Dopamine Release in Nucleus Accumbens Is under Tonic Inhibition by Adenosine A₁Receptors Regulated by Astrocytic ENT1 and Dysregulated by Ethanol

Abstract

Striatal adenosine A 1 receptor (A 1 R) activation can inhibit dopamine release. A 1 Rs on other striatal neurons are activated by an adenosine tone that is limited by equilibrative nucleoside transporter 1 (ENT1) that is enriched on astrocytes and is ethanol-sensitive. We explored whether dopamine release in nucleus accumbens core is under tonic inhibition by A 1 Rs, and is regulated by astrocytic ENT1 and ethanol. In ex vivo striatal slices from male and female mice, A 1 R agonists inhibited dopamine release evoked electrically or optogenetically and detected using fast-scan cyclic voltammetry, most strongly for lower stimulation frequencies and pulse numbers, thereby enhancing the activity-dependent contrast of dopamine release. Conversely, A 1 R antagonists reduced activity-dependent contrast but enhanced evoked dopamine release levels, even for single optogenetic pulses indicating an underlying tonic inhibition. The ENT1 inhibitor NBTI reduced dopamine release and promoted A 1 R-mediated inhibition, and conversely, virally-mediated astrocytic overexpression of ENT1 enhanced dopamine release and relieved A 1 R-mediated inhibition. By imaging the genetically encoded fluorescent adenosine sensor GRAB-Ado, we identified a striatal extracellular adenosine tone that was elevated by the ENT1 inhibitor and sensitive to gliotoxin fluorocitrate. Finally, we identified that ethanol (50 mM) promoted A 1 R-mediated inhibition of dopamine release, through diminishing adenosine uptake via ENT1.Together, these data reveal that dopamine output dynamics are gated by a striatal adenosine tone, limiting amplitude but promoting contrast, regulated by ENT1, and promoted by ethanol. These data add to the diverse mechanisms through which ethanol modulates striatal dopamine, and to emerging datasets supporting astrocytic transporters as important regulators of striatal function. SIGNIFICANCE STATEMENT (119 words)Dopamine axons in the mammalian striatum are emerging as strategic sites where neuromodulators can powerfully influence dopamine output in health and disease. We found that ambient levels of the neuromodulator adenosine tonically inhibit dopamine release in nucleus accumbens core via adenosine A 1 receptors (A 1 Rs), to a variable level that promotes the contrast in dopamine signals released by different frequencies of activity. We reveal that the equilibrative nucleoside transporter 1 (ENT1) on astrocytes limits this tonic inhibition, and that ethanol promotes it by diminishing adenosine uptake via ENT1. These findings support the hypotheses that A 1 Rs on dopamine axons inhibit DA release and, furthermore, that astrocytes perform important roles in setting the level of striatal dopamine output, in health and disease.

Dual role of striatal astrocytes in behavioral flexibility and metabolism in the context of obesity

“…Several studies indicate that obesity and HFHS exposure enhances DA signaling in both humans (Volkow and Wise, 2005) and rodents (Johnson and Kenny, 2010; Tellez et al, 2013), and recent studies point to a role of astrocytes in regulating the level of DA release in the striatum (Roberts et al, 2022). Since DA transmission regulates behavioral flexibility (Izquierdo et al, 2017), we investigated the role of DS astrocytes in DA transmission during the reversal learning.…”

Monoallelic loss of the F-actin-binding protein radixin facilitates startle reactivity and pre-pulse inhibition in mice

“…Notably, radixin expression was very prominent in the dorsal striatal glia cells. It has been shown that glial cells perform important functions regulating striatal dopamine output ( Tome et al, 2007 ; Roberts et al, 2022 ), one of the most important neurotransmitters involved in PPI modulation ( Kodsi and Swerdlow, 1995 ; Swerdlow et al, 2001 ). Hence, although the exact mechanisms and pathways remain to be investigated, our data indicate a significant role of Rdx in the regulation of PPI expression, possibly at multiple loci within the circuits underlying PPI of the acoustic startle reflex.…”

“…The molecular mechanisms by which differential ERM protein levels impact on neuronal function are largely unknown and likely diverse. For instance, ERM proteins may modulate glia-synaptic interactions by regulating the formation of peripheral astrocyte processes as well as glial glutamate uptake or dopamine release ( Derouiche and Geiger, 2019 ; Roberts et al, 2022 ). Dendritic filopodia motility during neuronal synapse formation may also be influenced by ERM function ( Furutani et al, 2007 ; Furutani et al, 2012 ).…”

Presynaptic adenosine receptor heteromers as key modulators of glutamatergic and dopaminergic neurotransmission in the striatum

“…The significant functional role of A 1 Rs localized in dopaminergic terminals in the establishment of a local, tonic, glutamate-independent, adenosine-mediated inhibitory modulation of dopamine release was recently validated by a recent in vitro study in mouse striatal slices by the research group of Stephanie Cragg, using fast-scan cyclic voltammetry, optogenetic and fiber-photometry techniques (Roberts et al, 2022). However, glutamate-dependent dopamine release could still be demonstrated in striatal areas other than the shell of the NAc, such as the dorsal striatum upon conditions of cortico-striatal stimulation (Quiroz et al, 2009).…”

“…With whole-cell voltage clamping, it was then shown that activation of A 1 Rs in cholinergic interneurons reduces currents mediated by Gi-dependent inhibition of the N-type voltage-dependent Ca 2+ channel (Song et al, 2000). However, although this may be a mechanism by which adenosine reduces striatal acetylcholine release, the recent study by the Stephanie Cragg group showed that application of the α 4 -β 2 * nAChR antagonist dihydro-β-eritroidine did not counteract the inhibitory effect of an A 1 R agonist on dopamine release (Roberts et al, 2022). This showed that activation of A 1 Rs can suppress dopamine release independently of any indirect effects through cholinergic input to the nAChRs localized at the dopaminergic terminals.…”