eLife assessment
This valuable study by Bartas and colleagues examined how patterns of monosynaptic input to specific cell types in the ventral tegmental area are altered by drugs of abuse. The authors applied a dimensionality reduction approach (principal component analysis) and showed that various drugs of abuse, and somewhat surprisingly the anesthesia alone (ketamine/xylasin), caused changes in the distribution of inputs labeled by the transsynaptic rabies virus. While there are some issues to be addressed, the evidence supporting the conclusions is overall solid, and provides information that is of value to the field, as well as a cautionary note on the interpretation of rabies virus-based tracing experiments.