Sildenafil enhances locomotor activity in young mice and exerts anxiogenic effects in both young and aged mice

The evaluation of anti-breast cancer activity and safety pharmacology of the ethanol extract of Aralia elata Seem. leaves

Aralia elata Seem. is a traditional folk Chinese medicinal plant and its leaves have been used to treat many diseases. We aimed to evaluate the anti-breast cancer activity and safety pharmacology of the ethanol extract of A. elata Seem. leaves (ELE). Cytotoxicity was evaluated on human tumor cell lines by MTT assay in vitro. A tumor bearing-nude mice model was used to assess antitumor activity in vivo. Cell apoptosis was determined by Hoechst 33258 staining, flow cytometry and TUNEL staining. The protein levels were determined by western-blotting and immunohistochemical staining. In safety evaluation, ICR mice and beagle dogs were orally administered ELE at different doses to determine its adverse effects on the central nervous system and cardiorespiratory system. ELE significantly inhibited tumor growth and induced cell apoptosis in MCF-7 cells in vitro and in vivo. The protein levels including caspase-3, caspase-9, bax, bcl-2, PARP, and cytochrome c were significantly changed. For the central nervous system, no treatment-related changes in behavior, motor activity or coordination were observed in mice. For the cardiorespiratory system, no significant differences in cardiorespiratory parameters including heart rate, PR interval, RR interval, P wave duration, QRS duration, QTcF interval, respiratory frequency, tidal volume, body temperature, and blood pressure were observed in beagle dogs between the ELE treatment and control group. In conclusion, ELE possessed anti-breast cancer activity by activating a mitochondrial-mediated apoptotic pathway with high biological safety in animals, which indicates it could be a potential therapeutic agent for treating human breast cancer in the future.

Amantadine exerts anxiolytic like effect in mice: Evidences for the involvement of nitrergic and GABAergic signaling pathways

Amantadine is a glutamatergic antagonist that works by inhibiting the NMDA receptor. Besides the inhibition of NMDA receptors amantadine also stabilizes the glutamatergic system and protects the neurons against the NMDA toxicity. Amantadine treatment also reduces the production of NO and metabolism of GABA. Therefore amantadine modulates glutamate, GABA and NO which are known to be implicated in the pathogenesis of anxiety and related behavior. The present study was designed to investigate the anxiolytic like effect of amantadine in mice. Nitrergic and GABAergic signaling influence in the anxiolytic like effect of amantadine was also studied. Amantadine (25, 50 and 75 mg/kg, i.p.) was administered and the anxiety related behavior was determined using light and dark box (LDB) and elevated plus maze (EPM) methods. Further, the effect of various treatments on the whole brain glutamate, nitrite and GABA levels were also determined. The results obtained demonstrated that the amantadine (50 mg/kg, i.p.) exerted anxiolytic like effect in mice and reduced the levels of glutamate, nitrite and GABA in the brain of mice as compared to control. Further, the influence of NO and GABA in the anxiolytic like effect of the amantadine was also determined. The results obtained demonstrated that NO donor counteracted while NO inhibitor potentiated the anxiolytic like effect of amantadine in mice. Also the combined treatment of amantadine (25 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.) did not affect the anxiety related behavior, brain GABA and nitrite level of mice but reduced the levels the brain glutamate levels significantly as compared to amantadine (25 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.) treated mice. Thus, amantadine exerted anxiolytic like effect in mice and the anxiolytic like effect of amantadine was modulated by nitrergic and GABAergic signaling pathway.

Lithium potentiated, pyridoxine abolished and fluoxetine attenuated the anxiolytic effect of diazepam in mice

In the present study, the anxiolytic effect of diazepam (1 and 2 mg/kg, i.p.) was determined alone and in combination with lithium (50 mg/kg, i.p.), pyridoxine (90 mg/kg, i.p.) and fluoxetine (10 mg/kg, i.p.) using elevated plus maze (EPM) and light/dark box (LDB) tests in experimental mice. The effect of various treatments on the brain GABA levels and glutamic acid decarboxylase (GAD) expression were also determined. The results obtained suggested that the diazepam (2 mg/kg, i.p.) exerted anxiolytic effect and significantly increased the brain GABA levels and GAD expression as compared to control group. Fluoxetine (10 mg/kg, i.p.) exerted anxiogenic effects, but did not affect the brain GABA levels and GAD activity significantly as compared to control. Pretreatments of pyridoxine (90 mg/kg, i.p.) abolished; lithium (50 mg/kg, i.p.) potentiated while fluoxetine (10 mg/kg, i.p.) attenuated the anxiolytic and neurochemical effects of diazepam (1 and 2 mg/kg, i.p.) treatment in mice. Therefore, the combined treatment of lithium and diazepam might be a promising treatment for anxiety.

Nitrergic signaling modulation by ascorbic acid treatment is responsible for anxiolysis in mouse model of anxiety

The present study was designed to investigate the effect of ascorbic acid (AA) treatment on the anxiety related behavioral and neurochemical alterations. AA (50, 100 and 200 mg/kg, i.p.) was administered to the mice and anxiety related behavior and levels of glutamate and nitrite in the brain of mice were determined. The results obtained revealed that the administration of AA (100 mg/kg, i.p.) significantly reduced the anxiety related behavior and the levels of nitrite in the brain of mice. Nitrergic interactions were further determined by the pretreatment of mice with nitric oxide (NO) modulator and AA treatment followed by behavioral and neurochemical measurements. The results obtained suggested that NO inhibition potentiated the anxiolytic like activity of AA in mice. It was also observed that the glutamate and nitrite level in the brain of mice were significantly reduced by the NO inhibitor pretreatment. Thus, the present study demonstrated the possible nitrergic pathways modulation in the anxiolytic like activity of AA in mice.

NO-sGC-cGMP signaling influence the anxiolytic like effect of lithium in mice in light and dark box and elevated plus maze

Glutamate is an excitatory neurotransmitter implicated in the pathogenesis of psychiatric disorders. Glutamate results in the activation of an enzyme called glycogen synthase kinase-3 (GSK-3) acting through N-methyl-d-aspartate (NMDA) receptors. Impaired expression of GSK-3 affects behavior and neurochemicals level in the brain responsible for the pathogenesis of mood disorders. It has been reported that lithium acts as an inhibitor of GSK-3 and inhibit the enzyme GSK-3 in an uncompetitive manner. In the present study, anxiolytic like effect of lithium in mice is investigated through light and dark box (LDB) and elevated plus maze (EPM). Lithium (50, 100 and 200 mg/kg, i.p.) was administered to the mice to determine the anxiety related behavior. Results obtained suggests that the administration of lithium (100 mg/kg, i.p.) reversed the anxiety related behavior of mice and decreased the levels of glutamate and nitrite as compared to control. Glutamate acting through the NMDA receptor has been found to regulate the expression of enzyme neuronal nitric oxide synthase (nNOS), which is responsible for the release of nitric oxide (NO), suggesting a possible link between NO and GSK-3 also. Therefore, to determine the possible interaction with NO, sub-effective dose of lithium was administered in combination with NO donor i.e. l-Arginine (50 mg/kg, i.p.), NOS and soluble guanylate cyclase (sGC) inhibitor i.e. methylene blue (1 mg/kg, i.p.) and phosphodiesterase inhibitor i.e. sildenafil (1 mg/kg, i.p.). The results obtained demonstrated that the anxiolytic like effect of lithium was abolished by the pretreatment with NO donor and potentiated by the pretreatment with NOS inhibitor. Therefore, it is suggested that NO signaling pathway influence the anxiolytic like activity of lithium in mice, further suggesting the link between the GSK-3 and NO signaling in the regulation of anxiety related behavior.

Evaluation of the role of different neurotransmission systems in the anticonvulsant action of sildenafil in the 6 Hz-induced psychomotor seizure threshold test in mice

Sildenafil influences seizure activity in animal seizure models, and its both proconvulsant and anticonvulsant effects were reported. We previously found that this PDE5 inhibitor significantly increased seizure threshold for the 6 Hz-induced psychomotor seizures in mice and therefore we aimed to investigate the influence of some modulators of neurotransmitter receptors, i.e., diazepam (GABA/benzodiazepine receptor agonist), flumazenil (GABA/benzodiazepine receptor antagonist), N-methyl-d-aspartic acid (NMDA glutamate receptor agonist), CGP 37849 (NMDA receptor antagonist), metergoline (serotonin receptor antagonist), 8-cyclopentyl-1,3-dipropylxanthine (adenosine A₁ receptor antagonist) and β-funaltrexamine (μ opioid receptor antagonist), on the anticonvulsant effect of sildenafil in this test. Additionally, we estimated influence of the studied compounds and their combinations with sildenafil on the muscular strength (assessed in the grip strength test) and motor coordination (assessed in the chimney test) in mice. Our results indicate that anticonvulsant properties of sildenafil in the 6 Hz test in mice might be related to its interactions with the GABAergic, glutamatergic, serotonergic and adenosinergic neurotransmission. We did not find interactions between sildenafil and μ opioid receptors. Neither the studied ligands nor their combinations with sildenafil impaired muscular strength and motor coordination. In conclusion, sildenafil has complex and extensive influence on neurotransmission and seizure generation in the CNS.

Anxiolytic-like effect of pyridoxine in mice by elevated plus maze and light and dark box: Evidence for the involvement of GABAergic and NO-sGC-cGMP pathway

Present study was carried out to investigate the 'anxiolytic-like' effect of pyridoxine in mice. Pyridoxine (90, 180 and 360 mg/kg) was administered by intraperitoneal (i.p.) route to the experimental mice and anxiety-related behavior was evaluated by light and dark box (LDB) and elevated plus maze (EPM) models. Glutamate, GABA and nitrite levels were also determined in the isolated whole brain of mice. It was observed that pyridoxine (180 mg/kg, i.p.) exerted 'anxiolytic-like' effect in mice in EPM and LDB models. Also, there was a significant increase in the levels of GABA whereas; the levels of glutamate and nitrite were decreased as compared to the control group. Administration of pentamethylene tetrazole (PTZ; 20 mg/kg, i.p.) exerted anxiogenic effects in mice, but the combination of PTZ and pyridoxine (180 mg/kg, i.p.) abolished the 'anxiolytic-like' effect of pyridoxine, thereby, suggesting the possible role of GABA in the 'anxiolytic-like' effect of pyridoxine in mice. Further, the influence of NO-sGC-cGMP pathway was investigated by administering the sub-effective dose of pyridoxine in combination with sub-threshold doses of NO modulators i.e. l‑arginine (50 mg/kg, i.p.; NO donor); methylene blue (1 mg/kg, i.p.; NO and soluble guanylate cyclase inhibitor) and sildenafil (1 mg/kg, i.p.; phosphodiesterase inhibitor and cGMP modulator). It was observed that the 'anxiolytic-like' effect of pyridoxine in mice was counteracted by the NO donor and potentiated by the NO inhibitors. Thus, the present study confirmed the involvement of GABAergic and NO-sGC-cGMP pathway in the 'anxiolytic-like' effect of pyridoxine in mice.

Tadalafil enhances working memory, and reduces hippocampal oxidative stress in both young and aged mice

Tadalafil, a type-5 phosphodiesterase enzyme inhibitor with long half-life used to treat erectile dysfunction. Recently it has been reported that tadalafil improves cognitive function. Here, we aimed to investigate the age dependent effects of tadalafil on memory, locomotor, behavior, and oxidative stress in the hippocampus. Tadalafil was orally administered everyday (5 mg/kg) to young (2 months) and old (16 months) healthy mice for 4 weeks. Control mice from each group received equal volume of 0.9% normal saline for the same duration. Memory and locomotor activity were tested using radial arm maze and open field test respectively. The level of malondialdehyde (MDA), nitric oxide (NO), and advanced protein oxidation product (APOP) was analyzed and catalase activity was determined from the isolated hippocampus. Treatment with tadalafil in aged mice improves working memory than the corresponding tadalafil treated young mice in radial arm maze test. Tadalafil treated mice traveled less distance in the center and the mean speed of tadalafil treated aged mice was significantly lower than the tadalafil treated young mice in open field test. Tadalafil treatment elicited a decrease of MDA level in the hippocampus of aged mice than that of young mice. APOP level was decreased only in aged mice treated with tadalafil. Treatment with tadalafil decreased NO and increased catalase activity in both young and aged mice. On the basis of previous and our findings, we conclude that tadalafil treatment reduces oxidative stress while increased cGMP level in the hippocampus might be responsible for memory enhancement.