RT Journal Article SR Electronic T1 nNOS-Expressing Neurons in the Ventral Tegmental Area and Substantia Nigra Pars Compacta JF eneuro JO eNeuro FD Society for Neuroscience SP ENEURO.0381-18.2018 DO 10.1523/ENEURO.0381-18.2018 VO 5 IS 5 A1 Eleanor J. Paul A1 Eliza Kalk A1 Kyoko Tossell A1 Elaine E. Irvine A1 Nicholas P. Franks A1 William Wisden A1 Dominic J. Withers A1 James Leiper A1 Mark A. Ungless YR 2018 UL http://www.eneuro.org/content/5/5/ENEURO.0381-18.2018.abstract AB GABA neurons in the VTA and SNc play key roles in reward and aversion through their local inhibitory control of dopamine neuron activity and through long-range projections to several target regions including the nucleus accumbens. It is not clear whether some of these GABA neurons are dedicated local interneurons or if they all collateralize and send projections externally as well as making local synaptic connections. Testing between these possibilities has been challenging in the absence of interneuron-specific molecular markers. We hypothesized that one potential candidate might be neuronal nitric oxide synthase (nNOS), a common interneuronal marker in other brain regions. To test this, we used a combination of immunolabelling (including antibodies for nNOS that we validated in tissue from nNOS-deficient mice) and cell type-specific virus-based anterograde tracing in mice. We found that nNOS-expressing neurons, in the parabrachial pigmented (PBP) part of the VTA and the SNc were GABAergic and did not make detectable projections, suggesting they may be interneurons. In contrast, nNOS-expressing neurons in the rostral linear nucleus (RLi) were mostly glutamatergic and projected to a number of regions, including the lateral hypothalamus (LH), the ventral pallidum (VP), and the median raphe (MnR) nucleus. Taken together, these findings indicate that nNOS is expressed by neurochemically- and anatomically-distinct neuronal sub-groups in a sub-region-specific manner in the VTA and SNc.