Interaction of bilateral baroreceptor signals in conscious toads

Unilateral electric stimulation of the central stump of one of the laryngeal nerves of conscious toads induced increases and falls in arterial blood pressure. The falls were more frequent when the contralateral laryngeal nerve was also sectioned. Simultaneous bilateral electric stimulation of the central stump of the laryngeal nerves induced hypotension in 45% of the animals and bradycardia in 28.5% of them, the magnitudes of the responses being equal to the sum of the responses obtained by individual stimulation of each nerve. In other animals, the hypotensive responses (55% of cases) resulting from bilateral stimulation exceeded by 60% the sum of the individual responses, and bradycardia (71.5% of cases) did so by 116%, i.e. potentiation occurred. Potentiation of the hypotensive response may be accompanied by potentiation or only summation of the heart rate response, and vice versa, showing that the two parameters are individually regulated. The possible mechanisms inducing these results are discussed in terms of the central organization of the circuits involved and of the interference of factors of a sensory nature present in unanesthetized animals.