Cellular distributions of AMPA glutamate receptor subunits in fetal ventral mesencephalon transplants in the dopamine-depleted striatum of a rat

Morphological changes in immunopositive cells of ionotropic glutamate receptor subunits during the development of transplanted fetal ventral mesencephalic neurons

To elucidate the morphological changes in immunopositive cells of ionotropic glutamate receptors within intrastriatal 'developing' grafts of fetal ventral mesencephalon (VM) in 6-hydroxydopamine-lesioned rats, immunohistochemistry was performed to detect cells expressing N-methyl-D-aspartate (NMDA) receptor subunit 1 (NR1), the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunits (GluR1, GluR2/3, and GluR4), or tyrosine hydroxylase (TH) in the intrastriatal VM grafts at 1, 4, and 12 weeks following transplantation. One week after transplantation, TH-positive cells were detected without any immunoreactivity of the NMDA and AMPA receptor subunits in the grafts. Four weeks after transplantation, TH-positive cells, distributed homogeneously in the grafts, appeared to be multipolar and larger compared to those at 1 week post-grafting. At this stage, we could observe immunopositive cells of NMDA and AMPA receptors distributed homogeneously in the grafts. Twelve weeks after transplantation, the numbers of NR1- and GluR1-positive cells were smaller than that at 4 weeks post-grafting, whereas TH-positive cells appeared to be more matured in shape and size. On the other hand, the numbers of GluR2/3- and GluR4-positive cells were not changed as compared with those at 4 weeks post-grafting. These results suggest that the ionotropic glutamate receptors have differential roles during the developmental period of the intrastriatal VM grafts.

Cellular distribution of the NMDA receptor subunit NMDAR1 in fetal ventral mesencephalon transplants in the dopamine-depleted striatum of a rat

Immunohistochemistry was performed to demonstrate the cellular distribution of N-methyl-D-aspartate (NMDA) receptor subunit NMDAR1 in the intrastriatal grafts of a rat model of Parkinson's disease. Unilateral 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal pathway were produced in young adult female rats. Neural transplantation was performed with fetal ventral mesencephalon (VM) tissue (at embryonic day 15) 3 weeks after the 6-OHDA lesions. In the fetal VM in which the tyrosine hydroxylase (TH) immunoreactivity was intensely observed, no NMDAR1 subunit immunoreactivity was detected. Immunopositive cells of NMDAR1 were densely distributed in the intact SNc contralateral to the lesions, in which intense immunoreactivity for TH was observed. In contrast, the cells positive for NMDAR1 in the SNr were scattered. The immunoreactivity for NMDAR1 was markedly decreased in the SNc, but not in the SNr on the lesioned side. Double immunostaining revealed that most TH-positive cells in the SNc showed moderate NMDAR1 immunoreactivity. Within the intrastriatal fetal VM grafts containing TH-positive cells, NMDAR1-positive cells tended to locate homogeneously within the grafts. These were composed of various cell sizes and shapes, but they were mainly medium-sized and aspiny cells. Double immunostaining revealed that a part of the TH-positive cells in the grafts was also immunopositive for NMDAR1. Taken together with our previous studies, it is suggested that both dopaminergic neurons and nondopaminergic neurons in the VM transplants appear to be modified functionally by glutamatergic afferents via various glutamate receptors, including NMDAR1.