A circuit mechanism for the coordinated actions of opposing neuropeptide and neurotransmitter signals

Abstract

Fast-acting neurotransmitters and slow, modulatory neuropeptides are commonly co-released from neurons in the central nervous system (CNS), albeit from distinct synaptic vesicles1. The mechanisms of how co-released neurotransmitters and neuropeptides that have opposing actions, e.g., stimulatory versus inhibitory, work together to exert control of neural circuit output remain unclear. This question has been difficult to resolve due to the inability to selectively isolate these signaling pathways in a cell- and circuit-specific manner. To overcome these barriers, we developed a genetic-based anatomical disconnect procedure that utilizes distinct DNA recombinases to independently facilitate conditional in vivo CRISPR/Cas9 mutagenesis2 of neurotransmitter- and neuropeptide-related genes in distinct cell types in two different brain regions simultaneously. With this approach we demonstrate that the stimulatory neuropeptide neurotensin (Nts) and the inhibitory neurotransmitter{gamma} -aminobutyric acid (GABA), which are co-released from neurons in the lateral hypothalamus (LH), work coordinately to activate dopamine neurons of the ventral tegmental area (VTA-DA). We show that GABA release from LH-Nts neurons acts on GABA neurons within the VTA to rapidly disinhibit VTA-DA neurons, while Nts signals through the Nts receptor 1 (Ntsr1) on VTA-DA neurons to promote a slow depolarization of these cells. Thus, these two signals act on distinct time scales through different cell types to enhance mesolimbic dopamine neuron activation, which optimizes behavioral reinforcement. These data demonstrate a circuit-based mechanism for the coordinated action of a neurotransmitter and neuropeptide with opposing effects on cell physiology.