Corticocortical Connections of the Rostral Forelimb Area in Rats: A Quantitative Tract-Tracing Study

Abstract

The rostral forelimb area (RFA) in the rat is considered to be a premotor cortical region based primarily on its efferent projections to the primary motor cortex. The purpose of the present study was to identify corticocortical connections of RFA, and to describe the relative strength of connections with other cortical areas. This will allow us to better understand the broader cortical network in which RFA participates, and thus, determine its function in motor behavior. In the present study, the RFA of adult male Long-Evans rats (n=6) was identified using intracortical microstimulation techniques and injected with the tract tracer, biotinylated dextran amine (BDA). In post-mortem tissue, location of BDA-labeled terminal boutons and neuronal somata were plotted and superimposed on cortical field boundaries. The results demonstrated that the RFA has dense to moderate reciprocal connections with primary motor cortex, the frontal cortex medial and lateral to RFA, primary somatosensory cortex (S1), and lateral somatosensory areas. Importantly, S1 connections were dense to moderate in dysgranular zones, but sparse to negligible in granular zones. Cortical connections of RFA in rat are strikingly similar to cortical connections of the ventral premotor cortex in non-human primates, suggesting that these areas share similar functions.