322 



ERNST FLOREY 



Fig. 4. Interaction of changes in mechanical and chemical conditions of the 

 environment on slow adapting stretch receptor neuron of Camharus viiilis. o indi- 

 cates washing with saline medium. The acetylcholine (ACh) concentration is given 

 in g/ml, that of the inhibitory Factor I in crayfish units {c.u.) which correspond 

 each to the inhibitory action of about 2 /<g of GABA/ml. (From Florey, 1957; 

 with permission of J. Gen. Physiol.) 



tion and adaptation in the postsynaptic neuron, and inhibition caused by 

 repetitive release of inhibitory transmitter can Hkewise induce accommoda- 

 tion. And, if the transmitter is suddenly removed "rebound" phenomena 

 should occur which produce states of inhibition when excitatory agents are 

 removed, and excitation when inhibitory agents are removed. Thus, one and 

 the same transmitter should be able to produce both excitation and inhibition. 

 The degree of the "rebound" phenomenon would depend on the speed with 

 which the transmitter is removed. The situation is explained in the diagram 

 of Fig. 5. 



Assuming rapid removal (enzymatic inactivation, diffusion, absorption, 

 etc.) of released transmitter one can state: removal of excitatory stimulation 

 has the same effect as application of an inhibitory agent and conversely, 

 removal of an inhibitory agent acts like application of excitatory stimulation. 



The consequences of this scheme of events is illustrated in Fig. 6. In a chain 

 of neurons where the transmission of information is the important feature, 

 events which cause temporary excitation of the first neuron are more or less 

 faithfully transmitted to the last neuron in the chain, even if transmission is 

 not one-to-one but simply causes depolarization in the postsynaptic neuron 

 which in turn sets up a corresponding frequency of firing. At the cessation of 

 stimulation of the first neuron rebound inhibition of the first cell takes place 

 and the same happens in all the following neurons as soon as presynaptic 

 stimulation ceases. But since information is carried in the form of spike 

 potentials, these inhibitory states are without information value. The situation 

 is quite different if one of the neurons in the chain (the first one in Fig. 6, 2) 

 is an inhibitory neuron (which presumably acts by hyperpolarizing the 

 postsynaptic cell). Excitation will cause the repeated release of inhibitory 

 transmitter (one quantum per impulse) but the action of the transmitter will 

 have no information value since it does not lead to the formation of conducted 



