Cholinergic/opioid interaction in anterior cingulate cortex reduces the nociceptive response of vocalization in guinea pigs.

The objective of this study was to investigate the participation of opioid and cholinergic neurotransmission in the ACC on different nociceptive responses in guinea pigs. We used nociceptive tests of formalin and vocalization evoked by peripheral noxious stimuli (electric shock) to evaluate the behavioral expression of the sensory-discriminative and affective motivational components, respectively. We verified that the microinjection of morphine (4.4 nmol) in the ACC of guinea pigs promotes antinociception in the two experimental tests investigated. This effect is blocked by prior microinjection of naloxone (2.7 nmol). On the other hand, the microinjection of carbachol (2.7 nmol) in the ACC induces antinociception only in the vocalization test. This effect was prevented by prior microinjection of atropine (0.7 nmol) and naloxone (2.7 nmol). In fact, the blockade of ยต-opioids receptors with naloxone in ACC prevented the antinociceptive effect of carbachol in the vocalization test. Accordingly, we suggest that the antinociception promoted by carbachol was mediated by the activation of muscarinic receptors on local ACC opioid interneurons. The release of endogenous opioids seems to inhibited the expression of the behavioral response of vocalization. Therefore, we verified that the antinociceptive effect of morphine microinjection in ACC is broader and more robust than that promoted by carbachol. PMID: 28736107 [PubMed - as supplied by publisher]
Source: Brain Research - Category: Neurology Authors: Tags: Brain Res Source Type: research