Actions of a novel water-soluble benzodiazepine-receptor agonist JM-1232(−) on synaptic transmission in adult rat spinal substantia gelatinosa neurons

Although the intrathecal administration of JM-1232(−) reportedly produces antinociception, this action has not yet been examined at the cellular level. We examined the action of JM-1232(−) on synaptic transmission in spinal substantia gelatinosa (SG) neurons which play an important role in regulating nociceptive transmission from the periphery. The whole-cell patch-clamp technique was applied to the SG neurons of adult rat spinal cord slices. Bath-applied JM-1232(−) prolonged the decay phase of GABAA-receptor mediated spontaneous inhibitory postsynaptic current (sIPSC) and increased its frequency without a change in amplitude. The former but not latter action was sensitive to a benzodiazepine-receptor antagonist flumazenil. JM-1232(−) also increased glycinergic sIPSC frequency with no change in amplitude and decay phase. On the other hand, glutamatergic spontaneous excitatory transmission was unaffected by JM-1232(−). These results indicate that JM-1232(−) enhances inhibitory transmission by (1) prolonging the decay phase of GABAergic sIPSC through benzodiazepine-receptor activation and by (2) increasing the spontaneous release of GABA and glycine from nerve terminals without its activation. This enhancement could contribute to at least a part of the antinociceptive effect of intrathecally-administered JM-1232(−).

► JM-1232(−) is a novel benzodiazepine-receptor agonist. ► JM-1232(−) presynaptically enhanced inhibitory transmission in spinal dorsal horn. ► This action was not mediated by benzodiazepine receptors. ► This is one of cellular mechanisms for the antinociceptive action of JM-1232(−).