The Effects of Meprobamate on Perception

A number of recent studies of apparent movement have been designed with Kohler and Wallach's satiation theory or some similar theory of cortical processes as their basis. The work has been reviewed in some detail (4) and we shall concern ourselves here only with those studies that are both less equivocal and directly relevant to the present study.

The Effects of Meprobamate on Time Perception

The change in time perception produced by the administration of drugs has received a fair amount of attention. Frankenhaeuser (6) has reviewed the work on the effects of hashish and mescaline intoxication on the estimation of time. She concludes that “there seems to be some agreement in that time seems longer than usual in passing but shorter when regarded in retrospect”. But this work dealt with introspective reports regarding the passage of time rather than with quantitative changes and will not be discussed further here.

The Effects of Meprobamate on Perception

A review of the history and experimental findings relating to the spiral after-effect can be found elsewhere (5) and will not be repeated here. The reliability of the after-effect, the major role played by the cortex in its production and the evidence already obtained that the after-effect is modifiable in accordance with Eysenck's drug action hypothesis (2) indicated it to be a promising test in the investigation into the effects of meprobamate on perception.

The Effects of Meprobamate on Perception

There is no discussion in Stevens' (16) or Osgood's (14) textbooks of experimental psychology of the contribution of cortical functions to the production of visual after-images. Woodworth (19) presents a theory of after-images involving the cortex in the first edition of his book. It is not repeated in the second edition. There is, however, a large number of reported studies indicating the importance of cortical functions in the production of after-images (e.g. 1, 3, 6, 9, 11, 12, 13, 15, 17). In view of these studies it was decided to use the afterimage in a further attempt to verify or disprove the drug action hypothesis advanced by Eysenck in a previous paper (2). This hypothesis stated that stimulant drugs increased excitatory potential and decreased inhibitory potential, while depressant drugs decreased excitatory potential and increased inhibitory potential.

Evaluation of CNS activities of aerial parts of Cynodon dactylon Pers. in mice

The dried extracts of aerial parts of Cynodon dactylon Pers. (Graminae) were evaluated for CNS activities in mice. The ethanol extract of aerial parts of C. dactylon (EECD) was found to cause significant depression in general behavioral profiles in mice. EECD significantly potentiated the sleeping time in mice induced by standard hypnotics viz. pentobarbitone sodium, diazepam, and meprobamate in a dose dependant manner. EECD showed significant analgesic properties as evidenced by the significant reduction in the number of writhes and stretches induced in mice by 1.2% acetic acid solution. It also potentiated analgesia induced by morphine and pethidine in mice. EECD inhibited the onset and the incidence of convulsion in a dose dependent manner against pentylenetetrazole (PTZ)-induced convulsion. The present study indicates that EECD has significant CNS depressant activities.

Stimulant and relaxant drugs combined with stimulant and relaxant information: a study of active placebo

RATIONALE

The active placebo hypothesis states that placebo effects are potentiated when an active drug is administered.

OBJECTIVE

This hypothesis was tested in an experiment where information about the effect of a drug was combined with administration of an active drug or placebo.

METHODS

Information that a drug acted as a relaxant, a stimulant, or as a placebo was crossed with oral administration of a relaxant drug (700 mg carisoprodol), a stimulant drug (400 mg caffeine) or placebo (lactose) in healthy volunteers ( n=94). Dependent variables were subjective and physiological measures of arousal, as well as serum carisoprodol and caffeine levels. Data were collected from 15 to 280 min after administration of drug or placebo.

RESULTS

Caffeine increased alertness, systolic and diastolic blood pressure, startle blink reflexes, and skin conductance responses. Subjects were calmer after carisoprodol, and heart rate was increased. There was a positive correlation between increased arousal and carisoprodol levels when stimulant information had been provided. However, this was only seen when carisoprodol levels were very low. There was no evidence that caffeine modulated the placebo response.

CONCLUSIONS

Active placebo responses were seen only transiently when carisoprodol levels were low, and only in the subjective arousal data. Caffeine did not support active placebo responses. The overall findings did not favour the active placebo hypothesis.

Comparative abuse liability and pharmacological effects of meprobamate, triazolam, and butabarbital

Implementation of regulations to control the prescribing of benzodiazepines in New York State in 1989 resulted in a 55% decrease in benzodiazepine prescribing, with a concomitant increase in the rates of prescribing older sedative-hypnotic compounds such as butabarbital (30% increase) and meprobamate (125% increase). In a double-blind, crossover, placebo-controlled study, we compared the behavioral and pharmacological effects of triazolam, meprobamate, and butabarbital in 14 recreational drug users. Placebo and three doses each of triazolam, meprobamate, and butabarbital were administered to each subject in a random order. Objective tests (motor performance, concentration) and subjective response questionnaires measured drug effects. Triazolam, meprobamate, and butabarbital showed comparable negative dose-response slopes on the objective measures. On the basis of these objective data, equivalent doses for the three compounds were determined to be as follows: 0.5 mg triazolam = 2,400 mg meprobamate = 400 mg butabarbital. Subjective effects data on equivalent doses show that butabarbital produced the highest peak score on Cole/ARCI Abuse Potential, ARCI Pentobarbital Chlorpromazine Alcohol Group (PCAG), and "drug strength" scales. Triazolam and butabarbital produced equivalent results on ARCI Morphine Benzedrine Group (MBG), Cole/ARCI Euphoria, and "drug liking" scales. Meprobamate was indistinguishable from placebo on euphoria and abuse potential scales. Behavioral economics analysis indicated a price crossover point two times higher for butabarbital (400 mg) than for any other drug condition. These data indicate a comparative abuse liability of butabarbital > triazolam > or = meprobamate, suggesting that the prescribing restrictions on benzodiazepines had little net benefit on abuse risk in the population and may have increased the risk of overdose morbidity and mortality.

Action of meprobamate on spinal monosynaptic reflexes and on inhibitory pathways

Meprobamate was administered intravenously to spinal cats, in cumulative doses of 30 to 40 mg./kg. each. Initial doses may have a variable action on monosynaptic reflexes. At times some reflexes are depressed, while others are enhanced or unaffected. When dose levels of 100 mg./kg. or higher are reached, monosynaptic reflexes, both flexor and extensor, are depressed. Monosynaptic reflexes can be strongly depressed by meprobamate, their input-output relations often remaining unchanged. In such cases there is thus no change in the spatial summation requirements of those motoneurons remaining in the excitable zone. Inhibitory pathways, both direct and disynaptic, are highly resistant to the action of meprobamate. The drug does not distinguish between the direct and disynaptic pathways. It is suggested that meprobamate acts as a general depressant of excitatory synaptic transmission.

Carisoprodol, meprobamate, and driving impairment

This paper considers the pharmacology of the centrally acting muscle relaxant carisoprodol, and its metabolite meprobamate, which is also administered as an anxiolytic in its own right. Literature implicating these drugs in impaired driving is also reviewed. A series of 104 incidents in which these drugs were detected in the blood of drivers involved in accidents or arrested for impaired driving was considered, with respect to the analytical toxicology results, patterns of drug use in these subjects, the driving behaviors exhibited, and the symptoms observed in the drivers. Symptomatology and driving impairment were consistent with other CNS depressants, most notably alcohol. Reported driving behaviors included erratic lane travel, weaving, driving slowly, swerving, stopping in traffic, and hitting parked cars and other stationary objects. Drivers on contact by the police displayed poor balance and coordination, horizontal gaze nystagmus, bloodshot eyes, unsteadiness, slurred speech, slow responses, tendency to doze off or fall asleep, difficulty standing, walking or exiting their vehicles, and disorientation. Many of these cases had alcohol or other centrally acting drugs present also, making difficult the attribution of the documented impairment specifically to carisoprodol and meprobamate. In 21 cases, however, no other drugs were detected, and similar symptoms were present. Impairment appeared to be possible at any concentration of these two drugs; however, the most severe driving impairment and most overt symptoms of intoxication were noted when the combined concentration exceeded 10 mg/L, a level still within the normal therapeutic range.

Naloxone potentiates anxiolytic-like actions of diazepam, pentobarbital and meprobamate but not those of Ro19-8022 in the rat

The elevated plus-maze test was used to determine if the opiate antagonist naloxone could potentiate the anxiolytic-like effects of the benzodiazepine diazepam, the barbiturate pentobarbital, the propanediol carbamate meprobamate and the partial benzodiazepine receptor agonist [R]-1-[(10-chloro-4-oxo-3-phenyl-4H-benzo[a]quinolizin-1-yl) carbonyl]-2-pyrrolidine-methanol (Ro19-8022) in the rat. A subeffective dose of each of these compounds was combined with naloxone, 10 mg/kg. Naloxone had no effect by itself, but potentiated all drugs except Ro19-8022. The proportion of entries on the open arm increased while the total number of arms entries was not modified. These results coincide with and extend data previously obtained in the mouse. One possible explanation for naloxone's effect could be that it blocks opioid inhibition of GABAergic (gamma-aminobutyric acid) neurons thereby enhancing the effects of benzodiazepines. Another possibility is that naloxone blocks opioid effects on adenosinergic systems.

Anxiolytic-like effects of meprobamate. Interactions with an opiate antagonist in Swiss and BALB/c mice

Naloxone has previously been shown to block the effects of benzodiazepines in the Swiss but not in the BALB/c strain. We have also reported that naloxone potentiates subeffective doses of benzodiazepines in Swiss mice. In the present studies we first determined whether naloxone could block anxiolytic-like effects of meprobamate in Swiss and BALB/c mice. Then we evaluated if subeffective doses of meprobamate could be potentiated in Swiss as well as in BALB/c mice. The elevated plus-maze test and the light/dark choice procedure were used. The lowest dose of meprobamate with anxiolytic-like effects was 60 mg/kg in the BALB/c mice. This dose was effective in both the plus-maze and in the light/dark choice procedure. In Swiss mice the same dose was effective in the plus-maze, whereas 120 mg/kg was required in the light/dark choice procedure. When an effective dose of meprobamate was combined with naloxone, 10 mg/kg, no blockade of anxiolytic-like effects was obtained in any strain in any procedure. To the contrary, when a subeffective dose of meprobamate was combined with naloxone, 10 mg/kg, an anxiolytic-like effect was obtained in both strains in both procedures. The present series of experiment shows that the ability of naloxone to block anxiolytic-like drug effects do not apply to meprobamate. However, the naloxone-induced potentiation of subeffective doses previously observed after treatment with benzodiazepines or buspirone was present also after treatment with meprobamate. Moreover, although blockade of anxiolytic-like drug effects with naloxone has not been observed in BALB/c mice, potentiation was as evident in that strain as in the Swiss. This suggests that the mechanisms behind naloxone's blockade of anxiolytic-like effects are independent from those behind its potentiation of such effects.

Recurrent conditioning in the cat spinal cord. Differential effect of meprobamate on recurrent facilitation and inhibition

The action of cumulative doses of meprobamate on antidromic conditioning has been studied in spinal cats. Recurrent facilitation is greatly reduced or completely abolished by total doses ranging from 210 to 400 mg./kg. The depth of recurrent inhibition is not affected in a consistent manner by meprobamate, but the duration of inhibition is markedly increased in all experiments. This differential action of meprobamate on facilitation and inhibition can be utilized to study conditioning effects consisting of combined inhibition and facilitation. If conditioning starts with an inhibitory phase, variable in duration, followed by facilitation, meprobamate depresses the facilitation and reveals an extended inhibitory curve. Facilitation, however, is not always accompanied by inhibition, since in some cases facilitation is depressed and no inhibition is uncovered. The results of these experiments are discussed in relation to the various types of conditioning that have been produced by antidromic stimulation.

Effect of meprobamate on the multiplication of Brucella abortus in monocytes

Peritoneal mononuclear phagocytes (monocytes) obtained from guinea pigs that had been treated with meprobamate do not support, in vitro, the intracellular growth of smooth Brucella abortus that is characteristic of monocytes from untreated animals. This modification of intracellular events appears to be due to an indirect action of the drug, since meprobamate does not produce any effects following direct exposure of monocytes or bacteria to the drug in vitro. Furthermore, the brucellacidal activity of serum from animals exposed to meprobamate is not increased. An interaction between monocytes and a component in the serum of animals exposed to meprobamate is required for the altered intracellular events.

Selectivity in the generalization profile in baboons trained to discriminate lorazepam: benzodiazepines, barbiturates and other sedative/anxiolytics

The discriminative stimulus effects of benzodiazepines often have been indistinguishable from those of barbiturates or other sedative/anxiolytics. However, baboons and rats trained to discriminate lorazepam did not reliably generalize to pentobarbital in previous studies, although animals comparably trained to discriminate pentobarbital reliably generalized to lorazepam. The present study investigated the generalization profile for a variety of anxiolytic, sedative and other drugs in baboons trained to discriminate oral lorazepam (1.8 mg/kg). Triazolam, alprazolam, diazepam, midazolam, bromazepam, temazepam and nordiazepam occasioned >80% of total responses on the lorazepam-paired lever, in that order of potency, 60 min after oral dosing; chlordiazepoxide did so in three of five baboons. However, barbiturates (amobarbital, hexobarbital, methohexital, pentobarbital, phenobarbital, secobarbital) and methypryIon occasioned lorazepam-appropriate responding in only one or two baboons. Testing barbiturates at different pretreatment times (amobarbital, hexobarbital, pentobarbital or secobarbital) or by an i.m. route of administration (methohexital, pentobarbital) did not produce an increase in generalization. Neither other classic sedatives/anxiolytics (chloral hydrate, clomethiazole, ethanol, methaqualone, meprobamate, triclofos), nor anticonvulsants (phenytoin, valproic acid), nor drugs from other pharmacological classes shared discriminative-stimulus effects with lorazepam. These results, together with those from previous studies in which lorazepam or another benzodiazepine served as the training stimulus, indicate that lorazepam training results in a more selective generalization profile with respect to sedative/anxiolytic drugs than does training with other benzodiazepines.

Felbamate and meprobamate: a comparison of their anticonvulsant properties

The anticonvulsant effect of felbamate and meprobamate were compared in a series of models for seizure activity and regarding their neurotoxic action. In the MES test, felbamate was active below neurotoxic doses. Meprobamate had an ED50 in the range of neurotoxic doses. The s.c. PTZ test was influenced by meprobamate in a fairly low dosage (ED50 66 mg/kg), but for felbamate no clearly dose-related effect could be shown up to 150 mg/kg. Reflex epilepsy in gerbils was stronger suppressed by meprobamate (ED50 34 mg/kg) than by felbamate (ED50 63 mg/kg). In amygdala kindled rats, meprobamate proved to be the most active compound, both regarding treatment of fully kindled rats, development of kindling and independent discharges from a mirror focus (secondary epileptogenesis), which were fully suppressed by oral treatment with 80 mg/kg for 30 days. Both drugs were weakly effective in a model for absence epilepsy in rats. The unexpectedly high activity of meprobamate justifies a second look at the anticonvulsant properties of the drug, especially since it was extensively used as an anxiolytic drug in the past with few obvious serious side effects.

Barbiturate-like actions of the propanediol dicarbamates felbamate and meprobamate

Felbamate and meprobamate are structurally related propanediol dicarbamates that possess distinct pharmacological profiles. Felbamate is a minimally sedative, broad-spectrum anticonvulsant, whereas meprobamate is a strong sedative-anxiolytic agent. Previously, we reported that felbamate potentiates gamma-aminobutyric acid(A) (GABA(A)) receptor Cl- currents and inhibits N-methyl-D-aspartate (NMDA) receptor currents. Here we further characterized the interaction of the two dicarbamates with GABA(A) receptors to determine the basis for their pharmacological differences. In whole-cell voltage-clamp recordings from cultured rat hippocampal neurons, meprobamate enhanced GABA-evoked responses in a concentration-dependent manner and, at high concentrations (>1 mM), exhibited a separate channel-blocking effect that limited the magnitude of GABA(A) receptor potentiation. At equivalent concentrations, meprobamate produced substantially greater potentiation than did felbamate. Furthermore, meprobamate (but not felbamate), in the absence of GABA, directly activated Cl- currents that could be attenuated by the GABA(A) receptor antagonists bicuculline and picrotoxin. The mean deactivation time constant of whole-cell currents evoked by 10 mM meprobamate (110 ms) or 1 and 3 microM GABA (180 ms) were faster than the deactivation time constant of 10 mM meprobamate (490 ms) or 3 mM felbamate (470 ms) in the presence of GABA. Meprobamate and felbamate prolonged the mean burst duration of GABA-activated unitary currents in excised outside-out membrane patches. In addition, at high (supratherapeutic) concentrations, meprobamate blocked NMDA-activated currents. We conclude that felbamate and meprobamate have barbiturate-like modulatory actions on GABA(A) receptors, but meprobamate has greater activity and, unlike felbamate, is able to directly activate the receptor.

[The effect of phytin, benzonal and their combination administered prophylactically on the pharmacodynamics of drugs metabolized in the liver in hypokinesia]

Hexenal, meprobamate, amidopyrine and ethylmorphine produced a significantly marked effect in animals under hypokinesia as compared with normal rats. When phytin, benzonal and their combination were used for preventive purposes, impaired pharmacodynamics of the tested drugs metabolizing in the liver disappeared. The investigations demonstrated that the preventive use of phytin in combination with benzonal is the most optimal in correcting the impairments of drug pharmacodynamics in hypokinesia.

[Effects of tranquilizing agents on bioelectrical activity of the rat brain]

The action of diazepam, meprobamate, trioxazine and mexidol on bioelectrical activity of sensorimotor cortex and dorsal hippocamp of the left and right hemisphere of the brain in conscious rat in free behavior has been studied. All the drugs produced a decline in the frequency of the dominant peak of EEG power spectra. Diazepam and meprobamate increased beta-activity. It is concluded that the decreased frequency may be due to an anxiolytic effect of the tranquilizers, whereas high beta-activity is related to muscle relaxant effect of some drugs.

Use of antianxiety drugs as countermeasures in the detection of guilty knowledge

To evaluate whether antianxiety drugs enable guilty subjects to appear innocent on polygraph tests, we compared the effects of diazepam, meprobamate, and propranolol on the outcome of a guilty knowledge test (GKT). Seventy-five undergraduate students were evenly divided among one innocent and four guilty groups. Subjects in each of the guilty groups received either one of the drugs or a placebo prior to the administration of the GKT and after viewing a videotape that depicted a burglary as seen from the perspective of the burglar. The results showed that drug status had no influence on the outcome of the GKT. Innocent subjects who coincidentally obtained high scores on a recognition memory test covering details of the mock crime tended to obtain higher guilt scores on the GKT.

Effects of olfactory stimulation on the sleep time induced by pentobarbital administration in mice

The effect on the pentobarbital sleep time by olfactory stimulation with various odorants was investigated using mice to appraise the physiological or psychological significance of olfactory information. The sleep time was determined as the time elapsed between intraperitoneal pentobarbital administration and the first time that the animal was able to spontaneously right itself. The sleep time was affected by inhalation of some odorants compared to pure air controls, but not by others. The sleep time was prolonged by terpinyl acetate and phenethyl alcohol, and was shortened by lemon oil and jasmin oil. However, neither potentiation nor attenuation of pentobarbital action by odorant inhalation was observed when using anosmic mice produced by intranasal zinc sulphate treatment. In conclusion, olfactory stimulation associated with odorant inhalation influences the pentobarbital sleep time, suggesting that olfactory information may have a more potent influence on the physiological and psychological status than has previously been thought.

Effects of anxiolytic drugs on escape behavior induced by dorsal central gray stimulation in rats

Each animal was chronically implanted with bipolar electrodes in dorsal central gray matter (DCG) and was trained to press a lever to decrease the DCG-stimulation current. Chlordiazepoxide (5-20 mg/kg, PO), diazepam (2-10 mg/kg, PO) and bromazepam (1-5 mg/kg, PO) produced dose-dependent increases in the DCG-stimulation threshold 1-4 h after administration without affecting motor performance. Meprobamate (200 mg/kg, PO) and pentobarbital (10 mg/kg, PO) also slightly increased the stimulation threshold. Their potency was in the order of bromazepam greater than diazepam greater than chlordiazepoxide greater than pentobarbital greater than meprobamate. The increase in the threshold induced by diazepam (10 mg/kg, PO) was inhibited by the GABA antagonists, bicuculline (1 mg/kg, IP) and picrotoxin (0.1 mg/kg, IP). These results suggest that decreased susceptibility to brain stimulation is involved in suppressing effects of anxiolytic drugs on the escape behavior, and also that the antiaversive action of benzodiazepines may be related to a GABAergic mechanism.

[Characteristics of drug pharmacodynamics in irradiated rats]

A whole-body exposure of rats to 8 Gy radiation is ineffective in 3 days, and in 6 days, it prolongs considerably the effect and increases the pharmacological activity of hexenal, meprobamate, ethylmorphine, and amidopyrine, inhibits the activity of amidopyrine demethylase, aniline hydroxylase, NADPH-cytochrome c reductase, and reduces the content of protein, cytochromes P-450 and b5 in a microsomal liver fraction.

Interactive effects of acute ethanol administration on meprobamate levels in blood and brain of rabbit and rat

In the simultaneous administration of meprobamate and ethanol to rabbits, the blood meprobamate concentration (BMC) increased greatly when the maximum blood ethanol concentration (BECmax) exceeded 1.0 mg/ml. Thus, we subjected the rabbits to continuous infusion of ethanol so as to make the blood ethanol concentration (BEC) constant and administered meprobamate by intravenous injection. Elimination of meprobamate became slow at about the BEC of 0.5 mg/ml and the degree reached almost maximum around the BEC of 1.0 mg/ml. The elimination rate did not change any more even when the BEC was raised higher. In the study conducted to elucidate the relationship between the BMC and brain meprobamate concentration (BrMC) using rats, it was found that meprobamate would show similar movements and its level would rise extremely by an acute administration of ethanol. It was indicated that the effect of ethanol on reinforcement of meprobamate activity would appear strongly by potentiation effect.

A new sensitive method which unlike the Vogel test detects the anxiolytic effect of tofisopam

A new, more sensitive than previously used anxiolytic test is described. The test consists in measuring of inhibition by punishment of drinking water necessary to swallow dry food by very hungry rats. This test reveals the anxiolytic properties of tofisopam, a clinically effective benzodiazepine anxiolytic, and of very low doses of chlordiazepoxide, both ineffective in the Vogel test, as well as anxiolytic properties of high doses of chlordiazepoxide and other anxiolytics, and confirms the lack of anxiolytic effects of major tranquilizers. The results suggest that chlordiazepoxide (and possibly other benzodiazepines) acts on two subgroups of benzodiazepine receptors, named BRI (high affinity) and BR2 (low affinity), while tofisopam acts specifically on BRI receptors. The new test is proposed as a tool for a search for drugs specifically acting on high affinity benzodiazepine BRI receptors.

Lorazepam and meprobamate dose effects in humans: behavioral effects and abuse liability

On a residential research ward, the acute effects of placebo, lorazepam (LZ) (1.5-9.0 mg) and meprobamate (MEP) (600-3600 mg) were examined using a within-subject double-blind Latin Square design in nine male subjects with histories of drug abuse. Drug effects were assessed with objective performance tasks, subject estimates of performance, staff ratings of drug effects and subject ratings of drug effects, sleep, mood, drug liking and monetary street value. Generally, both LZ and MEP produced comparable dose-related effects; LZ had a more rapid onset of action and on several measures showed a more shallow dose-response curve than MEP. With LZ, but not MEP, subjects under-estimated the degree to which their performance was impaired and under-rated drug effects as compared to analogous staff ratings. Both drugs produced sedation-like subject ratings of mood and sleep but generally did not produce tranquilization-like ratings. MEP produced subject ratings of drug liking and monetary street value which were equal to or in some cases greater than those of LZ. Relative potency estimations showed that LZ was 510 to 783 times more potent than MEP in producing performance impairment but was only 370 times more potent than MEP in producing subject ratings of drug liking. Overall, these data indicate that the likelihood of abuse of MEP is at least equal to if not greater than that of LZ although LZ may have a greater likelihood of producing adverse behavioral effects such as a performance impairment and under-estimates of the degree of impairment. These data in conjunction with previous results from this laboratory show that the behavioral effects of benzodiazepines can be differentiated from those of other types of sedative/anxiolytics and that MEP displays characteristics of a barbiturate-like profile of action.

Effects of meprobamate on plasma lipids, lipoproteins, and experimental atherosclerosis

The effects of the tranquilizer meprobamate (Equanil) on plasma lipids, lipoproteins, and atherogenesis in cockerels fed an atherogenic diet have been investigated. Gross gradings (visually assessed blindly) of the atherosclerosis of the thoracic and abdominal aortas of the meprobamate-treated plain mash were significantly more severe than the untreated plain mash controls. There were no significant differences in the gradings of thoracic and abdominal aortic lesions in the atherogenic groups, whether treated with meprobamate or not. Microscopic examination of the coronary arteries of birds on the atherogenic regimen treated with meprobamate revealed that these birds had atherosclerosis similar to the atherogenic diet group.

Influence of meprobamate and phenobarbital upon local cerebral glucose utilization: parallelism with effects of the anxiolytic diazepam

The [1-14C]2-deoxyglucose technique was employed for an evaluation of the regional pattern of alteration of brain metabolism induced by the anxiolytics phenobarbital (which is described in small doses as anxiolytic agent) and meprobamate. Their effects were compared with those produced by the anxiolytic benzodiazepine diazepam which we have described in a previous study. In low doses, both meprobamate (30 mg/kg i.v.) and phenobarbital (5 mg/kg i.v.) elicited a regional pattern of changes similar to those seen with diazepam. Thus, the local cerebral glucose utilization (LCGU) of the mammillary nuclei, the lateral and ventral thalamic nuclei, the anterior thalamic nuclei and the geniculate nuclei was significantly decreased. A doubling of the dose (meprobamate 60 mg/kg i.v.; phenobarbital 10 mg/kg i.v.), however, resulted in a decrement in LCGU in virtually every brain region examined. Further, at this higher dose, phenobarbital significantly increased LCGU in the interpeduncular nucleus. These data demonstrate that both meprobamate and phenobarbital, in moderate doses induce selective alterations in LCGU in particular brain regions with the pattern of changes similar to that induced by diazepam. The structures affected may be of general importance for the expression of the anxiolytic actions of each of those classes of minor tranquilizers in clinical use.

Classification of psychotropic drugs by rat EEG analysis: the anxiolytic profile in comparison to the antidepressant and neuroleptic profile

Electroencephalograms were recorded from the parietal and frontal cortex of freely moving rats held in constant vigilance by placing them in a slowly turning drum. The effects of 5 clinically effective anxiolytics, buspirone, meprobamate, phenobarbital, chlordiazepoxide and diazepam, were studied after intraperitoneal injection of different doses. After on-line fast Fourier transformation of the EEG signal, the drug effects were quantified by an Analysis of Variance. This resulted in a t profile for each drug dosage. Averaging the t profiles of all dosages of a drug results in a 'drug profile'. Averaging the drug profiles of the 5 anxiolytic drugs tested results in an 'anxiolytic profile'. This profile is characterized by a power decrease from 8 to 11 Hz and above 70 Hz and a power increase from 20 to 60 Hz. The anxiolytic profile is compared with the formerly defined antidepressant and neuroleptic profiles and can be clearly distinguished from the latter two.

Evaluation of two anticonvulsant amino-pyridazine derivatives in the conflict test in rats

Two amino-phenyl-pyridazine derivatives, SR 41378 and CM 40907, have been reported to antagonize seizures in mice, rats and Papio papio baboons with comparable potencies. Structurally, SR 41378 differs from CM 40907 by an additional chlorine in position 6 of the phenyl ring. In the present study the activity of these two compounds in the operant approach-avoidance conflict test in rats was examined and compared with that of diazepam, pentobarbital, meprobamate and valproate. SR 41378 increased punished responding, a measure of anticonflict activity (ED50 = 5.2 mg/kg), and decreased nonpunished responding, a measure of sedative activity, with a threshold active dose of 20 mg/kg i.p. The overall potency of SR 41378 was comparable to that of pentobarbital. CM 40907 (10-40 mg/kg i.p.) did not affect punished responding and decreased nonpunished responding at the dose of 40 mg/kg i.p. The duration of the anticonflict activity of SR 41378 increased with the dose and lasted over 4 h at the 20-mg/kg i.p. dose. At this dose, sedation lasted 1 h. An increase in anticonflict potency and tolerance to sedation were observed after a 5-day treatment with SR 41378 (20 mg/kg i.p.). The anticonflict and sedative activities of SR 41378 were not antagonized by Ro 15-1788 or CGS 8216. In vitro SR 41378 did not interact with benzodiazepine receptor sites. In conclusion, although CM 40907 and SR 41378 exhibit similar anticonvulsant activities, the present study reveals a major pharmacological difference between the two compounds because SR 41378 also possesses anticonflict properties.

The staircase test: some evidence of nonspecificity for anxiolytics

In the staircase test, a naive mouse is placed in a Plexiglas chamber containing a five-step staircase, and the number of rearings and steps climbed are recorded for 3 min. A claim for drug-class specificity has been made because conventional anxiolytics reduced rearings at doses that did not reduce steps climbed, while non-anxiolytics affected both measures in parallel. In the present study chlordiazepoxide, meprobamate, and ethanol registered the expected true positive effect by reducing rearings at doses that did not reduce steps climbed. Nicotine, which has some clinical anxiolytic action, registered a small true positive. The benzodiazepine anxiolytic alprazolam reduced both measures, a false negative, although it reduced rearings more than steps climbed. The putative novel anxiolytics CGS 9896, ketanserine, and tracazolate registered negatives, as did the known clinical anxiolytic buspirone. The non-anxiolytics phencyclidine and phenacetin registered true negatives, but morphine registered a clear false positive. The anxiogenics FG 7142 and pentylenetetrazol produced no significant effects. Because of the equivocal false negative for alprazolam, the clear false negative for buspirone, and the clear false positive for morphine, we concluded that the test lacks the degree of therapeutic-class specificity previously proposed but may still be useful in basic research.

A possible role of endogenous adenosine in the sedative action of meprobamate

The behavioral interaction of intraperitoneal (i.p.) injections of meprobamate with intracerebroventricular (i.c.v.) injections of adenosine or 5'-N-ethylcarboxamidoadenosine (NECA) was examined on spontaneous locomotor activity in mice. The locomotor depressant effect of meprobamate, an adenosine uptake inhibitor, was potentiated by adenosine, but not by NECA, an uptake-resistant adenosine analogue. These findings suggest that heightened endogenous adenosine levels could mediate some of the central actions of meprobamate.

Septal driving of hippocampal theta rhythm: role of gamma-aminobutyrate-benzodiazepine receptor complex in mediating effects of anxiolytics

In free-moving male rats, when the hippocampal theta rhythm is artificially driven by stimulation in the septum at frequencies between 5 and 10 Hz, the function relating frequency to the threshold current required to drive the theta rhythm has a minimum at 7.7 Hz. This minimum is eliminated by anxiolytic drugs. Dose-response curves for this effect are reported for chlordiazepoxide, diazepam and meprobamate. The effect of meprobamate was reversed by two gamma-aminobutyrateA antagonists, picrotoxin and bicuculline, which have previously been shown to be without effects of their own. The gamma-aminobutyrateB agonist, baclofen, also without effect on its own, blocked the elimination of the 7.7-Hz minimum caused by the gamma-aminobutyrateA agonist, muscimol. The beta-carboline, ethyl-beta-carboline-3-carboxylate, had mixed agonist/antagonist properties, blocking the effects of chlordiazepoxide, diazepam and muscimol (though not sodium amylobarbitone) but itself acting like a benzodiazepine. Coupled with earlier data, these findings support a role for gamma-aminobutyrate receptors in mediating the effects of anxiolytic drugs.

Auto-titration technique using intracranial self-stimulation and effects of antianxiety drugs

In order to study effects of antianxiety drugs on the threshold of intracranial self-stimulation (ICSS), the auto-titration technique was used in the two lever Skinner box. This procedure consisted of conventional ICSS except the brain stimulation current intensity was decreased after every 20 lever press for ICSS, and the animal could press the another reset lever (at any time) to reset the stimulation current intensity to the preseted level. The current intensity at which the animal pressed the reset lever (reset current) was defined as the threshold of ICSS. Since reset currents that the animals showed were very stable during this experiment, the effects of chlordiazepoxide, diazepam and meprobamate were studied. The reset current was significantly lowered by 5.0 mg/kg chlordiazepoxide, p.o., at 1 hr after administration accompanied by the significant increase of ICSS, and the reset current was significantly lowered by 20.0 mg/kg of chlordiazepoxide. On the other hand, diazepam did not lower the reset current, although a significant increase of ICSS was observed at 1.0 mg/kg, p.o. The reset current was lowered by meprobamate at 100 mg/kg, p.o., accompanied by the increase of ICSS, and a significant increase of ICSS was observed at 200 mg/kg but not accompanied by lowered reset current. From these results, increased susceptibility to the brain stimulation current may be involved in the facilitating effects of chlordiazepoxide and meprobamate on ICSS.

[Effect of diazepam, meprobamate and amizyl on the emotional reactions of the rabbit to hypothalamic stimulation]

The influence of minor tranquilizers (diazepam, meprobamate and beuactizine) on the hypothalamically elicited emotional responses was studied in chronic experiments on rabbits. The positive self-stimulation elicited from the lateral hypothalamus was facilitated by all used tranquilizers. On the first day of administration of the drugs the rate of self-stimulation increased markedly. The rate of self-stimulation was still mildly enhanced on the second day and returned to its initial value on the third day. The avoidance behaviour elicited from the medial hypothalamus changed to obvious self-stimulation after the administration of diazepam and meprobamate. The reversed behaviour preserved on the second day, while on the third day the animals resumed their avoidance behaviour. It was depressed by benactizine injection and some activation of exploratory behaviour was observed.

"Glucose effect" and rate limiting function of uroporphyrinogen synthase on porphyrin metabolism in hepatocyte culture: relationship with human acute hepatic porphyrias

The effect of glucose on drug-promoted induction of porphyrin synthesis was studied in chick embryo liver cell culture with and without the addition of exogenous delta-aminolaevulinic acid (ALA). Induction of ALA synthase was abolished by haemin or glucose. Less than 10% of porphobilinogen is converted into protoporphyrin. Protoporphyrin synthesis cannot be enhanced by high ALA concentrations. The conversion of exogenous ALA into porphyrins decreases with increasing concentrations of ALA from 0.1 to 2.0 mmol/l, whereas porphobilinogen accumulates, thus reflecting the rate limiting function of uroporphyrinogen synthase, which is not influenced by glucose. This needle-eye-like function of uroporphyrinogen synthase within the porphyrin biosynthetic chain explains the urinary increase of ALA and porphobilinogen in the acute phase of variegate and coproporphyria, similar to that in acute intermittent porphyria. The "glucose effect" was also investigated in vivo in humans in 32 courses of hereditary acute hepatic porphyrias (acute intermittent porphyria, variegate porphyria, coproporphyria and porphobilinogen synthase defect porphyria). Patients were treated with high carbohydrate intake (approximately 500 g/24 h), mainly in the form of glucose infusions. There was a resulting consistent and highly significant decrease of porphyrin biosynthesis metabolites, accompanied by clinical improvement in most of the patients.

The non-sedating anxiolytic CGS 9896 produces discriminative stimuli that may be related to an anxioselective effect

Sprague Dawley albino rats were trained to discriminate an internal stimulus associated with CGS 9896, a non-sedating pyrazoloquinoline that exhibits anxiolytic activity in animals. Classical anxiolytics (diazepam and meprobamate) and proposed anxiolytic drugs having low sedative potential (CL 218,872 and tracazolate) generalized to the CGS 9896 discriminative cue. The CGS 9896 cue appeared to be mediated by a pure anxiolytic action as previous research has shown that this compound does not produce sedation or muscle relaxation. As such, the CGS 9896 stimulus would have both research and clinical application in the investigation of selective anxiomodulation. This is the first report of discriminative stimuli established on one of the newer atypical anxiolytics in which the discriminative cue appeared related to an anxiolytic effect.

Effect of tranquilizers on the total acetylcholine content and acetylcholinesterase activity in the brain tissue of Arvicanthis niloticus

The effect of reserpine and meprobamate on the total acetylcholine content and acetylcholinesterase activity in the brain tissue of the kusu rat, Arvicanthis niloticus, was studied. The total acetylcholine content and acetylcholinesterase activity were determined 1 hr after i.p. injection of different doses of reserpine (0.25, 0.5 and 1 mg/ml/100 g body wt) and meprobamate (6.25, 12.5 and 25 mg/ml/100 g body wt). The effect of different time intervals (1, 10, 30 min, 1, 2.5, 5, 8, 12, 24 and 48 hr) on the total acetylcholine content and acetylcholinesterase activity was investigated after i.p. injection of 0.5 mg of reserpine and 12.5 mg of meprobamate/ml/100 g body wt. Both reserpine and meprobamate caused an increase in the total ACh content in the brain tissue of Arvicanthis niloticus which was suggested to be due to a decrease in the release of ACh, since both reserpine and meprobamate inhibited AChE activity after some tested periods. The effect of meprobamate was observed to be stronger than that of reserpine.

Diazepam-induced place preference conditioning: appetitive and antiaversive properties

The place conditioning paradigm was used to examine the reinforcing properties of diazepam. Rats were injected with diazepam (0.5-5.0 mg/kg, IP) and 30 min later were confined for 30 min to one side of a shuttle box, in which each of the two compartments had distinctive features. On alternate (control) days they received vehicle injections and were confined for 30 min to the opposite side. At almost all doses tested, diazepam produced place preference for the distinctive compartment that had been previously associated with the drug. Preference for the drug side developed regardless of whether diazepam was paired or unpaired with the least-preferred side, and regardless of whether testing was carried out in the undrugged or in the drugged state. The rats preferred the drug side over a novel compartment, but they did not change their initial preference for the side when diazepam was given after removal from the training box. Animals injected with meprobamate (70 mg/kg, PO), a non-benzodiazepine anxiolytic, also developed conditioned preference for the drug side, comparable to that seen following cocaine hydrochloride (10 mg/kg, IP). The diazepam (2.5 mg/kg)-induced place preference was antagonized by CGS 8216 (3 mg/kg, IP), picrotoxin (2 mg/kg, IP) and naloxone (0.8 mg/kg, SC), injected 3 min before and 15 and 20 min after diazepam respectively. Sodium valproate (200 mg/kg, IP) did not influence diazepam (1 mg/kg)-induced place preference. Sodium valproate by itself had marginal effects on place conditioning. Picrotoxin and naloxone, but not CGS 8816, produced place aversion which, in the case of picrotoxin, was due to state dependent learning.(ABSTRACT TRUNCATED AT 250 WORDS)

A purinergic component in the central actions of meprobamate

The anxiolytic propanediol carbamate, meprobamate, potentiates the depressant actions of adenosine on the firing of rat cerebral cortical neurons. Meprobamate inhibits the uptake of adenosine by rat cortical synaptosomes at concentrations within the therapeutic range. Potentiation of endogenously released adenosine can account for many of the central actions of meprobamate.

Oxazepam induced mouse killing by rats

Oxazepam (2.5-80 mg/kg) induced significant mouse killing among large samples (N = 100/dose) of Holtzman strain albino rats. Meprobamate (2.5-80 mg/kg) and Chlorpromazine (0.5-4 mg/kg) did not induce killing. Despite its lesser tendency to induce aggression in humans, Oxazepam is as potent as Chlordiazepoxide for inducing killing by rats. Induction of mouse killing by rats appears to the predict clinical potency rather than the aggressive side-effects of anxiolytic benzodiazepines.

Physical dependence on meprobamate after repeated oral administration in rats

The physical dependence potential of meprobamate (MPB) was compared with that of phenobarbital (PHB) and codeine (COD) to ascertain whether MPB produces definite physical dependence in the rat. Rats were treated orally with MPB (maintenance dosage = 800 mg/kg X 2/day), PHB (100 X 2) or COD (50 X 2) twice a day (10:00 a.m. and 5:00 p.m.) for a total of 21 days; the treatment was ceased for 3 days after administration for 7 days, and the last dosing was performed on day 27. During intoxication and after the withdrawal, the MPB treated rats exhibited behaviour and withdrawal signs similar to those seen in the PHB treated rats, but not the COD treated rats. After withdrawal of drugs, definite weight loss was observed in all the rats given drugs, and the recovery of the MPB and PHB treated rats was clearly later than that of the COD treated rats. A long-lasting increase in rectal temperature was observed after the withdrawal in the MPB and PHB treated rats; a decrease was seen in the COD treated rats. From these results, it is concluded that definite physical dependence on MPB, similar to that on PHB but different from that on COD, was developed after repeated oral administration for a total of 21 days in the rat.