Voltage-dependent block of N-methyl-D-aspartate receptors by the novel anticonvulsant dibenzylamine, a bioactive constituent of L-(+)-beta-hydroxybutyrate.

Previously we demonstrated that L-(+)-beta-hydroxybutyrate (L-BHB), acetoacetate (ACA), acetone, and dibenzylamine (DBA) were anticonvulsant in an audiogenic seizure-susceptible model, and that DBA was a bioactive contaminant identified in commercial lots of L-BHB. In the present study, we asked whether these effects could be mediated by ionotropic glutamate or gamma-aminobutyric acidA (GABAA) receptors. We studied the effects of both stereoisomers of BHB (as well as the racemate), ACA, and DBA on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5methyl-4-isoxazole-proprionic acid (AMPA), and GABAA receptors in cultured rodent neocortical neurons by using whole-cell voltage-clamp recording techniques. Only L-BHB and DBA exerted a concentration- and voltage-dependent block of NMDA-evoked currents, whereas none of the tested substrates affected AMPA- or GABA-activated currents. The kinetics of whole-cell block by L-BHB and DBA were similar, providing additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB. BHB and ACA do not exert direct actions on GABAA or ionotropic glutamate receptors in cultured neocortical neurons. In addition, we provide additional evidence that DBA is responsible for the anticonvulsant activity of L-BHB, and that this action may be mediated in part by voltage-dependent blockade of NMDA receptors.