Diazepam and flurazepam inhibit adenosine uptake by rat brain synaptosomes

Benzodiazepines alter nucleotide and nucleoside hydrolysis in zebrafish (Danio rerio) brain

Anxiety is characterized by unpleasant bodily sensations, such as pounding heart and intense fear. The therapy involves the administration of benzodiazepine drugs. Purinergic signaling participates in the induction of several behavioral patterns and their actions are inactivated by ectonucleotidases and adenosine deaminase (ADA). Since there is evidence about the involvement of purinergic system in the actions mediated by benzodiazepines, we evaluated the effects in vitro and in vivo of administration of diazepam and midazolam on nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, and ADA activities in zebrafish brain, followed by the analysis of gene expression pattern of these enzymes and adenosine receptors (A1, A2a1, A2a2, A2b). The in vitro studies demonstrated that diazepam decreased ATP (66 % for 500 µM) and ADP hydrolysis (40-54 % for 10-500 µM, respectively). Midazolam decreased ATP (16-71 % for 10-500 µM, respectively) and ADP (48-73.5 % for 250-500 µM, respectively) hydrolysis as well as the ecto-ADA activity (26-27.5 % for 10-500 µM, respectively). AMP hydrolysis was decreased in animals treated with of 0.5 and 1 mg/L midazolam (32 and 36 %, respectively). Diazepam and midazolam decreased the ecto-ADA activity at 1.25 mg/L and 1 mg/L (31 and 33 %, respectively), but only 0.1 mg/L midazolam induced an increase (40 %) in cytosolic ADA. The gene expression analysis demonstrated changes on ecto-5'-nucleotidase, A1, A2a1, A2a2, and A2b mRNA transcript levels after acute treatment with benzodiazepines. These findings demonstrated that benzodiazepine exposure induces a modulation of extracellular nucleotide and nucleoside metabolism, suggesting the purinergic signaling may be, at least in part, related to benzodiazepine effects.

Adenosine receptors and the central nervous system

The adenosine receptors (ARs) in the nervous system act as a kind of "go-between" to regulate the release of neurotransmitters (this includes all known neurotransmitters) and the action of neuromodulators (e.g., neuropeptides, neurotrophic factors). Receptor-receptor interactions and AR-transporter interplay occur as part of the adenosine's attempt to control synaptic transmission. A(2A)ARs are more abundant in the striatum and A(1)ARs in the hippocampus, but both receptors interfere with the efficiency and plasticity-regulated synaptic transmission in most brain areas. The omnipresence of adenosine and A(2A) and A(1) ARs in all nervous system cells (neurons and glia), together with the intensive release of adenosine following insults, makes adenosine a kind of "maestro" of the tripartite synapse in the homeostatic coordination of the brain function. Under physiological conditions, both A(2A) and A(1) ARs play an important role in sleep and arousal, cognition, memory and learning, whereas under pathological conditions (e.g., Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke, epilepsy, drug addiction, pain, schizophrenia, depression), ARs operate a time/circumstance window where in some circumstances A(1)AR agonists may predominate as early neuroprotectors, and in other circumstances A(2A)AR antagonists may alter the outcomes of some of the pathological deficiencies. In some circumstances, and depending on the therapeutic window, the use of A(2A)AR agonists may be initially beneficial; however, at later time points, the use of A(2A)AR antagonists proved beneficial in several pathologies. Since selective ligands for A(1) and A(2A) ARs are now entering clinical trials, the time has come to determine the role of these receptors in neurological and psychiatric diseases and identify therapies that will alter the outcomes of these diseases, therefore providing a hopeful future for the patients who suffer from these diseases.

Emotional instability but intact spatial cognition in adenosine receptor 1 knock out mice

Several lines of evidence point to the involvement of adenosine in the regulation of important central mechanisms such as cognition, arousal, aggression and anxiety. In order to elucidate the involvement of the adenosine A1 receptor (A1AR) in spatial learning and the control of exploratory behaviour, we assessed A1AR knockout mice (A1AR-/-) and their wild-type littermates (A1AR+/+) in a place navigation task in the water maze and in a battery of forced and free exploration tests. In the water maze, A1AR-/- mice showed normal escape latencies and were indistinguishable from controls with respect to measures of spatial performance during both training and probe trial. But despite normal performance they showed increased wall hugging, most prominently after the relocation of the goal platform for reversal training. Quantitative analysis of strategy choices indicated that wall hugging was increased mainly at the expense of chaining and passive floating, whereas the frequency of trials characterised as direct swims or focal searching was normal in A1AR-/- mice. These results indicate intact spatial cognition, but mildly altered emotional reactions to the water maze environment. In line with this interpretation, A1AR-/- mice showed normal levels and patterns of activity, but a mild increase of some measures of anxiety in our battery of forced and free exploration paradigms. These results are in line with findings published using a genetically similar line, but demonstrate that the magnitude of the changes and the range of affected behavioural measures may vary considerably depending on the environmental conditions during testing.

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.

Diazepam enhances the inhibitory action of adenosine on transmission at the frog neuromuscular junction

The effect of diazepam and its interaction with adenosine on evoked endplate potentials (e.p.p.s) and on twitch tension were investigated in innervated sartorius muscles of the frog. Diazepam (100 microM) reversibly decreased the amplitude of the e.p.p.s and the twitch responses evoked by indirect stimulation, and reversibly increased the resting membrane potential recorded from the endplates. In a concentration (30 microM) virtually devoid of an effect on the e.p.p.s, twitch responses, or resting membrane potential of the muscle fibres, diazepam potentiated the inhibitory action of adenosine on neuromuscular transmission, but not that induced by the stable analogue of adenosine 5'-N-ethylcarboxamide adenosine (NECA), which is not a substrate for the adenosine uptake system. The potentiating effect of diazepam was not observed in the presence of dipyridamole, an adenosine uptake blocker which potentiated the effect of adenosine on neuromuscular transmission. Diazepam shifted to the left the concentration-response curve obtained for adenosine in the presence of the adenosine receptor antagonist 8-phenyltheophylline (8-PT). The results suggest that diazepam acts at the frog neuromuscular junction by increasing the level of adenosine at the junction level; this increase probably results from inhibition in the uptake of the nucleoside.

Triazolines XV. Anticonvulsant profile of ADD 17014, a potentially unique 1,2,3-triazoline antiepileptic drug, in mice and rats

ADD 17014[1-(4-chlorophenyl)-5-(4-pyridyl) delta 2-1,2,3-triazoline], is a representative member of a hitherto unknown, structurally novel family of anticonvulsant agents. The anticonvulsant profile of ADD 17014 following intraperitoneal (i.p.) and oral administration in mice and rats was evaluated using a battery of well-standardized anticonvulsant tests and compared with phenytoin (PHT), phenobarbital (PB), ethosuximide (ESM), and valproate (VPA). The results indicate that ADD 17014 is effective in nontoxic i.p. doses in mice by the maximal electroshock seizure (MES), Metrazol (subcutaneous, s.c. Met), bicuculline (s.c. Bic) and picrotoxin (s.c. Pic) tests, but ineffective against strychnine-induced seizures; it is also effective after nontoxic oral doses in both mice and rats by the MES and s.c. Met tests. Protective indices (PI = TD50/ED50), calculated from i.p. data in mice, were highest for ADD 17014 by the s.c. Met (26.02) and s.c. Bic (93.93) tests; the PIs, after oral administration in mice and rats, were equal to or higher than those of the prototype agents. In vitro receptor binding studies of ADD 17014 and potential metabolites indicated no significant inhibitory activity except for the beta-amino alcohol, which displaced almost 93% of [3H]glutamate from the glutamate receptors, suggesting that ADD 17014 may be functioning as a prodrug and an excitatory amino acid antagonist. The overall results indicate that ADD 17014 is a relatively nontoxic agent that more closely resembles PB and VPA, with a broad and unique spectrum of anticonvulsant activity.

The suppression of hippocampal potentials by the benzodiazepine antagonist Ro 15-1788 may be mediated by purines

The benzodiazepine antagonist Ro 15-1788 has been reported to suppress paired pulse inhibition in the hippocampal slice. It is now shown that the depression of orthodromic synaptic transmission by Ro 15-1788 can be prevented by the adenosine antagonist 8-phenyl-theophylline, or by adenosine deaminase. Since Ro 15-1788 has previously been shown to inhibit adenosine-uptake into rat brain tissue, it is suggested that this property, leading to an accumulation of extracellular adenosine, may underlie its effects on synaptic transmission.

Possible mechanism of action of diazepam as an adenosine potentiator

Diazepam (10(-5)-3 X 10(-4) M) selectively enhanced the negative inotropic responses of guinea-pig atria and the relaxation of guinea-pig taenia coli caused by adenosine and ATP. In the atria, the effect of 2-chloroadenosine, a stable analog of adenosine, was not affected by diazepam. Segments of guinea-pig atria or taenia coli took up 3H-activity during incubation with [3H]adenosine but did not take up 32P-activity from [32P]ATP. Diazepam at concentrations sufficient to enhance the in vitro responses reduced by half the uptake of 3H-activity into the preparations. Adenosine (10(-6) M) and ATP (10(-6) M) were degraded to inactive inosine during incubation with atrial segments and their degradation was inhibited by diazepam. In contrast, in rat atria, diazepam did not enhance the negative inotropic effects of adenosine and ATP, and did not prevent the uptake of adenosine. These results suggest that in guinea-pig atria and taenia coli, diazepam like dipyridamole, acts as an adenosine potentiator by preventing the uptake and degradation of adenosine.

Methylxanthine discrimination in the rat: possible benzodiazepine and adenosine mechanisms

Rats were trained to discriminate either caffeine or theophylline from saline using a two-lever discrimination paradigm. Since methylxanthines have been found to interfere with agonist binding at both adenosine and benzodiazepine (BDZ) receptors, chlordiazepoxide (CDP) and L-PIA (an adenosine analog) were tested for generalization to and blockade of both xanthine cues. Neither L-PIA nor CDP generalized to either xanthine cue, although both produced dose-related decreases in response rate. CDP, but not L-PIA, produced dose-related decreases in drug-lever responses when combined with training doses of caffeine or theophylline. Response rates indicated a complex interaction between the xanthines and both L-PIA and CDP. When combined with the caffeine training dose, pentobarbital also produced a dose-dependent decrease in response rate but not in drug lever choices. Finally, papaverine generalized to the caffeine cue in a dose-dependent fashion. In a second experiment, rats trained to discriminate CDP from saline showed no generalization in L-PIA tests. CDP-appropriate responding was not significantly affected when the CDP training dose was combined with caffeine. These data indicate that: (a) methylxanthine interactions with L-PIA and CDP on response rate likely involve blockade of adenosine mechanisms; (b) the xanthine cue does not appear to depend on interactions with adenosine receptors; and (c) the xanthine cue may involve effects on cyclic AMP activity and/or interaction with the BDZ/GABA receptor complex.

Aminophylline antagonizes diazepam-induced anesthesia and EEG changes in humans

General anesthesia was induced in eight subjects by the slow IV injection of 60 mg diazepam. During the anesthetic effect, the EEG was characterized by 3-5 Hz high voltage activity. Immediate recovery of consciousness and reversal of the EEG pattern to fast low voltage activity was obtained after the IV injection of 60 mg aminophylline. On the other hand, three diazepam-treated subjects who received IV saline instead of aminophylline recovered from anesthesia 73-120 min after saline.

Benzodiazepines modulate the A2 adenosine binding sites on 108CC15 neuroblastoma X glioma hybrid cells

We have demonstrated high affinity diazepam binding sites of the Ro5-4864 benzodiazepine receptor subtype on 108CC15 neuroblastoma X glioma hybrid cells. These cells were previously shown to have purinoceptors of the A2 adenosine subtype and we have now found that [3H]-adenosine can be displaced from this binding site by the benzodiazepines and related compounds that can also bind to the Ro5-4864 site. Diazepam was found to have no intrinsic activity at the A2-receptor as measured by the stimulation of adenosine 3':5'-cyclic monophosphate (cyclic AMP) production in this cell line. At concentrations sufficient to compete for the A2-receptor, diazepam was shown to facilitate, by approximately 2 fold, the stimulation of cyclic AMP by adenosine. These effects are not due to inhibition of adenosine uptake or phosphodiesterase activity, but are probably a consequence of modulation of the coupling of the A2-receptor to cyclic AMP production in this hybrid cell line.

Anticonvulsant actions of fominoben: possible involvement of benzodiazepine receptors

The purpose of this study was to examine the benzodiazepine-like activity of fominoben-HCl, a compound with prominent antitussive and respiratory stimulant actions. Towards this end we examined the anticonvulsant actions of fominoben as well as its ability to displace benzodiazepine (BDZ) binding from brain membranes. Scatchard analysis of binding data demonstrated that fominoben displaced 3H-flunitrazepam binding from rat cortical membrane preparations. Furthermore when tested against 3H-ethyl-beta-carboline-3-carboxylate, the addition of GABA resulted in a mean (+/- SE) shift of the IC50 from 4.05 +/- 0.10 microM to 2.2 +/- 0.05 microM, a characteristic of benzodiazepine agonists. Seizures were induced in male, Swiss Webster mice with pentylenetetrazol (PTZ) or 3-mercaptoproprionic acid (3-MP). Fominoben (50 and 100 mg/kg) completely protected mice from seizures induced by 50 mg/kg PTZ and elevated the seizure latency against 75 mg/kg of PTZ. The anticonvulsant effects of fominoben were less pronounced against 3-MP-induced seizures. The benzodiazepine antagonist Ro 15-1788 antagonized the anticonvulsant action of fominoben against both convulsants. Taken together, these data suggest that the anticonvulsant action of fominoben may be mediated by agonistic actions at benzodiazepine binding sites.

Benzodiazepine inhibition of adenosine uptake is not prevented by benzodiazepine antagonists

Uptake of [3H]adenosine into rat cerebral cortex synaptosomes was studied. Hexobendine (10(-5) M) and the benzodiazepine agonists diazepam (10(-5) M) and flurazepam (10(-4) M) significantly inhibited this uptake, but only if the compounds were pre-incubated for 10 min in the case of the benzodiazepines. The benzodiazepine antagonists Ro15-1788 (10(-5) M) and CGS 8216 (10(-5) M) failed to reverse the action of benzodiazepine agonists or hexobendine on [3H]adenosine uptake. The results add weight to the view that inhibition of adenosine uptake processes by benzodiazepines do not contribute to their behavioural effects.

Possible selective inhibition of [3H]adenosine uptake by papaverine in vascular adrenergic nerves

The effect of the adenosine uptake inhibitors dipyridamole, papaverine and diazepam on the [3H]adenosine uptake was assessed using the rabbit pulmonary arterial segment. [3H]Adenosine uptake into the vascular segment was significantly diminished by dipyridamole (10(-6) -10(-5) M), papaverine (10(-5) -10(-4) M) or diazepam (5 x 10(-5) M) with potencies: dipyridamole greater than papaverine greater than diazepam. Dipyridamole (10(-6) M) or diazepam (5 x 10(-5) M) added 30 min before the incubation with [3H]adenosine reduced the high KCl-induced and epinephrine-induced [3H]purine effluxes equally, whereas papaverine (10(-5) M) selectively diminished the former efflux. KCl and epinephrine have been shown to act preferentially on the neuronal and extraneuronal sites, respectively. These results suggest that papaverine inhibits adenosine uptake into the vascular neuronal compartment, in preference to that into the extraneuronal compartment.

Inhibition of [3H]adenosine binding by stereoisomers of oxazepam hemisuccinate in guinea-pig brain synaptosomes

1. The stereoisomers of oxazepam sodium hemisuccinate have been tested for their ability to inhibit the [3H]adenosine binding in guinea-pig brain synaptosomes. 2. All three stereoisomers were able to inhibit the [3H]adenosine binding in a dose-dependent fashion. 3. The IC20 values of the D-, DL- and L-stereoisomers were approximately 5 X 10(-5) M, 7.5 X 10(-5) M and 10(-4) M respectively. 4. The results are consistent with hypothesis that adenosine may be the endogenous substrata mediating some actions of the benzodiazepines.

Interactions between the benzodiazepines, methylxanthines, and adenosine

Experimental evidence is cited in support of the proposal that benzodiazepines exert their anxiolytic effects by inhibiting the uptake of adenosine by central neurons and glia.