Muscle and Electric Organs 613 



Summation of contractile response of the earthworm body wall to repetitive 

 electrical stimulation is increased by eserine.^^ Eserine increases the muscular 

 responses of Sip^lnc^^lus, Hirudo, Arenicola, Aphrodite, and Lumhricus to 

 stimulation of the nerve cord.^^' ~" No such effect was observed when eserine 

 was applied to the nerve cord alone, but in perfusion experiments it appeared 

 that the leech body wall liberated ACh when the nerve cord was stimulated. 



The visceral muscles of annelids are spontaneously rhythmic. In earth- 

 worm crop-gizzard preparations the wave of contraction usually originates 

 in the crop; this preparation is stimulated and tone increased by acetylcholine 

 (lO'^-lO'^'^ without eserine and 10'^^ with eserine ).^'*'^ If cooled, spontan- 

 eity is abolished, but acetylcholine still causes contraction.^ The stimulating 

 action of ACh is antagonized by atropine; adrenalin augments the activity 

 when dilute (10"'^) and depresses at higher concentrations (10"^). Stimula- 

 tion of the ventral nerve cord inhibits the crop-gizzard activity, an effect an- 

 tagonized by ergotoxin; stimulation of the pharyngeal commissures excites, 

 an effect antagonized by atropine.-^^ Potassium enhances and calcium in- 

 hibits the visceral rhythm. An active crop-gizzard preparation liberates into 

 a perfusate a substance which induces ACh-Hke contractions in a test prepa- 

 ration.^ Antagonistic cholinergic and adrenergic control, as in mammals, is 

 therefore, indicated for the earthworm crop-gizzard. 



In the echinoderms as in annelids there is evidence for cholinergic motor 

 systems. The longitudinal retractors of holothurians contain ACh and are 

 rich in ChE, as are muscles from Echinus and Asterias}^ In the holothurian 

 Stichopiis the longitudinal muscles are sensitive to ACh, responding to dilu- 

 tions of 10~' without eserine and to dilutions of 10~" after eserine, and 

 this muscle has been used in bioassay,^'^ as has also Thy one muscle. '^° Re- 

 sponse to direct stimulation of the holothurian longitudinal retractor mus- 

 cles, nerve elements included, is potentiated by eserine and prevented by 

 atropine, and stimulation liberates into a perfusion bath a substance which 

 has the properties of ACh.^'^ Curare blocks conducted responses in Thyone 

 retractor muscles and prevents spontaneous contractions. "° Holothurian mus- 

 cles are excited by low concentrations of adrenalin and tyramine.^^- ^^ 



In molluscs much acetylcholine is found in nerve and muscle, for example, 

 in Aplysia foot and Sepia mantle (Table 73).^" Cholinesterase is also present 

 in Sepia mantle.-^ The muscular responses to ACh differ among various 

 species. The slow adductor muscle of Pecten is not stimulated bv ACh,^*' 

 whereas the retractor muscle of the buccal mass in Helix does respond to the 

 drug.^'"' Eserine fails to potentiate the response of the foot and siphon mus- 

 cles of Buccinium and Mya and the response of the mantle of Eledone to 

 nerve stimulation. However the cephalopod mantle is sensitive to ACh, and 

 denervation greatly increases the sensitivity as it does in many vertebrate 

 tissues. Bacq^^ perfused the mantle of Eledone with eserinized saline; the 

 outflowing perfusate contained an ACh-like substance, but stimulation of 

 the mantle nerve did hot increase its concentration in the perfusate. 



It is possible that some nerves in cephalopods liberate tyramine. The sali- 

 vary glands contain tyramine and histamine.^" The perfused stomach of 

 Sepia shows spontaneous contractions which are inhibited by ACh 10"^ and 

 stimulated by tyramine and histamine 10"*' and by Adr 10'^.^-- Cocaine 



