Figure 5

Neural-specific Gz proteins mediate supraspinal analgesic desensitization produced by CB1R and MOR agonists. A. Effect of Pertussis toxin (PTX) on the supraspinal analgesia produced by cannabinoid agonists. PTX injected icv to mice (0.5 μg) was given 6 days before the agonist [55]. Left panel: Open bars indicate controls; gray bars indicate mice treated with PTX. Right panel: The influence of PTX on the analgesic time-course of 20 nmol WIN55-212-2 and on its single-dose tolerance was studied. Either saline (S) or the priming dose of the agonist (W) was administered icv to mice. After 24 h, all groups received an icv test injection of WIN55,212-2 (S+W; W+W), and the analgesic effects were evaluated 10 min later. Values are mean ± SEM for groups of 8–10 mice. *Significantly different from the control group injected with saline instead of the priming dose of WIN55,212-2 and also receiving the test dose of agonist (S+W) (P < 0.05). B. Time-course for the supraspinal analgesic effects of WIN55,212-2 was evaluated in mice that had been subjected to different icv treatments. Reduction in the levels of certain proteins was attained using oligodeoxynucleotides directed against Gαq [51], Gαi2 [49, 50], Gαz [49, 50], RGS9 [48, 52], and RGSZ2 [47]. ODN-RD stands for the control mismatched ODN. Values are mean ± SEM from groups of eight mice. *Significantly different from the control group injected with either saline or the corresponding control ODN (P < 0.05). The effect of these treatments on the single-dose tolerance produced by 20 nmol WIN55,212-2 was studied as described above. C. The analgesic effects of WIN55,212-2, THC, ACEA and methanandamide was studied in mice with impaired expression of Gαz subunits. D. A parallel study was carried out with morphine in mice subjected to the indicated treatments. Data corresponding to the peak effect of morphine at 30 min are shown. Findings from RGS9 knockdown mice are also shown at 60 min. Values are mean ± SEM from groups of eight mice. *Significantly different from the control group injected with saline (for PTX) or the corresponding control ODN (P < 0.05). E. Recovery from the acute analgesic tolerance produced by morphine in control mice and mice with reduced expression of RGSZ2 protein. For details see Fig. 1, lower panel.