GENERALIZED ATONIA AND PROFOUND DYSREFLEXIA FOLLOWING TRANSECTION OF THE BRAIN STEM THROUGH THE CEPHALIC PONS

Abstract

Dogs with brain stem transections through varying levels of the midbrain and pons have been maintained and studied by gross clinical inspection for several wks. subsequent to the operation. The transections were made by blunt traction, so that the brain structures cephalad to the transection remained undisturbed in the cranium. During the operative procedure, the blood supply to the brain was not molested by ligation of the carotid, nor by temporary occlusion of the vertebrals. A generalized and enduring muscular atonia invariably followed a transection placed appropriately at an upper pons level. A profound dysreflexia followed a transection of the brain stem at any level of the midbrain and pons. It was selective to the extent that some reflexes were affected to a greater degree than others, and the extent that the reflexes were affected varied with the level of the transection. This dysreflexia was more inclusive and more profound following a transection through the upper pons. An obvious spontaneous extensor rigidity did not routinely follow midbrain transections. These prepns. did not exhibit undue resistance to passive manipulation of the limbs or trunk musculature, and the reflex standing stance was not exaggerated. Low midbrain prepns. did invariably exhibit a profound and permanently enduring impairment of the righting reflexes.