Interaction of CCK and 8-OH-DPAT in the satiation of alcohol intake

Interaction of TRH and CCK in the satiation of alcohol intake

Thyrotropin-releasing hormone (TRH) and cholecystokinin octapeptide (CCK) are endogenous neuropeptides known to inhibit intake of alcohol. Although both peptides are released by alcohol consumption and are hypothesized to satiate alcohol intake, their interaction has not been examined. We deprived ad-lib-fed male (n=6) and female (n=4) Wistar rats of water for 23 h and then gave them 30 min access to 5% w/v ethanol, followed by 30 min access to water. After adaptation to this schedule, rats were randomly assigned to receive intraperitoneal injections of either saline+saline, CCK (4 microg/kg)+saline, saline+TRH (10 mg/kg) or CCK+TRH immediately before alcohol access. Analyses of variance revealed a significant (P<.05) effect of CCK, and a significant interaction of CCK and TRH in control of ethanol consumption. CCK reliably reduced alcohol intake, and TRH blocked this satiation effect of CCK, increasing intake by 88.8% and 34.6% in males and females, respectively. TRH increased water intake in females, and CCK blocked this effect of TRH. Results indicate an infra-dose-additive interaction of CCK and TRH in satiation of alcohol intake, which may reflect a natural, endogenous neuropeptide interaction in the regulation of caloric intake.

Exogeneous and endogenous CCK inhibit ethanol ingestion in Sardinian alcohol-preferring rats

Ethanol ingestion, like food ingestion, stimulates release of the signaling molecule cholecystokinin (CCK) from the small intestine. Here, we investigated the possibility that ethanol-induced CCK release might be a negative-feedback control of ethanol ingestion, similar to its function as part of the mechanism by which ingested food produces meal-ending satiation. We used Sardinian alcohol-preferring (sP) and Marchesian Sardinian (msP) alcohol-preferring rats, two apparently identical substrains that spontaneously ingest pharmacologically relevant amounts of ethanol, as well as their background strain, Wistar (W) rats. We demonstrated that: (1) intraperitoneal (IP), but not intracerebroventricular, injections of 0.5-4 microg/kg CCK-8 produced transient, dose-related reductions in 10% ethanol ingestion; (2) this inhibitory effect of CCK-8 on ethanol intake appeared behaviorally similar to its inhibitory action on ingestion of sucrose solutions; (3) the inhibitory effect of IP CCK-8 on ethanol ingestion occurred without evidence of tolerance when tests were repeated on consecutive days; (4) IP CCK-8 reduced ethanol intake despite simultaneously reducing blood ethanol levels (BALs); and (5) antagonism of CCK1 receptors with devazepide increased ethanol intake, indicating that endogenous CCK normally limits the size of bouts of ethanol ingestion. These results implicate peripheral CCK in the control of ethanol ingestion in sP and msP alcohol-preferring rats.

Cholecystokinin reduces ethanol consumption in golden hamsters

In experimental conditions, golden hamsters (Mesocricetus auratus) avidly consume ethanol solutions. However, they are relatively resistant to the deleterious effects of ethanol even after months of continuous consumption, apparently because they metabolize ethanol rapidly and efficiently. Male hamsters with ad libitum access to food and water were presented with isocaloric solutions [weight/weight (wt./wt.)] of 10% ethanol and 17.75% glucose for 40-min periods on alternate days. When hamsters were injected with 0.9% saline before solution presentation the mean intake of ethanol solution (0.55 g) was about half that of glucose solution (1.08 g). Hamsters derived a mean of 0.36 g/kg/40 min of absolute ethanol from the ethanol solution, an amount that does not seem to exceed their metabolic capacity for ethanol. An intraperitoneal injection of a 2.0-microg/kg dose of the C-terminal octapeptide of cholecystokinin (CCK-8) reduced intakes of both solutions by >50% if administered 5 min before solution presentation, but it was ineffectual if administered 45 min before presentation. When citric acid (2.5 g/l) was added to the glucose solution the baseline intakes of the two solutions were virtually equivalent, and when CCK-8 was administered over a range of doses (0.5-2.0 microg/kg) the intakes of the solutions did not differ significantly at any dose, supporting the suggestion that the pharmacological properties of ethanol play little or no role in mediating the consumption-inhibiting effect of exogenously administered cholecystokinin (CCK). Prior administration of lorglumide, a selective CCK type A receptor antagonist, completely attenuated the inhibitory effect of CCK-8. Findings are consistent with the notion that endogenous CCK plays a key role in the short-term control of ethanol intake in hamsters.

The inability of CCK to block (or CCK antagonists to substitute for) the stimulus effects of chlordiazepoxide

To further examine the relationship between cholecystokinin (CCK) and GABA, the present study assessed the ability of the CCK-A antagonist devazepide and the CCK-B antagonist L-365,260 to substitute for the stimulus effects of chlordiazepoxide (CDP), as well as the ability of CCK-8s to block these effects, in female Long-Evans rats within the conditioned taste aversion baseline of drug discrimination learning. Both devazepide and L-365,260 failed to substitute for the discriminative stimulus properties of CDP, and CCK-8s failed to block its stimulus effects. The benzodiazepine diazepam did substitute for, and the benzodiazepine antagonist flumazenil did block, the stimulus effects of CDP. This suggests that the lack of substitution for, or antagonism of, CDP by the CCK antagonists and CCK-8s, respectively, was not due to the inability of the present design to assess such effects. Possible bases for the current findings, e.g., necessity of an anxiogenic baseline, drug and receptor specificity, as well as the dose-response nature of the interaction, were discussed. Given that a relationship between CCK and GABA has been reported in other designs, the present results suggest that such a relationship may be preparation specific.