Learning of physiological responses: I. Habituation, sensitization, and classical conditioning.

Rats with chronic neuromuscular block (NMB) maintained by continuous infusion of alpha-bungarotoxin were classically conditioned. All rats showed reliable discriminative-conditioned tibial nerve firing, hind limb vasoconstriction, hypertension, bradycardia, and electroencephalographic (EEG) desynchronization. A regression analysis indicated that the conditioned vasoconstriction was neither centrally mediated by, nor inextricably linked to, skeletal (tibial) nerve firing. Throughout the experiment there were normal blood gases, pH, Na, serum protein, hematocrit, blood pressure, heart rate, vasomotor tone, and tibial nerve activity. The vital signs, EEG spectra, and cortical evoked potentials reflected regular sleep-wakefulness cycles and responsiveness to mild stimuli. The NMB rat preparation with its stable physiological state and fully intact central nervous system may be a useful model for a variety of physiological, medical, and neurobehavioral studies.