Familiar taste induces higher dendritic levels of activity-regulated cytoskeleton-associated protein in the insular cortex than a novel one

The immediate early gene (IEG) Arc is known to play an important role in synaptic plasticity; its protein is locally translated in the dendrites where it has been involved in several types of plasticity mechanisms. Because of its tight coupling with neuronal activity, Arc has been widely used as a tool to tag behaviorally activated networks. However, studies examining the modulation of Arc expression during and after learning have yielded somewhat contradictory results. Although some have reported that higher levels of Arc were induced by initial acquisition of a task rather than by reinstating a learned behavior, others have failed to observe such habituation of Arc transcription. Moreover, most of these studies have focused on the mRNA and, surprisingly, relatively little is known about how learning can affect Arc protein expression levels. Here we used taste recognition memory and examined Arc protein expression in the insular cortex of rats at distinct times during taste memory formation. Interestingly, we found that more Arc protein was induced by a familiar rather than by a novel taste. Moreover, this increase was inhibited by post-trial intrahippocampal anisomycin injections, a treatment known to inhibit safe-taste memory consolidation. In addition, confocal microscopy analysis of immunofluorescence stained tissue revealed that the proportion of IC neurons expressing Arc was the same in animals exposed to novel and familiar taste, but Arc immunoreactivity in dendrites was dramatically higher in rats exposed to the familiar taste. These results provide novel insights on how experience affects cortical plasticity.