Some experimental pain indices and their applications in the study of analgesic mechanisms

This communication presents some insights into the controversies and complications in experimental pain research using laboratory animals. In particular, I have singled out two experimental pain indices that are used in my laboratory for a decade, viz, dental pain model and hot-plate algesiometric assay for discussion. Using these two models, my colleagues and I have identified that morphine may promote analgesia by enlisting synergistic actions from the central cholinergic and dopaminergic systems, in a process that involves shifting of balance between various neurotransmitter systems. We confirmed the medullary nucleus reticularis gigantocellularis as a site for clonidine- and morphine-induced and stimulation-produced antinociception. Finally, a progressive increase in pain sensitivity and a gradual reduction in the analgesic potency of morphine and clonidine are unveiled in aging rats.