Effects of 2-AG on peripheral afferent synaptic transmission to spinal cord motoneuron in vitro
Objective:To investigate effects of 2-arachidonoylglycerol(2-AG,one of endocannabinoids)on the excitatory postsynaptic potential(iDR-EPSP)evoked by peripheral inputs in isolated spinal motorneuron(MN)of newborn rats in vitro.Methods:Neonatal SD rats(8-14 days old)were used to prepare the transverse spinal cord slices(400-500 μm in thickness).The experiment was conducted using intracellular recording technique from spinal MN,aiming to observe the effect of 2-AG on the iDR-EPSP in MN evoked by electrical stimulation of ipsilateral dorsal roots.Results:In the 11 MN,perfusion of 5 μmol/L 2-AG for 15 min induced a depolarizing response accompanied by an increase in membrane resistance(P<0.01).In the 15 MN,perfusion of 5 μmol/L 2-AG for 15 min resulted in a decrease in both the amplitude and area under curve of iDR-EPSP(n=15,P<0.01).In another 9 MN,cumulative perfusion of 1,5,and 25 μmol/L 2-AG for 15 min each induced depolarizing responses and concentration-dependently reduced iDR-EPSP amplitude(P<0.01)and area under curve(P<0.05).Apparent receptor kinetic analysis was performed on iDR-EPSP of 17 MN perfused with 25 μmol/L 2-AG for 15 min,which demonstrated reduced apparent maximum response(Vmax)and apparent dissociation rate constant(K2)of iDR-EPSP(P<0.05),yet the difference was insignificant in the changes of apparent association rate constant(K1)and apparent equilibrium dissociation constant(KT)(P>0.05).Conclusion:2-AG can produce a concentration-dependent inhibitory effects on the peripheral afferent excitatory synaptic transmission to spinal cord MNs in vitro.