516 Editor: M. WINITZ 
The sequence of events after the administration of DDT to animals is quite different from those 
noted when dieldrin is given. With a single large dose of the former compound the animal first 
exhibits muscle twitching, which is followed by generalized body tremors gradually increasing in 
intensity that last for several hours. Finally the animal goes into a convulsion, collapses and dies?. 
On the other hand, with a lethal dose of dieldrin, the animal becomes hyperexcitable, and in a 
short time begins to have a series of epileptoid convulsions which terminate in collapse and 
death*®. This marked difference in symptomatology suggests a difference in mode of action between 
the two insecticides. Under these circumstances, any change noted with one compound and not 
with the other might reveal some clue as to a specific mode of action. 
In the present experiments, female albino rats were given approximately two times the LD;, 
dose of dieldrin or DDT by the oral route+. Then the animals were sacrificed at time intervals 
which previous experience had shown would produce severe poisoning but would not permit the 
rats to become moribund. The animals given DDT were killed after two hours of violent tremor; 
those given dieldrin were sacrificed during their fourth convulsions. The concentration of alanine, 
y-aminobutyric acid, glutamine and glutamic acid in the brains of these animals and their controls 
was estimated by quantitative filter paper chromatography. 
It was found that there were no significant changes in the levels of these amino acids in the 
brains of the animals given DDT. Where dieldrin was administered, a rise of 24° was noted in 
the level of y-aminobutyric acid. However, the most striking change, easily visible on the chro- 
matograms, was an increase of 80% in the concentration of alanine. These changes were shown 
to be significant by statistical analysis. 
Dr. Roperts, in his review of metabolism of the free amino acids of the nervous system, points 
out that the most significant changes that have occurred in the levels of alanine, y-aminobutyric 
acid, aspartic acid, glutamic acid or glutamine, have resulted from procedures which directly or 
indirectly affect the oxidation of intermediates of the KRreEBs’ cycle. Therefore, it seems most 
probable that the above increases in the levels of alanine and y-aminobutyric acid in the brains 
of rats poisoned with dieldrin are not the result of the direct effect of the insecticide on the metab- 
olism of these amino acids, but rather manifestations of an inhibition of the oxidation of py- 
ruvate through the KReEBs’ cycle. Changes in the levels of the keto acids in the Kress’ cycle 
could lead through transamination reactions to changes in the concentrations of these amino 
acids. As a working hypothesis, we suggest that dieldrin may inhibit some specific reaction of 
the cycle. The fact that DDT did not inhibit the respiration of the mammalian brain®: * and 
does not change the level of brain free amino acids is consistent with this hypothesis. However, 
the effects of dieldrin on the oxidation of pyruvate and on the individual steps of the KREBs’ 
cycle in the brain have not been investigated. Therefore, proof of this hypothesis must await 
further experimental work. 
HosEINn and co-workers’: ® have claimed that dieldrin and certain other convulsants bring 
about the release from the brain of a coenzyme A ester of y-aminobutyrobetaine from a bound 
to a free form, and that this free ester is the cause of convulsion. The esters of y-aminobutyro- 
betaine have pharmacological properties similar to those of acetylcholine®. However, the proof 
of the identity of this coenzyme A ester with the convulsant substance and evidence for its for- 
mation from y-aminobutyric acid have not been published so far as we are aware. Oxidative 
reactions are known to be involved in a number of processes in which permeability of mem- 
branes are changed. Thus the present hypothesis that dieldrin may act to inhibit the oxidations 
of the Kress’ cycle is compatible with, but does not necessarily support, the theory proposed 
by HosEIn. 
At the previous symposium, McKuHANN and co-workers!® reported confirmation of KESSEL’s 
observation" that the level of y-aminobutyric acid was increased in the brains of animals given 
the convulsant 2,4-diaminobutyric acid. BAXTER AND ROBERTS! showed that a rise in y-amino- 
butyrate could occur if hydroxylamine and thiosemicarbazide were given together. Both groups 
concluded that seizures may occur whether the y-aminobutyrate content of the whole brain is 
abnormally high or low. Our results, which show that the administration of dieldrin also increases 
the y-aminobutyrate level of the brain, are in agreement with these conclusions. 
E. Roperts: I think that the results first of all suggest a possibility that both the a-ketoglutarate 
oxidase and pyruvate oxidase might be inhibited by dieldrin. 
With regard to the interest in raising or lowering levels of y-aminobutyric acid (yABA) in the 
central nervous system and convulsive seizures, the relationships appear to be more complex 
than originally envisioned. Good correlations were found between the decreases in yABA levels 
and the occurrence of seizures when thiosemicarbazide was administered to animals and between 
the increases in seizure thresholds and elevations of brain yABA levels after injection of hydro- 
xylamine. However, when both thiosemicarbazide and hydroxylamine were administered to rats, 
seizures occurred which were characteristic of those usually produced by thiosemicarbazide alone 
even though the yABA levels were elevated (see BAXTER AND RoBeErRTS', and RoBerts!). These 
results indicated clearly that a general depression of yABA levels is not a necessary requirement 
References p. 524 
