Does the reversal of the anticonflict effect of phenobarbital by beta-CCE and FG 7142 indicate benzodiazepine receptor-mediated anxiogenic properties?

An unescapable looming threat paradigm for assessing anxiety-like responses in rats

Rapidly approaching visual stimuli (i.e. looming objects) are known to evoke unconditioned defense responses across species. In rodents, this threat reactivity repertoire includes freezing and fleeing behavior. Although components of the circuitry underlying unconditioned response to a looming threat have been elucidated, both a temporal characterization and drug effects on the freezing response have not yet been reported. Here, we describe a modified version of a looming threat task in which no escape route is available. In this task, we observed unconditioned freezing prior to, during, and after exposure to a looming threat stimulus. In Long Evans (LE) and Sprague-Dawley (SD) rats, we report looming stimulus-specific freezing response. We further explored the specificity and pharmacosensitivity of this response in male and female LE rats. Administration of a GABA-A receptor negative allosteric modulator (FG-7142) did not re-establish freezing in habituated animals; however, administration of a GABA-A receptor positive allosteric modulator (diazepam) in naïve LEs significantly reduced freezing during the post-looming period in a sex-dependent manner. Presentation of an unescapable looming stimulus results in freezing that extends beyond the acute threat exposure. Because freezing responses outlast the initial threat, and display only modest sensitivity to conventional anxiolytic therapy, this may represent a platform for screening agents in treatment-refractory anxiety.

Design and synthesis of β-carboline derivatives with nitrogen mustard moieties against breast cancer

To discover the promising antitumor agents, a series of β-carboline derivatives with nitrogen mustard moieties were designed and synthesized. Most target derivatives showed antiproliferative activity against MCF-7 and MDA-MB-231 cells. Among them, (1-methyl-9H-pyrido[3,4-b]indol-3-yl)methyl (S)-3-(4-(bis(2-chloroethyl)amino)phenyl)-2-formamidopropanoate possessed the most potent antiproliferative activity with IC₅₀ values of 1.79 μM and 4.96 μM, respectively, which were significantly higher than that of the parent compounds, and the efficacy was comparable to that of the positive control doxorubicin. More importantly, it showed weak cytotoxicity against human normal breast cell line MCF-10A (IC₅₀ > 20 μM), exhibiting certain selectivity. Subsequently, further mechanism exploration indicated that it induced G2/M phase cell cycle arrest and apoptosis in MDA-MB-231 cells. The DCFH-DA fluorescent probe assay and comet assay showed that this compound could cause intracellular ROS accumulation and DNA damage. In addition, it exerted potent inhibitory effect on the migration, invasion and adhesion of MDA-MB-231 cells in vitro. In short, (1-methyl-9H-pyrido[3,4-b]indol-3-yl)methyl (S)-3-(4-(bis(2-chloroethyl)amino)phenyl)-2-formamidopropanoate was considered as a promising compound for anti-breast cancer.

β-Carbolines as potential anticancer agents

β-Carbolines are indole alkaloids having a tricyclic pyrido[3,4-b]indole ring in their structure. Since the isolation of first β-carboline from Peganum harmala in 1841, the isolation and synthesis of various β-carboline derivatives surged in the following centuries. β-Carboline derivatives due to their widespread availability from natural sources, structural flexibility, quick reactivity and interaction with varied anticancer targets such as DNA (intercalation, groove binding, etc.), enzymes (GPX4, topoisomerases, kinases, etc.) and proteins (tubulin, ABCG2/BRCP1, etc.) have established themselves as promising lead compounds for the synthesis of various anticancer active agents. The current review covers the synthesis and isolation, anticancer activity, mechanism of action and SAR of various β-carboline containing molecules, its derivatives and congeners.

Sex differences in anxiety and emotional behavior

Research has elucidated causal links between stress exposure and the development of anxiety disorders, but due to the limited use of female or sex-comparative animal models, little is known about the mechanisms underlying sex differences in those disorders. This is despite an overwhelming wealth of evidence from the clinical literature that the prevalence of anxiety disorders is about twice as high in women compared to men, in addition to gender differences in severity and treatment efficacy. We here review human gender differences in generalized anxiety disorder, panic disorder, posttraumatic stress disorder and anxiety-relevant biological functions, discuss the limitations of classic conflict anxiety tests to measure naturally occurring sex differences in anxiety-like behaviors, describe sex-dependent manifestation of anxiety states after gestational, neonatal, or adolescent stressors, and present animal models of chronic anxiety states induced by acute or chronic stressors during adulthood. Potential mechanisms underlying sex differences in stress-related anxiety states include emerging evidence supporting the existence of two anatomically and functionally distinct serotonergic circuits that are related to the modulation of conflict anxiety and panic-like anxiety, respectively. We discuss how these serotonergic circuits may be controlled by reproductive steroid hormone-dependent modulation of crfr1 and crfr2 expression in the midbrain dorsal raphe nucleus and by estrous stage-dependent alterations of γ-aminobutyric acid (GABAergic) neurotransmission in the periaqueductal gray, ultimately leading to sex differences in emotional behavior.

Cholinergic inputs to the rat medial prefrontal cortex mediate potentiation of the cardiovascular defensive response by the anxiogenic benzodiazephine receptor partial inverse agonist FG 7142

Consistent with its putative anxiogenic actions, administration of the benzodiazepine receptor partial inverse agonist FG 7142 has been shown to potentiate defensive-like cardiovascular reactivity to an acoustic stimulus in the rat, an effect that appears to be mediated by the basal forebrain cholinergic system. The present studies tested the hypothesis that the basal forebrain cholinergic projections to the medial prefrontal cortex, an area that has been implicated in both anxiety and autonomic control, may be a relevant pathway underlying this response potentiation. Infusions of the muscarinic receptor agonist carbachol into the medial prefrontal cortex, but not into the lateral prefrontal cortex or the basolateral amygdala, mimicked the effects of systemically administered FG 7142 on the cardioacceleratory response. Infusions of the muscarinic antagonist atropine blocked this effect, as well as the response-potentiating actions of FG 7142. The effects of FG 7142 were also blocked by lesions of the cholinergic inputs to the medial prefrontal cortex produced by local infusions of the immunotoxin 192 immunoglobulin G-saporin into this area. These findings indicate that cholinergic activation of the medial prefrontal cortex is sufficient to enhance the cardioacceleratory defensive response, and that cholinergic inputs to the medial prefrontal cortex are necessary for the response-potentiating effects of FG 7142. These results are consistent with a recent neurobiological model of anxiety and autonomic control that attributes the enhanced processing of anxiety-related stimuli and contexts to increases in activity in cortical cholinergic inputs.

The cardiovascular startle response: anxiety and the benzodiazepine receptor complex

Benzodiazepine receptor (BZR) agonists are prototypic anxiolytic agents, whereas BZR inverse agonists exert anxiogenic effects. The effects of these compounds offer a potentially important pharmacological model system to examine the central mechanisms of anxiety. In accord with its putative anxiogenic properties, we previously found that the BZR partial inverse agonist, FG 7142, enhances the cardiovascular defensive response to a nonsignal acoustic stimulus in rats. In contrast, we found in the present study that this agent attenuates both the somatic and cardiovascular components of the acoustic startle response. BZR agonists and inverse agonists are known to modulate the basal forebrain cortical cholinergic system, and we consider the potential involvement of this system in the disparate psychophysiological actions of FG 7142 and in anxiety states in general.

Neurochemical mediators of anxiety have inconsistent effects on hypothalamic self-stimulation in rats

We studied effects of anxiogenic and anxiolytic compounds on the electric self-stimulation of the medial fore-brain bundle in male rats to find out if there is a link between reward and anxiety-related behaviours. The cholecystokinin agonist, caerulein (25-100 micrograms/kg) and the 5-HT agonist 1-(3-chlorophenyl)piperazine (0.2-1 mg/kg) dose-dependently inhibited the electric self-stimulation. The 5-HT2A antagonist, ketanserin, at 2.5 mg/kg, increased the self-stimulation at high currents but not at threshold current. The 5-HT3 antagonist ondansetron (10 and 100 micrograms/kg). The alpha 1-adrenergic antagonist, prazosin (0.125 and 0.5 mg/kg), the beta-adrenergic antagonist, propranolol (5 and 10 mg/kg) and the alpha 2-adreno-receptor antagonist, atipamezole (4 mg/kg), did not affect the self-stimulation. Nor did the benzodiazepine agonist, diazepam (5-15 mg/kg), a benzodiazepine receptor antagonist flumazenil (at 10 and 25 mg/kg) or the inverse agonist of benzodiazepine receptors, N-methyl-beta-carboline-3-carboxamide (10 and 20 mg/kg), cause any substantial changes of the self-stimulation. We conclude that only two anxiolytic drugs (caerulein and 1-(3-chlorophenyl)piperazine) suppress the electric self-stimulation. These findings indicate that anxiogenicity as such is not able to weaken the hypothalamic electric self-stimulation. Anxiety and reward are apparently mediated through separate neural pathways.

A central cholinergic link in the cardiovascular effects of the benzodiazepine receptor partial inverse agonist FG 7142

Previous work demonstrated that systemic administration of the benzodiazepine receptor (BZR) partial inverse agonist beta-carboline FG 7142 (FG) augments the cardiovascular response to non-signal stimuli, similar to the effects of an aversive context. Analysis of the parasympathetic and sympathetic contributions to the effects of FG prompted the hypothesis that increases in central cholinergic activity mediates the potentiation of the cardioacceleratory response by FG. Consistent with this hypothesis, the present experiments demonstrate: (a) intracerebroventricular (ICV) infusion of the cholinergic receptor agonist carbachol mimics the response-potentiating effects of FG; (b) this effect of carbachol was blocked by ICV co-administration of the muscarinic antagonist atropine; (c) ICV infusions of atropine blocked the potentiation of the cardioacceleratory response by systemically administered FG, but did not alter the basal response to the stimulus; and (d) 192 IgG-saporin-induced lesions of basal forebrain cholinergic neurons prevented the FG-induced potentiation of the cardioacceleratory response, again without altering the basal cardiac response. These data strongly support the hypothesis that the effects of FG on cardiac reactivity are mediated via an activation of central muscarinic cholinergic mechanisms.

Evaluation of exposure level of N-methyl-beta-carboline-3-carboxamide (FG 7142), an anxiogenic agent in humans

beta-Carboline-3-carboxylic acid methylamide (FG 7142), an anxiogenic agent, has been detected in human urine. The urinary excretion level of FG 7142 in non-smokers was found to be 0.503 +/- 0.25 ng per day (mean +/- S.D., n=10), while that in smokers was found to be 2.418 +/- 0.384 ng per day (n=10). This suggests that humans are exposed to FG 7142 and that smokers are exposed to higher levels of FG 7142 than non-smokers. Considering the previous findings that FG 7142 is present in cigarette smoke, indoor and outdoor air and smoke condensate of tree leaves, humans may be exposed to FG 7142 via the airways and lungs, although we cannot exclude the possibility of exposure via foodstuffs. Results of animal experiments suggest that FG 7142 which enters the bloodstream is excreted into the urine via the kidneys within 24 h in an unchanged form. Therefore, monitoring the level of FG 7142 in urine may be useful for monitoring the exposure level of FG 7142.

N-Methyl-beta-carboline-3-carboxamide (FG 7142): An anxiogenic agent in cigarette smoke condensate and its mechanism of formation

beta-Carboline-3-carboxylic acid methylamide (FG 7142), an anxiogenic agent has been found in cigarette smoke condensate, but not in the cigarette itself. When a cigarette, except its filter portion, was immersed in 20 ml of potassium phosphate buffer, pH 7.4, then heated at 60 degrees C for 2 days with or without presence of methylamine, FG 7142 was detected only in the mixture containing methylamine. Furthermore, when the mixtures of beta-carboline derivatives and various amounts of methylamine hydrochloride were heated at 60 degrees C for 5 days, FG 7142 was formed only in the mixtures containing methylamine and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-caroxylic acid (MTCA) or 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (TCCA). FG 7142 was also produced in the mixture of glucose, l-tryptophan and methylamine when heated at 200 degrees C in a dry condition. These observations suggest that FG 7142 is formed through the smoking process and that methylamine in cigarette smoke may play an important role in the formation of FG 7142.

N-Methyl-beta-carboline-3-carboxamide (FG 7142), an anxiogenic agent in airborne particles and cigarette smoke-polluted indoor air

beta-Carboline-3-carboxylic acid methylamide (FG 7142), an anxiogenic agent, has been measured in airborne particles, automobile-exhaust particles, incinerator ash, smoke condensate of tree leaves and cigarette-smoke-polluted indoor air by high-performance liquid chromatography. This compound has been detected in indoor as well as outdoor air. The source of this compound in indoor air was determined as cigarette smoke, identified from smoking machine studies. This anxiogenic agent was detected in smoke condensate of tree leaves and incinerator ash from garbage burning plants, but not in diesel-exhaust particles. Considering the present results, together with the previous finding that cigarette smoke contains this compound, FG 7142 is likely to be formed through combustion of plants. Our data also suggest that this compound may be widely distributed in the environment.

Cardiovascular effects of the benzodiazepine receptor partial inverse agonist FG 7142 in rats

Effects of the benzodiazepine receptor (BZR) partial inverse agonist FG 7142 (FG) on basal and reactive cardiovascular measures were examined in freely moving rats. FG (8 mg/kg) modestly increased basal heart period, but had no effects on basal blood pressure. More notably, however, FG augmented the cardioacceleratory response to an auditory stimulus relative to vehicle controls. Selective blockade of sympathetic (atenolol, 1 mg/kg) or parasympathetic (scopolamine methylnitrate, 0.1 mg/kg) effects on the heart under control conditions revealed that the stimulus-evoked cardiac response originated from a concurrent (reciprocal) sympathetic activation and vagal withdrawal. Following FG pretreatment, both atenolol and scopolamine blocked the cardioacceleratory response to the auditory stimulus. Thus, although FG minimally increased basal heart period, FG significantly enhanced a reactive cardioacceleration. More importantly, these results demonstrate that the cardiovascular effects of BZR inverse agonists are more fully characterized by an assessment of both tonic and reactive cardiovascular responses.

The effect of Ro 15-4513, an inverse agonist at the benzodiazepine receptor, on the exploratory response to novelty in the playground maze

The effects of chlordiazepoxide and the inverse agonist, Ro 15-4513, were compared on the exploratory response of rats to a novel object introduced into a familiar environment containing seven familiar objects. While chlordiazepoxide (5 mg/kg) increased the novelty response, Ro 15-4513 reduced the response in a dose-dependent manner (0.5-5.0 mg/kg). This action was specific to novelty since the response to the familiar objects was unaffected. Both drugs produced some reduction in ambulation. The effects of both drugs were blocked by flumazenil (10 mg/kg), which at this dose did not itself have any intrinsic effect on the response. Muscimol (0.001 mg/kg) had a weak chlordiazepoxide-like effect and baclofen (3 mg/kg) had a weak effect in the opposite direction.

Combination of buspirone and other drugs with beta-CCE in monkeys: effects on respiration and behavior

The respiratory and behavioral effects of the benzodiazepine receptor (BZR) inverse agonist ethyl-beta-carboline-3-carboxylate (beta-CCE) were determined alone and in combination with buspirone, lorazepam, flumazenil, and SR 95195 in rhesus monkeys. For the respiratory studies, one group of monkeys inhaled either air or 5% CO2 mixed in air according to a fixed alternating schedule; respiratory frequency and minute volume were monitored. For the behavioral studies, another group of monkeys responded under a fixed-ratio (FR 30) schedule of food presentation. The respiratory stimulant effects of beta-CCE in both air and 5% CO2 were enhanced by prior treatment with the 5-hydroxytryptamine1A (5-HT1A) partial agonist buspirone (0.03 and 0.3 mg/kg) and a weak BZR inverse agonist, SR 95195 (10.0 mg/kg). Coadministration of buspirone (0.1 and 0.3 mg/kg) also potentiated the rate-decreasing effects of beta-CCE under the FR schedule. The BZR agonist lorazepam (3.0 mg/kg) and BZR antagonist flumazenil (1.0 mg/kg) attenuated the effects of beta-CCE on respiratory frequency and minute volume particularly under the 5% CO2 condition, and lorazepam (0.1 and 0.3 mg/kg) and flumazenil (0.1 and 0.3 mg/kg) attenuated the effects of beta-CCE on FR responding. These latter results show that the respiratory and behavioral effects of beta-CCE in rhesus monkeys are at least in part due to effects at BZRs. Moreover, the findings suggest either that coactivation of benzodiazepine and 5-HT1A sites lead to a greater than additive effect or that beta-CCE and buspirone share a common mechanism of action that is unrelated to the receptor at which BZR inverse agonists act.

Selective antagonism of acute ethanol-induced motor disturbances by centrally administered Ro 15-4513 in mice

Results of the present investigation demonstrated that Ro 15-4513 when given ICV selectively antagonized ethanol-induced motor disturbances at doses that did not produce motor incoordination and lacked proconvulsant activity. Ro 15-4513 in 10-, 15-, and 22-ng doses antagonized, roughly in a dose-dependent manner, ethanol-induced motor incoordination. The 10-ng dose produced an optimal effect with nearly complete antagonism within 30 min postethanol. The higher, 15 and 22 ng, doses of Ro 15-4513 antagonized, as well as probably reversed, ethanol-induced motor incoordination. The stimulation and inhibition of spontaneous motor activity by 1 and 2 g/kg IP ethanol, respectively, were also selectively antagonized by Ro 15-4513. Neither an alteration in the latency and/or duration of pentylenetetrazol-induced convulsions nor an antagonism to sodium pentobarbital-induced motor incoordination and inhibition of spontaneous motor activity by Ro 15-4513 at dose levels that showed antiethanol effects were observed. Only the 150-ng dose of Ro 15-4513, which exhibited intrinsic activity as proconvulsant, attenuated sodium pentobarbital-induced motor incoordination. When given alone at doses higher than those used in motor coordination experiments, Ro 15-4513 markedly increased spontaneous motor activity dose dependently.

Test-specific effects of FG-7142 on isolation-induced aggression in mice

Treatment with FG-7142 decreased isolation-induced attack, but not defense, by male mice when the residents' home cages contained only a sawdust substrate. When a small wooden nesting box was added to the cage (Experiment 2), however, FG-7142 somewhat increased levels of attack. Time spent in the nesting box was also increased, while overall levels of social interaction were decreased, by drug treatment in Experiment 2. The latter findings are consistent with FG-7142's well-documented anxiogenic properties and indicate that this drug is probably proaggressive in its actions. The antiaggressive effects of FG-7142 in Experiment 1 may have resulted from drug-induced fear behaviors that were incompatible with attack. Alternatively, Experiment 2 suggests the possibility that species-typical attack may be defensively motivated under some circumstances. Although the antiagressive properties of eltoprazine and yohimbine were unaffected by the addition of the nest box (Experiment 3), the provision of some sort of refuge within the testing apparatus may be an important methodological consideration for studies employing resident-intruder paradigms.

Effects of chlordiazepoxide and beta-carboline 3-carboxylic acid ethyl ester on non-suppressed and minimally-suppressed responding in the squirrel monkey

Lever-pressing of squirrel monkeys was maintained under a multiple fixed-interval (FI) 5-min schedule of food presentation. In one component, responding was suppressed to various degrees by the presentation of electric shock following each 30th response. When responding was either substantially or minimally suppressed, intermediate doses of chlordiazepoxide (CDAP, 1-30 mg/kg) increased both suppressed and non-suppressed responding. Beta-carboline 3-carboxylic acid ethyl ester (beta-CCE, 0.1-3 mg/kg) had little effect at low to intermediate doses (0.1-0.3 mg/kg) and decreased both minimally-suppressed and non-suppressed responding to a comparable extent at higher doses. Repeated daily dosing with beta-CCE (up to 10 mg/kg) resulted in rapid tolerance to its rate-decreasing effects. As agonists do not typically exhibit rapid tolerance for anxiolytic efficacy, the current results suggest that some behavioral effects of inverse agonists may not be strictly opposite those of benzodiazepines.

Behavioral effects of benzodiazepine ligands in non-dependent, diazepam-dependent and diazepam-withdrawn baboons

Acute i.m. injections of benzodiazepine receptor ligands were administered to baboons before 1-h observational sessions. The agonist midazolam produced sedative effects, the antagonist flumazenil produced no behavioral effects, the inverse agonist FG7142 produced tremor and the inverse agonist 3-carboethoxy-beta-carboline hydrochloride (beta CCE) produced tremor, vomiting, jerks and seizures. Co-administration of these drugs (midazolam + beta CCE, midazolam + flumazenil or flumazenil + beta CCE) produced a mutual antagonism of these effects. Compared to the non-dependent condition, in the diazepam-dependent condition (baboons maintained on 20 mg/kg per day diazepam) and withdrawn condition (dependent baboons tested during withdrawal), midazolam produced decreased sedative effects, flumazenil produced increased effects (i.e., tremor, vomiting and jerks), and beta CCE produced increased frequency of seizures. Taken together, these data suggest that (1) benzodiazepine receptor ligands lie on a continuum of behavioral activity, and (2) chronic diazepam administration alters the behavioral effects of these benzodiazepine ligands, producing a shift in the direction of the inverse agonist.

Dorsal hippocampal lesion abolishes the response to FG-7142 in the rat

The effects of the anxiogenic beta-carboline FG-7142 (15 mg/kg IP) on exploratory locomotor activity were assessed in rats with sham or ibotenic acid (IA) lesions of the dorsal or ventral hippocampus. FG-7142 reduced exploratory activity similarly in control animals as well as in those with IA lesions of the ventral hippocampus. In contrast, FG-7142 had no effect on rats with dorsal hippocampal lesions. The results suggest that the dorsal hippocampus plays a unique role in FG-7142-mediated attenuation of locomotor exploration. Other studies suggest that serotonergic systems may mediate these properties of FG-7142.

Stimulant effect of the beta-carboline FG 7142 in the open-field test

The anxiogenic activity of N-methyl-beta-carboline-3-carboxamide (FG 7142) is sometimes difficult to observe in rats. As the open field has recently been applied successfully to test the anxiogenic potential of n-butyl-beta-carboline-3-carboxylate (beta-CCB) in mice, a comparable experiment was performed with FG 7142 (1, 5, 10, 30 mg/kg i.p.) in rats. In contrast to the inhibitory effects measured with beta-CCB, FG 7142 significantly increased the ambulation and rearing scores and induced aggressivity in some animals. A differential sensitivity of mice and rats to beta-carbolines, predominant analeptic properties of FG 7142, and differences in the types of anxiety induced are proposed to account for this discrepancy.

Anxiogenic beta-carboline FG 7142 produces activation of noradrenergic neurons in specific brain regions of rats

By measuring the levels of two major metabolites of rat brain noradrenaline (NA), 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG), we investigated the effects of anxiogenic beta-carboline FG 7142, an inverse agonist of benzodiazepine (BZD) receptors, on brain noradrenergic activity of rats. Thirty min after treatment with FG 7142 (15 mg/kg IP), levels of both MHPG and DHPG in the hypothalamus, amygdala and thalamus, but not in the hippocampus and cerebral cortex, significantly increased. These increases were significantly antagonized by pretreatment with BZD receptor antagonist Ro 15-1788 (15 mg/kg, IP). Sixty min after treatment with FG 7142 at the same dose, significant increases in both metabolite levels occurred in the hypothalamus, amygdala, thalamus and cerebral cortex, and increases in MHPG levels only were observed in the hippocampus. These increases were significantly blocked by pretreatment with alpha 2-adrenoreceptor agonist clonidine (100 microgram/kg, IP). The present findings suggest that FG 7142 can produce increases in brain noradrenergic activity in specific brain regions by interacting with BZD receptors, and may support the hypothesis that hyperactivity of brain noradrenergic systems may be one neural mechanism in provocation of aversive emotional changes (anxiety, fear or panic).

Pentobarbital attenuates stress-induced increases in noradrenaline release in specific brain regions of rats

To examine whether anxiolytic action of drugs acting at the GABA/BZD-chloride channel complex may be related to the brain noradrenergic system, we investigated the effect of pentobarbital, a typical barbiturate which has potent GABA modulating properties, on increased NA release in nine brain regions of stressed rats. Pentobarbital (10 and 25 mg/kg) was injected IP 65 min before sacrifice (5 min before one-hour immobilization stress). Levels of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO4), the major metabolite of brain noradrenaline (NA), and of plasma corticosterone, were fluorometrically determined. Pentobarbital treatment by itself increased MHPG-SO4 levels in the thalamus, locus coeruleus (LC) region, midbrain and basal ganglia of nonstressed rats. Stress produced increases in MHPG-SO4 levels in all brain regions examined and elevation of plasma corticosterone levels. Pentobarbital attenuated, in a dose-dependent manner, stress-induced increases in MHPG-SO4 levels in the hypothalamus, thalamus, anterior cerebral cortex, LC region and basal ganglia and also attenuated the stress-induced elevation of plasma corticosterone levels. These data suggest that pentobarbital can attenuate both stress-induced increases in NA release in specific brain regions as well as activation of the hypothalamo-pituitary-adrenocortical system. These attenuating effects may be related to the anxiolytic action of barbiturates.

Characterization of dopamine release in the rat medial prefrontal cortex as assessed by in vivo microdialysis: comparison to the striatum

Using the technique of perfusion microdialysis combined with a small-bore liquid chromatography system we have measured the basal and drug-induced fluxes of extracellular dopamine in the medial prefrontal cortex of chloral hydrate-anesthetized rats and have compared our findings in the cortex to that observed in the striatum. The results were as follows. (1) At a flow rate of 2 microliter/min, the basal level of dopamine in the medial prefrontal cortex was 0.28 +/- 0.1 (n = 32) fmol/microliter perfusate, which was nearly an order of magnitude less than that obtained from the striatum. (2) alpha-Methyl-para-tyrosine (150 mg/kg i.v.) significantly decreased the extracellular levels of striatal and cortical dopamine. The magnitude and duration of the responses were similar in both regions. (3) Local perfusion with 30 mM K+ had a more profound effect on dopamine release in the striatum than in the medial prefrontal cortex. The K(+)-induced release in both regions was significantly attenuated in the absence of Ca2+. (4) The anxiogenic beta carboline FG 7142 (15 mg/kg, i.p.) enhanced the release of cortical dopamine by about 50% while it was without an effect in the striatum. (5) Amphetamine (1 mg/kg, i.v.) significantly elevated, while reserpine (5 mg/kg, i.p.) rapidly attenuated, the dopamine level in the medial prefrontal cortex. These studies demonstrate that perfusion microdialysis, in conjunction with small-bore liquid chromatography with electrochemical detection, can be used to measure the basal release of dopamine in the rat medial prefrontal cortex and that the dopamine release process in this region, as has been shown in the striatum, is sensitive to stimulation conditions and pharmacological manipulations.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of ethanol and Ro 15-4513 in an electrophysiological model of anxiolytic action

Previous research has implicated hippocampal rhythmical slow activity in the mechanisms of action of the anxiolytic drugs. In this study ethanol and a putative ethanol antagonist, Ro 15-4513, were investigated with reticular elicitation of rhythmical slow activity. Doses of ethanol between 0.6 and 3.1 g/kg were used. Ethanol reduced the frequency of reticular-elicited rhythmical slow activity in the same way as has been reported for anxiolytic barbiturates and benzodiazepines. This effect was linearly related to log dose of ethanol in the range of 1.7-3.1 g/kg. Ro 15-4513 at a dose of 2 mg/kg reduced the effect of ethanol (2.0 g/kg) but had no action itself. Ethanol also decreased the slope of the stimulation voltage-rhythmical slow activity frequency function but this effect was not reduced by Ro 15-4513. These results show that ethanol acts in a similar manner to conventional anxiolytic drugs but that only one component of this action can be reduced by Ro 15-4513.

The pharmacology of human anxiety

The human pharmacology of anxiety disorders, including panic disorder, is detailed. The major theories center around the role of benzodiazepine receptor, noradrenergic and serotonergic dysfunction. The contribution that challenge tests with lactate, hyper- and hypocapnia, beta- and alpha-2-adrenoceptor agonists, peptides, pentylenetetrazol, and caffeine make to our understanding of the biological basis of anxiety and these major theories are described and discussed.

Effects of anxiolytic and anxiogenic drugs on exploratory activity in a simple model of anxiety in mice

Chlordizaepoxide, pentylenetrazole, phenobarbital, N-methyl-beta-carboline-3-carboxamide (FG-7142), buspirone and the novel serotonin3 receptor (5-HT3) antagonist, 3-tropanyl-indole-3-carboxylate (ICS 205-930), were examined in the two-compartment exploratory model (Crawley and Goodwin, 1980). The results indicated that, utilizing the time mice spend in the dark side of the apparatus as an index of anxiety, increased the sensitivity of the model and enabled both anxiolytic and anxiogenic agents to be detected.

Behavioral studies with the beta-carboline FG 7142 combined with related drugs in monkeys

The beta-carboline FG 7142 was studied alone and in combination with Ro 15-1788, CGS 8216 and lorazepam in squirrel monkeys trained to respond under a fixed-interval (FI) schedule of food presentation. FG 7142 (0.3-5.6 mg/kg i.v.) produced dose-related decreases in the rate of FI responding, effects opposite to those of moderate doses of lorazepam (0.03-0.3 mg/kg i.v.). Pretreatment with low doses of Ro 15-1788 (0.1 and 0.3 mg/kg i.v.) shifted the dose-response curve of FG 7142 progressively to the right indicating pharmacological antagonism at benzodiazepine recognition sites. In comparison, pretreatment with the pyrazoloquinoline CGS 8216 (0.1-1.0 mg/kg i.v.), which alone decreased responding, did not alter the effects of FG 7142 in a systematic manner. Combinations of behaviorally active doses of FG 7142 and lorazepam had primarily additive effects: the opposing actions of one drug tended to cancel the other's effect on responding. These results show that the reduction in behavior by FG 7142 is modified predictably by Ro 15-1788 but not by CGS 8216, and behaviorally active doses of both FG 7142 and lorazepam may be needed for their mutual antagonism.

Ro 15-4513, a partial inverse agonist for benzodiazepine recognition sites, has proconflict and proconvulsant effects in the rat

The present report describes the effects of Ro 15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo-(1,5-a) (1,4)-benzodiazepine-3-carboxylate) in the conflict test, on convulsions induced by isoniazid and DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) and on the binding of [3H]gamma-aminobutyric acid ([3H]GABA) to rat brain membrane preparations. Ro 15-4513 produced a dose-dependent proconflict effect that was prevented by the administration of the benzodiazepine antagonist, Ro 15-1788. In addition, Ro 15-4513 was not convulsant per se but enhanced the convulsions produced by isoniazid and completely blocked the convulsions induced by the full inverse agonist, DMCM. In vitro, Ro 15-4513, like ethyl-beta-carboline-3-carboxylate (beta CCE), antagonized the increase in [3H]GABA binding induced by diazepam. The results indicate that Ro 15-4513 is anxiogenic and interacts with benzodiazepine recognition sites as a partial inverse agonist.

Effects of benzodiazepine and GABA antagonists on anticonflict effects of antianxiety drugs injected into the rat amygdala in a water-lick suppression test

In order to elucidate the role of the amygdala in rat conflict behavior in a water lick suppression test, we examined the effect of lesions of various nuclei of the amygdaloid complex on this behavior. An anticonflict effect was produced by a lesion of the anterior part of central and basolateral amygdala, and lesion to the posterior part of the central amygdala, but not by posterior of the basolateral amygdala or medial amygdala lesions. These results suggest that the amygdala, especially the anterior part of the central and basolateral nuclei, plays an important role in conflicting behavior of rats in the water lick test. In a second experiment, the effects of benzodiazepine- and GABA-antagonists on the anticonflict action of diazepam, zopiclone, and phenobarbital injected into the anterior part of central and basolateral amygdala were examined, also using a water lick suppression test. A dose-dependent anticonflict action was produced by systemic administration as well as by intra-amygdala injection of diazepam, zopiclone, lormetazepam, flurazepam and phenobarbital. The order of potency was lormetazepam greater than zopiclone greater than or equal to diazepam greater than flurazepam greater than or equal to phenobarbital for both routes of injection. The anticonflict effects of diazepam and zopiclone injected into the amygdala were completely reversed by Ro15-1788 and beta-CCM but not by bicuculline, while the anticonflict effect of phenobarbital was reversed by beta-CCM but not by Ro15-1788 or bicuculline. The present results strongly suggest that the anterior nuclei of central and basolateral amygdala are important sites of action of antianxiety drugs, and that an anticonflict action produced by intra-amygdala injection of benzodiazepines or barbiturate is mediated through the different receptor mechanisms.

Interactions of ethanol with benzodiazepine receptor ligands in tests of exploration, locomotion and anxiety

The ability of benzodiazepine receptor ligands to modify the behavioral effects of ethanol in tests of exploration, locomotion and anxiety are reviewed. Drugs with inverse agonist activity appear capable of consistently antagonizing the reductions in exploration and anxiety caused by ethanol. In contrast, the locomotor stimulant action of ethanol has appeared relatively insensitive to inverse agonists, suggesting that this effect may not be mediated primarily by an action of ethanol at the benzodiazepine/GABA receptor complex.

Discriminative stimulus properties of CGS 9896: interactions within the GABA/benzodiazepine receptor complex

Male rats were trained to discriminate the stimulus effects of CGS 9896 (30.0 mg/kg) from its vehicle. Once trained, discriminative performance was observed to be dose-responsive in the 3.75-30.0 mg/kg range and analysis of the dose-response curve generated an ED50 of 6.44 mg/kg. Generalization testing with chlordiazepoxide and pentobarbital produced CGS 9896-appropriate responding, whereas administration of the GABA agonists SL 75 102 resulted in 75% (intermediate) generalization to the CGS 9896 discriminative stimulus. Although full antagonism of the CGS 9896 cue was obtained following administration of Ro15-1788 and pentylenetetrazole, the inverse agonist DMCM failed to provide complete antagonism. These results suggest that the discriminative properties of CGS 9896 are consistent with its activity as a benzodiazepine receptor agonist.

The imidazobenzodiazepine Ro 15-4513 antagonizes methoxyflurane anesthesia

Parenteral administration of the imidazobenzodiazepine Ro 15-4513 (a high affinity ligand of the benzodiazepine receptor with partial inverse agonist qualities) produced a dose dependent reduction in sleep time of mice exposed to the inhalation anesthetic, methoxyflurane. The reductions in methoxyflurane sleep time ranged from approximately 20% at 4 mg/kg to approximately 38% at 32 mg/kg of Ro 15-4513. Co-administration of the benzodiazepine receptor antagonist Ro 15-1788 (16 mg/kg) or the inverse agonists DMCM (5-20 mg/kg) and FG 7142 (22.5 mg/kg) blocks this effect which suggests that the reductions in methoxyflurane sleep time produced by Ro 15-4513 are mediated via occupation of benzodiazepine receptors. Moreover, neither DMCM (5-20 mg/kg) nor FG 7142 (22.5 mg/kg) reduced methoxyflurane sleep time which suggests this effect of Ro 15-4513 cannot be attributed solely to its partial inverse agonist properties. These observations support recent findings that inhalation anesthetics may produce their depressant effects via perturbation of the benzodiazepine/GABA receptor chloride channel complex, and suggest that Ro 15-4513 may serve as a prototype of agents capable of antagonizing the depressant effects of inhalation anesthetics such as methoxyflurane.

Anxiogenic properties of beta-CCE and FG 7142: a review of promises and pitfalls

The behavioral effects of the benzodiazepine (BZP)-receptor partial inverse agonists, beta-CCE and FG 7142, are reviewed and the claim that these compounds possess "anxiogenic" properties is examined. Results obtained from human studies and global observations in animals, as well as those from experiments on aggression in animals or from studies of pentylenetetrazole discrimination cannot be considered conclusive. Contradictory findings have been obtained in studies using animal testing procedures derived from BZP-sensitive models of anxiety and in newer experimental situations and these are discussed from various theoretical perspectives: (1) the ability of the models to measure increased anxiety; (2) the possible ability of the drugs to reveal latent anxiety which generalizes from a punished to an otherwise non-fearful component of a testing procedure ("spreading anxiety"); (3) anxiety produced by a pro- or pre-convulsant state. Finally, several hypotheses are considered to account for the behavioral effects of beta-CCE and FG 7142 without assuming anxiogenic properties. These include the possible existence of different forms of anxiety, rate dependency, and drug-induced motivational changes. It is concluded that available data are insufficient to strongly support the notion that FG 7142 and beta-CCE are the anxiogenic drugs "par excellence" they are often claimed to be.

Interactions of Ro 15-4513 with diazepam, sodium pentobarbital and ethanol in a holeboard test

Ro 15-4513 (1.5 mg/kg) decreased the exploratory activity of mice in a holeboard test. This effect was reversed by diazepam (1 mg/kg), ethanol (1 g/kg) and sodium pentobarbital (15 mg/kg). Higher doses of these three agents reduced the number of exploratory head-dips, and Ro 15-4513 antagonised these effects. These observations are consistent with the suggestion that Ro 15-4513 is a partial inverse agonist at benzodiazepine receptors and acts by reducing the efficacy of GABA. Ro 15-4513's interaction with ethanol in the holeboard closely resembled its interaction with the barbiturate.

Bidirectional changes in the consumption of food produced by beta-carbolines

beta-Carboline derivatives provide examples of benzodiazepine receptor ligands which span the range: full agonist-partial agonist-antagonist-partial inverse agonist-full inverse agonist. Taken together, the effects of these compounds illustrate two important principles: firstly, the bidirectionality of effects which can be achieved using benzodiazepine receptor ligands; secondly, the selectivity of effects which are produced by partial agonists. Applied to the study of feeding processes, these principles imply that both hyperphagic and anorectic effects can be generated by actions of selected ligands at benzodiazepine receptors. Furthermore, they suggest that a hyperphagic effect may occur in the absence of side-effects (e.g., sedation, muscle-relaxation), which are characteristic of classical benzodiazepines. Experimental data in support of these predictions are presented. A microstructural approach to feeding behavior indicated that a benzodiazepine receptor agonist and an inverse agonist extend and abbreviate, respectively, the duration of individual bouts of eating. Preference for a saccharin solution was attenuated by the beta-carboline inverse agonist, FG 7142, but rejection of a quinine solution was not increased. Adrenalectomy had no effect on the anorectic effect of inverse agonists.

Effects of beta-carbolines in animal models of anxiety

Animal models of anxiety can be classified into three main groups: those based on conflict or conditioned fear; those exploiting the anxiety produced by novelty; those in which anxiety or aversion is chemically induced. This review briefly describes the existing tests and, where available, the results obtained with beta-carbolines. Many of the beta-carbolines are anxiogenic in the tests, however ZK 91296 and ZK 93423 appear to have anxiolytic properties, and ZK 93426 has a similar profile to that of the benzodiazepine receptor antagonist RO 15-1788. By the results across the spectrum of tests, the reliability and sensitivity of the tests is assessed. The evidence that the anxiogenic and anxiolytic actions of the beta-carbolines are mediated by the BDZ binding sites is also discussed.

The activation of mesoprefrontal dopamine neurons by FG 7142 is absent in rats treated chronically with diazepam

Administration of methyl-beta-carboline-3-carboxamide (FG 7142, 15 mg/kg i.p.) to rats has previously been shown to cause a selective increase in the levels of 3,4-dihydroxy-phenylacetic acid (DOPAC) in the prefrontal cortex and ventral tegmental area (VTA) via an interaction with benzodiazepine receptors. On withdrawal 3 days following chronic treatment with diazepam for 21 days, FG 7142 no longer increased DOPAC levels in either the prefrontal cortex or the VTA. Chronic diazepam treatment alone was ineffective in altering dopamine metabolism in the eight brain regions examined. The present findings indicate that chronic diazepam treatment may cause changes at the level of GABA/benzodiazepine receptor macromolecular complex, which is normally functionally integrated with the mesoprefrontal dopaminergic neurons, so that FG 7142 can no longer exert its intrinsic actions.

Proconflict and electrocorticographic effects of drugs modulating GABAergic neurotransmission

Proconflict and electrocorticographic effects of drugs acting on the benzodiazepine (BDZ)/GABA/chloride-ionophore receptor complex were studied in rats in an attempt to correlate their anxiogenic and epileptogenic activities. Evidence for proconflict activity was assessed by means of an operant conflict procedure based on the simultaneous reward and punishment of a conditioned task, while epileptogenic properties were assessed by monitoring the electrocorticogram (ECoG) of free-moving rats. Pentylenetetrazole and picrotoxin, which act through a site on the chloride channel, and the benzodiazepine (BDZ) inverse agonist FG 7142 showed epileptogenic alterations in the ECoG at doses, respectively, 8, 2 and 3 times higher than those eliciting a significant proconflict effect. For the partial inverse agonist CGS 8216, a ratio of about 60 was found while the BDZ antagonist Ro 15-1788 showed neither epileptogenic nor proconflict activity, except at the highest tested dose for the latter effect (40 mg X kg-1 PO). Inhibition of GABA transmission may mediate both anxiogenic and epileptogenic actions, and a link between these properties may exist as a continuous spectrum of negative intrinsic efficacy at the central BDZ/GABA/chloride-ionophore receptor complex.

Effects of beta-carboline-3-carboxylic acid ethyl ester on suppressed and non-suppressed responding in the rhesus monkey

The effects of the putative 'anxiogenic' compound beta-carboline-3-carboxylic acid ethyl ester (beta-CCE) were studied on non-suppressed and suppressed responding of rhesus monkeys. Responding was maintained under a fixed-interval 2 min schedule of food presentation (non-suppressed responding) and a fixed-interval 2 min schedule of food presentation where each 10th response produced a 3-5 mA footshock (suppressed responding). Rates of suppressed responding were 60-90% lower than those for non-suppressed responding. beta-CCE reliably decreased non-suppressed responding over the range of 0.03-0.3 mg/kg (ED50 approximately 0.04 mg/kg) while consistent decreases in suppressed responding were not obtained in all animals until doses of 1-3 mg/kg (ED50 approximately 2 mg/kg) were given. Doses of beta-CCE greater than 0.01 mg/kg slightly increased blood pressure, moderately increased heart rate and greatly increased plasma ACTH levels for both types of response. In contrast, diazepam increased suppressed responding without affecting non-suppressed responding at low doses (0.3-1 mg/kg), while higher doses were required to decrease suppressed responding. Diazepam had little effect on blood pressure or mean heart rate. Ro 15-1788 (1 mg/kg) blocked the rate-decreasing effects of beta-CCE on non-suppressed responding, suggesting the decrease is mediated via a benzodiazepine recognition site. These results show that under conditions where relatively low doses of diazepam have an anxiolytic effect (i.e. selectively increase rates of suppressed responding), relatively low doses of beta-CCE selectively decrease non-suppressed responding, questioning current notions of how to define an anxiogenic drug effect.