Pressoceptive and chemoceptive aortic reflexes in decorticate and in decerebrate cats

Graded electrical stimulation of three different components of the aortic nerve has been performed in decorticate cats, and later repeated after intercollicular decerebration. Threshold stimuli, involving only the largest fibers probably originating from pressoceptors, slightly decrease blood pressure and respiration both in quiet decorticate and in decerebrate cats. However, in decorticate animals during "spontaneous" fits of sham rage, inhibition of all somatic and visceral components of rage behavior is observed. When aortic nerve stimuli also involve intermediate-threshold fibers presumably of chemoceptive origin, excitation of rage behavior accompanied by strong hypertension and hyperventilation is seen in decorticate preparations, while after decerebration reflex hyperpnea is accompanied by hypotension or by no consistent pressor change. Stronger stimuli activating smaller fibers of probable pressoceptive origin still have conspicuous excitatory effects in decorticate animals, as shown by appearance of rage activity and pressor reactions, whereas after decerebration prominent hypotension with hyperpnea is observed. The predominance of excitatory cardiovascular responses to aortic nerve stimuli in decorticate animals, and of inhibitory reactions after decerebration, is discussed.