Dentate gyrus-selective colchicine lesion and performance in temporal and spatial tasks

The effects of multiple-site, intradentate, colchicine injections on the performance of a temporal, 'differential reinforcement of low rates of responding' (DRL-20s) task and a spatial, 'delayed non-matching-to-place' (DNMTP) task in a plus-maze were investigated in rats trained in both tasks prior to the lesion. Quantitative analysis revealed a greater than 86% reduction in the dentate gyrus (DG) of the colchicine-injected rats compared to the sham-operated controls. Dentate gyrus damage rendered rats less efficient than sham-operated controls in the performance of the DRL-20s task. The DRL inter-response time (IRT) distribution for the DG-lesioned rats and the sham-operated controls was similar; however, while the distribution peak for the control rats was 20s, it was 16s for the DG-lesioned rats, indicating that the latter rats underestimated time. Performance of the DG-lesioned rats was also disrupted in the DNMTP task. However, DG-lesioned rats recovered control levels of performance during repeated training with an intertrial interval equal to 3s. An increase in intertrial interval in lesioned and sham-operated controls disrupted performance in both groups; however, while DG-lesioned rats performed at chance levels when the intertrial interval was increased to 4min or longer, the sham-operated controls performed at chance levels only when the intertrial interval was increased to 16min. These results seem most parsimoniously interpreted following the cognitive map theory of hippocampal function.