Abstract
Whole-cell recordings were made from substantia gelatinosa (SG, lamina II of the spinal cord) neurons of urethane-anesthetized rats and spinal cord slices to analyze excitatory and inhibitory synaptic responses evoked by cutaneous natural and dorsal root stimulation. Under an artificial ventilation, the lumbar spinal cord was exposed and then the animal was placed in a stereotaxic apparatus. Patch electrodes were inserted into the SG and whole-cell voltage-clamp recordings were obtained from SG neurons. In most SG neurons examined, pinch and air stimulation produced a barrage of EPSCs. At a holding potential of 0 mV, air stimuli evoked a barrage of IPSCs. On the other hand, pinch stimulus elicited IPSCs only at beginning and end of the stimulation. The size of receptive field of IPSCs was larger than that of EPSCs in the same neurons. Electrical stimulation of the dorsal roots evoked EPSCs and IPSCs in SG neurons of horizontal spinal cord slices. L5 dorsal root stimulation elicited IPSCs in SG neurons at L2 spinal level without any EPSCs in the same neurons. It is concluded that the extension of inhibitory synaptic pathway is more widespread than that of excitatory circuitry. This extended inhibitory pathway in the spinal dorsal horn may be a possible mechanism for the lateral inhibition produced by innocuous stimulation. [Jpn J Physiol 54 Suppl:S158 (2004)]
