| Abstract: | The brain dopaminergic system is involved in the process of long-term selection for reduced aggressive reaction towards man in Norway rats. The dopamine levels in the striatum as well as the nucleus accumbens with the tuberculum olfactorium were significantly lower in domesticated rats than in their wild counterparts. A substantial decrease was found in homovanillic acid level in the n. accumbens and tuberculum olfactorium. Specific binding of 3H]spiperone which labels D-2 dopamine receptors was higher in the mesolimbic structure of tame rats, whereas binding of 3H]SCH 23390 (D-1 receptors) was unchanged in this area. No substantial differences were detected in D-1 and D-2 binding in striatum. Apomorphine (0.3 mg/kg) elicited less locomotion in tame animals, reflecting a decrease of sensitivity of postsynaptic dopamine receptors. Tame rats showed fewer aggressive contacts in a foot-shock test than wild rats and the D-2 receptor antagonist sulpiride (25 mg/kg) significantly decreased the foot-shock aggression only in wild rats. Therefore, domestication, which diminishes defensive behavior and emotional reactivity of animals, is associated with decreases of dopamine level in the striatum, changed metabolism of dopamine in mesolimbic system, and an alteration in density and senstivity of D-2 receptors. |
