CB₁‐independent inhibition of dopamine transporter activity by cannabinoids in mouse dorsal striatum

Abstract

Cannabinoid drugs are known to affect dopaminergic neurotransmission in the basal ganglia circuitry. In this study, we used in vitro and in vivo techniques to investigate whether cannabinoid agonists and antagonist could affect dopaminergic transmission in the striatum by acting at the dopamine transporter. Incubation of striatal synaptosomes with the cannabinoid agonists WIN55,212-2 or methanandamide decreased dopamine uptake (IC 50 = 2.0 lmol/L and 3.1 lmol/L, respectively). A similar inhibitory effect was observed after application of the inactive WIN55,212-2 isomer, S())WIN55,212-3. The CB 1 antagonist AM251 did not reverse WIN55,212-2 effect but rather mimicked it. WIN55,212-2 and AM251 partially displaced the binding of the cocaine analog [ 3 H]WIN35,428, thus acting as dopamine transporter pseudosubstrates in the high micromolar range. High-speed chronoamperometry measurements showed that WIN55,212-2 (4 mg/kg, i.p.) caused significant release of endogenous dopamine via activation of CB 1 receptors, followed by a reduction of dopamine clearance. This reduction was CB 1 -independent, as it was mimicked by S())WIN55,212-3. Administration of AM251 (1 and 4 mg/kg, i.p.) increased the signal amplitude and reduced the clearance of dopamine pressure ejected into the striatum. These results indicate that both cannabinoid agonists and antagonists inhibit dopamine transporter activity via molecular targets other than CB 1 receptors. Keywords: anandamide, basal ganglia, cannabinoid, chronoamperometry, dopamine transporter, striatum. To date, there is no indication that cannabinoid drugs affect DA transmission by acting directly at DAergic neurons, which is consistent with the absence of CB 1 receptors on these cells (Herkenham et al. 1991). Cannabinoid-induced DA efflux in the striatum (Malone and Taylor 1999) has been attributed to CB 1 -mediated inhibition of GABA release from afferents projecting to the substantia nigra (Miller and Walker 1995;Wallmichrath and Szabo 2002), thus leading to increased firing of DAergic neurons. In addition, CB 1 -dependent and -independent inhibition of glutamate release has been implicated in the modulation of the nigrostriatal pathway (Szabo et al. 2000;Gerdeman and Lovinger 2001 Abbreviations used: DA, dopamine; DAergic, dopaminergic; DAT, dopamine transporter; DMSO, dimethyl sulfoxide; mAEA, methanandamide; NAc, nucleus accumbens; S())WIN, S())WIN55,212-3; T 80 , time required for the signal to decline by 80% of its peak amplitude; WIN, WIN55,212-2.

Lack of a Significant Effect of Cannabinoids upon the Uptake of 2-Deoxy-<i>D</i>-Glucose by Caco-2 Cells

“…Considering that cytochalasin B is a specific inhibitor of GLUT2 (see review by Drozdowski and Thompson [30] ), these results point to the involvement of GLUT2 in the apical uptake of both the low and high concentration of 3 H-DG. Moreover, phloridzin is a specific inhibitor of SGLT1-mediated transport, but we do not believe that SGLT1 is involved in the uptake of a low concentration of serotonin [51] and dopamine [52] transporters. Cannabinoids also interfere with P-glycoprotein [53] , with an equilibrative nucleoside transporter [54] , and with the placental uptake of the vitamin folate [55] .…”

Strain Differences in Cannabinoid-Reinforced Lever Press Discrimination

“…To test the effects of CB 1 receptor blockade on WIN self-administration, AM251 (4 mg/kg, IP) was injected 30 min before the start of session 21. This dose of AM251 is effective in reducing food intake [8] and increases dopamine signal amplitude in the striatum while reducing the clearance of dopamine in this area [9]. To minimize the potential stress of the injection procedure, a vehicle injection was administered 30 min before the start of sessions 19 and 20.…”

Endocannabinoid Systetm: Neuropharmacological Implications

“…This is the central motive to hypothesize CB1 receptor as a therapeutic target to regulate the imbalance of glutamatergic or GABAergic neurons in PD and dyskinesia [47]. There is also a report that eCBs and cannabinoid agonists decrease dopamine re-uptake by inhibiting dopamine transporters [48] Furthermore, augmented oxidative stress has long been linked with PD [50]. Reactive oxygen species (ROS) derived from mitochondria is involved in PD pathology as weakened mitochondrial function and increased oxidative marker.…”