Electron microscopy of selectively denervated canine carotid sinuses

Selective denervation as used to characterize the nerve endings in the carotid sinus wall of the dog. Areas of dense innervation were identified by acetylcholinesterase histochemical technique and sampled for electron microscopic study following survival periods of 48 to 144 hours after selective neurectomies were done. Large varicosities, similar to previously described mechanoreceptor endings, showed signs of degeneration after transection of the sinus nerve, but not after cranial cervical ganglionectomy or section of the glossopharyngeal nerve proximal to its sensory ganglia. These were concluded to be endings of afferent neurons. Histochemical reactions at the fine structure level demonstrated such varicosities to be acetylcholinesterase positive. Smaller varicosities containing granulated synaptic vesicles degenerated after cranial cervical ganglionectomy was done. These were interpreted to be postganglionic sympathetic endings. This study represents an example where denervation, coupled with short survival periods, serves as a technique for studying selected areas of the peripheral nervous system.