EFFECTS ON NERVE FUNCTION 



231 



Turning to the effects of iodoacetate on synaptic function, we find a 

 much greater sensitivity compared to axons, due presumably to the greater 

 penetration of the inhibitor. Larrabee and Bronk (1952) recorded pre- and 

 postganglionic action potentials from the stellate and superior cervical gan- 

 glia of cats, and found that at a time when the preganglionic spike is re- 

 duced 20% by 0.1 mM iodoacetate acting for 40 min, the post-ganglionic 

 spike is depressed 48%. The selective action here is not very great. The 

 spontaneous activity of crayfish ganglia is not affected by 1 mM iodoace- 

 tate, indicating that it does not depend on glycolysis (Prosser and Buehl, 

 1939). Von Ledebur (1932 a) perfused the isolated frog spinal cord with 0.54 

 mM iodoacetate and within 7 min all reflex activity had been abolished, 

 indicating a potent depressant action on synaptic transmission. After the 

 loss of reflexes, the muscles can still be stimulated through their motor 

 nerves. Holmes (1933) also perfused frogs with iodoacetate and found that 

 0.7 mM reduces the number of animals convulsing with strychnine. He 

 further showed that animals can still convulse occasionally even though 

 lactate formation is blocked, showing that the activity is not related to 

 glycolysis. The changes in lactate, creatine-P, and function are shown in 

 Fig. 1-24. The superior cervical ganglion of the cat is also quite sensitive, 

 reversible transmission depression occurring at 0.01-0.05 mM iodoacetate, 



i 50 ^ 



Fh;. 1-24. Effects of O.-li mM iodoacetate on the levels of 



lactate and labile phosphate in frog brain, and the per cent 



convulsing after the administration of strychnine. (From 



Holmes, 1933.) 



