Effects of spinal cord lesions on cutaneously elicited reflexes in the decerebrate cat. Tonic bulbospinal and spinobulbar inhibitory systems

Regulation of polysynaptic reflexes (ipsilateral extensor, flexor, and digital) in forelimbs and hind limbs was studied in 19 decerebrate cats. Clinical pattern, reflexogenous zones, modality of the eliciting stimulus, and relationship to extensor tone were explored. The location of tonic descending inhibitory and excitatory pathways was investigated by making bilateral and unilateral spinal cord lesions. The Schiff-Sherrington effect on the forelimbs was investigated, and an attempt was made to separate ascending pathways responsible for inhibition of extensor tone from those responsible for inhibition of polysynaptic reflexes, by dorsal and ventral hemisections at T-8 and C-2. Polysynaptic reflexes (both extensor and flexor) in response to pinch were inhibited all over the body, although they were more easily obtained from certain reflexogenous zones than from others. Responses to touch, pressure, and stroke were readily elicited from the perineum but were inhibited from other areas. Tonic bulbospinal inhibitory pathways were located in the dorsal part of the lateral funiculi and facilitatory pathways in the ventral funiculi and ventral parts of the lateral funiculi. Both increased extensor tone and decreased flexor reflex activity of the forelegs after thoracic transection (Schiff-Sherrington phenomenon) were due to the interruption of ascending inhibitory fibers of spinal origin which act upon brain stem centers. The tonic spinobulbar pathways which have the effect of inhibiting brain stem centers responsible for decerebrate inhibition of polysynaptic reflexes ascend through the dorsal part of the lateral funiculi. The fibers inhibiting the brain stem inhibitory centers for extensor tone ascend in more ventral pathways.