Identification of Neurotensin Receptor Expressing Cells in the Ventral Tegmental Area across the Lifespan

Neurotensin (Nts) promotes activation of dopamine (DA) neurons in the ventral tegmental area (VTA) via incompletely understood mechanisms. Nts can signal via the G protein-coupled Nts receptors 1 and 2 (NtsR1 and NtsR2), but the lack of methods to detect NtsR1- and NtsR2-expressing cells has limited mechanistic understanding of Nts action. To overcome this challenge, we generated dual recombinase mice that express FlpO-dependent Cre recombinase in NtsR1 or NtsR2 cells. This strategy permitted temporal control over recombination, such that we could identify NtsR1- or NtsR2-expressing cells and determine whether their distributions differed between the developing and adult brain. Using this system, we found that NtsR1 is transiently expressed in nearly all DA neurons and in many non-DA neurons in the VTA during development. However, NtsR1 expression is more restricted within the adult brain, where only two thirds of VTA DA neurons expressed NtsR1. By contrast, NtsR2 expression remains constant throughout lifespan, but it is predominantly expressed within glia. Anterograde tract tracing revealed that NtsR1 is expressed by mesolimbic, not mesocortical DA neurons, suggesting that VTA NtsR1 neurons may represent a functionally unique subset of VTA DA neurons. Collectively, this work reveals a cellular mechanism by which Nts can directly engage NtsR1-expressing DA neurons to modify DA signaling. Going forward, the dual recombinase strategy developed here will be useful to selectively modulate NtsR1- and NtsR2-expressing cells and to parse their contributions to Nts-mediated behaviors.