Distinct Signaling by Ventral Tegmental Area Glutamate, GABA, and Combinatorial Glutamate-GABA Neurons in Motivated Behavior

David H Root,David J Barker,David J Estrin,Jorge A Miranda-Barrientos,Bing Liu,Shiliang Zhang,Hui-Ling Wang,Francois Vautier,Charu Ramakrishnan,Yoon Seok Kim,Lief Fenno,Karl Deisseroth,Marisela Morales

doi:10.1016/j.celrep.2020.108094

David H Root, David J Barker + Show 11 more

Open Access

https://doi.org/10.1016/j.celrep.2020.108094

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Abstract

SUMMARYVentral tegmental area (VTA) neurons play roles in reward and aversion. We recently discovered that the VTA has neurons that co-transmit glutamate and GABA (glutamate-GABA co-transmitting neurons), transmit glutamate without GABA (glutamate-transmitting neurons), or transmit GABA without glutamate (GABA-transmitting neurons). However, the functions of these VTA cell types in motivated behavior are unclear. To identify the functions of these VTA cell types, we combine recombinase mouse lines with INTRSECT2.0 vectors to selectively target these neurons. We find that VTA cell types have unique signaling patterns for reward, aversion, and learned cues. Whereas VTA glutamate-transmitting neurons signal cues predicting reward, VTA GABA-transmitting neurons signal cues predicting the absence of reward, and glutamate-GABA co-transmitting neurons signal rewarding and aversive outcomes without signaling learned cues related to those outcomes. Thus, we demonstrate that genetically defined subclasses of VTA glutamate and GABA neurons signal different aspects of motivated behavior.

Highlights

The ventral tegmental (VTA) area has been traditionally considered a dopaminergic structure that plays important roles in motivated behavior, but accumulating evidence indicates that Ventral tegmental area (VTA) dopamine neurons are intermingled with neurons that utilize GABA or glutamate as signaling molecules (Barker et al, 2016; Morales and Margolis, 2017; Root et al, 2016)
We used associated viral (AAV)-CON/FON-mCherry vectors requiring both Cre recombinase and Flp recombinase for mCherry expression to target VGluT2+ VGaT+ neurons; AAV-CON/FOFF-eYFP vectors requiring the presence of Cre recombinase and the absence of Flp recombinase for expression of enhanced yellow fluorescent protein to target VGluT2+ VGaTÀ neurons, and AAV-COFF/FON-blue fluorescent protein (BFP) vector requiring the absence of Cre recombinase and presence of Flp recombinase for the expression of BFP to target VGluT2À VGaT+ neurons (Figure 1B)
After confirming VTA neuronal expression of mCherry (Figure 1C), eYFP (Figure 1D), or BFP (Figure 1E), we examined the expression of VGluT2 or VGaT mRNAs within each type of fluorescent VTA neuron (Figures 1C–1E)

Summary

Introduction

The ventral tegmental (VTA) area has been traditionally considered a dopaminergic structure that plays important roles in motivated behavior, but accumulating evidence indicates that VTA dopamine neurons are intermingled with neurons that utilize GABA or glutamate as signaling molecules (Barker et al, 2016; Morales and Margolis, 2017; Root et al, 2016). The VTA has combinatorial neurons that co-release dopamine with either glutamate (Zhang et al, 2015) or GABA (Tritsch et al, 2012) and combinatorial glutamate neurons that co-release glutamate and GABA (Root et al, 2014b, 2018b). Optogenetic behavioral studies have shown that VTA VGaT (Tan et al, 2012) and VGluT2 neurons (Root et al, 2014a; Wang et al, 2015; Yoo et al, 2016) participate in motivated behavior, but it is unclear the extent to which different aspects of motivated behaviors are mediated by neurons that co-transmit glutamate and GABA (VGluT2+ VGaT+ neurons), release glutamate without GABA (VGluT2+ VGaTÀ neurons), or release GABA without glutamate (VGluT2À VGaT+ neurons). By crossing Vglut2-Cre mice with Vgat-FlpO mice, we generated dual Cre/FlpO transgenic mice that, together with intra-VTA injections of newly developed INTRSECT2.0

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