Coexistence of D₃R typical and atypical signaling in striatonigral neurons during dopaminergic denervation. Correlation with D₃nf expression changes

Abstract

Dopamine D3R are widely expressed in basal ganglia where interact with D1R. D3R potentiate cAMP accumulation and GABA release stimulated by D1R in striatonigral neurons through “atypical” signaling. During dopaminergic denervation, D3R signaling changes to a “typical” in which antagonizes the effects of D1R, the mechanisms of this switching are unknown. D3nf splice variant regulates membrane anchorage and function of D3R and decreases in denervation; thus, it is possible that D3R signaling switching correlates with changes in D3nf expression and increases of membranal D3R that mask D3R atypical effects. We performed experiments in unilaterally 6‐hydroxydopamine lesioned rats and found a decrease in mRNA and protein of D3nf, but not of D3R in the denervated striatum. Proximity ligation assay showed that D3R‐D3nf interaction decreased after denervation, whereas binding revealed an increased Bmax in D3R. The new D3R antagonized cAMP accumulation and GABA release stimulated by D1R; however, in the presence of N‐Ethylmaleimide (NEM), to block Gi protein signaling, activation of D3R produced its atypical signaling stimulating D1R effects. Finally, we investigated if the typical and atypical effects of D3R modulating GABA release are capable of influencing motor behavior. Injections of D3R agonist into denervated nigra decreased D1R agonist‐induced turning behavior but potentiated it in the presence of NEM. Our data indicate the coexistence of D3R typical and atypical signaling in striatonigral neurons during denervation that correlated with changes in the ratio of expression of D3nf and D3R isoforms. The coexistence of both atypical and typical signaling during denervation influences motor behavior.

Presynaptic nigral GPR55 receptors stimulate [3H]‐GABA release through [3H]‐cAMP production and PKA activation and promote motor behavior

“…Since the GPR55 effect on [ 3 H]‐GABA release depends on external Ca 2+ entry. We tested if the coupling to Gi or Gs proteins participates in GPR55 effects because nigral presynaptic GPCRs that modulate GABA release are coupled to these proteins usually (Campos Campos et al., 2020; Nava‐Asbell et al., 2007; Rangel‐Barajas et al., 2011). As shown in Figure 5(a), blockade of Gi proteins by pretreatment with PTX did not modify LPI effects on release (Figure 5(a); [ 3 H]‐GABA release median LPI 142% rank 141–149% vs. median LPI‐PTX 145% rank 135–146%, mean rank difference 0, p = .99, ns, n = 4 experiments, KS = 9.955, p = .0027, Kruskal–Wallis test followed by Dunn's).…”

Dopamine D3 receptor modulates D2 receptor effects on cAMP and GABA release at striatopallidal terminals—Modulation by the Ca2+–Calmodulin–CaMKII system

“…Probably in the case of pathological conditions, the interacting D 2 R–D 3 R function becomes more apparent. Dopaminergic denervation increases the membranal expression of D 3 R in both D 1 R and D 2 R striatal coexpressing neurons (Campos Campos et al, 2020; Prieto et al, 2009, 2011). In the case of striatopallidal neurons, D 3 R contributes to increasing the inhibition of Ca 2+ currents at the soma, increasing the inhibitory effect on the firing rate by dopamine; in the striatopallidal terminal D 3 R increment D 2 R effect on GABA release.…”

Modulation of D3R Splicing, Signaling, and Expression by D1R through PKA→PTB Phosphorylation

“…The D 3 R typical signal (in which D 3 R opposes the D 1 R stimulation of cAMP accumulation and GABA release) masks the normal atypical signaling, with D 3 R potentiating both parameters. This phenomenon was related to an increase in the expression of D 3 R in the membrane [10]. The dopamine D 3 R isoform D 3 nf regulates the canonical D 3 R expression in the membrane [11][12][13][14].…”

“…In typical signaling, the D 3 R G i -mediated effects oppose D 1 R G s/olf effects [1][2][3][4]; in atypical signaling, D 3 R synergizes and potentiates D 1 R effects via a dimeric interaction mediated by G s/olf ( [1,[5][6][7][8][9]. In the nigral projections from the dorsal striatum, dopaminergic denervation promotes the apparition of D 3 R typical signaling that coexists with the normal atypical version [10]. The D 3 R typical signal (in which D 3 R opposes the D 1 R stimulation of cAMP accumulation and GABA release) masks the normal atypical signaling, with D 3 R potentiating both parameters.…”

“…The dopamine D 3 R isoform D 3 nf regulates the canonical D 3 R expression in the membrane [11][12][13][14]. During dopaminergic denervation, decreased D 3 nf isoform expression and protein-protein interaction with D 3 R allows D 3 R to be inserted into the membrane and signal [10,15]. These findings indicate the altered regulation of D 3 R membranal location and its mRNA alternative splicing during dopaminergic denervation, which can explain the appearance of functional D 3 R that opposes D 1 R. However, to date, the mechanism that generates these changes remains unknown.…”