Effects of prenatal bisphenol-A exposure and postnatal overfeeding on cardiovascular function in female sheep.

Bisphenol-A (BPA) is a widely used endocrine-disrupting chemical. Prenatal exposure to BPA is known to affect birth weight, but its impact on the cardiovascular system has not been studied in detail. In this study, we investigated the effects of prenatal BPA treatment and its interaction with postnatal overfeeding on the cardiovascular system. Pregnant sheep were given daily subcutaneous injections of corn oil (control) or BPA (0.5 mg/kg/day in corn oil) from day 30 to day 90 of gestation. A subset of female offspring of these dams were overfed to increase body weight to ~30% over that of normal fed controls. Cardiovascular function was assessed using non-invasive echocardiography and cuff blood pressure (BP) monitoring at 21 months of age. Ventricular tissue was analyzed for gene expression of cardiac markers of hypertrophy and collagen at the end of the observation period. Prenatal BPA exposure had no significant effect on BP or morphometric measures. However, it increased atrial natriuretic peptide gene expression in the ventricles and reduced collagen expression in the right ventricle. Overfeeding produced a marked increase in body weight and BP. There were compensatory increases in left ventricular area and internal diameter. Prenatal BPA treatment produced a significant increase in interventricular septal thickness when animals were overfed. However, it appeared to block the increase in BP and left ventricular area caused by overfeeding. Taken together, these results suggest that prenatal BPA produces intrinsic changes in the heart that are capable of modulating morphological and functional parameters when animals become obese in later life.

High fat diet affects reproductive functions in female diet-induced obese and dietary resistant rats.

The incidence of ovulatory disorders is common in obese animal models. The mechanism behind this effect is unclear. We hypothesised that a high-fat (HF) diet induces alterations in neuroendocrine mechanisms resulting in anovulation in diet-induced obese (DIO) animals. Adult female DIO and diet-resistant (DR) rats were fed either chow or a HF diet (45% calories from fat) for 6 weeks. Oestrous cyclicity and body weight were monitored regularly. At the end of treatment, rats were implanted with a jugular catheter to monitor luteinising hormone (LH) levels on the day of pro-oestrous. Rats were sacrificed on the next pro-oestrous, and their brains and ovaries were collected. Plasma from trunk blood was analysed for oestradiol and leptin concentrations. Ovaries were fixed and sectioned for histological analysis. Brains were removed, frozen and sectioned, and norepinephrine (NE) concentrations in discrete hypothalamic areas were measured using high-performance liquid chromatography with electrochemical detection. A HF diet exposure affected oestrous cyclicity in both DIO and DR rats, with the effect being more pronounced in DIO animals. HF diet exposure increased leptin levels in both DIO and DR rats. Oestradiol levels were low in the DIO-HF group. NE levels in the hypothalamus were unaffected by HF diet or genotype. A normal LH surge was observed in DR-Chow rats and LH levels were low in the remaining groups. These results lead to the conclusion that DIO rats have an inherently reduced reproductive capacity and exposure to a HF diet decreases it further. A reduction in oestradiol and LH surge levels could contribute to this effect; however, the underlying mechanisms need to be investigated further.

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.

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.

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.

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.

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.

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.

Chronic hyperprolactinemia and changes in dopamine neurons.

The tuberoinfundibular dopaminergic (TIDA) system is known to inhibit prolactin (PRL) secretion. In young animals this system responds to acute elevations in serum PRL by increasing its activity. However, this responsiveness is lost in aging rats with chronically high serum PRL levels. The purpose of this study was to induce hyperprolactinemia in rats for extended periods of time and examine its effects on dopaminergic systems in the brain. Hyperprolactinemia was induced by treatment with haloperidol, a dopamine receptor antagonist, and Palkovits' microdissection technique in combination with high-performance liquid chromatography was used to measure neurotransmitter concentrations in several areas of the brain. After 6 months of hyperprolactinemia, dopamine (DA) concentrations in the median eminence (ME) increased by 84% over the control group. Nine months of hyperprolactinemia produced a 50% increase in DA concentrations in the ME over the control group. However, DA response was lost if a 9-month long haloperidol-induced hyperprolactinemia was followed by a 1 1/2 month-long extremely high increase in serum PRL levels produced by implantation of MMQ cells under the kidney capsule. There was no change in the levels of DA, norepinephrine (NE), serotonin (5-HT), or their metabolites in the arcuate nucleus (AN), medial preoptic area (MPA), caudate putamen (CP), substantia nigra (SN), and zona incerta (ZI), except for a decrease in 5-hydroxyindoleacetic acid (5-HIAA) in the AN after 6-months of hyperprolactinemia and an increase in DA concentrations in the AN after 9-months of hyperprolactinemia. These results demonstrate that hyperprolactinemia specifically affects TIDA neurons and these effects vary, depending on the duration and intensity of hyperprolactinemia. The age-related decrease in hypothalamic dopamine function may be associated with increases in PRL secretion.