5-H Treceptors and the sweet tooth

Effect of dexfenfluramine on saccharin drinking: behavioural and pharmacological studies

We have previously reported that the 5-hydroxytryptamine (5-HT) releaser/reuptake blocker dexfenfluramine suppresses voluntary ethanol intake. To further analyse the generality of these findings, in the present study we examined the effect of equivalent doses of dexfenfluramine (0.5-2.5 mg/kg) on the intake of another preferred fluid, saccharin. Saccharin was made available for 2 h daily across a wide concentration range chosen to promote varying degrees of intake. Following stable levels of intake, the behaviour of vehicle-pretreated rats was assessed immediately prior to (anticipatory/preparatory phase) and during (consumatory phase) saccharin access. These behaviours were compared and contrasted with those produced following dexfenfluramine pretreatment at the optimally preferred saccharin concentration (0.2%). In a preliminary study the effects of various 5-HT antagonists were also examined against the dexfenfluramine response. The present results suggest that dexfenfluramine produced a dose-related suppression of saccharin intake at doses similar to those which reduced ethanol intake. However, the magnitude of this suppression was similar across each saccharin concentration. Behavioural analysis indicated that the profile of the dexfenfluramine (0.5- and 1-mg/kg doses only) suppression of the 0.2% solution was similar to that observed in vehicle-pretreated rats presented with saccharin solutions of lesser palatability to this concentration. Pharmacological studies indicated a 5-HT1 (non-5-HT1C) receptor involvement in the dexfenfluramine response. These studies imply that at certain doses dexfenfluramine may produce a subtle alteration in the motivation to consume a preferred fluid.

5-HT and alcohol abuse

Recent experimental data, both in animals and the clinic, suggest that drugs selectively interacting with the 5-HT system may reduce alcohol intake. Although the precise mechanisms underlying these drug effects are unknown, it seems that there are at least two pharmacological strategies available, described in this review by Edward Sellers and colleagues. The first is enhancement of 5-HT neuronal activity using compounds that will release 5-HT, block 5-HT reuptake, or act as selective 5-HT receptor agonists. A second approach involves selective 5-HT3 receptor antagonists. If the initial research findings with these drugs are confirmed and extended, they may present useful therapies for the treatment of alcohol abuse, especially if used in conjunction with psychosocial therapy.

Effects of dexfenfluramine on the feeding behavior of rats foraging in the cold for palatable bait

An alimentary/thermic conflict of motivation was used to explore the effects of very low doses of dexfenfluramine (dFF), an anorectic serotoninergic agonist, on the parameters of food motivation, drive and incentive (or palatability). Six rats trained to feed 2 hr/day, were given the possibility to feed on chow in a shelter (25 degrees C), and to get a snack of shortcake, a highly palatable bait, from a feeder placed 16 m away in a very cold environment (-15 degrees C). dFF at 0.6 or 1.25 mg/kg decreased neither the chow intake in the shelter, nor the mean duration of the snacks in the cold, which is the parameter believed to be the best indicator of incentive. In contrast, dFF reduced the number of trips to the bait in the cold as well as the total mass of palatable bait ingested and the mean amount ingested by snack. Such an effect was no longer observed after a food restriction had reduced the body weight of the rats to 90% of its initial value. It is concluded that, even at doses too small to reduce the consumption of basic food, dFF decreases the drive to get palatable food.