Denial of food to the hungry rat: A novel paradigm for induction and evaluation of anger-like emotion

Abstract

Background Anger is one of the primary emotions that profoundly impacts our daily life. Although the neural basis of anger needs to be explored on high priority, the field has not sufficiently advanced, perhaps due to the lack of a suitable animal model. New method We fabricated arenas in which the hungry rat can see and smell food but can not consume it. These animals seemed hyperactive and we monitored the (a) motor activity to access food, (b) biting behaviour, (c) blood pressure, heart rate and nor-epinephrine (NE) in plasma, (d) 5-HT and its metabolite in CSF, (e) effect of diazepam, 5-HT agonist, and antagonist on the behaviour, and (f) expression of immediate early gene in discrete areas of the brain. Results The fasted animal frantically tries to acquire food. It engages in intense biting of the separator plate; the behaviour was considered as an expression of anger-like emotion. These behaviours were attenuated following pre-treatment with diazepam, fluoxetine (both ip) or 5-HT1A receptor agonist (icv), but potentiated by 5-HT1A antagonist (icv). Concomitantly, an increase in the blood pressure, heart rate and NE in plasma, but a decrease in 5-HT and 5-HIAA in the CSF was noted. The animals showed activation of neuronal c-Fos in different brain areas compared to fasted or refed controls. Comparison with existing methods A novel animal paradigm for assessment of anger. Conclusions The protocol enables us to generate and evaluate anger-like responses in rat and permits insights into the neurological basis of anger.