Strain differences in convulsions induced by alarm substance

Rats exhibit considerable immobility in the forced swim test when tested in fresh water but almost no immobility when tested in soiled water, that is, water previously swum in by another rat. In this study, we examined the response of different strains of rats to soiled water after treatment with imipramine, which precipitates convulsions in rats tested in soiled water. Male Long-Evans, Sprague-Dawley, Wistar, or Fischer rats were injected with imipramine (20 or 30 mg/kg, IP) and subsequently tested in water soiled by either a Sprague-Dawley or Wistar rat. Significantly more animals convulsed when the soiled water was produced by a Sprague-Dawley rat than a Wistar. More rats also convulsed after receiving the 30-mg/kg dose. Different strains did not react differently to soiled water. This study corroborates and extends previous findings that alarm substances can induce convulsions in imipramine-treated rats and indicates that some strains produce a more potent alarm substance than others.