Fig. 6. Comparison of the antinociceptive effects imparted by intra-NAc microinjection of 4, 8 or 12 µg of AIP on the HWLs of naïve rats and rats showing morphine tolerance. A and B depict HWLs to noxious thermal stimulation; C and D represent HWLs to noxious mechanical stimulation. Left HWLs are presented in A and C; right HWLs are depicted in B and D. The antinociceptive effects are evaluate 30 minutes after drug injection. The data of the experiment are expressed as the mean ± standard error of the mean. Two-tailed student’s t-test was used to assess statistical differences among experimental groups. *P < 0.05, **P < 0.01 indicate compared with the control group. 4 A, 8 A or 12 A represent intra-NAc microinjection of 4, 8 or 12 µg of AIP to naïve rats; 4 A, 8 A or 12 A + morphine represent intra-NAc microinjection of 4, 8 or 12 µg of AIP to morphine-tolerant rats. AIP: autocamtide-2-related inhibitory peptide, HWL: hindpaw withdrawal latency, NAc: nucleus accumbens.
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