Neuromuscular blocking drugs and heart rate changes after direct nerve stimulation and during classical conditioning...

Two experiments investigated cardiovascular responses to several common neuromuscular blocking compounds. Experiment 1, employing 16 cats, assessed ganglionic transmission in sympathetic and parasympathetic systems controlling heart rate and blood pressure after d-tubocurarine chloride (d-T.C.), dimethyl d-tubocurarine iodide (D. d-T.I.), succinylcholine chloride (SC), or saline. Cardiovascular responses to sympathetic stimulation were essentially unaffected at drug levels that blocked evoked electromyograms; however, vagally evoked bradycardia and corresponding blood pressure decrease were blocked by d-T.C. and redduced by D. d-T.I. and SC. Experiment 2 compared heart responses of 12 cats under the same blocking compounds during differential classical aversive conditioning. Differential conditioned responses and unconditioned responses occurred under D. d-T.I., less under SC, but not under d-T.C. However, animals trained under d-T.C. and tested under D. D-T.I. showed differential conditioned responses.