Experienced-induced immediate early gene expression in hippocampus after granule cell loss

vii, 60 leaves : ill. (some col.) ; 29 cmAdrenalectomy (ADX) has been shown to cause selective degeneration of granule cells in the dentate gyrus (DG). This occurs due to the reduction of corticosterone (CORT) and behavioural deficits are associated with the loss of these neurons. Dentate lesions and cell loss associated with ADX have been shown to effect behaviour in a number of spatial tasks. In contras, it has been shown granule cell loss does not affect the specificity of place cells in CA3 and CA1. We used the ADX model to examine the role of DG granule cells plays in representing space using immediate early gene (IEG) activation in the principal hippocampal subfields after exploration of novel environments. Rats were allowed to free explore multiple novel environments and then the mRNA for the IEG Homer 1a (H1a) was used as a marker of neural activity. After degeneration of approximately half of the DG granule cells we found a significant increase in number of active cells in the DG, CA3 and CA1 in ADX animals. The results indicate a reduction in granule cells causes a dramatic increase in the proportion of remaining DG granule cells in response to exploration. The change in DG activation disrupts the representations in CA3 and CA1 and thereby affects behaviour