Dihydrogenated ergot compounds bind with high affinity to GABAA receptor-associated Cl- ionophore

The binding of t-[3H]butylbicycloorthobenzoate ([3H]TBOB) to crude synaptosomal membranes of the mouse brain (cerebrum minus cortex) in the presence of dihydroergotoxine, dihydroergosine, dihydroergotamine and gamma-aminobutyric acid (GABA) was studied in vitro. [3H]TBOB binding was inhibited by all drugs used. The rank order of potency was dihydroergotoxine greater than GABA greater than dihydroergosine greater than dihydroergotamine. This suggests that dihydrogenated ergot compounds, especially dihydroergotoxine, possess appreciable binding activity (comparable to that of benzodiazepines and barbiturates) at the GABAA receptor-associated C1- ionophore.