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Standard water-reinforced drug discrimination model was employed to train Wistar rats to discriminate the intraperitoneal injections of tricyclic antidepressant amitriptyline (5.4 mg/kg) and physiological saline. To examine the role of GABA A receptors in psychotropic action of amitriptyline, the substitution tests were performed with muscimol (0.1-1.0 mg/kg) and pregnenolone (30-50 mg/kg). Similar tests were carried out with amitriptyline interoceptive antagonists bicuculline (1 mg/kg), flumazenil (15 mg/kg), finasteride (5 mg/kg), and indomethacin (7.5 mg/kg). The study showed that interoceptive effects of amitriptyline depend on functional activity of GABA A receptors but not on the neurosteroid site of GABA A receptor complex.

The antidepressant-like effect of fluoxetine (20 mg/kg i.p.) has been assessed using the forced swimming test (FST) in IRC (CD-1) mice exposed or not to a pretest session of different duration (5 or 20 min). The influence of the mitochondrial translocator protein (TSPO) activity on the antidepressant-like effect of fluoxetine (20 mg/kg i.p.) in the FST was also studied. The antidepressant-like effect of fluoxetine was observed only in mice subjected to a 5-min pretest session 24 h before the FST. The TSPO antagonist PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide; 1 or 3 mg/kg i.p.] inhibited the antidepressant activity of fluoxetine in the FST. In the present study, fluoxetine or PK11195 was administered for a short duration. We suppose that the functional activity of TSPO may depend on a pretest session and that using this procedure is necessary to detect antidepressant activity of fluoxetine-like drugs.

The anxyolitic effects of diazepam and afobazole on the anxiety model caused by subconvulsive doses of pentylenetetrazole have been studied in the open field test and drug discrimination in rodents. It is found that diazepam (I and 5 mg/kg, i.p.) and afobazole (1 mg/kg, i.p.) reduced the pentylenetetrazole-induced (20 mg/kg, i.p.) anxiety in Wistar rats in the open field test. Only diazepam (1 mg/kg, i.p.) in Balb/c mice and only afobazole (1 mg/kg, i.p.) in C57B11/6 mice decreased anxiety caused by pentylenetetrazole (30 mg/kg, i.p.). Afobazole (20 mg/kg, i.p.) partially inhibited the effect of pentylenetetrazole (20 mg/kg, i.p.) in drug discrimination paradigm in Wistar rats learned in the Skinner box, in contrast to diazepam (5 mg/kg, i.p.) that fully blocked the stimulus properties of non-competitive GABA(A) receptor antagonist. The obtained results suggest that restorative effects of diazepam and afobazole on pentylenetetrazole-induced anxiety depend on the type of emotional stress reaction in rodent species and mice strains, though anxiogenic effects of pentylenetetrazole are not influenced by interstrain differences.

It was studied the anxiolytic properties of 4,6-dimethyl-2-(4-chlorophenyl)-2,3-dihydro-1Í-pyrazolo[4,3-c]pyridin-3-one chloralhydrate (GIZh-72, 20 mg/kg, i.p.) and afobazole (1 mg/kg, i.p.) in comparison to fluoxetine (20 mg/kg, i.p.) and diazepam (1 mg/kg, i.p.) in open-field and marble burying tests on male mice of inbred strains BALB/C and C57BL/6. It is established that GIZh-72 administered both 30 min and 24 h before testing produces anxiolytic effect in the open-field test. The open field anxiety response patterns following GIZh-72 administration differed from these in diazepam or afobazole treated BALB/C mice. This drug also decreased the number of buried marbles in both BALB/C and C57BL/6 mice, the effect being comparable to that of afobazole and fluoxetine. In operant drug discrimination liquid-reinforcement paradigm in male Wistar rats, GIZh-72 failed to antagonize or substitute for the interoceptive stimulus cues of pentylenetetrazole evoking the saline-like responses in the latter case, which was evidence for the absence of properties of a ligand bearing positive modulator sites of GABA-A receptor.

The role of GABA-A receptors in psychotropic effects of pyrrolo[1,2-a][1,4]diazepine derivatives GMAL-24 and GMAL-27 has been studied on an operant method with liquid reinforcement of drug discrimination in male Wistar rats. It is established that, in substitution tests, GMAL-24 (2, 5, 10 mg/kg) and GMAL-27 (2, 5, 10 mg/kg) do not produce interoceptive effects of phenazepam (1 mg/kg) and fail to inhibit interoceptive effects of corasol (20 mg/kg). The obtained results indicate that pyrrolo[1,2-a][1,4]diazepine derivatives do not exhibit GABA-A receptor-positive modulator properties in vivo.

Interoceptive stimulus properties of amitriptyline (54 mg/kg body weight), fluoxetine (10 mg/kg), and pyrrolo[1,2-a][1,4]diazepine derivative GMAL-24 (10 mg/kg) were studied in a standard operant model with liquid reinforcement of drug discrimination (DD) in male Wistar rats. A new experimental schedule that includes subchronic (7-day) administration of a training drug was used to perform DD learning. For the first time, it was found that amitriptyline has a discriminative interoceptive stimulus properties. Neither fluoxetine nor GMAL-24 did exhibit interoceptive properties. Imipramine (15 mg/kg, i.p.) fully substitutes for amitriptyline stimulus in substitution test. Fluoxetine (5 - 20 mg/kg, i.p.) failed to substitute with amitriptyline. Thus, amitriptyline/saline drug discrimination should be used for a comparative analysis of the central mechanisms of action of psychotropic substances, rather than for screening specific antidepressant activity.