156 THE PHYSIOLOGY OF EARTHWORMS 



Trajtsmitter Substances 



The identification of possible transmitter substances in oligo- 

 chaetes at present depends upon the comparative pharmacological 

 effects of organ extracts and synthetic substances. By means of 

 studying muscle responses and antagonistic actions Umrath (1952) 

 showed that nerve extracts of annelids, including Liimbricus, 

 Liimbriculus and Tubifex contain acetylcholine. Enders (1952) also 

 demonstrated acetylcholine in extracts of the nervous system of 

 Liimbricus. Adrenaline is also present (Enders, 1952) although 

 Ostlund (1954) was unable to obtain enough material to estimate 

 the adrenaline content by paper chromatography. Unpublished 

 experiments (Laverack, 1958), however, have demonstrated that 5 

 hydroxytryptamine has very similar intestinal excitatory effects to 

 those described above, and Welsh and Moorhead (1960) have now 

 suppHed evidence that 5HT is present at a concentration of 104 ixgjg 

 fresh wt. No physiological function is at present known for it. 



The evidence for the presence of acetylcholine seems fairly con- 

 clusive and is as follows : 



(1) Stimulation of the gut nerves causes a rise in tone and 

 motility of the gut wall, and is mimicked by the addition of syn- 

 thetic acetylcholine. 



(2) These actions are both depressed by atropine. 



(3) They are also both stimulated by eserine. 



(4) Cholinesterase is present. 



(5) Acetylcholine-like substances are released in the presence of 

 eserine which inhibits cholinesterase. 



(6) Acetylcholine accelerates, and then stops in systole, the beat 

 of the pseudohearts oi Lumbriciis (Prosser and Zimmerman, 1943). 



(7) Nicotine abolishes nerve effects on the body wall. 



The probability of adrenaHne being present is indicated thus : 



(1) Chromaffin cells are present in the ganglia of the ventral 

 nerve cord (Gaskell, 1914). 



(2) The rate of contraction of the blood vessels is accelerated by 

 adrenaline. 



(3) Adrenaline sometimes antagonizes and sometimes poten- 

 tiates the action of acetylcholine on the gut musculature. 



(4) Extracts of the worm ventral nerve cord cause increases in 

 bipod pressure when injected into cats (Ostlund, 1954). 



