Computer-aided drug design for the benzodiazepine receptor site.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
M F Davies
Publications and source records attributed to M F Davies.
Selective effect on punished versus unpunished responding in a conflict test as the criterion for anxiogenic activity.
The punished drinking test has been used successfully for identifying and studying anxiolytic agents. By reducing the level of punishment (i.e., decreasing the intensity of shock), it has also been used as a method for measuring anxiogenic activity. Because anxiogenic behavior is a novel and important concept that is not yet fully established, we have reinvestigated the effects of two putative inverse benzodiazepine agonists and pentylenetetrazol in this conflict test. In a series of experiments, using both our version of the procedure and a replication of a previously published method, we were unable to demonstrate a selective reduction in punished responding over unpunished responding caused by CGS 8216 (3 to 40 mg/kg), FG 7142 (2 to 6 mg/kg), and pentylenetetrazol (10 to 20 mg/kg) as reported previously. A careful comparison of the details of our method and the published procedure failed to reveal the source of this discrepancy. If anxiogenic behavior is to be defined as a selective effect of a drug on punished response, the value of this test will depend on identification of its critical variables.
Animals↗
Cutaneous haemangioendothelioma: a possible link with chronic exposure to vinyl chloride.
A patient who worked with polyvinyl chloride developed a malignant haemangioendothelioma of a toe. This rare tumour is more commonly found in the liver where it has been reported to arise in association with exposure to the vinyl chloride monomer.
Chemical Industry↗
Intestinal obstruction secondary to uterine perforation: an unusual cause of vaginal bleeding.
A patient with intestinal obstruction is described in whom small bowel was incarcerated within the uterine lumen. This is thought to have arisen as a result of undiagnosed uterine perforation during a previous dilatation and curettage.
Adult↗
Modulatory actions of serotonin on ionic conductances of hippocampal dentate granule cells.
Pressure ejection of serotonin (2 x 10(-4) M) onto dentate granule neurons in vitro produced a short-lasting membrane hyperpolarization associated with a 10-30% decrease in the input resistance. The hyperpolarization magnitude depended on the extracellular K+ concentration but not on the extra or intracellular Ca2+ concentration. It was followed by a depolarization, especially when serotonin was applied onto the perisomatic area of the neuron. The post-spike-train afterhyperpolarization, which represents a Ca2+-dependent K+ conductance, was decreased by serotonin by 10-100% and remained reduced for 2-10 min following the serotonin-induced hyperpolarization. Decreased adaptation of cell firing was also observed following serotonin application. Ca2+ action potentials evoked by intracellular depolarizing current pulses in the presence of the Na+ channel blocker tetrodotoxin and the K+ channel blocker tetraethylammonium were followed by a large afterhyperpolarization, which was markedly reduced for several minutes following serotonin application. The preceding Ca2+ action potential was either unaffected or prolonged. The hyperpolarization occurring in response to localized application of serotonin, and the reduction of the afterhyperpolarization, may represent two different mechanisms of serotonin action, probably mediated by different mechanisms. The slow time course of the late depolarization and the afterhyperpolarization depression represent modulatory effects of serotonin on dentate granule neurons.
Action Potentials↗
Molecular determinants of benzodiazepine receptor affinities and anticonvulsant activities.
In vivo convulsant activities profiles and receptor binding studies together with the techniques of theoretical chemistry were used to characterize 15 compounds, from five different chemical families, known to bind to the BDZ receptor. The experimental goals of this study were to determine the affinity of these analogs for this receptor, the effect of gamma-aminobutyric acid on the affinity, and, in a self-consistent manner, the nature of the activity, agonist (anticonvulsant), antagonist, or inverse agonist (proconvulsant, convulsant), elicited by binding to this receptor. To these ends, in vivo studies were made to determine the proconvulsant, convulsant, and anticonvulsant activities and antagonism to anticonvulsant activities of the 15 analogs. Their receptor affinities at 25 degrees were also determined by competitive inhibition of [3H] flunitrazepam and [3H]Ro 15-1788 in the absence and presence of gamma-aminobutyric acid. The goal of the theoretical studies was to identify and calculate molecular properties that modulate these affinities and types of activities and from them to develop a model of receptor recognition and activation that could consistently explain observed behavior and predict new results. Thus, molecular orbital calculations were carried out for all analogs, using semiempirical quantum mechanical methods. In addition to the optimization of structures, a number of electronic properties, such as polarizations, partition coefficients, and proton and electron affinities were computed and examined for their ability to modulate relative affinities and modes of activation of the receptor. From these studies, a model for receptor recognition involving two anchoring hydrogen bond-acceptor sites and for activation involving interaction of the most lipophilic aromatic region of each compound with the receptor was developed, which could systematically account for the three different types of behavior, agonist, antagonist, and inverse agonist, observed for these analogs. Electronic rather than structural properties were found to be the principal modulator of both recognition and activation. A possible mechanism of agonist activation of the receptor involving electron transfer to the agonist, as well as a possible induced conformational change in the receptor, is also suggested by these results. Finally, by complementarity, some steric and electronic characteristics of the receptor binding site could be deduced.
Animals↗
Idiopathic spontaneous haemoperitoneum.
A case is described of bleeding arising from the falciform ligament which occurred in the absence of obvious local pathology. Spontaneous bleeding from this site hitherto has not been reported. Previously described cases of idiopathic spontaneous haemoperitoneum and factors implicated in the aetiology of this rare condition are reviewed.
Aged↗
Hyperexcitability of hippocampal CA1 neurons in brain slices of rats chronically administered clonazepam.
The neuronal manifestations and mechanisms of sedative-anticonvulsant (benzodiazepine) drug withdrawal have been investigated in the CA1 region of hippocampal slices prepared from rats administered clonazepam for 1 month. Slices from clonazepam-treated rats exhibited epileptiform activity evidenced by multiple extracellular population spikes after orthodromic stimulation. These slices also demonstrated abnormally steep and variable stimulus intensity-population spike curves. Intracellular recordings showed spontaneous bursts and slow paroxysmal depolarizations. To investigate the neuronal activity before and immediately after drug withdrawal, slices from drug-naive and drug-exposed rats were maintained in solution containing the approximate concentration of clonazepam (20 nM) measured in the cerebrospinal fluid of clonazepam-treated rats. Compared to CA1 neurons in hippocampal slices from drug-naive animals, neurons from clonazepam-administered animals showed an increased tendency to fire in a bursting (i.e., epileptiform) pattern when the cell was depolarized by current injection, or by orthodromic or antidromic stimulation. Upon withdrawal of clonazepam from the perfusate, the frequency of spontaneous excitatory postsynaptic potentials and spiking activity increased in cells from clonazepam-treated animals and was associated with a shortening of the long-lasting postspike train after hyperpolarization. However, no change in the dendritic gamma-aminobutyric acid response was noted. This study indicates that abnormal epileptiform activity can be detected and studied in brain slices from animals chronically treated with clonazepam.
Animals↗
Benzodiazepine-induced epileptiform activity in vitro.
Drug naive rat hippocampal slices were incubated in artificial cerebrospinal fluid (ACSF) containing 20 nM clonazepam, a concentration approximating those measured in the cerebrospinal fluid (CSF) of rats treated with high doses of clonazepam which resulted in behavioral hyperexcitability and convulsions upon withdrawal. In the slice, epileptiform activity began within 2 h of incubation in clonazepam. This activity was enhanced upon drug withdrawal. Measured intracellularly, the long-lasting post-spike train afterhyperpolarization was reduced in duration in drug-treated cells whereas just subthreshold antidromic or orthodromic IPSPs were not changed. As some of the hyperexcitability phenomena noted here were similar to those observed in slices taken from rats chronically administered with clonazepam, the technique of long-term in vitro exposure to substances which cause tolerance and dependence may be a useful model of drug withdrawal epilepsy.
Animals↗
Two distinct effects of 5-hydroxytryptamine on single cortical neurons.
The ability of the indoleamine serotonin (5-hydroxytryptamine; 5-HT) to alter membrane characteristics of neocortical neurons was analyzed using intracellular recording techniques. The present study demonstrates that 5-HT primarily depolarized 68% of cortical neurons probably by decreasing a resting K+ conductance, an effect blocked by the antagonists ritanserin and cinanserin and apparently mediated by 5-HT2 receptors. A hyperpolarization associated with an increased conductance state and insensitive to 5-HT2 antagonists was observed in 26% of the neurons and could be mimicked by the selective 5-HT1A agonist (+/-)-8-hydroxy-2-(di-N-propyl-amino)tetralin (8-OH-DPAT). Therefore cortical pyramidal neurons contain at least two distinct functional 5-HT receptors whose activation produces opposing effects on membrane potential and conductance.
Animals↗
gamma-Aminobutyric acid hyperpolarizes rat hippocampal pyramidal cells through a calcium-dependent potassium conductance.
Application of gamma-aminobutyric acid (GABA) to the dendrites of CA1 pyramidal cells in hippocampal slices produced depolarizing and hyperpolarizing responses. Picrotoxin (50 microM) blocked the depolarizing response of the dendrites to GABA but not the hyperpolarizing responses of the dendrites. The hyperpolarizing response of the cell body to GABA was reduced but not blocked by picrotoxin, suggesting the presence of a complex response at the cell body. The depolarizing response of the dendrites and the hyperpolarizing response of the cell body appeared to be at least partly Cl- dependent as they were respectively increased and decreased in size in low-Cl- artificial cerebrospinal fluid (ACSF), while the hyperpolarizing response of the dendrites was unaffected. The hyperpolarizing response of the dendrites was increased in amplitude in low-K+ ACSF and the extrapolated reversal potential of the response became more negative, suggesting that the response was K+ dependent. The hyperpolarizing response of the dendrites was decreased in size in high-K+ ACSF and could be readily inverted by current injection. The reversal potential became less negative in high-K+ ACSF in a similar manner to that of the slow after-hyperpolarization following a train of spikes, indicating that the response was a K+ conductance. Perfusion of the slice with normal or 0-Ca2+ ACSF containing Cd2+ or Mn2+ blocked synaptic transmission, increased spike duration and blocked the slow phase of the spike after-hyperpolarization (a.h.p.). This latter potential is thought to be mediated by a Ca2+-dependent K+ conductance. Later, the hyperpolarizing response of the dendrites to GABA was blocked without an effect on the other GABA responses. Pressure application of Cd2+ (0.2-2 mM) onto the surface of the slice rapidly reduced or blocked the slow a.h.p. and the dendritic hyperpolarizing response to GABA. Intracellular injection of EGTA rapidly blocked the slow phase of the a.h.p. and then later blocked or reduced the dendritic hyperpolarizing response to GABA. We conclude that the hyperpolarizing response of the dendrites to GABA is mediated by a Ca2+-dependent K+ conductance.
Action Potentials↗
The effects of benzodiazepines on spinal homosynaptic depression.
Clonazepam (0.5 mg/kg, i.v.) changed the characteristic pattern of the exponential decline of the monosynaptic responses, the early tetanic rundown, evoked by trains of 10 stimuli (2, 5 or 10 Hz) applied to either the biceps-semitendinosus or triceps surae nerve, and recorded from the ventral root in spinal cats. In the case of the biceps-semitendinosus, clonazepam did not affect the first monosynaptic response or the last five monosynaptic responses forming the plateau, while the second monosynaptic response was markedly depressed, especially at the higher frequencies tested. The triceps surae reacted differently to the administration of clonazepam, in that the first response was increased and the amount of depression of the second response was lessened, with no change of the plateau. All the effects of clonazepam were reversed by the benzodiazepine antagonist, ethyl 8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a] [1,4]benzodiazepine-3-carboxylate (Ro15-1788; 5 mg/kg, i.v.), which alone had no effect of its own on any parameters, suggesting that the effects of clonazepam were mediated by central benzodiazepine receptors. Diazepam (1.0 mg/kg, i.v.), caused the same changes in the homosynaptic depression of the biceps-semitendinosus pathway as did clonazepam, but increased the plateau instead of the second response in that of the triceps surae pathway.
Animals↗
A GABAergic component in homosynaptic depression in the spinal monosynaptic pathway. A requirement for action of benzodiazepines.
Spinal monosynaptic responses, evoked by repetitive stimulation, undergo homosynaptic depression the pattern of which is altered by 0.5 mg/kg of clonazepam. The dependence of this effect of clonazepam on the GABAergic system was examined in spinal unanaesthetized cats. Topical application of bicuculline to the spinal cord did not change any feature of the homosynaptic depression in the biceps-semitendinosus (BST) or triceps surae (TS) monosynaptic pathway but antagonized the action of clonazepam. Semicarbazide (200 mg/kg, i.v.) also prevented the effect of the benzodiazepine but alone had actions of its own. Evidence is presented that clonazepam influenced homosynaptic depression of the biceps-semitendinosus pathway by lengthening the primary afferent depolarization (PAD). This prolongation of the primary afferent depolarization did not last for the entire duration of the train as primary afferent depolarization also underwent depression. Therefore later responses in the train were unaffected by clonazepam. Homosynaptic depression of the triceps surae pathway was not similarly affected because activation of triceps surae afferents does not cause significant depolarization of its own afferents. It is suggested that the enhancement of GABAergic transmission at least partially underlies the effect of clonazepam on homosynaptic depression.
Animals↗
Enhanced neuronal K+ conductance: a possible common mechanism for sedative-hypnotic drug action.
It is commonly thought that central nervous system depressant drugs exert their actions through enhancement of gamma-aminobutyrate (GABA)-mediated mechanisms. Recently, the cellular electrophysiological evidence from this laboratory and others suggests that both sedative hypnotics and general anaesthetics inhibit central neurons by increasing potassium conductance (GK). We have utilized the mammalian in vitro hippocampal and cerebellar slice preparations at 34-36 degrees C. Intracellular recordings from CA1, CA3, and cerebellar Purkinje cells were obtained. Low dose (sedative) concentrations of ethanol (less than or equal to 20 mM), two different benzodiazepines (midazolam and clonazepam in low nanomolar concentrations), and pentobarbital (10(-6) to 10(-4) M) were applied by pressure ejection or were bath perfused. All drugs caused a hyperpolarization with decreased spontaneous activity, and enhanced post spike afterhyperpolarizations (AHPs). These long-lasting AHPs are presumably due to enhanced calcium-mediated GK. Increased responsiveness to focally applied GABA was only seen at higher doses (ethanol, 100 mM; midazolam, 10(-7) M; pentobarbital, 10(-4) M). These data suggest that the above neurodepressant drugs, when applied at sedative doses to hippocampal pyramidal cells, enhance GK and not the actions of GABA.
Animals↗
Effects of ammonium chloride on synaptic transmission in the rat hippocampal slice.
Effects of ammonia on excitatory synaptic transmission were studied in the rat hippocampal slice preparation. Population spikes, elicited by orthodromic or antidromic stimulation, were recorded in the cell body layer of the CA1, CA3 and dentate regions. Perfusion with 5 mM ammonium chloride induced a profound and reversible depression of orthodromically evoked population spikes in all three regions. Antidromic population spikes were not depressed in any of the regions, indicating that neither axonal conduction nor electrical excitability were affected by ammonia. The paired-pulse test revealed a transient disinhibition during the early phase of perfusion. Iontophoretic application of glutamate evoked unit firing even when the synaptically evoked responses were reduced by ammonia, indicating that the postsynaptic sensitivity to the putative transmitter was not depressed. Depression of release of the excitatory transmitter, probably because of depletion following the block of transmitter synthesis, is the likely explanation of these findings. It is suggested that ammonia-induced depression of excitatory transmission may account for coma and other symptoms of central nervous system depression encountered in hyperammonemic states.
Ammonium Chloride↗
GABA-mediated responses are not selectively depressed by 3-mercaptopropionic acid in the spinal cord.
The competitive inhibitor of glutamic acid decarboxylase (GAD), 3-mercaptopropionic acid (MPA), causes depletion of gamma-aminobutyric acid and convulsions. We expected it to be a superior GABA depleting agent for in vivo experiments to the frequently used semicarbazide. The dorsal root potentials (DRP) and monosynaptic reflex responses (MSR) evoked by adjacent dorsal root and peripheral nerve stimulation, respectively, were recorded in spinal unanaesthetized cats. MPA (100-200 mg/kg) caused a gradual decrease in DRP, reaching a peak in about 40 min after drug administration. This was usually associated with convulsive activity. Postsynaptic direct inhibition was not substantially affected. However, the MSR was consistently decreased, within 10 min after injection of MPA. It is concluded that MPA is not a suitable tool, at least in the spinal cord, for the selective reduction of GABAergic transmission.
3-Mercaptopropionic Acid↗
Food palatability and hunger modulated effects of CGS 9896 and CGS 8216 on food intake.
The effect of food palatability and duration of food deprivation on the modulation of food intake by two benzodiazepine receptor (BDZR) ligands, CGS 9896 and CGS 8216, were investigated. Three diets differing in palatability (high, medium, or standard) and three different periods of food deprivation (0, 16, or 24 h) were used in all combinations to compare the effect of these variations on the observed modulation of food consumption by both BDZR ligands. Increasing diet palatability and/or food deprivation increased the baseline food consumption and reduced the sensitivity of the test to the detection of the hyperphagic effect of CGS 9896 but increased the sensitivity to detect the anorexic effect of CGS 8216. Only for the intermediate conditions of food deprivation (16 h) and for a standard or medium palatable diet were both significant hyperphagic effect of CGS 9896 and anorexic effect of CGS 8216 detected. Neither increased palatability nor hunger enhanced the modulation of feeding, indicating that neither "taste preference" nor "hunger" is the key factor in the mechanism of BDZR ligand-induced feeding response.
Animals↗