290 John H. Welsh 



suitable for further study of possible paralyzing agents. The first to be tried was 

 tetramethylammonium chloride (MeiN) for the following reasons: (1) it is a normal 

 constituent of coelenterates (Ackerman, Holtz and Reinwein, 1923, and the 

 hydroxide was named tetramine by these workers); (2) it has long been known to 

 have curare-like properties in the vertebrates ; and (3) there were earlier indications 

 that it caused paralysis in insects and crustaceans (Welsh, unpublished). 



Tetramethylammonium chloride was dissolved in sea water and appropriate 

 dilutions were made such that various amounts could be introduced by injection of a 

 constant volume of fluid. After injection, legs were tested in the manner described for 

 extracts. The results of two series of tests are given in Table II. It is clear that MciN 

 is a moderately effective inhibitor of autotomy in U. mordax. 



Since a tetraethylammonium salt (EtiN) often has an action opposing that of 

 Me4N (e.g. Welsh and Taub, 1950), this was injected in amounts of 0-5 mg and 0-05 

 mg. At the lower concentration the frequency of autotomy was 36/40, 39/40 and 

 40/40 in three experiments. After Et4N, legs autotomized with remarkable ease. 



Table II 

 Effect of several concentrations of tetramethylammonium chloride {MciN) on the 



autotomy reflex of Uca mordax 



Me^N 



Series 1 

 Series 2 



5 mg 0-5 mg 05 mg 005 mg 



0/40 11/40 30/40 38/40 



0/40 22/40 30/40 40/40 



If acetylcholine is involved in the normal autotomy reflex in U. mordax, as it appears 

 to be in Petrolisthes (Welsh and Haskin, 1939), injected acetylcholine might facilitate 

 autotomy or it might reduce it by raising the level to the inhibitory or paralytic range. 

 With U. mordax, injected acetylcholine (0-5 mg/crab) reduced the frequency of auto- 

 tomy. The triethyl analogue of acetylcholine (EtgAch) may antagonize acetylcholine 

 (Welsh and Taub, 1950). When 0-5 mg. of EtsAch was injected into U. mordax, 

 legs autotomized with remarkable ease when grasped, and in each series there was 

 100 per cent autotomy. When Mt^H and EtiN, or Ach and EtgAch, were injected 

 simultaneously in 0-5 mg amounts, there was a significant antagonistic action between 

 the pairs of compounds, and the tendency to drop legs was greater than with Me4N or 

 Ach injected alone. 



Atropine, which blocks Ach at certain neuro-eff'ector junctions, facilitated autotomy 

 in U. mordax, when injected in a dose of 0-005 mg. Eserine, which prevents Ach from 

 destruction by cholinesterase and therefore permits its accumulation, reduced auto- 

 tomies to 31 of 40 at 0-001 mg and to of 40 at 0-005 mg. 



These results suggest that acetylcholine is involved in the autotomy reflex in U. 

 mordax, and that any increase over normal body concentration results in some degree 

 of paralysis. Me4N, frequently shown to act like Ach in small amounts and to be 

 paralytic in larger amounts, produces paralysis resembling that produced by the 

 coelenterate extracts. Agents which may antagonize Ach and MciN, such as EtgAch 

 and EtiN, have actions on U. mordax which support the view that a methylated 

 quaternary ammonium base might be a constituent of nematocyst toxins. There is yet 



