The study of the central grey matter in mechanisms of different kinds of analgesia: Effects of lesions

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Abstract
The effect of the central gray matter (CG) on pain sensitivity was investigated in rats. It was demonstrated that baseline pain thresholds, tested by the hot plate method (HPM) after surgical operation, were significantly greater in CG-lesioned rats than in controls. Baseline tail flick latencies did not differ from those in the control group of animals. In the CG-lesioned rats, the latencies of pain responses, measured by the hot plate and tail flick tests after stress and auricular electroacupuncture, were significantly shorter than in the control group. The analgesia in the CG-lesioned rats after auricular electrostimulation was less than that after stress. Obtained data suggest that the significance of the CG in the regulation of baseline pain sensitivity, tested by different methods, is variable. CG mechanisms do not play a leading role in producing the tail flick response, whereas hind paw licking is mediated through CG-dependent mechanisms. The antinociceptive effect of stress and acupuncture is mediated by the CG. The role of the CG in analgesic mechanisms is greater in acupuncture than in stress. Apart from the CG, other antinociceptive systems are involved in the mechanisms of stress-induced analgesia.