Pilot Study Using the Tail Suspension Test

Purpose: The Porsolt Swim Test (PST) is an established protocol to study the antidepressant-like effect of potential CNS agents. The purpose of this study is to introduce a complimentary behavioral model to assess this central effect; specifically, in this study, we implemented the Tail Suspension Test (TST) to our lab. The validation of the TST model was performed by exploiting the well-known antidepressant-like effect of thyrotropin releasing hormone (TRH) in a comparative fashion with that of the PST. Method: We constructed an apparatus to perform the TST where mice are suspended by their tails. The motionless hanging of an animal is associated with a depressive state, and the time an animal spends in this state is called immobility time. In the PST, on the other hand, an animal is placed in an inescapable water-filled cylinder, and immobility time is defined as when an animal only makes minimal movements to keep its head above the water. To validate the newly introduced TST, CD1 mice received either vehicle or various concentrations of TRH via dorsal s.c. injection 30 min before testing in both paradigms. Two independent observers measured immobility time for the duration of the experiment, after which animals were sacrificed and tissues harvested for future TRH quantification. Mice were only exposed to these experimental conditions on the day of the experiment and each mouse was only subjected to a single dose and subsequent test -no preconditioning was required. Results: Comparisons of the TRH-treated groups and the control group showed a statistically significant difference in immobility time, indicating the antidepressant-like effect of this small neuropeptide. A dose-dependent reduction of immobility time was observed in both the PST and the TST; moreover, the calculated ED50 values were not significantly different from each other. Specifically, ED50 was approximated at 2 µmol/kg body weight in the PST, and about 1.5 µmol/kg body weight in the TST. Conclusion: We have successfully implemented the TST, a complimentary paradigm to the PST, to study potential antidepressant-like agents. Moreover, we have also shown that TRH, a neuropeptide with well-known antidepressant effect exhibits similar potency in both experimental paradigms.