CONDITIONAL REFLEX ACTIVATION OF SYMPATHETIC CHOLINERGIC VASODILATOR NERVES IN DOG

Sympathetic, cholinergic kasodilatation in skeletal muscle was induced as orienting and conditional reflex responses in conscious dogs. A sound stimulus elicited an orienting reflex accompanied by an atropine‐sensitive vasodilatation in the skeletal muscles of the hind limb. Further, a tachycardia and a slight blood pressure rise were noticed. The orienting reflex response disappeared gradually on repetition of the sound stimulus. The same cardiovascular events were obtained as conditional reflexes to both electrical cutaneous stimulation and exercise on a treadmill. The conditional responses were not diminished if the conditional reflexes were reinforced by training. Graded conditional responses were obtained when the intensities of the unconditional stimuli were varied. The increase in blood flow to the hind limb following treadmill exercise was not influenced by atropine. Our findings indicate that the sympathetic vasodilator system is activated prior to situations when an increased muscle blood flow is suddenly required. The results also suggest that activation of the dilator nerves takes place not only in emotionally charged situations, such as the defence reaction, but also in anticipation of exercise when the emotional involvement is less prominent. © 1969 Scandinavian Physiological Society