NEONATAL GAMMA-RAY IRRADIATION IMPAIRS LEARNING AND MEMORY OF AN OLFACTORY ASSOCIATIVE TASK IN ADULT-RATS

Adult neonatally gamma-irradiated rats were compared with control anim als in a non-spatial olfactory associative task using two different pr ocedures. Irradiation induced a clear reduction in the total mean area of the olfactory bulbs and hippocampus but not of the orbital prefron tal cortex, diagonal band and cell layers of the entorhinal and pirifo rm cortex. The gamma-irradiation affected the granule cells of the olf actory bulbs and differentially altered the cell layers of the subfiel ds of the ammonic fields and the dorsal and ventral blades of the dent ate gyrus. In the CA1 ammonic field, dorsal and ventral blades of the dentate gyrus, the cellular loss was significant in comparison with co ntrol adult rats. The behavioural data indicated that irradiated rats were deeply disturbed in learning the odour-reward association, and su bstantially impaired in a reversal experiment, but not in the discrimi nation of the odours per se. The cellular loss in the olfactory bulbs, in the CA1 and in the ventral blade of the gyrus dentatus was positiv ely correlated with the deficit in behavioural performance. The data s upport the findings that the hippocampal system participates in the od our-reward associations and facilitates the long-term storage of assoc iations after learning is achieved in this olfactory associative task.