CCKB RECEPTORS IN THE PERIAQUEDUCTAL GREY ARE INVOLVED IN ELECTROACUPUNCTURE ANTINOCICEPTION IN THE RAT COLD-WATER TAIL-FLICK TEST

Cholecystokinin octapeptide (CCK-8) (0.25-2.0 ng), the CCKA receptor a ntagonist L-364,718 (60-100 ng) or the CCKB receptor antagonist L-365, 260 (0.3125-1.25 ng) was administered into the periaqueductal grey (PA G) of male SD rats. The antinociceptive effect induced by electroacupu ncture (EA) stimulation of different frequencies was then measured by the cold water tail-flick (CWT) test. The results showed that (1) micr oinjection of CCK-8 into the PAG can significantly block the antinocic eptive effect induced by all frequencies of EA stimulation. The effect iveness of the blockade was 100 > 2 Hz. In addition, CCK-8 blocks the antinociception seen following termination of the electrical stimulati on at 100 Hz; (2) microinjection of L-365,260 (1.25 ng) into the PAG s ignificantly increased the 100 Hz EA antinociceptive effect but not th e 2 Hz EA antinociceptive effect and microinjection of L-364,718 into PAG did not affect either 2 or 100 Hz EA antinociception. These result s 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 CCKB receptor, but not the CCKA receptor. (C) 1998 Els evier Science Ltd. All rights reserved.