Inhibition of Climbing and Mossy Fiber Input to Mouse Cerebellar

Cholecystokinin (CCK)-8S was found both to decrease basal and to antagonize harmaline-dependent increases in cerebellar cydic GMP (cGMP) in the mouse. These actions were not blocked by parenteral pretreatment with naloxone, progIume or CR-1409, indicating a central-type CCK receptor activation with no involvement of oploid systems. These data were further confirmed by the greater potency (200x) of intraventricular rela-tive to s.c. doses for CCK-8S. The intraventricular administration of CCK-4, t.BOC.CCK-4 and CCK-8US also resulted in de-creased cerebellar CGMP levels, consistent with a central-type CCK receptor action. Direct administration of CCK-8S into the cerebellum felled to after either basal or harmaline-stimulated cerebellar CGMP levels, indicating that the actions of this peptide on cerebellar CGMP are not directly at the level of the cerebellum. The convulsants, picrotoxin and pentylenetetrazol, elevated car