Oscillatory behavior of the sympathetic system induced by picrotoxin.

Abstract

In cats anesthetized with sodium pentobarbital, paralyzed with gallamine, atropinized, and artificially ventilated, an intravenous injection of picrotoxin (dose between 2 and 5 mg/kg) consistently induced sustained oscillations of arterial blood pressure (BP). Because of their form, and regularity of repetition (range: 0.3 to 4 cycles/min), these oscillations can be considered analogous to vasomotor waves (Mayer waves), which are known to occur in conditions such as hemorrhage, metabolic acidosis, and cerebral ischemia. The BP oscillations characteristic of picrotoxin intoxication have the following properties: (i) they are generated in the CNS since they are abolished by ventral root block; (ii) they are accompanied in most cases by oscillations of the nictitating membrane tension of the same frequency; and (iii) they occur in animals with complete transection of the spinal cord at a cervical level and in those with sectioned ninth and tenth nerves; hence they are not dependent upon afferent impulse traffic arising in baro- and chemo-receptors. Furthermore, nictitating membrane tension oscillation has been seen when BP was maintained stable. The latter observations indicate that for maintaining the oscillation in the sympathetic system the concomitant hemodynamic changes are not essential. It would appear that the oscillation is the result of epileptiform activity of sympathetic neurons. Perhaps some types of spontaneously occurring vasomotor waves have a similar origin.