Elsevier

Neuroscience Letters

Volume 220, Issue 2, 13 December 1996, Pages 133-136
Neuroscience Letters

Down-regulation of endogenous nitric oxide synthase in late-pregnancy and parturition in the rat hypothalamic magnocellular neurons and neurohypophysis

https://doi.org/10.1016/S0304-3940(96)13248-1Get rights and content

Abstract

Several recent lines of evidence suggest that nitric oxide (NO) may be an endogenous inhibitory regulator of the neurosecretory mechanism in magnocellular neurons of the paraventricular and the supraoptic nuclei in the hypothalamus. The NO synthase (NOS) system in the hypothalamo-neurohypophysial axis is regulated in an activity-dependent manner. The present study examined NOS activity in the magnocellular neurons and neurohypophysis during pregnancy and parturition by using the nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry and assay of the specific NOS enzyme activity, respectively. In the paraventricular and supraoptic nuclei, the density and number of NADPH-diaphorase-positive cells decreased in late-pregnancy and parturition. The specific activity of NOS in the neurohypophysis also decreased in late-pregnancy through parturition, and increased shortly afterward. Together with the ability of a NO donor to significantly delay the progress of parturition when administered centrally in parturient rats, these observations suggest that this down-regulation of NOS activity in the hypothalamo-neurohypophysial axis in late-pregnancy and parturition may be of physiological importance in the onset and/or progress of parturition.

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Cited by (25)

  • Nitric oxide synthase activity and expression are decreased in the paraventricular nucleus of pregnant rats

    2009, Brain Research
    Citation Excerpt :

    In contrast to the studies discussed above, and similar to our results, other laboratories have reported decreased nNOS in the PVN and SON of near-term pregnant rats. For example, compared to nonpregnant and mid-term pregnant rats, NADPH-diaphorase staining in the PVN decreased in days 19–21 pregnant rats and then increased post-partum (Okere and Higuchi, 1996). In another study, nNOS mRNA was decreased in the SON and tended to decrease in the PVN of late pregnant rats prior to changes in plasma oxytocin levels.

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