BRAIN SOMATOSTATINERGIC SYSTEM AT LATE PREGNANCY, PARTURITION AND THEEARLY POSTPARTUM PERIOD IN THE RAT

During pregnancy and postpartum rats experience a wide variety of beha vioural changes. Since the somatostatinergic system has been implicate d in the control of some of these changes, the present study examined somatostatin (SS) content and specific binding in the frontoparietal c ortex and hippocampus of non-pregnant, pregnant (17 to 18 days), partu rition and postpartum (10 and 30 days) rats as well as in ovariectomiz ed rats which were or were not treated with estradiol valerianate. The content of somatostatin-like immunoreactivity (SSLI) was increased at 17 days of pregnancy in frontoparietal cortex and decreased at partur ition and 10 days postpartum in that region and the hippocampus under study when compared with SSLI levels in non-pregnant rats. At 30 days postpartum the SSLI content returned to non-pregnant values in both br ain regions. Scatchard analysis showed that the decrease in [I-125]Tyr 11-SS binding observed at 17 days of pregnancy in the frontoparietal c ortex was due to the decrease in the number of SS receptors. In contra st, on the day of delivery the number of SS receptors in the same brai n region increased. The affinity of the SS receptors was consistently unchanged in pregnant and non-pregnant rats in both regions. At 10 day s postpartum the value of specific binding of the tracer to SS recepto rs in the frontoparietal cortex was not significantly different from t hat in the non-pregnant rats, although the actual number of receptors was slightly higher. Pregnancy did not change SS binding in the hippoc ampus. Neither ovariectomy nor the treatment of ovariectomized rats wi th estradiol valerianate affected cortical and hippocampal SS content and binding in the rats. These changes in the somatostatinergic system associated with late pregnancy, parturition and the early postpartum period may well be important because of their possible role in some of the behavioural changes observed during these periods.