Learned fear: a cause of arrhythmia onset in the presence of digitalis.

In earlier studies we have shown that guinea pigs exposed to signal-shock pairs develop digitalis toxicity earlier than control pigs on a test day when shocks are not delivered. Presenting subjects with signal-shock pairs is known to produce learned changes in autonomic tone thought to reflect fear. However, we were unable to find evidence of such changes in that model.

Cholinergic activation produces psychosomatic digitalis toxicity.

The purpose of this study was first to develop an animal model for stress-induced digitalis toxicity in such a way that physical and psychological factors might be kept separate. The other purpose was to begin an analysis of the mechanism of this psychosomatic effect. To do this, free-ranging guinea pigs were subjected to repeated sessions of signaled shock (Pavlovian fear conditioning) or to signal alone.

The role of shock predictability during aversive conditioning in producing psychosomatic digitalis toxicity.

Guinea pigs were subjected to Pavlovian fear conditioning (signaled shock) and then infused with a fast acting digitalis preparation on a day when all experimental stimuli except shock were delivered. A significant shortening in latency to the onset of life-threatening digitalis toxicity was found when comparisons were made to control pigs that had never been shocked. This effect was not found in other guinea pigs infused with ouabain after exposure to sessions of unsignaled shock.