Activity of several GABAergic agents on the behavioral “despair” test in rats

Progesterone reduces immobility in rats forced to swim

BACKGROUND

Among its behavioral actions, progesterone reduces anxiety in several species including humans; however, any antidepressant-like properties remain to be explored.

METHODS

In the present study, Wistar rats received injections (i.p.) of progesterone (0.20-3.0 mg/kg) 24 and 2 h before being submitted to the forced swim, a test in which antidepressants regularly reduce immobility and exert few or no actions on locomotor activity. In order to discard the cumulative effects of progesterone and a possible effect from the repetition of the swimming test, all animals received one of several progesterone doses in a different sequence following a completely randomized experimental intrasubject design.

RESULTS

Ovariectomy did not modify immobility in the forced swim test as compared to control tests practiced before surgery. A dose of 0.80 mg/kg strongly reduced the total time of immobility in forced swim test (p < 0.001), but did not modify locomotor activity. In a drug-free control test applied 1 week after the last injection of progesterone, immobility returned to the higher values observed in the control tests.

CONCLUSIONS

From these results, it is concluded that progesterone may possess some anti-depressant-like activity.

Administration of antidepressants, diazepam and psychomotor stimulants further confirms the utility of Flinders Sensitive Line rats as an animal model of depression

Flinders Sensitive Line (FSL) rats have been proposed as an animal model of depression because they resemble depressed humans in that they have elevated REM sleep, reduced activity, and increased immobility and anhedonia after exposure to stressors. The present paper reviews experiments on the drug treatment of FSL and control Flinders Resistant Line (FRL) rats related to their utility as an animal model of depression, and presents new information. FSL rats exhibited exaggerated immobility in the forced swim test which is counteracted by the tricyclic antidepressants imipramine and desipramine and the serotonin reuptake blocker sertraline; the low immobility exhibited by the FRL rats is generally unaffected by these compounds. In contrast to these "therapeutic" effects of well recognized antidepressants, lithium and bright light treatment did not alter the exaggerated immobility of FSL rats. Novel data indicated that neither FSL nor FRL rats exhibited alterations in swim test immobility following chronic administration of the psychomotor stimulant amphetamine (2 mg/kg) and the anticholinergic scopolamine (2 mg/kg), which typically reduce immobility after acute administration. However, it was found that the calcium channel blockers verapamil (5 and 15 mg/kg) and nicardipine (10 mg/kg) did reduce the exaggerated immobility in FSL rats following chronic administration, suggesting that these compounds need to be evaluated further in humans. Previous studies have indicated no differences between FSL and FRL rats evaluated in the elevated plus maze, either at baseline or after the administration of diazepam, suggesting that the FSL rat may not differ from controls in anxiety-related behavior. Another recently published study showed that the FSL rat also did not differ from normal Sprague-Dawley rats in startle tests, indicating that the FSL rats do not exhibit behaviors shown in animal models of schizophrenia. These findings confirm the utility of FSL rats as an animal model of depression because the FSL rats do not appear to exhibit behaviors analogous to anxiety or schizophrenia and because they respond "therapeutically" to antidepressants and not psychomotor stimulants.

Picrotoxin changes the effects of imipramine and desipramine in rats in the forced swimming test

The aim was to find whether the chloride channel blocker, picrotoxin, at subconvulsant doses could affect the activity of imipramine or desipramine in the 'forced swimming' test with rats. It was found that picrotoxin enhanced the anti-immobility effects of imipramine and desipramine whereas open field activity remained unaffected or was even decreased by the same treatments. The results seem consistent with recent reports showing direct interactions between several antidepressant drugs and the GABAA receptor/benzodiazepine receptor/chloride ionophore complex (GABAA/benzodiazepine/Cl complex). The results also conform with the hypothesis that a reduction in the functionality of this complex could be related to the clinical effects of antidepressant drugs.