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

Abstract

This is a review of the anatomic localization evidences and the role played by opioid peptides in the processing of nociceptive and no nociceptive sensorial information in the spinal cord. Some per se constituted mechanisms in complex states generators are analyzed, such as allodynia, that is, no nociceptive sensorial stimuli producing pain. An experimental method is suggested by wich prolonged recordings are obtained (more than 2 h.) of unicellular activity of recorded neurons in the dorsal horn of the spinal cord of the complete and anesthesized rat (urethan, 1500 mg/kg). This preparation identifies the recorded neurons by means of the direct activation of the sensorial area. Changes in the sensorial codification are induced by means of the subcutaneous infiltration of carrageenan (200 ul at 1%) in the same area. Results show an increase in the firing frequency of neurons, wich in a control situation respond only to soft tactile stimulation or to hair movement. This increase is what we consider as pain because it reverted with morphine 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 opioid system.