CHOLINERGIC INFLUENCES ON THE SPINAL CARDIOVASCULAR NEURONS

In bilaterally vagotomized and spinal cord (C1)-transected dogs, intrathecal (i.t.) injection of pilocarpine decreased while DMPP [dimethylphenyl piperazinium] increased the blood pressure. These responses were antagonized by i.t. pretreatment with ethylbenztropine and chlorisondamine, respectively. No change in the resting heart rate occurred after i.t. injection of cholinergic drugs in these animals. The postcoronary artery ligation cardiac arrhythmia, in bilaterally vagotomized and spinal (C1)-transected dogs, was inhibited by i.t. pilocarpine and chlorisondamine and facilitated by ethylbenztropine and DMPP. The effects of muscarinic and nicotinic receptor agonists on the arrhythmia were blocked by their respective blockers. Evidently, the muscarinic receptors are inhibitory while nicotinic receptors are facilitatory for spinal control of vasomotor tone and the postcoronary artery ligation cardiac arrhythmia. The spinal muscarinic and nicotinic receptors do not appear to have a significant role in the regulation of normal heart rate.