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

Abstract

SummaryFast-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 γ-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.

Dynorphin modulates motivation through a pallido-amygdala cholinergic circuit

“…The development of CRISPR/Cas9 mutagenesis viruses has made it possible to study their functions in isolation (Hunker et al, 2020). The present study is in line with recent studies showing that neuropeptides have functions distinct from those of fast-acting neurotransmitters (Li et al, 2022;Soden et al, 2023). In our study, deletion of dynorphin or KORs in the NAc Pdyn →VP Gad2 circuit does not affect behavior in the RTPP test, suggesting that the slow-acting dynorphinergic transmission in this circuit is not essential for valence processing.…”

“…Neurons in subcortical nuclei, such as the NAc, the bed nucleus of the stria terminalis, the central amygdala and hypothalamic areas, often express various neuropeptides that can be co-released with fast-acting neurotransmitters from the same neurons (Castro and Bruchas, 2019;Fellinger et al, 2021;Li et al, 2022;Soden et al, 2023). The development of CRISPR/Cas9 mutagenesis viruses has made it possible to study their functions in isolation (Hunker et al, 2020).…”

Ventral pallidum GABA and glutamate neurons drive approach and avoidance through distinct modulation of VTA cell types

“…Moreover, when VP GABA stim was sustained for 5s, the VTA DA neuron response was biphasic, with a rapid peak followed by a slower ramp, but the slow ramp was absent when stim delivery was behaviorcontingent. A recent study indicates a similar slow signal in DA neurons is mediated by peptide release from GABA neurons in lateral hypothalamus 86 . Future investigations could explore the presence of a similar peptide mechanism from VP GABA neurons and how such signals relate to reward pursuit or expectation.…”

Opto-seq reveals input-specific immediate early gene induction in ventral tegmental area cell types

“…disinhibition or feed-forward excitation) is a major contributor to local VTA circuitry. In addition, many, if not most, glutamatergic and GABAergic inputs corelease neuropeptides that can strongly impact downstream neuronal activity (van den Pol, 2012, Soden et al, 2023). Importantly, the opto-seq approach goes beyond monosynaptic circuit mapping to reveal the net activation of monosynaptic, polysynaptic, and peptidergic signaling.…”