Electrophysiological and Micro‐electrophoretic Studies on Sympathetic Preganglionic Neurones in the Spinal Cord

Preganglionic sympathetic neurones in the thoracic cord of the spinal cat were located by recording antidromic extracellular potentials in response to stimulation of preganglionic fibres in the superior splanchnic nerve. Antidromic potentials were only recorded in the region of the intermedio‐lateral cell column. Few units were firing spontaneously or could be orthodromically activated. The conduction velocities in the preganglionic axons of units from which recordings were obtained ranged from 1.5 to 9 m/sec. Local micro‐electrophoretic applications of DL‐homocysteic acid fired the cells but noradrenaline had no excitatory effect and did not inhibit spontaneous, synaptic or antidromic firing or the firing to the excitant amino acid. Acetylcholine had no effect on the few cells tested.