Abstract
8-L-Arginine vasopressin ([Arg8]VP) receptors are expressed transiently in the rat facial nucleus during the perinatal period. Electrophysiological studies suggest that at least part of these receptors is located on facial motoneurones. In the present study we report that, in the adult rat, unilateral section of a facial nerve results in a massive and transient reexpression of [Arg8]VP receptors in the deeferented facial nucleus. Data were obtained by quantitative film autoradiography. During the first 2 postoperative weeks, binding of an iodinated ligand selective for V1a-type receptors increased about 10-fold. Maximal levels of binding were maintained for 1-2 weeks and then started to decrease. Binding was not strictly restricted to the facial nucleus but included the neuropile between motoneuronal pools and the perifacial area, which may indicate a dendritic localization of [Arg8]VP receptors. To investigate whether other motor nuclei also react to axotomy by up-regulating [Arg8]VP receptors, we sectioned either a hypoglossal nerve or a sciatic nerve. Two weeks after surgery, the hypoglossal nucleus or sciatic motoneuronal pools ipsilateral to the lesion were intensely labeled with the iodinated ligand. In contrast, nerve section had no effect on oxytocin binding sites in facial, hypoglossal, or sciatic motor nuclei. The results suggest that [Arg8]VP receptor expression in motor nuclei may depend upon neuromuscular contacts and, thus, that [Arg8]VP may be involved in the establishment of neuromuscular connections during development and in their reestablishment after nerve injury.