Supraspinal inhibition of the excitation of dorsal horn neurones by impulses in unmyelinated primary afferents: lack of effect by strychnine and bicuculline.

In barbiturate anaesthetized cats, tonic descending inhibition of the excitation of lumbar dorsal horn neurones by impulses in unmyelinated primary afferents was measured by reversibly cooling a more cephalic segment. Administered electrophoretically in the substantia gelatinosa and at sites progressively closer to cell bodies, amounts of bicuculline and strychnine adequate to reduce segmental inhibition failed to reduce supraspinal inhibition. Intravenous bicuculline and strychnine also failed to reduce supraspinal inhibition.