Effects of nitrazepam and phenobarbital on hippocampal and lateral geniculate neurones in the cat

Benzodiazepines and the mammalian retina. II. Actions on retinal ganglion cells

The effects of intravenously and iontophoretically applied benzodiazepines, midazolam and flurazepam and their receptor antagonist, flumazepil (RO 15 1788), on visually evoked and spontaneous activities of the mammalian retinal ganglion cells have been studied. Intravenously applied midazolam and flurazepam suppressed both light-evoked and spontaneous firing of rat optic tract fibres. They reduced both the sensitivity to light and the temporal resolution of the fibres. Flumazepil (RO-15-1788), on the other hand, enhanced both light-evoked and spontaneous firing of the optic tract fibres. It increased their light sensitivity but did not affect their temporal resolution. In the cat, iontophoretically applied benzodiazepines suppressed and flumazepil increased the receptive field centre and surround response as well as the spontaneous firing of ON-type retinal ganglion cells which mainly receive GABAergic inputs. However, these drugs did not affect the activities of the OFF-type cells which mainly receive glycinergic inputs. These results suggest not only that the action of benzodiazepines on the retinal ganglion cells is mediated by benzodiazepine receptors that are linked with GABA receptors, but also that the retinal benzodiazepine receptors receive an endogenous benzodiazepine receptor ligand.

Effects of antiepileptic drugs on pentylenetetrazole-induced epileptiform activity in the in vitro hippocampus

We studied the effects of four antiepileptic drugs on pentylenetetrazole-induced burst discharges in the CA3 region of the in vitro hippocampus. Diazepam and carbamazepine abolished the bursting activity in a gradual and dose-dependent manner. Phenobarbital only decreased the burst frequency. Valproic acid was either ineffective or actually caused an increase in both burst frequency and amplitude. The findings in this model were compared with results obtained by other investigators in a penicillin-induced model of epileptiform activity in the hippocampal slice. Diazepam had a similar effect on both pentylenetetrazole- and penicillin-induced burst discharges, but phenobarbital was ineffective in the pentylenetetrazole model, indicating that these chemically induced hippocampal epileptiform activities may be differentially sensitive to antiepileptic drugs.

Flurazepam effects on rat cerebellar Purkinje cells

1. Cerebellar Purkinje cell activity was recorded in urethane anaesthetized rats. 2. Flurazepam, infused intravenously in divided doses totalling 4 mg/kg, decreased simple spike activity, increased complex spike activity and prolonged local surface inhibition. 3. Iontophoretically applied flurazepam enhanced the effect of GABA and elicited a bursting pattern of discharge when released using larger currents for ejection.

Receptors for the age of anxiety: pharmacology of the benzodiazepines

Investigation of the actions of the benzodiazepines has provided insights into the neurochemical mechanisms underlying anxiety, seizures, muscle relaxation, and sedation. Behavioral, electrophysical, pharmacological, and biochemical evidence indicates that the benzodiazepines exert their therapeutic effects by interacting with a high-affinity binding site (receptor) in the brain. The benzodiazepine receptor interacts with a receptor for gamma-aminobutyric acid, a major inhibitory neurotransmitter, and enhances its inhibitory effects. The benzodiazepine receptor may also interact with endogenous substances and several naturally occurring compounds, including the purines and nicotinamide, are candidates for this role. Both the purines and nicotinamide possess some benzodiazepine-like properties in vivo, although further work will be required to confirm their possible roles as endogenous benzodiazepines.

Effects of diazepines and barbiturates on hippocampal recurrent inhibition

The effects of two diazepines (diazepam and Ro 11-7800) and 3 barbiturates (thiamylal, pentobarbitol and phenobarbital) on GABA-mediated recurrent inhibition were assessed on single hippocampal pyramidal cells and on population spikes using extracellular recording techniques. Recurrent inhibition was evoked in spontaneously active CA1 pyramidal cells by stimulation of the fimbria or the alveus with single shocks. Microiontophoretic application of Ro 11-7800 or systemic application of diazepines or barbiturates resulted in an increase of the duration of the inhibition and in a concomitant depression of the spontaneous firing in most neurones tested. When the firing rates were kept constant artificially, using excitant amino acids, a prolongation of the recurrent inhibition was observed with barbiturates but not with diazepines. The duration of the inhibition, which was assessed from CA1 population spikes elicited by double shocks to the fimbria, was prolonged following systemic application of diazepines or barbiturates. It is concluded that both diazepines and barbiturates are able to potentiate GABAergic recurrent inhibition in the hippocampus. The demonstration of this effect appears to depend critically on certain experimental conditions.