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 vasopressin receptor binding in the adult rat facial nucleus, suggesting an increased number of vasopressin receptors. These receptors were pharmacologically undistinguishable from peripheral V(1a) vasopressin receptors. In the present study, we show, using in situ hybridization and reverse transcriptase-polymerase chain reaction (RT-PCR), that axotomy regulates the expression of the vasopressin V(1a) receptor mRNA in the facial nucleus. Results were obtained from adult male rats killed 1 week following crush of the right facial nerve. In situ hybridization was performed with a (35)S-labelled riboprobe. A specific hybridization signal was detected in both left and right facial 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 nucleus, i.e., glial or epithelial cells. RT-PCR analysis of unlesioned facial tissue 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 the rat facial nucleus is due, at least to a large extent, to an increase of the V(1a) vasopressin receptor mRNA in facial motoneurons.