348 DAVID R. CURTIS 



between this substance and the inhibitory transmitter. In addition, if the 

 manner by which the strychnine molecule interacts with the inhibitory 

 receptors can be determined, the structure of these receptors may be elucidated 

 and this in turn may give some indication of the molecular structure of the 

 inhibitory transmitter itself. 



CONCLUSION 



Although it must be agreed with Paton (1958) that all of the foregoing 

 criteria must be satisfied by a substance before it can be fully classified as an 

 inhibitory transmitter, the finding of a chemical substance in brain extracts, 

 which, when applied to neurons in the same areas from which the extracts 

 were made, produces a membrane hyperpolarization due to an increase in 

 the membrane conductance of K+ and CI" ions, would be strong evidence 

 that the substance was an inhibitory transmitter. If in addition this action 

 was blocked by strychnine, the failure to satisfy fully the other criteria dis- 

 cussed above, because of technical difficulties, need not prevent the provisional 

 acceptance of the substance as an inhibitory transmitter. 



REFERENCES 



Albe-Fessard, D. and Buser, P. (1955) Activites intracellulaires recueillies dans le 



cortex sigmoide du chat : participation des neurones pyramidaux au 'potentiel evoque' 



somethesique. J. Physiol. {Paris) 47 : 67-69. 

 BiRKS, R. I. and Macintosh, F. C. (1957) Acetylcholine metabolism at nerve-endings. 



Brit. Med. Bull. 13 : 157-161. 

 Blaschko, H. (1956) Hypotensive Drugs (ed. by Harrington, M.) Pergamon Press, 



London. 

 DEL Castillo, J. and Katz, B. (1955) On the localization of acetylcholine receptors. 



J. Physiol. {Lomlon) 128 : 157-181. 

 DEL Castillo, J. and Katz, B. (1956) Biophysical aspects of neuro-muscular transmission. 



Progr. in Biophys. and Biophys. Cheni. 6 : 121-170. 

 Coombs, J. S., Eccles, J. C. and Fatt, P. (1955) The specific ionic conductances and the 



ionic movements across the motoneuronal membrane that produce the inhibitory 



post-synaptic potential. J. Physiol. (London) 130 : 326-373. 

 Crossland, J. (1957) Metabolism of the Nervous System (ed. by Richter, D.) Pergamon 



Press, London. 

 Curtis, D. R. (1959) Pharmacological investigations upon inhibition of spinal moto- 



neurones. J. Physiol. {London) 145 : 175-192. 

 Curtis, D. R. and Eccles, R. M. (1958) The excitation of Renshaw cells by pharmaco- 

 logical agents applied electrophoretically. /. Physiol. {London) 141 : 435^45. 

 Curtis, D. R. and Eccles, J. C. (1959) The time courses of excitatory and inhibitory 



synaptic actions. /. Physiol. {London) 145 : 529-546. 

 Curtis, D. R. and Phillis, J. W. (1960) The action of procaine and atropine on spinal 



neurones. J. Physiol. {London). 153 : 17-34. 

 Curtis, D. R. and Watkins, J. C. (1960a) In Conference on Inhibition in the Nervous System 



and y-Aminobutyric Acid. Pergamon Press, London. 

 Curtis, D. R. and Watkins, J. C. (1960b) The excitation and depression of spinal neurones 



by structurally related amino acids. /. Neurochem. 6 : 117-141. 



