pathology may partially depend on its conversion to estrogen and consequent changes in maternal and fetal endocrine environments. Pregnant Suffolk sheep were administered either cottonseed oil (control) or testosterone propionate in cottonseed oil (100 mg, i.m. twice weekly), from Day 30 to Day 90 of gestation (term is ~147 d). Maternal (uterine) and fetal (umbilical) arterial samples were collected at Days 64-66, 87-90, and 139-140 (range; referred to as D65, D90, and D140, respectively) of gestation. Concentrations of gonadal and metabolic hormones, as well as differentiation factors, were measured using liquid chromatography/mass spectrometer, radioimmunoassay, or ELISA. Findings indicate that testosterone treatment produced maternal and fetal testosterone levels comparable to adult males and D65 control male fetuses, respectively. Testosterone treatment increased fetal estradiol and estrone levels during the treatment period in both sexes, supportive of placental aromatization of testosterone. These steroidal changes were followed by a reduction in maternal estradiol levels at term, a reduction in activin A availability, and induction of intrauterine growth restriction in D140 female fetuses. Overall, our findings provide the first direct evidence in support of the potential for both androgenic as well as estrogenic contribution in the development of adult reproductive and metabolic pathology in prenatal testosterone-treated sheep.

Chronic exposure to a high-fat diet affects stress axis function differentially in diet-induced obese and diet-resistant rats

OBJECTIVE

Consumption of a high-fat (HF) diet is a contributing factor for the development of obesity. HF diet per se acts as a stressor, stimulating hypothalamo-pituitary-adrenal (HPA) axis activity resulting in elevated glucocorticoid levels; however, the mechanism behind this activation is unclear. We hypothesized that consumption of an HF diet activates HPA axis by increasing norepinephrine (NE) in the paraventricular nucleus (PVN) of the hypothalamus, leading to elevation in corticotrophin-releasing hormone (CRH) concentration in the median eminence (ME) resulting in elevated serum corticosterone (CORT).

SUBJECTS

To test this hypothesis, diet-induced obese (DIO) and diet-resistant (DR) rats were exposed to either chow or HF diet for 6 weeks.

MEASUREMENTS

At the end of 6 weeks, NE in the PVN was measured using HPLC, CRH in the ME, and CORT and leptin levels in the serum were measured using RIA and ELISA, respectively. The gene expression of tyrosine hydroxylase (TH), the rate-limiting enzyme in NE synthesis, and leptin receptor in brainstem noradrenergic nuclei were also measured.

RESULTS

HF diet increased PVN NE in both DIO and DR rats (P<0.05). However, this was accompanied by increases in CRH and CORT secretion only in DR animals, but not in DIO rats. Leptin receptor mRNA levels in the brainstem noradrenergic areas were not affected in both DIO and DR rats. However, HF diet increased TH mRNA levels only in DIO rats.

CONCLUSION

Significant differences occur in all the arms of HPA axis function between DIO and DR rats. Further studies are needed to determine whether this could be a causative factor or a consequence to obesity.

Chronic exposure to low levels of oestradiol-17beta affects oestrous cyclicity, hypothalamic norepinephrine and serum luteinising hormone in young intact rats

Chronic exposure to oestrogens is known to inhibit the secretion of luteinising hormone (LH) in rats, leading to anovulation. Hypothalamic catecholamines, norepinephrine and dopamine play an important role in LH regulation. However, the effects of chronic exposure to low levels of oestradiol on hypothalamic catecholamines have not been investigated thoroughly. In the present study, adult female Sprague-Dawley rats were either sham implanted or implanted with 17beta-oestradiol (E(2)) pellets (20 ng/day) for 30 (E-30), 60 (E-60) or 90 (E-90) days. E(2) exposure affected oestrous cyclicity and ovarian morphology in a duration-dependent manner. There was no change in oestrous cyclicity in E-30 rats; however, 75% of E-60 and 95% of E-90 rats were acyclic (P < 0.05). Cycling rats from E-30 or the control group were killed at different time points on the afternoon of pro-oestrous. E-30 rats in oestrous, constant oestrous rats in the E-60 and E-90 groups and a group of old constant oestrous (OCE) rats were killed at 12.00 h. LH was measured in the serum by radioimmunoassay. Individual hypothalamic nuclei that are involved in LH regulation were microdissected and analysed for norepinephrine and dopamine levels using high-performance liquid chromatography/electrochemical detection. Norepinephrine levels in the hypothalamic nuclei increased significantly in control and E-30 groups during the afternoon of pro-oestrous, which was accompanied by a rise in LH levels (P < 0.05). On the day of oestrous, norepinephrine concentrations in hypothalamic nuclei and serum LH were significantly lower in E-60, E-90 and OCE rats compared to E-30 and control rats. On the other hand, dopamine levels declined significantly in one hypothalamic nucleus. These results indicate that chronic E(2) exposure affects hypothalamic catecholamine and serum LH levels in a duration-dependent manner. This coincides well with the loss of cyclicity observed in these animals. These results suggest that repeated exposure to endogenous oestrogens could play a role in reproductive senescence.

Effect of L-dopa on interleukin-1 beta-induced suppression of luteinizing hormone secretion in intact female rats

BACKGROUND

The cytokine, interleukin-1 beta (IL-1 beta), increases during immune stress and is known to suppress the preovulatory luteinizing hormone (LH) surge in female rats by decreasing hypothalamic norepinephrine (NE). We hypothesized that IL-1 beta could produce this effect by decreasing NE biosynthesis.

METHODS

Female Sprague-Dawley rats were implanted with a push-pull cannula in the medial preoptic area (MPA) of the hypothalamus and a catheter in the jugular vein. They were treated i.p. with the vehicle or 5 microg of IL-1 beta, the NE precursor, L-dopa, or a combination of L-dopa and IL-1 beta at 1300 hours on the day of proestrus. They were subjected to push-pull perfusion and serial blood sampling. Perfusates were analyzed for NE levels and serum samples for LH.

RESULTS

IL-1 beta treatment blocked the increase in NE levels in the MPA and the LH surge. Treatment with L-dopa was able to partially restore both NE and LH levels during the afternoon of proestrus. IL-1 beta treatment caused failure of ovulation and this effect was also reversed by L-dopa.

CONCLUSIONS

These results suggest that IL-1 beta could decrease NE levels in the MPA to suppress reproductive functions and L-dopa can be used to counter this effect.

Interaction between GABA and norepinephrine in interleukin-1beta-induced suppression of the luteinizing hormone surge

Interleukin-1beta (IL-1beta), a cytokine that is closely associated with inflammation and immune stress, is known to interfere with reproductive functions. Earlier studies have demonstrated that IL-1beta inhibits the luteinizing hormone (LH) surge during the afternoon of proestrus in female rats. We have shown that this effect is most probably mediated through a reduction in norepinephrine (NE) levels in the medial preoptic area (MPA) of the hypothalamus. However, the mechanism by which IL-1beta decreases NE levels in the MPA is unclear. We hypothesized that the inhibitory neurotransmitter, GABA could play a role in decreasing NE levels in the MPA. To test this, ovariectomized, steroid-primed rats were injected (i.p.) with either PBS-BSA (control) or 5 microg of IL-1beta, alone or in combination with i.c.v. administration of GABA-A and GABA-B receptor antagonists, Bicuculline and CGP 35348 (CGP) respectively. Animals were subjected to push-pull perfusion of the MPA and perfusates collected at 30 min intervals were analyzed for both NE and GABA levels using HPLC-EC. Simultaneously, serial plasma samples were obtained through jugular catheters and were analyzed for LH levels using RIA. Compared to control rats, NE levels decreased significantly in the MPA in IL-1beta-treated rats (p<0.05). Concurrently, there was a significant increase in GABA levels in the MPA (p<0.05). The GABA-A receptor antagonist, bicuculline, was able to reverse the effect of IL-1beta on NE and LH, while the GABA-B receptor antagonist, CGP 35348 was without any effect. This leads us to conclude that the IL-1beta-induced suppression of the LH surge is most probably mediated through an increase in GABA levels in the MPA which causes a reduction in NE levels. This is probably one of the mechanisms by which IL-1beta inhibits reproductive functions.

Developmental programming of cardiovascular disorders: focus on hypertension

Increasing evidence suggests that adult cardiovascular disorders, e.g. hypertension, can be "programmed" in utero. The mechanisms that affect the developing fetus and lead to future cardiovascular disease are not fully established. This review addresses the possible involvement of maternal nutrition, sex steroids and other endocrine factors in the programming of hypertension in adulthood. Some possible mechanisms of subsequent development of hypertension in adulthood, such as elevated sympathetic and renin-angiotensin system activity, and failure of nephron development, also are discussed. Previous studies suggest that maternal undernutrition could be a major factor in fetal programming, but in light of the increased worldwide prevalence of obesity, maternal overnutrition is now receiving increased attention. Special emphasis is given here to this phenomenon. Obesity is associated with increased serum and tissue levels of proinflammatory cytokines, and loss of sensitivity to the adipokine leptin. It is postulated that this causes dysregulation of the hypothalamo-pituitary-adrenal axis, resulting in increased levels of circulating glucocorticoids. These factors could play a major role in programming, during the in utero period, of future hypertension in the offspring of obese mothers.

Human adenovirus 36 induces adiposity, increases insulin sensitivity, and alters hypothalamic monoamines in rats

OBJECTIVE

Human adenovirus 36 (Ad-36) increases adiposity and reduces serum lipids in chicken, mouse, and non-human primate models, and it is linked to obesity in sero-epidemiological studies in humans. Involvement of the central nervous system (CNS) or adipose tissue in the mechanism of Ad-36-induced adiposity is unknown. The effects of Ad-36 on adiposity and on the neuroendocrine system were investigated in a rat model.

RESEARCH METHODS AND PROCEDURES

Five-week-old male Wistar rats were inoculated intraperitoneally with Ad-36 or medium.

RESULTS

Despite similar food intakes, infected rats attained significantly greater body weight and fat pad weight by 30 weeks post-inoculation. Epididymal-inguinal, retroperitoneal, and visceral fat pad weights of the infected group were greater by 60%, 46%, and 86%, respectively (p < 0.00001). The fasting serum insulin level and homeostasis model assessment index indicated greater insulin sensitivity in the infected group. Visceral adipose tissue expression of glycerol 3-phosphate dehydrogenase, peroxisome proliferator-activated receptor gamma, and CCAAT/enhancer-binding protein alpha and beta was markedly increased in the infected animals compared with controls. Ad-36 decreased norepinephrine levels significantly in the paraventricular nucleus in infected vs. control rats (mean +/- standard error, 8.9 +/- 1.1 vs. 12.8 +/- 1.2 pg/microg protein; p < 0.05). Ad-36 markedly decreased serum corticosterone in infected vs. control rats (mean +/- standard error, 97 +/- 41.0 vs. 221 +/- 111 ng/mL; p < 0.005).

DISCUSSION

The results suggest that the pro-adipogenic effect of Ad-36 may involve peripheral as well as central effects. The male Wistar rat is a good model for the elucidation of metabolic and molecular mechanisms of Ad-36-induced adiposity.

Activation of the stress axis and neurochemical alterations in specific brain areas by concentrated ambient particle exposure with concomitant allergic airway disease

OBJECTIVE

Exposure to ambient particulate matter (PM) has been linked to respiratory diseases in people living in urban communities. The mechanism by which PM produces these diseases is not clear. We hypothesized that PM could act on the brain directly to stimulate the stress axis and predispose individuals to these diseases. The purpose of this study was to test if exposure to PM can affect brain areas involved in the regulation of neuroendocrine functions, especially the stress axis, and to study whether the presence of preexisting allergic airway disease aggravates the stress response.

DESIGN

Adult male rats (n = 8/group) with or without ovalbumin (OVA)-induced allergic airway disease were exposed to concentrated air particles containing PM with an aerodynamic diameter pound 2.5 microm (PM(2.5)) for 8 hr, generated from ambient air in an urban Grand Rapids, Michigan, community using a mobile air research laboratory (AirCARE 1). Control animals were exposed to normal air and were treated with saline.

MEASUREMENTS

A day after PM(2.5) exposure, animals were sacrificed and the brains were removed, frozen, and sectioned. The paraventricular nucleus (PVN) and other brain nuclei were microdissected, and the concentrations of aminergic neurotransmitters and their metabolites were measured using high-performance liquid chromatography with electrochemical detection. Serum corticosterone levels were measured using radioimmunoassay.

RESULTS

A significant increase in the concentration (mean +/- SE, pg/microg protein) of norepinephrine in the PVN was produced by exposure to concentrated ambient particles (CAPs) or OVA alone (12.45 +/- 2.7 and 15.84 +/- 2.8, respectively) or after sensitization with OVA (19.06 +/- 3.8) compared with controls (7.98 +/- 1.3 ; p < 0.05). Serum corticosterone (mean +/- SE, ng/mL) was significantly elevated in the OVA + CAPs group (242.786 +/- 33.315) and in the OVA-presensitized group (242.786 +/- 33.315) compared with CAP exposure alone (114.55 +/- 20.9). Exposure to CAPs (alone or in combination with OVA pretreatment) can activate the stress axis, and this could probably play a role in aggravating allergic airway disease.

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 μg ip), or central (0 or 5 μg 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.

Systemic Interleukin-1β stimulates the simultaneous release of norepinephrine in the paraventricular nucleus and the median eminence

Interleukin-1beta (IL-1beta), a cytokine with pronounced central effects such as fever, anorexia, analgesia, etc., is also known to activate the hypothalamo-pituitary-adrenal (HPA) axis. Corticotropin releasing hormone (CRH) neurons located in the hypothalamus are important for HPA activation. The cell bodies of CRH neurons are located in the paraventricular nucleus (PVN) and their terminals are present in the median eminence (ME). Although the catecholamines, norepinephrine (NE) and dopamine (DA) are believed to be crucial factors in the stimulation of CRH neurons, it is not clear if they affect the cell bodies or terminals of these neurons to cause HPA activation. This study was done to determine if IL-1beta affects NE and DA release at the level of CRH cell bodies or their terminals. Adult male Sprague-Dawley rats were implanted with two push-pull cannulae, one in the PVN and another in the ME, and were subjected to push-pull perfusion. They were treated either with 0, 1 or 5 microg of IL-1beta. Perfusates were collected for 2 h after treatment and analyzed for NE concentrations using HPLC-EC. NE levels in the control and low dose groups did not change significantly during the entire period of observation both in the PVN and ME. In contrast, treatment with 5 microg of IL-1beta produced a marked increase in NE release in the PVN at 20 and 40 min post-treatment. NE release in the ME increased from 10 to 140 min post-treatment. There were no significant changes in the release of DA from both these areas. These results indicate that IL-1beta increases NE levels both in the PVN and in the ME and this could be a possible mechanism by which it stimulates the HPA axis.

Aging alters norepinephrine release in the medial preoptic area in response to steroid priming in ovariectomized rats

Changes in luteinizing hormone (LH) secretion that are observed in aging animals have been attributed to a reduction in hypothalamic norepinephrine (NE). The reason for the reduction in NE levels with aging is unclear. We hypothesized that the responsiveness of noradrenergic neurons to ovarian steroids is altered during aging. To test this, regularly cycling female Sprague-Dawley rats (young: 4-5 months old and middle age: 8-11 months old) were implanted with a push-pull cannula in the medial preoptic area (MPA) and ovariectomized bilaterally. On the 8th day after ovariectomy, they were injected with estrogen (30 microg/100 microl corn oil, s.c.) at 1000 h and on the 9th day they were implanted with a jugular catheter. On the 10th day they were injected with progesterone (2 mg/100 microl corn oil, s.c.) at 1000 h and subjected to push-pull perfusion. Perfusate samples from the MPA were collected at the rate of 10 microl/min every 30 min from 1300 to 1800 h and blood samples (0.3 ml) were collected hourly. The perfusate samples were analyzed for NE and dopamine (DA) concentrations using high performance liquid chromatography with electrochemical detection and serum LH levels were determined by RIA. In young animals, NE release (mean+/-S.E., pg/min) was 4.0+/-1.1 pg/min at 1300 h and increased significantly (p<0.05) to 10.4+/-4.3 pg/min at 1500 h and remained elevated until 1600 h and then declined to 6.8+/-2.5 at 1730 h. In contrast, the increase in NE release occurred briefly in middle-aged animals and was delayed by an hour. LH patterns in both age groups followed the pattern in NE release. There was no change in the release of DA in both young and middle-aged animals. It is concluded that the altered responsiveness of noradrenergic neurons to steroid priming in middle-aged rats probably plays a critical role in the alterations seen in LH secretion in older animals.

Leptin inhibits norepinephrine efflux from the hypothalamus in vitro: role of gamma aminobutyric acid

Leptin, a hormone secreted by adipocytes, produces a number of central and neuroendocrine effects, the mechanisms behind which are not completely understood. Hypothalamic norepinephrine (NE) is involved in many of the neuroendocrine effects that are associated with leptin. Therefore, we hypothesized that leptin could affect hypothalamic NE activity to bring about its central and neuroendocrine effects. Because gamma aminobutyric acid (GABA) is known to affect the release of NE, we also tested the possibility that leptin-induced changes in NE could be mediated through GABA. The mediobasal hypothalami from adult male rats were incubated in an in vitro incubation system for four consecutive incubation periods of 60 min each at 37 degrees C in Krebs Ringers Henseleit (KRH) solution in an atmosphere of 95% O(2) and 5% CO(2.) After determining the basal release, the hypothalami were challenged with 0, 0.1, 1 or 10 nm of leptin, bicuculline (a GABA-A receptor antagonist; 10 microM) and bicuculline (10 microM) +10 nM of leptin during the second incubation period. Residual effects of leptin were measured in the third incubation where tissues were incubated with KRH alone, and the viability of tissues was determined in the fourth incubation when tissues were exposed to high K(+) KRH. NE levels in the incubation medium were measured using high-performance liquid chromatography with electrochemical detection (HPLC-EC). Leptin inhibited NE efflux from the hypothalamus in a dose-dependent manner. Moreover, incubation of hypothalami with 10 nM of leptin and bicuculline, a completely blocked the leptin-induced decrease in NE efflux. These results demonstrate for the first time that leptin could act directly on the hypothalamus to inhibit NE efflux through GABA. It was concluded that leptin could probably produce its central and neuroendocrine effects by modulating NE and GABA levels in the hypothalamus.

Central adaptation to chronic administration of interleukin-1beta (IL-1beta) in rats

Interleukin-1beta (IL-1beta), a cytokine, has been shown to induce a number of central and neuroendocrine effects. Prolonged treatment with IL-1beta is associated with adaptive responses in feeding, body temperature and hormone profiles. The purpose of the present study was to see if these effects are accompanied by changes in hypothalamic norepinephrine (NE) and to compare it with the acute effects of IL-1beta. Adult male Sprague-Dawley rats were treated (i.p.) with 5 microg of IL-1beta once (acute) or daily for 5 consequent days (chronic). The control animals received an injection of the vehicle for IL-1beta (0.1% PBS-BSA). Body weight, food intake, and rectal temperature were monitored daily. At the end of treatment, the animals were sacrificed, and specific areas of the hypothalamus were microdissected and analyzed for NE concentrations. Corticosterone levels were measured in the serum. Both acute and chronic IL-1beta treatment produced significant changes in a number of parameters. However, there were marked differences between the two treatment regimens. While acute treatment with IL-1beta increased NE concentrations in both the paraventricular nucleus and the median eminence (ME), chronic treatment increased NE concentrations only in the ME. A corresponding increase in serum corticosterone levels was observed with acute IL treatment. Chronic treatment with IL-1beta decreased body weight, and produced an initial decrease in food intake which returned to control levels by the fourth day of treatment. Chronic IL treatment also produced an initial increase in body temperature that returned to control levels by day 4. These results indicate that the effects of IL-1beta on central and neuroendocrine functions are dependent on the duration of the treatment and that the adaptive responses observed in feeding and body temperature after chronic IL treatment are accompanied by similar responses in brain NE.

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.

Effects of interleukin-1 beta on the steroid-induced luteinizing hormone surge: role of norepinephrine in the medial preoptic area

Interleukin-1beta (IL-1beta), a cytokine, is known to inhibit the preovulatory surge of luteinizing hormone (LH); however, the mechanism by which it does so is unclear. This study was done to see if this effect is mediated through hypothalamic catecholamines. Adult female Sprague-Dawley rats were ovariectomized and implanted with a push-pull cannula in the medial preoptic area (MPA) of the hypothalamus. They were injected subcutaneously with 30 microg of Estradiol on the day 8 after surgery and with 2mg of Progesterone on day 10 at 1000 h. On the day of perfusion (day 10), the rats were injected with IL-1beta or its vehicle at 1300 h. Perfusate samples from the MPA and blood samples from a jugular catheter were collected from 1300 to 1800 h. Catecholamine concentrations in the perfusate were measured using high performance liquid chromatography (HPLC)-EC and LH levels in the serum using RIA. Norepinephrine release in the MPA of control rats increased significantly at 1530, 1600, and 1630 h paralelling an increase in LH at 1600 h. In contrast, IL-1beta treatment blocked the LH surge and the rise in norepinephrine release in the MPA. No changes were observed in dopamine release, both in control and IL-treated animals. These results demonstrate for the first time that IL-induced suppression of the LH surge is probably mediated through inhibition of norepinephrine release in the MPA.

Lipopolysaccharide stimulates norepinephrine efflux from the rat hypothalamus in vitro: blockade by soluble IL-1 receptor

Lipopolysaccharide (LPS) has been shown to produce a number of central and neuroendocrine effects. While all mechanisms are not clear, it is believed that central catecholamines could be involved in this process. This study was done to investigate the direct effects of LPS on norepinephrine (NE) efflux from the medial basal hypothalamus in adult male rats using a combination of an in vitro incubation system and high performance liquid chromatography with electrochemical detection. Basal NE efflux was determined by incubating the hypothalami with Krebs Ringers Henseleit (KRH) alone for 60 min. Then, the hypothalami were incubated with KRH alone (control) or KRH containing 100 ng or 200 ng of LPS, 15 microg of soluble IL-1 receptor (sIL-1R) or a combination of 200 ng LPS and 5 or 15 microg of sIL-1R. In the third incubation period, the hypothalami were incubated with KRH alone to check for the residual effects of LPS if any. In the fourth incubation period, the hypothalami were incubated with high K+KRH to check for tissue viability. Incubation with LPS stimulated NE efflux in a dose-dependent manner. Incubation of hypothalami with 200 ng of LPS and 15 microg of sIL-1R completely blocked LPS-induced increase in NE efflux. These results indicate that LPS could act directly on the hypothalamus to stimulate the efflux of NE and this effect is probably mediated through IL-1.

Deprenyl stimulates the efflux of monoamines from the rat hypothalamus in vitro

The direct effects of L-deprenyl, a monoamine oxidase inhibitor, on the hypothalamus of male Sprague-Dawley rats was investigated by measuring the efflux of norepinephrine (NE), dopamine (DA), serotonin (5-HT), dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) using a combination of high performance liquid chromatography with electrochemical detection and an in vitro incubation system. After measuring basal efflux by incubating the hypothalami with Krebs-Ringers Henseleit (KRH) alone during the first incubation period, hypothalami were incubated either with the medium, KRH alone (0 mM), or KRH containing 0.1, 1, and 10 mM L-deprenyl. During the third incubation period, hypothalami were again incubated with KRH alone to measure the residual effects if any. During the final incubation period, the hypothalami were stimulated with high K(+) KRH. Deprenyl produced a dose-dependent increase in the efflux of NE, DA, and 5-HT from the hypothalami. Neurotransmitter efflux returned to pretreatment levels when L-deprenyl was removed from the medium. In contrast to NE, DA, and 5-HT, the efflux of the metabolites DOPAC and 5-HIAA was inhibited in a dose-dependent fashion after incubation with L-deprenyl. Results from this study demonstrate that L-deprenyl is capable of stimulating the efflux of neurotransmitters in vitro by a direct action on the hypothalamus.

The estrous cycle affects pseudorabies virus (PRV) infection of the CNS

Previous work had suggested that mucosal immunity may be affected by the stage of the estrous cycle. Here, susceptibility to a neurotropic virus infection at different stages of the estrous cycle was assessed in a rodent model after direct injection of the virus into visceral organs. In the first two experiments, female Sprague-Dawley rats were infected with pseudorabies virus (PRV, Bartha's K-strain) by injection into either the cervix or the kidney after monitoring their estrous cycle. After either 4- or 5-day survival period post-infection, the rats were euthanized by transcardially perfusion and peripheral and central nervous system tissues were removed for immunocytochemical staining. The number of infected neurons was counted in various regions. Statistical analysis revealed that: (1) the number of infected cells in the sympathetic or parasympathetic ganglion, or the dorsal root ganglia was not affected regardless of the stage of the estrous cycle after cervix injection with PRV; (2) in contrast, the number of infected neurons in the spinal cord was affected significantly by the stage of the estrous cycle during viral infection of the cervix; (3) after kidney infection, the number of infected neurons found within the spinal cord or dorsal root ganglia varied significantly across the estrous cycle. In both cases, animals infected in proestrus or estrus had fewer infected neurons than animals infected in diestrus I or diestrus II (proestrous and estrous animals had less than 20% of infected cells found in diestrus I or diestrus II rats). In the third experiment, older, persistent estrous or persistent diestrous rats were infected by kidney injection and given a 4-day survival period, prior to virus isolation from lower thoracic spinal cord. Animals in persistent estrous had significantly less virus per gram of tissue than the persistent diestrous rats. These data suggest that the CNS of animals in proestrus or estrus is less susceptible to PRV infection compared to animals in either diestrus I or diestrus II. Because estrogen replacement therapy is known to restore some immune functions during reproductive ageing, it is speculated that plasma estrogen levels modulate the central nervous system's susceptibility to viral infections.

Effects of chronic bromocriptine treatment on tyrosine hydroxylase (TH) mRNA expression, TH activity and median eminence dopamine concentrations in ageing rats

The purpose of this study was to investigate the age-related changes in the responsiveness of tuberoinfundibular dopamine (TIDA) neurones to chronic hypoprolactinemia induced by treatment with bromocriptine, a dopamine receptor agonist. In one experiment, TIDA neuronal activity after acute hypoprolactinemia or exogenous prolactin was monitored by measuring tyrosine hydroxylase (TH) activity in the stalk median eminence of middle-aged cycling female rats (10-12 months), old constant oestrous rats (18-20 months) and old pseudopregnant rats (22-24 months). In another experiment, middle-aged cycling (10-12 months) rats were treated with bromocriptine for 6 or 12 months. TH activity was measured in the stalk median eminence, TH mRNA levels were measured in the arcuate nucleus and dopamine concentrations were measured in the arcuate nucleus and median eminence. Responsiveness of TIDA neurones to exogenous prolactin and to the withdrawal of bromocriptine in these rats was also tested. While the TIDA neurones in all three age groups responded to acute hypoprolactinemia by showing a reduction in TH activity, older rats failed to respond to exogenous prolactin administration. In contrast, chronic hypoprolactinemia for 12 months enabled the rats to retain TIDA neuronal responsiveness to exogenous prolactin. It also decreased TIDA neuronal function as measured by dopamine concentrations in the median eminence, TH activity in the stalk median eminence and TH mRNA in the arcuate nucleus of ageing rats. The restoration of the responsiveness of these neurones to prolactin stimulation in older rats demonstrates for the first time that hypoprolactinemia produced by chronic bromocriptine treatment indeed provides a neuroprotective effect on TIDA neurones. These results indicate that maintaining a low level of neuronal activity by lowering prolactin levels may be a contributing factor in retaining the plasticity of TIDA neurones.

Correlations of norepinephrine release in the paraventricular nucleus with plasma corticosterone and leptin after systemic lipopolysaccharide: blockade by soluble IL-1 receptor

The purpose of the study was to investigate the effects of systemic lipopolysaccharide (LPS) on norepinephrine (NE) release in the paraventricular nucleus (PVN) and on plasma concentrations of corticosterone and leptin. Soluble IL-1 receptor (sIL-1R) was used to determine the role of interleukin-1 (IL-1) in these effects. Adult male rats were implanted with a push-pull cannula in the PVN and a jugular catheter to facilitate blood sampling. On the day of the experiment, after the collection of a pretreatment blood and perfusate sample, rats were injected (i.p.) with the vehicle for LPS (saline), 2.5 or 10 microg/kg BW LPS. Other groups of animals were treated i.p. with 25 microg of sIL-1R, or a combination of 10 microg/kg BW of LPS and 25 microg of sIL-1R, 5 min before and 90 min after LPS. Blood and perfusate samples were collected at 30-min intervals for 6 h. NE concentrations in the perfusate were measured using HPLC-EC and corticosterone and leptin levels in the plasma were measured using radioimmunoassay. NE release in the PVN was dose dependent and increased significantly within 90 min in response to the high dose of LPS and reached maximum levels around 180 min before declining gradually to pretreatment levels at 330 min. The corticosterone profile in LPS-treated animals was similar to the NE release profile in the PVN. In contrast, the LPS-induced increase in leptin levels reached a maximum at 210 min and remained elevated even at the end of the observation period. Treatment with sIL-1R completely blocked the LPS-induced effects. It is concluded that LPS stimulates NE release in the PVN and increases plasma concentrations of corticosterone and leptin and that these effects are mediated at least in part by IL-1.

Effects of bacterial lipopolysaccharide on central monoamines and fever in the rat: involvement of the vagus

Lipopolysaccharide (LPS) is known to produce a number of central and neuroendocrine effects but the mechanisms involved are still unclear. This study was done to investigate the possibility that LPS-induced fever and activation of central monoamines are mediated through the vagus. Adult male rats were subjected to sub-diaphragmatic vagotomy (SDV), or sham operation and treated with saline or LPS in saline (10 microg/kg bw) 2 h later. Rectal temperature was monitored at half-hourly intervals for 5 h after which the animals were sacrificed and monoamine concentrations in hypothalamic nuclei were measured using HPLC-EC. SDV delayed the rise in rectal temperature induced by LPS by 1 h when compared to Sham animals. It also increased the concentrations of monoamines in the paraventricular nucleus of both Sham and SDV rats. This indicates that routes other than the vagus probably mediate LPS' actions on the central nervous system.

Systemic administration of lipopolysaccharide increases plasma leptin levels: blockade by soluble interleukin-1 receptor

Lipopolysaccharide (LPS) is known to produce several central and neuroendocrine effects and some of these effects are believed to be mediated through cytokines and other proteins. One such protein, leptin, produced by adipose tissue has been shown to cause anorexia, a central effect associated with LPS treatment. This raised the possibility that LPS-induced effects on feeding behavior may be mediated through leptin. This study was done to investigate the effects of systemic administration of LPS on plasma leptin levels in rats and the possible involvement of interleukin-1 (IL-1) in this mechanism. Adult male rats were implanted with indwelling jugular catheters and after collecting two pretreatment blood samples, the animals were injected (i.p.) with saline, 5 microg, 10 microg, or 25 microg/kg BW of LPS, or treated with 25 microg of soluble IL-1 receptor (sIL-1R) 5 min before and 90 min after 25 microg/kg BW of LPS. Posttreatment blood samples were collected at 30 min intervals for a period of 6 h. Plasma leptin concentrations were measured by radioimmunoassay. Treatment with saline did not produce any change in plasma leptin levels. In contrast, each of the three doses of LPS produced a dose-dependent increase in plasma leptin levels within 120 min. Leptin levels remained elevated for the next 4 h. Treatment with sIL-1 R completely blocked the LPS-induced increase in leptin levels, indicating that this effect is in fact mediated through IL-1. These results indicate that leptin could be a possible mediator of LPS-induced effects on feeding.

Lipopolysaccharide-induced changes in monoamines in specific areas of the brain: blockade by interleukin-1 receptor antagonist

The purpose of this study was to examine the specificity in the effects of lipopolysaccharide (LPS) on monoamine concentrations in different areas of the brain and the involvement of interleukin-1 (IL-1) in the LPS-induced effects. Adult male rats were injected i.p. with saline, 10 micrograms/kg body weight of LPS, or treated with 250 micrograms of IL-1 receptor antagonist (IL-1ra) 5 min before and 2 h after LPS. Several brain areas including the hippocampus (HI), caudate putamen (CP), the hypothalamic paraventricular nucleus (PVN), arcuate nucleus (AN), median eminence (ME) and the medial preoptic area (MPA) were microdissected and analyzed for neurotransmitter concentrations by HPLC-EC. LPS treatment produced marked increases in the concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the PVN. In the AN, it increased DA concentrations and was without any effect on the MPA, ME, CP and HI. Treatment with IL-1ra in combination with LPS completely blocked the LPS-induced effects. It is concluded that LPS produces highly specific changes in monamine metabolism in the hypothalamus and that these effects are mediated at least in part by IL-1beta.

Specificity of interleukin-1beta-induced changes in monoamine concentrations in hypothalamic nuclei: blockade by interleukin-1 receptor antagonist

The purpose of this study was to examine specificity in the effects of interleukin-1beta (IL-1beta) on monoamines in various areas of the hypothalamus. Adult male rats were injected i.p. with saline or 2.5 or 5.0 microg of IL-1beta or were pretreated with 500 microg of IL-1 receptor antagonist (IL-1ra) followed 5 min later by 5 microg of IL-1beta. The paraventricular nucleus (PVN), arcuate nucleus (AN), median eminence (ME), and medial preoptic area (MPA) were microdissected and analyzed for neurotransmitter concentrations by high-performance liquid chromatography with electrochemical detection (HPLC-EC). In the PVN, IL treatment produced significant increases in the concentrations of norepinephrine (NE), dopamine (DA), DA metabolite dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), and its metabolite 5-hydroxyindoleacetic acid (5-HIAA). IL-1 treatment increased the concentrations of NE and DA in the AN but only of NE in the ME, and it was without any effect in the MPA. Pretreatment with IL-1ra completely blocked the IL-1 effects. It is concluded that IL-1 induces highly specific changes in monoamine metabolism in the hypothalamus, and the nature of these changes depends on specific hypothalamic nuclei.

Responsiveness of tuberoinfundibular dopaminergic neurons to 5-hydroxytryptophan: effects of aging

Serotonin is known to stimulate prolactin secretion by decreasing tyrosine hydroxylase (TH) activity in the tuberoinfundibular dopaminergic (TIDA) neurons. However, the effects of aging on the responsiveness of TIDA neurons to serotonin are not known. An effective way to increase serotonergic activity is to administer 5-hydroxytryptophan (5-HTP), a serotonin precursor. The present study was done to investigate the effects of 5-HTP on TIDA neuronal activity in aging animals. Middle-aged (10-12 mo), old (18-20 mo), and very old (22-24 mo) female Sprague-Dawley rats were bilaterally ovariectomized. Ten days later, they were injected iv with 50 mg/kg body wt of 5-HTP or the vehicle for 5-HTP (PBS-HCI). Twenty minutes later, m-hydroxybenzylhydrazine (NSD), a DOPA decarboxylase inhibitor, was administered. Ten minutes later, the animals were killed, and tyrosine hydroxylase (TH) activity was determined by measuring L-DOPA accumulation in the stalk median eminence by HPLC-EC. In all three groups, administration of 5-HTP increased serum prolactin levels significantly. In control middle-aged rats, TH activity (L-DOPA pg/ microg protein) was 33.0+/-5.6. Treatment with 5-HTP decreased TH activity by 60%. Similarly, 5-HTP treatment decreased TH activity by 52 and 56% in 18- to 20- and 22- to 24-mo-old rats, respectively, compared to the control rats. The magnitudes of the 5-HTP-induced decreases in TH activities in middle-aged, old, and very old rats were not different from each other. These results indicate that TIDA neuronal responsiveness to serotonin does not change with age and that 5-HTP is capable of stimulating PRL release even in very old rats.

Effects of chronic hyperprolactinemia on tuberoinfundibular dopaminergic neurons

Prolactin (PRL) secretion is under the inhibitory regulation of the tuberoinfundibular dopaminergic (TIDA) system. Short-term elevation in PRL levels has been shown to increase the activity of TIDA neurons, however, the responsiveness of TIDA neurons to chronically elevated serum PRL levels is controversial. The purpose of this study was to investigate the effects of prolonged elevations of serum PRL on TIDA neuronal activity. Female Sprague-Dawley rats (2-3 months old) were ovariectomized and implanted (s.c.) with haloperidol (HAL), a dopamine receptor antagonist for 6 or 9 months to produce hyperprolactinemia. Ovariectomized, sham-implanted rats were used as controls. Other groups of intact rats were implanted with HAL or sham-implanted for 9 months and then were implanted with PRL-producing MMQ cells for 6 weeks to further increase circulating PRL levels. TIDA neuronal activity was measured in terms of tyrosine hydroxylase (TH) activity in the stalk-median eminence and was correlated with changes in serum PRL levels. After 6 months of treatment, TH activity in HAL-treated rats was 130% higher than that in the control rats. After 9 months of treatment, TH activity in HAL-treated rats was 81% higher than that in control rats. This increase was significantly less than the increase that occurred after 6 months of treatment. Nine months of HAL-induced hyperprolactinemia followed by implantation of PRL-producing MMQ cells, which resulted in very high levels of PRL, did not increase TH activity in the stalk-median eminence. These results demonstrate that hyperprolactinemia over a prolonged period reduces the responsiveness of TIDA neurons, and these effects vary depending on the duration and intensity of hyperprolactinemia.

Deprenyl stimulates the release of luteinizing hormone from the pituitary in vitro

The direct effects of deprenyl on the pituitary were investigated by measuring the release of luteinizing hormone (LH) from the pituitary glands of male Sprague-Dawley rats in vitro. Basal release of LH was determined by incubating the pituitaries in Krebs-Ringer Henseleit (KRH) solution with 0, 0.1, 1, or 10 mM of deprenyl for 1 h. In the control group, LH release was not different in pre- and posttreatment periods. In contrast, in the 10 mM group, LH release increased by 436% (p<0.01). Incubation of pituitaries with 0.1 or 1 mM deprenyl did not alter LH release. It is concluded that deprenyl a monoamine oxidase inhibitor, can also act directly on the pituitary.

Cyclic changes in the release of norepinephrine and dopamine in the medial basal hypothalamus: effects of aging

Push-pull perfusion and HPLC were used to measure the release of norepinephrine (NE) and dopamine (DA) in the medial basal hypothalamus of young (4-5 months old), middle-aged (8-10 months old), and old (22-24 months old) rats. In the young animals, the afternoon of proestrus was characterized by a gradual increase in NE release and a simultaneous gradual decrease in DA release. The peak in NE release and the nadir in DA release occurred at about the time when the proestrous surges in serum LH and PRL are known to occur. No changes in NE and DA releases occurred in the afternoon of diestrus when serum LH and PRL are known to remain stable. In the middle-aged proestrous animals, the patterns of NE and DA releases were similar to those in the young proestrous animals, but the peak in NE release was attenuated and did not reach statistical significance. This corresponded with the reported attenuation in the LH surge in middle age. In the old persistently diestrous animals, NE and DA were released at constant rates, which correlated with the well-documented constant levels of serum LH and PRL in old age. These data provide an explanation for the simultaneous proestrous surges of LH and PRL and lead us to conclude that NE plays a facilitatory role in the LH surge, while DA, through its inhibitory action, regulates the PRL surge.(ABSTRACT TRUNCATED AT 250 WORDS)

Deprenyl reduces serum prolactin concentrations in rats

The effects of i.v. administration of deprenyl (2.5, 5, and 10.0 mg/Kg body wt), a monoamine oxidase inhibitor, on serum prolactin (PRL) concentrations were investigated in female Sprague-Dawley rats. In the rats treated with the highest dose (10 mg/Kg), serum PRL decreased by 48% (p < 0.05) within 30 min and remained depressed during a 240-min period. Serum PRL concentrations also decreased by 38% (p < 0.05) within 30 min in the rats treated with the 5 mg dose and remained low during the remainder of the period of observation. Serum PRL levels showed no change in the group treated with 2.5 mg of deprenyl/Kg BW, except at 240 min when it was 48% (p < 0.05) below the pretreatment levels. In the control group, injected with the vehicle (0.5 ml saline) no decreases in PRL levels were observed. The average serum PRL concentrations during the entire posttreatment period were 45% above the pretreatment levels in the control group, whereas they were 31% and 43% below the respective pretreatment levels in the 5 and 10 mg groups, respectively. In the 2.5 mg group, the average serum PRL levels during the posttreatment period were not different from those in the pretreatment period. It is concluded that deprenyl is a potent inhibitor of PRL release in the rat.

Systemic administration of interleukin-1 stimulates norepinephrine release in the paraventricular nucleus

The purpose of this study was to investigate the effects of circulating interleukin-1 beta (IL-1 beta) on the release of norepinephrine (NE) in the paraventricular nucleus (PVN). After intraperitoneal administration of IL-1 beta, NE was measured by high performance liquid chromatography in the perfusate collected from the PVN of conscious, freely moving rats by the technique of push-pull perfusion. IL-1 beta produced an increase in NE release. Both the strength and duration of NE release were dose-dependent. It is concluded that circulating IL-1 beta activates the noradrenergic innervation to the PVN and that this is part of the mechanism by which it stimulates the release of the corticotropin-releasing hormone (CRH) and produces its other neuroendocrine and central effects.