Distribution of cholecystokinin binding sites in the North American opossum cerebellum.

Previous studies in our laboratory have reported on the differential distribution of several neuropeptides, including the octapeptide cholecystokinin (CCK8), in the cerebellar cortex and nuclei of the North American opossum (Didelphis marsupialis virginiana). The present account reports on the distribution of CCK8 binding sites as determined from serial autoradiographic images of the cerebellum which were labelled by using [125I]Bolton Hunter sulfated CCK8. Evidence for the limited presence of CCK8-like immunoreactivity and CCK8 binding sites in several other species suggests that the distribution of this peptide and its receptor(s) may be species specific. In the opossum, CCK8-like immunoreactivity is present in mossy fiber terminals that distribute throughout the cerebellar cortex; it has a very limited distribution in climbing fibers (King and Bishop (1990) J. Comp. Neurol. 238, 373-384. CCK8 binding sites are present throughout all lobules of the cerebellar cortex and the cerebellar nuclei, which correlates well with the distribution of the peptide. CCK8-like immunoreactivity is located primarily in the granule cell layer, although the greatest density of binding sites is in the molecular layer. The presence of CCK8 is mossy fiber terminals, coupled with the presence of CCK8 binding sites in the cerebellar cortex, and the fact that CCK8 alters the firing rate of Purkinje cells (Madtes et al. (1992) Neurosci. Abstr. 18, 853) indicate this peptide may function as a neuromodulator in the cerebellum of the North American opossum.(ABSTRACT TRUNCATED AT 250 WORDS)