222 A. ARVANITAKI AND N. CHALAZONITIS 



Mechanisms of the infra-red inhibitions. Infra-red radiations injected in a 

 cell may be operative in various ways: important cellular macromolecules 

 strongly absorb infra-red radiations (Klotz, Griswold and Gruen, 1949; 

 Ambrose and Elliott, 1951a, 1951b; Elliott, 1951). Thus, significant changes 

 in the configuration of the macromolecules and in their interactions may be 

 ehcited. Transitions may hence be expected: (1) in functions involving 

 enzyme actions and depending upon specific interactions of these macro- 

 molecules; (2) in functions involving a specific sequence of chemical 

 groups. Such transitions might thus act by introducing changes in the velocity 

 constants of significant chain reactions, in specific loci, and relative to the 

 inhibitory processes observed by infra-red action. The reactions involved 

 might be relevant to those which are actually triggered by the arrival of the 

 inhibitory impulses at the presynaptic terminals. Extensive studies are now 

 available on various blocking molecules extracted from nervous tissue (see 

 Hayashi, 1959), especially y-aminobutyric acid which accounts for nearly all 

 the activities of Florey's Factor I (Florey, 1954; Florey and MacLennan, 

 1955a, 1955b; Elliott and Florey, 1956; Wiersma, Furshpanand Florey, 1953) 



The spectacular effects of GABA on neuronal activity acquire all the more 

 interest in so far as GABA is involved in energy metabolism in nervous 

 tissue. GABA is formed in the brain from glutamic acid by the action of an 

 enzyme found only in the CNS, an L-glutamic acid decarboxylase. Important 

 relations must exist between the enzymes involved in the metabolism of 

 GABA and those of the tricarboxylic acid cycle. The attraction of such 

 a perspective lies in providing a pattern wherein mechanisms of release of a 

 chemical transmitter would be identified with activation of a definite enzy- 

 matic reaction involved in the normal energy metabolism of the cell. It is 

 obvious that besides the biochemical and electrophysiological information 

 on the GABA properties, knowledge of the cellular loci wherein its enzymatic 

 cycle is implied, and of specific tools to activate the latter, would be highly 

 promising. 



DISCUSSION 



The value of the foregoing photoactivation data lies mainly in providing 

 means for the analysis of a series of outstanding cellular reactions: among 

 others, the excitatory and inhibitory processes, the generator depolarization, 

 and the integrative processes taking place in sensory and central organs. 



The interesting point is here twofold. On one hand, to use injections of 

 light as cellular stimuli is actually to handle an instrumental tool: photons 

 act specifically in definite cellular sites where they are absorbed and there- 

 from act through specific pathways. On the other hand, the fact that the 

 reactions are fairly similar in the nerve cell and in the axon, which is free of 

 synaptic structures, affords several sound conclusions in otherwise contro- 

 versial mechanisms. 



