Motoneuron survival and expression of neuropeptides and neurotrophic factor receptors following axotomy in adult and ageing rats.

Three months after facial nerve transection, total numbers of motoneurons in the facial nucleus of six month (adult) Fischer 344 and Wistar rats were reduced to 83% and 75% of contralateral values, respectively (P < 0.05). This procedure in 22-26 month (ageing) Fischer 344 rats and Wistar rats resulted in a reduction of motoneuron numbers to 77% and 60% of the respective contralateral values (P < 0.05). Compared to adults, contralateral facial nuclei of aging Fischer 344 rats contained 10% fewer motoneurons (non-significant), while ageing Wistar rats had 22% fewer (P < 0.05). No significant changes were found in the proportion of surviving motoneurons expressing calcitonin gene-related peptide, galanin, receptor tyrosine kinase-C or the alpha subunit of the ciliary neurotrophic factor receptor. We conclude that ageing reduces facial motoneuron number and increases their vulnerability to axotomy in Wistar rats, but not in Fischer 344 rats. In neither strain, however, does the proportion of surviving motoneurons expressing the above neuropeptides or neurotrophic factor receptors change. This information may be relevant to those hypotheses of age-related neuronal degenerations which assume that decreased neurotrophic support renders ageing neurons more vulnerable to injury.