Differential gene expression in the rat hippocampus during learning of an operant conditioning task

Changes in transcription levels of brain-derived neurotrophic factor (BDNF), cyclic adenosine monophos-phate (cAMP) response element binding (CREB), Synapsin I, Ca²⁺/calmodulin-dependent protein kinase II (CamKII), activ-ity-regulated cytoskeleton-associated protein (Arc), c-jun and c-fos have been associated to several learning paradigms in different brain areas. In this study, we measured mRNA ex-pression in the hippocampus by real time (RT)-PCR mRNA levels of BDNF, CREB, Synapsin I, CamKII, Arc, c-jun and c-fos, during learning and operant conditioning task. Exper-imental groups were as follows: control (C, the animals never left the bioterium), when the animals reached 50-65% of the expected response (Incompletely Trained, IT), when animals reached 100% of the expected response with a latency time lower than 5 s (Trained, Tr), Box Control of Incompletely Trained (BCIT), animals spent the same time as the IT in the operant conditioning box and Box Control of Trained (BCTr) animals spent the same time as the Tr in the operant condi-tioning box. All rats were killed at the same time by cervical dislocation 15 min after training and hippocampi were re-moved and processed. We found increments of mRNA levels of most genes (BDNF, CREB, Synapsin I, Arc, c-jun and c-fos) in IT and Tr groups compared to their box controls, but increments in Tr were smaller compared with IT. These re-sults describe a differential gene expression in the rat hip-pocampus when the animals are learning and when animals have already learned. Taking together the results presented herein with the known functions of these genes, we propose a link between changes in gene expression in the hippocam-pus and different degrees of cellular activation and plasticity during learning of an operant conditioning task.