MORPHOLOGICAL AND BEHAVIORAL-EFFECTS OF GRANULE CELL DEGENERATION INDUCED BY INTRAHIPPOCAMPAL FLUID INJECTIONS IN INTACT AND FIMBRIA-FORNIXLESIONED RATS

This study was aimed al determining whether granule cell degeneration induced by intragyral injections of a neutral fluid (0.9% NaCl with 0. 6% glucose, pH 7.0, 2 sites per hippocampus, 2 mu l/site, 1 mu l/min) produced behavioural deficits in rats which, 2 weeks prior to the inje ctions, had received either fimbria-fornix lesions or sham-operations. In both sham-operated and lesioned rats, we found such injections to induce a comparable, topographically-limited loss of granule cells in the dorsal leaf of the dentate gyrus and, in the close vicinity of the degeneration area, a severe shrinkage of the molecular layer with con comitant morphological reorganizations (e.g. acetylcholinesterase reac tion products were distributed uniformly throughout the molecular laye rs of sham-operated rats). While the fimbria-fornix lesions produced c lassically reported behavioural deficits (hyperactivity in both a fami liar and an unfamiliar environment, reduced T-maze alternation rates a nd impaired radial-maze performance), we could not detect adversive ef fects of the granule cell degeneration on either of these variables in sham-operated and lesioned rats. Our data suggest that limited granul e cell degeneration induced by intragyral fluid injections has no effe ct on locomotor activity, spontaneous alternation and spatial learning . Therefore, we may also infer that the granule cell damage observed a fter an intragyral implantation of a fetal neural cell suspension does probably not account for the behavioural deficits which, in some expe riments, have been found in fimbria-fornix lesioned rats bearing intra gyral cell suspension grafts.