Using IEG's to uncover pathways for spatial learning in the rat.

This thesis concentrates on the induction of the immediate early genes zif268 and c-fos in a functional and dysfunctional brain network. Initial studies focused on the creation of a task to allow the study of immediate early gene activation after working memory. Previous studies using such a paradigm have compared the animals performing the experimental task with poorly matched control groups. Experiments in this thesis attempted to rectify this. A group of experiments using the water maze found decreases in Zif268 activation in the experimental group as compared to control groups, mainly in the hippocampus and some parahippocampal areas. This was believed to have arisen because of a streamlining of the brain network in the Working Memory group. An increase in c-Fos immunoreactivity was seen in the Working Memory group as compared to controls in prefrontal regions. Structural equation modelling analysis was performed, which allows immediate early gene counts to be used to analyse networks of brain regions. In the Working Memory group connections were seen between the parahippocampal regions and the subiculum that progressed via the hippocampus, indicating that the hippocampus was still engaged by the task. In the control group analysed no such hippocampal pathway was found. This water maze task was then used to study zif268-EGFP activation in a novel transgenic rodent model, where the Zif268 promoter drives the expression of a fluorescent protein EGFP. Activation of both EGFP and Zif268 immunoreactivity was seen in the CA1 region of the animals performing the control task. No EGFP activation was seen in this region in the Working Memory group even though EGFP expression was seen in other regions. The GFP protein was also able to be seen under direct visualisation in the CA1 and dentate gyrus region of control animals. Concerning the dysfunctional brain, gene expression was analysed in the retrosplenial cortex after NMDA lesions of the anterior thalamic nuclei. Previous research has shown that lesions produce a dramatic hypoactivity in the protein products of the immediate early genes c-fos and zif268. Microarray analysis of retrosplenial tissue revealed that as well as decreases in expression of genes related to repair and cell adhesion/neurogenesis, an increase in c-fos mRNA was seen in the lesion hemisphere of the brain. This pattern of expression is opposite to that of the protein. Possible reasons for this are discussed