RESUMO
Transverse slices of the spinal cord with dorsal root attached were prepared from adult rats and used to record the response of the spinal substantia gelatinosa neurons evoked by repetitive stimulation of the dorsal root with a whole cell patch clamp method. The repetitive stimulation of 10 trains (20 pulses at 100 Hz/train) with an intensity necessary to activate C-fibers, but not A-fibers alone, evoked slow depolarization (SD) during it and the SD disappeared within 1 min after the termination of it. The SD was completely inhibited by 500 nM of tetrodotoxin (TTX), but not significantly changed by 50 nM of TTX, nor 20 microM CNQX + 50 microM AP5, nor 1 microM CP-99994. DAMGO inhibited the SD in a concentration dependent manner (10 nM-1 microM), but 1 microM DPDPE and 1 microM U-50488H did not. The inhibitory effect of DAMGO (1 microM) was reversed by naloxone (1 microM). These results suggest that the SD of substantia gelatinosa neurons evoked by repetitive stimulation of C-fibers of the dorsal root is an event relevant to nociception in the spinal dorsal horn.