Peripheral nerve grafts to the frog optic tectum: a morphological study of the axon reaction in trigeminal motor and sensory neurons.
The mandibular branch of the trigeminal nerve was severed and the proximal stump was grafted onto the optic tectum in adult Rana pipiens. The resultant changes occurring in the cell bodies of origin in the ipsilateral trigeminal motor and mesencephalic nuclei were studied qualitatively and quantitatively. Nucleolar, nuclear, and somal cross-sectional areas increased in size significantly approximately 3 days after surgery and peaked at 6 weeks postsurgery. This swelling, in which the nucleolus was most severely affected, gradually reversed itself and disappeared by 24 weeks after surgery. Despite the cell enlargement, cytoplasmic basophilia was maintained or even slightly increased. These morphologic changes suggest a strong anabolic reaction. Two differences were found between the motoneurons and the sensory neurons. First, the morphometric cell changes occurred at a faster rate in neurons of the trigeminal motor nucleus than in those of the mesencephalic nucleus. The time course of the motoneuron response correlated well with that of axonal regeneration from the nerve graft. Second, there was a delayed loss of mesencephalic nucleus cells between 12 and 24 weeks after surgery, whereas cells of the trigeminal motor nucleus were maintained at all survival times studied. Taken together with sensory cell loss in the trigeminal ganglion, this suggests a greater viability of regenerating motoneurons.
D000818:Animals; D001369:Axons / Q000648:ultrastructure*; D002470:Cell Survival; D008297:Male; D008340:Mandibular Nerve / Q000502:physiology / Q000637:transplantation*; D008636:Mesencephalon / Q000648:ultrastructure; D009046:Motor Neurons / Q000648:ultrastructure*; D009416:Nerve Regeneration; D009475:Neurons, Afferent / Q000648:ultrastructure*; D011894:Rana pipiens; D013477:Superior Colliculi / Q000601:surgery*; D014278:Trigeminal Nuclei / Q000648:ultrastructure*