Recurrent inhibition of sympathetic preganglionic neurons of the lateral horns of the spinal cord

Abstract

32.5% of the lateral horn sympathetic preganglionic neurons (B2-SPN) recorded in T3, T8-9 and L2 spinal segments of anaesthetized and immobilized cats were able to respond antidromically to repeated stimuli with time interval (16 ms and more) considerably exceeding the refractoriness of these neurons. This effect was not associated with axonal subnormality. A prolonged time interval between antidromic discharges correlated with the ability of orthodromic spikes to inhibit the generation of antidromic discharges throughout the same period which was substantially longer than the possible collision time. Preceding antidromic activation of a fraction of the described neurons partly inhibited the responses of other neurons in this segment elicited by stimulation of segmental nerves or spinal descending pathways. These data indicate that certain lateral horn sympathetic preganglionic neurons have a recurrent inhibitory mechanism.