Immediate early genes expression in the cerebellar cortex correlates with LTP and LTD induction

Abstract

The consolidation of changes following activity-dependent neural plasticity are believed to involve specific patterns of gene expression. In the hippocampus, immediate early genes are thought to contribute to long-term synaptic plasticity (LTP and LTD); this phenomenon may occur also in the cerebellum, in which the transcription factors c-Fos and P-CREB have been identified. The cerebellum granular layer (GL) can manifest both LTP and LTD following a Theta Burst Stimulus (TBS) delivered to the mossy fibers. We have employed VSD imaging in rat cerebellar slices (P18-24) in order to map the spatial distribution of LTP and LTD in the cerebellum GL. Fluorescence changes were correlated to LTP or LTD in two different post-TBS time ranges (15 and 120 min). Slices were then fixed and processed for immunohistochemistry in order to identify levels of c-Fos and P-CREB expression. The induction of long-term plasticity increased the average level of P-CREB both at 15 min (+39±4.9, p<0.01%) and 120 min (+24±7.2, p<0.05%) after TBS. The level of c-Fos was unaltered at 15 min, while it significantly increased at 120 min (+37±8.9, p<0.05%). By spatially correlating longterm synaptic plasticity with the corresponding variation of P-CREB and c-Fos, we observed that regions showing LTP well correlated (p<0.05) with positive variations of P-CREB and c-Fos. Conversely, areas showing LTD correlated exclusively (p<0.05) with negative variations of P-CREB. Slices were also evaluated by in situ hybridization and a similar analysis was performed. The levels of fos and CREB mRNA expression and their spatial correlation with the sign of long-term synaptic plasticity corresponded with the immunohistochemical results. As a further test, VSD recordings showed that the induction of granular layer LTP and LTD could be prevented by applying 50 mM D-APV, a selective NMDA receptor blocker. Moreover, in situ hybridization and immunohistochemistry analysis evidenced that in these conditions both mRNA and protein expression levels of c-fos and CREB were unchanged, confirming the involvement of these two transcription factors in cerebellar granular layer plasticity.