Distribution of cholecystokinin binding sites in the North American opossum cerebellum

Repeated administration of methamphetamine blocked cholecystokinin-octapeptide injection-induced c-fos mRNA expression without change in capsaicin-induced junD mRNA expression in rat cerebellum

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

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.