Gene expression and neurochemical characterization of the rostromedial tegmental nucleus (RMTg) in rats and mice
The rostromedial tegmental nucleus (RMTg), also known as the tail of the ventral tegmental area (tVTA), is a GABAergic structure identified in 2009 that receives strong inputs from the lateral habenula and other sources, sends dense inhibitory projections to midbrain dopamine (DA) neurons, and plays increasingly recognized roles in aversive learning, addiction, and other motivated behaviors. In general, little is known about the genetic identity of these neurons. However, recent work has identified the transcription factor FoxP1 as enhanced in the mouse RMTg (Lahti et al. in Development 143(3):516–529, 2016). Hence, in the current study, we used RNA sequencing to identify genes significantly enhanced in the rat RMTg as compared to adjacent VTA, and then examined the detailed distribution of two genes in particular, prepronociceptin (Pnoc) and FoxP1. In rats and mice, both Pnoc and FoxP1 were expressed at high levels in the RMTg and colocalized strongly with previously established RMTg markers. FoxP1 was particularly selective for RMTg neurons, as it was absent in most adjacent brain regions. We used these gene expression patterns to refine the anatomic characterization of RMTg in rats, extend this characterization to mice, and show that optogenetic manipulation of RMTg in mice bidirectionally modulates real-time place preference. Hence, RMTg neurons in both rats and mice exhibit distinct genetic profiles that correlate with their distinct connectivity and function.
KeywordstVTA VTA Dopamine Prepronociceptin FoxP1
The authors would like to thank Jacqui Joseph, Jennifer Hergatt, Nicki Pullmann, Nathan Burnham, and Haley Spencer for excellent technical assistance. We thank Drs. Marisela Morales and Huiling Wang for contributing rat Pnoc ISH results, and Drs. Elin Lehrmann and William Freed for DNA microarray results that preceded the RNA-seq findings shown here. This work was supported by National Institutes of Health Grants R21 DA037744 (RJS) and R03 DA034431 (TCJ), as well as Department of Defense Grant W911NF-16-2-0070 (TCJ).
Funding provided by National Institutes of Health Grants R21 DA037744 (RJS) and R03 DA034431 (TCJ), and Department of Defense Grant W911NF-16-2-0070 (TCJ).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All animal studies were conducted in accordance with the Guide for the Care and Use of Laboratory Animals, and were approved by the Institutional Animal Care and Use Committee at MUSC.
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