Interactions between GABA and benzodiazepines

Mouse lines selected for genetic differences in diazepam sensitivity

Selective breeding techniques were used to alter allelic frequencies responsible for diazepam sensitivity and resistance. We used the rotarod test to determine the duration of diazepam-induced neurologic deficit in genetically heterogeneous mice. Males were more sensitive than females in the initial population. We then selectively bred for diazepam resistance and sensitivity. A significant difference between the lines was apparent in both sexes after two generations, and divergence has continued over seven generations. Brain benzodiazepine assays indicated that absorption and distribution of diazepam do not differ in the two lines. Differences in brain benzodiazepine concentrations at recovery from ataxia indicated that the two lines differ in central nervous system sensitivity. We found diazepam-induced rotarod impairment to be blocked in a dose-dependent manner by the specific benzodiazepine antagonist Ro 15-1788, indicating that this effect is mediated through BZ receptors. A dose-response curve obtained from generations 6 and 7 indicates a 9- to 14-fold difference in dose required to obtain similar effects in the two lines. These mice are expected to be useful experimental subjects in studies of benzodiazepine mechanisms.

The mesencephalic locomotor region in cat: effects of local applications of diazepam and gamma-aminobutyric acid

In decorticate unanaesthetized cats, displaying sequences of stereotyped locomotor movements in response to electrical stimulation of their footpad, local injections were made into the mesencephalic locomotor region (MLR). Diazepam (at 10 micrograms) and GABA (at 500 micrograms) induced complete suppression for 5-10 min, followed by partial amplitude recovery. It is suggested that: (i) MLR contains both diazepam and GABA receptors, and (ii) diazepam (and GABA) blockade is only short lasting because of a substitution (vicariancy) process through other structures also involved in locomotion.

Characterization of solubilized benzodiazepine and muscimol binding sites from rat brain

Binding sites for muscimol and flunitrazepam were solubilized and their properties studied by ultrafiltration, isoelectro-focusing and cation-exchange chromatography methods. The heterogenity of binding sites for flunitrazepam was demonstrated in the ultrafiltration experiments: the binding sites with a molecular weight of more than 300,000 dalton were sensitive to stimulation by gamma-aminobutyric acid (GABA) and those with a molecular weight of less than 300,000 dalton were not. The binding sites for flunitrazepam appeared to be low acidic molecules with pI 5.6-6.0 and binding sites for muscimol an apparently more heterogenous distribution in the range of pH 4.6 to 5.9 was detected. Cation-exchange chromatography revealed two subpopulations of binding sites for muscimol one of which copurified together with binding sites for flunitrazepam. Each subpopulation exhibited only one class of binding site with Kd = 20 nM for a subpopulation copurifying together with binding sites for flunitrazepam and Kd = 9 nM for the other.

Effect of benzodiazepines on cyclic GMP formation in rat cerebellar slices

Cyclic 3',5' guanosine monophosphate (cGMP) levels, stimulated in brain slices by ouabain, potassium, and sodium azide depolarization, have been found to be inhibited in a dose-dependent fashion by both behaviorally active and inactive benzodiazepines. ED50's for these benzodiazepines bear no relation to potencies established from receptor membrane binding studies; however, these values do correspond to ED50's calculated for several known membrane stabilizing agents tested in this system. The concentration of [3H]flunitrazepam necessary to saturate the benzodiazepine receptor in identical slice preparations is considerably lower than that needed to initiate inhibition of depolarization-induced cGMP stimulation. Some of the reported in vivo actions of benzodiazepines on cGMP formation may be the result of membrane stabilizing actions of the benzodiazepines or mediated indirectly.