Nucleus identified in the medial ventral tegmental area that borders the red nucleus and superior cerebellar peduncle dorsally, the medial lemniscus laterally, the subtantia nigra pars compacta and paranigral nucleus ventrally and the rostral linear nucleus and interfascicular nucleus medially. Generally, the largest nucleus in the ventral tegmental area, occupying an average of 50% of the total volume as measured in rat, cat, monkey and human. [ ]