Effect of diazepam on GABAergic cuneate neurons

Effects of GABA and anxiolytics on the single unit discharge of suprachiasmatic neurons in rat hypothalamic slices

The effects of gamma-aminobutyric acid (GABA), muscimol, baclofen and the anxiolytics; diazepam (DZP), flurazepam (FZP) and zopiclone on single-unit neural activities in the suprachiasmatic nucleus (SCN) were investigated using the rat hypothalamic slice preparation. Exposure of the slice to GABA 10(-4) M produced inhibitory responses in 65% of the 49 SCN neurons examined. The threshold concentration of GABA ranged from 10(-6) to 10(-4) M. Neurons responsive to GABA were not found to be restricted to a subdivision of the SCN, but were diffusely distributed throughout the nucleus. DZP, FZP and zopiclone produced responses similar to those of GABA. The inhibitory effects of GABA (10(-5) M) were potentiated by coadministration of DZP (10(-5) M). Muscimol and baclofen (10(-7) M to 10(-4) M) also inhibited SCN neuronal activity in a dose-dependent manner. Bicuculline (10(-5) M-10(-4) M) scarcely affected the baclofen-induced inhibition (1/6) but strongly antagonized the effects of muscimol (6/6), GABA (6/8) and DZP (4/5). These results suggest that the receptors mediating the inhibitory effects of GABA and anxiolytics within the SCN may be GABAA and/or GABAB or GABA-BDZ receptor complex, respectively.

Effects of diazepam on the carotid sinus baroreflex control of circulation in rabbits

To examine the effects of diazepam on the carotid sinus baroreflex control of circulation, bilateral carotid occlusion was performed on 14 conscious rabbits with aortic denervation. The responses of mean arterial pressure, heart rate, cardiac output and total peripheral resistance were obtained. The haemodynamic responses to carotid occlusion were evaluated at cumulative doses of 0.5 and 1.0 mg kg-1 of diazepam. The administration of diazepam decreased cardiac output and increased total peripheral resistance significantly, but did not affect the arterial pressure and heart rate. The response of total peripheral resistance to carotid occlusion was significantly increased from 0.118 +/- 0.018 (mean +/- SE) to 0.154 +/- 0.026 mmHg min ml-1 at 1.0 mg kg-1 of diazepam. The heart rate response was attenuated significantly from 41 +/- 5 to 24 +/- 4 beats min-1 at 1.0 mg kg-1 of diazepam. Diazepam did not alter the response of arterial pressure to carotid occlusion. We suggest that the dissociated effects of diazepam on the reflex control of circulation reflect the dissociated influences of diazepam on the central sympathetic and vagal-mediated pathways.

Electrophysiology of benzodiazepine receptor ligands: multiple mechanisms and sites of action

Electrophysiology of BZR ligands has been reviewed from different points of view. A great effort was made to critically discuss the arguments for and against the temporarily leading hypothesis of the mechanism of action of BZR ligands, the GABA hypothesis. As has been discussed at length in the present article, an impressive body of electrophysiological and biochemical evidence suggests an enhancement of GABAergic inhibition in CNS as a mechanism of action of BZR agonists. Biochemical data even indicate a physical coupling between GABA recognition sites and BZR which, together with the effector site build-up by Cl- channels, form a supramolecular GABAA/BZR complex. By binding to a specific site on this complex, BZR agonists allosterically increase and BZR inverse agonists decrease the gating of GABA-linked Cl- channels, whereas BZR antagonists bind to the same site without an appreciable intrinsic activity and block the binding and action of both agonists as well as inverse agonists. While this model is supported by many electrophysiological experiments performed with BZR ligands in higher nanomolar and lower micromolar concentrations, it does not explain much controversial data from animal behavior and, more importantly, is not in line with electrophysiological effects obtained with low nanomolar BZ concentrations. The latter actions of BZR ligands in brain slices occur within a concentration range compatible with concentrations of BZ observed in CSF fluid, which would be expected to be found in the biophase (receptor level) during anxiolytic therapy in man. Enhanced K+ conductance seems to be a suitable candidate for this effect of BZR ligands. This direct action on neuronal membrane properties may underlie the many electrophysiological observations with extremely low systemic doses of BZR ligands in vivo which demonstrated a depressant effect on spontaneous neuronal firing in various CNS regions. Skeletomuscular spasticity and epilepsy are two neurological disorders, where both the enhanced GABAergic inhibition and increased K+ conductance may contribute to the therapeutic effect of BZR agonists, since electrophysiological and behavioral studies strongly support GABA-dependent as well as GABA-independent action of BZR ligands elicited by low to intermediate doses of BZ necessary to evoke anticonvulsant and muscle relaxant effects. Somewhat higher doses of BZR ligands, inducing sedation and sleep, lead perhaps to the only pharmacologically relevant CNS concentrations (ca. 1 microM) which might be due entirely to increased GABAergic inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Development of enhanced sensitivity to naloxone

The effects of naloxone were examined over a period of three and a half years in squirrel monkeys responding under a mult FR, FI schedule of food presentation. During the initial observation of naloxone's effects, monkeys were drug naive. At that time, doses of naloxone up to 3.0 mg/kg had very little effect on rates of responding under the multiple schedule. The effects of naloxone were then examined in combination with meperidine. Doses of naloxone between 0.3 and 3.0 mg/kg produced a dose-dependent antagonism of meperidine's effects. Monkeys were then exposed to ketocyclazocine and phencyclidine, alone and in combination with naloxone. When the naloxone dose-effect curve was redetermined subsequently, it had shifted to the left. Monkeys were then exposed to buprenorphine and diprenorphine, alone and in combination with naloxone. Redetermination of the naloxone dose-effect curve following this exposure revealed a further shift to the left. The effects of naloxone were then reexamined in combination with meperidine, and it was found that the leftward shift in the naloxone dose-effect curve was not accompanied by a decrease in the doses of naloxone which would reverse the effects of meperidine. Naloxone's effects were then examined in combination with either acute or chronic diazepam. The naloxone dose-effect curve determined during the chronic diazepam regimen was shifted to the right of that obtained prior to chronic diazepam.

The GABA postsynaptic membrane receptor-ionophore complex. Site of action of convulsant and anticonvulsant drugs

The function of the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA), has been implicated in the mode of action of many drugs which excite or depress the central nervous system. Many convulsant agents appear to block GABA action whereas anticonvulsants enhance GABA action. Some of these drug effects involve altered GABA-mediated synaptic transmission at the level of GABA biosynthesis, release from nerve endings, uptake into cells, and metabolic degradation. A greater number of agents of diverse classes appear to affect GABA action at the postsynaptic membrane, as determined from both electrophysiological and biochemical studies. The recently developed in vitro radioactive receptor binding assays have led to a wealth of new information about GABA action and its alteration by drugs. GABA inhibitory transmission involves the regulation, by GABA binding to its receptor site, of chloride ion channels. In this GABA receptor-ionophore system, other drug receptor sites, one for benzodiazepines and one for barbiturates/picrotoxinin (and related agents) appear to form a multicomponent complex. In this complex, the drugs binding to any of the three receptor categories are visualized to have an effect on GABA-associated chloride channel regulation. Available evidence suggests that the complex mediates many of the actions of numerous excitatory and depressant drugs showing a variety of pharmacological effects.

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.