[Excitatory and aversive behaviors - electrophysiological observation of anterior cingulate cortex (ACC) in rats]

Increasing activities in anterior cingulate cortex (ACC) can enhance the aversion reactions associated with noxious stimuli. It has been known that opioid receptors activation can trigger endogenous analgesic effect. This study tried to explore whether opioid receptors activation in the ACC region could reduce the aversion associated with noxious stimuli.

The experimental rats were randomly divided into seven groups, Complete Freund's adjuvant (CFA) + normal saline (NS) group, normal saline (NS) + normal saline (NS) group, normal saline (NS) +DAMGO ((DAla², NMe-Phe⁴, Gly-ol⁵)enkephinlin, μ-opioid receptor agonist) group, complete Freund's adjuvant (CFA)+ 0.01/0.04/0.2/1 μg/μl DAMGO group(n=6). The experimental period was three days. The basal value was measured on the first day. The second day, 1 μl was administered through the ACC area, and then 0.08 ml of complete Freund's adjuvant (CFA) was injected into the left hind paw of the rat. CPA response, paw withdrawal reflex latency (PWL) and electrical activity in the ACC brain region of rats were observed on the third day.

①PWL was significantly decreased in rats after CFA was injected into left hind paw compared with post-injection(P＜0.05).② In the pain side of the apparatus, it took rats less residence time than that in the non-pain side. ③ 0.04/0.2/1 μg/μl DAMGO was given before CFA-injection, C-CPA reactions could be revised significantly. ④ Given 0.04/0.2/1 μg/μl DAMGO in the ACC region could decrease the increasing discharge frequency induced by CFA in ACC neurons.

The activation of the mu-opioid receptor in the ACC region alleviates the aversion induced by noxious stimulation.