Modulation of hypothalamic arcuate nucleus on gastric motility in rats

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Neuropeptide W influences the excitability of neurons in the rat hypothalamic arcuate nucleus

Neuropeptide W (NPW) is a ligand of the recently deorphaned receptor GPR7. Intracerebroventricular injection of this peptide results in reduced serum growth hormone concentration. Using whole-cell patch clamp recordings from somatostatin (SS) neurons in the hypothalamic arcuate nucleus, identified post-hoc using single-cell RT-PCR, we investigated the effects of NPW on membrane excitability. NPW application in acute slices of the arcuate nucleus resulted in the depolarization of the majority (62.5%) of the SS neurons tested, while smaller proportions of cells showed hyperpolarization or no response. Both the depolarization and hyperpolarization of arcuate SS neurons were preserved during recordings where voltage-gated sodium channels were blocked with tetrodotoxin, suggesting direct effects of NPW on the excitability of SS neurons. The observed depolarization of the majority of the SS neurons tested suggests that the central effects of NPW to inhibit growth hormone release results from activation of arcuate SS neurons, which could result in an inhibition of GHRH-releasing neurons.     

Hemigonadectomy-induced unilateral changes in the protein-synthesizing activity of the rat hypothalamic arcuate nucleus.

The effect of unilateral ovariectomy on the protein-synthesizing activity of the hypothalamic arcuate and dorsomedial nucleus on both sides was studied in vivo as well as in vitro. Four weeks after the removal of 1 ovary, there was a significant increase in labelled amino acid incorporated into the arcuate neurons contralateral to the removed ovary as compared to those incorporated into the nerve cells of the nucleus on the ipsilateral side. In the dorsomedial nucleus, there was no difference between the 2 sides. On the basis of the present findings, the existence of a neural pathway between the ovary and the hypothalamic arcuate nucleus is assumed.     

地方性甲状腺肿大鼠子代下丘脑弓状核的实验形态学研究

本文应用半薄切片,超薄切片对地甲肿大鼠5个月子代下丘脑弓状核进行了光镜和电镜观察。结果表明,实验组大鼠弓状核神经细胞中尼氏小体含量显著增加,核仁样小体大小不等,形态各异,不仅出现在细胞质中,在树突中也可见到。粗面内质网丰富,分泌颗粒增多,溶酶体体积增大,电子密度增强,以次级溶酶体居多。     

Alterations in insulin and glucagon secretion by monosodium glutamate lesions of the hypothalamic arcuate nucleus

This study was performed to determine the effects of monosodium glutamate (MSG) induced lesions of the hypothalamic arcuate nucleus (ARC) on glucose tolerance and insulin and glucagon secretion in male golden hamsters. Eight day old hamsters were given a single s.c. injection of 5.8 mg/g BW MSG or hypertonic saline (controls). Studies were initiated when the hamsters were 3 months of age. At this age there were no body weight differences. Glucose (180 mg/100 g BW) was administered via stomach tube to 18 control and 18 MSG-treated hamsters. Animals were anesthetized with ether and a single blood sample from the portal vein was taken either before or at 30 or 60 min after glucose administration (n = 6/group). Glucose concentrations were similar in both groups at all time periods. Insulin concentrations in the MSG group were significantly (P less than 0.05) elevated in MSG-treated hamsters compared to controls at the 60 min time point. Glucose suppressed glucagon (P less than 0.05) in control but not in MSG-treated hamsters. The MSG group had significantly more glucagon (P less than 0.05) in portal vein blood at 30 min after glucose administration than did the control hamsters. Molar insulin/glucagon ratios did not differ between the 2 groups which likely accounts for the lack of differences in blood glucose levels. These results suggest a role for the ARC in regulating pancreatic function.     

Insulin suppresses ghrelin-induced calcium signaling in neuropeptide Y neurons of the hypothalamic arcuate nucleus

Neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus (ARC) play an important role in feeding regulation. Plasma levels of ghrelin and insulin show reciprocal dynamics before and after meals. We hypothesized that ghrelin and insulin also exert reciprocal effects on ARC NPY neurons. Cytosolic Ca2? concentration ([Ca2?](i)) was measured by fura-2 microfluorometry in single neurons isolated from ARC of adult rats, followed by immunocytochemical identification of NPY neurons. Ghrelin at 10?1? M increased [Ca2?](i) in isolated ARC neurons, and co-administration of insulin concentration-dependently suppressed the ghrelin-induced [Ca2?](i) increases. Insulin at 10?1? M, 10?1? M, 10?12 M and 10?1? M counteracted ghrelin action in 26%, 41%, 61% and 53% of ghrelin-responsive neurons, respectively, showing a maximal effect at 10?12 M, the estimated postprandial concentration of insulin in the brain. The majority (>70%) of the ghrelin-activated insulin-inhibited neurons were shown to contain NPY. Double-immunohistochemistry revealed that 85% of NPY neurons in ARC express insulin receptors. These data demonstrate that insulin directly interacts with ARC NPY neurons and counteracts ghrelin action. Our results suggest that postprandial increase in plasma insulin/ghrelin ratio and insulin inhibition of ghrelin action on ARC NPY neurons cooperate to effectively inhibit the neuron activity and terminate feeding.     

Protein kinase C signaling in the hypothalamic arcuate nucleus regulates sexual receptivity in female rats

Rapid membrane-mediated estradiol signaling regulating sexual receptivity requires the interaction of the estrogen receptor (ER)-alpha and the metabotropic glutamate receptor 1a (mGluR1a). A cell signaling antibody microarray revealed that estradiol activated 42 proteins in the arcuate nucleus of the hypothalamus (ARH). To begin an analysis of various signaling pathways, protein kinase A and protein kinase C (PKC)-theta, whose signaling pathways have been implicated in the estradiol regulation of sexual receptivity, were examined. In the ARH sample, the increase in phospho-protein kinase A could not be confirmed by Western blotting, in either cytosolic or membrane fractions. However, the increase in phosphorylated PKCtheta seen with the pathway array was verified by Western blotting. To study whether rapid estradiol activation of PKC regulates the ARH-medial preoptic nucleus pathway regulating lordosis, mu-opioid receptor (MOR) internalization and lordosis reflex were tested. Blocking PKC in ARH with 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]3-(1H-indol-3-yl) maleimide significantly attenuated estradiol-induced MOR internalization. Furthermore, disruption of PKC signaling within the ARH at the time of estradiol treatment significantly diminished the lordosis reflex. Moreover, blocking PKC prevented MOR internalization when the circuit was activated by the mGluR1a agonist, (RS)-3,5-dihydroxyphenylglycine. Activation of PKC with phorbol 12, 13-dibutyrate induced MOR internalization, indicating that PKC was a critical step for membrane ERalpha-initiated mGluR1a-mediated cell signaling and phorbol 12, 13-dibutyrate significantly facilitated the lordosis reflex. Together these findings indicate that rapid membrane ERalpha-mGluR1a interactions activate PKCtheta cell signaling, which regulates female sexual receptivity.     

Corticotropin-releasing factor receptor expression in the pituitary of fetal sheep after lesion of the hypothalamic paraventricular nucleus.

Both the capacity of CRF to release ACTH and the number of binding sites for CRF in the anterior pituitary decline during the final weeks of gestation in fetal sheep. The present study examined regulation of pituitary CRF receptor expression by the hypothalamic paraventricular nucleus (PVN) during late gestation in fetal sheep. Bilateral radiofrequency lesions of the PVN (PVN-Lx; n = 4) or sham lesions (SHAM; n = 5) were performed in fetal sheep at 118-122 days of gestational age (dGA). Pituitary glands from PVN-Lx and SHAM fetuses were collected at 139-142 dGA (term, approximately 148 dGA). Dual-label in situ hybridization was performed using a digoxigenin-labeled ovine POMC complementary RNA, together with a 35S-labeled ovine CRF type I (CRF1) receptor complementary RNA, to localize and quantify CRF1 receptor mRNA in POMC-hybridizing cells. Binding of [125I]-ovine CRF was also examined in the fetal pituitary of both PVN-Lx and SHAM fetuses using in situ autoradiography. The hybridization signal for the CRF1 receptor mRNA was primarily restricted to POMC-expressing cells in the anterior pituitary of both PVN-Lx and SHAM fetuses; no hybridization signal for the CRF1 receptor was observed in the neurointermediate lobe (NIL) in either group. The hybridization signal for CRF1 receptor mRNA in anterior pituitary corticotropes of PVN-Lx fetuses was significantly lower in both the inferior and superior regions of the anterior pituitary, compared with SHAM fetuses (P < 0.05). In the inferior region of the anterior pituitary, the percentage of POMC-hybridizing cells containing CRF1 receptor hybridization signal was significantly greater in PVN-Lx (90+/-7%; mean +/- SEM), compared with SHAM (67+/-6%; P < 0.05) fetuses. No differences in the percentage of POMC cells containing CRF1 receptor hybridization signal were observed in the superior region of the anterior pituitary between PVN-Lx (89+/-8%) and SHAM (87+/-9%). Binding of [125I]-ovine CRF (oCRF) was significantly greater in anterior pituitaries of PVN-Lx (140+/-19 mean arbitrary densitometry U +/- SEM), compared with SHAM (73+/-23; P < 0.05) fetuses. For both PVN-Lx and SHAM fetuses, there were no differences within group in [125I]-oCRF binding between the inferior and superior regions of the anterior pituitary. A weak, but significant (P < 0.05), autoradiographic signal for [125I]-oCRF binding was observed in the NIL of both SHAM and PVN-Lx fetal sheep. The level of [125I]-oCRF binding was significantly lower in the NIL, compared with anterior pituitary, for both SHAM (P < 0.01) and PVN-Lx fetuses. There were no differences in [125I]-oCRF binding in the NIL between SHAM and PVN-Lx fetal sheep. Our findings support a role for the PVN in regulating anterior pituitary CRF1 receptor expression in the late-gestation sheep fetus.     

Involvement of the beta-endorphin neurons of the hypothalamic arcuate nucleus in ethanol-induced place preference conditioning in mice

Background: Increasing evidence indicates that mu‐ and delta‐opioid receptors are decisively involved in the retrieval of memories underlying conditioned effects of ethanol. The precise mechanism by which these receptors participate in such effects remains unclear. Given the important role of the proopiomelanocortin (POMc)‐derived opioid peptide beta‐endorphin, an endogenous mu‐ and delta‐opioid receptor agonist, in some of the behavioral effects of ethanol, we hypothesized that beta‐endorphin would also be involved in ethanol conditioning. Methods: In this study, we treated female Swiss mice with estradiol valerate (EV), which induces a neurotoxic lesion of the beta‐endorphin neurons of the hypothalamic arcuate nucleus (ArcN). These mice were compared to saline‐treated controls to investigate the role of beta‐endorphin in the acquisition, extinction, and reinstatement of ethanol (0 or 2 g/kg; intraperitoneally)‐induced conditioned place preference (CPP). Results: Immunohistochemical analyses confirmed a decreased number of POMc‐containing neurons of the ArcN with EV treatment. EV did not affect the acquisition or reinstatement of ethanol‐induced CPP, but facilitated its extinction. Behavioral sensitization to ethanol, seen during the conditioning days, was not present in EV‐treated animals. Conclusions: The present data suggest that ArcN beta‐endorphins are involved in the retrieval of conditioned memories of ethanol and are implicated in the processes that underlie extinction of ethanol‐cue associations. Results also reveal a dissociated neurobiology supporting behavioral sensitization to ethanol and its conditioning properties, as a beta‐endorphin deficit affected sensitization to ethanol, while leaving acquisition and reinstatement of ethanol‐induced CPP unaffected.     

Proteins regulated by gonadal steroids in the medial preoptic and ventromedial hypothalamic nucleic of male and female rats

Protein profiles of brain areas mediating effects of steroid hormones on copulation were compared between animals in gonadal steroid states predictive of either the presence or absence of copulatory activity. A broad range of proteins present in micropunches of tissue from the medial preoptic area (MPO) and from the ventromedial hypothalamus (VMH) were compared between male and female rats with gonadal steroids present or absent. Half of the animals of each gender were gonadectomized 1 month prior to sacrifice. The remaining males were left intact, while the remaining females were gonadectomized, implanted with estrogen capsules, and injected with progesterone prior to sacrifice. These females were screened for sexual receptivity immediately prior to sacrifice. Proteins from the MPO and VMH of each animal were separated by two-dimensional gel electrophoresis, silver stained, and quantified by computerized optical densitometry. Several proteins differed in density between gels of high-steroid males and and females and between high-steroid and absent-steroid animals of one or both genders. Two previously reported sex differences were replicated and found to depend on activational effects of gonadal steroids. Several interesting reversal patterns were noted between MPO and VMH, including three proteins that were affected by gonadectomy in the MPO of males, but not females, and in the VMH of females, but not males, thus correlating with sexual function. These included serum albumin (a possible index of local area blood flow) and neuron-specific enolase, a glycolytic enzyme of anaerobic metabolism. A probable genetic polymorphism was discovered at a locus whose expression appears to be regulated by gonadal steroids.(ABSTRACT TRUNCATED AT 250 WORDS)     

The supraoptic nucleus in the pig hypothalamus: postnatal development and the effect of gonadal steroids.

Postnatal development of the supraoptic nucleus (SON) in the pig hypothalamus was studied morphometrically. The volume of the SON increased from 6.2 +/- 0.45 (S.E.M.) mm3 at 7 weeks postnatally to 18.5 +/- 1.35 mm3 at 2.5 years of age. A sex difference was found at the development point when the SON volume increased, with earlier SON enlargement in males. This sex difference was 30% at 30 weeks and 50% at 1 year of age. At 2.5 years of age no difference in volume was apparent between the sexes. The number of SON neurones was similar for all age groups concerned (43,500 +/- 1475), except for the 2.5-year-old females where 40% more were found (55,500 +/- 3285). No significant difference was found in neurone number between gonadectomized and sham-operated animals, but the operation caused a 30% reduction in the number of neurones and SON volume. Testosterone supplementation following gonadectomy, during the first 4 weeks postnatally, resulted in sexual dimorphism, the males having more SON neurones than the females. The volume showed only a trend in the same direction. Testosterone supplementation at other ages did not result in any difference when compared with controls. The results of this study show that the postnatal development of the SON of the pig is sexually dimorphic, and that it continues after puberty in females. In contrast to the vasopressin- and oxytocin-containing nucleus, the development of the SON was not influenced by gonadectomy and only slightly by gonadal steroids.