Nootropic nefiracetam inhibits proconvulsant action of peripheral-type benzodiazepines in epileptic mutant EL mice.

Piracetam and structurally related nootropics are known to potentiate the anticonvulsant effects of antiepileptic drugs. It remains to be seen, however, whether these nootropics inhibit proconvulsant actions of many toxic agents including Ro 5-4864, a specific agonist for peripheral-type benzodiazepine receptors (PBR). The present study was designed to address this issue using EL mice, an animal model of epilepsy. In behavioral pharmacological experiments, EL mice were highly susceptible to convulsions induced by Ro 5-4864 (i.p.) in comparison with nonepileptic DDY mice. Nefiracetam administered orally to EL mice inhibited spontaneous seizures. In DDY mice, convulsions induced by Ro 5-4864 were prevented by nefiracetam when administered by i.v. injection. Aniracetam (i.v.) was partially effective, but piracetam and oxiracetam were ineffective as anticonvulsants. Binding assay for brain tissues revealed a higher density of mitochondrial PBR in EL mice compared with DDY mice. Binding of the PBR ligands Ro 5-4864 to either EL or DDY mouse brain was inhibited by micromolar concentrations of these nootropic agents in the sequence of nefiracetam > aniracetam >> oxiracetam, piracetam. This rank order is identical to potency as anticonvulsants. These data suggest that nefiracetam may prevent toxic effects of PBR agonists through interacting with PBR.

Negative regulation of opioid receptor-G protein-Ca2+ channel pathway by the nootropic nefiracetam.

It has recently been reported that nefiracetam, a nootropic agent, is capable of attenuating the development of morphine dependence and tolerance in mice. The mechanism of this antimorphine action is not clear. The present study was designed to address this issue using Xenopus oocytes expressing delta-opioid receptors, G proteins (G(i3alpha) or G(o1alpha)), and N-type (alpha1B) Ca2+ channels. Membrane currents through Ca2+ channels were recorded from the oocytes under voltage-clamp conditions. The Ca2+ channel currents were reduced reversibly by 40-60% in the presence of 1 microM leucine-enkephalin (Leu-Enk). The Leu-Enk-induced current inhibition was recovered promptly by nefiracetam (1 microM), while control currents in the absence of Leu-Enk were not influenced by nefiracetam. A binding assay revealed that 3H-nefiracetam preferentially bound to the membrane fraction of oocytes expressing G(i3alpha). When delta-opioid receptors were coexpressed, the binding was significantly increased. However, an additional expression of alpha1B Ca2+ channels decreased the binding. The results suggest that nefiracetam preferentially binds to G(i3alpha) associated with delta-opioid receptors, thereby inhibiting the association of G proteins with Ca2+ channels. In conclusion, nefiracetam negatively regulates the inhibitory pathway of opioid receptor-G protein-Ca2+ channel.

The long-term effects of nefiracetam on learning in older rabbits.

Classical conditioning of the nictitating membrane (NM)/eyeblink response has proven utility in the study of age-related memory disorders. The 750 ms delay eyeblink conditioning procedure was used to investigate the magnitude and duration of the nootropic drug nefiracetam's effect on retention and relearning. After administering daily injections of 0 (vehicle), 5, 10, or 15 mg/kg nefiracetam to 34 retired breeder rabbits during 15 days of acquisition, we tested retention and relearning 1, 5, and 12 weeks post-training. Rabbits received no drug after the initial 15 daily injections. Significant relearning was observed in the 10 mg/kg nefiracetam group 1 and 5 weeks after initial acquisition. Differences in tone-alone retention did not achieve statistical significance, although responses were numerically greater in the 10 mg/kg nefiracetam group. The effect of nefiracetam upon the ability of older rabbits to relearn a previously learned task is apparent up to 5 weeks after drug administration. Under normal conditions, a drug is administered continuously. In this experiment, nefiracetam had a significant effect long after drug administration had ceased. Prolonged administration of nefiracetam may have ameliorating effects greater than those observed in only 15 days of drug administration.

Nefiracetam improves the impairment of local cerebral blood flow and glucose utilization after chronic focal cerebral ischemia in rats.

In this study we investigated the effects of nefiracetam (DM-9384) on local cerebral blood flow (LCBF) and local cerebral glucose utilization (LCMR(glc)) in the chronic phase after middle cerebral artery (MCA) occlusion in rats. Nefiracetam (10 mg/kg) was administered orally once a day for 2 weeks from day 15 after MCA occlusion. On day 28 after MCA occlusion, LCBF and LCMR(glc) were measured by an autoradiographic image-processing method. In MCA-occluded rats, LCBF and LCMR(glc) in the ischemic side of seven regions including the frontal cortex were significant decreased compared with those of the nonischemic side. Nefiracetam significantly improved the impairment of LCBF in the frontal cortex, parietal cortex, caudate putamen, ventral thalamus, amygdaloid nucleus and hippocampus. It also improved the decrease of LCMR(glc) in the frontal cortex, ventral thalamus and hippocampus. These results suggested that nefiracetam has ameliorating effects on chronic disorders of LCBF and LCMR(glc) induced by MCA occlusion.