Increased GABA-gated chloride ion influx in the hypothalamus of low-anxiety rats

Pachymic Acid Enhances Pentobarbital-Induced Sleeping Behaviors via GABAA-ergic Systems in Mice

This study was investigated to know whether pachymic acid (PA), one of the predominant triterpenoids in Poria cocos (Hoelen) has the sedative-hypnotic effects, and underlying mechanisms are mediated via γ-aminobutyric acid (GABA)-ergic systems. Oral administration of PA markedly suppressed locomotion activity in mice. This compound also prolonged sleeping time, and reduced sleep latency showing synergic effects with muscimol (0.2 mg/kg) in shortening sleep onset and enhancing sleep time induced by pentobarbital, both at the hypnotic (40 mg/kg) and sub-hypnotic (28 mg/kg) doses. Additionally, PA elevated intracellular chloride levels in hypothalamic primary cultured neuronal cells of rats. Moreover, Western blotting quantitative results showed that PA increased the amount of protein level expression of GAD_65/67 over a broader range of doses. PA increased α- and β-subunits protein levels, but decreased γ-subunit protein levels in GABA_A receptors. The present experiment provides evidence for the hypnotic effects as PA enhanced pentobarbital-induced sleeping behaviors via GABA_A-ergic mechanisms in rodents. Taken together, it is proposed that PA may be useful for the treatment of sleep disturbed subjects with insomnia.

Anxiolytic and antidepressant-like activity of a standardized extract from Galphimia glauca

An infusion prepared with aerial parts from Galphimia glauca has been widely used in Mexican traditional medicine as a remedy for nervous excitement. The sedative activity of a methanolic extract from this plant has been demonstrated by neuropharmacological tests. This effect was attributed to the nor-secotriterpene named galphimine B (GB). In the present work, the anxiolytic and antidepressant-like effects of G. glauca methanolic extract (standardized on GB content, 8.3mg/g) were assayed by using the elevated plus-maze, light-dark test and the forced swimming paradigm, on ICR albino mice. This extract, administered orally, three times (24, 18 and 1h before the test), and in different doses (125, 250, 500, 1,000 and 2,000 mg/kg) was able to increase significantly (p<0.05) the number of entries, as well as the time spent in the open arms of the elevated plus-maze, indicating an anxiolytic-like effect. A similar effect was observed in the light-dark paradigm test, the time spent in the light box was increased in treated mice. Nevertheless, this treatment was unable to change any parameter in the forced swimming test. Altogether, these results suggest an anxiolytic-like effect to the methanolic standardized extract of G. glauca on ICR inbred mice.

Pharmacological characterisation of cortical gamma-aminobutyric acid type A (GABAA) receptors in two Wistar rat lines selectively bred for high and low anxiety-related behaviour

Two Wistar rat lines that have been selectively bred for high-anxiety-related behaviour (HAB) and low-anxiety-related behaviour (LAB) in the elevated plusmaze test may be considered as a genetically prone animal model to study the neurochemical correlates of anxiety-related behaviour. Because there are pronounced differences between the two lines both in baseline levels of open-arm exploration in the elevated plus-maze test and in sensitivity to the anxiolytic effects of 1 mg/kg diazepam, we used these lines to investigate the pharmacology of the benzodiazepine binding site and the GABA binding site of cortical GABAA receptors. No difference in characteristics of flunitrazepam, zolpidem or muscimol binding to cortical GABAA receptors could be detected between the two lines. Although there was an increase in the brain concentration of the anxiolytic neuroactive steroid allopregnanolone, a potent positive allosteric modulator of GABAA receptors, both in HAB and LAB animals after a forced swim stress, allopregnanolone concentrations did not differ between the two lines. Moreover, plasma dehydroepiandrosterone (DHEA) concentrations were similar in HAB and LAB animals. We conclude that anxiety-related behaviour and benzodiazepine sensitivity in these rat lines are likely to be independent of the pharmacology of cortical GABAA receptors.