Heart rate conditioning in the pigeon immobilized with alpha-bungarotoxin

Previous in vitro studies have yielded conflicting results concerning the physiological effects of alpha-bungarotoxin (alpha-BTX) at avian autonomic ganglia. In the present study heart rate change was classically conditioned in pigeons immobilized with alpha-BTX to assess the effects of this agent on autonomic function in the intact animal. When compared with non-immobilized controls, alpha-BTX had no significant effect on basal heart rate or on the rate of acquisition, magnitude or dynamics of conditioned heart rate change. Furthermore, a significant difference in performance between groups receiving conditioning and sensitization paradigms clearly indicated the establishment of conditioned responding. It is concluded that alpha-BTX has little or no effect on the cardiac innervation at doses sufficient to block neuromuscular transmission. The irreversible blockade of neuromuscular transmission by alpha-BTX without the side-effects produced by most other paralytics makes it an ideal choice as an immobilizing agent in acute preparations.