112 FACTORS AFFECTING CILIARY ACTIVITY 



Aiello (1957, 1960) and Gosselin (1961) have found that 

 serotonin accelerates both the frequency of beat and the meta- 

 chronal wave velocity of lateral ciUa of Mytilus gill, e.g. by about 

 100 per cent at a concentration of 2 x 10~^ mol (Aiello). By assay 

 using the clam heart, it was estimated that 1 g (wet weight) of gill 

 tissue possessed an activity equivalent to 0-4 to 7-6 fig of sero- 

 tonin. Gosselin and Ernst (1958), who used photofluorimetric 

 analysis to estimate the serotonin concentration in lamellibranch 

 gill tissue found values between 0*7 and 1*0 fig/g (wet weight), 

 which agree well with the result obtained by Aiello. These 

 authors obtained a prompt and sustained acceleration of the 

 beat of lamellibranch gill cilia, which was graded over a wide 

 concentration range from as little as 10-^° mol serotonin; they 

 also obtained an acceleration of beat with known antagonists of 

 serotonin like tryptamine, 5-hydroxytryptophan, dihydroer- 

 gotamine, LSD and brom-LSD. Further confirmation of the 

 presence and activity of serotonin has been provided by Blaschko 

 and Milton (1960), who found that serotonin is oxidised in 

 homogenates of Mytilus gill tissue, so that a system is available 

 for the removal of the substance after it has acted on the ciliary 

 mechanism. 



The tentative suggestion that serotonin may be released by, or 

 by the action of, the branchial nerve of Mytilus^ which runs near 

 the gill axis, has been put forward by Aiello (1960). It is possible 

 that it is carried in the blood spaces from the nerve endings to the 

 gill filaments, where it acts on the ciliary mechanism. More work 

 on this substance should provide exciting results, although no 

 very marked response has been obtained in experiments on the 

 membranelles of Stentor^ and preliminary reports of other 

 investigations do not agree. 



Many more attempts have been made to find a relationship 

 between acetyl choline (ACh) and ciliary activity. Some thirty 

 years ago Plattner and Hou (1931) and Ishikawa and Ohzono 

 (1931) reported that the activity of cilia of the frog's pharynx was 

 increased by ACh. The latter authors found that the action of 

 ACh is prevented by atropine, and suggested that the parasym- 

 pathetic nervous system is concerned with the control of these 

 cilia, while the former authors believed that the tissues lack 

 ninervation and that the ACh was acting directly on the ciliary 



