Abstract
We have previously reported an inhibition by cannabinoids of excitatory transmission in substantia gelatinosa (SG) neurons. In order to know further a role of cannabinoids in regulating nociceptive transmission, their actions on inhibitory transmission in SG neurons were examined using whole-cell voltage-clamp recordings. In 18 of 23 neurons examined, superfusing an endocannabinoid, anandamide (10μM), for 2 min resulted in reducing the amplitude of glycinergic focally-evoked IPSCs (eIPSCs); this reduction persisted over at least 6 min with an extent of 27± 3% (2 min after its washout). A similar reduction was also seen for GABAergic eIPSC amplitudes in 17 of 24 neurons tested; this extent was 42± 4%. These inhibitons were reversed by superfusing a cannabinoid-receptor antagonist, SR141716A (5μM), following anandamide washout. A ratio of the second to first glycinergic or GABAergic eIPSC amplitude in paired-pulse experiments was increased by anandamide. Glycinergic and GABAergic spontaneous IPSCs were also reduced in frequency by anandamide (10μM) by 46± 5 and 35± 7% (each n = 5), respectively, without a change in the amplitudes. Another endocannabinoid, 2-arachdonoyl glycerol (20μM), and a synthetic cannabinoid-receptor agonist, WIN55212-2 (5μM), also reduced glycinergic and GABAergic IPSC amplitudes. It is concluded that cannabinoids presynaptically inhibit both glycinergic and GABAergic transmission to SG neurons; this would contribute to a modulation of nociceptive transmission. [Jpn J Physiol 54 Suppl:S156 (2004)]
