NEURAL GRAFTING TO ISCHEMIC CA1 LESIONS IN THE RAT HIPPOCAMPUS - AN AUTORADIOGRAPHIC STUDY

Fetal hippocampal neurons were stereotaxically transplanted to five-da y-old ischemic CA1 lesions in adult rat hippocampi. The recipient brai ns were examined 14 or 100 days later. The grafts survived well, and t ransplanted cells usually formed clusters in the host CA1 subfield. In vitro receptor autoradiography was employed to map the following rece ptors, the ligands indicated in parentheses being used for labeling: m uscarinic cholinergic ([H-3]quinuclidinyl benzilate), adenosine A1 ([H -3]cyclohexyl-adenosine), kainate ([H-3]kainic acid), spirodecanone ([ H-3]spiperone), opioid ([H-3]naloxone), and GABA, ([H-3]muscimol). The receptor autoradiographic technique showed significant binding of the six ligands in all hippocampal grafts two weeks after transplantation . One hundred days following transplantation, almost all receptors, es pecially muscarinic cholinergic, adenosine A1 and opioid receptor bind ings in grafts, had significantly increased compared to bindings two w eeks after transplantation. At this time, kainate and muscarinic choli nergic receptors in grafts had increased up to the near normal level o f the CA1 in the hippocampus. Interestingly, adenosine A1 receptors in the grafted side had significantly increased not only in the CA1 but also in the stratum oriens of the CA3 compared with that in the non-gr afted side. The increase of [H-3]quinuclidinyl benzilate binding corre sponded well with the innervation of acetylcholinesterase-positive fib ers at 100 days after grafting. These results demonstrate that the tra nsplanted neurons, which showed both pre- and post-synaptic autoradiog raphic markers in the ischemic CA1 lesions, are able to develop their properties and express the nature of normal hippocampal neurons.