442 THE BIOLOGY OF MARINE ANIMALS 



Effects of Pharmacological Agents on Junctional Transmission 



Information about transmitter action at synapses has been secured by 

 applying pharmacological agents to nerve and muscle. Acetylcholine acti- 

 vates the end-plate and ganglionic synapse, brings about contraction of 

 striated muscle, slowing of the heart, discharge from electric organs, pig- 

 ment dispersion in fish chromatophores, etc. Many of the usual effects of 

 acetylcholine can be mimicked by muscarine; acetylcholine is then said to 

 have a muscarinic action. Nicotine in small doses has a stimulatory effect 

 on the ganglionic synapse and on muscle, and the action of acetylcholine 



Fig. 10.19. Synaptic Transmission in the Stellate Ganglion of Loligo 



Single shock was delivered to pre-ganglionic fibres at start of each sweep recurring 

 33 times per sec. (a). Recording from ganglion and post-ganglionic fibre. With continued 

 stimulation the post-ganglionic spike progressively fatigues, arising later out of the 

 local potential and finally failing. Time, 0-5 msec. (b). Recording from pre-ganglionic 

 fibre just in front of the ganglion, and from the post-ganglionic fibre. Time, 0-25 msec. 

 (From Bullock, (22).) 



at these loci is referred to as the nicotine action. Eserine and di-isopropyl 

 fluorophosphate (DFP) potentiate the action of acetylcholine. Curarine, 

 by preferentially competing with acetylcholine at the end-plate, blocks 

 transmitter action. The effect of stimulating adrenergic nerves can be 

 mimicked by application of adrenaline; its action is blocked by ergotoxine. 

 Pharmacological Observations. In previous chapters (3 and 9), deal- 

 ing with circulatory systems and effectors, we have classified some cardio- 

 regulator and motor nerves as cholinergic or adrenergic. Evidence for 

 chemical transmitters in nervous systems of many invertebrate groups is 

 fragmentary. To supplement the accounts given in earlier pages, a brief 

 survey is presented of chemical transmitter activity in nervous systems of 

 lower phyla. 



