FAWN-HOODED RATS SHOW ENHANCED ACTIVE BEHAVIOR IN THE FORCED SWIMMINGTEST, WITH NO EVIDENCE FOR PITUITARY-ADRENAL AXIS HYPERACTIVITY

Fawn-hooded (FH) rats have been reported to have high basal corticoste rone levels that can be normalized by antidepressant administration. I II the present work, some behavioural and endocrine aspects were compa red in FH and Sprague-Dawley (SD) rats. No interstrain differences in basal corticosterone levels or response to acute tail-cut stress were observed either in the morning or in the evening. Relative adrenal wei ght was lower in FH than SD, and relative thymus weight was, according ly, higher in FH than SD rats, FH rats were hyperactive in the holeboa rd and showed behaviour similar to that of SD in the plus-maze. In con trast, FH rats showed greater levels of active behaviour (struggling) and lower levels of immobility than SD rats in the forced swimming tes t (FST). After desipramine (DMI) administration the differences betwee n the two strains in the FST were more marked than in vehicle-treated animals. These results indicate that FH rats show no signs of pituitar y-adrenal (PA) hyperactivity or depression-like behaviour, and therefo re they are not an appropriate animal model of depression.