Anatomic resolution of neurotransmitter-specific projections to the VTA reveals diversity of GABAergic inputs.

The ventral tegmental area (VTA) is important for reward processing and motivation. The anatomic organization of neurotransmitter-specific inputs to the VTA remains poorly resolved. In the present study, we mapped the major neurotransmitter projections to the VTA through cell-type-specific retrograde and anterograde tracing. We found that glutamatergic inputs arose from a variety of sources and displayed some connectivity biases toward specific VTA cell types. The sources of GABAergic projections were more widespread, displayed a high degree of differential innervation of subregions in the VTA and were largely biased toward synaptic contact with local GABA neurons. Inactivation of GABA release from the two major sources, locally derived versus distally derived, revealed distinct roles for these projections in behavioral regulation. Optogenetic manipulation of individual distal GABAergic inputs also revealed differential behavioral effects. These results demonstrate that GABAergic projections to the VTA are a major contributor to the regulation and diversification of the structure.