Subcellular Control of Dopamine-mediated Behavior

Abstract

The complex morphology of neurons is thought to be essential for input-output processing, with particular relevance for GABAA receptor-mediated synaptic inhibition. Each subcellular compartment tends to receive inhibitory input from certain cell types: the soma is inhibited predominantly by basket cells; the axon initial segment by chandelier cells. This suggests a subcellular logic for distinct streams of incoming information. Biophysical evidence also suggests that location shapes computation: distal dendritic inhibitory inputs suppress excitation in a subtractive manner, whereas somatic inhibition resembles division, scaling the input-output gain. Nevertheless, it has not been possible to functionally interrogate this subcellular architecture in awake, behaving animals. To address this gap, I developed novel subcellular-specific pharmacology tools based on DART (Drug Acutely Restricted by Tethering)—a cell type-specific pharmacology method in which drugs are captured by cells expressing the HaloTag protein. To further restrict drugs to the soma, I discovered new design principles for subcellular protein trafficking—surpassing prior soma-targeting designs. These principles were essential for functional specificity—achieving nearly complete antagonism of perisomatic GABAA receptors, with negligible impact on distal dendrites. In behaving mice, I discovered that two dissociable aspects of locomotion—speed and direction bias—are controlled by dopamine-neuron GABAA receptors in the dendrites and soma, respectively. I next extended the approach to other subcellular compartments, developing an approach for projection-specific axon pharmacology that exploits a natural diffusion barrier between the axon and soma. Preliminary application of the approach in live mice revealed a locomotor role for GABAA receptors on dopamine-neuron axons, which extend a great distance from the cell body. Finally, I engineered a primary cilia-targeted version of DART, along with an assay to validate its specificity via an all-optical assay of drug-receptor binding. Altogether, this body of work establishes the principles and toolset for subcellular-specific pharmacology. These advances provide a foundation for causal interrogation of subcellular signaling in awake behaving animals.