Dopamine binds a D1-D2 heteromer coupled to Gq to activate a phospholipase C dependent mechanism to increase dendritic branching in the developing Medium Spiny Neuron

The Medium Spiny Neuron (MSN) composes approximately 95% of the neurons in the striatum in the brain. MSNs are GABAergic neurons that modulate the movement and reward pathways. Cortical and substantia nigra pars compacta neurons release glutamate and dopamine on MSNs, respectively. These inputs are required for the MSN to grow into its typical highly branched, spiny morphology. The Lanier lab found that dopamine increases dendritic branching in the developing MSN. The goal of the current study is to find the mechanism by which dopamine enhances MSN dendritic arborization. The hypothesis is that dopamine increases dendritic branching by binding a D1-D2 heteromer coupled to Gq, which activates phospholipase C (PLC). A striatal-cortical co-culture prepared from day 16 mouse embryos was used to grow MSNs with their afferent cortical neurons. The experimental treatments were: 1) D1 receptor agonist SKF81297, D2 receptor agonist quinpirole, and both SKF81297 & quinpirole, 2) chemogenetic activation of Gq, and 3) PLC antagonist U73122. Treatments were administered in vitro at day 4, and regularly administered until fixation at day 19. It was found that SKF81297 and quinpirole, together and in isolation, were not able to replicate dopamine’s increased branching effect. In addition, it was found that Gq activation, using a chemogenetic approach, resulted in increased branching almost to the same extent as dopamine addition caused. Further, U73122 had no effect on branching on its own, but U73122 significantly attenuated dopamine’s branching effects. Taken together, this data support the hypothesis that dopamine enhances branching by binding a D1-D2 heteromer coupled to Gq, to activate phospholipase C