Braking Dopamine Systems: A New GABA Master Structure for Mesolimbic and Nigrostriatal Functions

A new mesopontine structure exerting a strong influence on dopamine systems has been recently defined: the tail of the ventral tegmental area / rostromedial tegmental nucleus (tVTA/RMTg). This review presents a neuroanatomical, physiological and behavioral overview of some of the recent and ongoing research on this brain region and its relationship with dopamine systems. The tVTA/RMTg sends dense GABA projections to VTA and substantia nigra neurons. The inhibitory influence of tVTA/RMTg on dopamine neurons is supported by both neuroanatomical and electrophysiology data. The latter studies also revealed the tVTA/RMTg as a substrate for morphine and cannabinoid action on dopamine cells. In primates, the tVTA/RMTg has been implicated in reward prediction error signals, through a basal ganglia - lateral habenula - tVTA/RMTg - dopamine - basal ganglia circuit. In rodents, the tVTA/RMTg has been shown to play a critical role in aversive behaviors, particularly those involving behavioral inhibition, such as freezing and avoidance. These findings highlight the functional importance of the tVTA/RMTg as a major GABA brake for dopamine systems