Validation of aversion towards open space and height as a measure of anxiety in the genetically based animal model of depression.

Abstract

Experiments were performed in the adult normotensive rats of Wistar strain and in the genetically hypertensive rats of Koletsky type; measurements were carried out in both sexes. The behaviour of control and drug treated rats were traced in the holeboard and in the elevated plus-maze. In the control animals when compared to the normotensive rats of both sexes, the genetically hypertensive rats of both sexes show increased aversion towards open space and high in the elevated plus-maze (when the number of visits of centre and open arms is considered in the first session); the latter type of rats also show elevated total time of locomotor-exploratory activity in both sessions, reduced rate of intra-session habituation of locomotor-exploratory activity in both sessions, and decreased percentage of time spent head dipping in both sessions. Tranylcypromine treatment at the dose 5 mg/kg b. w. increased number of visits in centre and in open arms only in the second session in the normotensive males, and this drug shows decrease in the latter parameter in the second session in the genetically hypertensive females. Tranylcypromine increased time spent in centre and in open arms in the first session only in the genetically hypertensive males, in the second session this drug shows increase in time spent in centre and in open arms in the normotensive females and decrease in the genetically hypertensive females. Caffeine treatment at the dose 10 mg/kg b. w. remained without effect in both strains of rats and in both sessions in the elevated plus-maze, except the decrease in the number of entries in centre and in open arms in the first session in the normotensive females. Diazepam treatment at the dose 1 mg/kg b. w. shows "anxiolytic" effect i.e., increase number of visits and time spent in centre and in open arms in both sessions and in both sexes of the genetically hypertensive rats. Thus diazepam shown its "anxiolytic" effect in very profound and stable manner only in the animals which show CNS neurotransmitter abnormalities reminding the CNS neurochemical abnormalities in human forms of depression and anxiety. It is worthwhile to note that diazepam only in the latter mentioned strain of rats very profoundly elevates the percentage of time spent head dipping. Thus this drug elevates the reactivity towards stimuli which show biological sense for the rats, i. e., to look up the small and dark space. This type of reaction is decreased in the genetically hypertensive rats of both sexes relative to the control normotensive rats of Wistar strain.