Automated analysis of antidepressants' effect in the forced swim test

The forced swim test (FST) is a commonly used procedure of preclinical screening of drugs for the antidepressant activity. It has high predictive validity for a large group of antidepressant drugs blocking serotonin and noradrenaline reuptakes and improvement of immobility time evaluation in the FST is an important problem of preclinical psychopharmacology. Here a new automated version of the FST was developed. This version includes 4 inventions: (1) transmitted lighting instead of reflected lighting, (2) mouse silhouette tracking, (3) automated choice of immobility threshold and (4) the permutation test of drug's effect. Experiment was carried out on adult males of C57BL/6J and BALB/cJ mouse strains. The mice were treated with tricyclic antidepressant imipramine (15 and 30 mg/kg, i.p.). Mouse was placed in water tank, its movements were recorded by a rater and the silhouette alterations were automatically tracked. The sequence of silhouette alterations was scanned for immobility bouts with a threshold algorithm. Threshold was gradually altered and the value which maximized the difference between control and treated groups was chosen. The immobility values obtained with the procedure were compared with the permutation test. The data obtained with this procedure did not differ from those obtained by the rater. Imipramine dose dependently attenuated immobility time in C57BL/6 mice without any effect on BALB/c mice. The new procedure has been implemented in the EthoStudio software. It provides an objective automated evaluation of immobility time in the FST.