Effects of Neurotensin on VTA Neuron Physiology and Methamphetamine Use - Methamphetamine (METH) use disorder is a growing public health crisis with significant medical, social, and economic impacts. Despite its prevalence, there are currently no FDA-approved pharmacological treatments. The ventral tegmental area (VTA) of the mesocorticolimbic circuit plays a crucial role in incentive salience, the desire or craving for a reward and the associated motivation to obtain the reward. Methamphetamine (METH) hyperactivates brain reward circuits through VTA dopamine neurons, increasing dopamine release and blocking its reuptake. As METH use rises, identification of novel targets of reward signaling pathways are crucial to curb METH use risks, such as overdose. While research has focused on dopamine neurons in the VTA, the contributions of non-dopamine neurons remain unexplored. The neuropeptide, neurotensin, modulates reward behavior via its receptors NTR1 and NTR2. Previous studies have focused on dopamine neuron NTR1 and its contribution to neuronal hyperexcitability and METH consumption. However, preliminary electrophysiological evidence shows that neurotensin exerts additional strong control over VTA GABA neurons, suggesting the existence of a novel mechanism in reward signaling. Using patch clamp electrophysiology and behavioral assessment techniques, this study will examine the effect of neurotensin, the specific roles of NTR1 and NTR2, in GABA and dopamine neurons, and explore the impacts of these on METH use behaviors. The central hypothesis of this study is that neurotensin signaling activated by METH induces a two-hit amplification of the reward system: NTR1 on dopamine neurons enhances dopamine release by mitigating autoinhibitory D2 receptor signaling, while NTR2 on GABA neurons reduces inhibitory control, further potentiating dopamine neuron activity. This dual modulation contributes to METH’s reinforcing effects and promotes addiction. By leveraging novel NTR1 and NTR2 floxed transgenic mouse models crossed to dopamine and GABA neuron- specific Cre recombinase drivers, this project will define the cell-specific effects of neurotensin signaling at the molecular, cellular, and behavioral levels. Electrophysiological experiments will use perforated patch-clamp recordings in acute brain slices to measure the effects of neurotensin and METH on intrinsic firing rates, and action potential dynamics. Behavioral studies will employ intravenous METH self-administration paradigms, dose-response curves, and progressive ratio tasks to evaluate sensitivity and motivation for METH. Additionally, abstinence-induced “incubation of craving” will be assessed to understand the long-term impact of neurotensin signaling on relapse vulnerability. Additionally, optogenetic strategies will be utilized to stimulate neurotensinergic afferents to the VTA and cell-type-specific Cre-lox recombination, to dissect the molecular and circuit-level contributions of neurotensin. By uncovering novel mechanisms of neuropeptide modulation in addiction, these findings will provide actionable insights for the development of targeted therapies for METH use disorder.
