Mitsue Kurasawa

Anxiolytic effects of aniracetam in three different mouse models of anxiety and the underlying mechanism.

The anxiolytic effects of aniracetam have not been proven in animals despite its clinical usefulness for post-stroke anxiety. This study, therefore, aimed to characterize the anxiolytic effects of aniracetam in different anxiety models using mice and to examine the mode of action. In a social interaction test in which all classes (serotonergic, cholinergic and dopaminergic) of compounds were effective, aniracetam (10-100 mg/kg) increased total social interaction scores (time and frequency), and the increase in the total social interaction time mainly reflected an increase in trunk sniffing and following. The anxiolytic effects were completely blocked by haloperidol and nearly completely by mecamylamine or ketanserin, suggesting an involvement of nicotinic acetylcholine, 5-HT2A and dopamine D2 receptors in the anxiolytic mechanism. Aniracetam also showed anti-anxiety effects in two other anxiety models (elevated plus-maze and conditioned fear stress tests), whereas diazepam as a positive control was anxiolytic only in the elevated plus-maze and social interaction tests. The anxiolytic effects of aniracetam in each model were mimicked by different metabolites (i.e., p-anisic acid in the elevated plus-maze test) or specific combinations of metabolites. These results indicate that aniracetam possesses a wide range of anxiolytic properties, which may be mediated by an interaction between cholinergic, dopaminergic and serotonergic systems. Thus, our findings suggest the potential usefulness of aniracetam against various types of anxiety-related disorders and social failure/impairments.

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.

Scopolamine model of delirium in rats and reversal of the performance impairment by aniracetam

Scopolamine causes functional impairment of cognition and neuropsychological delirium in humans. We attempted to develop a scopolamine model of delirium in middle‐aged rats using a choice reaction performance task (CRP). Psychological properties were assessed by behavioral measures such as choice reaction time (CRT), percent correct, percent omission, and premature response. Scopolamine (0.3 mg/kg ip) produced an impairment of the task performance observed as a prolongation in CRT, decrease in percent correct, and increase in percent omission, indicating attentional deficits and a reduced arousal or vigilance. The performance impairments in rats seemed to resemble delirium seen in healthy subjects loaded with scopolamine and in patients with dementia, both behaviorally and psychologically. In this model, aniracetam (10 mg/kg po) reversed all of the performance impairments and two (N‐anisoyl‐GABA and p‐anisic acid: 30 mg/kg po) of the three major metabolites acted on the performance impairments effectively. Tacrine tended to decrease only the percent omission at an impairing dose (10 mg/kg po). Haloperidol showed no improvement at a nonimpairing dose (0.025 mg/kg sc) and rather worsened several measures at an impairing dose (0.05 mg/kg sc). Only 2‐pyrrolidinone (0.1 μM) of the metabolites enhanced in vitro [3H]‐pirenzepine binding to the rat pons‐midbrain. The present results suggest that scopolamine‐induced behavioral disturbances in the CRP task seems to be a useful delirium model, and aniracetam may improve the delirium‐like state through an additional or combined effect of its major metabolites. 2‐Pyrrolidinone, at least in part, might facilitate muscarinic M1 receptor function at the mesopontine area. Drug Dev. Res. 43:85–97, 1998.

Impulsivity and AMPA receptors: aniracetam ameliorates impulsive behavior induced by a blockade of AMPA receptors in rats

The study aimed to ascertain the involvement of central AMPA receptors in impulsive behaviors of aged rats and to examine the effects of aniracetam. Premature response in the two-lever choice reaction task was assessed as an index of impulsivity. Intracerebroventricular injection of 2, 3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX), an AMPA receptor antagonist, dose-dependently (10.1-1009 ng/rat) increased only premature response without altering responding speed and choice accuracy 30 min after the injection. Aniracetam (30 mg/kg p.o.), a positive allosteric modulator of AMPA receptors, or AMPA (55.9 ng/rat, co-injected with NBQX) completely restored the NBQX-induced increase in impulsivity. These results indicate that AMPA receptors are tonically involved in the regulation of impulsivity.

Recovery of Diminished Mealtime-Associated Anticipatory Behavior by Aniracetam in Aged Rats

Disease- or age-related neuropsychiatric symptoms and cognitive and chronobiological impairments greatly aggravate the activities of daily living (ADL) in patients. The present study evaluates the effects of aniracetam on a decline in mealtime-associated anticipatory behavior in aged rats, as an animal model of temporally regulated behaviors or habitual daily activities. Aged rats showed a lower but typical nocturnal motor activity rhythm than young rats when the animals were fed ad lib. Mealtime-associated anticipatory behavior emerged in young rats when the rats were fed at a fixed time for 6 days, but the activity in aged rats was diminished. Repeated administration of aniracetam (100 mg/kg PO) or physostigmine (0.1 mg/kg SC) for 7 days ameliorated the impaired anticipatory behavior in aged rats. Nefiracetam (10 mg/kg PO) was ineffective. All compounds tested had no effect on appetite or motor ability. These results indicate that aging disturbs the timing or temporal regulation of anticipatory behavior, probably resulting from dysfunction in a food-entrainable oscillator linked to central cholinergic systems. The restoration of the time-keeping ability by aniracetam may be mediated by the facilitation of reticulothalamic cholinergic neurotransmission, and the action may lead to the improvement of declined ADL in stroke patients.

Dextrorphan attenuates the behavioral consequences of ischemia and the biochemical consequences of anoxia: possible role of N-methyl-d-aspartate receptor antagonism and ATP replenishing action in its cerebroprotecting profile

The acute anti-ischemic and anti-anoxic effects of dextrorphan (DX) were compared with those of dizocilpine (MK-801) in a variety of animal models, and in vivo and in vitro testings under anoxic conditions. DX reduced the incidence of death in ischemic mice and improved the rotarod performance of mice with brain ischemia. The ischemically-impaired memory of mice treated with DX markedly improved, as shown in the step-through type passive avoidance test, Morris water maze and in the habituation of exploratory behavior test. MK-801 likewise improved the water maze performance of the ischemically-impaired mice, but to a lesser extent. The step-through type passive avoidance performance of ischemic mice was not improved by MK-801. In the passive avoidance task with normal mice, DX, like MK-801, produced anterograde amnesia at doses higher than those needed to attenuate the behavioral effects of ischemia. DX, intravenously or centrally administered, markedly and dose-dependently reduced the incidence of death in mice receiving potassium cyanide (KCN). DX lessened the reduction in adenosine triphosphate (ATP) and increased lactate contents in mice dosed with KCN and also lessened the reduction in ATP in the TCA cycle and oxidative phosphorylation reactions caused by KCN (0.58 mmol/l), whereas MK-801 failed to show any effect on ATP formation pathways in vivo and in vitro, and failed to protect mice against KCN-induced lethal toxicity in vivo. In the in vitro studies, DX increased the adenylate kinase activity of the rat brain homogenate. DX was found to be a cerebroprotectant with anti-ischemic and anti-anoxic actions, the effects probably stemming from its N-methyl-d-aspartate receptor antagonistic property in cooperation with its ATP replenishing action.

Aniracetam attenuates the 5-HT2 receptor-mediated head-twitch response in rodents as a hallucination model

The effects of aniracetam on the head‐twitch response (HTR) induced by 5‐hydroxy‐L‐tryptophan (5‐HTP) and (±)‐1‐(4‐iodo‐2,5‐dimethoxyphenyl)‐2‐aminopropane hydrochloride (DOI) as a model of hallucination were examined in rodents. 1) Aniracetam produced a dose‐related (30, 100, and 300 mg/kg po) reduction in the frequency of HTR induced by 5‐HTP at 300 mg/kg ip in mice. p‐Anisic acid (300 mg/kg po), one of the main metabolites of aniracetam, inhibited the HTR as the intact drug did. Other nootropics, tacrine (10 mg/kg po) and idebenone (100 mg/kg po), but not propentofylline, also reduced HTR. Ritanserin (0.1 and 1 mg/kg po) and cyproheptadine (1 mg/kg po) markedly antagonized it, but ondansetron (1 and 10 mg/kg po) and metoclopramide (1 mg/kg po) did not. Although scopolamine alone (1 mg/kg sc) produced no HTR, it, but not butylscopolamine, potentiated the HTR induced by 5‐HTP at the minimum effective dose (200 mg/kg ip). The potentiation of the HTR induced by the combined 5‐HTP and scopolamine was inhibited by aniracetam (100 mg/kg po), tacrine (10 mg/kg po), and ritanserin (1 mg/kg po). 2) The DOI (1 mg/kg sc)‐induced HTR was inhibited by aniracetam (30 and 100 mg/kg po), tacrine (3 mg/kg po), and ritanserin (1 mg/kg po). 3) Aniracetam and its metabolites had no effect on the 5‐HT2 and 5‐HT3 binding in vitro. These results indicate that clinical efficacy of aniracetam on delirium associated with the sequelae of cerebrovascular diseases may be partly due to the indirect regulation of serotonergic functions via an inhibitory cholinergic mechanism. Drug Dev. Res. 44:131–139, 1998.

Cholinergic and dopaminergic mechanisms involved in the recovery of circadian anticipation by aniracetam in aged rats

We have reported that repeated administration of aniracetam (100 mg/kg p.o.) for 7 consecutive days recovers mealtime-associated circadian anticipatory behavior diminished in aged rats. The present study examines the mode of action underlying the restoration by aniracetam with various types of receptor antagonists. Coadministration of scopolamine (0.1 mg/kg i.p.) or haloperidol (0.1 mg/kg i.p.) for the last 3 days significantly reduced the restorative effects of aniracetam without affecting the timed feeding-induced anticipatory behavior by each receptor antagonist itself. The other receptor antagonists, mecamylamine (3 mg/kg i.p.), 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)quinoxaline (NBQX, 1 microg/rat i.c.v.) had no effect on either the basal or aniracetam-elicited circadian anticipation. In contrast, ketanserin (1 mg/kg i.p.) itself recovered the diminished anticipatory behavior as aniracetam did, but it did not alter the restorative effects of aniracetam. Among the receptor antagonists tested, NBQX reduced appetite and haloperidol induced circadian hypoactivity. These results suggest that the food-entrainable circadian oscillations or the temporal regulatory system of behavior is modulated by cholinergic, dopaminergic and serotonergic systems. Furthermore, aniracetam may restore the aging-diminished behavioral anticipation by activating muscarinic acetylcholine (ACh) and/or dopamine (DA) D2 receptors through the enhanced release of ACh and/or DA in the brain.

3-O-Methyldopa Attenuates the Effects of Madopar on the Haloperidol-lnduced Cataleptic Behavior and the Locomotor Activity in the Mouse

The effects of Madopar (levodopa plus benserazide) on the cataleptic behavioral response to haloperidol and on the locomotor activity in mice were quantitatively compared before and after the administration of 3-O-methyldopa (3OMD). The intraperitoneal administration of 3OMD (200-400 mg/kg) alone did not modify the haloperidol (1.0 mg/kg s.c.)-induced catalepsy. Madopar, depending on the dose regimen, markedly antagonized the haloperidol-induced catalepsy. Pretreatment with 3OMD tended to reverse the antagonistic property of Madopar on the cataleptic behavior in response to haloperidol. The ability of 3OMD to significantly inhibit Madopar effects was observed in the locomotor testing paradigm; the locomotor hyperactivity in Madopar-treated animals was significantly inhibited by a prior intraperitoneal injection of 3OMD. The results from our animal experiments may provide further evidence that impediment of 3OMD formation is meaningful in the treatment of Parkinsons disease with Madopar or levodopa.