Effects of dopamine D₁ and D₂ receptor agonists and antagonists on bombesin-induced behaviors

Abstract

Central administration of bombesin elicits excessive grooming and locomotor activity in rats. This grooming activity is one characterised by vigorous scratching of the face, nape and body flanks. Pretreatment with the D₁ receptor antagonist SCH 23390 inhibited the expression of bombesin-induced activity with grooming being more inhibited than locomotion. Blockade of D₂ receptors with eticlopride significantly attenuated the behavioral responses to bombesin. When SCH 23390 and eticlopride were administered concurrently, it was apparent that D₁ blockade had a greater effect on grooming and D₂ blockade a larger effect on locomotion. Stimulation of D₁ receptors by SKF 38393 elicited non-stereotyped locomotor activity and a form of grooming behavior characterised by vigorous washing of the face and ventral body surfaces. Co-administration of bombesin and SKF 38393 resulted in a form of grooming which resembled that elicited by SKF 38393 alone. The specific D₂ agonist PPHT elicited a form of locomotion characterised by a downward oriented head posture and slow ambulatory activity around the cage perimeter. Co-administration of PPHT and bombesin resulted in a complete suppression of bombesin-induced behaviors and was largely indistinguishable from activity observed under PPHT alone conditions. These data implicate both D₁ and D₂ receptor based mechanisms in the modulation/mediation of the behavioral effects of bombesin. Part of the bombesin-induced behavioral effects may be explained by (indirect) activation of (a) dopamine system(s).