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, 224 (2), 277-87

An Allosteric Enhancer of M₄ Muscarinic Acetylcholine Receptor Function Inhibits Behavioral and Neurochemical Effects of Cocaine

Affiliations

An Allosteric Enhancer of M₄ Muscarinic Acetylcholine Receptor Function Inhibits Behavioral and Neurochemical Effects of Cocaine

Ditte Dencker et al. Psychopharmacology (Berl).

Abstract

Rationale: The mesostriatal dopamine system plays a key role in mediating the reinforcing effects of psychostimulant drugs like cocaine. The muscarinic M₄ acetylcholine receptor subtype is centrally involved in the regulation of dopamine release in striatal areas. Consequently, striatal M₄ receptors could be a novel target for modulating psychostimulant effects of cocaine.

Objectives: For the first time, we here addressed this issue by investigating the effects of a novel selective positive allosteric modulator of M₄ receptors, VU0152100, on cocaine-induced behavioral and neurochemical effects in mice.

Methods: To investigate the effect of VU0152100 on the acute reinforcing effects of cocaine, we use an acute cocaine self-administration model. We used in vivo microdialysis to investigate whether the effects of VU0152100 in the behavioral studies were mediated via effects on dopaminergic neurotransmission. In addition, the effect of VU0152100 on cocaine-induced hyperactivity and rotarod performance was evaluated.

Results: We found that VU0152100 caused a prominent reduction in cocaine self-administration, cocaine-induced hyperlocomotion, and cocaine-induced striatal dopamine increase, without affecting motor performance. Consistent with these effects of VU0152100 being mediated via M₄ receptors, its inhibitory effects on cocaine-induced increases in striatal dopamine were abolished in M₄ receptor knockout mice. Furthermore, selective deletion of the M₄ receptor gene in dopamine D₁ receptor-expressing neurons resulted in a partial reduction of the VU0152100 effect, indicating that VU0152100 partly regulates dopaminergic neurotransmission via M₄ receptors co-localized with D₁ receptors.

Conclusions: These results show that positive allosteric modulators of the M₄ receptor deserve attention as agents in the future treatment of cocaine abuse.

Conflict of interest statement

Disclosure: The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1
Behavioral effects of the M4 receptor PAM, VU0152100 in NMRI mice. a In the acute self-administration model, cocaine (0.03 mg/kg/inf., black column; n=14) induced a significant increase in the number of nose-pokes as compared to saline (white column; n=11). Pretreatment with VU0152100 (0.1 and 1 mg/kg, i.p., grey columns; n=13 and 11, respectively) dose-dependently inhibited nose-poking for cocaine, reaching significance at 1 mg/kg. b In the activity boxes, cocaine (30 mg/kg, s.c. black column; n=6) induced hyperlocomotion as revealed by a significant increase in the number of total activity counts as compared to saline (white column; n=6). Pretreatment with VU0152100 (0.1, 1, 10 mg/kg, i.p., grey columns; n=5–6) significantly reduced cocaine-induced hyperlocomotion. c Time spent on rotorod after i.p. pretreatment with vehicle (veh, white column), haloperidol (hal, 0.5 mg/kg; black column), or VU0152100 (VU, 10 mg/kg; grey column) (n=9 in each group). Haloperidol significantly reduced time spent on the rotorod when compared to vehicle. In contrast, VU0152100 had no effect on rotorod performance. All data represent group mean ± SEM. #p<0.05, ##p<0.01 vs. vehicle i.p. followed by saline (veh-sal); *p<0.05, **p<0.01 vs. vehicle i.p. followed by cocaine (veh-coc); ‹‹p<0.01 vs. veh (one-way ANOVA followed by Dunnett’s multiple comparison test)
Fig. 2
Fig. 2
In situ hybridisation analysis of cfos mRNA expression in NMRI mice after motor activation in the rotorod test. Treatment with haloperidol (hal, 0.5 mg/kg, i.p.; black columns) induced a significant increase in cfos expression in both the striatal regions, caudate-putamen (CPU) and nucleus accumbens (NAcc) compared to vehicle control (veh, white columns). Treatment with VU0152100 (VU, 10 mg/kg, i.p.; grey columns) alone gave no significant increase in cfos expression compared to vehicle. All data represent group mean ± SEM (n=6 per group). ‹‹p<0.01, ‹‹‹p<0.001 vs. veh (one-way ANOVA followed by Bonferroni-corrected pairwise comparisons)
Fig. 3
Fig. 3
Extracellular striatal dopamine levels in response to cocaine and VU0152100 (VU) in NMRI mice. Cocaine (30 mg/kg, veh-coc, black circles; n=5) significantly increased extracellular dopamine compared to saline-treated controls (veh-sal, white circles; n=5). This response was significantly reduced by pretreatment with VU0152100 (1 mg/kg, i.p.; grey circles; n=5). #p<0.05, ##p<0.01 vs. veh-sal; *p<0.05, **p<0.01 vs. veh-coc (two-way repeated measures ANOVA followed by Bonferroni-corrected pairwise comparisons). The insert shows cocaine-induced dopamine levels as AUC from 60–120 min. All three doses of VU0152100 caused a significant reduction in dopamine levels (n=4–6). ##p<0.01 vs. veh-sal; **p<0.01 vs. veh-coc (one-way ANOVA followed by Dunnett’s multiple comparison tests). All data represent group mean ± SEM
Fig. 4
Fig. 4
Extracellular striatal dopamine levels in response to cocaine and VU0152100 in M4-KO mice. Cocaine (30 mg/kg, s.c., black circles; n=5) significantly increased dopamine compared to saline in M4-KO mice (white circles; n=6). The cocaine-induced dopamine increase could not be attenuated by pretreatment with VU0152100 (1 mg/kg, i.p., grey circles; n=4) in M4-KO mice. #p<0.05, ##p<0.01 vs. veh-sal in M4-KO mice (two-way repeated measures ANOVA followed by Bonferroni-corrected pairwise comparisons). The insert shows dopamine levels as AUC from 60–120 min in WT and M4-KO mice after saline (veh-sal), cocaine (veh-coc) or cocaine+VU0152100 (VU-coc) treatment. ###p<0.001 vs. veh-sal within genotype; ***p<0.001 vs. veh-coc within genotype, $$$p<0.001 vs. same treatment group between genotypes (two-way ANOVA followed by Bonferroni-corrected pairwise comparisons; n=4–8). All data represent group mean ± SEM
Fig. 5
Fig. 5
Extracellular striatal dopamine levels in response to cocaine and VU0152100 in D1-M4-KO mice. Cocaine (30 mg/kg, s.c., black circles; n=5) significantly increased extracellular dopamine compared to saline (white circles; n=4). Pretreatment with VU0152100 (1 mg/kg, i.p., grey circles; n=5) appeared to only partially reduce the effect of cocaine in D1-M4-KO mice. ##p<0.01 vs. veh-sal in D1-M4-KO mice (two-way repeated measures ANOVA followed by Bonferroni-corrected pairwise comparisons). The insert shows dopamine levels as AUC from 60–120 min in WT and D1-M4-KO mice after saline (veh-sal), cocaine (veh-coc) or cocaine+VU0152100 (VU-coc) treatment. ##p<0.01, ###p<0.001 vs. veh-sal within genotype, **p<0.01, ***p<0.001 vs. veh-coc within genotype, $$p<0.001 vs. same treatment group between genotypes (two-way ANOVA followed by Bonferroni-corrected pairwise comparisons; n=4–5). All data represent group mean ± SEM.
Fig. 6
Fig. 6
In situ hybridisation autoradiograms showing M4 mRNA levels in treatment-naive floxed WT (a) and D1-M4-KO (b) mice at the level of the dorsal striatum. Magnification bar = 1 mm. (c) Quantification revealed a prominent reduction in the nucleus accumbens (NAcc) and the caudate-putamen (CPU) in D1-M4-KO mice compared to WT mice while there were no significant differences in the frontal cortex (FC), hippocampal dentate gyrus (DG) and subfields CA3/CA1. Data represent group mean ± SEM. **p<0.01, ***p<0.001 vs. WT (Student’s t-test; n=6)

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