Fetal nigral grafts in the anterior eye chamber of adult rats: a long-term morphological study

Abstract

Substantia nigral grafts of 16 and 17 gestation days showed phenotypic characteristics in the anterior eye chamber of adult rats until the third month after transplantation. Thereafter by the sixth month a number of neurons showed somal and dendritic thickening, reduced population of endoplasmic reticulum, increase in lysosomes, and clear areas devoid of organelles, indicating age changes. These changes were progressive and affected more neurons by the end of 1 year, the longest period studied. The observations suggest that the maturation of nigral neurons is independant of specific afferent input, whereas target influence is necessary for the continued maintenance of the mature neurons. All the synapses observed in the transplant were of the asymmetric variety, reminiscent of the few intrinsic synapses of the intact nigra. This suggested establishment of mutual connectivity among the transplanted neurons in the absence of a target and the type of synapse formed may have been influenced by the local environment. Large glial processes, very prominant during the 4- to 6-month period became less significant afterward but continued to be present until the end of the period studied. Though there was no morphological evidence of lymphocytic infiltration, this might suggest an immunologic reaction.