Altered expression of src tyrosine kinase after axotomy

Although most peripheral neurons show regenerative changes after axotomy, neurons of some nuclei show degenerative changes. To study the mechanisms responsible for such differences in neuronal reactions after axotomy, we investigated the changes of pp60c-src and phosphotyrosine (pTyr) in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus after transection of each nerve in adult rats using immunohistochemistry. Polyclonal antibody against pp60v-src stained the cytoplasm of neurons homogeneously in both the severed and non-severed sides of the vagal and hypoglossal nuclei from days 1 to 56 after axotomy. On the other hand, the monoclonal antibody against pp60v-src (mAb327, which recognizes src homology 3 region in pp60src as an epitope) showed different immunoreactivities. No pp60c-src immunoreactivity was observed in neurons in either the vagal and hypoglossal nuclei of the non-severed side between days 1 and 56, whereas in the severed side of the hypoglossal nucleus intense pp60c-src immunoreactivity was observed along the plasma membrane of neurons from days 5 to 28 after axotomy. In contrast, in the severed side of the vagal nucleus pp60c-src immunoreactivity appeared along the plasma membrane of neurons on day 5 and remained until day 7. Conformational changes accompanying the activation of pp60c-src are suggested to cause differences in immunoreactivities of these antibodies. The expression (or activation) of pp60c-src in the neurons was stronger and longer lasting in the hypoglossal nucleus, which regenerates successfully after axotomy, than in the dorsal motor nucleus of the vagus nerve, which undergoes necrobiotic reaction. These results indicate that pp60c-src plays an important role in regeneration after axotomy.