OPIOID-PEPTIDES IN PAIN SENSORY INTEGRATI ON AND PERCEPTUAL DYSFUNCTION IN THE SPINAL-CORD

This is a review of the anatomic localization evidences and the role p layed by opioid peptides in the processing of nociceptive and no nocic eptive sensorial information in the spinal cord. Some per se constitut ed mechanisms in complex states generators are analyzed, such as allod ynia, that is, no nociceptive sensorial stimuli producing pain. An exp erimental method is suggested by wich prolonged recordings are obtaine d (more than 2 h.) of unicellular activity of recorded neurons in the dorsal horn of the spinal cord of the complete and anesthesized rat (u rethan, 1500 mg/kg). This preparation identifies the recorded neurons by means of the direct activation of the sensorial area. Changes in th e sensorial codification are induced by means of the subcutaneous infi ltration of carrageenan (200 ul at 1%) in the same area. Results show an increase in the firing frequency of neurons, wich in a control situ ation respond only to soft tactile stimulation or to hair movement. Th is increase is what we consider as pain because it reverted with morph ine administration (15 mg/kg iv). Nalaxone administration (1 mg/kg iv) increased the frequency eighty minutes after carrageenan infiltration . Data has been obtained from this experimental approach, reproducing the allodynia phenomena and indicating that it is mediated by the opio id system.