Spinal cord participation in the Cushing reflex in the dog

Abstract

✓ The vasopressor response to increased intradural pressure (Cushing reflex) is caused by decreased arterial perfusion (hypoxia) and the mechanical effects of pressure acting in concert. Increased pressure in the range 50–200 mm Hg alters ongoing activity in all neurons concerned with the autonomic nervous system at multiple levels of the neuroaxis. Therefore, the response of an intact organism is highly variable and unpredictable. Conversely, the response to increased pressure exerted upon the spinal cord of a spinal animal is relatively uniform and predictable. Spinal neurons of both the somatic and autonomic nervous systems show facilitation followed by inhibition, but the time course and magnitude of these events are much different for the two systems. Autonomic neurons retain the ability to fire under very adverse conditions, thus enhancing the organism's chance for survival.