CAPSAICIN FACILITATES EXCITATORY BUT NOT INHIBITORY SYNAPTIC TRANSMISSION IN SUBSTANTIA-GELATINOSA OF THE RAT SPINAL-CORD

Actions of capsaicin were examined on synaptic transmissions in the su bstantia gelatinosa (SG) of adult rat spinal cord slices using the who le-cell patch-recording technique. Bath-applied capsaicin at a concent ration of 2 mu M activated a slow inward current (having an amplitude of 33 pA at -70 mV), which was accompanied by an increase in the frequ ency of glutamatergic spontaneous excitatory postsynaptic currents (sE PSCs; by 234%); these actions were blocked by a capsaicin-receptor ant agonist, capsazepine (10 mu M). The capsaicin-induced increase in sEPS C frequency was resistant to tetrodotoxin (0.5-1 mu M). On the other h and, capsaicin (2 mu M) did not affect either glycine- or gamma-aminob utyric acid-mediated spontaneous synaptic transmission. The results in dicate that capsaicin enhances excitatory but not inhibitory synaptic transmission, possibly through a direct action on primary afferent ter minals in the SG. As the SG has been thought to participate in nocicep tive pathway, it is suggested that such a presynaptic action of capsai cin contributes to nociceptive transmissions. (C) 1998 Elsevier Scienc e Ireland Ltd. Ail rights reserved.