Tail-suspension induced hyperthermia: a new measure of stress reactivity.

The tail suspension test (TST), an antidepressant screening paradigm, uses the uncontrollable, inescapable stressor of tail suspension to elicit immobility. As hyperthermia occurs following numerous stressors, hyperthermia might exist following the TST. We tested whether tail suspension induced hyperthermia (TSIH) was a distinct variable for TST. Hyperthermia was measured by two methods: a rectal probe and a subcutaneously implanted microchip (ELAMS()). In outbred ICR male mice, TSIH was robustly demonstrated compared to control (No-TST) mice. TSIH peaked after TST and remained elevated at 120 min. Among five (129/SvEvTac, A/J, C57BL/6J, NMRI and ICR) strains examined for TSIH, significant strain variations were detected. NMRI showed the highest temperature rise (2.3 degrees C) and A/J mice showed the lowest (0.6 degrees C). Sex differences were found for the C57BL/6J and NMRI strains on TSIH. TSIH and duration of immobility were not significantly correlated (r=0.22, P=0.17) in outbred mice. Both duration of TST immobility and TSIH were measured when ICR male mice were administered diazepam, imipramine (a TCA antidepressant), venlafaxine (a SNRI antidepressant), sertraline and paroxetine (SSRI antidepressants), propranolol and nadolol (beta-adrenergic receptor blockers), CP-154,526 (a CRF(1) receptor antagonist), and indomethacin (a cyclo-oxygenase inhibitor). Diazepam dose-dependently increased immobility and decreased TSIH. Propranolol blocked TSIH, but nadolol had no effect. Antidepressants showed more complex patterns of effects with venlafaxine, sertraline, and paroxetine inhibiting TSIH. TSIH demonstrated inter-strain variability, sex differences and a distinct pharmacology, suggesting that TSIH provides an independent, robust physiologic parameter to supplement the TST paradigm. This TSIH method may prove useful for pharmacologic, transgenic, and mechanistic studies.