Spatial distributions of cytoskeletal proteins and the nerve growth factor receptor in septal transplants in oculo: Protection from abnormal immunoreactivity by hippocampal co-grafts

Intraocular grafts of embryonic rat septum and co-grafts of septum plus hippocampus were studied with immunohistochemical markers after one and six months (short term) and 12 months (long term) of survival. Neurons in all the septal tissues expressed the epitope for the rat beta-nerve growth factor receptor in sections reacted with the monoclonal antibody 192-IgG. Stained fibers traversed the interface of the short and long term co-grafts and 192-IgG-positive processes were most prominent in the septum when combined with the hippocampal formation. In contrast, labeled processes were sparse and the perikarya of positive neurons appeared shrunken in the long term single septal transplants. Axon and dendrite profiles in the grafts were examined with antibodies that recognize the phosphorylated heavy neurofilament unit (RT97) and the high molecular weight microtubule-associated protein termed MAP 2, respectively. In the short term single and double grafts, characteristic arrays of RT97-positive processes defined the tissues and axonal tracts connecting the septum with the hippocampus. Typical immunostaining of the neuronal somas and the dendrite arbors were were outlined with the MAP 2 antibody. After one year in oculo, extensive changes in the patterns of axonal and dendritic immunoreactivity were noted in the isolated septal grafts. Abnormalities identified with the RT97 antibody included hypertrophied axons, short fragments of kinked axons and neurofilaments in the neuronal perikarya. The formation of circular "abnormal fiber aggregates" composed of densely packed abnormal and normal axonal processes were also distinctive in only the long term single septal transplants. In addition, a reduction in the density of dendrites and the presence of truncated arbors stained with the MAP 2 antibody suggested that regression of the dendrites had occurred. These spatial modifications in axonal and dendritic staining were not present in the septal portion of the combined preparations. In astrocytes, an increase in the antigenicity to glial fibrillary acidic protein paralleled the age of the transplant and was most extensive in the septal grafts. The results illustrate that intraocular co-grafts of hippocampus protect septal neurons and glial cells from abnormal changes in immunoreactivity to antibodies directed against cytoskeletal proteins and exemplify the long term supportive effects of the hippocampus on the morphology of septal neurons, including neurons that express the receptor for nerve growth factor.