Projections to the midbrain from the medial versus lateral prefrontal cortices of the rat

Microinjections of horseradish peroxidase were made into the medial or lateral prefrontal cortex (PFC) of rats. The trajectory of descending, orthogradely labeled axons in route to the midbrain was then charted. The descending pathways originating from the medial versus lateral PFC were noticeably different. In general the medial PFC projected to dorsal aspects of the midbrain (e.g. dorsolateral periaqueductal gray and deep layers of superior colliculus), whereas the lateral PFC projected to the lateral and ventral aspects of the midbrain (e.g. ventral periaqueductal gray and laterally adjacent reticular formation). These differences suggest that the medial and lateral PFC may have different functions in regard to their potential influences upon the midbrain. Potential influences upon midbrain analgesic mechanisms are discussed.