Sympathetic responses evoked by vestibular stimulation and their interactions with somato-sympathetic reflexes.

In chloralose anesthetized cats mass reflex discharges of the renal sympathetic nerve were recorded following stimulations of low threshold, large myelinated afferents in vestibular and superficial peroneal nerves. Reflex responses caused by stimuli applied to both nerves were quite similar; a brief excitatory phase was followed by a long inhibitory phase or "silent-period'. Decerebration did not have any appreciable effects on either reflex but decerebellation (in addition to decerebration) greatly increased the excitatory response and shortened the inhibitory phase or "silent period' of the vestibulo-sympathetic reflex. The somato-sympathetic reflex response however, was not much altered by this procedure. When a vestibular nerve stimulus, given as a conditioning shock, preceded a testing stimulus applied to the cutaneous nerve by less than 300 msec, the test response was completely inhibited. The "recovery curve' of this conditioning--testing response showed that after decerebellation the inhibitory effect of vestibular conditioning stimulus on testing response was much reduced. The autonomic effector responses, blood pressure, heart rate and galvanic skin reflex (GSR) following low intensity stimulation of vestibular and cutaneous nerves were also studied. Repetitive stimulations applied to either nerves evoked a depressor response kand augmented GSRs but caused no significant changes in heart rate. Decerebellation reduced the depressor response produced by repetitive stimulation of vestibular nerves. The study indicates that vestibular nerves, as well as cutaneous afferents, which are powerful imputs for evoking somatic reactions, also elicit autonomic reflexes and that similarity and interactions between sympathetic reactions evoked by these two inputs suggest a common central mechanism.