Mapping long-term changes in inputs to the ventral tegmental area after a single drug exposure

Abstract

ABSTRACTExposure to drugs of abuse causes long-lasting changes in connectivity to ventral tegmental area dopamine cells that contribute to drug-induced behavioral adaptations. However, it is not known which inputs are altered, largely due to technological limitations of previous methods. Here we used a rabies virus-based mapping strategy to quantify rabies-labeled inputs to ventral tegmental area cells after a single exposure to one of a variety of abused drugs – cocaine, amphetamine, methamphetamine, morphine, and nicotine – and compared the relative global input labeling across conditions using dimensionality reduction approaches. We observed that all tested drugs of abuse elicited input changes onto dopamine cells, in particular those projecting to the lateral shell of the nucleus accumbens and amygdala, and that these changes were common to all drugs tested. Interestingly, we also noticed that animals anesthetized with a ketamine/xylazine mixture exhibit a different brain-wide input pattern from those anesthetized with isoflurane, indicating that the method of anesthesia can influence rabies input labeling by inducing long-lasting changes in circuit connectivity. In addition, many input changes were common between animals anesthetized with ketamine/xylazine and those anesthetized with isoflurane but also given a single dose of a drug of abuse, suggesting that the ketamine/xylazine mixture can induce these long-lasting input changes. We found that many of the brain regions that exhibited changes in rabies input labeling in drug- vs. saline-treated mice were preferentially interconnected, and that select communities of brain regions showed similar changes for both drugs of abuse and ketamine/xylazine anesthesia. Lastly, the basal expression patterns of several gene classes were highly correlated with the extent of both addictive drug- or ketamine/xylazine-induced input changes, especially calcium channels. These results indicate that the expression of calcium channels is related to whether these inputs to dopamine cells are altered by drug exposure. Furthermore, ketamine/xylazine anesthesia induces a similar but different set of long-lasting input changes onto midbrain dopamine cells, indicating that caution should be taken when using ketamine/xylazine-based anesthesia in rodents when assessing motivated behaviors.