Research reportThe time course of activity-regulated cytoskeletal (ARC) gene and protein expression in the whisker-barrel circuit using two paradigms of whisker stimulation

•These experiments investigated ARC as a molecular marker of circuit activation.•Whisker stimulation revealed a primary (30 min) and secondary (300 min) peak of ARC gene expression in the S1BF.•The time course of ARC gene expression is repeatable between paradigms and the magnitude of ARC mRNA transcription is input dependent.•Manual whisker stimulation-induced ARC gene expression is specific to the S1BF, not the hippocampus.

Immediate early genes have previously demonstrated a rapid increase in gene expression after various behavioral paradigms. The main focus of this article is to identify a molecular marker of circuit activation after manual whisker stimulation or exploration of a novel environment. To this end, we investigated the dynamics of ARC transcription in adult male rats during whisker somatosensation throughout the whisker barrel circuit. At various time points, tissue was biopsied from the ventral posterior medial nucleus (VPM) of the thalamus, primary somatosensory barrel field (S1BF) cortex and hippocampus for quantification using real-time PCR and western blot. Our results show that there were no significant differences in ARC gene or protein expression in the VPM after both types of stimulation. However, manual whisker stimulation resulted in increased ARC gene expression at 15, 30, 60 and 300 min in the S1BF, and 15 min in the hippocampus (p < 0.05). Also, exploration of a novel environment resulted in increased ARC mRNA expression at 15 and 30 min in the S1BF and at 15 min in the hippocampus (p < 0.05). The type of stimulation (manual versus exploration of a novel environment) influenced the magnitude of ARC gene expression in the S1BF (p < 0.05). These data are the first to demonstrate that ARC is a specific, quantifiable and input dependent molecular marker of circuit activation which can serve to quantify the impact of brain injury and subsequent rehabilitation on whisker sensation.