Picrotoxin blocks the anxiolytic- and panicolytic-like effects of sodium valproate in the rat elevated T-maze

The effect of acute sodium valproate administration, an anxiolytic and putative panicolytic drug, was evaluated in rats tested in the elevated T-maze, an animal model that measures two defensive reactions: avoidance (inhibitory avoidance), related to generalized anxiety, and escape (escape from open arms), related to panic. Additionally, the involvement of gamma-aminobutyric acid (GABA) neurotransmission in sodium valproate effects was studied by picrotoxin co-administration. Sodium valproate (300 mg/kg, intraperitoneally, 30 min before the test) impaired both avoidance latency (time to leave the closed arm) and one-way escape (latency to enter the closed arm) indicating anxiolytic and panicolytic effects, respectively. Pre-treatment with picrotoxin (0.5 mg/kg, intraperitoneally, 5 min before sodium valproate administration) blocked the effects of sodium valproate on inhibitory avoidance and one-way escape. No locomotor effect was seen in the open-field. These data suggest that sodium valproate exerts anxiolytic-like and panicolytic-like effects in the elevated T-maze and that these effects were mediated by picrotoxin-sensitive GABA type A receptors.

The anxiolytic-like properties of two selective MAOIs, moclobemide and selegiline, in a standard and an enhanced light/dark aversion test

The present study was designed to investigate the putative anxiolytic effects of moclobemide (MOC), a reversible inhibitor of type A monoamine oxidase enzyme (RIMA) antidepressant, in an experimental model of anxiety in mice. The test selected was the light/dark aversion test. In the present investigation, an anxiogenic-like behavior was induced by light, alone as the stimulus (standard version of the test) or by pretreatment with a subconvulsant dose of pentylenetetrazole (PTZ) (15 mg/kg IP) 45 min before testing ("enhanced" version of the test). In mice, the effect of repeated administration for 2 weeks of MOC (0.5, 1, and 5 mg/kg IP) was compared with those of selegiline (SEL) (5, 10, and 20 mg/kg IP), an irreversible and selective MAO-B inhibitor. For comparative purpose, the chronic effect of an established reference anxiolytic, such as lorazepam (LOR) (0.025, 0.05, and 0.10 mg/kg IP), was also evaluated. Results demonstrated that PTZ-treated mice showed a decrease in the number of transitions as well as in the time spent in the lit area, when compared with vehicle controls, an effect characteristic of an anxiogenic response. This anxiogenic-like behavior was reduced by chronic administration of LOR as well as MOC, suggesting an anxiolytic-like effect (as shown in the "standard" version of the test). In addition, the increased aversion of mice for the light compartment of the light/dark box was significantly reduced compared to PTZ-treated mice or vehicle controls. SEL failed to significantly alter the anxiogenic-like behavior induced by subconvulsant doses of PTZ. These data provide additional evidence for the anxiolytic-like effects of MOC administered chronically in the mouse.

Increased anxiety and altered responses to anxiolytics in mice deficient in the 65-kDa isoform of glutamic acid decarboxylase

The larger isoform of the enzyme glutamate decarboxylase, GAD67, synthesizes >90% of basal levels of gamma-aminobutyric acid (GABA) in the brain. In contrast, the smaller isoform, GAD65, has been implicated in the fine-tuning of inhibitory neurotransmission. Mice deficient in GAD65 exhibit increased anxiety-like responses in both the open field and elevated zero maze assays. Additionally, GAD65-deficient mice have a diminished response to the anxiolytics diazepam and pentobarbital, both of which interact with GABA-A receptors in a GABA-dependent fashion to facilitate GABAergic neurotransmission. Loss of GAD65-generated GABA does not appear to result in compensatory postsynaptic GABA-A receptor changes based on radioligand receptor binding studies, which revealed no change in the postsynaptic GABA-A receptor density. Furthermore, mutant and wild-type animals do not differ in their behavioral response to muscimol, which acts independently of the presence of GABA. We propose that stress-induced GABA release is impaired in GAD65-deficient mice, resulting in increased anxiety-like responses and a diminished response to the acute effects of drugs that facilitate the actions of released GABA.

Ethopharmacological analysis of the effects of putative 'anxiogenic' agents in the mouse elevated plus-maze

The literature on the effects of anxiety-provoking agents in humans and animals is replete with inconsistent and contradictory findings as well as data that may have alternate explanations. To further our understanding in this area, ethological methods were used to assess in detail the effects of four putative anxiogenic agents in the murine elevated plus-maze test. Compounds studied were FG 7142 (1.25-10.0 mg/kg), pentylenetetrazol (PTZ; 1.875-30.0 mg/kg), isoproterenol (0.125-1.0 mg/kg), and sodium lactate (32.75-262.0 mg/kg). FG 7142 produced an anxiogenic-like profile at 10 mg/kg, an effect that could not be attributed to seizure activity or nonspecific behavioural suppression. PTZ exerted biphasic effects, with low doses (1.875-3.75 mg/kg) producing anxiolytic-like effects and high doses (20.0-30.0 mg/kg) anxiogenic-like effects. With the exception of the highest dose tested, which radically disrupted behavior, these effects of PTZ were also seen to be behaviorally specific. Although some minor behavioural changes were evident with sodium lactate and isoproterenol, neither compound altered anxiety-related measures under present test conditions. Data are discussed in relation to distinctions between anxiety and panic, and the nature of anxiety expressed in and detected by animal models.

Effects of valproate and lorazepam on experimental anxiety: tolerance, withdrawal, and role of clonidine

The anxiolytic-like effects tolerance and withdrawal from chronic treatment with sodium valproate [200, 300, and 400 mg/kg, intraperitoneally (i.p.)] were compared with those of a known anxiolytic drug, lorazepam (0.025, 0.05, and 0.10 mg/kg, i.p.), in the light-dark aversion test in mice. Furthermore, we investigated whether acute treatment with clonidine, 0.03 mg/kg i.p., an alpha 2-adrenoceptor agonist, could reduce the increased anxiety on withdrawal from chronic treatment. Mice were given 14 daily i.p. injections of valproate, lorazepam, or vehicle and were tested in the light-dark aversion test 30 min or 24 or 48 h after the last drug or vehicle administration. Results showed that both acute and chronic valproate treatment reduced the aversion of mice for the light area, as well as increased the number of transitions, thus indicating an anxiolytic-like potential. Furthermore, in contrast to lorazepam, tolerance to the anxiolytic-like effects of valproate did not occur, and withdrawal from chronic treatment (300 mg/kg, i.p.) in our behavioral paradigm was not associated with any behavioral disturbances referring to an increased anxiety state. Finally, low doses of clonidine (0.03 mg/kg, i.p.) were shown to have anxiolytic properties and to reverse the anxiogenic effects of lorazepam on withdrawal.