D₂Dopamine Receptors Reduce N-Type Ca²⁺Currents in Rat Neostriatal Cholinergic Interneurons Through a Membrane-Delimited, Protein-Kinase-C-Insensitive Pathway

Abstract

Dopamine has long been known to regulate the activity of striatal cholinergic interneurons and the release of acetylcholine. Yet, the cellular mechanisms by which this regulation occurs have not been elucidated. One way in which dopamine might act is by modulating voltage-dependent Ca2+ channels. To test this hypothesis, the impact of dopaminergic agonists on Ca2+ channels in neostriatal cholinergic interneurons was studied by combined whole cell voltage-clamp recording and single-cell reverse transcription-polymerase chain reactions. Cholinergic interneurons were identified by the presence of choline acetyltransferase mRNA. Nearly, all interneurons tested (90%, n = 17) coexpressed D2 (short and long isoforms) and D1b (D5) dopamine receptor mRNAs. D1a receptor mRNA was found in only a small subset (20%) of the sample and D3 and D4 receptor mRNAs were undetectable. D2 receptor agonists rapidly and reversibly reduced N-type Ca2+ currents. D1b/D1a receptor activation had little or no effect on Ca2+ currents. The D2 receptor antagonist sulpiride blocked the effect of D2 agonists. Dialysis with guanosine-5'-O-(2-thiodiphosphate) or brief exposure to the G protein (Gi/o) alkylating agent N-ethylmaleimide also blocked the D2 modulation. The reduction in N-type currents was neither accompanied by kinetic slowing nor significantly reversed by depolarizing prepulses. The D2 receptor effects were mediated by a membrane-delimited pathway, because the modulation was not seen in cell-attached patches when agonist was applied to the bath and was not disrupted by perturbations in cytosolic signaling pathways known to be linked to D2 receptors. Activation of M2 muscarinic receptors occluded the D2 modulation, suggesting a shared signaling element. However, activation of protein kinase C attenuated the M2 modulation without significantly affecting the D2 modulation. Taken together, our results suggest that activation of D2 dopamine receptors in cholinergic interneurons reduces N-type Ca2+ currents via a membrane-delimited, Gi/o class G protein pathway that is not regulated by protein kinase C. This signaling pathway may underlie the ability of D2 receptors to reduce striatal acetylcholine release.

Acute and chronic modulation of striatal endocannabinoid‐mediated plasticity by nicotine

“…It is also in agreement with previous studies showing that antagonists targeting nAChRs on dopaminergic terminals impair eCB-signaling (Partridge et al 2002). Inhibition of nAChRs on dopaminergic terminals has been postulated to reduce the activation of dopamine D2 receptors located on cholinergic interneurons, thereby increasing acetylcholine-release and mAChR activation, resulting in reduced postsynaptic calcium influx (Yan et al 1997;Partridge et al 2002). Elevated postsynaptic calcium is a prerequisite for eCB production (Adermark & Lovinger 2007a), and mAChRs exert a strong control over calcium influx in rat striatal neurons (Howe & Surmeier 1995;Wang et al 2006) (Fig.…”

“…nAChRs are located on dopaminergic terminals and could exert its influence over eCB production by altering dopamine-release (Fig. 1a) (Yan, Song, & Surmeier 1997;Partridge et al 2002). Supporting this theory, the dopamine D2 receptor agonist quinpirole occluded nicotine-induced facilitation of LTD (F (1, 23) = 1.62, P > 0.05) (Fig.…”

Cholinergic activity and levodopa‐induced dyskinesia: a multitracer molecular imaging study

“…Acetylcholine directly promotes dopamine release via activation of presynaptic nAChRs at nigrostriatal terminals,26 dopamine acting via D2 receptors inhibits the release of acetylcholine from the cholinergic interneurons 27. However, dopamine, acting via D1/D5 receptors, potentiates the excitability of cholinergic neurons and their responsiveness to glutamatergic input 28.…”

Cholinergic interneuron characteristics and nicotinic properties in the striatum

“…The striatal cholinergic interneurons contain mainly the D 2 receptor in both the short and long forms, and also contain D 5 receptors (Bergson et al, 1995;Yan et al, 1997). D 5 receptors are mainly in the somatodendritic areas such that they may regulate the excitability and ACh release from cholinergic interneurons.…”

“…Indeed, D 1 -like (probably D 5 ) receptor activation can depolarize cholinergic interneurons and enhance ACh release (Damsma et al, 1990;Imperato et al, 1993;DeBoer and Abercrombie, 1996;Aosaki et al, 1998;Pisani et al, 2000). In contrast, activation of D 2 -like receptors on cholinergic interneurons inhibits striatal ACh efflux (DeBoer and Abercrombie, 1996), probably by suppressing N-type Ca 2ϩ channels that directly initiate ACh release (Yan et al, 1997).…”