EXCITATORY AND INHIBITORY PROCESSES 



INITIATED BY LIGHT AND INFRA-RED RADIATIONS 



IN SINGLE IDENTIFIABLE NERVE CELLS 



(GIANT GANGLION CELLS OF APLYSIA) 



A. Arvanitaki* and N. Chalazonitis* 



Recent experiments performed in different pigmented cells permitted the 

 recognition of bioelectrical reactivity to light as a widespread cellular prop- 

 erty. Moreover, in nerve cells, it has been established that inhibitory pro- 

 cesses as well as excitatory ones may be triggered by radiations of different 

 wave lengths (Arvanitaki and Chalazonitis, 1947, 1949a. b and c, 1950, 

 1958a, 1960; Chalazonitis, 1954). 



The approach to such problems at the cellular level holds interest 

 for many reasons. For instance, it is hoped that the knowledge of 

 how light energy specifically trapped by known molecules located in known 

 cellular sites (see Table 1) leads to electrical work might provide an 

 insight into mechanisms of importance in general neurophysiology. As 

 a matter of fact, photons absorbed by suitable cellular molecules serve to 

 activate or trigger a system to which these molecules are functionally coupled, 

 and which partially converts the absorbed energy into electrical work. But 

 this system is activated just as well by any other stimulus, whether it be 

 electrical, chemical, or mechanical, whose sites and mechanisms of action 

 are, however, less specific than that of the photic stimulus. 



It is hoped that this common cellular photosensitivity might be basically 

 compared to that which is at the origin of the performances of a functional 

 photoreceptor cell. 



Simultaneous intracellular recordings in many photoactivated nerve cells 

 revealed patterns of activity in which excitation in a given cell is accompanied 

 by inhibition in the immediately neighbouring ones, recaUing the "contrasting 

 effects" already known to occur in different receptor organs, in the retina 

 (Hartline, 1941, 1949; Granit, 1947, 1952; Kuftler, 1953; Hartline, Wagner 

 and Ratliff, 1956), in the auditory system (Galambos and Davis, 1944) and. in 

 cerebral patterns of activity (Mountcastle, 1957; etc.). Obviously, the interest 



* Centre National de la Recherche Scientifique, Paris. 

 Laboratoire d'^lectrobiologie, Faculte des Sciences, Universite de Lyon. 

 Institut Oceanographique, Monaco. 



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