The central reciprocal control of nasal vasomotor oscillations.

1. Nasal vasomotor oscillations were studied in 23 anaesthetised cats. The oscillations occurred in all cats and showed both respiratory (vasoconstriction in inspiration) and non-respiratory rhythms. In all cases the oscillations were asymmetrical between the two sides of the nose, and the side with greater oscillations also had a higher level of nasal vasoconstriction. 2. Oscillations shifted from one side to the other, both spontaneously and in response to stimulation of the brain-stem reticular formation. Induced shifts were nearly always to the stimulated side, and preceded by ipsilateral vasoconstriction and contralateral vasodilation. This reciprocal pattern was shown in 19 out of 89 responsive sites, and is similar to changes shown spontaneously in the nasal cycle. 3. Non-respiratory oscillations were seen at some time in most preparations and varied from frequency doubling to complete independence from respiration. 4. The evidence presented indicated that nasal vasomotor oscillations are driven from sympathetic oscillators which may be independent of, or can be entrained by, central respiratory activity. The oscillators show reciprocal inhibition, and electrical stimulation over a poorly-defined area of the brainstem reticular formation can shift the balance of activity between them, though responses from any one site depend on the existing state of the oscillating system.