Parasagittal thalamic knife-cuts and cardiac changes

Rabbits received knife-cuts either medial or lateral to the mediodorsal nucleus of the thalamus (MD), and had stimulating electrodes implanted in MD. These animals were compared to animals with sham knife-cuts for (1) the cardiac component of the orienting reflex (OR) to novel tone stimuli; (2) differential pavlovian heart rate (HR) conditioning, utilizing tones of different frequencies as CSs and paraorbital shock as the US; and (3) heart rate, blood pressure, electromyographic activity, and respiration changes elicited by electrical stimulation in MD. Medial knife-cuts led to faster habituation of the OR, and to somewhat attenuated HR conditioning, but had no effect on stimulation-elicited changes. Lateral knife-cuts, on the other hand, enhanced the stimulation-elicited HR response, but had little effect on the HR OR. The HR CR was unaffected by lateral cuts during an initial conditioning session, but was attenuated in both knife-cut groups during a second session, compared to sham control animals.