Transplantation of embryonal cerebral cortex to the adult rat cerebellum: the fiber connections made by cortical transplants and the cerebellum
Kitakami, A.
No Shinkei Geka. Neurological Surgery 18(4): 347-353
1990
ISSN/ISBN: 0301-2603 PMID: 2374645 Document Number: 360590
Fifteen-day-old embryonic neocortical tissue was transplanted into the mature cerebella of normal adult rats (Fischer 344) heterotopically. After 5 - 8 months, WGA-HRP was injected into the host inferior olivary nucleus, pontine raphe, pontine nuclei, and neocortical transplants, 0.3 .mu.l respectively. The animals were sacrificed 48 hours later, and the HRP positive neuron and nerve fibers were examined in the transplants and host brain stem. Other animals were sacrificed for anti-dopamine-.beta.-hydoxylase immunohistochemical study and electron microscopic observation. Anterograde and retrograde tracing methods with the HRP method revealed on the light microscopic level that the transplants had received afferents from the host's locus coeruleus, and the inferior olivary nucleus. In one case, HRP injected into the host inferior olive was almost limited within the inferior olivary nucleus. Therefore, HRP-labelled fibers in the cerebellum were thought to be climbing fibers. The climbing fibers from the host inferior olivary nucleus entered the transplant from the host cerebellar medullary layers and branched in the transplant. The fiber ingrowth was limited within 300-500.mu.m for the distance. In another case, HRP injected into the inferior olive extended to the lateral reticular and the pontine nuclei. HRP labelled fibers entered the graft from the host medullary layers and many granular patterns like axon terminals were observed in the graft. In cases, in which HRP was injected into the pontine raphe and pontine nuclei, HRP labelled fibers did not grow into the graft. Retrograde tracing method with HRP injected into the graft showed labelled neurons in the host locust coeruleus. No labelled neuron was observed in other nuclei of the afferent system of the cerebellum. Anti-dopamine- .beta.-hydroxylase (DBH) immunohistochemical study showed a lot of DBH positive fibers in the graft. These fibers were considered to be noradrenaline (NA) fibers initiating from the host locus coeruleus. They have many varicosities and rosette-like structures. On electron microscopy, axon terminals which had granular synaptic vesicles indicative of NA fiber were observed in the transplant, and were seen to make synaptic connections with nerve cell processes in the transplant. The present study showed that fiber connections developed between the inferior olive and the cerebral cortex having no specificity. Regrowth capacity of host nerve fibers played an important role on the connectivity of neural transplants in the adult.