Ultrastructural observations on transganglionic degeneration in trigeminal primary sensory neurons in the neonatal rat.

Transganglionic degeneration was studied ultrastructurally in the trigeminal nucleus caudalis of newborn rats 2-6 days after a transection of the infraorbital nerve. Darkened degenerating terminals containing more or less numerous vacuoles and darkened unmyelinated axons were observed already 2 days postoperatively, but became more frequent at 3 days survival, and again less frequent at 6 days survival. Degenerating myelinated axons were most frequent 6 days postoperatively. Another conspicuous finding was the appearance of degenerating cells, in less advanced stages interpreted as being neurons.