I40 PHYSIOLOGICAL TRIGGERS 



explain the adjuvant effects of sympathetic stimulation (Orbeli effect) of 

 adrenaline on neuromuscular transmission of the fatigued preparation (117). 

 Suggestive of this are also the effects of adrenergic agents on the cholinergic 

 system of autonomic ganglia (cf. 144). 



An instructive and probably a clinically important interrelation is to be seen 

 in the effects of blocking agents on cardiac actions of vagal and sympathetic 

 stimuli (163a). Whereas rf-tubocurarine has a well-known vagolytic action 

 (i.e., block of vagus-induced depression of cardiac rhythm) a depolarizing synap- 

 tic blocker (32), succinylcholine, eliminates the effects of both vagal and sympa- 

 thetic stimulation in the cat. The mechanism of this action is presumably 

 different from that of the non-depolarizing curare effect. Nevertheless, injection 

 of J-turbocurarine eliminates the sympathetic block, but not the vagal, pro- 

 duced by previous administration of succinylcholine. Therefore, the former 

 drug is an adjuvant to adrenergic action and presumably combines with 

 adrenoceptive membrane as well as with cholinoceptive. 



The inhibitory transmitter agent for invertebrate muscle fibers exerts its 

 effects not only on the specific synaptic sites tending to hyperpolarizing electro- 

 genesis, but also depresses the sensitivity of the depolarizing, excitatory re- 

 ceptors to their synaptic transmitter (71). This is presumed to be caused by 

 competitive combination of the inhibitory transmitter with the excitatory 

 synaptic receptor, and therefore indicates that both the excitatory and inhibi- 

 tory receptors of the membrane have a similar molecular structure. 



Modifications in a common receptor molecular structure are likely for the 

 chemo-transducers of olfaction, taste and vision. The possibility that mechano- 

 transducer membrane is also chemo-receptive (59, 188) because of a common 

 molecular structure of the transducers and the implications of this for sensitivity 

 to 'adequate' and 'inadequate' stimuli were noted earlier. Elaborations of func- 

 tional differences based on a common ground structure are also found among 

 the respiratory pigments, enzymes and hormones, and are particularly well 

 known for the biologically active steroids. 



Syuaplic slruclure and neurochemistry. Pharmacological and electrophysio- 

 logical considerations are not, however, sufficient to develop our knowledge of 

 membrane phenomena. Neurochemical investigation has evolved only recently 

 and, despite the growing volume of its work (67, 145, 147, 182), it still has not 

 supplied the important clues to membrane structure in the same sense, for 

 example, as has the much older muscle chemistry (148) to the field of muscle 

 physiology. The difficulties faced by neurochemists are formidable. The imme- 

 diate structural components of electrogenesis probably reside in the boundary 

 surface of neuroplasm. The manifestations of activity depend upon the integrity 

 of this organized surface, and are evanescent. Even in the largest mass of neural 

 tissue, the brain, neurochemical study is hampered by the intermixture of 

 inactive components and, as has been pointed out in the foregoing, by the 



