ii2 Effects of Denervation 



facts. For instance, preganglionic parasympathetic denervation of 

 the parotid gland causes a diminished cholinesterase activity and 

 an increased acetylcholine sensitivity; after postganglionic section 

 the enzyme activity is further reduced and the sensitivity further 

 raised. After excision of the superior cervical ganglion, however, 

 there is a supersensitivity to acetylcholine but no detectable change 

 in esterase activity. It is not easy to explain the sensitization to 

 agents resistant to the action of enzymes, for instance pilocarpine 

 or corbasil, on the basis of the enzyme hypothesis. The work is 

 furthermore hampered by our defective knowledge of the physio- 

 logical mode of elimination of the sympathetic transmitter. So far, 

 no experiments have been carried out on the effect of denervation 

 on the methylating enzyme recently assumed to be engaged in the 

 breakdown of the transmitter molecule. 



SECRETION AFTER DENERVATION 



Although the salivary gland, disconnected from the central ner- 

 vous system, does not usually show any secretory activity (if not 

 secreting spontaneously) it may under certain conditions enter into 

 activity. It still responds to injected secretory agents, and usually 

 even more readily than the normal gland, as discussed above. 

 Agents released into the circulation may under special circum- 

 stances attain a concentration high enough to excite the sensitized 

 gland cells. It is known, for instance, that in asphyxia the hor- 

 mones of the adrenal medulla may cause a secretion from a dener- 

 vated gland. The phenomenon of paralytic secretion can probably 

 be explained in a similar way. Secretion may occur for some days 

 in a denervated gland while the cut postganglionic parasympathetic 

 neurone is degenerating (the "paroxysmal salivary secretion"). 



Paralytic secretion. Some days after section of the chorda tym- 

 pani in a dog Claude Bernard (1862, 1864) discovered a flow of 

 saliva from the decentralized submaxillary gland, a "paralytic 

 secretion". In order to explain this puzzling phenomenon Bernard 

 assumed that the chorda normally exerts an inhibitory action on 

 the gland cells. A number of other explanations have been pro- 

 posed by later investigators (for literature see Emmelin, 1952a:). 

 Fleming and Macintosh (1935) suggested that the secretion is in 

 some way connected with the supersensitivity to sympathetic 

 impulses and adrenaline which follows section of the chorda. 



Recent experiments indicate that the paralytic secretion is not 



