| Abstract: | The effect of the corticosteroid hormone hydrocortisone on electrical activity in the lumbosacral portion of the spinal cord was studied in acute experiments on cats anesthetized with urethane and chloralose and immobilized with succinylcholine. The amplitude of mono- and polysynaptic discharges arising in the ventral roots in response to stimulation of various afferents of the animal's hind limb was increased by a statistically significant degree after intravenous injection of the hormone. The potentiating action of the hormone was strongest and most stable with respect to early and late postsynaptic potentials of the spinal cord. The dorsal cord potentials were not significantly changed by hydrocortisone. Spontaneous unit activity in the intermediate nucleus of the spinal cord rose sharply after administration of hydrocortisone. Before the action of the hormone the mean frequency of spontaneous discharges of 46 neurons was 7.91/sec, rising to 20/sec after the injection. The number of neurons with a high spontaneous firing rate also was increased. Prolonged extracellular recording of the spontaneous activity of the same neuron before and after administration of hydrocortisone also revealed a marked increase in the frequency of its discharges. The results are evidence of the activating effect of hydrocortisone on spinal interneuronal activity. |
