Effect of chronic treatment with TFMPP, a 5-HT1 receptor agonist, on food intake, weight gain, plasma insulin and neuropeptide mRNA expression in obese Zucker rats

Pharmacological targeting of the serotonergic system for the treatment of obesity

The attenuation of food intake as induced by an increase in serotonergic (5-hydroxytryptamine, 5-HT) efficacy has been a target of antiobesity pharmacotherapies. However, the induction of tolerance and/or side-effects limited the clinical utility of the earliest serotonin-related medications. With the global prevalence of obesity rising, there has been renewed interest in the manipulation of the serotonergic system as a point of pharmacological intervention. The serotonin(2C) receptor (5-HT(2C)R), serotonin(1B) (rodent)/serotonin(1Dbeta) (human) receptor (5-HT(1B/1Dbeta)R) and serotonin(6) receptor (5-HT(6)R) represent the most promising serotonin receptor therapeutic targets. Canonical serotonin receptor compounds have given way to a myriad of novel receptor-selective ligands, many of which have observable anorectic effects. Here we review serotonergic compounds reducing ingestive behaviour and discuss their clinical potential for the treatment of obesity.

Evaluation of chronic opioid receptor antagonist effects upon weight and intake measures in lean and obese Zucker rats

Body weight and food intake are significantly reduced in rats during development of dietary obesity following chronic central administration of mu (beta-funaltrexamine, BFNA), mu1 (naloxonazine), kappa1 (nor-binaltorphamine, NBNI), delta1 ([D-Ala2,Leu5,Cys6]-enkephalin, DALCE) and delta2 (naltrindole isothiocyanate, NTII) opioid receptor subtype antagonists. In contrast, rats made obese by maintainance on a 'cafeteria' diet failed to display weight loss following chronic mu1 receptor antagonism. To test the hypothesis that chronic administration of opioid antagonists are less effective in controlling intake and weight in obese animals, the present study assessed whether chronic, central administration of either BFNA (20 micrograms), naloxonazine (50 micrograms), NBNI (20 micrograms), DALCE (40 micrograms) or NTII (20 micrograms) altered weight and intake in lean and obese Zucker rats over seven days. Body weight was reduced following chronic mu (lean: 42 g; obese: 49 g), mu1 (lean: 71 g; obese: 38 g), kappa1 (lean: 30 g; obese 14 g), delta1 (lean: 43 g; obese: 22 g) or delta2 (lean: 37.5 g; obese: 36 g) antagonism. Overall food intake was reduced following chronic mu (lean: 8.8 g; obese: 16.1 g), mu1 (lean: 12.6 g; obese: 17.0 g), kappa1 (lean: 6.5 g; obese 7.0 g), delta1 (lean: 9.7 g; obese: 11.1 g) or delta2 (lean: 9.4 g; obese: 14.3 g) antagonism. Therefore, both lean and obese Zucker rats display weight loss and reduced intake following chronic central administration of opioid receptor subtype antagonists.

State-dependent changes of brain endogenous opioids in mammalian hibernation

Endogenous opioids belonging to three opioid families were measured in different states of the hibernation cycle in brain of the Columbian ground squirrels. Using high-performance liquid chromatography-EC detection, the hypothalamic and septal concentrations of met-enkephalin were found to be significantly higher (p < 0.05) in the hibernating state than that in the nonhibernating state. In contrast, met-enkephalin content in the medulla decreased significantly during hibernation. Leuenkephalin content was only increased in the hypothalamus of hibernating animals. Using radioimmunoassay, dynorphin A-like immunoreactivity was observed to increase in the claustrum and striatum, whereas beta-endorphin-like peptides showed a significant increase in the hypothalamus during hibernation. It is evident that the changes in endogenous opioids in brain during hibernation are state dependent, type specific and region specific. These specific alterations of various endogenous opioids may imply their different roles in hibernation.