Oxytocin and vasopressin release within the supraoptic and paraventricular nuclei of pregnant, parturient and lactating rats: A microdialysis study

doi:10.1016/0306-4522(93)90285-N

Neuroscience

Volume 53, Issue 1, March 1993, Pages 65-75

https://doi.org/10.1016/0306-4522(93)90285-N Get rights and content

Abstract

The release of the nonapeptides oxytocin and vasopressin within the hypothalamic supraoptic and paraventricular nuclei was measured in 30-min microdialysates in conscious female rats in the last three days of pregnancy, during parturition, immediately after parturition and during suckling, all in the same rats, and in virgin controls. Nonapeptide release within the supraoptic and paraventricular nuclei was unchanged during late pregnancy compared to virgin rats, but intranuclear oxytocin and not vasopressin release was elevated during parturition (relative to late pregnancy, supraoptic nucleus: to 254%, paraventricular nucleus: to 300%; P < 0.01) and during suckling also on days 8–10 of lactation (relative to pre-suckling, supraoptic nucleus: to 407%, paraventricular nucleus: to 275%; P < 0.02). Suckling-induced release of oxytocin was significantly reduced using Ca²⁺-free, EDTA-containing (10⁻⁴ M) microdialysis fluid and further stimulated by high K⁺-(56 mM), veratridine-containing (50 μM) microdialysis fluid. The opioid antagonist naloxone whether given by subcutaneous injection (5 mg/kg) or directly into the supraoptic nucleus by microdialysis (5 × 10⁻⁶M) or microinjection (1.5 μl, 10⁻⁶M) did not further enhance oxytocin release within either the supraoptic or paraventricular nuclei during parturition.

In contrast to the selective release of oxytocin within the supraoptic and paraventricular nuclei during parturition and suckling, direct osmotic stimulation of the nuclei by microdialysing hypertonic medium (artificial cerebrospinal fluid; 1 M NaCl) increased intranuclear release of both oxytocin and vasopressin which was further enhanced after replacement of hypertonic with isotonic fluid. This rebound phenomenon served to confirm the precise location of the microdialysis probe ante mortem and the ability of the nuclei to adequately respond to the osmotic stimulus at the end of the experiment.

The study has shown that oxytocin is released in the supraoptic and paraventricular nuclei during parturition as well as in lactation unrestrained by endogenous opioids during parturition. This intranuclear release of oxytocin may act by local positive feedback stimulation of oxytocin neurons to excite further oxytocin release in the brain and into blood during both parturition and lactation.

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Oxytocin and vasopressin release within the supraoptic and paraventricular nuclei of pregnant, parturient and lactating rats: A microdialysis study

Abstract

Neurosci. Biobehav. Rev.

Eur. J. Pharmac.

Brain Res.

Neuroscience

Brain Res. Bull.

Brain Res.

Prog. Neurobiol.

Brain Res.

Physiol. Behav.

Brain Res.

Brain Res.

Brain Res.

Neurosci. Lett.

Brain Res.

Prog. Brain Res.

Neuroscience

Neurosci. Lett.

Neuroscience

Brain Res.

Molec. Brain Res.

Brain microdialysis

J. Neurochem.

The regulation of oxytocin mRNA levels in the medial preoptic area

Ann. N.Y. Acad. Sci.

The distribution and synaptic release of oxytocin in the central nervous system

Oxytocin and vasopressin immunoreactivity in hypothalamic and extrahypothalamic sites in late pregnancy and post partum rats

Neuroendocrinology

Hypothalamic opiatergic tone during pregnancy, parturition and lactation in the rat

Neuroendocrinology