Involvement of central dopamine and D1 receptors in stress-induced colonie motor alterations in rats

Abstract

The role of central versus peripheral influence of dopamine (DA) in the genesis of emotional stress (ES) induced by fear to receive electric footshocks on colonic motility was evaluated in rats equipped with implanted electrodes on the proximal colon. In control rats, the frequency of colonic spike bursts increased from 7.5 ± 1.9 to 16.0 ± 2.1 per 10 min when the rats were placed in a test box where they had previously received electric footshocks. This increase induced by ES was significantly p < 0.05, reduced by previous ICV or IP administration of (+)SCH 23390 (a D1receptor antagonist) at doses of 10 and 100 μg/Kg, respectively. Although sulpiride (a D2 antagonist) injected ICV or IP at similar doses had no effect on the ES-induced increase in the frequency of colonic spike bursts. DA (100 μg/kg), and the selective D1 (SKF 38383) or D2 (quinpirole) receptor agonist injected ICV at a dose of 5 μg/kg also increased significantly by 48.7, 54.8, and 68.7%, respectively, the colonie spike burst frequency whereas they are inactive when injected IP at similar and higher doses. These results suggest that, in rats, (a) emotional stress stimulates colonie motility through the stimulation of dopaminergic neurons involving D1 receptors and (b) exogenous activation of central D1 and D2 receptors similarly stimulate colonic motility by increasing the occurrence of colonic spike bursts.