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Morphine action on cholecystokinin octapeptide release from rat periaqueductal grey slices: sensitisation by naloxone
1Department of Biochemistry, Charing Cross & Westminster Hospital Medical School, London, U.K.
Abstract:
Cholecystokinin (CCK) has potent antinociceptive properties when given either peripherally or centrally. An interaction between opiate and CCK-induced antinociception is indicated as CCK-induced analgesia is potentiated by naloxone. Since CCK cells in Periaqueductal grey (PAG) are known to be sensitive to both noxious stimuli and i.v. morphine, the possibility that the PAG was the site of such an interaction was investigated by an in vitro study of the effects of morphine and naloxone on CCK release in PAG. The K+-evoked release of CCK from tissue slices of PAG was unaffected by a wide range of concentrations of morphine. However, after pretreatment with naloxone (10(-9) M), morphine (10(-7)-10(-6) M) caused a significant, dose dependent attenuation of CCK release (70% inhibition at 10(-6) M). These results suggest that the release of CCK in PAG is modulated by opioid systems.