LOSS OF HIPPOCAMPAL CA1 NEURONS AND LEARNING IMPAIRMENT IN SUBICULAR LESIONED RATS

30-Day-old male Wistar rats were tested for acquisition and retention of operant conditioned behavior after bilateral subicular lesions made either electrolytically or chemically (ibotenic acid). The acquisitio n of operant learning was carried out in lesioned rats by assessing th e number of sessions required to learn the operant task, whereas the r etention test was performed after lesions by assessing performance on a previously learnt operant task. The acquisition of pedal press opera nt learning was significantly delayed in both types of lesioned mts, w ithout any impairment in the retention of the previously learned task after lesioning. In these animals the cell densities were quantified i n cresyl violet-stained sections in different subfields of hippocampus . Following the lesion of subiculum, selective degeneration of CA1 cel ls without the involvement of other hippocampal subfields was observed . This might be due to the loss of target area (subiculum) through whi ch hippocampus is connected with neocortical and subcortical structure s. This, in turn, might have resulted in behavioral deficits. The data suggest that the subiculum might be involved in the acquisition of ne w information rather than in retention.