Regional Characteristics of [125I] Cholecystokinin Octapeptide Specific Binding to Rat Brain Membranes Following 6-Hydroxydopamine Treatment

The relative changes in the amount of specific [125I] cholecystokinin octapeptide (CCK8) bound to regional brain membrane preparations after 6-hydroxydopamine (6-OHDA) treatment were examined. The specific binding in the frontal cortex and striatum decreased and reached a minimum on the 3rd day after 6-OHDA treatment. Thereafter, the specific binding recovered to 60% and 65% of control values in the frontal cortex and striatum respectively on the 28th day. On the other hand, in the nucleus accumbens, where CCK8 co-exists in the dopamine neuron, the specific binding decreased gradually, and its recovery was delayed compared with that of the frontal cortex and striatum. In the hippocampus, 6-OHDA treatment had no effect on the specific binding throughout the experimental period. The decrease of [125I] CCK8-specific binding could be caused by enhanced release of CCK8 in the frontal cortex, striatum, and nucleus accumbens, and the recovery of specific binding could be induced by depletion of CCK8 in nerve terminals. Particularly in the nucleus 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.