Chronic constriction injury reduces cannabinoid receptor 1 activity in the rostral anterior cingulate cortex of mice

Abstract

The present studies examined the effect of chronic neuropathic pain on cannabinoid receptor density and receptor-mediated G-protein activity within supraspinal brain areas involved in pain processing and modulation in mice. Chronic constriction injury (CCI) produced a significant decrease in WIN 55,212-2-stimulated [(35)S]GTPgammaS binding in membranes prepared from the rostral anterior cingulate cortex (rACC) of CCI mice when compared to sham-operated controls. Saturation binding with [(3)H]SR 141716A in membranes of the rACC showed no significant differences in binding between CCI and sham mice. Analysis of levels of the endocannabinoids anandamide (AEA) or 2-arachidonoylglycerol (2-AG) in the rACC following CCI showed no significant differences between CCI and sham mice. These data suggest that CCI produced desensitization of the cannabinoid 1 receptor in the rACC in the absence of an overall decrease in cannabinoid 1 receptor density or change in levels of AEA or 2-AG. These data are the first to show alterations in cannabinoid receptor function in the rostral anterior cingulate cortex in response to a model of neuropathic pain.

Figure 1

Sciatic nerve ligation produced a significant reduction in paw withdrawal latency to thermal stimulus in the ipsilateral paw of CCI mice when compared to sham control (***p< 0.0001) and baseline (‡ p< 0.0001) measures. This effect was observed at Day 3 post-CCI surgery and Day 10.

Figure 2

WIN 55, 212-2 stimulated stimulated [³⁵S] GTPγS binding in the rACC shows a significant decrease in E_max values in CCI mice at day 10 post surgery when compared to sham operated controls (n = 8). There were no significant differences in WIN 55, 212-2 stimulated [³⁵S] GTPγS binding in the PAG (panel b) (n = 6) or thalamus (panel c) (n = 6). Data are expressed as percent of net stimulated binding above basal binding.

Figure 2

WIN 55, 212-2 stimulated stimulated [³⁵S] GTPγS binding in the rACC shows a significant decrease in E_max values in CCI mice at day 10 post surgery when compared to sham operated controls (n = 8). There were no significant differences in WIN 55, 212-2 stimulated [³⁵S] GTPγS binding in the PAG (panel b) (n = 6) or thalamus (panel c) (n = 6). Data are expressed as percent of net stimulated binding above basal binding.

Figure 2

WIN 55, 212-2 stimulated stimulated [³⁵S] GTPγS binding in the rACC shows a significant decrease in E_max values in CCI mice at day 10 post surgery when compared to sham operated controls (n = 8). There were no significant differences in WIN 55, 212-2 stimulated [³⁵S] GTPγS binding in the PAG (panel b) (n = 6) or thalamus (panel c) (n = 6). Data are expressed as percent of net stimulated binding above basal binding.

Figure 3

Time course evaluation showed that the E_max value of WIN 55, 212-2 was significantly decreased in the rACC of CCI relative to sham mice only on day 10 (n = 8, **p < 0.01) and was not significantly different at day 1 (n = 6) or day 3 (n = 5) post surgery. There were no significant differences in EC₅₀ values at any time point examined. E_max and EC₅₀ values are expressed as difference between the group means of CCI and sham mice.

Figure 3

Time course evaluation showed that the E_max value of WIN 55, 212-2 was significantly decreased in the rACC of CCI relative to sham mice only on day 10 (n = 8, **p < 0.01) and was not significantly different at day 1 (n = 6) or day 3 (n = 5) post surgery. There were no significant differences in EC₅₀ values at any time point examined. E_max and EC₅₀ values are expressed as difference between the group means of CCI and sham mice.

Figure 4

[³H] SR 141716A receptor binding was conducted on the rACC at day 10 post CCI surgery. There were no significant differences in CB1 receptor binding between CCI (B_max = 2.43 pmol/mg ± 0.492, K_D = 1.21 nM ± 0.565) and sham mice (B_max = 1.88 pmol/mg ± 0.172, K_D =0.601 nM ± 0.179) in the rACC. Data are expressed as group means ± S.E.M. (n = 5).

Figure 5

CCI did not alter levels of the endocannabinoids AEA or 2-AG in the rACC at day 1 (n = 6) or day 10 (n = 6) post-surgery. Data are expressed as group means ± SEM.

Figure 5

CCI did not alter levels of the endocannabinoids AEA or 2-AG in the rACC at day 1 (n = 6) or day 10 (n = 6) post-surgery. Data are expressed as group means ± SEM.