Journal of neuroendocrinology
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J. Neuroendocrinol. · Oct 2000
Effect of suckling on NADPH-diaphorase (Nitric oxide synthase, NOS) reactivity and NOS gene expression in the paraventricular and supraoptic nuclei of lactating rats.
This study examined the effect of suckling on nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d, a histochemical marker for nitric oxide synthase, NOS) reactivity and neuronal NOS mRNA expression in the paraventricular (PVN) and supraoptic (SON) nuclei of lactating rats. Freely nursing (non-separated) dams and those separated from pups for 12 h and then reunited for 0, 15, 30, 60, 90, 120 and 180 min were used for the study. ⋯ A pattern of NADPH-d reactivity and neuronal NOS mRNA expression indistinguishable from that observed during free lactation was reinstated shortly (15 min) after the restoration of suckling stimulus, suggesting that the NADPH-d reactivity in lactation depends on the presence of the suckling stimulus. These results show that suckling stimulus may play a modulatory role in the regulation of NOS reactivity in the magnocellular neurones of the hypothalamic PVN and SON during lactation.
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J. Neuroendocrinol. · Oct 2000
Comparative StudySelective blockade of the mineralocorticoid receptor impairs hypothalamic-pituitary-adrenal axis expression of habituation.
The present study investigated the role of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in the expression of habituation of the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Male rats were restrained for 1 h per day for six consecutive days. On day 6, 1 h prior to restraint stress, both restraint-naive and repeatedly restrained rats were injected s.c. with either vehicle (propylene glycol) or one of three corticosteroid receptor antagonist treatments: selective MR antagonist (RU28318 or spironolactone), selective GR antagonist (RU40555), or both MR and GR antagonists combined (RU28318 + RU40555). ⋯ This result indicates that the expression of habituation and its blockade by corticosteroid receptor antagonists is not a result of altered pituitary-adrenal response to CRH. Overall, this study suggests that MR plays an important role in constraining the HPA axis response to restraint stress in restraint-habituated rats. The dependence of the HPA axis on MR-mediated corticosteroid negative feedback during acute stress may be an important mechanism that helps maximize the expression of stress habituation and thereby minimize exposure of target tissues to corticosteroids in the context of repeated stress.