Cholecystokinin (CCK)-like material and CCK mRNA levels in the rat brain and spinal cord after acute or repeated morphine treatment

Abstract

The effects of a single or repeated administrations of morphine on the tissue levels of cholecystokinin-like material (CCKLM) and pre pro cholecystokinin mRNA (CCK mRNA) were examined in various brain and spinal cord regions (cerebral cortex, cerebellum, hippocampus, septum, substantia nigra, lumbar enlargement) in adult rats using a specific radioimmunoassay and ‘Northern blot’ analysis, respectively. Although a clear parallelism existed between the regional distribution of CCKLM (septum > cerebral cortex ≥ hippocampus ⪢ lumbar enlargement, dorsal zone > substantia nigra > lumbar enlargement, ventral zone ⋙ cerebellum) and that of CCK mRNA, some mismatch was found notably in the septum where CCK mRNA levels were less than in other regions except the cerebellum. Neither CCKLM nor CCK mRNA levels were altered one hour after an acute administration of morphine (5 mg/kg i.p.). Similarly, morphine addiction after a four-day treatment with this drug was not associated with any change in the tissue levels of CCKLM and CCK mRNA. These data indicate that the previously reported modulatory action of opioids on central CCKergic systems could occur without affecting the preproCCK gene transcription and the tissue peptide concentrations.