Descending mechanisms of cannabinoid stress analgesia
Suplita, Richard Lee
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Stress- induced analgesia (SIA) is a state of decreased responsiveness to noxious stimulation following exposure to an environmental stressor. Inescapable foot-shock causes either opioid or non-opioid stress analgesia in rats depending on shock duration or intensity. Recent research from our laboratory indicates that non-opioid SIA elicited by brief continuous footshock is mediated by endogenous cannabinoids. The present study tested the hypothesis that pharmacological inactivation of cannabinoid receptors in brainstem nuclei modulating descending pain control attenuates non-opioid SIA. The competitive CB1 antagonist SR141716A was microinjected into the dorsolateral periaqueductal gray (dPAG), rostroventral medulla (RVM) and onto the lumbar spinal cord to evaluate the sites of action of non-opioid stress analgesia. Antagonist infusion into the dPAG and RVM, but not onto the spinal cord, was associated with decreased latency of responding to noxious stimulation. These results support the hypothesis that a descending cannabinergic neural system is activated in response to environmental stressors to modulate pain sensitivity.