PERIPHERAL AUTONOMIC MECHANISMS 



991 



glionic fibers has been reported, although it is not 

 always of a conclusive nature. In deafferented and 

 preganglionically denervated frog legs Speranskaja- 

 Stepanowa (394) observed vasoconstriction and vaso- 

 dilatation in vessels of the web on faradic stimulation 

 of various skin areas in the vicinity of and even far 

 away from the responding vessels. The vasomotor 

 responses persisted three to four days after section of 

 the sciatic nerve but disappeared thereafter. On this 

 basis they were interpreted as being caused by axon 

 reflexes in branching postganglionic fibers. No evi- 

 dence for the existence of branches supplying skin 

 areas so widely apart has appeared since then. In 

 apparently well-controlled experiments on human 

 skin, Wilkins el al. (441) obtained a local sweat re- 

 sponse within areas some centimeters wide on faradic 

 stimulation of certain points of the skin, and the re- 

 sponse was proved to be mediated by sympathetic 

 sudomotor fibers. The same gland could be activated 

 from different points up to 2 cm apart and the areas 

 activated from any particular point showed consider- 

 able overlapping. It is apparent that the sudomotor 

 response s are evoked by ax on reflexes in terminal 

 ramifications of postganglionic fibers, each of which 

 branches near its innervation territory and sends fila- 

 ments in all directions within a small skin ar ea, and 

 that these axon syst ems overlap each other to a con- 

 siderable extent. Similar studies have been made on 

 pilomotor fibers (289, 429). 



Postganglionic axon reflexes have recently become 

 of new interest from a pharmacological point of view. 

 This started with the discovery by Coon & Rothman 

 (87-89, 372) that drugs with nicotine-like action in- 

 jected intradermally elicit sudomotor, pilomotor and 

 vasomotor activity in areas surrounding the site of 

 injection. As these responses are abolished by local 

 anesthetics and by degeneration of the peripheral 

 nerves, they are presumably evoked by axon reflexes. 

 On the basis of the stimulating and the paralyzing 

 action of drugs on the axonal receptor points, it was 

 suggested that these points possess several properties 

 characteristic of autonomic ganglia. This has been 

 further stressed by later investigators who have shown 

 that the excitatory action of the drugs on the receptor 

 points is inhibited by ganglion-blocking agents (20, 

 114, 228, 428). Although the suggested analogy may 

 have no physiological significance, interesting new 

 views on the properties and organization of the 

 peripheral autonomic innervation apparatus may 

 come out of these investisrations. 



Other Types of Reflexes Mediated by 

 Autonomic Ganglia 



Although there is no proof that autonomic ganglia 

 isolated from the central nervous system are able to 

 exert an independent tonic activity, it does not follow 

 that decentralized ganglia are unable to perform some 

 kind of reflex activity. The old claim of Dogiel (106) 

 that sensory neurons may be present in autonomic 

 ganglia once gave rise to speculations concerning this 

 problem. Dogiel's interpretations are quite uncon- 

 vincing, however, and all the neurohistological work 

 since then has failed to demonstrate their existence. 

 Considerable physiological evidence has accumulated 

 indicating the uonexiste nce of neiirons_suJjseEving 

 intragangiipnic reflexe^_and_jthe inability of isolated 

 ganglia to exert reflex activities. Thus it has been 

 shown, for instance, that stimulation of one of the 

 sympathetic postganglionic nerves to the heart does 

 not give rise to discharge in another of the.se nerves, 

 a fact indicating that no afferents connect with the 

 postganglionic neurons in the stellate ganglion (49, 

 69). Another example is that no vasomotor reflexes 

 mediated through the ganglia of the sympathetic 

 trunk are observed after destruction of the spinal cord 

 or after preganglionic denervation (4, 14, 34, 201). 

 Two studies are often taken as evidence for an inde- 

 pendent ganglionic reflex activity. In one of them 

 (380), it was claimed that sudomotor activity could 

 be evoked in the cat's forepaw by a reflex solely in- 

 volving the stellate ganglion. This has been shown to 

 be due to an incomplete decentralization of the gan- 

 glion (190). In the other study (440), a small discharge 

 was found on stimulating one ciliary nerve and re- 

 cording from another. As accessory ganglia are often 

 present (442), this finding probably has its explana- 

 tion in a preganglionic axon reflex. 



There are many observations, however, indicating 

 that the prevertebral ganglia have mechanisms me- 

 diating reflexes between different parts of the ab- 

 dominal viscera. It has been claimed (157, 283, 284) 

 that the decentralized inferior mesenteric ganglion 

 exerts a motor control of the large intestine, but this 

 does not necessarily mean the involvement of reflexes. 

 In a series of investigations Kuntz and his associates 

 (248, 249, 255, 254) have found that some synaptic 

 structures persist in the celiac and the inferior mesen- 

 teric ganglia after degeneration of the preganglionic 

 fibers and observed that intcstinointestinal reflexes 

 synaptically relayed in the ganglia could still be 

 evoked after decentralization. These findings have 

 been confirmed by Warkentin et al. (431), but severely 



