Action of capsaicin on dorsal root-evoked synaptic transmission to substantia gelatinosa neurons in adult rat spinal cord slices

An action of capsaicin was investigated on dorsal root-evoked synaptic transmission to substantia gelatinosa (SG) neurons in adult rat spinal cord slices by use of the whole-cell voltage-clamp technique. In 79% of neurons examined, superfusing capsaicin (1 μM) for 30 s depressed a C-fiber-evoked excitatory synaptic current in a manner sensitive to a capsaicin-receptor antagonist, capsazepine (10 μM). On the contrary, Aδ-fiber-evoked excitatory and inhibitory synaptic currents were unaffected by capsaicin in all of cells tested. It is concluded that capsaicin specifically acts on C-afferents, resulting in an inhibition of evoked excitatory transmission to the SG; this may contribute to, at least in part, an acute analgesic action of capsaicin.