Journal of neuroendocrinology
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J. Neuroendocrinol. · Jan 1999
Changes in NADPH-d staining in the paraventricular and supraoptic nuclei during pregnancy and lactation in rats: role of ovarian steroids and oxytocin.
Staining for nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), a histochemical marker for nitric oxide synthase (NOS), is increased in the supraoptic (SON) and paraventricular (PVN) nuclei in late pregnant rats. To determine whether increases in staining were evident at other times during pregnancy and lactation the number of cells that stained for NADPH-d in the SON and PVN in rats on days 4, 12, 16, and 22 of pregnancy and on days 4, 12, and 20 of lactation was compared to that in virgin females. In a second experiment the influence of ovarian hormones on NADPH-d staining was assessed by comparing staining in the SON and PVN among ovariectomized animals exposed to either a steroid hormone replacement schedule that mimics late pregnancy (oestrogen and progesterone with progesterone removal), oestrogen alone, oestrogen and progesterone, or cholesterol alone. ⋯ The number of cells showing dense staining for NADPH-d in both the SON and PVN increased on days 12 and 22 of pregnancy and 4 and 12 of lactation compared to that observed in virgins. NADPH-d staining in these areas was also increased by both the steroid treatment that mimicked late pregnancy and chronic central OT infusion in oestrogen-primed animals. These data suggest that NADPH-d staining in the SON and PVN is increased at times when oxytocinergic cells are known to be active and that the hormonal state associated with late pregnancy is sufficient to increase NADPH-d staining.
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J. Neuroendocrinol. · Jan 1999
Differential regulation of hippocampal glucocorticoid receptors mRNA and fast feedback: relevance to post-traumatic stress disorder.
Hippocampal glucocorticoid receptors (GR and MR) play an important role in glucocorticoid negative feedback. Abnormalities in negative feedback are found in depression and in post-traumatic stress disorder (PTSD), suggesting that GR and MR might be involved in the pathophysiology of these disorders. Enhanced negative feedback, the PTSD-specific neuroendocrine abnormality, can be induced in animals using a single prolonged stress (SPS) paradigm (a number of different stressors in one prolonged session, 'no stress' interval and a testing session one week later). ⋯ The MR/GR ratio was decreased only in animals that had enhanced fast feedback. These findings suggest that the increase in GR, in hippocampus is involved in the fast feedback hypersensitivity observed in the SPS animals, and might also underlie enhanced dexamethasone sensitivity found in PTSD. Since differential activation of GR and MR can modulate memory, behavioural responsivity, anxiety and fear, change in MR/GR ratio might also explain other PTSD-related phenomena.
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J. Neuroendocrinol. · Oct 1998
Role of endogenous opiates in glucoprivic inhibition of the luteinizing hormone surge and fos expression by preoptic gonadotropin-releasing hormone neurones in ovariectomized steroid-primed female rats.
In female mammals, the preovulatory luteinizing hormone (LH) 'surge' elicits ovulation and the subsequent transformation of Graafian follicles into corpora lutea, and is thus a critical component of successful reproduction. In light of evidence that this surge is impaired as a consequence of caloric restriction, the following experiments utilized pharmacological strategies to determine whether glucose substrate homeostasis influences the magnitude and/or duration of this pivotal hormonal event. Groups of oestrogen-and progesterone-primed ovariectomized (OVX) rats were injected intravenously (i.v.) with the glucose antimetabolite, 2-deoxy-D-glucose (2DG: 100 or 400 mg/kg), or the vehicle, saline, prior to onset of the expected LH surge. ⋯ Animals pretreated with 2DG i.c.v showed a significant decrease in mean numbers of GnRH neurones exhibiting Fos-ir, whereas coadministration of 2DG and NALT resulted in numbers of double-labelled neurones that were similar to those detected in the non-drug-treated controls. These studies show that magnitude of the LH surge is decreased by glucose substrate imbalance, and that regulatory effects of this metabolic challenge on the reproductive neuroendocrine axis is correlated with alterations in the transcriptional activation of preoptic GnRH neurones by gonadal steroid positive feedback. The present results also support a role for central opiatergic neurotransmission in glucoprivic regulation of cyclic LH secretion in this animal model.
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J. Neuroendocrinol. · Jan 1997
Immunotargeted lesions of paraventricular CRF and AVP neurons in developing rats reveal the pattern of maturation of these systems and their functional importance.
Pituitary ACTH secretion in the rat is controlled by a number of hypothalamic secretagogues, like CRF and AVP and by inhibitory feedback provided by glucocorticoids. During development, little is known about the precise regulation of ACTH release by hypothalamic neuropeptides and glucocorticoids. We used immunotargeted chemical PVN lesions to investigate the role of CRF and AVP neurons of the hypothalamic paraventricular nucleus (PVN) in the control of ACTH secretion in neonatal rats under basal conditions and 5 days after adrenalectomy (ADX). ⋯ During the first 10 days of life, within the adrenal stress hyporesponsive period, hypothalamic CRF and AVP neurons are not sensitive to glucocorticoid feedback and basal ACTH secretion appears to be relatively independent from hypothalamic input. After the second week of life, maturation of glucocorticoid receptors, neuronal phenotype and connections of the PVN to other brain structures (bed nucleus of the stria terminalis, central amygdala) allows for the full expression of corticosterone effect on hypothalamic neurons and for compensatory changes to occur following lesions. These results emphasize the extraordinary capacity of the developing central nervous system to adapt to changes in functionning of some neuronal areas critical for homeostatic balance and the important potential role of intra-hypothalamic and extrahypothalamic relationships in maintaining control over ACTH and glucocorticoid production during development.
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J. Neuroendocrinol. · Jun 1996
Food or water deprivation modulate nitric oxide synthase (NOS) activity and gene expression in rat hypothalamic neurones: correlation with neurosecretory activity?
Nitric oxide (NO) is produced by the enzyme NO synthase (NOS) and may be involved in the regulation of nutrient and endocrine homeostasis via actions on neurones of the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei. The effects of water deprivation or food deprivation for 4 days on the abundance of messenger RNA encoding NOS in these nuclei in rats were examined using in situ hybridization. Water deprivation markedly increased the abundance of NOS mRNA in both the SON and PVN (225 +/- 11% of control, P < 0.05 and 261 +/- 34% of control, P < 0.01 respectively). ⋯ Food deprivation decreased NOS mRNA abundance in the SON and PVN (42 +/- 6% and 52 +/- 7% of control respectively, both P < 0.05), while withdrawal of both food and water produced no significant net changes in the abundance of NOS mRNA. Treatment-induced alterations in NOS mRNA abundance were reflected by changes in NOS activity, as assessed by NADPH-diaphorase histochemistry, and NADPH-diaphorase staining was observed in neurones both positive and negative for oxytocin-like immunoreactivity. These findings suggest that NOS mRNA abundance, NOS enzymatic activity and presumably NO production are modulated in an activity-dependent manner in hypothalamic (magnocellular and parvocellular) neurones by alterations in fluid and nutrient homeostasis, and support data from other studies suggesting a role for NO in the central regulation of water and food intake in the rat.