Mechanisms of spinal reflex depressant effects of CS-722, a newly synthesized centrally acting muscle relaxant, in spinal rats

Preferential enhancement of inhibitory synaptic transmission by CS-722 in the ventral horn neurons of neonatal rat spinal cord

We studied the modulatory effect of (R)-4-chloro-2-(2-hydroxy-3-morpholinopropyl)-5-phenyl-4-isoxaz olin-3-one hydrochloride (CS-722), a centrally acting muscle relaxant, on synaptic transmission in the ventral horn neurons of neonatal rat lumbar spinal cord in slices using whole cell recording techniques. Pharmacologically isolated excitatory or inhibitory postsynaptic currents (EPSCs and IPSCs) were evoked by stimulating neighboring neurons. CS-722 preferentially enhanced IPSCs with little effects on EPSCs. Moreover, CS-722 reduced paired pulse facilitation of gamma-aminobutyric acid (GABA)-mediated IPSCs, suggesting its action on the presynaptic terminal. Preferential facilitatory effects on inhibitory synaptic transmission seem to be one of the mechanisms underlying muscle relaxation of this compound.

The effects of the muscle relaxant, CS-722, on synaptic activity of cultured neurones

1. The pharmacological properties of the centrally acting muscle relaxant, CS-722, were studied in cultured hippocampal cells and dorsal root ganglion cells of the rat using the whole-cell variation of the patch clamp technique. 2. CS-722 inhibited the occurrence of spontaneous excitatory and inhibitory postsynaptic currents in hippocampal neurones at concentrations of 100-300 microM, but had no effect on postsynaptic currents evoked by the application of glycine, gamma-aminobutyric acid, glutamate or N-methyl-D-aspartate. 3. CS-722 reduced voltage-gated sodium currents, while shifting the sodium channel inactivation curve to more negative membrane potentials. This effect is similar to that reported for local anaesthetics. Voltage-gated potassium currents were decreased by CS-722 by approximately 20%, whereas voltage-activated calcium currents were inhibited by about 25%. 4. CS-722 inhibited evoked inhibitory postsynaptic currents. However, the spontaneous quantal release of inhibitory transmitter was not affected. 5. The inhibitory effect of CS-722 on spontaneous inhibitory postsynaptic currents and excitatory postsynaptic currents in hippocampal cultures probably results from an inhibition of both sodium and calcium currents. This inhibitory effect is likely to be amplified in polysynaptic neuronal circuits.