A Tale of Two Prefrontal Cortices: Connections of the Orbitofrontal Cortex in the Rat

Abstract

The prefrontal cortex (PFC) is most commonly defined as the frontal cortical area receiving a mediodorsal (MD) thalamic innervation, however other have put forth that the PFC in the zone of convergent innervation from the MD, basolateral amygdala (BLA), and midbrain dopamine neurons. The prelimbic area in the medial wall of the rat frontal cortex receives innervation from the MD, BLA, and dopaminergic midbrain. A second frontal area, the orbitofrontal cortex (OFC), is another the target of these three projections, however the extent of convergence in the OFC is unclear. We assessed the afferent innervation of the different areas within the OFC, with a focus on projections arising from the mediodorsal thalamic nucleus, the basolateral nucleus of the amygdala, and the midbrain dopamine neurons. Although there were specific inputs to various OFC areas, a simplified organizational scheme could be defined, with medial areas of the OFC receiving thalamic inputs, lateral areas of the OFC receiving amygdala afferents, with a central zone that was the target of midbrain dopamine neurons. Anterograde tracer data were consistent with this segmentation, and revealed that the OFC inputs from these three subcortical sites were largely spatially segregated. These findings highlight the heterogeneity of the OFC, and suggest possible functional attributes the three different OFC areas.