Comparison of the effects of ethylenediamine analogues and gamma-aminobutyric acid on cortical and pallidal neurones.

1 The actions of ethylenediamine (EDA) and structurally related compounds were investigated by microiontophoresis in Wistar rats. 2 EDA inhibited, via a bicuculline-sensitive mechanism, the spontaneous firing rate of all cortical and pallidal cells tested. 3 The results with the analogues suggest that two amine groups are required for this neuronal depressant action whereas a carboxyl grouping is not. N-substitution reduces the depressant effect. The length of the molecule is also critical, more than 3 methylene components seriously reducing its effectiveness. A rigid analogue of EDA, piperazine, was also active. In addition the apparent transport numbers of EDA and gamma-aminobutyric acid (GABA) were calculated, showing a close similarity between the two. 4 The results are discussed wih respect to the possibility that EDA may represent a new class of GABA-mimetics, or may indicate the existence of a novel diamine receptor mediating bicuculline-sensitive inhibition in the rat CNS.