Urine from stressed rats increases immobility in receptor rats forced to swim: Role of 2-heptanone

The present study was aimed to determine whether the urine from donor rats, which were physically stressed (UD-PS) by unavoidable electric footshocks, produces despair in receptor partner rats (RP) in the long-term. For each trial, an RP rat was placed during 10 min once per day for 21 days in a small non-movement-restricting cage impregnated with the urine collected from a UD-PS rat. Control rats, free of stimulation, maintained their locomotion and immobility scores at basal values throughout the 21-day test. After 21 days of stressing experience [F(2,90) = 15.22, P < 0.0001] locomotion significantly increased in RP rats (r = 0.938, P < 0.01), whereas in the UD-PS group locomotion decreased (r = − 0.606, P < 0.05). The RP and UD-PS groups displayed the longest time of immobility [F(2,90) = 8.83, P < 0.001] in the forced-swim test (RP, r = 0.886, P < 0.05; UD-PS, r = 0.962, P < 0.001) compared with the control group (r = − 0.307, NS). We conclude that the RP became similarly despaired as the UD-PS group through the action of 2-heptanone, a ketonic compound identified in UD-PS urine by HS-GC/MS techniques. This ketone was found to be increased [F(2,15) = 3.50, P < 0.05] from the 1st day of unavoidable electric footshocks, and to induce despair, an effect reverted [F(2,21) = 16.5, P < 0.0001] by imipramine (5.0 mg/kg) in another group of rats.