Autoradiographic localization of cholecystokinin binding sites in human cerebellar system using a [(125)I]CCK8 probe

Carboxyl-terminal cholecystokinin octapeptide (CCK8) binding sites were studied in the human cerebellar system by autoradiography. High affinity CCK8 binding sites were demonstrated in the main cerebellar afferent nuclei, namely the inferior olivary complex and the pontine nuclei. This localization of CCK8 binding sites was partly correlated with already described CCK containing terminals. In the cerebellar cortex, high affinity CCK8 binding sites were detected with a laminar distribution. Levels were higher in the granular layer (mostly in the superficial part) and lower in the white matter and the Purkinje cell layer. The non-specific binding was homogenous and particularly low (9%) in the cerebellar cortex but a non-specific binding was selectively localized in the deep cerebellar nuclei. Those results illustrate the species variability of CCK binding sites in the cerebellum and are briefly discussed in relation with the low level of CCK immunoreactivity in this structure. The presence of CCK8 binding sites in cerebellar afferent nuclei and cortex suggests a role of CCK in human cerebellar physiology and particularly in the modulation of afferent inputs to the cerebellum.