Up-regulation of vasopressin V-1a receptor mRNA in rat facial motoneurons following axotomy

We have reported previously that axotomy induced a marked increase of vasop ressin receptor binding in the adult rat facial nucleus, suggesting an incr eased number of vasopressin receptors. These receptors were pharmacological ly undistinguishable from peripheral V-1a vasopressin receptors. In the pre sent study, we show, using in situ hybridization and reverse transcriptase- polymerase chain reaction (RT-PCR), that axotomy regulates the expression o f the vasopressin V-1a receptor mRNA in the facial nucleus. Results were ob tained from adult male rats killed 1 week following crush of the right faci al nerve. In situ hybridization was performed with a S-35-labelled riboprob e. A specific hybridization signal was detected in both left and right faci al nuclei, with a significantly higher intensity in the nucleus ipsilateral to the lesion. V-1a receptor transcripts were found associated with large facial motoneuronal cell bodies, not with other cells present in the nucleu s, i.e., glial or epithelial cells. RT-PCR analysis of unlesioned facial ti ssue revealed the presence of mRNAs encoding vasopressin V-1a, vasopressin V-1b and oxytocin receptors, whereas only the V-1a receptor mRNA was found to be increased following axotomy in the lesioned facial tissue. These data suggest that the axotomy-induced expression of vasopressin receptors in th e rat facial nucleus is due, at least to a large extent, to an increase of the V-1a vasopressin receptor mRNA in facial motoneurons. (C) 1999 Elsevier Science B.V. All rights reserved.