Postganglionic Neurones 63 



on the normal gland and on the gland previously postganglionically 

 denervated, and sensitized to acetylcholine. The eserine was in- 

 jected through the ducts so as to make it possible to treat the 

 glands separately. 



The most reasonable explanation of these experiments seems to 

 be that there is a small continuous release of acetylcholine from the 

 postganglionic, parasympathetic nerve endings, similar to the leak- 

 age from the motor nerve terminals, sufficient to cause a secretion 

 only when the cholinesterase has been inhibited. 



That an effect is obtained at all after the auriculo-temporal nerves 

 have degenerated presents in itself a problem. It probably indicates 

 that some cholinergic fibres are still present in the parotid gland; 

 some auriculo-temporal fibres may have been left, or some fibres 

 may reach the gland by other channels, as discussed in the next 

 section of this chapter. 



During the period in which the auriculo-temporal fibres are 

 degenerating a curious phenomenon, a "paroxysmal salivary 

 secretion", can be seen (Emmelin and Stromblad, 19586). Attacks 

 of secretory activity occur, alternating with periods of rest. The 

 flow, as will be discussed later in Chapter VI, is probably due to 

 bursts of acetylcholine released from the endings of the degenerat- 

 ing fibres. Normally, however, the continuous release is apparently 

 not large enough to cause a secretion when acetylcholine is not 

 preserved by a cholinesterase inhibitor. The question naturally 

 arises whether the acetylcholine released has any effect. Dirnhuber 

 and Evans (1954) suggest that this acetylcholine may perhaps keep 

 the gland in a condition of constant subliminal excitation. 



Investigations in quite a different field may give some indication 

 that continuously released acetylcholine normally exerts some 

 action on the gland cells. When the chorda tympani has been cut, 

 the secretory cells of the submaxillary gland acquire a super- 

 sensitivity to chemical agents, which develops progressively and 

 reaches a maximum within three weeks. In order to study whether 

 the same would happen when the gland cells were deprived of 

 chorda impulses in some other way, cats were treated with repeated 

 injections of atropine over some weeks. A supersensitivity was 

 found to ensue, and like the one following section of the chorda it 

 was unspecific ; therefore, a substance like adrenaline could be used 

 for testing the level of sensitivity, even in the presence of atropine 

 (Emmelin and Muren, 1951). Further examination disclosed 



