CHANGES IN OXYTOCIN RECEPTOR MESSENGER-RNA IN RAT-BRAIN DURING PREGNANCY AND THE EFFECTS OF ESTROGEN AND INTERLEUKIN-6

Changes in brain oxytocin receptor (OTR) binding sites during the cour se of pregnancy may influence the sudden onset of maternal behavior in female rats at parturition. In situ hybridization was used to identif y changes in OTR messenger ribonucleic acid (mRNA) expression during p regnancy and parturition. Two patterns of mRNA regulation were observe d, Relative to diestrus virgin control females, OTR mRNA was elevated in the lateral septum and medial preoptic area at days 13-15 of pregna ncy but not on the morning of parturition. In the central nucleus of t he amygdala and ventromedial nucleus of the hypothalamus (VMH), OTR mR NA was most abundant on the morning of parturition. Strong signals for OTR mRNA were detected in the bed nucleus of the stria terminalis, hy pothalamic paraventricular nucleus, supraoptic nucleus and suprachiasm atic nucleus, However no group differences were detected in these area s. As estrogen and interleukin-6 have been suggested to modulate OTR g ene expression and both are elevated at the time of parturition, their effects on OTR mRNA in the brain were examined. Estrogen and interleu kin-6, given simultaneously, significantly elevated the concentration of OTR mRNA in the VMH, but not in the amygdala. The increase in the V MH was significantly greater than that produced by estrogen alone, and interleukin-6 alone had no effects. These results demonstrate that tr anscriptional regulation of OTR gene expression mediates changes in re ceptor density in the brain in a region specific manner during pregnan cy and suggests a potential mechanism for some of these changes.