“Opiate Intervention; Reduction in Opioid on “Emotional” Information Processing”
Antinociceptive /an·ti·no·ci·cep·tive/ (an″te-) (an″ti-no″sĭ-sep´tiv) reducing sensitivity to painful stimuli.
The amygdaloid complex is a prominent temporal lobe region that is associated with “emotional” information processing. Studies in the rodent have also recently implicated the amygdala in the processing and modulation of pain sensation, the experience of which involves a considerable emotional component in humans.
New research sought to establish the relevance of the amygdala to pain modulation in humans by investigating the contribution of this region to antinociceptive processes in nonhuman primates. Using magnetic resonance imaging guidance, the amygdaloid complex was lesioned bilaterally in six rhesus monkeys (Macaca mulatta) through microinjection of the neurotoxin ibotenic acid.
This procedure resulted in substantial neuronal cell loss in all nuclear subdivisions of this structure. In awake non-operated control monkeys, systemic administration of the prototypical opioid morphine or the cannabinoid receptor agonist WIN55,212-2 produced dose-dependent anti-nociception on a warm-water tail-withdrawal assay.
The anti-nociceptive effects of each drug were reversible with an appropriate antagonist. In monkeys with bilateral amygdala lesions, however, the anti-nociceptive effects of each drug were significantly reduced. These results constitute the first causal data demonstrating the necessity of neurons in a specific brain region for the full expression of opioid- and cannabinoid-induced anti-nociception in the primate.
Because our amygdala lesioned monkeys exhibited both a reduction in antinociception and a reduction in behavioral indices of fear (Emery et al., 2001), the possibility should be considered that, in the primate, “anti-nociceptive circuitry” and “fear circuitry” overlap at the level of the amygdala.
This possibility is very important in correlation with research that indicates that heroin and opiates my increase pain sensitivity.