Action Of Benzodiazepines Research Articles

Independence of benzodiazepine and opiate action in the suppression of isolation distress in rat pups.

To determine whether benzodiazepines (BDZs) quiet isolation distress in 10-day-old rat pups by causing a release of endogenous opioids, a blockade of the effects of chlordiazepoxide (CDP) by the opiate antagonist naltrexone (NLX) was sought. Nonsedating doses of morphine (MOR) (0.125 mg/kg) and CDP (2.0 mg/kg) were equally effective in reducing ultrasonic vocalizations and other indices of isolation distress. Appropriate blocking agents NLX, (0.5 mg/kg) against MOR and Ro 15-1788 (4.0 mg/kg) against CDP returned distress measures to levels of saline-treated rat pups. However, NLX failed to reverse the quieting effects of CDP. If CDP potentiates endogenous opioid release, then NLX should block the CDP effect. A higher dose of CDP did not reveal a release of endogenous opioids, and a higher dose of NLX did not antagonize CDP. The quieting effects of BDZs on isolation distress do not appear to be mediated by the opiate system.

Mechanisms of action of benzodiazepines

Mechanisms of action of benzodiazepines

Antiproliferative Action of Benzodiazepines in Cultured Brain Cells Is Not Mediated Through the Peripheral‐Type Benzodiazepine Acceptor

The benzodiazepines, Ro 5-4864, diazepam, clonazepam, and also PK-11195, inhibited, at micromolar concentrations, the proliferation of rat C6 glioma and mouse neuro-2A neuroblastoma cells in culture. The cells possessed high levels of "peripheral-type" high-affinity benzodiazepine binding sites as judged by binding assays and displacement potencies. However, the different potencies and specificities of compounds for the antiproliferative actions and binding affinities for the binding site suggest that the antiproliferative actions were not mediated through the peripheral-type binding site. In support of this, these compounds have also been shown to inhibit proliferation of some nonneuronal cultured cell lines, e.g., mouse SP2/O-Ag 14 hybridoma and rat NCTC epithelial cells, which have no detectable high-affinity peripheral-type benzodiazepine binding sites.

Persistent alterations in GABA A receptor binding and function after prenatal lorazepam administration in the chick

Behavioral abnormalities have been reported in young and adult animals exposed to benzodiazepines prenatally. The presence of neurochemical alterations in the GABAergic system after prenatal benzodiazepine exposure was assessed in a chick model which avoids prenatal and postnatal maternal effects. The GABA A receptor complex, the presumed site of benzodiazepine action, was altered in adult chickens previously exposed to lorazepam for 10 days in ovo. Binding was decreased at the putative chloride channel site labeled by [ 35S]TBPS, coupling was decreased between this site and the GABA binding site, and function of the GABA A receptor in chloride uptake was diminished in animals exposed to prenatal lorazepam. Persistent neurochemical alterations in the GABAergic system accompany prenatal benzodiazepine exposure, and may influence subsequent behavior and development.

Alprazolam but not diazepam protects hamsters with heart disease from the medical consequences of stress

We have previously shown that subjecting cardiomyopathic hamsters in the lesion-developing period of their heart disease to cold-immobilization stress had lethal consequences which could be blocked by alprazolam treatment. This experiment replicated that finding and also examined the efficacy of diazepam in this paradigm. In contrast to alprazolam, diazepam did not prevent the cardiomyopathic subjects from succumbing to the stressor. Thus, the effect of alprazolam in reducing stress-induced mortality did not reflect a generic benzodiazepine action.

Benzodiazepine-induced shaking behavior in the rat: Structure-activity and relation to serotonin and benzodiazepine receptors

In studying the role of serotonin (5-HT) in the mechanism of action of benzodiazepine(BDZ)-induced wetdog shakes (WDS), only certain 1,4-substituted BDZ agonists were found to induce WDS at doses up to 60 mg/kg in the rat with the rank order of potency at peak dose effect clonazepam > nitrazepam = flunitrazepam ⪢ nimetazepam = lorazepam. BDZs evoking WDS at lowest doses contained an R 7 nitro group on the A ring. Non-BDZ agonists (CL 218,872), inverse agonists (β-CCE), peripheral type receptor agonists (Ro 5-4864), and BDZ antagonists (Ro 15-1788) did not induce shaking behavior. Several 5-HT 1 and 5-HT 2 agonists and antagonists were tested as blockers, but only putative 5-HT 1A agonists reduced WDS, 8-OH-DPAT and ipsapirone but not PAPP and 5-MeO-DMT having a significant effect. The effect of 8-OH-DPAT was dose dependent, with an ID 50 of 0.86 mg/kg, but it was not reversed by 5-HT or adrenergic antagonists at the doses studied. Intracisternal 5,7-dihydroxytryptamine lesions did not alter frequency, latency, or time course of BDZ-induced WDS. BDZ-evoked WDS were enhanced by Ro 15-1788 (which inhibited ataxia) but were unaffected by the various types of BDZ agonists. Several BDZ agonists induced both WDS and ataxia, but ataxia was not blocked by serotonergic drugs. No significant correlation with ataxia, BDZ radioligand binding, antipentylenetetrazol activity, or other BDZ property was found. BDZ-evoked WDS may relate to the unique predominance of BDZ II and 5-HT 1A receptors in the hippocampus, an important site for WDS, but 5-HT 1A agonists appear to modulate WDS by opposing pharmacologic actions rather than by direct receptor antagonism. These data indicate a species difference in the shakes induced by BDZs in rats (5-HT 2 independent) and in mice (5-HT 2 related).

The effects of midazolam on hippocampal dentate gyrus granule neurons from young and old Fischer 344 rats.

The effects of midazolam (3 nM) perfusion on the membrane and synaptic properties of dentate gyrus granule neurons were examined in hippocampal slices obtained from young adult (4-6 months) and old (24-26 months) Fischer 344 rats. In young neurons, midazolam perfusion resulted in a hyperpolarization of the resting membrane potential with no apparent change in the input resistance. Midazolam perfusion also produced a significant increase in the amplitude of the post-spike train afterhyperpolarization (AHP). In neurons obtained from old animals, midazolam perfusion also produced a hyperpolarization of the resting membrane potential but did not significantly change the AHP. These effects may result from altered calcium homeostasis in neurons of the aged brain, and suggest that at least some of the direct actions of benzodiazepines on mammalian central neurons are altered during aging.

Enhancement of sleep by microinjection of triazolam into the medial preoptic area.

A growing literature suggests that the basal forebrain may contain structures involved in the regulation of sleep. As part of a series of studies designed to locate the site(s) of hypnotic action of benzodiazepines, we have injected triazolam into the medial preoptic area (MPA) of the hypothalamus of rats. Total sleep time was increased, due primarily to an increase in non-rapid eye movement (non-REM) sleep and a trend toward a decrease in intermittent waking time. A previous study from this laboratory reported that injections into the raphe nucleus decreased sleep, whereas injections at adjacent sites were without effect. These studies indicate the selectivity with which different brain regions respond to triazolam in terms of actions on sleep.

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.

Quantitative and comparative analyses of pro-aggressive actions of benzodiazepines in maternal aggression of rats

The pro-aggressive effects of low doses of benzodiazepines on maternal aggression in rats were studied. Chlordiazepoxide, diazepam, oxazepam and alprazolam produced bell-shaped dose-response curves, with increased aggression at low doses. Only alprazolam significantly reduced aggression at higher doses. A comparison of the drug effects on different aggressive elements revealed that chlordiazepoxide and oxazepam increased the frequency of more elements of the aggressive repertoire than diazepam or alprazolam. Thus, although all benzodiazepine receptor agonists increased aggression, there were significant quantitative differences in their effects.

Differences among nine 1,4-benzodiazepines: an ethopharmacological evaluation in mice

The present study explored whether the profiles of action of benzodiazepines on intraspecies conflict behavior in mice are different. The occurrence of seven behavioral elements was observed in aggressive and timid singly-housed male mice treated with drugs in paired interactions with untreated non-aggressive males. At low doses, some benzodiazepines (alprazolam, oxazepam and diazepam) inhibited defenses, escapes, or attacks, but did not reduce other activities (social sniffing, walking, rearing), and actually increased most of them. At comparable doses, other benzodiazepines (flunitrazepam, nitrazepam, clonazepam and chlordiazepoxide) stimulated only social sniffing, but reduced rearing or walking. Further benzodiazepines (triazolam and lorazepam) reduced defenses, escapes and attacks only at doses that suppressed most of the remaining activities as well. Thus, the nine benzodiazepines tested exhibited different profiles of action in the present study. Alprazolam, oxazepam and diazepam appeared least sedative, while triazolam and lorazepam were most sedative.

Benzodiazepines and the mammalian retina. III. Postnatal development

Iontophoretic effects of the benzodiazepine receptor agonist, flurazepam, and antagonist, flumazepil (RO-15-1788) on the retinal ganglion cells of kittens (7–9 weeks of age) have been compared with those of adult cats (18–22 weeks of age). In the adult retina, flurazepam decreased and flumazepil increased the visually evoked and spontaneous firing of ON-, but produced no effects on the response of OFF-retinal ganglion cells. However, in the kittens retina, in which ON-cells' selectivity to GABA is not fully developed 3, both the visually evoked and spontaneous activities of ON- and OFF-cells were inhibited by flurazepam and enhanced by flumazepil. This suggests that postnatal development of benzodiazepine action parallels that of GABA action at the retinal ganglion cells in the cat retina.

Actions of benzodiazepines on the housefly 2. Penetration and internal distribution following topical application on the dorsal thoracic surface

1. 1. The rates of integument penetration of benzodiazepines (BZDs) and their levels inside the body were determined in houseflies treated topically at a dose of 10 μg/fly. 2. 2. Concentrations of various BZDs in hemolymph were relatively associated with their biological activities against the housefly. 3. 3. Concentrations of BZDs detected inside the body were higher than the concentrations required to inhibit specific binding of tritiated BZDs to thorax-abdomen homogenates. 4. 4. Biological effects of BZDs appear to be secondary effects even if they are caused by an action on the thorax-abdomen binding sites.

Actions of benzodiazepines on the housefly. 3. In vitro binding of [ 3H]Ro5-4864 responding to GABA receptor ligands

1. 1. Characteristics of benzodiazepine (BZD) binding sites in the housefly are investigated using [ 3H]Ro5-4864, a ligand for the mammalian peripheral BZD receptor. 2. 2. [ 3H]Ro5-4864 specifically binds with low-nanomolar affinity to freshly prepared homogenates from the thorax plus abdomen. 3. 3. As to structural requirements for binding, housefly BZD binding sites resemble the peripheral BZD receptor of mammals. 4. 4. [ 3H]Ro5-4864 binding is modified by several compounds acting on the mammalian GABA receptor, suggesting that housefly BZD binding sites possess functional properties analogous to those of the GABA receptor-coupled, central BZD receptor of mammals. 5. 5. Such modifications have not been observed in [ 3H]diazepam binding to freeze-thawed preparations, suggesting that the insect GABAergic system is more labile than the mammalian counterpart.

Stress-Related Effects of Ethanol in Mammals

The interactions of ethanol and stress are complex; some experimental models of stress cause increases in voluntary consumption of ethanol by animals, but others do not. Conversely, low doses relieve the effects of some stressors but not of others, while high doses of ethanol give rise to stress, and tolerances can develop to both effects. Recent studies of the molecular mechanisms of action of ethanol and benzodiazepines have not yet revealed fully the basis of the anti-stress effects of either. Clinical and epidemiological studies suggest that both the stress-relieving and -inducing actions of ethanol are important in human disease.

The anxiolytic action of benzodiazepines is not present in handling-habituated rats

The acquisition of two-way shuttle avoidance (40 first trials) was used to test the anxiolytic activity of diazepam (2 and 4 mg/kg) and alprazolam (1.25 mg/kg) vs. vehicle, IP, in rats. These rats had received three different previous treatments: acute, acute with previous handling habituation for 15 days, and handling habituation combined with chronic treatment for 15 days. Results of the acute treatment showed a comparable anxiolytic action of diazepam and alprazolam, reflected by an improvement in avoidance acquisition. After handling habituation, no effect on shuttle box acquisition was obtained in rats acutely treated with diazepam, whereas the alprazolam-treated group showed a significantly impaired avoidance performance. When handling habituation was combined with chronic benzodiazepine treatment, the drugs' anxiolytic action persisted although there was a complete disappearance of their sedative effects. These behavioral results are discussed in relation to the emotional changes induced by the procedures of handling. They are tentatively linked with possible changes in the functionality of GABA neurotransmission, possibly at the level of the GABA-benzodiazepine receptor which some studies have found associated to handling habituation.

Structural dependency of the inhibitory action of benzodiazepines and related compounds on the mitochondrial Na +-Ca 2+ exchanger

Na +-induced Ca 2+-release from guinea-pig heart mitochondria is inhibited by benzodiazepines such as clonazepam (compound II, ic 50: 12 μM). The capacity of various related compounds to inhibit the rapid Ca 2+-efflux induced by 20 mM Na + was examined. The potency of inhibition was found to depend on several factors, such as a 2'-halogen substitution and the preence of a secondary amido group. Very effective inhibitors were identified among the triazolo derivatives of benzodiazepines or obtained by replacing the diazepine ring by an oxazepine or a thiazepine. Some of these favourable structural modifications were compounded in the benzothiazepine 7-chloro-3,5-dihydro-5-phenyl-1 H- 4,1-benzothiazepine-2-on (compound XVI), which proved to be about 20 times more potent than the related compounds clonazepam and diltiazem. Compound XVI, which has an ic 50 in the submumolar range, is the most potent selective inhibitor of the mitochondrial exchanger so far reported. The structural requirements found for the inhibition of the mitochondrial Na +-Ca 2+ exchanger were quite distinct from those described for the binding of benzodiazepines to their central-type and peripheral- type sites.

The lateral vestibular nucleus is a site for the depressant action of benzodiazepines on the crossed extensor reflex

The effects of diazepam microinjected into the subcerebellar nuclei, the lateral vestibular nucleus (LVN), the red nucleus and the substantia nigra were investigated using the crossed extensor reflex (CER) model in chloralose-anesthetized rats. Microinjections of diazepam at doses of 1 and 25 ng/animal into the left LVN, ipsilateral to the testing muscle, produced a dose-related CER depression, while injections of diazepam at a dose of up to 100 ng/animal into the right LVN and into other regions tested produced little effect. The CER depression produced by diazepam could be clearly reversed by a subsequent intravenous administration of Ro 15-1788, a benzodiazepine antagonist. Electrical lesions of the left LVN decreased the amplitude of CER in otherwise untreated rats. Intravenously administered diazepam at a dose of 0.01 or 0.05 mg/kg decreased spontaneous firing of LVN neurons. Iontophoretically applied GABA or flurazepam, a water-soluble benzodiazepine, decreased the spontaneous firing of LVN neurons. Depressant actions on neuronal activity in the LVN produced by both diazepam and flurazepam were clearly antagonized by intravenously administered Ro 15-1788, while it failed to reverse the depression produced by GABA. These findings indicate that the LVN is a major site of the CER depressant action of benzodiazepines and a possible mechanism of action is discussed.

Chronic administration of diazepam downregulates adenosine receptors in the rat brain.

Following chronic administration (10 or 20 days) of diazepam (5 mg/kg/day, subcutaneous pellets) or RO 15-1788 (5 mg/kg/day, intraperitoneally), adenosine and benzodiazepine receptors in different rat brain areas were assessed by radioligand binding studies using [3H]R-PIA for A1 receptors, [3H]NECA and [3H]R-PIA for A2 receptors and [3H]FNZ for benzodiazepine receptors. Chronic administration of diazepam for 10, but not for 20 days, decreased A2 receptors in the striatum by 46% (p less than 0.05) and A1 receptors in the hippocampus by 13% (p less than 0.05). Administration of diazepam for 10 days and 20 days failed to alter [3H]FNZ binding in all brain areas studied. However, 20 days of diazepam administration decreased the magnitude of GABA enhancement of [3H]FNZ binding in the cortex by 25% (p less than 0.05). In contrast, chronic administration of RO 15-1788 failed to alter [3H]R-PIA, [3H]NECA and [3H]FNZ binding in all brain areas. These results suggest that adenosine receptors may play a role in the CNS actions of benzodiazepines.

Benzodiazepine-induced hyperphagia: a test of the hunger-mimetic model.

The 'hunger-mimetic' model is a prominent explanatory account of benzodiazepine-induced hyperphagia. A salient feature of food deprivation (hunger) in laboratory animals is 'finicky' eating, or an enhanced reactivity to the palatability of food. If the hunger-mimetic model is correct, a similar finicky pattern of increased eating should be observed both in hungry (food-deprived) rats and in benzodiazepine-treated, hyperphagic rats. Two groups of rats were matched on measures of ad lib baseline intake of both a highly palatable food (sweetened condensed milk) and a food low in palatability (milk adulterated with 37.5 mg% quinine). Subsequently one group was placed on a moderate food deprivation schedule while the second group was maintained on ad lib food but was injected (IP) with 5 mg/kg chlordiazepoxide (CDP) 30 min prior to food presentation tests. Single-bottle tests indicated that while the food deprived animals exhibited a greater augmentation of eating when given the high-palatability food, the animals pretreated with CDP exhibited an indiscriminate elevation of eating across both foods. Similarly, on two-bottle choice tests the food-deprived rats exhibited an enhanced preference for the high-palatability food, whereas the CDP-treated animals did not change from baseline food preference. These results fail to support the hunger-mimetic model of benzodiazepine-induced hyperphagia. Alternative models based on a perseverative, disinhibitory action of benzodiazepines are discussed.