REGIONAL CHARACTERISTICS OF [(125)]CHOLECYSTOKININ OCTAPEPTIDE SPECIFIC BINDING TO RAT-BRAIN MEMBRANES FOLLOWING 6-HYDROXYDOPAMINE TREATMENT

The relative changes in the amount of specific [I-125]cholecystokinin octapeptide (CCK8) bound to regional brain membrane preparations after 6-hydroxydopamine (6-OHDA) treatment were examined. The specific bind ing in the frontal cortex and striatum decreased and reached a minimum on the 3rd day after 6-OHDA treatment. Thereafter, the specific bindi ng recovered to 60% and 65% of control values in the frontal cortex an d striatum respectively on the 28th day. On the other hand, in the nuc leus accumbens, where CCK8 co-exists in the dopamine neuron, the speci fic binding decreased gradually, and its recovery was delayed compared with that of the frontal cortex and striatum. In the hippocampus, 6-O HDA treatment had no effect on the specific binding throughout the exp erimental period. The decrease of [I-125]CCK8-specific binding could b e caused by enhanced release of CCK8 in the frontal cortex, striatum, and nucleus accumbens, and the recovery of specific binding could be i nduced by depletion of CCK8 in nerve terminals. Particularly in the nu cleus accumbens, the delayed recovery of specific binding suggests the loss of the pre-synaptic binding site, which exists in the CCK8/DA co -existing neuron, together with a change in CCK8 release.