Opposite effects of CCKB agonists in grooming behaviour in rats: further evidence for two CCKB subsites

1. The hypothesis of the existence of two CCK_B receptor subsites, CCK_B1 and CCK_B2 corresponding probably to different coupling states of CCK_B receptors, was studied by measuring grooming behaviour in rats.
2. The B1 receptor agonist, BC197 (300 μg kg⁻¹, i.p.) produced a 45–50% decrease in grooming activity, which was prevented by both the CCK_B receptor antagonists CI-988 (20 μg kg⁻¹ i.p.) and L-365,260 (200 μg kg⁻¹, i.p.).
3. In contrast, 3, 10 and 30 μg kg⁻¹, i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150–190%). This effect was prevented by previous injection of 75 μg kg⁻¹ of L-365,260 while higher doses (200 μg kg⁻¹, i.p.) produced only a partial antagonism. Moreover, CI-988 (20 μg kg⁻¹, i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 μg kg⁻¹ of CI-988 tended to suppress the increase of grooming induced by BC264.
4. The effects of BC264 were prevented by the D₁ receptor (SCH 23390) and D₂ receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems.
5. This study brings additional evidence for the existence of the two CCK_B receptor subsites and suggests that particular attention should be focused on the selectivity of CCK_B receptor agonists, notably to explain the fact that some compounds such as Boc-CCK4 induce anxiogenic-like effects while others, including BC264, are devoid of these effects.