Galanin modulates oxytocin release from rat hypothalamo-neurohypophysial explant in vitro - the role of acute or prolonged osmotic stimulus.

INTRODUCTION

Galanin (Gal) may be involved as the neuromodulator of different processes in the central nervous system in the regulation of neurohypophysial function. The aim of the present study was to examine the influence of Gal on oxytocin (OT) release in vitro: an acute or prolonged osmotic stimulus was used as the stimulatory agent.

MATERIAL AND METHODS

Experiments were carried out on three-month old male rats which acted as donors of isolated rat hypothalamus (Hth), neurohypophysis (NH) or hypothalamo-neurohypophysial explants (Hth-NH). The effect of Gal on OT secretion was studied under conditions of non-osmotic (i.e. K(+)-evoked) (series 1), direct osmotic (i.e. Na(+)-evoked) (series 2) or indirect osmotic stimulation (series 3; neural tissues were obtained from animals drinking 2% NaCl). OT content was determined by radioimmunoassay.

RESULTS

Galanin added into incubative media caused the inhibition of basal OT release from NH and Hth-NH explants prepared from euhydrated rats but stimulated basal and K(+)-stimulated OT release from the Hth tissue. Gal did not exert any influence on Na(+)-evoked OT secretion. We observed increased basal OT secretion from NH and K(+)-evoked respective OT release from Hth and Hth-NH explants taken from osmotically challenged rats under the influence of Gal.

CONCLUSIONS

Present experiments in vitro show that: 1. Galanin plays the role of an inhibitory neuromodulator of OT release from the neurohypophysis; its effect is opposite at the hypothalamic level. 2. Galanin acts as the stimulatory neuromodulator of OT release in response to prolonged osmotic stimulus; an acute osmotic stimulus blocks OT-ergic neurons susceptible to Gal.