EFFECTS OF FENTANYL UPON THE SPINAL INTER NEURONS ACTIVATED BY Aδ AFFERENT FIBERS OF THE CUTANEOUS NERVE OF THE CAT

In our previous papers (1, 2) it was shown that narcotic analgesics have common characteristics of selectively depressing or blocking the late phase of the inhibition of spinal extensor monosynaptic reflex evoked by the stimulation of either cutaneous or high threshold muscle afferent fibers, It was also demonstrated that the depressed phase of the cutaneous inhibition after narcotic analgesics was produced from Aδ a Reren t fibers (1). Since these facts suggested that some spinal intcrncurons activated by such small fibers might be depressed by narcotic analgesics, it was attempted to find such neurons in the spinal cord of unaesthetized low spinal cats. All surgical operations were performed under ether anesthesia. The laminectomy was carried out from L3-L7 and the spinal cord was transected at T5, under local anesthesia with procaine. In a few experiments, the spinal cord was also exposed from T5-T7 and a pair of Ag-ball electrodes were placed on the dorsal part of the lateral funiculus of this part for antidrimic stimulation. A collar-type electrode was implanted on the ipsilateral quadriceps nerve for stimulation. Two of these were aso attached to the ipsilateral saphenous nerve, one for stimulation at proximal and another for recording at distal part. After the operation was completed, anesthesia was discontinued and animals were immobilized with gallamine triethiodide and were maintained under artificial respiration. A glass pipette microelectrode filled with 1M K-acetate solution saturated with methylblue (1-10 MΩ) was inserted into the lumbar spinal cord, and the neuronal activity was projected on the cathode-ray oscilloscope (Taktronix 565)