Unconsciously Implanted Visuoauditory Memory in the Presence of Cholecystokinin Retrieved in Behavioral Contexts

SUMMARYWe investigated whether visuoauditory association can be artificially implanted in rodents and then retrieved in a behaviorally relevant context. Rats were trained to approach the left or right hole of a behavioral apparatus to retrieve a reward depending on the side of electrical stimulation of the auditory cortex (EAC) they received and mice were fear-conditioned to EAC. Next, an irrelevant visual stimulus (VS) was repeatedly paired with EAC in the presence of cholecystokinin (CCK) or with activation of terminals of entorhinal CCK neurons in the auditory cortex. In subsequent behavioral testing with VS, rats approached the hole associated with reward availability and mice showed a freezing response to the VS. A CCK antagonist blocked the establishment of visuoauditory association, whereas a CCK agonist rescued the deficit of association. Our findings provide a scientific foundation for “memory implantation” and indicate that CCK is the switching chemical for formation of visuoauditory association.

Induction of early response genes in trypsin inhibitor-induced pancreatic growth

Endogenous CCK release induced by a synthetic trypsin inhibitor, camostat, stimulates pancreatic growth; however, the mechanisms mediating this growth are not well established. Early response genes often couple short-term signals with long-term responses. To study their participation in the pancreatic growth response, mice were fasted for 18 h and refed chow containing 0.1% camostat for 1–24 h. Expression of 18 early response genes were evaluated by quantitative PCR; mRNA for 17 of the 18 increased at 1, 2, 4, or 8 h. Protein expression for c-jun, c-fos, ATF-3, Egr-1, and JunB peaked at 2 h. Nuclear localization was confirmed by immunohistochemistry of c-fos, c-jun, and Egr-1. Refeeding regular chow induced only a small increase of c-jun and none in c-fos expression. JNKs and ERKs were activated 1 h after camostat feeding as was the phosphorylation of c-jun and ATF-2. AP-1 DNA binding evaluated by EMSA showed a significant increase 1–2 h after camostat feeding with participation of c-jun, c-fos, ATF-2, ATF-3, and JunB shown by supershift. The CCK antagonist IQM-95,333 blocked camostat feeding-induced c-jun and c-fos expression by 67 and 84%, respectively, and AP-1 DNA binding was also inhibited. In CCK-deficient mice, the maximal response of c-jun induction and AP-1 DNA binding were reduced by 64 and 70%, respectively. These results indicate that camostat feeding induces a spectrum of early response gene expression and AP-1 DNA binding and that these effects are mainly CCK dependent.

Cholecystokinin blockade triggers earlier and enhanced intra-acinar oxygen free radical generation in acute pancreatitis induced by pancreatic duct obstruction in rats

Cholecystokinin (CCK) has been suggested to be a contributory mediator in acute pancreatitis (AP). The aim of the present study was to assess the role of CCK in the development of oxidative stress at different stages of AP induced by pancreatic duct obstruction (PDO) in rats, using L364,718 (a potent CCK-receptor antagonist) to block CCK action. Intra-acinar oxygen free radical (OFR) generation was analysed by flow cytometry using dihydrorhodamine-123 as a fluorogenic dye. Parallel measurements of pancreatic levels of reduced glutathione (GSH) and of several parameters for the diagnosis of AP were performed in both untreated PDO rats and PDO rats receiving L364,718 (0.1 mg·12 h-1·kg-1). Diagnosis parameters indicated a greater severity of AP in rats treated with the CCK antagonist. The increase in OFR generation observed in acinar cells up to 12 h after inducing AP was triggered at an earlier stages and reached higher values when L364,718 was administered. Accordingly, greater pancreatic GSH depletion was observed in rats with AP treated with the CCK antagonist. Two populations of acinar cells that were differentiated by flow cytometry, R1 and R2, showed similar behaviour with regard to OFR generation in PDO rats; however, R1 cells showed greater sensitivity to L364,718 administration, and thus OFR production was increased in R1 cells earlier than in R2 cells. In conclusion, CCK blockade anticipates and enhances the amount of OFR produced in acinar cells as a consequence of AP, thus leading to earlier development of and more severe disease. The detrimental effect of L364,718 in AP induced by PDO suggests that plasma CCK does not play a major role in the development of this AP model.

Interaction of serotonin and cholecystokinin in the lateral parabrachial nucleus to control sodium intake

Serotonin [5-hydroxytryptamine (5-HT)] and CCK injected into the lateral parabrachial nucleus (LPBN) inhibit NaCl and water intake. In this study, we investigated interactions between 5-HT and CCK into the LPBN to control water and NaCl intake. Male Holtzman rats with cannulas implanted bilaterally in the LPBN were treated with furosemide + captopril to induce water and NaCl intake. Bilateral LPBN injections of high doses of the 5-HT antagonist methysergide (4 μg) or the CCK antagonist proglumide (50 μg), alone or combined, produced similar increases in water and 1.8% NaCl intake. Low doses of methysergide (0.5 μg) + proglumide (20 μg) produced greater increases in NaCl intake than when they were injected alone. The 5-HT2a/2c agonist 2,5-dimetoxy-4-iodoamphetamine hydrobromide (DOI; 5 μg) into the LPBN reduced water and NaCl intake. After proglumide (50 μg) + DOI treatment, the intake was not different from vehicle treatment. CCK-8 (1 μg) alone produced no effect. CCK-8 combined with methysergide (4 μg) reduced the effect of methysergide on NaCl intake. The data suggest that functional interactions between 5-HT and CCK in the LPBN may be important for exerting inhibitory control of NaCl intake.