The preovulatory luteinizing hormone (LH) surge in female rats is dependent upon signals from the suprachiasmatic nucleus (SCN), the site of a dominant circadian pacemaker. Various lines of evidence indicate that arginine-vasopressin (AVP)-containing projections from the SCN to the preoptic area (POA) contribute to the production of the surge of LH-releasing hormone (LHRH). These actions may be mediated by V1a because the transcript for this AVP receptor subtype is predominant within the POA of the female rat. In this study, in situ hybridization histochemistry was used to examine V1a mRNA expression, either by itself or together with LHRH or glutamic acid decarboxylase 65 (GAD65) mRNA, within the POA of ovariectomized rats in the presence or absence of oestrogen. V1a mRNA was found in cells across the rostro-caudal axis of the POA; some were in close proximity to cells expressing LHRH mRNA. Coexpression of V1a and LHRH mRNAs was detected only very rarely. By contrast, cells with V1a mRNA commonly displayed GAD65 mRNA. The density of V1a mRNA-expressing cells was particularly high within the anteroventral periventricular nucleus; at this site, V1a mRNA expression was elevated following oestrogen treatment. The present results indicate that V1a-mediated AVP actions may influence LHRH release via cells in the immediate vicinity of LHRH neurones and/or via oestrogen-regulated cells in the anteroventral periventricular nucleus, which is a site that lacks LHRH neurones but plays an essential role in initiating the preovulatory LH surge.
- Luteinizing hormone releasing hormone
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience