A pharmacological evaluation of the pull-up test for muscle relaxation in rats

The pull-up test for muscle relaxation is described and validated. At testing, rats were evaluated for their ability to recover ('pull-up') from a fully inverted head-down position. Control animals rapidly regained position (median: 1 s). Known muscle relaxants increased latency to pull-up compared to controls. The test proved sensitive to the effects of barbiturates and benzodiazepines which produced graded dose-response functions. In general, results in the pull-up test corresponded with known potencies, with weaker muscle relaxants such as clobazam and oxazepam being less active. The test was relatively insensitive to non-benzodiazepine compounds (e.g., haloperidol, etomidate, morphine, fentanyl and risperidone) producing cataleptic, catatonic, neuroleptic, analgesic, sedative or hypnotic effects. In terms of ED50 values for barbiturates and benzodiazepines, the pull-up test correlated significantly with ED50s from the rotarod test, the antipentylenetetrazol test, ataxia in rats and muscle relaxation in cats. It was concluded that the pull-up test was relatively specific for muscle relaxation and provided a simple alternative to more time-consuming or equipment-intensive tests.