Cocaine disinhibits dopamine neurons by potentiation of GABA transmission in the ventral tegmental area

Drug-evoked synaptic plasticity in the mesolimbic system reshapes circuit function and drives drug-adaptive behavior. Much research has focused on excitatory transmission in the ventral tegmental area (VTA) and the nucleus accumbens (NAc). How drug-evoked synaptic plasticity of inhibitory transmission affects circuit adaptations remains unknown. We found that medium spiny neurons expressing dopamine (DA) receptor type 1 (D1R-MSNs) of the NAc project to the VTA, strongly preferring the GABA neurons of the VTA. Repeated in vivo exposure to cocaine evoked synaptic potentiation at this synapse, occluding homosynaptic inhibitory long-term potentiation. The activity of the VTA GABA neurons was thus reduced and DA neurons were disinhibited. Cocaine-evoked potentiation of GABA release from D1R-MSNs affected drug-adaptive behavior, which identifies these neurons as a promising target for novel addiction treatments

Insulin induces long-term depression of ventral tegmental area dopamine neurons via endocannabinoids.

The prevalence of obesity has markedly increased over the past few decades. Exploration of how hunger and satiety signals influence the reward system can help us understand non-homeostatic feeding. Insulin may act in the ventral tegmental area (VTA), a critical site for reward-seeking behavior, to suppress feeding. However, the neural mechanisms underlying insulin effects in the VTA remain unknown. We demonstrate that insulin, a circulating catabolic peptide that inhibits feeding, can induce long-term depression (LTD) of mouse excitatory synapses onto VTA dopamine neurons. This effect requires endocannabinoid-mediated presynaptic inhibition of glutamate release. Furthermore, after a sweetened high-fat meal, which elevates endogenous insulin, insulin-induced LTD is occluded. Finally, insulin in the VTA reduces food anticipatory behavior in mice and conditioned place preference for food in rats. Taken together, these results suggest that insulin in the VTA suppresses excitatory synaptic transmission and reduces anticipatory activity and preference for food-related cues