Journal of neuroendocrinology
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J. Neuroendocrinol. · May 2008
Comparative StudyPituitary-adrenal response to acute and repeated mild restraint, forced swim and change in environment stress in arginine vasopressin receptor 1b knockout mice.
Arginine vasopressin and corticotrophin-releasing hormone synthesised and released from the hypothalamic paraventricular nucleus are the prime mediators of the hypothalamic-pituitary-adrenal (HPA) axis response to stress. These neurohormones act synergistically to stimulate adrenocorticotophin (ACTH) secretion from the anterior pituitary, culminating in an increase in circulating glucocorticoids. Arginine vasopressin mediates this action at the arginine vasopressin 1b receptor (Avpr1b) located on pituitary corticotrophs. ⋯ Irrespective of genotype, there was no difference in the plasma ACTH or corticosterone concentrations in response to acute and repeated stressors. The data show that a functional Avpr1b is required for an intact pituitary ACTH response to the acute and chronic stressors used in this study. Furthermore, the normal corticosterone response to repeated exposure to change in environment stress also requires the Avpr1b to drive HPA axis responsiveness.
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J. Neuroendocrinol. · Aug 2007
5-Aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside stimulates tyrosine hydroxylase activity and catecholamine secretion by activation of AMP-activated protein kinase in PC12 cells.
The activity of AMP-activated protein kinase (AMPK) is regulated by the metabolic and nutritional state of the cell. 5-Aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) is transformed into riboside monophosphate (ZMP) via phosphorylation by adenosine kinase inside the cell and exerts it effect by stimulating AMPK. AICAR significantly induces an increase in AMPK activity in a dose- and time-dependent manner in the rat pheochromocytoma cell line PC12. In addition, compound C, an AMPK inhibitor, as well as 5'-amino-5'-dAdo, an adenosine kinase inhibitor, inhibits the AICAR-induced AMPK activity. ⋯ The present study also shows that H89, a protein kinase A inhibitor, abolishes the AICAR-induced increase in the level of TH mRNA, as well as the corresponding enzyme activity and Ser40 phosphorylation. Finally, AICAR significantly increases dopamine secretion from PC12 cells. These findings indicate that AICAR activates catecholamine synthesis and secretion through AMPK activation in chromaffin cells.
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J. Neuroendocrinol. · Jun 2007
Rhythm-dependent light induction of the c-fos gene in the turkey hypothalamus.
Day length (photoperiod) is a powerful synchroniser of seasonal changes in the reproductive neuroendocrine activity in temperate-zone birds. When exposed to light during the photoinducible phase, reproductive neuroendocrine responses occur. However, the neuroendocrine systems involved in avian reproduction are poorly understood. ⋯ The lack of c-fos up-regulation in the pineal gland and vSCN following photostimulation during the photoinducible phase lends credence to the hypothesis that these areas are not involved in the photic initiation of avian reproduction. On the other hand, c-fos mRNA increases in the nCPa, ME, and OVLT support other studies showing that these areas are involved in the onset of reproductive behaviour initiated by long day lengths. The present study provides novel data showing that the PMM in the caudal hypothalamus is involved in the neuronally mediated, light-induced initiation of reproductive activity in the turkey hen.
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J. Neuroendocrinol. · Apr 2007
Multicenter StudySex differences in the chloride cotransporters, NKCC1 and KCC2, in the developing hypothalamus.
In immature neurones, high basal [Cl(-)](i) results in membrane depolarisation following GABA(A) receptor activation, which is critical for various developmental processes including steroid-mediated sexual differentiation of the hypothalamus. Previously, we demonstrated that oestradiol enhances GABA-mediated Ca(2+) influx in neonate hypothalamus and that Ca(2+) induced activation of the transcription factor, cyclicAMP response element binding protein (CREB), was higher in male (high oestradiol) relative to female neonate hypothalamus. Based on these results, we hypothesised that expression of developmentally regulated chloride cotransporters may be sexually dimorphic. ⋯ By contrast, KCC2 mRNA levels were significantly lower in males relative to females on PND0. KCC2 protein was not detectable on ED20 or PND0 but was significantly lower in males relative to females on PND5. These results suggest a complex relationship between KCC2 and NKCC1 mRNA and protein in developing brain that is not easily linked to regulation by oestradiol.
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In mammals, daily rhythms in behaviour and physiology are driven by a circadian timing system comprised, in a hierarchical way, of a master pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus and of peripheral oscillators in most body cells. At the molecular level, in both the SCN and peripheral oscillators, the circadian clock mechanism is built from interconnected feedback loops in gene expression that operate in a cell-autonomous and self-sustained fashion. The SCN clock is mainly entrained by light/dark cycles. ⋯ In addition, there may be one or more oscillator sites that would play an integral role as a food-entrained oscillator (FEO), responsible for anticipation of meal-time. The site housing, or the network underlying, this putative FEO is still unknown. The aim of this review is to summarise our current knowledge of the central and peripheral circadian clocks and how they can be entrained by feeding at the physiological and molecular levels.