Involvement of the cholinergic system in the effects of nefiracetam (DM-9384) on carbon monoxide (CO)-induced acute and delayed amnesia.

The effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)-acetamide (DM-9384, nefiracetam), a cyclic derivative of GABA, were investigated in the carbon monoxide (CO)-induced amnesia model in mice using the passive avoidance task. Memory deficiency occurred when mice were exposed to CO before memory was completely consolidated after training (acute amnesia), at 7 days before training and 7 days after training (delayed amnesia). DM-9384 prolonged the step-down latency in mice with CO-induced amnesia. Scopolamine blocked the anti-amnesic effect of DM-9384 on delayed amnesia that had been induced by pre- or post-training exposure to CO. Bicuculline had a tendency to antagonize the anti-amnesic effect of DM-9384, but this tendency was not significant. Under these conditions, no significant change in the activity of choline acetyltransferase and glutamic acid decarboxylase was observed in the frontal cortex, striatum and hippocampus. These results suggest that DM-9384 potentiates cholinergic neuronal function and that it may modify acquisition and/or consolidation of memory.     

Effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)acetamide (DM-9384) on learning and memory in rats

Effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide (DM-9384) on learning and memory were studied using four different experimental rat models. In electroconvulsive shock- or scopolamine-induced amnesia in the step-through passive avoidance task, DM-9384 improved both types of amnesia when administered before the training trial. Aniracetam also showed similar but somewhat weaker effects. Furthermore, in the scopolamine amnesia model, an improvement was confirmed with arecoline. The dose-response curves for these compounds were bell-shaped. In the shuttle box active avoidance task, DM-9384 administered daily 1 hr before each training session facilitated the acquisition process of the avoidance response. In addition, the experiment of light-dark discrimination task with positive reinforcement showed that this compound administered daily after each session slightly accelerated the acquisition process of the correct response. These results suggest an ability of DM-9384 to enhance cognitive functions.     

Protective effect of DM-9384, a novel pyrrolidone derivative, against experimental cerebral anoxia

The protective effects of DM-9384 [N-(2,6-dimethylphenyl)-2-(2-oxo- 1-pyrrolidinyl) acetamide] against cerebral anoxia were investigated using various animal models. Oral administration of DM-9384 resulted in a significant prolongation of survival time in mice and rats subjected to the normobaric hypoxia; its minimal effective doses were 30 and 10 mg/kg, respectively. A significant protection by this drug against hypobaric hypoxia, histotoxic anoxia and cerebral ischemia also occurred in mice at a dose of 100 mg/kg, p.o. Bifemelane (100-300 mg/kg, p.o.) was protective against these models except for hypobaric hypoxia, and the effects of piracetam, aniracetam and pramiracetam (1000 mg/kg, p.o.) were variable depending on the type of anoxia model used. DM-9384 (100 mg/kg and lower) attenuated the hypolocomotion and the disturbance of cerebral energy metabolism such as a decrease in ATP, an increase in lactate and lactate/pyruvate ratio induced by hypoxia in rats. The spontaneous motor activity, uptake and utilization of brain glucose in normal animals, however, were not influenced by this drug. Based on these results, DM-9384 is characterized as a broad spectrum anti-anoxic drug with negligible CNS depression, and the cerebral protective effect of this drug may be, at least in part, attributable to its ability to improve the cerebral energy metabolic disturbance.     

Reversal effect of DM-9384 on scopolamine-induced acetylcholine depletion in certain regions of the mouse brain

The effect of a new cognition enhancer, DM-9384, N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl) acetamide, on regional acetylcholine (ACh) levels and against scopolamine-induced ACh depletion was examined in mouse brain. In addition, the effects of DM-9384 were compared with those of oxiracetam, physostigmine and tacrine. Independent administration of DM-9384 (1, 3, 10 or 30 mg/kg, PO) or oxiracetam (10 or 50 mg/kg, PO) to mice had no effect on the ACh level in the hippocampus, frontal cortex, amygdala and striatum. Nevertheless, in all brain regions, pretreatment with DM-9384 significantly reduced the depletion of ACH induced by scopolamine (0.5 mg/kg, IP) in a non-dose-related bell-shaped manner. By contrast, oxiracetam attenuated the effect of scopolamine in the hippocampus, frontal cortex and striatum but not in the amygdala. Physostigmine (0.2 mg/kg, SC) significantly increased ACh levels and reversed the scopolamine-induced ACh depletion in all brain regions. Unlike physostigmine, tacrine (10 mg/kg, PO) increased ACh levels in the striatum but not in the other regions. Tacrine reversed the effect of scopolamine in the hippocampus, amygdala and striatum, but not in the frontal cortex. In the present study, DM-9384 more effectively inhibited scopolamine-induced depletion of ACh levels than the other agents tested. The results obtained indicate that the protective action of DM-9384 against scopolamine-induced amnesia is due to its ability to reverse the ACh depletion.     

Nootropic drug modulation of neuronal nicotinic acetylcholine receptors in rat cortical neurons

Nefiracetam (DM-9384) is a new pyrrolidone nootropic drug being developed for the treatment of Alzheimer's type and poststroke vascular-type dementia. Because the cholinergic system plays an important role in cognitive functions and Alzheimer's disease dementia, the present study was conducted to elucidate the mechanism of action of nefiracetam and aniracetam on neuronal nicotinic acetylcholine receptors (nnAChRs). Currents were recorded from rat cortical neurons in long-term primary culture using the whole-cell, patch-clamp technique. Two types of currents were evoked by acetylcholine (ACh): alpha-bungarotoxin-sensitive, alpha 7-type currents and alpha-bungarotoxin-insensitive, alpha 4 beta 2-type currents. Although nefiracetam and aniracetam inhibited alpha 7-type currents only weakly, these nootropic agents potentiated alpha 4 beta 2-type currents in a very potent and efficacious manner. Nefiracetam at 1 nM and aniracetam at 0.1 nM reversibly potentiated alpha 4 beta 2-type currents to 200 to 300% of control. Nefiracetam at very high concentrations (approximately 10 microM) also potentiated alpha 4 beta 2-type currents but to a lesser extent, indicative of a bell-shaped dose-response relationship. Nefiracetam markedly increased the saturating responses induced by high concentrations of ACh. However, human alpha 4 beta 2 subunits expressed in human embryonic kidney cells were inhibited rather than potentiated by nefiracetam. The specific protein kinase A inhibitors (H-89, KT5720, and peptide 5-24) and protein kinase C inhibitors (chelerythrine, calphostin C, and peptide 19--63) did not prevent nefiracetam from potentiating alpha 4 beta 2-type currents, indicating that these protein kinases are not involved in nefiracetam action. The nefiracetam potentiating action was not affected by 24-h pretreatment of neurons with pertussis toxin, but was abolished by cholera toxin. Therefore, G(s) proteins, but not G(i)/G(o) proteins, are involved in nefiracetam potentiation. These results indicate that nnAChRs are an important site of action of nefiracetam and G(s) proteins may be its crucial target.     

Effects of DM-9384, a pyrrolidone derivative, on ischemia-induced changes in the central monoamine systems.

Alterations in brain tissue levels of monoamines and monoamine metabolites were studied in gerbils 60 min after cerebral ischemia induced by 10 min carotid ligation after pretreatment with the antiischemic drug DM-9384 (1, 3, 10, 30 mg/kg, PO). The DA levels decreased in striatum after the ischemia, while cortical and hippocampal DA levels increased. The DOPAC levels increased in cortex, but were essentially unaffected in other regions. The HVA levels increased in all forebrain regions studied. NA levels decreased in hippocampus and superior colliculus, while a general increase in MHPG levels was seen. Decreases in 5-HT levels were seen in all forebrain regions except cortex. The 10 mg/kg and 30 mg/kg doses of DM-9384 counteracted the decrease in striatal 5-HT and hypothalamic MHPG/NA ratio, respectively. Thus pretreatment with DM-9384 exerted minor protective effects on the alterations induced in monoamine systems by transient forebrain ischemia.     

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

Summary In order to assess the effects of inverse benzodiazepine agonists and antagonists on brain function, computerized EEG (CEEG) analysis was performed in rats following the i. p. administration of SR 95195 (7-phenyl-3-methyl-1,2,4 triazolo-[4,3-b]pyridazine) and CGS 8216 (2-phenylpyrazolo-[4,3c]-quinoline-3-[5H]-one) two benzodiazepine receptor inverse agonists (BRIAGs) and of flumazepil (Ro 15-1788), a benzodiazepine receptor antagonist (BRANT). The EEG effects of SR 95195 (3, 10, 30 and 60 mg/kg), CGS 8216 (10 and 30 mg/kg) and flumazepil (3, 10, 30 and 60 mg/kg) were compared to those of the psychostimulant drugs DL-amphetamine (0.1, 0.3 and 1 mg/kg), and caffeine (10 and 30 mg/kg) and those of aniracetam (100 and 300 mg/kg), a nootropic pyrrolidone derivative. The CEEG profiles of SR 95195, CGS 8216 and flumazepil were mainly characterized by a power increase in the 20–32 Hz frequency range and by a power reduction in the 8–16 Hz range. These effects were quite similar to those of the psychostimulants DL-amphetamine and caffeine as well as to those of the nootropic aniracetam. Other psychotropic drugs with CNS-depressant properties, namely diazepam (10 mg/kg p. o.), pentobarbital (30 mg/kg p. o.), chlorpromazine (10 mg/kg i.p.) and imipramine (10 mg/kg i.p.) induced quite different EEG power modifications. These results show that BRIAGs and BRANTs possess a marked intrinsic activity at the central level and suggest that this activity is CNS-activating in nature.Part of this work has been presented at the 16th Annual Meeting, Society for Neuroscience, November 9–14,1986, Washington, DC, USASend offprint requests to V. Santucci at the above address     

Nefiracetam improves Morris water maze performance following traumatic brain injury in rats

Nefiracetam, a pyrrolidone derivative, is a nootropic agent that has facilitated cognitive function in a wide variety of animal models of cognitive dysfunction. The purpose of this study was to investigate the efficacy of the chronic postinjury administration of nefiracetam (DM-9384) in improving cognitive performance following central fluid percussion brain injury in rats. Twenty-four hours following surgical preparation, a sham injury or a moderate fluid percussive injury (2.1 atm) was delivered. Nefiracetam was administered chronically (0 or 9 mg/kg, po, for sham animals and 0, 3, or 9 mg/kg for injured animals) on postinjury days 1-15. Cognitive performance was assessed using the Morris water maze (MWM) on postinjury days 11-15. Chronic administration of 3 and 9 mg/kg nefiracetam attenuated MWM deficits produced by central fluid percussive brain injury. Importantly, the MWM performance of the injured animals treated with 9 mg/kg did not significantly differ from uninjured, sham animals. The 9-mg/kg dose of nefiracetam did not have a positive or negative effect on MWM performance of uninjured animals. The results of the present experiment suggest that a nootropic such as nefiracetam may be an appropriate treatment for trauma-induced cognitive dysfunction.     

Interactions of the novel antipsychotic aripiprazole (OPC-14597) with dopamine and serotonin receptor subtypes.

OPC-14597 {aripiprazole; 7-(-4(4-(2,3-dichlorophenyl)-1-piperazinyl) butyloxy)-3,4-dihydro-2(1H)-quinolinone} is a novel candidate antipsychotic that has high affinity for striatal dopamine D2-like receptors, but causes few extrapyramidal effects. These studies characterized the molecular pharmacology of OPC-14597, DM-1451 (its major rodent metabolite), and the related quinolinone derivative OPC-4392 at each of the cloned dopamine receptors, and at serotonin 5HT6 and 5HT7 receptors. All three compounds exhibited highest affinity for D2L and D2S receptors relative to the other cloned receptors examined. Both OPC-4392 and OPC-14597 demonstrated dual agonist/antagonist actions at D2L receptors, although the metabolite DM-1451 behaved as a pure antagonist. These data suggest that clinical atypicality can occur with drugs that exhibit selectivity for D2L/D2S rather than D3 or D4 receptors, and raise the possibility that the unusual profile of OPC-14597 in vivo (presynaptic agonist and postsynaptic antagonist) may reflect different functional consequences of this compound interacting with a single dopamine receptor subtype (D2) in distinct cellular locales.     

Effects of the novel compound aniracetam (Ro 13-5057) upon impaired learning and memory in rodents

The effect of aniracetam (Ro 13-5057, 1-anisoyl-2-pyrrolidinone) was studied on various forms of experimentally impaired cognitive functions (learning and memory) in rodents and produced the following effects: (1) almost complete prevention of the incapacity to learn a discrete escape response in rats exposed to sublethal hypercapnia immediately before the acquisition session; (2) partial (rats) or complete (mice) prevention of the scopolamine-induced short-term amnesia for a passive avoidance task; (3) complete protection against amnesia for a passive avoidance task in rats submitted to electroconvulsive shock immediately after avoidance acquisition; (4) prevention of the long-term retention- or retrieval-deficit for a passive avoidance task induced in rats and mice by chloramphenicol or cycloheximide administered immediately after acquisition; (5) reversal, when administered as late as 1 h before the retention test, of the deficit in retention or retrieval of a passive avoidance task induced by cycloheximide injected 2 days previously; (6) prevention of the deficit in the retrieval of an active avoidance task induced in mice by subconvulsant electroshock or hypercapnia applied immediately before retrieval testing (24 h after acquisition). These improvements or normalizations of impaired cognitive functions were seen at oral aniracetam doses of 10–100 mg/kg. Generally, the dose-response curves were bell-shaped. The mechanisms underlying the activity of aniracetam and its therapeutic window are unknown. Piracetam, another pyrrolidinone derivative was used for comparison. It was active only in six of nine tests and had about one-tenth the potency of aniracetam. The results indicate that aniracetam improves cognitive functions which are impaired by different procedure and in different phases of the learning and memory process.     

Oxidative one-carbon cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes

1. The oxidative one-carbon cleavage reaction in the octyl side chain of olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide], a new potent biguanide antiseptic, was characterized in dog liver microsomes. 2. Olanexidine was initially biotransformed to a monohydroxylated metabolite, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-2-octanol (DM-215), and DM-215 was subsequently oxidized to the diol derivative, 8-[5-(3,4-dichlorobenzyl)-1-biguanidino]-1,2-octandiol (DM-220). DM-220 was further biotransformed to 2-hydroxy aldehyde derivative, 2-hydroxy carboxylic acid derivative, and an oxidative C-1-C-2 bond cleavage metabolite, 7-[5-(3,4-dichlorobenzyl)-1-biguanidino] heptanoic acid [DM-223 (C7), a seven-carbon chain derivative], after incubation with dog liver microsomes. 3. DM-223 formation required NADPH as a cofactor and was inhibited by quinidine and quinine, relatively selective inhibitors of CYP2D subfamilies in dogs. 4. The results suggest that the one-carbon fragment of the octyl side chain of olanexidine could be removed by the oxidative C-C bond cleavage with the possible involvement of cytochrome P450 systems such as CYP2D subfamily. This oxidative C-C bond cleavage reaction by cytochrome P450s could play an important role in the removal of one-carbon fragment of other drugs or endogenous compounds containing aliphatic chains.     

In vitro characterization of the oxidative cleavage of the octyl side chain of olanexidine, a novel antimicrobial agent, in dog liver microsomes.

The metabolism of olanexidine [1-(3,4-dichlorobenzyl)-5-octylbiguanide], a new potent biguanide antiseptic, was investigated in dog liver microsomes to characterize the enzyme(s) catalyzing the biotransformation of olanexidine to C-C bond cleavage metabolites. Olanexidine was initially biotransformed to monohydroxylated metabolite 2-octanol (DM-215), and DM-215 was subsequently oxidized to diol derivatives threo-2,3-octandiol (DM-221) and erythro-2,3-octandiol (DM-222). Diols were further biotransformed to a ketol derivative and C-C bond cleavage metabolite (DM-210, hexanoic acid derivative), an in vivo end product, in the incubation with dog liver microsomes. The formations of DM-215, DM-221, DM-222, and DM-210 followed Michaelis-Menten kinetics, and Eadie-Hofstee analysis of the metabolite formation activity confirmed single-enzyme Michaelis-Menten kinetics. The K(m) and V(max) values for the formation of DM-210 appeared to be 2.42 microM and 26.6 pmol/min/mg in the oxidation of DM-221 and 2.48 microM and 30.2 pmol/min/mg in the oxidation of DM-222. The intrinsic clearance (V(max)/K(m)) of the C-C bond cleavage reactions was essentially the same with either DM-221 or DM-222 as substrate. These oxidative reactions were significantly inhibited by quinidine, a selective inhibitor of CYP2D subfamilies, indicating the metabolic C-C bond cleavage of the octyl side chain of olanexidine to likely be mediated via the CYP2D subfamily in dog liver microsomes. This aliphatic C-C bond cleavage by cytochrome P450s may play an important role in the metabolism of other drugs or endogenous compounds possessing aliphatic chains.     

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.     

Diazepam-induced release of behavior in an extinction procedure: its reversal by Ro 15-1788

The effects of the benzodiazepine receptor antagonist Ro 15-1788, an imidazobenzodiazepine derivative, were studied with respect to three pharmacological activities exerted by diazepam in rats. Two of these, release of shock-induced suppression of drinking and attenuation of non-reward-induced cessation of responding for food, reflect the anxiolytic property of benzodiazepines. The amnesic-like effect of diazepam was also investigated. Ro 15-1788 (in doses ranging from 4 to 16 mg/kg p.o.) completely reversed diazepam (2 mg/kg)-induced release of behavior in both punishment and non-reward procedures. In contrast, Ro 15-1788 reduced but did not completely abolish diazepam-induced amnesia. These data suggest that the anticonflict and anti-frustration effects of benzodiazepines probably involve similar receptor types which nevertheless differ from those chiefly implicated in the amnesic-like activity of benzodiazepines.     

The ameliorating effect of the water layer of Fructus Schisandrae on cycloheximide-induced amnesia in rats: interaction with drugs acting at neurotransmitter receptors.

Our previous study indicated that the water layer present in Fructus Schisandra(FS(w)) at 10 and 25 mg kg(-1)significantly counteracted cycloheximide (CXM)-induced amnesia. Therefore, the mechanism of action of the ameliorating effect of FS(w)on CXM-induced amnesia in the passive avoidance task was investigated in rats. The ameliorating effect of FS(w)on CXM-induced amnesia was depressed by scopolamine. The serotonin releaser, p -chloroamphetamine significantly antagonized the ameliorating effect of FS(w)on CXM-induced amnesia. Furthermore, the ameliorating effect was also inhibited by the 5-HT(1A)receptor agonist 8-OH-DPAT, but potentiated by the 5-HT(2)receptor antagonist ritanserin. Finally, the GABA(A)receptor antagonist bicuculline blocked the ameliorating effect of FS(w). These results suggest that the beneficial effect of FS(w)on CXM-induced amnesia is amplified by treatment with serotonergic 5-HT(2)receptor antagonists, but reduced by serotonergic 5-HT(1A)receptor agonists as well as GABA(A)and cholinergic receptor antagonists.     

Serotonergic mechanisms involved in the attentional and vigilance task performance of rats and the palliative action of aniracetam

Central serotonergic systems play an important role in regulating mood/emotion, cognition, sleep and wakefulness, appetite and locomotion and body temperature via multiple receptor subtypes. Among them, 5-HT1A and 5-HT2A/2C receptors have opposite effects with respect to certain functions. The aim of the present study was to compare the effects of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a selective 5-HT1A receptor agonist, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), a selective 5-HT2A/2C receptor agonist, on the performance of middle-aged rats in a two-lever choice reaction task that assessed attention and vigilance functions. We also examined the effects of aniracetam, a cognition enhancer, and its major metabolites on the induced performance impairments. 8-OH-DPAT (0.3 mg/kg s.c.) reduced response speed and choice accuracy and increased response omission with a reduction of task-associated motor activity without inducing motor inability or motivational changes. These findings indicate a specific disturbance of attentional and vigilance processes. DOI caused similar impairments at the highest dose tested (3 mg/kg s.c.); at a lower dose (1 mg/kg s.c.), however, it selectively attenuated the response speed, suggesting a selective attention deficit. (-)-Alprenolol, a non-selective 5-HT1A receptor antagonist, and ritanserin, a preferential 5-HT2A receptor antagonist, blocked the 8-OH-DPAT- and DOI-induced performance impairments respectively. Aniracetam ameliorated all the performance deficits, and the metabolites N-anisoyl-GABA and 2-pyrrolidinone partially mimicked the aniracetam effect in the 8-OHDPAT-induced attentional and vigilance impairments. Nefiracetam, another cognition enhancer, improved only the 8-OH-DPAT-induced impairments. Each compound tested alone had no effect on task performance. These results indicate that both serotonergic regulations, possibly via presynaptic 5-HT1A receptors and more likely via postsynaptic 5-HT2A receptors, lead similarly to attention deficits.     

The attenuation of learning impairments induced after exposure to CO or trimethyltin in mice by sigma (sigma) receptor ligands involves both sigma1 and sigma2 sites.

1. Sigma (sigma) receptor ligands were previously reported to alleviate learning and memory impairments on several pharmacological and pathological rodent models of amnesia. Such effect was demonstrated as involving the sigma1 subtype of sigma receptor. 2. In this study, we characterized the pharmacological effect mediated by sigma ligands on two lesional models of amnesia in mice: (1) the hypoxia-related learning and memory impairment model induced by repeated exposure to carbon monoxide (CO) gas; and (2) the intoxication with trimethyltin (1 mg kg(-1)). 3. The selective sigma1 ligand PRE-084 (1 mg kg(-1)) or the non-selective sigma1/sigma2 compounds DTG (0.1 mg kg(-1)), BD1008 (3 mg kg(-1)), and haloperidol (0.1 mg kg(-1)) reversed significantly the spontaneous alternation deficits observed 7 days after exposure to CO or 14 days after intoxication with trimethyltin. 4. The selective sigma1 receptor antagonist NE-100 (1 mg kg(-1)) was ineffective by itself, but blocked completely the PRE-084 effects, partially the DTG effects, and did not affect the effects induced by BD1008 or haloperidol. 5. A similar pharmacological profile was observed in the step-down type passive avoidance test performed 8 days after exposure to CO. 6. These results show that, in contrast to the previously reported amnesia models, the impairments induced after exposure to CO or intoxication with trimethyltin could be alleviated not only by sigma1 receptor agonists but also by sigma2 agonists. The particular pattern of neurodegeneration observed in these lesional models may explain these differences.     

Influence of N-methyl D-aspartate receptor mechanism on WIN55,212-2-induced amnesia in rat dorsal hippocampus

In this study, we investigated the effects of both N-methyl D-aspartate (NMDA) and MK-801 on WIN55,212-2(WIN)-induced amnesia in rats. Step-through inhibitory avoidance of memory was used to examine the retrieval of memory, 24 h after training. All drugs were injected bilaterally into the dorsal hippocampus (intra-CA1) of rats. Pretraining and posttraining or pretesting administration of the nonselective CB1/CB2 receptor agonist, WIN (0.5 μg/rat), decreased the step-through latency. However, amnesia induced by pretraining or posttraining injections of WIN was reversed by a pretest administration of WIN (0.25 and 0.5 μg/rat). Pretest microinjections of different doses of NMDA (0.1, 0.5, and 1 μg/rat) elicited no response, but NMDA (0.5 and 1 μg/rat) did induce full recovery from amnesia induced by WIN (0.5 μg/rat). The posttraining and pretest injection of a higher dose of the NMDA receptor antagonist, MK801 (MK; 4 μg/rat), caused an impairment in the memory retrieval. However, amnesia induced by posttraining injections of MK (4 μg/rat) was reversed by a pretest administration of MK (4 μg/rat). In addition, pretest administration of different doses of the antagonist (2 and 4 μg/rat) induced full recovery of WIN-induced amnesia, but did not influence memory recovery in the subjects, which had received posttraining (0.5 μg/rat) and pretest WIN (0.25 and 0.5 μg/rat). Pretesting coadministration of ineffective doses of WIN (0.1 μg/rat) with NMDA (0.1 μg/rat), but not with MK (1 μg/rat), restored WIN-induced (0.5 μg/rat) amnesia. It can be concluded that the NMDA receptor mechanism located in the dorsal hippocampus may be involved in WIN-induced amnesia.     

Piracetam and TRH analogues antagonise inhibition by barbiturates, diazepam, melatonin and galanin of human erythrocyte D-glucose transport

1 Nootropic drugs increase glucose uptake into anaesthetised brain and into Alzheimer's diseased brain. Thyrotropin-releasing hormone, TRH, which has a chemical structure similar to nootropics increases cerebellar uptake of glucose in murine rolling ataxia. This paper shows that nootropic drugs like piracetam (2-oxo 1 pyrrolidine acetamide) and levetiracetam and neuropeptides like TRH antagonise the inhibition of glucose transport by barbiturates, diazepam, melatonin and endogenous neuropeptide galanin in human erythrocytes in vitro. 2 The potencies of nootropic drugs in opposing scopolamine-induced memory loss correlate with their potencies in antagonising pentobarbital inhibition of erythrocyte glucose transport in vitro (P<0.01). Less potent nootropics, D-levetiracetam and D-pyroglutamate, have higher antagonist Ki's against pentobarbital inhibition of glucose transport than more potent L-stereoisomers (P<0.001). 3 Piracetam and TRH have no direct effects on net glucose transport, but competitively antagonise hypnotic drug inhibition of glucose transport. Other nootropics, like aniracetam and levetiracetam, while antagonising pentobarbital action, also inhibit glucose transport. Analeptics like bemigride and methamphetamine are more potent inhibitors of glucose transport than antagonists of hypnotic action on glucose transport. 4 There are similarities between amino-acid sequences in human glucose transport protein isoform 1 (GLUT1) and the benzodiazepine-binding domains of GABAA (gamma amino butyric acid) receptor subunits. Mapped on a 3D template of GLUT1, these homologies suggest that the site of diazepam and piracetam interaction is a pocket outside the central hydrophilic pore region. 5 Nootropic pyrrolidone antagonism of hypnotic drug inhibition of glucose transport in vitro may be an analogue of TRH antagonism of galanin-induced narcosis.     

Inhibition of morphine-induced amnesia in morphine-sensitized mice: involvement of dorsal hippocampal GABAergic receptors

In the present study, the effects of bilateral injections of the GABAergic receptor agents into the dorsal hippocampal CA1 regions (intra-CA1) on morphine-induced amnesia were examined in morphine sensitized-mice. Pre-training subcutaneous (s.c.) administration of morphine (5 mg/kg) suppressed the learning of a one-trial passive avoidance task. Amnesia induced by pre-training morphine was significantly reversed in mice which had previously received once daily injections of morphine (20 and 30 mg/kg, s.c.) for 3 days, which may be due to behavioral sensitization. Intra-CA1 injections of GABAA receptor agonist, muscimol (0.125, 0.25, 0.5 and 1 microg/mouse) or the GABAB receptor agonist, baclofen (1, 1.5 and 2 microg/mouse) prior to injection of morphine (20 mg/kg per dayx3 days) decreased the reversion of morphine-induced amnesia in morphine sensitized-mice. Daily intra-CA1 injections of muscimol or baclofen plus saline for 3 days did not alter memory formation. Furthermore, during development of sensitization, the combination of GABAA receptor antagonist, bicuculline (0.25, 0.5, 1 and 2 microg/mouse) with an ineffective dose of morphine (5 mg/kg, s.c.) reversed the amnesia induced by pre-training morphine. However, the same treatment with GABAB receptor antagonist, CGP35348 (2.5-40 microg/mouse) had no effect on the morphine response. On the other hand, daily intra-CA1 injections of bicuculline or CGP35348 alone for 3 days did not alter the amnesia induced by pre-training injection of morphine. The results suggest that morphine sensitization reverses the impairment of memory induced by morphine and that GABAergic receptors of the dorsal hippocampus may play an important role in this effect.