Cellular and Behavioral Function of Astrocytic Dopamine Signaling

Abstract It has long been known that that astrocytes in the nucleus accumbens (NAc) and other motivation-regulatory brain regions express dopamine receptors, but the cellular and behavioral function of astrocytic dopamine- signaling remains underexplored. Experiments designed in this application aim at elucidating the synaptic role

of astrocytic dopamine D1 receptors (D1R) in the NAc in the context of cue-conditioned motivational behaviors and cue-induced cocaine relapse. When animals search for reward, previously neutral environmental cues that are paired with reward taking acquire motivational value that drives subsequent reward seeking. Such cue-

reward conditioning is essential for survival, but it is also usurped by drugs of abuse to establish the cue-drug association that promotes drug seeking and relapse. The NAc is a key brain region where conditioned cues are tagged with motivational value. When animals search and take reward, cue-encoding inputs from the ventral

hippocampus (vH) are simultaneously activated with reward-encoding inputs from the basolateral amygdala (BLA), resulting in synced activation of vH and BLA synapses that are heterosynaptically aligned on the dendrites of principal medium spiny neurons (MSNs) in the NAc. In brain slices, previous and preliminary

results from the PI’s lab demonstrate that synced activation of vH and BLA synapses selectively induces long- term potentiation (LTP) in vH-to-NAc glutamatergic transmission. This novel form of heterosynaptic LTP, termed hLTP, can increase the likelihood of vH-to-NAc transmission that encodes reward-contingent cues to

excite NAc MSNs for operant responding. Additional results from the PI’s lab show that either a general inhibition of D1R or selective disruption of astrocyte function prevents the induction of hLTP. These and other results lead to the overarching hypothesis that D1R-coupled astrocytic signaling is essential for hLTP at vH-to-

BLA synapses and cue-conditioned motivated behaviors. Guided by this hypothesis, proposed experiments will characterize the role of NAc astrocytic D1R and its downstream signaling in the induction and expression of hLTP as well as in the acquisition and performance of cue-induced nondrug versus drug seeking. Synaptic

plasticity has long been thought to be primarily mediated by neuronal signaling within the pre- and postsynaptic terminals. The proposed research is conceptually innovative in that it will generate novel results demonstrating the essential role of astrocytic signaling in sophisticated forms of synaptic plasticity that involve extracellular

signaling. Furthermore, characterizing behavioral roles of astrocytic D1R-signaling may reveal new cellular targets through which cue-conditioned drug seeking and relapse can be manipulated. As such, the proposed research is also clinically important and consistent with the mission of NIH in identifying and characterizing

novel therapeutic targets to treat substance use disorders.