Psychogenic vagotonia in a family of beagle dogs

Eight inbred beagle dogs, litter mates of two generations, exhibited psychogenic vagotonia (long sinus pauses and transient atrioventricular block of the heart) during orienting to tones. This was intensified during tones following “one-trial conditioning” to a single painful leg-shock. It was potentiated during conditional stimuli (CS+) regularly reinforced by leg-shock; whereas unreinforced tones (CS?) elicited less vagotonia. Additional evidence of differentiation was observed in one dog when the differential magnitudes of the responses were reversed following reversal of the significance of the conditional stimuli. The possible mechanisms of these changes and correlations with clinical material are discussed. Results of this study illustrate the interplay between constitutional predisposition and psychological factors in prominent cardiovascular changes.