Rapid tolerance and crosstolerance to motor impairment effects of benzodiazepines, barbiturates, and ethanol

Tolerance to alcohol: A critical yet understudied factor in alcohol addiction

Alcohol tolerance refers to a lower effect of alcohol with repeated exposure. Although alcohol tolerance has been historically included in diagnostic manuals as one of the key criteria for a diagnosis of alcohol use disorder (AUD), understanding its neurobiological mechanisms has been neglected in preclinical studies. In this mini-review, we provide a theoretical framework for alcohol tolerance. We then briefly describe chronic tolerance, followed by a longer discussion of behavioral and neurobiological aspects that underlie rapid tolerance in rodent models. Glutamate/nitric oxide, γ-aminobutyric acid, opioids, serotonin, dopamine, adenosine, cannabinoids, norepinephrine, vasopressin, neuropeptide Y, neurosteroids, and protein kinase C all modulate rapid tolerance. Most studies have evaluated the ability of pharmacological manipulations to block the development of rapid tolerance, but only a few studies have assessed their ability to reverse already established tolerance. Notably, only a few studies analyzed sex differences. Neglected areas of study include the incorporation of a key element of tolerance that involves opponent process-like neuroadaptations. Compared with alcohol drinking models, models of rapid tolerance are relatively shorter in duration and are temporally defined, which make them suitable for combining with a wide range of classic and modern research tools, such as pharmacology, optogenetics, calcium imaging, in vivo electrophysiology, and DREADDs, for in-depth studies of tolerance. We conclude that studies of the neurobiology of alcohol tolerance should be revisited with modern conceptualizations of addiction and modern neurobiological tools. This may contribute to our understanding of AUD and uncover potential targets that can attenuate hazardous alcohol drinking.

Essential role for neuronal nitric oxide synthase in acute ethanol-induced motor impairment

The cerebellum is widely known as a motor structure because it regulates and controls motor learning, coordination, and balance. However, it is also critical for non-motor functions such as cognitive processing, sensory discrimination, addictive behaviors and mental disorders. The cerebellum has the highest relative abundance of neuronal nitric oxide synthase (nNos) and is sensitive to ethanol. Although it has been demonstrated that the interaction of γ-aminobutyric acid (GABA) and nitric oxide (NO) might play an important role in the regulation of ethanol-induced cerebellar ataxia, the molecular mechanisms through which ethanol regulates nNos function to elicit this behavioral effect have not been studied extensively. Here, we investigated the dose-dependent effects of acute ethanol treatment on motor impairment using the rotarod behavioral paradigm and the alterations of nNos mRNA expression in cerebellum, frontal cortex (FC), hippocampus and striatum. We also examined the link between acute ethanol-induced motor impairment and nNos by pharmacological manipulation of nNos function. We found that acute ethanol induced a dose-dependent elevation of ethanol blood levels which was associated with the impairment of motor coordination performance and decreased expression of cerebellar nNos. In contrast, acute ethanol increased nNos expression in FC but did not to change the expression for this enzyme in striatum and hippocampus. The effects of acute ethanol were attenuated by l-arginine, a precursor for NO and potentiated by 7-nitroindazole (7-NI), a selective inhibitor of nNos. Our data suggests that differential regulation of nNos mRNA expression in cerebellum and frontal cortex might be involved in acute ethanol-induced motor impairment.

Clonazepam: Indications, Side Effects, and Potential for Nonmedical Use

After participating in this activity, learners should be better able to:• Assess the misuse potential of clonazepam• Characterize the nonmedical use of clonazepam• Identify the health problems associated with long-term use of clonazepam ABSTRACT: Clonazepam, a benzodiazepine, is commonly used in treating various conditions, including anxiety disorders and epileptic seizures. Due to its low price and easy availability, however, it has become a commonly misused medication, both in medical and recreational contexts. In this review, we aim to highlight the behavioral and pharmacological aspects of clonazepam and its history following its approval for human use. We examine the circumstances commonly associated with the nonmedical use of clonazepam and raise points of particular concern. Clonazepam, alone or in combination with other psychoactive substances, can lead to unwanted effects on health, such as motor and cognitive impairment, sleep disorders, and aggravation of mood and anxiety disorders. Prolonged use of clonazepam may lead to physical dependence and tolerance. There is therefore a need to find safer therapeutic alternatives for treating seizures and anxiety disorders. Greater awareness of its frequent nonmedical use is also needed to achieve safer overall use of this medication.

Benzodiazepine-induced spatial learning deficits in rats are regulated by the degree of modulation of α1 GABA(A) receptors

Despite significant advances in understanding the role of benzodiazepine (BZ)-sensitive populations of GABAA receptors, containing the α1, α2, α3 or α5 subunit, factual substrates of BZ-induced learning and memory deficits are not yet fully elucidated. It was shown that α1-subunit affinity-selective antagonist β-CCt almost completely abolished spatial learning deficits induced by diazepam (DZP) in the Morris water maze. We examined a novel, highly (105 fold) α1-subunit selective ligand-WYS8 (0.2, 1 and 10 mg/kg), on its own and in combination with the non-selective agonist DZP (2 mg/kg) or β-CCt (5 mg/kg) in the water maze in rats. The in vitro efficacy study revealed that WYS8 acts as α1-subtype selective weak partial positive modulator (40% potentiation at 100nM). Measurement of concentrations of WYS8 and DZP in rat serum and brain tissues suggested that they did not substantially cross-influence the respective disposition. In the water maze, DZP impaired spatial learning (acquisition trials) and memory (probe trial). WYS8 caused no effect per se, did not affect the overall influence of DZP on the water-maze performance and was devoid of any activity in this task when combined with β-CCt. Nonetheless, an additional analysis of the latency to reach the platform and the total distance swam suggested that WYS8 addition attenuated the run-down of the spatial impairment induced by DZP at the end of acquisition trials. These results demonstrate a clear difference in the influence of an α1 subtype-selective antagonist and a partial agonist on the effects of DZP on the water-maze acquisition.

α4-Containing GABA(A) Receptors are Required for Antagonism of Ethanol-Induced Motor Incoordination and Hypnosis by the Imidazobenzodiazepine Ro15-4513

Alcohol (ethanol) is widely consumed for its desirable effects but unfortunately has strong addiction potential. Some imidazobenzodiazepines such as Ro15-4513 are able to antagonize many ethanol-induced behaviors. Controversial biochemical and pharmacological evidence suggest that the effects of these ethanol antagonists and ethanol are mediated specifically via overlapping binding sites on α4/δ-containing GABA_A-Rs. To investigate the requirement of α4-containing GABA_A-Rs in the mechanism of action of Ro15-4513 on behavior, wildtype (WT) and α4 knockout (KO) mice were compared for antagonism of ethanol-induced motor incoordination and hypnosis. Motor effects of ethanol were tested in two different fixed speed rotarod assays. In the first experiment, mice were injected with 2.0 g/kg ethanol followed 5 min later by 10 mg/kg Ro15-4513 (or vehicle) and tested on a rotarod at 8 rpm. In the second experiment, mice received a single injection of 1.5 g/kg ethanol ± 3 mg/kg Ro15-4513 and were tested on a rotarod at 12 rpm. In both experiments, the robust Ro15-4513 antagonism of ethanol-induced motor ataxia that was observed in WT mice was absent in KO mice. A loss of righting reflex (LORR) assay was used to test Ro15-4513 (20 mg/kg) antagonism of ethanol (3.5 g/kg)-induced hypnosis. An effect of sex was observed on the LORR assay, so males and females were analyzed separately. In male mice, Ro15-4513 markedly reduced ethanol-induced LORR in WT controls, but α4 KO mice were insensitive to this effect of Ro15-4513. In contrast, female KO mice did not differ from WT controls in the antagonistic effects of Ro15-4513 on ethanol-induced LORR. We conclude that Ro15-4513 requires α4-containing receptors for antagonism of ethanol-induced LORR (in males) and motor ataxia.

Acute cross tolerance to midazolam, and not pentobarbital and pregnanolone, after a single dose of chlordiazepoxide in monkeys discriminating midazolam

Although cross tolerance can develop among positive gamma-aminobutyric acidA (GABAA) modulators acting at the same modulatory site, cross tolerance does not always develop to drugs acting at sites that are different from the site of action of the drug administered chronically. To examine the relationship between cross tolerance and site of action, four rhesus monkeys discriminated midazolam and, on separate occasions, received 32 mg/kg of chlordiazepoxide 24 h before dose-effect determinations for drugs acting at different sites. Midazolam, pentobarbital, and pregnanolone produced >80% midazolam-lever responding. Although monkeys responded on the midazolam lever 2-4 h after 32 mg/kg of chlordiazepoxide, they responded on the saline lever 24 h later. Twenty-four hours after an acute injection of 32 mg/kg of chlordiazepoxide, midazolam dose-effect curves were shifted 4.6-fold to the right, whereas pregnanolone dose-effect curves were shifted three-fold to the left. Sensitivity to pentobarbital increased in one monkey and decreased in others 24 h after chlordiazepoxide administration. Decreased sensitivity to midazolam shows that acute cross tolerance develops after chlordiazepoxide administration, although it does not develop to drugs acting at other sites on GABAA receptors. These differences among positive GABAA modulators suggest that even short-term benzodiazepine administration changes GABAA receptors, and those changes impact modulatory sites differently.

AMPA receptor potentiation can prevent ethanol-induced intoxication

We present a substantial series of behavioral and imaging experiments, which demonstrate, for the first time, that increasing AMPA receptor-mediated neurotransmission via administration of potent and selective biarylsulfonamide AMPA potentiators LY404187 and LY451395 reverses the central effects of an acutely intoxicating dose of ethanol in the rat. Using pharmacological magnetic resonance imaging (phMRI), we observed that LY404187 attenuated ethanol-induced reductions in blood oxygenation level dependent (BOLD) in the anesthetized rat brain. A similar attenuation was apparent when measuring local cerebral glucose utilization (LCGU) via C14-2-deoxyglucose autoradiography in freely moving conscious rats. Both LY404187 and LY451395 significantly and dose-dependently reversed ethanol-induced deficits in both motor coordination and disruptions in an operant task where animals were trained to press a lever for food reward. Both prophylactic and acute intervention treatment with LY404187 reversed ethanol-induced deficits in motor coordination. Given that LY451395 and related AMPA receptor potentiators/ampakines are tolerated in both healthy volunteers and elderly patients, these data suggest that such compounds may form a potential management strategy for acute alcohol intoxication.

GABA(A) receptor trafficking and its role in the dynamic modulation of neuronal inhibition

GABA (gamma-aminobutyric acid) type A receptors (GABA(A)Rs) mediate most fast synaptic inhibition in the mammalian brain, controlling activity at both the network and the cellular levels. The diverse functions of GABA in the CNS are matched not just by the heterogeneity of GABA(A)Rs, but also by the complex trafficking mechanisms and protein-protein interactions that generate and maintain an appropriate receptor cell-surface localization. In this Review, we discuss recent progress in our understanding of the dynamic regulation of GABA(A)R composition, trafficking to and from the neuronal surface, and lateral movement of receptors between synaptic and extrasynaptic locations. Finally, we highlight a number of neurological disorders, including epilepsy and schizophrenia, in which alterations in GABA(A)R trafficking occur.

Mechanisms of reversible GABAA receptor plasticity after ethanol intoxication

The time-dependent effects of ethanol (EtOH) intoxication on GABA(A) receptor (GABA(A)R) composition and function were studied in rats. A cross-linking assay and Western blot analysis of microdissected CA1 area of hippocampal slices obtained 1 h after EtOH intoxication (5 g/kg, gavage), revealed decreases in the cell-surface fraction of alpha4 and delta, but not alpha1, alpha5, or gamma2 GABA(A)R subunits, without changes in their total content. This was accompanied (in CA1 neuron recordings) by decreased magnitude of the picrotoxin-sensitive tonic current (I(tonic)), but not miniature IPSCs (mIPSCs), and by reduced enhancement of I(tonic) by EtOH, but not by diazepam. By 48 h after EtOH dosing, cell-surface alpha4 (80%) and gamma2 (82%) subunit content increased, and cell-surface alpha1 (-50%) and delta (-79%) and overall content were decreased. This was paralleled by faster decay of mIPSCs, decreased diazepam enhancement of both mIPSCs and I(tonic), and paradoxically increased mIPSC responsiveness to EtOH (10-100 mm). Sensitivity to isoflurane- or diazepam-induced loss of righting reflex was decreased at 12 and 24 h after EtOH intoxication, respectively, suggesting functional GABA(A)R tolerance. The plastic GABA(A)R changes were gradually and fully reversible by 2 weeks after single EtOH dosing, but unexplainably persisted long after withdrawal from chronic intermittent ethanol treatment, which leads to signs of alcohol dependence. Our data suggest that early tolerance to EtOH may result from excessive activation and subsequent internalization of alpha4betadelta extrasynaptic GABA(A)Rs. This leads to transcriptionally regulated increases in alpha4 and gamma2 and decreases in alpha1 subunits, with preferential insertion of the newly formed alpha4betagamma2 GABA(A)Rs at synapses.

Co-modulation of acute ethanol-induced motor impairment by mouse cerebellar adenosinergic A1 and GABAA receptor systems

We have previously demonstrated that cerebellar adenosine modulates ethanol ataxia. Using Rotorod method, we investigated the role of cerebellar GABA(A) receptors in the adenosinergic modulation of ethanol ataxia in mice. Direct cerebellar microinfusion of GABA(A) agonist, muscimol (2.5, 5 and 10 ng) and antagonist, bicuculline (50, 100 and 200 ng), via permanently implanted guide cannulas, produced a marked and dose-dependent accentuation and attenuation, respectively, of ethanol (2g/kg; IP) ataxia. The accentuation of ethanol ataxia by intracerebellar muscimol was through GABA(A) receptor because intracerebellar pretreatment with bicuculline virtually abolished muscimol effect. Intracerebellar microinfusion of adenosine A(1) agonist, N(6)-cyclohexyladenosine (CHA: 4 ng), and antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX: 100 ng) markedly accentuated and attenuated, respectively, ethanol ataxia consistent with our previously published data. Intracerebellar microinfusion of CHA (4 ng) or DPCPX (100 ng) markedly enhanced and reduced, respectively, muscimol (10 ng)-induced accentuation of ethanol ataxia suggesting co-modulation of ethanol ataxia by cerebellar adenosinergic A(1) and GABA(A) receptors. Similarly, intracerebellar bicuculline (200 ng) pretreatment not only prevented CHA-induced accentuation of ethanol ataxia, but caused further decrease in ethanol ataxia. No change in the normal coordination was observed when microinfusion of the highest dose of muscimol, bicuculline, DPCPX or CHA alone or in combination was followed by saline injection instead of ethanol. The results of the present study suggest a functional similarity between GABA(A) and adenosine A(1) receptors even though both receptor types are known to couple to different signaling system and their location is on the opposite ends of the cerebellar granule cells, axons and axonal terminals (i.e., GABA(A) at the granule cells and adenosine A(1) on axons and axonal terminals of the granule cells) and act as co-modulators of ethanol ataxia.

Periadolescent exposure to ethanol and diazepam alters the aversive properties of ethanol in adult mice

Evidence suggests that the developing adolescent brain may be especially vulnerable to long-term neurobehavioral consequences following ethanol exposure and withdrawal. In the present study, we examined the long-term effect of adolescent ethanol withdrawal on a subsequent EtOH-induced conditioned taste aversion (CTA). Periadolescent and adult C3H mice were exposed to 64 h of continuous (single withdrawal) or intermittent (multiple withdrawal) ethanol vapor. Following each ethanol exposure, animals received either 0, 1, 2, or 3 mg/kg diazepam (DZP) in an attempt to counteract the possible effect of ethanol withdrawal. About 6 weeks following ethanol and DZP treatment, animals were tested for an EtOH-induced CTA. As expected, exposure to EtOH during adolescence attenuated the EtOH-induced CTA as compared to controls. Unexpectedly, administration of DZP during withdrawal did not spare but rather mimicked the attenuation of the EtOH-induced CTA seen in animals exposed to ethanol in adolescence. This attenuation was not evident when EtOH and/or DZP was administered in adulthood. Given the similar mode of action of EtOH and DZP on the GABA system, the principal implication of the present findings is that the intoxicating effect of ethanol on the developing brain can result in long-term changes in the aversive properties of EtOH.

Low dose acute alcohol effects on GABA A receptor subtypes

GABA(A) receptors (GABA(A)Rs) are the main inhibitory neurotransmitter receptors and have long been implicated in mediating at least part of the acute actions of ethanol. For example, ethanol and GABAergic drugs including barbiturates and benzodiazepines share many pharmacological properties. Besides the prototypical synaptic GABA(A)R subtypes, nonsynaptic GABA(A)Rs have recently emerged as important regulators of neuronal excitability. While high doses (> or =100 mM) of ethanol have been reported to enhance activity of most GABA(A)R subtypes, most abundant synaptic GABA(A)Rs are essentially insensitive to ethanol concentrations that occur during social ethanol consumption (< 30 mM). However, extrasynaptic delta and beta3 subunit-containing GABA(A)Rs, associated in the brain with alpha4 or alpha6 subunits, are sensitive to low millimolar ethanol concentrations, as produced by drinking half a glass of wine. Additionally, we found that a mutation in the cerebellar alpha6 subunit (alpha6R100Q), initially reported in rats selectively bred for increased alcohol sensitivity, is sufficient to produce increased alcohol-induced motor impairment and further increases of alcohol sensitivity in recombinant alpha6beta3delta receptors. Furthermore, the behavioral alcohol antagonist Ro15-4513 blocks the low dose alcohol enhancement on alpha4/6/beta3delta receptors, without reducing GABA-induced currents. In binding assays alpha4beta3delta GABA(A)Rs bind [(3)H]Ro15-4513 with high affinity, and this binding is inhibited, in an apparently competitive fashion, by low ethanol concentrations, as well as analogs of Ro15-4513 that are active to antagonize ethanol or Ro15-4513's block of ethanol. We conclude that most low to moderate dose alcohol effects are mediated by alcohol actions on alcohol/Ro15-4513 binding sites on GABA(A)R subtypes.

Low-dose alcohol actions on alpha4beta3delta GABAA receptors are reversed by the behavioral alcohol antagonist Ro15-4513

Although it is now more than two decades since it was first reported that the imidazobenzodiazepine Ro15-4513 reverses behavioral alcohol effects, the molecular target(s) of Ro15-4513 and the mechanism of alcohol antagonism remain elusive. Here, we show that Ro15-4513 blocks the alcohol enhancement on recombinant "extrasynaptic" alpha4/6beta3delta GABA(A) receptors at doses that do not reduce the GABA-induced Cl(-) current. At low ethanol concentrations (< or =30 mM), the Ro15-4513 antagonism is complete. However, at higher ethanol concentrations (> or =100 mM), there is a Ro15-4513-insensitive ethanol enhancement that is abolished in receptors containing a point mutation in the second transmembrane region of the beta3 subunit (beta3N265M). Therefore, alpha4/6beta3delta GABA receptors have two distinct alcohol modulation sites: (i) a low-dose ethanol site present in alpha4/6beta3delta receptors that is antagonized by the behavioral alcohol antagonist Ro15-4513 and (ii) a site activated at high (anesthetic) alcohol doses, defined by mutations in membrane-spanning regions. Receptors composed of alpha4beta3N265Mdelta subunits that lack the high-dose alcohol site show a saturable ethanol dose-response curve with a half-maximal enhancement at 16 mM, close to the legal blood alcohol driving limit in most U.S. states (17.4 mM). Like in behavioral experiments, the alcohol antagonist effect of Ro15-4513 on recombinant alpha4beta3delta receptors is blocked by flumazenil and beta-carboline-ethyl ester (beta-CCE). Our findings suggest that ethanol/Ro15-4513-sensitive GABA(A) receptors are important mediators of behavioral alcohol effects.

Possible role of mouse cerebellar nitric oxide in the behavioral interaction between chronic intracerebellar nicotine and acute ethanol administration: Observation of cross-tolerance

Many studies have reported cross-tolerance between nicotine and ethanol. Previously we demonstrated that intracerebellar nicotine attenuates ethanol-induced motor impairment. In this study, intracerebellar nicotine (0.625, 2.5, 5 ng; once daily for five days) significantly attenuated ethanol-induced motor impairment in a dose-dependent fashion suggesting the development of cross-tolerance between nicotine and ethanol in male CD-1 mice. Using the same paradigm, intracerebellar nicotine (5 ng) microinfused for 1, 2, 3, 5, 7 days significantly attenuated ethanol-induced motor impairment in all groups except the 1-day treatment group. Cross-tolerance, which developed optimally in 5-day nicotine treatment group, was reversible and detectable up to 40 h post-nicotine microinfusion. Intracerebellar microinfusion of hexamethonium (1 mug once daily for 5 days): (i) did not alter ethanol-induced motor impairment indicating no tonic nicotine receptor involvement; (ii) 10 min prior to daily intracerebellar nicotine treatment virtually abolished the cross-tolerance between nicotine and ethanol indicating nicotinic acetylcholine receptor participation; (iii) when microinfused 10 min after daily intracerebellar nicotine treatment, failed to abolish the cross-tolerance which suggested possible participation of downstream second messenger mechanisms. Chronic intracerebellar microinfusion of nicotine: (i) failed to attenuate acute pentobarbital (25mg/kg i.p.)-induced motor impairment; and (ii) produced no change in normal motor coordination when followed by saline injection. Finally, the cerebellar concentration of total nitric oxide products (nitrite+nitrate; NO(x)); (i) was increased after 5-day intracerebellar nicotine; (ii) was decreased by acute ethanol administration; and (iii) decreased due to acute ethanol administration which was opposed by chronic intracerebellar nicotine treatment. These results support a functional correlation between the cerebellar nitric oxide production and ethanol-induced motor impairment and suggest possible participation of nitric oxide as a factor in the observed cross-tolerance between nicotine and ethanol.

Selection for pentobarbital withdrawal severity: correlated differences in withdrawal from other sedative drugs

In mice, withdrawal from agents that depress central nervous system function, such as barbiturates and benzodiazepines, results in the production of a withdrawal syndrome, one feature of which is increased severity of handling induced convulsions (HICs). High and Low Pentobarbital Withdrawal mice (HPW and LPW) were selectively bred to display severe and mild pentobarbital withdrawal HICs, respectively. These mice provide a valuable means to assess genetic correlations between withdrawal from pentobarbital and other sedative agents. We tested HPW and LPW mice for severity of HICs elicited during withdrawal from ethanol, diazepam, and zolpidem, and measured consumption of and preference for pentobarbital solutions in HPW and LPW mice. HPW mice displayed greater HICs than LPW mice during ethanol and zolpidem withdrawal, but differed less robustly during diazepam withdrawal. LPW mice consumed more pentobarbital in a solution of a moderate concentration than did HPW mice, but did not consume more pentobarbital at a higher or lower concentration. These results indicate that some of the same genes that affect the severity of withdrawal from pentobarbital also influence ethanol and zolpidem withdrawal, but that diazepam withdrawal may be less influenced by these genes.

Clinical impairment of benzodiazepines--relation between benzodiazepine concentrations and impairment in apprehended drivers

BACKGROUND

Acute intake of benzodiazepines is followed by concentration-dependent deterioration of performance in controlled experimental studies. Whether this is true in a population of benzodiazepine users is uncertain. We studied the relationship in a population of suspected drugged drivers.

METHODS

In Norway physicians examine and take blood samples from nearly all suspected drivers. Our material comprised 818 samples containing only one benzodiazepine and our reference group consisted of 10,759 cases containing only alcohol.

RESULTS

159 drivers (19%) were considered as not impaired and 659 (81%) as impaired. None of the background factors, e.g. gender, age or time of day when apprehended, related significantly to either the physician's conclusion or to blood levels of benzodiazepines. Impaired subjects had significantly higher blood levels of diazepam (n=411) (P<0.001), oxazepam (n=73) (P<0.05) and flunitrazepam (n=211) (P<0.05) than those not impaired. The risk of being assessed as impaired did rise with increasing benzodiazepine blood level, with odds ratios (ORs) for being assessed as impaired of 1.61, 3.65 and 4.11 for the three supratherapeutic drug levels. The corresponding OR found for different elevated blood-alcohol concentrations were 1.49, 2.94 and 10.49.

CONCLUSION

The blood concentration of benzodiazepines was the only characteristic which was related to impairment. This indicated a drug-concentration related effect of benzodiazepines on performance and paves the way for a discussion on legal limits for benzodiazepines in relation to driving.

Evaluation of 1,1,1-trichloroethane and flurothyl locomotor effects following diazepam treatment in mice

The abused volatile solvent 1,1,1-trichloroethane (TCE) shares many acute behavioral effects with central nervous system (CNS) depressants; however, demonstration of tolerance to these effects has been difficult. The purpose of the present study was to investigate the development of TCE-induced changes in locomotor activity in mice following repeated injections with diazepam. In the initial concentration-effect curve determinations, diazepam decreased locomotor activity at all doses tested and TCE produced a biphasic effect, increasing locomotor activity at lower concentrations with return to control levels at a high (16,000 ppm) concentration. Flurothyl, a vapor with convulsive properties, had no pronounced effects on locomotor activity at subconvulsant concentrations. Following four daily injections with vehicle or with 10 mg/kg/day diazepam, mice were administered the same concentration of drug/inhalant that they received initially and were retested for locomotor activity effects. Concentration-effect curves for diazepam and flurothyl were not altered by this modest regimen of repeated dosing with diazepam. In contrast, sensitization to the locomotor-stimulating effects of TCE was observed in diazepam-treated mice, but not in vehicle-treated mice. These results suggest that the development of sensitization to TCE involves common mechanisms with those that are affected by repeated dosing with the CNS depressant diazepam.

Midazolam for continuous sedation in Japanese critical care patients: phase II study

This prospective study was undertaken to evaluate the efficacy and safety of midazolam as a sedative agent in 14 critically ill patients without coma admitted to the intensive care unit at Nihon University Itabashi Hospital, Japan. Adequate sedation (sedation score [SS] 4-6) was induced with 0.058- 0.372 mg/ kg midazolam and maintained with a dose range of 0.03-0.4 mg/kg per h. Most burn or trauma patients required higher midazolam doses than patients with cardiovascular disease. The most frequent adverse events observed were hypotension, heart-rate fluctuation and electrocardiogram abnormalities. Pharmacokinetic analysis of the population suggested that lower drug clearance rates correlated with presence of complications. Plasma concentrations (EC50) of SS 5, estimated by logistic regression analysis, varied among patients (mean 194 ng/ml). Midazolam infusion achieved successful sedation in this critical care setting, but the optimum dose differed by patient and was influenced by the presence of complications.

A behavioral economic analysis of polydrug abuse in alcoholics: asymmetrical substitution of alcohol and cocaine

Economic concepts can be used to assess how drug prices affect consumption patterns. Increases in price for a commodity typically result in reductions in consumption. Demand is considered elastic if decreases in consumption are proportionally greater than increases in price, and inelastic if they are proportionally smaller than rises in price. The price of one commodity can also affect consumption of others. Commodities can function as substitutes, complements or independents, and these concepts refer to increases, decreases, or no change in the consumption of one item as the price of another increases. This study evaluated the effects of drug prices on hypothetical drug-purchasing decisions in 53 alcohol abusers. Experiments 1, 2, and 3 examined how alcohol, cocaine, and Valium prices, respectively, influenced purchases of alcohol, cocaine, Valium, heroin, marijuana and nicotine. As price of alcohol rose in Experiment 1, alcohol purchases decreased and demand for alcohol was inelastic. Cocaine was a complement to alcohol, but other drugs purchases were independent of alcohol prices. In Experiment 2, demand for cocaine was elastic as its price increased. Alcohol was a substitute for cocaine, but other drug purchases did not change significantly. In Experiment 3, demand for Valium was elastic as its price rose, and all other drug purchases were independent of Valium prices. Hypothetical choices were reliable between and within subjects and associated with urinalysis results and lifetime histories of drug abuse. These results suggest that, among alcohol abusers, cocaine is a complement to alcohol, but alcohol is a substitute for cocaine.

Chronic cocaine differentially affects diazepam's anxiolytic and anticonvulsant actions. Relationship to GABA(A) receptor subunit expression

Benzodiazepines are used to treat the anxiety associated with cocaine withdrawal, as well as cocaine-induced seizures. Since cocaine exposure was shown to affect BZ binding density, abuse liability, subjective hypnotic actions and seizure susceptibility, we assessed whether chronic cocaine alters diazepam's anxiolytic and anticonvulsant actions. Changes in GABA(A) receptor subunit protein expression were also assessed as they may relate to BZ activity at the receptor. Male Sprague-Dawley rats were injected with cocaine-HCl (15 mg/kg, i.p.) or saline once daily for 14 days. One day after the last injection, DZP (1 mg/kg i.p.) significantly increased time spent on and entries into open arms of an elevated plus maze in both saline- and cocaine-treated groups, yet the effect was greater in cocaine-treated rats. Eight days after cessation of treatment DZP did not have a significant anxiolytic effect in either group. To assess the effect of cocaine on DZP's anticonvulsant actions, PTZ was infused at a constant rate via the lateral tail vein and clonus onset was recorded in the presence and absence of DZP (5 mg/kg, i.p). DZP significantly elevated seizure threshold in both groups of rats. Chronic cocaine also had no effect on the beta-CCM seizure threshold. Quantitative immunohistochemistry of GABA(A) receptor subunit protein demonstrated significant regulation of alpha2 (-10%) and beta3 (+9%) subunits in the hippocampal dentate gyrus and CA1 regions, respectively. Small changes in GABAR subunit expression in specific brain areas may relate to DZP's enhanced anxiolytic effectiveness whereas it's anticonvulsant actions likely remain intact following cocaine administration.

Genetic determinants of severity of acute withdrawal from diazepam in mice: commonality with ethanol and pentobarbital

Potentially life-threatening seizures can occur following withdrawal from benzodiazepines, ethanol, or barbiturates. In animals, withdrawal severity has been shown to be partially genetically determined for each drug class. Susceptibility to these drugs is partially determined by common genetic factors, but the evidence is conflicting. We tested the hypothesis that acute benzodiazepine withdrawal convulsions are influenced by at least some genes that also affect withdrawal from ethanol and pentobarbital. Results in inbred mouse strains demonstrate that strain susceptibility is genetically correlated with susceptibility to ethanol and pentobarbital. The proportion of variance accounted for by genetic factors common to diazepam and ethanol was estimated at 69%. Results contrast with previous data obtained in mice that were serially tested for withdrawal severity from ethanol, pentobarbital, and then diazepam, because serial testing of mice significantly affected the previous results for some strains. Diazepam withdrawal severity was also genetically correlated with pentobarbital withdrawal. Together, these results suggest that some genes influence severity of withdrawal from several types of depressant drugs.