Cerebral-activating (EEG) properties of two inverse agonists and of an antagonist at the benzodiazepine receptor in the rat

Modulation of food consumption and sleep-wake cycle in mice by the neutral CB1 antagonist ABD459

The brain endocannabinoid system is a potential target for the treatment of psychiatric and metabolic conditions. Here, a novel CB1 receptor antagonist (ABD459) was synthesized and assayed for pharmacological efficacy in vitro and for modulation of food consumption, vigilance staging and cortical electroencephalography in the mouse. ABD459 completely displaced the CB1 agonist CP99540 at a Ki of 8.6 nmol/l, and did not affect basal, but antagonized CP55940-induced GTPγS binding with a KB of 7.7 nmol/l. Acute ABD459 (3-20 mg/kg) reliably inhibited food consumption in nonfasted mice, without affecting motor activity. Active food seeking was reduced for 5-6 h postdrug, with no rebound after washout. Epidural recording of electroencephalogram confirmed that ABD459 (3 mg/kg) robustly reduced rapid eye movement (REM) sleep, with no alterations of wakefulness or non-REM sleep. Effects were strongest during 3 h postdrug, followed by a progressive washout period. The CB1 antagonist AM251 (3 mg/kg) and agonist WIN-55,212-2 (WIN-2: 3 mg/kg) also reduced REM, but variously affected other vigilance stages. WIN-2 caused a global suppression of normalized spectral power. AM251 and ABD459 lowered delta power and increased power in the theta band in the hippocampus, but not the prefrontal cortex. The neutral antagonist ABD459 thus showed a specific role of endocannabinoid release in attention and arousal, possibly through modulation of cholinergic activity.

Global slowing of network oscillations in mouse neocortex by diazepam

Benzodiazepines have a broad spectrum of clinical applications including sedation, anti-anxiety, and anticonvulsive therapy. At the cellular level, benzodiazepines are allosteric modulators of GABA(A) receptors; they increase the efficacy of inhibition in neuronal networks by prolonging the duration of inhibitory postsynaptic potentials. This mechanism of action predicts that benzodiazepines reduce the frequency of inhibition-driven network oscillations, consistent with observations from human and animal EEG. However, most of existing data are restricted to frequency bands below ∼30 Hz. Recent data suggest that faster cortical network rhythms are critically involved in several behavioral and cognitive tasks. We therefore analyzed diazepam effects on a large range of cortical network oscillations in freely moving mice, including theta (4-12 Hz), gamma (40-100 Hz) and fast gamma (120-160 Hz) oscillations. We also investigated diazepam effects over the coupling between theta phase and the amplitude fast oscillations. We report that diazepam causes a global slowing of oscillatory activity in all frequency domains. Oscillation power was changed differently for each frequency domain, with characteristic differences between active wakefulness, slow-wave sleep and REM sleep. Cross-frequency coupling strength, in contrast, was mostly unaffected by diazepam. Such state- and frequency-dependent actions of benzodiazepines on cortical network oscillations may be relevant for their specific cognitive effects. They also underline the strong interaction between local network oscillations and global brain states.

Substantia nigra: the involvement of central and peripheral benzodiazepine receptors in physical dependence on diazepam as evidenced by behavioral and EEG effects

Male rats chronically exposed to diazepam (DZ) slowly released from subcutaneously implanted silastic capsules along with empty capsule control rats were focally injected (1 microl) into the substantia nigra (SNR) with the central (CBR) and peripheral (PBR) benzodiazepine receptor antagonists, flumazenil [(FLU) 6.25, 12.5, 25 microg] and PK 11195 [(PK) 3.125, 6.25, 12.5, 25 microg], respectively (weekly intervals; Latin square design). Rats were observed for signs of withdrawal and the EEG was recorded simultaneously from the site of injection (SNR), caudate putamen, thalamus, hippocampus, and frontal cortex. In DZ-dependent rats the Precipitated Abstinence Score (PAS) was significantly related to dose of FLU. The PAS increased with increasing doses of PK (3.125-12.5 microg); however, the highest dose of PK (25 microg) showed less effect. The rapid onset of the PAS was accompanied by a rise in the total power (1-32 Hz) of the EEG (TP(EEG)) in the SNR and other brain areas. The PAS and TP(EEG) had similar time courses. Intranigrally injected FLU and PK did not evoke clonic and tonic-clonic convulsions; however, both antagonists induced dose-related twitches and jerks. Additionally, FLU precipitated a dose-related tachypnea and increases in turning and backing. Chronic DZ treatment altered the spectral content of the EEG, as indicated by a decrease and an increase of the slow and fast frequency bands, respectively. FLU and PK rapidly but transiently reversed the EEG. Data suggest that in the SNR the CBR mediate autonomic and motor signs of DZ withdrawal, while both the CBR and PBR are responsible for twitches and jerks and alteration of the EEG. It is possible that PK also acts on the site linked to a GABA(A)/CBR/ionophore.

Apomorphine-induced hypoattention in rats and reversal of the choice performance impairment by aniracetam

Aging-, disease- and medication-related imbalance of central dopaminergic neurons causes functional impairment of cognition and neuropsychological delirium in humans. We attempted to develop a new delirium model using the direct dopamine agonist, apomorphine, and a choice reaction performance task performed by middle-aged rats. The psychological properties of the model were assessed by determining behavioral measures such as choice reaction time, % correct and % omission. Apomorphine (0.03-0.3 mg/kg s.c.) produced a dose-dependent impairment of task performance. The dose of 0.1 mg/kg prolonged choice reaction time, decreased % correct and increased % omission, indicating that rats had attentional deficits and a reduced arousal or vigilance but no motor deficits or reduced food motivation. This psychological and behavioral impairment of performance resembled that of clinically defined delirium. In this model, the cholinomimetic, aniracetam (10 mg/kg p.o.), reversed the performance impairment induced by apomorphine. Its two metabolites, 2-pyrrolidinone (10 and 30 mg/kg p.o.) and N-anisoyl-gamma-aminobutyric acid (GABA, 10 mg/kg p.o.), effectively reversed the performance impairment as the intact drug did. Another pyrrolidinone derivative, nefiracetam (10 and 30 mg/kg p.o.), tended to worsen the apomorphine effect. The cholinesterase inhibitor, tacrine (10 mg/kg p.o.), markedly worsened all of the behavioral measures. Neuroleptics, haloperidol (0.025 mg/kg s.c.), tiapride (30 mg/kg p.o.) and sulpiride (10 and 30 mg/kg p.o.), antagonized the apomorphine effect. The present results suggest that apomorphine-induced behavioral disturbances in the choice reaction performance task seems to be a useful delirium model and aniracetam may improve delirium through the action of 2-pyrrolidinone and N-anisoyl-GABA, presumably by facilitating dopamine release in the striatum by acting as an AMPA or metabotropic glutamate receptor agonist.

Arousal-enhancing properties of the CB1 cannabinoid receptor antagonist SR 141716A in rats as assessed by electroencephalographic spectral and sleep-waking cycle analysis

The effects of the central (CB1) cannabinoid receptor antagonist SR 141716A on the sleep-waking cycle were investigated in freely-moving rats using time scoring and power spectral analysis of the electroencephalogram (EEG). Over a 4-hour recording period, SR 141716A (0.1, 0.3, 1, 3, and 10 mg/kg I.P.) dose-dependently increased the time spent in wakefulness at the expense of slow-wave sleep (SWS) and rapid eye movement sleep (REMS), delayed the occurrence of REMS but did not change the mean duration of REMS episodes. Moreover, the compound induced no change in motor behavior. At the efficient dose of 3 mg/kg I.P., SR 141716A reduced the spectral power of the EEG signals typical of SWS but did not affect those of wakefulness. Taken together, these results demonstrate that the EEG effects of SR 141716A reflect arousal-enhancing properties. In addition, the present study suggests that an endogenous cannabinoid-like system is involved in the control of the sleep-waking cycle.

Different kinetics of tolerance to behavioral and electroencephalographic effects of chlordiazepoxide in the rat

The daily oral administration of chlordiazepoxide (40 mg/kg) over 9 weeks in rats elicited full tolerance to muscle relaxant effects within 7 weeks, as revealed by twice weekly evaluations of abdominal tone myorelaxation and decreased grip strength. No full tolerance was achieved, however, during the 9 weeks of treatment in terms of ataxia. Electroencephalographic (EEG) studies showed that this tolerance to the behavioural effects was accompanied by a progressive decrease in mean power spectra, associated with a progressive decrease in the beta band, but in this case, full tolerance was reached within 4 weeks. Once weekly evaluations of the ability of chlordiazepoxide to protect the animals against pentylenetetrazole seizures revealed a similar pattern. Treatment with flumazenil (50 mg/kg p.o.) 24 h after the last chlordiazepoxide administration induced a clear withdrawal syndrome associated with EEG changes which consisted of an increase in total power spectra associated with an increase in the delta band (in comparison with chlordiazepoxide-dependent rats not given the antagonist). These findings suggest that the different kinetics of the tolerance to anticonvulsant and EEG effects in comparison to myorelaxant effects can be attributed to a different involvement of benzodiazepine receptor subtypes.

Influence of nootropic and antidepressive drugs on open field and running wheel behavior in spontaneously high and low active mice

Mice differentiated by their running wheel activity into low and high active animals were chronically treated with the nootropics meclophenoxate, piracetam, vinpocetine, methylglucaminorotate, and the antidepressants lithium, desipramine, amitriptyline, and clomipramine. The influence of chronic drug treatment on running-wheel activity and open field locomotor behaviour was analyzed. Whereas with antidepressants rather sedative effects were observed in both activity types, the effects of nootropics were different in high and low active mice. Running-wheel scores increased in low active mice but decreased in high-active animals with an improvement in efficiency of locomotor behaviour in the open field of these mice after chronic nootropic treatment. In general, the effects of antidepressants seemed to be more uniform than those of the nootropics used.

Piracetam and other structurally related nootropics

Nearly three decades have now passed since the discovery of the piracetam-like nootropics, compounds which exhibit cognition-enhancing properties, but for which no commonly accepted mechanism of action has been established. This review covers clinical, pharmacokinetic, biochemical and behavioural results presented in the literature from 1965 through 1992 (407 references) of piracetam, oxiracetam, pramiracetam, etiracetam, nefiracetam, aniracetam and rolziracetam and their structural analogues. The piracetam-like nootropics are capable of achieving reversal of amnesia induced by, e.g., scopolamine, electroconvulsive shock and hypoxia. Protection against barbiturate intoxication is observed and some benefit in clinical studies with patients suffering from mild to moderate degrees of dementia has been demonstrated. No affinity for the alpha 1-, alpha 2-, beta-, muscarinic, 5-hydroxytryptamine-, dopamine, adenosine-A1-, mu-opiate, gamma-aminobutyric acid (GABA) (except for nefiracetam (GABAA)), benzodiazepine and glutamate receptors has been found. The racetams possess a very low toxicity and lack serious side effects. Increased turnover of different neurotransmitters has been observed as well as other biochemical findings, e.g., inhibition of enzymes such as prolylendopeptidase. So far, no generally accepted mechanism of action has, however, emerged. We believe that the effect of the racetams is due to a potentiation of already present neurotransmission and that much evidence points in the direction of a modulated ion flux by, e.g., potentiated calcium influx through non-L-type voltage-dependent calcium channels, potentiated sodium influx through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor gated channels or voltage-dependent channels or decreases in potassium efflux. Effects on carrier mediated ion transport are also possible.

Amelioration by aniracetam of abnormalities as revealed in choice reaction performance and shuttle behavior

To delineate the possible effects of aniracetam PO on abnormal behaviors, we analyzed disrupted shuttle behavior and choice reaction (CR) performance in both aged and juvenile animals subjected to an ischemic (permanent occlusion of both carotid arteries)-hypoxic (17-min exposure to 93% N2 and 7% O2 mixture gas) or ischemic (20-min occlusion of both carotid arteries) insult and/or treated with methamphetamine given IP. Aniracetam at single PO doses of 10 and 30 mg/kg significantly decreased the number of incorrect lever pressings induced by IP methamphetamine in young adult rats subjected to the CR test battery. A 21-day PO regimen with aniracetam (30 mg/kg/day) resulted in an increase in the number of correct responses and a decrease in the CR latency as detected in the CR task with young adult rats inflicted with an ischemic-hypoxic insult. Aniracetam (1-100 mg/kg PO) was also evaluated in the electrostimulation-induced hyperreactivity assay (an increase in the number of shuttle responses) in both juvenile and aged mice subjected to a 20-min ischemic insult; there again a significant improvement of performance was clearly observed. The outcomes of these behavioral pharmacological analyses suggest that aniracetam has the ability to normalize the disrupted behavior, cognition, and self-regulation or decision-making process in a comprehensive way.