Axon reaction in dorsal motor vagal and hypoglossal neurons of the adult rat. Light microscopy and RNA-cytochemistry.

Qualitative light microscopical observations, morphometric measurements, and cytophotometric values for nucleolar and cytoplasmic RNA were compared in axotomized rat dorsal motor vagal and hypoglossal neurons. These data were correlated with consective cell counts and examination of the peripheral nerves. Vagal neurons showed an early prominent chromatolysis, later accompanied by increased cytoplasmic basophilia. Morphometric data showed a transient slight cytoplasmic enlargement but no nucleolar hypertrophy. Nucleolar RNA was unchanged, but cytoplasmic RNA was elevated 7 to 84 days postoperatively. Cell counts demonstrated a final cell loss of about 70%. Hypoglossal neurons showed a moderate chromatolysis. Nucleolar and cytoplasmic areas were enlarged for a short period. Nucleolar and cytoplasmic RNA were elevated about 3 to 14 days and about 3 to 28 days postoperatively, respectively. Cell counts demonstrated a loss of 25% at the longest postoperative survival period. The results indicate that axotomized adult mammalian extrinsic neurons--even those destined to die--accumulate RNA. This response contrasts with axon reaction in many axotomized mammalian intrinsic neurons which appear to undergo depletion of RNA.