Downregulation of prolactin-releasing peptide gene expression in the hypothalamus and brainstem of diabetic rats

We investigated the prolactin-releasing peptide (PrRP) mRNA levels in the hypothalamus and brainstem of streptozotocin (STZ)-induced diabetic rats and fa/fa Zucker diabetic rats, using in situ hybridization histochemistry. PrRP mRNA levels in the hypothalamus and brainstem of STZ-induced diabetic rats were significantly reduced in comparison with those of control rats. PrRP mRNA levels in the diabetic rats were reversed by both insulin and leptin. PrRP mRNA levels in the fa/fa diabetic rats were significantly reduced in comparison with those of Fa/? rats. PrRP mRNA levels in the fa/fa diabetic rats were significantly increased by insulin-treatment, but did not reach control levels in the Fa/? rats. We also investigated the effect of restraint stress on PrRP mRNA levels in STZ-induced diabetic rats. The PrRP mRNA levels in the control and the STZ-induced diabetic rats increased significantly after restraint stress. The diabetic condition and insulin-treatment may affect the regulation of PrRP gene expression via leptin and other factors, such as plasma glucose level. The diabetic condition may not impair the role of PrRP as a stress mediator.     

Nicotine stimulates prolactin-releasing peptide (PrRP) cells and non-PrRP cells in the solitary nucleus

Nicotine has been reported to regulate food intake and body weight. But the mechanisms underlying these roles have not been fully elucidated. In the present study, we showed that acute administration of nicotine (0.5 mg/kg s.c.) could activate prolactin-releasing peptide (PrRP)-bearing neurons in the A2 area of the NTS of rats, suggesting that PrRP may be associated with nicotine-induced effects in the central nervous system (CNS). We next treated rats with nicotine chronically (4 mg/kg/day for 7 days i.p.), and the results showed that the body weight was strongly reduced and food intake was greatly suppressed compared to the vehicle control group (p<0.01). Immunocytochemical studies revealed that PrRP-bearing neurons in the NTS were evidently activated after chronic administration of nicotine, suggesting that PrRP was involved in the regulation of nicotine-mediated body weight loss and food intake suppression in rats. We also found that acute/chronic administration of nicotine activated PrRP-negative neurons in the NTS, and the majority of these neurons were shown to be TH-negative, suggesting that noncatecholaminergic, PrRP-negative neurons in the NTS are associated with the roles of nicotine. Nicotine has also been shown to stimulate the secretion of ACTH, a stress responsive hormone. In the present study, rats received nicotine (0.5 mg/kg s.c.) or saline followed by restraint stress for 30 min. The immunocytochemical results showed that nicotine/stress and saline/stress both activated the majority of the PrRP neurons in the NTS, there being no significant difference between the two treatments (p>0.05). Nicotine/stress also greatly activated PrRP/TH-negative neurons in the NTS. Saline/stress, however, caused much lower effect on the activation of PrRP/TH-negative neurons. In addition, the activation effect of nicotine/stress on PrRP/TH-negative neurons was much stronger than that of nicotine alone (p<0.01). These results indicated that PrRP was associated with stress responses, but it had little effect on nicotine-mediated stress responses. On the other hand, nicotine and restraint stress may synergistically activate PrRP/TH-negative neurons in the NTS. Taken together, our data show that PrRP is involved in the nicotine-induced regulation of body weight and food intake, but may not be involved in the mediation of nicotine on stress responses. PrRP/TH-negative neurons in the NTS are also associated with the roles of nicotine in the CNS.     

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

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

Characterization of a naturally-occurring polymorphism in the UHR-1 gene encoding the putative rat prolactin-releasing peptide receptor

The rat orphan receptor UHR-1 and its human orthologue, GPR10, were first isolated in 1995. The ligand for this receptor, prolactin-releasing peptide (PrRP), was identified in 1998 by reverse pharmacology and has subsequently been implicated in a number of physiological processes. As supported by its localization and regulation in the hypothalamus and brainstem, we have shown previously that PrRP is involved in energy homeostasis. Here we describe a naturally occurring polymorphism in the UHR-1 gene that results in an ATG to ATA change at the putative translational initiation site. The presence of the polymorphism abolished the binding of 125I PrRP in rat brain slices but did not affect the ability of PrRP to reduce fast-induced food intake. Together this data suggest that PrRP may be exerting its feeding effects through a receptor other than UHR-1.     

Effects of haloperidol and melatonin on the in situ activity of nigrostriatal tyrosine hydroxylase in male Syrian hamsters

Haloperidol, an antipsychotic drug, was tested for its effects on the in situ activity of nigrostriatal and hypothalamic tyrosine hydroxylase, in control male Syrian hamsters and in those receiving a high daily dose of melatonin. After receiving daily ip injections (1.25 mg/kg ip) of haloperidol for 21 days, the animals were sacrificed and brain tissue collected for analysis of dopamine and metabolites by HPLC with electrochemical detection. In situ activity of tyrosine hydroyxlase (TH) activity was determined by measuring the accumulation of L-Dopa after administration of the L amino acid decarboxylase inhibitor, mhydroxybenzylhydrazine. Tissue content of dopamine and its metabolites, DOPAC and HVA, was depressed in striatum of animals receiving haloperidol, and tyrosine hydroxylase (TH) activity was significantly decreased 20-24 h after the last injection (from 1823 +/- 63 to 1139 +/- 85 pg l-dopa/mg tissue). The decrease in TH activity in striatum was significantly inhibited by daily injections of a high dose of melatonin (2.5 mg/kg ip) (from 1139 +/- 85 to 1560 +/- 116 pg L-dopa/mg tissue). In the substantia nigra and in the hypothalamus, on the other hand, haloperidol significantly increased the activity of tyrosine hydroxylase. Melatonin administration did not significantly influence TH activity in the substantia nigra, but inhibited TH activity in the hypothalamus and in the pontine brainstem. One explanation for these data is that chronic haloperidol administration in Syrian hamsters increases TH activity in hypothalamus and substantia nigra, but decreases TH activity in striatum by a mechanism involving D2 presynaptic receptors and a melatonin sensitive kinase which regulates TH phosphorylation.     

Identification of the prolactin-releasing peptide-producing cell in the rat adrenal gland

Prolactin-releasing peptide (PrRP) is a novel peptide found in bovine hypothalamus as an endogenous ligand of an orphan G-protein-coupled receptor (hGR3). It is known that PrRP is widely distributed and plays roles in the central nervous system (CNS). In particular, PrRP acts as a neurotransmitter that mediates stress and activates the hypothalamo-pituitary-adrenal axis. On the other hand, only a few studies have so far been performed on PrRP in peripheral tissues. Among peripheral tissues, appreciable levels of PrRP are found only in the adrenal gland; however, the PrRP-producing cells in the adrenal gland have not been identified. In this study, we detected PrRP mRNA in the rat adrenal medulla. So, we tried to identify the PrRP-producing cells in primary culture cells of the adrenal medulla. We found immunopositive PrRP cells among the cultured cells from the adrenal gland, but not in the adrenal gland tissue, by means of immunocytochemistry. The PrRP immunopositive cells were double positive for tyrosine hydroxylase (TH) and for phenylethanolamine N-methyltransferase (PNMT), which indicates that PrRP may be produced in a part of the adrenaline cells in the adrenal gland. This is the first report that PrRP is produced in the adrenaline-containing cells of the adrenal gland.     

Effect of estradiol benzoate and clomiphene on tyrosine hydroxylase activity and on luteinizing hormone and prolactin levels in ovariectomized rats

The effects of estradiol benzoate (EB) on tyrosine hydroxylase (TH) activity in the medial basal hypothalamus (MBH) and on plasma levels of luteinizing hormone (LH) and prolactin were studied in long-term ovariectomized rats. Administration of 10 μg EB produced significant elevation of TH activity on Days 1 and 3 following injection. LH levels were significantly lower than controls throughout the three day treatment period, although there was a significant increase from Day 1 to Day 2. TH activity and LH levels were inversely related throughout the experimental period. Clomiphene (15 μg/rat/day), a purported estrogen antagonist, was administered over a period of three days to control and EB-treated rats to determine whether the effect of EB on plasma LH levels was causally related to changes in TH activity. In rats receiving both EB and clomiphene, TH activity was lower and plasma LH was higher than after EB alone. The results support the hypothesis that the feedback effects of estradiol on LH release involve an action on the tuberoinfundibular dopaminergic (TIDA) neurons of the MBH and that clomiphene can oppose the inhibitory effect of estradiol on LH release by directly inhibiting TIDA neuron activity. Furthermore, EB-induced release of prolactin does not appear to involve detectable changes in the activity of TIDA neurons.     

Apoptotic signaling proteins: possible participation in the regulation of vasopressin and catecholamines biosynthesis in the hypothalamus

The role of apoptotic signaling proteins for long-lived neurons in the mature brain is poorly understood. Recently, we have shown that water deprivation leads to the activation of vasopressin (VP) secretion and expression of Bcl-2 and caspase-9 apototic proteins in the hypothalamus of the rat brain. In the present work, we continued to study a possible relationship between the functional activity of neurosecretory cells of the hypothalamus and apoptosis related proteins. We found that water deprivation leads to simultaneous activation of synthesis of VP and p53 and Bcl-2 apoptotic proteins in the mouse brain. To study a possible effect of apoptotic proteins on the functional state of hypothalamic neurons, the VP and tyrosine hydroxylase (TH) synthesis were analyzed in p53, p21^Waf1/Cip1 and Bcl-2 deficient mice. Loss of p53 and Bcl-2 significantly reduced VP synthesis in paraventricular and supraoptic nuclei and TH expression in arcuat, periventricular and zona incerta nuclei of the hypothalamus. Surprisingly, in contrast with the loss of p53, the inactivation of p21^Waf1/Cip1 up-regulates the expression of VP and TH. These data indicate that p53, p21^Waf1/Cip1 and Bcl-2 proteins, besides affecting cell cycle, tumor suppression and apoptosis, may act as modulators of neurosecretory activity of hypothalamic neurons; however, this problem remains to be determined more detailed.     

Evidence implicating utilization of different T cell receptor-associated signaling pathways by TH1 and TH2 clones

We have reported recently that high concentrations of anti-CD3 mAb inhibited IL-2-dependent proliferation of TH1 but not TH2 clones. The selective inhibitory effect on TH1 clones suggested that the two helper T lymphocyte subsets might utilize different TCR-associated signal transduction mechanisms. In the present study, we demonstrate that this distinction was not due to a gross difference in the level of TCR expression by TH1 and TH2 clones. Inhibition of TH1 proliferation by anti-CD3 mAb appeared to depend on calcium for maximal effect, suggesting that a substantial elevation of intracellular free calcium concentration ([Ca2+]i) might not occur after ligation of the TCR complex of TH2 clones. Calcium ionophore inhibited IL-2-dependent proliferation of both subsets, suggesting that receptor/ligand systems which stimulate elevated [Ca2+]i would be expected to inhibit proliferation. Although elevated [Ca2+]i and generation of inositol phosphates were readily detected in TH1 clones, these second messengers were not detected following stimulation of TH2 clones via the TCR complex. In addition, lymphokine production by TH1 clones was more sensitive to inhibition by cholera toxin, 8-bromoadenosine 3':5'-cyclic monophosphate, and cyclosporin A than was lymphokine production by TH2 clones. Collectively, these results suggest that TH1 and TH2 clones utilize distinct TCR-associated signal transduction mechanisms for lymphokine gene expression. The difference in signaling mechanisms suggests a potential pharmacologic target for intervention in situations where inappropriate activation of TH1 or TH2 cells occurs in vivo.     

Collapsin response mediator protein 4 affects the number of tyrosine hydroxylase‐immunoreactive neurons in the sexually dimorphic nucleus in female mice

In the sexually dimorphic anteroventral periventricular nucleus (AVPV) of the hypothalamus, females have a greater number of tyrosine hydroxylase‐immunoreactive (TH‐ir) and kisspeptin‐immunoreactive (kisspeptin‐ir) neurons than males. In this study, we used proteomics analysis and gene‐deficient mice to identify proteins that regulate the number of TH‐ir and kisspeptin‐ir neurons in the AVPV. Analysis of protein expressions in the rat AVPV on postnatal day 1 (PD1; the early phase of sex differentiation) using two‐dimensional fluorescence difference gel electrophoresis followed by MALDI‐TOF‐MS identified collapsin response mediator protein 4 (CRMP4) as a protein exhibiting sexually dimorphic expression. Interestingly, this sexually differential expressions of CRMP4 protein and mRNA in the AVPV was not detected on PD6. Prenatal testosterone exposure canceled the sexual difference in the expression of Crmp4 mRNA in the rat AVPV. Next, we used CRMP4‐knockout (CRMP4‐KO) mice to determine the in vivo function of CRMP4 in the AVPV. Crmp4 knockout did not change the number of kisspeptin‐ir neurons in the adult AVPV in either sex. However, the number of TH‐ir neurons was increased in the AVPV of adult female CRMP4‐KO mice as compared with the adult female wild‐type mice. During development, no significant difference in the number of TH‐ir neurons was detected between sexes or genotypes on embryonic day 15, but a female‐specific increase in TH‐ir neurons was observed in CRMP4‐KO mice on PD1, when the sex difference was not yet apparent in wild‐type mice. These results indicate that CRMP4 regulates the number of TH‐ir cell number in the female AVPV. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 73: 502–517, 2013     

Nicotinic α4 Receptor-Mediated Cholinergic Influences on Food Intake and Activity Patterns in Hypothalamic Circuits

Nicotinic acetylcholine receptors (nAChRs) play an important role in regulating appetite and have been shown to do so by influencing neural activity in the hypothalamus. To shed light on the hypothalamic circuits governing acetylcholine’s (ACh) regulation of appetite this study investigated the influence of hypothalamic nAChRs expressing the α4 subunit. We found that antagonizing the α4β2 nAChR locally in the lateral hypothalamus with di-hydro-ß-erythroidine (DHβE), an α4 nAChR antagonist with moderate affinity, caused an increase in food intake following free access to food after a 12 hour fast, compared to saline-infused animals. Immunocytochemical analysis revealed that orexin/hypocretin (HO), oxytocin, and tyrosine hydroxylase (TH)-containing neurons in the A13 and A12 of the hypothalamus expressed the nAChR α4 subunit in varying amounts (34%, 42%, 50%, and 51%, respectively) whereas melanin concentrating hormone (MCH) neurons did not, suggesting that DHβE-mediated increases in food intake may be due to a direct activation of specific hypothalamic circuits. Systemic DHβE (2 mg/kg) administration similarly increased food intake following a 12 hour fast. In these animals a subpopulation of orexin/hypocretin neurons showed elevated activity compared to control animals and MCH neuronal activity was overall lower as measured by expression of the immediate early gene marker for neuronal activity cFos. However, oxytocin neurons in the paraventricular hypothalamus and TH-containing neurons in the A13 and A12 did not show differential activity patterns. These results indicate that various neurochemically distinct hypothalamic populations are under the influence of α4β2 nAChRs and that cholinergic inputs to the lateral hypothalamus can affect satiety signals through activation of local α4β2 nAChR-mediated transmission.     

Prolactin-releasing peptide, food intake, and hydromineral balance in goldfish

A potential role for prolactin-releasing peptide (PrRP) in appetite regulation and hydromineral balance in goldfish was examined. PrRP was found to be expressed in discrete regions of the goldfish brain, in particular, the hypothalamus. Intraperitoneal (IP) or intracerebroventricular administration of PrRP had dose-dependent effects to suppress food intake in goldfish. Hypothalamic PrRP mRNA expression significantly increased after feeding, as well as after 7 days of food deprivation. Refeeding fish after 7 days food deprivation did not result in a postprandial increase in PrRP mRNA expression. These data suggest an anorexigenic role for PrRP in the short term around a scheduled meal time, but not over the longer term. IP injection of PrRP significantly increased pituitary prolactin (PRL) mRNA levels, suggesting involvement in the regulation of lactotroph activity. Acclimating goldfish to an ion-poor environment decreased serum osmolality and increased PrRP and PRL mRNA levels, providing evidence for PrRP involvement in hydromineral balance through its actions on lactotrophs. Acclimation to ion-poor water diminished the anorexigenic properties of PrRP in goldfish, indicating that a role for PrRP in goldfish satiation is counterbalanced by alternate systemic needs (i.e., osmoregulatory). This was further supported by an ability to reinstate the anorexigenic actions of PrRP in fish acclimated to ion-poor water by feeding a salt-rich diet. These studies provide evidence that PrRP is involved in regulating appetite and hydromineral balance in fish, and that the degree of involvement in either process varies according to overall systemic needs in response to environmental conditions.     

Tyrosine hydroxylase‐synthesizing cells in the hypothalamus of prairie voles (Microtus ochrogaster): Sex differences in the anteroventral periventricular preoptic area and effects of adult gonadectomy or neonatal gonadal hormones

The vertebrate hypothalamus and surrounding region contain a large population of cells expressing tyrosine hydroxylase (TH), the rate limiting enzyme for synthesis of dopamine and other catecholamines. Some of these populations are sexually dimorphic in rats. We here examined sex differences in TH‐immunoreactive populations in the forebrain of gonadally intact and gonadectomized prairie voles (Microtus ochrogaster), a species that sometimes shows unusual sexual differentiation of brain and behavior. A sex difference was found in the anteroventral periventricular preoptic area (AVPV; likely analogous to the rat rostral A14) only in gonadectomized subjects, which was due to a 50% reduction in the number of TH‐immunoreactive cells after castration in males. There was no significant sex difference or effects of gonadectomy on the number of TH‐immunoreactive cells in the anteroventral preoptic area (AVP), periventricular anterior hypothalamus (caudal A14), arcuate nucleus (A12), zona incerta (A13), or posterodorsal hypothalamus (A11). In a second experiment, testosterone propionate (TP; 500 μg), diethylstilbestrol (DES; 1 μg), or estradiol benzoate (EB; 30 μg) injected daily during the first week after birth each significantly reduced later TH expression in the AVPV of females by approximately 40–65% compared to oil‐treated controls. Unlike rats, therefore, a sex difference in TH expression in the prairie vole AVPV is found only after removal of circulating gonadal hormones in males. Furthermore, unlike our previous findings on the generation of sex differences in extra‐hypothalamic arginine‐vasopressin expression in prairie voles, TH expression in the AVPV of female prairie voles can be highly masculinized by neonatal exposure to either aromatizable androgens or estrogens. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006     

Tyrosine Hydroxylase Is Short-Term Regulated by the Ubiquitin-Proteasome System in PC12 Cells and Hypothalamic and Brainstem Neurons from Spontaneously Hypertensive Rats: Possible Implications in Hypertension

Aberrations in the ubiquitin-proteasome system (UPS) are implicated in the pathogenesis of various diseases. Tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamines biosynthesis, is involved in hypertension development. In this study we investigated whether UPS regulated TH turnover in PC12 cells and hypothalamic and brainstem neurons from spontaneously hypertensive rats (SHR) and whether this system was impaired in hypertension. PC12 cells were exposed to proteasome or lysosome inhibitors and TH protein level evaluated by Western blot. Lactacystin, a proteasome inhibitor, induced an increase of 86±15% in TH levels after 30 min of incubation, then it started to decrease up to 6 h to reach control levels and finally it rose up to 35.2±8.5% after 24 h. Bafilomycin, a lysosome inhibitor, did not alter TH protein levels during short times, but it increased TH by 92±22% above basal after 6 h treatment. Before degradation proteasome substrates are labeled by conjugation with ubiquitin. Efficacy of proteasome inhibition on TH turnover was evidenced by accumulation of ubiquitinylated TH after 30 min. Further, the inhibition of proteasome increased the quantity of TH phosphorylated at Ser40, which is essential for TH activity, by 2.7±0.3 fold above basal. TH protein level was upregulated in neurons from hypothalami and brainstem of SHR when the proteasome was inhibited during 30 min, supporting that neuronal TH is also short-term regulated by the proteasome. Since the increased TH levels reported in hypertension may result from proteasome dysfunction, we evaluate proteasme activity. Proteasome activity was significantly reduced by 67±4% in hypothalamic and brainstem neurons from SHR while its protein levels did not change. Present findings show that TH is regulated by the UPS. The impairment in proteasome activity observed in SHR neurons may be one of the causes of the increased TH protein levels reported in hypertension.     

Bee venom acupoint stimulation increases Fos expression in catecholaminergic neurons in the rat brain

Fos immunocytochemistry was combined with tyrosine hydroxylase (TH) or dopamine-beta-hydroxylase (DBH) immunolabeling to examine brainstem catecholaminergic neuronal activation resulting from bee venom (BV) stimulation of the Zusanli acupoint (ST36) in Sprague-Dawley rats. BV injection into the Zusanli acupoint caused increased Fos expression in catecholaminergic neurons located in the hypothalamic arcuate nucleus (Arc), the dorsal raphe (DR), the A5 cell group (A5) and the locus coeruleus (LC). BV acupoint stimulation significantly increased Fos-TH double-labeled neurons in the Arc, LC and DR. Fos-DBH positive neurons were also increased by BV acupoint stimulation in the LC and A5. In contrast BV stimulation of a non-acupoint only increased Fos expression and Fos-TH double-labeled neurons in the Arc. These data indicate that BV acupoint stimulation activates brainstem catecholaminergic neurons and that this activation underlies BV acupoint-induced antinociception.     

Carnitine and carnitine orotate affect the expression of the prolactin-releasing peptide gene

Carnitine is involved in fatty acid metabolism in mammals and is widely used as a nutritional supplement; carnitine orotate is a more absorbable form of carnitine. We investigated the effects of carnitine and carnitine orotate on mouse prolactin-releasing peptide (PrRP) mRNA expression. Twenty-four female mice were randomly divided into four groups of six; control mice were orally drenched with physiological saline solution (250 mg/kg body weight) and treatment mice were orally drenched with carnitine (250 mg/kg) or carnitine orotate (250 or 750 mg/kg), once a day, for 20 days from parturition. The carnitine or carnitine orotate was dissolved in saline solution before administration. The hypothalamus, pituitary and ovary were sampled on day 21 after parturition, and PrRP mRNA levels in these tissues were measured by semi-quantitative PCR, with glyceraldehyde 3-phosphate dehydrogenase as a control. Expression of PrRP in mice treated with carnitine and carnitine orotate was significantly increased in the ovary and significantly reduced in the pituitary gland. Compared with the control, hypothalamus PrRP mRNA increased significantly in the carnitine and low-dose carnitine orotate groups and decreased significantly in the high-dose carnitine orotate group. We conclude that carnitine and carnitine orotate regulate expression of PrRP in the pituitary gland and ovaries.     

Effects of Systemic Administration of 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine to Mice on Tyrosine Hydroxylase, l-3,4-Dihydroxyphenylalanine Decarboxylase, Dopamine β-Hydroxylase, and Monoamine Oxidase Activities in the Striatum and Hypothalamus

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg subcutaneously per day for 8 days) to C57BL/6N mice were studied on tyrosine hydroxylase (TH), L-3,4-dihydroxyphenylalanine decarboxylase (DDC), and monoamine oxidase (MAO) activities in the striatum, and TH, DDC, dopamine-beta-hydroxylase (DBH), and MAO activities in the hypothalamus. Treatment with MPTP led to a large decrease in TH activity and a parallel decrease in DDC activity in the striatum, as compared with the saline controls. In contrast, MPTP administration did not cause a decrease of the activities of TH, DDC, and DBH in the hypothalamus. There was also no reduction in MAO activities of striatum and hypothalamus. These data indicate that MPTP administration to mice results in specific degeneration of the dopaminergic nigrostriatal pathway and that DDC in the mouse striatum may mainly be localized in the dopaminergic neurons with TH.     

The importance of the olfactory rosettes in maintaining pituitary prolactin and prolactin-releasing peptide levels during hyposmotic acclimation in silver sea bream (Sparus sarba)

A potential role of the olfactory rosettes in maintaining prolactin (PRL) and prolactin-releasing peptide (PrRP) levels was examined in the euryhaline silver sea bream (Sparus sarba). The olfactory rosettes were surgically removed in silver sea bream adapted to hypo- (6 ppt) and hyper-osmotic (33 ppt) salinities and the mRNA expression of the two previously identified freshwater-adapting factors, prolactin (PRL) and prolactin-releasing peptide (PrRP), in silver sea bream was measured. The elevation of pituitary PRL and PrRP mRNA expression levels as seen in 6 ppt-adapted fish was abolished by surgical removal of the olfactory rosettes. The PRL and PrRP expression levels in fish adapted to 6 ppt were significantly lowered following olfactory rosette removal. On the other hand, hypothalamic PrRP mRNA expression in 6 ppt-adapted fish did not change. Specific signals for Na(+)-K(+)-ATPase but not CFTR mRNA expression were detected in the surface layers of olfactory epithelial cells by in situ hybridization. The mRNA abundance of CFTR and Na(+)-K(+)-ATPase α and β subunits remained unchanged in the olfactory rosette of silver sea bream adapted to 0, 6, 12, 33 and 50 ppt for 4 weeks and in fish abruptly transferred from 33 ppt to 6 ppt. Data obtained from the olfactory rosette removal experiments suggest a possible role of the olfactory system for maintaining PRL and PrRP expression during hyposmotic acclimation in sea bream.     

Ghrelin-containing neuron in cerebral cortex and hypothalamus linked with the DVC of brainstem in rat

Ghrelin is a newly discovered brain-gut peptide and an endogenous ligand for growth hormone secretagogues receptor (GHS-R). Ghrelin and GHS-R present extensively in central and peripheral tissues such as stomach, brain and other organs of rodent and human, which suggest it has multiple biological effects. It has been reported that ghrelin has significant role in the regulation of energy homeostasis, food intake and appetite. The organization of central circuitry appears to play an important role in integrating orexigenic effects of ghrelin, but the detail is not fully clear. In this study, we examined the expression of ghrelin, ghrelin mRNA and GHS-R mRNA in cerebrum and brainstem by RT-PCR and immunofluorescence histochemistry, and analyzed the connection among the cerebral cortex, hypothalamus, dorsal vagal complex (DVC). The results showed that the positive staining of ghrelin was found on the pyramidal neuron of layer V in the sensorimotor area of cerebral cortex, cingulate gyrus, as well as in the neuron of lateral hypothalamus (LH), PVN and ARC. The expression of ghrelin mRNA and GHS-R mRNA were also found in the sensorimotor cortex and hypothalamus by method of RT-PCR. The GHS-R mRNA was also found in the DVC of medulla oblongata. Other finding is that the FG/ghrelin dual labeled neurons were found in LH of hypothalamus (not in cortex). The ghrelin-containing neuron in the LH projects its axon to the DVC with the method of retrograde tracing. In conclusion, the ghrelin neurons are located not only in hypothalamus (LH, PVN, ARC), but also in the cortex (sensorimotor area, cingular gyrus), and the fibers of ghrelin neurons in hypothalamus projected directly to the DVC. It suggests that ghrelin plays its role from hypothalamus to brainstem as a neurotransmitter or neuromodulator to regulate function of vagal nuclei in brainstem.