CCK B receptors in the periaqueductal grey are involved in electroacupuncture antinociception in the rat cold water tail-flick test

Abstract

Cholecystokinin octapeptide (CCK-8) (0.25–2.0 ng), the CCK A receptor antagonist L-364,718 (60–100 ng) or the CCK B receptor antagonist L-365,260 (0.3125–1.25 ng) was administered into the periaqueductal grey (PAG) of male SD rats. The antinociceptive effect induced by electroacupuncture (EA) stimulation of different frequencies was then measured by the cold water tail-flick (CWT) test. The results showed that (1) microinjection of CCK-8 into the PAG can significantly block the antinociceptive effect induced by all frequencies of EA stimulation. The effectiveness of the blockade was 100>2 Hz. In addition, CCK-8 blocks the antinociception seen following termination of the electrical stimulation at 100 Hz; (2) microinjection of L-365,260 (1.25 ng) into the PAG significantly increased the 100 Hz EA antinociceptive effect but not the 2 Hz EA antinociceptive effect and microinjection of L-364,718 into PAG did not affect either 2 or 100 Hz EA antinociception. These results demonstrate that CCK-8 in the PAG can antagonize the antinociceptive effect induced by EA stimulation, and the CCK effect is likely to be mediated by the CCK B receptor, but not the CCK A receptor.