Tail Suspension Test

The tail suspension test (TST), developed by Steru et al. (1985), measures behavioral despair in mice by suspending the animal by its tail from an elevated bar and quantifying the alternation between active struggling and passive immobility. When suspended, mice initially engage in vigorous escape-oriented behaviors — body contortions, limb movements, and torso swinging — before transitioning to an immobile posture interpreted as behavioral despair. The TST engages limbic-cortical circuitry including the infralimbar prefrontal cortex, ventral hippocampus, basolateral amygdala, and monoaminergic brainstem nuclei. This test is exclusively used in mice, as rats are too heavy for reliable tail suspension without tissue damage.

The primary outcome is total immobility time during the standard 6-minute test session. Unlike the FST, the TST does not involve water exposure and is therefore free from thermoregulatory confounds and swimming ability artifacts. The test is sensitive to all major classes of antidepressants including SSRIs, SNRIs, tricyclics, MAOIs, and atypical agents. Key secondary measures include latency to first immobility, number of immobility bouts, power spectral analysis of body movements, and the temporal distribution of immobility across the session. Curling behavior (mice climbing their own tail) must be detected and excluded, as it represents a confound rather than an escape attempt.

ConductMaze automates TST scoring using a strain gauge or piezoelectric force sensor attached to the suspension bar, providing continuous high-resolution measurement of movement force. The software applies validated thresholds to classify active versus immobile states, automatically detects and flags tail-climbing episodes for exclusion, and generates second-by-second activity traces. Force-based scoring eliminates inter-rater reliability concerns inherent in manual video scoring and enables power spectral analysis of movement vigor.