Caffeine antagonizes several central effects of diazepam

Caffeine Consumption among Adults on Benzodiazepine Therapy: United States 1988–1994

The concomitant use of benzodiazepines and caffeine was studied to learn if caffeine consumption varied as a function of benzodiazepine use. Caffeine may antagonize the effects of benzodiazepine and even relatively small amounts can aggravate symptoms associated with anxiety disorders. In addition, caffeine can cause or aggravate insomnia, one of the main reasons cited for use by the subjects in this analysis. Given this, there would seem to be sufficient reason for at least some users of benzodiazepines to consider, with their physicians, avoiding or limiting caffeine consumption. Data from the Third National Health and Nutrition Examination Survey were analyzed to obtain a nationally representative sample of benzodiazepine users. Subjects included 253 individuals (64% women) whose median age was 54 yr. Approximately 88% of benzodiazepine users reported caffeine consumption in the 24-hr. Dietary Recall. 26% of benzodiazepine users and 23% of nonusers reported consuming greater than 250 mg of caffeine during the 24-hr. reference period. In regression analyses, no significant relationships were found between reported caffeine consumption and benzodiazepine use. This study suggests that users and nonusers of benzodiazepines ingest similar amounts of caffeine even though some users should probably avoid or limit caffeine use.

Pharmacokinetic and Pharmacodynamic Interactions Between Zolpidem and Caffeine

The kinetic and dynamic interaction of caffeine and zolpidem was evaluated in a double-blind, single-dose, six-way crossover study of 7.5 mg zolpidem (Z) or placebo (P) combined with low-dose caffeine (250 mg), high-dose caffeine (500 mg), or placebo. Caffeine coadministration modestly increased maximum plasma concentration (C(max)) and area under the plasma concentration-time curve of zolpidem by 30-40%, whereas zolpidem did not significantly affect the pharmacokinetics of caffeine or its metabolites. Compared to P+P, Z+P significantly increased sedation, impaired digit-symbol substitution test performance, slowed tapping speed and reaction time, increased EEG relative beta amplitude, and impaired delayed recall. Caffeine partially, but not completely, reversed most pharmacodynamic effects of zolpidem. Thus, caffeine only incompletely reverses zolpidem's sedative and performance-impairing effects, and cannot be considered as an antidote to benzodiazepine agonists.

Diazepam alters caffeine-induced effects on beta-endorphin levels in specific rat brain regions

The present study was conducted to evaluate the effects of caffeine and the benzodiazepine agonist diazepam, and a combination of both on beta-endorphin (beta-EN) levels in specific rat brain regions. Male Sprague-Dawley rats (150-200 g) adapted to a 12-hour light: 12-hour dark illumination cycle were used in this study. Caffeine (10 mg/kg), diazepam (2 mg/kg) or a combination of caffeine (10 mg/kg) and diazepam (2 mg/kg) were administered intraperitoneally to rats at 11:00 hr. Control animals were injected with saline. Animals were sacrificed by decapitation 1 h after injection, the brains were immediately removed; the cortex, hippocampus, hypothalamus and midbrain were dissected and their B-EN levels measured by radioimmunoassay. Caffeine administration significantly increased B-EN levels in the cortex. Similarly, administration of diazepam alone resulted in a significant increase of B-EN levels in cortex. However, concurrent administration of diazepam and caffeine resulted in higher increase of B-EN levels in cortex. No significant changes in B-EN levels were detected in hippocampus and midbrain after administration of either caffeine or diazepam alone. On the other hand, when diazepam and caffeine were concurrently administered a significant increase of B-EN levels were observed in the midbrain. Moreover, administration of diazepam alone resulted in a significant increase of B-EN levels in hypothalamus. This increase was still observed following concurrent administration of diazepam and caffeine. These results clearly indicate that diazepam alters caffeine-induced effects on B-EN in specific rat brain regions.

Is GABA involved in the development of caffeine tolerance?

Caffeine (10 or 20 mg/kg per day, po)-induced stimulation of locomotor activity (LA) reached its peak following 4 consecutive days of caffeine administration. Caffeine-induced stimulation of LA was restored to the control values following caffeine tolerance after 16 or 12 consecutive days of caffeine treatment at a dose of 10 or 20 mg/kg per day, po. Biochemical studies showed that caffeine in the nontolerant condition reduced GABAergic activity in cerebral cortex, corpus striatum, cerebellum, hypothalamus and pons-medulla; but tolerance to caffeine (10 or 20 mg/kg per day, po) pushed up the GABAergic activity to the control value in all these regions of brain. Further, it was found that muscimol reduced the LA while bicuculline stimulated LA in the caffeine tolerant condition. Thus, from the present study it may be concluded that: (a) caffeine-induced stimulation of LA is dependent on dose and duration of caffeine treatment, (b) development of tolerance to caffeine is dependent on the dosage of caffeine, and (c) the reduction of central GABAergic activity in the caffeine-nontolerant condition pushed up and restored the LA to the control level on the development of tolerance to caffeine.

Alprazolam, caffeine and their interaction: relating DRL performance to pharmacokinetics

Three-hour sessions of differential reinforcement of low-rate behavior (DRL 45-s) in rats were used to investigate alprazolam, caffeine, and their interactions at the onset, peak and disappearance of serum alprazolam, while caffeine level remained constant. The dose-response curve (DRC) method of Pöch permitted an extensive evaluation of the kind (additivity or independence) of interactions occurring in combined drug effects. The alprazolam and caffeine DRCs were used to derive theoretical additive and independent relations, and the observed combined effects compared to these functions. Behavior-time profiles of the combined effects were similarly compared. Serum alprazolam and caffeine concentrations correlated with their respective behavior-time profiles. No acute tolerance was observed either for the individual drugs or their combinations. Alprazolam was more potent than caffeine in disrupting DRL behavior. Because alprazolam is much shorter-lived (t1/2 = 32 min) than caffeine (t1/2 = 3 h) in rats, potency ratios between alprazolam and caffeine changed across session time (from 123 to 4), which determined the expression of the combined effects. Although the combined effects were not distinguishable in terms of additivity or independence in both the DRCs and in the behavior-time profiles, they showed neither synergism nor antagonism. The pharmacokinetics of alprazolam were not altered by caffeine, but those of caffeine were affected by alprazolam.

Potentiation by neurosteroids of muscimol/adenosine interactions in rat hippocampus

Extracellular recordings were made from the CA1 pyramidal cell layer of hippocampal slices in response to stimulation of Schaffer collateral fibres in stratum radiatum. Alphaxalone and 5 alpha-pregnan-3 alpha-ol-20-one potentiated the inhibitory effect of muscimol on the population spike size at low concentrations (0.5 and 1 microM) that had no significant effect on the spike size by themselves. This profile is in agreement with other reports which have described the effect of these neurosteroids as barbiturate-like. Alphaxalone and 5 alpha-pregnan-3 alpha-ol-20-one also at low concentrations potentiated the inhibitory effect of adenosine alone and in the presence of 1 mM barium which blocked adenosine activated potassium channels. Alphaxalone failed to potentiate the inhibitory effect of adenosine in the presence of 1 microM bicuculline. It is concluded that these neurosteroids enhanced the potentiative interaction between adenosine and muscimol in the presence of barium. The results indicate that adenosine's effects are normally enhanced by virtue of the potentiative interaction occurring with endogenous GABA.

Influence of chronic aminophylline on antielectroshock activity of diazepam and aminophylline-induced convulsions in mice

The effects of chronic administration of aminophylline (AMPH; 50 mg/kg, twice daily for 14 consecutive days) were studied on both antielectroshock efficacy of diazepam (DZP) and convulsive activity of AMPH in mice. AMPH injected acutely at a dose of 50 mg/kg significantly reduced anticonvulsant action of DZP elevating ED50 from 10.9 (control) to 15.9 mg/kg (p < 0.01). After the administration of AMPH for 3 days, ED50 value was still higher compared with control. Chronic treatment with AMPH resulted in further increase of ED50 of DZP, which was 20.2 mg/kg, and this elevation was significant not only when compared with saline-treated animals, but also with acute and 3-day administration of the xanthine (p < 0.01, 0.05, and 0.001, respectively). Therefore, no tolerance to this AMPH-mediated effect was found, and even an enhancing influence was observed. On the other hand, chronic treatment with AMPH decreased convulsive activity of AMPH elevating ED50 for induction of clonic seizures from 218 to 252 mg/kg (p < 0.01). The remaining seizure parameters were unaffected. Furthermore, in both cases pharmacokinetic interactions were excluded, at least in terms of total plasma levels of the drugs. The results suggest that the mechanisms governing AMPH-induced reversal of the anticonvulsant efficacy of DZP qualitatively differ from those underlying AMPH-induced convulsions. Moreover, these data support the claim that AMPH should be avoided in patients suffering from different types of epilepsy.

Perceptual masking of the chlordiazepoxide discriminative cue by both caffeine and buspirone

Twelve male Sprague-Dawley rats were trained to discriminate between the interoceptive stimulus attributes of 5 mg/kg chlordiazepoxide (CDP) and saline in a two-lever operant task under a fixed-ratio 10 (FR-10) schedule of food reinforcement. Caffeine, buspirone, and Ro 15-1788 failed to engender complete generalization when tested in combination with saline. In drug interaction test sessions caffeine (56 mg/kg) blocked the discriminative stimulus properties of the training dose of CDP and shifted the CDP discriminative dose-response function to the right. This rightward shift in CDP discriminative function was paralleled by a concomitant downward shift in the rate-of-responding dose-response function. Drug interaction test sessions conducted with 3.2 mg/kg of buspirone in combination with various doses of CDP engendered a downward shift in both the discriminative and rate-of-responding dose-response functions. Because 3.2 mg/kg buspirone in combination with the training dose of CDP resulted in complete response rate suppression, additional combination tests were conducted with 3 mg/kg CDP, a dose which reliably engendered > 90% CDP-appropriate responding, and various doses of buspirone. Similar to the CDP-caffeine interactions, buspirone blocked the cueing properties of 3 mg/kg CDP with a parallel reduction in response rates. Interaction test sessions conducted with Ro 15-1788 and CDP resulted in rightward shifts in both the discriminative and rate functions of CDP. We suggest that the interactions between CDP and both caffeine and buspirone resulted from the perceptual masking of the interoceptive (subjective) effects of CDP, whereas the interaction between Ro 15-1788 and CDP reflect pharmacological antagonism.

Influence of aminophylline and 8-(p-sulfophenyl)theophylline on the anticonvulsive action of diphenylhydantoin, phenobarbital, and valproate against maximal electroshock-induced convulsions in mice

Aminophylline (theophylline2.ethylenediamine) in the dose of 12.5 mg/kg (i.p.) was ineffective upon all antiepileptic drugs studied and at the higher dose of 25 mg/kg, impaired the anticonvulsant action of phenobarbital and valproate against maximal electroshock in mice. The protection offered by diphenylhydantoin was diminished by aminophylline at 50 mg/kg (0.238 mmol of anhydrous theophylline/kg). In contrast, 8-(p-sulfophenyl)theophylline (a theophylline derivative unable to cross the blood-brain barrier) in the dose of 80 mg/kg (0.238 mmol/kg) did not influence the protective activity of diphenylhydantoin, phenobarbital, and valproate. It might be concluded that the aminophylline-induced impairment of the anticonvulsant action of common antiepileptic drugs results from the central effects of this methylxanthine.

Effects on open-field behavior of diazepam and buspirone alone and in combination with chronic caffeine

Effects of diazepam (1, 2 mg/kg) and buspirone (1.25, 2.5 mg/kg) on locomotor and rearing activity were observed in rats tested in an open field. Both doses of each drug reduced ambulation. However, for buspirone, this effect was confined to females. Walking and rearing was reduced by the higher dose of diazepam and rearing by both doses of buspirone. In rats that had ingested approximately 26 mg/kg/day of chronic caffeine for seven days prior to and immediately before testing, all effects of diazepam observed earlier failed to achieve significance except for ambulation. However, all earlier buspirone effects (including female-only decreased ambulation) were unaffected by the caffeine treatment. It was concluded that buspirone may be preferable to diazepam as an anxiolytic when in the presence of regular caffeine ingestion.

Effects of benzodiazepine administration on A1 adenosine receptor binding in-vivo and ex-vivo

The adenosine receptor has been implicated in the central mechanism of action of benzodiazepines. The specific binding of an A1-selective adenosine antagonist radioligand, [3H]8-cyclopentyl-1,3-dipropylxanthine, was measured in-vivo in mice treated with alprazolam (2 mg kg-1, i.p.), lorazepam (2 mg kg-1, i.p.) and vehicle. Binding studies were performed in-vivo and ex-vivo in mice receiving continuous infusion of alprazolam (2 mg kg-1 day-1), lorazepam (2 mg kg-1 day-1) and vehicle by mini-osmotic pumps for 6 days. Continuous infusion of alprazolam and lorazepam significantly decreased specific binding by 34 and 53%, respectively, compared with vehicle treatment (P less than 0.01). Single doses of alprazolam and lorazepam induced a similar trend in specific binding in-vivo (P = 0.07). There were no alterations in A1-receptor density (Bmax) or affinity (Kd) in cortex, hippocampus or brainstem in ex-vivo studies. Benzodiazepine treatment may diminish A1- receptor binding in-vivo by inhibiting adenosine uptake or by direct occupancy of the A1 adenosine receptor recognition site.

Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects

Caffeine is the most widely consumed central-nervous-system stimulant. Three main mechanisms of action of caffeine on the central nervous system have been described. Mobilization of intracellular calcium and inhibition of specific phosphodiesterases only occur at high non-physiological concentrations of caffeine. The only likely mechanism of action of the methylxanthine is the antagonism at the level of adenosine receptors. Caffeine increases energy metabolism throughout the brain but decreases at the same time cerebral blood flow, inducing a relative brain hypoperfusion. Caffeine activates noradrenaline neurons and seems to affect the local release of dopamine. Many of the alerting effects of caffeine may be related to the action of the methylxanthine on serotonin neurons. The methylxanthine induces dose-response increases in locomotor activity in animals. Its psychostimulant action on man is, however, often subtle and not very easy to detect. The effects of caffeine on learning, memory, performance and coordination are rather related to the methylxanthine action on arousal, vigilance and fatigue. Caffeine exerts obvious effects on anxiety and sleep which vary according to individual sensitivity to the methylxanthine. However, children in general do not appear more sensitive to methylxanthine effects than adults. The central nervous system does not seem to develop a great tolerance to the effects of caffeine although dependence and withdrawal symptoms are reported.

Caffeine Moderately Antagonizes the Effects of Triazolam and Zopiclone on the Psychomotor Performance of Healthy Subjectsf

To determine whether caffeine antagonizes the decremental effects of triazolam and zopiclone on human performance, oral single doses of 0.250 mg triazolam, 7.5 mg zopiclone, or respective placebos, with and without 300 mg caffeine, were given to parallel groups of student volunteers in two double-blind studies. Objective tests and subjective visual analogue ratings were done at baseline and 30 min. and 90 min. after the intake. In Study I, triazolam produced drowsiness at 30 min. but did not differ from the placebo in other tests. Caffeine induced alerting effects in various tests and differed from triazolam in some (digit substitution, drowsiness, calmness, mental slowness) but not all variables measured. Caffeine and triazolam were interpreted as being antagonists. In Study II, zopiclone impaired digit substitution and flicker fusion, produced exophoria and lowered systolic blood pressure. Caffeine differed from zopiclone in several test functions, but it also differed from caffeine + zopiclone whereas zopiclone differed from caffeine + zopiclone only in two tests (Maddox wing, systolic blood pressure). Thus, zopiclone counteracted the effects of caffeine more easily than caffeine counteracted the decremental effects of zopiclone. We conclude that triazolam may not differ importantly from diazepam as regards their antagonism towards caffeine, whereas further research on the antagonism between zopiclone and caffeine needs to be done.

Sustained synergism by chronic caffeine of the motor control deficit produced by midazolam

To evaluate the effects of chronic caffeine on the impairment of discriminative fine motor control produced by midazolam, rats were trained to hold a force transducer steady to deliver food pellets. Chronic, daily doses of midazolam (3 mg/kg SC) led to a stable level of motor impairment. Chronic caffeine (20 mg/kg IP) alone usually produced a more moderate deficit or, for one animal, no deficit. Combined, chronic administration of these doses yielded a sustained synergism in motor performance impairment, which contrasted with the antagonism usually found between the benzodiazepines and methylxanthines when performance is evaluated by psychomotor tests not requiring fine motor control. The observed synergism was not explicable in terms of measured disposition of the drugs. The synergistic production of fine motor dyskinesia by the concurrent administration of caffeine and midazolam may be relevant to the triggering of anxiety attacks by caffeine observed in panic disorder patients.

Synergism by caffeine and by cocaine of the motor control deficit produced by midazolam

To evaluate the effects of caffeine and cocaine on the impairment of discriminative motor control produced by midazolam, rats were trained to hold a force transducer operated with a paw so that it remained between upper and lower limits of a force band for a continuous 1.5-s period to deliver each food pellet. Acute doses of 3 mg/kg midazolam SC impaired motor performance. Except for one animal, caffeine (10-40 mg/kg IP) had little or no effect on performance, while cocaine (3.75-22.5 mg/kg IP) produced dose-related impairment. When each dose of caffeine was combined with 3 mg/kg midazolam, a marked synergism in motor performance impairment occurred. Cocaine plus midazolam produced mainly an additive synergism. The conspicuous synergistic action of caffeine on the motor control deficit produced by midazolam contrasts with the typical antagonism found between the benzodiazepines and methylxanthines when performance is evaluated by psychomotor tests not requiring fine motor control.

Gestational exposure to diazepam increases sensitivity to convulsants that act at the GABA/benzodiazepine receptor complex

Experiments examining seizure sensitivity were conducted on adult male offspring exposed to diazepam at 1.0 or 2.5 mg/kg per day in utero over gestational days 14-20. Threshold dosages to facial clonus, myoclonic jerk, clonic seizure, and extensor tonus were determined via i.v. infusion of bicuculline, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), picrotoxin, pentylenetetrazol, caffeine and strychnine. Relative to uninjected and vehicle-exposed adult male offspring, prenatal diazepam administration reduced the threshold for bicuculline- and DMCM-induced facial clonus and myoclonic jerk by 40-50%. The threshold dosages to facial clonus, myoclonic jerk and clonic seizure from picrotoxin infusion were similarly reduced in animals exposed to diazepam in utero. In contrast, seizure thresholds to pentylenetetrazol, caffeine and strychnine were not affected by early developmental exposure to diazepam. In parallel biochemical studies, an increased sensitivity to the antagonistic effects of bicuculline methiodide on gamma-aminobutyrate (GABA)-stimulated chloride influx was observed in cortical synaptoneurosomes from adult male progeny of diazepam-treated dams. The results are interpreted to reflect a long-lasting alteration in the function of the GABA/benzodiazepine receptor complex by prenatal diazepam exposure that is manifest at the behavioral and neurochemical level in a pharmacologic specific manner.

Caffeine-induced anxiety and increase of kynurenine concentration in plasma of healthy subjects: a pilot study

The concentration of kynurenine, a neuroactive tryptophan metabolite, in blood plasma after pharmacologically induced anxiety was studied. Anxiety was provoked in 15 healthy volunteers by an anxiogenic dose of caffeine. Kynurenine concentration was markedly increased at the peak of anxiety and returned to normal after anxiety had abated. Possible causes responsible for this effect are discussed. There is a correlation between kynurenine concentration in blood plasma and indices of state and trait anxiety (Spielberger-Khanin scale) and anxiety (Hamilton scale) at baseline. The correlation disappears at the peak of anxiety. It is suggested that kynurenine is involved in caffeine-induced anxiety in humans. The absence of correlation at the peak of caffeine-induced anxiety is discussed.

Chronic benzodiazepine treatment and cortical responses to adenosine and GABA

The effects of chronic treatment of mice with clonazepam have been examined on the responses of neocortical slices to adenosine, 5-hydroxytryptamine (5-HT) and gamma-aminobutyric acid (GABA). Responses to these agonists were measured as changes in the depolarisation induced by N-methyl-D-aspartate (NMDA). Added to the superfusion medium diazepam blocked responses to adenosine but not 5-HT; this effect was not observed with 2-chloroadenosine or in the presence of 2-hydroxynitrobenzylthioguanosine. GABA was inactive in control slices but chronic treatment with clonazepam induced responses to GABA and enhanced responses to adenosine but not 5-HT. It is suggested that the induction of GABA responses may reflect the up-regulation of GABA receptors, but the increase of adenosine responses by clonazepam implies that there is no simple relationship between adenosine receptor binding and functional responses.

Adenosine receptor antagonism accounts for the seizure-prolonging effects of aminophylline

The mechanism of action of aminophylline in prolonging seizures was tested in amygdala-kindled rats. Aminophylline prolonged the afterdischarge duration of kindled seizures. This seizure-prolonging action of aminophylline was strongly antagonized by the adenosine A1 agonist cyclohexyladenosine and partially antagonized by the benzodiazepine partial agonist RO 15-1788. However, the specific benzodiazepine antagonist CGS 8216 did not affect the seizure-prolonging action of aminophylline. Also, the potent anticonvulsant effect of diazepam on kindled seizures, which was completely antagonized by CGS 8216, was unaffected by aminophylline. Furthermore, a range of benzodiazepine inverse agonists, GABA antagonists, phosphodiesterase inhibitors and xanthines did not prolong afterdischarge durations. These results demonstrate that the seizure-prolonging action of aminophylline is due to block of A1 adenosine receptors since it is prevented by adenosine A1 agonists.

Peripheral type benzodiazepine receptors and response to adenosine on the guinea-pig isolated trachea

It has been reported that dipyridamole, an adenosine uptake inhibitor, and some benzodiazepines potentiate the responses to adenosine in peripheral organs and in particular, on guinea-pig isolated atria. In this paper, we have examined the potentiation of responses to adenosine produced by dipyridamole, diazepam and four compounds with selective agonistic activity towards the central (clonazepam) or peripheral (Ro5-4864) type benzodiazepine receptors or antagonistic activity towards the central (flumazenil) or peripheral (PK 11195) benzodiazepine receptors in guinea-pig trachea in vitro. In preparations under basal tone and in the absence of adenosine, dipyridamole (10(-5) M) and benzodiazepines (10(-4) M) with the exception of flumazenil induced a relaxation of the airway smooth muscle. In addition, diazepam (10(-4) M) attenuated the phasic response to histamine (10(-5) M). Dipyridamole, and the benzodiazepine agonists diazepam, Ro5-4864 and clonazepam (10(-5) to 10(-4) M) produced potentiation of the tracheal response to adenosine, the rank order of potency being dipyridamole (pKi = 7.77 +/- 0.12, n = 8) greater than Ro5-4864 (pKi = 5.43 +/- 0.18, n = 6) greater than or equal to diazepam greater than clonazepam (pKi = 4.84 +/- 0.11, n = 6). The two benzodiazepine receptor antagonists, flumazenil and PK 11195, gave a significant but small potentiation to adenosine only at 10(-4) M. In the presence of dipyridamole (10(-5) M), diazepam (10(-4) M) did not cause any further potentiation to adenosine. Additionally, the potentiation produced by diazepam was not antagonised by flumazenil, whereas it was potently antagonised by PK 11195. Similarly, PK 11195 potently inhibited the adenosine potentiation produced by Ro5-4864.(ABSTRACT TRUNCATED AT 250 WORDS)

Separate and combined effects of caffeine and alprazolam on motor activity and benzodiazepine receptor binding in vivo

CD-1 mice received single intraperitoneal (IP) doses of caffeine-sodium benzoate (caffeine doses: 0, 20 and 40 mg/kg) followed by injections of alprazolampropylene glycol (0, 0.05, and 2 mg/kg, IP) to determine brain concentrations, effects on in vivo receptor binding of a specific high-affinity benzodiazepine receptor ligand [3H]Ro15-1788, and effects on motor activity over a 1-h period. A behavioral monitoring device, using infrared sensors, measured horizontal and ambulatory activity. Caffeine produced significant increases in all motor activity measures as compared to vehicle treatment, with low dose caffeine (with brain concentrations of 13 micrograms/g) stimulating activity to a greater degree than the high dose (with brain concentrations of 30 micrograms/g). The overall effect of caffeine on benzodiazepine receptor binding was not significant. Alprazolam significantly diminished motor activity and altered benzodiazepine receptor binding. Low dose alprazolam increased binding, while the high dose diminished it. Caffeine and alprazolam antagonized each other's behavioral effects in this study, but did not alter each other's uptake into brain. Alprazolam's antagonism of caffeine-induced motor stimulation was associated with decreases in receptor binding, whereas caffeine's reversal of alprazolam-induced motor depression was not associated with any changes in binding. The lack of a clear association between drug effects on benzodiazepine binding and on motor activity suggests that behavioral effects of caffeine and alprazolam may be mediated by other sites in addition to the benzodiazepine receptor.

Central effects of corticotropin releasing factor (CRF): evidence for similar interactions with environmental novelty and with caffeine

Centrally administered rat/human corticotropin-releasing factor (rCRF) increases low levels of locomotor activity by rats tested in a familiar environment but suppresses the higher levels of activity associated with exposure of the animals to a novel environment. These opposing responses do not appear to be manifestations of a simple rate-dependent effect, since ICV-administered rCRF did not lower the higher levels of locomotor activity associated with the dark (active) phase of the animal's activity cycle. Caffeine, which has anxiogenic effects in man, produces effects in rats which are similar to those of rCRF. That is, both compounds elevate activity in a familiar environment but lower activity in a novel environment. Furthermore, caffeine appears to substitute for novelty in determining the direction of the locomotor effect of rCRF. Animals made hyperactive by caffeine show decreased activity when co-administered rCRF. These findings are consistent with the view that CRF acts through pathways which also subserve the responsiveness to novelty and to the anxiogenic compound caffeine.

Interaction of caffeine with the GABAA receptor complex: alterations in receptor function but not ligand binding

Behavioral and neurochemical evidence indicates interactions between caffeine and other adenosine receptor ligands and the gamma-aminobutyric acid (GABA)-benzodiazepine system. To assess the effects of caffeine on binding and function at the GABAA receptor, we studied the effects of behaviorally-active doses of caffeine on benzodiazepine and Cl- channel binding and on overall function of the GABAA receptor as measured by Cl- uptake. There was no effect of caffeine on benzodiazepine receptor binding in cortical synaptosomal membranes at concentrations of 1-100 microM. No effects on benzodiazepine binding were found ex vivo in mice treated with caffeine, 20 and 40 mg/kg. At the putative Cl- channel site labeled by t-butylbicyclophosphorothionate (TBPS), binding was unchanged in vitro after caffeine treatment (1 and 10 microM) in washed and unwashed membranes. However, in ex vivo studies caffeine (20 and 40 mg/kg) increased numbers of TBPS sites in unwashed but not washed membranes. Muscimol-stimulated Cl- uptake into cortical synaptoneurosomes was decreased in mice treated with caffeine, 20 and 40 mg/kg. Similar results were observed in in vitro preparations treated with 50 microM but not 100 microM caffeine. These results indicate that caffeine administration significantly alters the Cl- transport function of the GABAA receptor complex.

Anxiolytic effect of caffeine and caffeine-clonazepam interaction: evaluation by NaCl solution intake

The administration of drugs with anxiolytic action to rehydrating rats augments the intake of 1.5% NaCl solution. In order to clarify the status of caffeine as an anxiolytic agent and its possible interaction with a benzodiazepine having high potency and efficacy in this regard, caffeine (0.78-100 mg/kg) alone and caffeine (0.78-50 mg/kg) plus clonazepam (0.05 or 0.50 mg/kg) injections (IP) were administered to rehydrating rats prior to 1-hr sessions during which they drank 1.5% NaCl solution. When given alone, caffeine, within a particular dose range, and clonazepam at both doses, augmented NaCl solution intake, but when administered in combination, caffeine antagonized the effects of clonazepam.

Caffeine-induced anxiogenesis: the role of adenosine, benzodiazepine and noradrenergic receptors

The purpose of this study was to determine the mechanism by which caffeine increases anxiety. Rats were tested in the social interaction test of anxiety after administration of caffeine (20 or 40 mg/kg) alone or in combination with various compounds. In order to investigate the role of adenosine receptors, caffeine was given in combination with 2-chloroadenosine (0.1 and 1 mg/kg). To investigate the role of benzodiazepine receptors, chlordiazepoxide (5 mg/kg), a benzodiazepine antagonist, flumazenil (RO 15-1788, 1 and 10 mg/kg) and a triazolobenzodiazepine U-43,465 (32 mg/kg) were used. Finally, an alpha 2-receptor agonist, clonidine (0.1 and 0.025 mg/kg) and a beta-adrenoceptor antagonist, DL-propranolol (5 mg/kg), were used to study the role of noradrenergic systems in the effects of caffeine. Caffeine (20 and 40 mg/kg) reduced the time spent in social interaction and this effect was antagonized by chlordiazepoxide, U-43,465 and DL-propranolol, but not by flumazenil, 2-chloroadenosine or clonidine. It was therefore concluded that the anxiogenic effect of caffeine was unlikely to be due to its effects at adenosine or benzodiazepine receptors. It is suggested that the reversal of caffeine's effects by chordiazepoxide may have been "functional," i.e., merely a cancellation of two opposite effects. It is discussed whether the reversal of caffeine's effects by propranolol and U-43,465 are functional, or reflect a noradrenergic site of action.

Theophylline antagonizes the effect of diazepam on ventricular automaticity

The effect of diazepam on ventricular automaticity induced by a local injury was investigated in the isolated right ventricle of the rat in the presence of the diazepam central antagonist, RO 15-1788, and of the adenosine antagonist, theophylline. Theophylline but not RO 15-1788 antagonized the inhibitory effect induced by diazepam on ventricular automaticity. The inhibitory effect of adenosine but not that of 2-chloroadenosine was potentiated in the presence of diazepam. The results suggest that the inhibitory effect of diazepam on ventricular automaticity results from the inhibition of adenosine uptake.

The effect of benzodiazepines on the 5-HT agonist-induced head-twitch response in mice

The effects of four benzodiazepines (diazepam, clonazepam, oxazepam and clobazam) were studied on the head-twitch response induced in mice by several 5-HT receptor agonists. All the benzodiazepines tested potentiated the effects of the directly acting agonists 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), quipazine and mescaline, without themselves inducing head-twitches. In contrast, none of them potentiated head-twitches induced by the indirectly acting agonist 5-hydroxytryptophan (5-HTP; with carbidopa 25 mg/kg), and in some experiments a clear inhibition was seen. The clonazepam (10 mg/kg) potentiation of 5-MeODMT-induced head-twitches was not antagonised by flumazenil, (+)-bicuculline, or by pretreatment with p-chlorophenylalanine. Neither was it mimicked by muscimol, which inhibited head-twitches. These results indicate that the observed potentiation is not mediated by benzodiazepine receptors and that it occurs postsynaptically to the initiating 5-HT receptors. The inability of the benzodiapines to potentiate 5-HTP-induced head-twitches probably reflects a reduction in 5-HT neuronal activity mediated by benzodiazepine receptors, as co-administration of flumazenil and clonazepam potentiated the effects of 5-HTP whereas each compound alone had no effect.

Chronic administration of diazepam downregulates adenosine receptors in the rat brain

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

Psychophysiological aspects of caffeine consumption

Caffeine may be the psychoactive compound most widely used in the United States. Caffeine appears in coffee, tea, cola drinks, chocolate bars and cocoa, cold and diet medications, and sleep-prevention compounds; the amount of caffeine varies in different substances and according to preparations. Research on caffeine's effects on alcoholic drinks, alertness, anxiety, heart rate, performance, and sleep is reviewed. Caffeine is usually not harmful, although long-range effects of caffeine have not been thoroughly investigated. Caffeine's effects often have been studied by means of ingestion of coffee but substances other than caffeine may be active in coffee and tea. The placebo effect contributes to some of the effects experienced by coffee-caffeine users.

Anticonvulsant activity of carbamazepine and N6-L-phenylisopropyladenosine in rabbits. Relationship to adenosine receptors in central nervous system

The present work deals with an EEG and behavioral study on the effects of carbamazepine (CBZ) and N6-L-phenylisopropyladenosine (L-PIA) against the convulsions due to caffeine and pentylenetetrazole (PTZ) in rabbits. Pretreatment with L-PIA (1, 3 and 4 mg/kg) caused a dose-related inhibition of the motor convulsions and the EEG "grand mal" ictal seizure induced by caffeine (75 mg/kg IV). On the contrary, L-PIA given at the high dose of 5 mg/kg IV partially inhibited the EEG and motor seizures elicited by PTZ (20 mg/kg IV). CBZ completely antagonized the EEG and motor convulsions induced by caffeine, while exerted only a protective action towards the EEG and motor convulsions due to PTZ. The administration of an ineffective dose of CBZ (5 mg/kg IV) was able to enhance the protective action of L-PIA towards caffeine-induced convulsions. This synergistic action between CBZ and L-PIA is also present towards the spike-and-wave complexes elicited by PTZ (10 mg/kg). These results confirm that the purinergic system plays an important role in the regulation of the CNS excitability. They suggest therefore, that the anticonvulsant properties of CBZ may be at least partially explained by an influence of this drug on the purinergic system.

Electrophysiology of benzodiazepine receptor ligands: multiple mechanisms and sites of action

Electrophysiology of BZR ligands has been reviewed from different points of view. A great effort was made to critically discuss the arguments for and against the temporarily leading hypothesis of the mechanism of action of BZR ligands, the GABA hypothesis. As has been discussed at length in the present article, an impressive body of electrophysiological and biochemical evidence suggests an enhancement of GABAergic inhibition in CNS as a mechanism of action of BZR agonists. Biochemical data even indicate a physical coupling between GABA recognition sites and BZR which, together with the effector site build-up by Cl- channels, form a supramolecular GABAA/BZR complex. By binding to a specific site on this complex, BZR agonists allosterically increase and BZR inverse agonists decrease the gating of GABA-linked Cl- channels, whereas BZR antagonists bind to the same site without an appreciable intrinsic activity and block the binding and action of both agonists as well as inverse agonists. While this model is supported by many electrophysiological experiments performed with BZR ligands in higher nanomolar and lower micromolar concentrations, it does not explain much controversial data from animal behavior and, more importantly, is not in line with electrophysiological effects obtained with low nanomolar BZ concentrations. The latter actions of BZR ligands in brain slices occur within a concentration range compatible with concentrations of BZ observed in CSF fluid, which would be expected to be found in the biophase (receptor level) during anxiolytic therapy in man. Enhanced K+ conductance seems to be a suitable candidate for this effect of BZR ligands. This direct action on neuronal membrane properties may underlie the many electrophysiological observations with extremely low systemic doses of BZR ligands in vivo which demonstrated a depressant effect on spontaneous neuronal firing in various CNS regions. Skeletomuscular spasticity and epilepsy are two neurological disorders, where both the enhanced GABAergic inhibition and increased K+ conductance may contribute to the therapeutic effect of BZR agonists, since electrophysiological and behavioral studies strongly support GABA-dependent as well as GABA-independent action of BZR ligands elicited by low to intermediate doses of BZ necessary to evoke anticonvulsant and muscle relaxant effects. Somewhat higher doses of BZR ligands, inducing sedation and sleep, lead perhaps to the only pharmacologically relevant CNS concentrations (ca. 1 microM) which might be due entirely to increased GABAergic inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

The chlordiazepoxide/pentylenetetrazol discrimination: characterization of drug interactions and homeostatic responses to drug challenges

Rats were trained to discriminate chlordiazepoxide (CDP) from pentylenetetrazol (PTZ) in a two-lever food motivated discrimination task. Training drug doses were adjusted until subjects emitted approximately 50% of their responses on each of the two drug-appropriate levers during saline injection tests. Tests that followed injection of CDP/PTZ combinations illustrated a reciprocal antagonism between the two drugs. Saline-injection tests that followed large dose injections of CDP revealed a period of predominantly PTZ-appropriate responding that persisted after the initial period of predominantly CDP-appropriate responding. These data are interpreted to suggest that, unlike some other drugs that have been shown to antagonize the behavioral and CNS effects of benzodiazepines, the interoceptive stimulus generated by PTZ occupies a position opposite to that of CDP along some single affective continuum. In addition, these data suggest that drug/drug (DD) discriminations are capable of characterizing the interactions between training drugs. Finally, the data suggest that the CDP/PTZ discrimination is a sensitive detector of bidirectional shifts in interoceptive stimulus state along the CDP/PTZ continuum.

The role of adenosine in the central actions of the benzodiazepines

1. Evidence is presented which indicates that the central actions of the benzodiazepines cannot be fully accounted for by assuming an action only at the GABAA-Cl- channel supramolecular complex. 2. The hypothesis is presented, together with supporting evidence, that inhibition of adenosine uptake can account for many of the actions of the benzodiazepines. 3. New findings showing that Ro 15-1788 and Ro 5-4864 have both potentiative and antagonistic interactions with adenosine are discussed. 4. The proconvulsant beta-carbolines are shown to be adenosine antagonists. 5. The concept that benzodiazepine action may involve several mechanisms is presented.

Effects of bicuculline-induced seizures on benzodiazepine and adenosine receptors in developing rat brain

The effects of seizures induced by an acute administration of bicuculline have been investigated on the central benzodiazepine and adenosine receptors in developing rats and in adults. Generalized seizures rapidly increased the total number of both benzodiazepine binding sites and adenosine A1 receptors, without changes in receptor affinity (KD). It was concluded that such a phenomenon may facilitate the anticonvulsant action of benzodiazepine and adenosine via receptor binding and that it could be an adaptative process to protect subjects against recurrent seizures, especially in newborns.

Caffeine-diazepam interaction and local cerebral glucose utilization in the conscious rat

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to study the effects of the acute administration of a sedative anticonvulsant dose of diazepam (2 mg/kg) on rat brain energy metabolism. This benzodiazepine was injected to rats chronically treated for two weeks either by caffeine (10 mg/kg/day) or by saline. After the administration of diazepam to saline-treated rats, average glucose utilization of the brain as a whole was reduced by 21% and rates of glucose utilization were deeply decreased in frontal and auditory cortex, mammillary body, lateral thalamus, medial and lateral geniculate. In caffeine-treated rats, the administration of diazepam induced the same effects of brain energy metabolism as in saline-treated rats. The results of the present study indicate that diazepam mainly decreases glucose utilization in structures widely believed to mediate anxiety.

GABAA receptor blockers reverse the inhibitory effect of GABA on brain-specific [35S]TBPS binding

Thirteen substances previously reported to antagonize the electrophysiological effects of gamma-aminobutyric acid (GABA) on neurons also reversed the inhibitory effects of GABA on specific [35S]t-butylbicyclophosphorothionate ([35S]TBPS) binding to sites on rat brain membranes in vitro with a rank-order of potencies similar to those found in electrophysiological systems (R 5135 greater than pitrazepin greater than bicuculline greater than SR 95103 greater than securinine) confirming the earlier conclusion that GABA inhibits [35S]TBPS binding by acting allosterically on physiologically relevant GABAA receptors. Pitrazepin is the most potent of a series of mono N-aryl piperazines that block GABAA receptors. The new aryl amino pyridazine GABA derivative SR 95531 was about 3-fold more potent than bicuculline and 39-fold more potent than the structurally related SR 95103. Four known GABA antagonists have the same rank orders of potencies as convulsants and as reversers of GABA's inhibitory action on [35S]TBPS binding (bicuculline greater than securinine greater than theophylline greater than caffeine). Reversal of GABA-induced suppression of [35S]TBPS binding provides a simple method for further characterizing GABAA receptors linked to TBPS binding sites, and facilitates identification of convulsants and novel, perhaps selective, GABA antagonists.

Ro 15-1788 both antagonizes and potentiates adenosine-evoked depression of cerebral cortical neurons

The effects of Ro 15-1788, a benzodiazepine antagonist with some agonist properties, were studied on adenosine and adenosine 5'-N-ethyl-carboxamide (NECA)-evoked depressions of rat cerebral cortical neuronal activity. Iontophoretically applied Ro 15-1788 had both antagonistic and potentiative interactions with adenosine. Reductions in the magnitude of adenosine-evoked depressions of firing were evident during the period of Ro 15-1788 application, with a long-lasting potentiative effect becoming apparent upon termination of the Ro 15-1788 application. Depressions of cell firing evoked by NECA, an uptake-resistant analog of adenosine, were antagonized by Ro 15-1788, with no subsequent potentiation. Larger applications of Ro 15-1788 had a depressant action on neuronal firing, which was antagonized by caffeine (20 mg/kg), an adenosine receptor blocker. These results indicate that Ro 15-1788 may be an antagonist at the adenosine receptor as well as a potentiator of the adenosine response. The prolongation of the adenosine depression is likely to be the result of a persistent inhibition of adenosine uptake by Ro 15-1788. These diverse effects on the adenosine response may account for some of the complex behavioral actions of Ro 15-1788.

The GABA/benzodiazepine receptor-chloride ionophore complex: nature and modulation

1. A high affinity, saturable, stereospecific binding site for Benzodiazepines has been found to be functionally and possibly structurally related to a GABA receptor-chloride ionophore complex. 2. There are both central (CNS) as well as "peripheral" binding sites, involving multiple organs. 3. Evidence strongly suggests that mutually exclusive Benzodiazepine agonists and antagonists bind to the same receptor, possibly in an agonist-antagonist-inverse agonist continuum. 4. The search for an endogenous ligand has been inconclusive and the question of such a substance remains open. 5. Although the relationship between this receptor and the Limbic System remains unclear, it seems certain that the Benzodiazepine receptor plays an important role in the modulation of Limbic System excitability.

Dissimilarities between benzodiazepine-binding sites and adenosine uptake sites in astrocytes and neurons in primary cultures

The question whether the benzodiazepine receptor site in astrocytes or in neurons might be identical to the adenosine uptake site was studied by determining pharmacological profiles, inhibition types, and the effects of benzodiazepine antagonists in primary cultures of either astrocytes or neurons. Fourteen different benzodiazepines and five different adenosine uptake inhibitors displaced [3H] diazepam and inhibited adenosine uptake in both astrocytes and neurons. However, the rank orders (determined as IC50 values) with which these two parameters were affected were profoundly different, indicating dissimilarities between these two sites. For several of the compounds a difference in inhibition type (competitive vs. noncompetitive) was observed between the benzodiazepine-binding site and the adenosine uptake site in astrocytes and/or neurons, which further corroborated the conclusion of a difference between the benzodiazepine-binding site and the adenosine uptake site. Finally, the neuronal benzodiazepine antagonists RO 15-1788 and CGS-8216 and the astrocytic benzodiazepine antagonist PK 11195, which reverse the action of benzodiazepines, were not able to reverse inhibition of adenosine uptake by diazepam but exerted an inhibitory effect of their own.

[Assessment of the efficacy and tolerance of a benzodiazepine antagonist (Ro 15-1788)]

The aim of this study was to evaluate the efficacy and the tolerance of Ro 15-1788, a specific benzodiazepine antagonist, in reversing the effects of midazolam. Six healthy male volunteers (mean age 32 +/- 3 years; mean weight 75.5 +/- 5 kg) took part in this study. Two of the three following drugs: midazolam (0.15 mg X kg-1), Ro 15-1788 (0.1 mg X kg-1) or placebo, diluted in 10 ml isotonic saline, were injected intravenously in 15 s at 5 min intervals in a double-blind manner in each subject during six randomized sessions: midazolam-placebo; Ro-placebo; placebo-midazolam; placebo-Ro; midazolam-Ro; Ro-midazolam. At least four days were allowed between each session for each subject. The evaluation of the effects on the central nervous system was as follows. At the time of injection of the first drug and, if possible, at the time of injection of the second drug, the subject was asked to count aloud to 150. The following variables were timed: start of dysarthria, cessation of counting, abolition and duration of absence of the ciliary reflex and duration of induced sleep. Retrograde and anterograde amnesia were evaluated by the recall of a playing card and a number. Haemodynamic effects (variations of systolic and diastolic pressures and pulses rate) as well as respiratory ones (apnoea) were also studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Buspirone decreases the activity of serotonin-containing neurons in the dorsal raphe in freely-moving cats

Buspirone, a non-benzodiazepine anxiolytic agent, produced a dose-dependent decrease in the activity of serotonin-containing neurons in the dorsal raphe nucleus of freely-moving cats. The response ranged from no significant change at doses of 0.05 mg/kg to a nearly total suppression of activity at 1 mg/kg. These data suggest that the anxiolytic properties of buspirone may be mediated, at least part, by an action on neurons in the dorsal raphe.

Reversal of the effect of centrally-administered diazepam on morphine antinociception by specific (Ro 15-1788 and Ro 15-3505) and non-specific (bicuculline and caffeine) benzodiazepine antagonists

Diazepam, injected into the lateral ventricles reduced the antinociceptive effect of morphine in rats, as measured by the tail-flick method. Specific antagonists of diazepam (Ro 15-1788 and Ro 15-3505) had no effect themselves but prevented inhibition by diazepam of morphine antinociception. Furthermore, the action of diazepam was partially reversed by intracerebroventricular injection of bicuculline or caffeine. These findings support the view that the depressant effect of diazepam on morphine antinociception is specific and GABAergic in nature and that some actions of diazepam are also mediated via the purinergic system.

Up-regulation of brain [3H]diazepam binding sites in chronic caffeine treated rats

Brain [3H]diazepam and [3H]L-phenylisopropyladenosine binding sites in caffeine treated (75 mg/kg/day, i.p. 12 days) and caffeine withdrawn (30 days) rats were examined. Treatment with caffeine (75 mg/kg/day) for 12 days increases the Bmax (maximum binding capacity) for [3H]diazepam binding by 30.9% whereas the same treatment increases the Bmax for [3H]L-PIA binding by 165%. The Bmax for [3H]diazepam binding sites returns to slightly below control levels but [3H]L-PIA binding sites remain elevated after 30 days of caffeine withdrawal. These findings suggest that the up-regulation of [3H]diazepam binding sites seen in caffeine treated rats may not be adequately explained by a direct antagonism of caffeine on benzodiazepine receptors. Other modes of interaction therefore must be considered.

Aminophylline and CGS 8216 reverse the protective action of diazepam against electroconvulsions in mice

Aminophylline (50 and 100 mg/kg) and CGS 8216 (20 and 40 mg/kg) decreased the anticonvulsant potency of diazepam (5 and 10 mg/kg) against electroshock-induced seizures. It should be emphasized that aminophylline moderately affected the protective action of the benzodiazepine at a dose of 5 mg/kg, whereas it was equipotent with CGS 8216 with regard to diazepam at a dose of 10 mg/kg. Consequently, participation of a purinergic component in the anticonvulsant action of diazepam is suggested. On the other hand, the use of aminophylline in epileptic patients suffering from asthma seems unjustified.