Abstract
The action of intravenous injection of a series of omega-amino acids on the cat spinal cord was investigated with intracellular recordings and test monosynaptic reflexes. The action of the omega-amino acids of carbon length seven and eight was opposite to that of the shorter chain omega-amino acids, producing a facilitation in extensor monosynaptic reflexes and a decrease in flexor reflexes.The action of the longer chain omega-amino acids was similar-to that of the shorter chain omega-amino acids in the following three criteria:(1) the effects on spinal reflexes were absent in decerebrate cats and present in spinal preparations, (2) the effect on flexor monosynaptic responses was reduced following administration of strychnine and (3) the effect on flexor monosynaptic responses abolished in the presence of conditioning volleys of high threshold afferent fibers from extensor muscles.
GABA (C4) produced depression of extensor motoneurons with an increase of the membrane potential and facilitation of flexor motoneurons with a decrease of the membrane potential. A long chain omega-amino acid (C8) depolarized extensor motoneurons and hyperpolarized flexor motoneurons. Some polysynaptic potentials were changed by injection of GABA without appreciable change in monosynaptic EPSP and IPSP from antagonistic muscle afferent fibers. Some intemeurons were depressed and other interneurons were facilitated by GABA. Significant effects of GABA were not found in Renshaw cells. It was suggested that short chain omega-amino acids selectively depress a certain spinal interneurons, while longer omega-amino acids activate these same interneurons.
The authors wish to thank Mr. S. TAKAI for his technical assistance. The authors also wish to express their appreciations to Dr. C. C. HUNT and Dr. E. R. PERL for their suggestions and criticism while preparing the manuscript. The present study was aided by a grant from the ministry of education of Japan and a grant, GA BMR 5809, from the Rockefeller Foundation.
