Oxytocin decreases corticosterone and nociception and increases motor activity in OVX rats

Objectives: In the present study the effects of oxytocin administered subcutaneously (s.c.) or intravaginally (i.vag.) on spontaneous motor activity, nociceptive thresholds and plasma corticosterone levels were examined in female ovariectomized (OVX) rats. Methods: Oxytocin (1 mg/kg s.c. or 100 mu g i.vag.) was administered once a day for 10 days to OVX rats. Controls received saline s.c. or cellulose gel i.vag. Spontaneous motor activity was observed in an open-field arena, nociceptive thresholds were investigated by the tail-flick test, and corticosterone and oxytocin plasma levels were measured by radioimmunassay, 3, 4 and 5 days respectively, after the end of the treatment period. Results: Both oxytocin administered s.c. and i.vag. increased forward locomotion (p < 0.05) and nociceptive thresholds (p < 0.05) significantly. In addition, oxytocin s.c. increased the amount of locomotor activity (p < 0.05). Plasma corticosterone levels were decreased (p < 0.05) and oxytocin levels were unchanged when measured 5 days after the last administration of oxytocin s.c. or i.vag. Conclusion: The present data indicate that oxytocin induces a spectrum of long-lasting effects in OVX rats, including an increase in spontaneous motor activity, elevation of nociceptive thresholds and decrease of corticosterone levels. Similar effects may be induced by estrogens. In addition, these data indicate that i.vag. administration of oxytocin may be used to induce oxytocin-mediated effects. (c) 2004 Elsevier Ireland Ltd. All rights reserved.