OBJECTIVE: The D2 dopamine receptor is found in different parts of the amygdala. However, its contribution to stress is unknown. Thus, in the present study, we examined the effects of excitation and inhibition of D2 dopamine receptors in the amygdala on the metabolic and hormonal changes in response to stress.

METHODS: Bilateral amygdala cannulation was carried out in Swiss-Webster mice (n = 7). On recovery, different doses of the dopamine D2 receptor antagonist, sulpiride (1, 5 and 10 µg/mouse) or the dopamine D2 receptor agonist, bromocriptine (1, 5 and 10 µg/mouse) were injected into the amygdala. The animals were then placed in stress apparatus (communication box) where they received an electric shock (10 mV voltage, 10 Hz frequency and 60 s duration) after 30 min. The animal's activities were recorded for 10 min before and 10 min after the stress induction. Locomotion, rearing and freezing were investigated. Metabolic changes, such as food and water intake and anorexia, were studied.

RESULTS: The results show that stress increased the concentration of plasma corticosterone, which was followed by a decrease in locomotion and rearing and an increase in freezing behavior. Furthermore, both weight and water and food intake were reduced. Administration of bromocriptine led to a reduction of corticosterone at doses of 1 and 5 µg/mouse and an increase of corticosterone at 10 µg/mouse. Additionally, lower doses of bromocriptine (1 and 5 µg/mouse) caused an increase in locomotion and rearing and a decrease in freezing behavior. Similar results were observed with sulpiride injection.

CONCLUSION: D2 dopamine receptors can play a major role in the amygdala in stress. Both an agonist and an antagonist of the D2 receptor attenuate the metabolic and hormonal changes observed in response to stress