Cholecystokinin modulation of spontaneous and excitatory amino acid-induced activity in the opossum cerebellum.

Cholecystokinin-B (CCK-8) is an octapeptide that was initially described in the gastrointestinal tract. Recent studies have shown that this peptide also has an extensive distribution in the central nervous system, including the cerebellum of the opossum. In addition to the protein, binding sites for CCK-8 also have been described in the granule cell and molecular layer of this species. These anatomical data suggest that CCK-8 has a functional role in cerebellar circuitry. In the present study we have determined the physiological effects of CCK-8 on spontaneous and amino acid-induced activity. The results indicate that this peptide has both excitatory and inhibitory effects on spontaneous activity as well as the excitatory responses elicited by application of the excitatory amino acids aspartate, glutamate and quisqualate. The data suggest that CCK-8 may influence more than one population of cerebellar neurons. The findings support a neuromodulatory role for this peptide in cerebellar circuitry.