Effects of naftopidil on inhibitory transmission in substantia gelatinosa neurons of the rat spinal dorsal horn in vitro

Although naftopidil was developed as an alpha-1 adrenoceptor antagonist, our previous spinal cord slice experiments showed that the activation of an alpha-1 adrenoceptor in substantia gelatinosa increases the frequency of mIPSCs. This result suggested that, under our conditions, naftopidil may interact with a receptor(s) other than an alpha-1 adrenoceptor in the spinal dorsal horn. The present results suggested that naftopidil enhances the release of GABA and glycine by activating inhibitory interneuron terminals in the spinal dorsal horn via a receptor other than an alpha-1 adrenoceptor, thereby modulating sensory transmission in the substantia gelatinosa.