5-hydroxytryptophan-stimulated prolactin levels in cafeteria diet fed rats: An in vivo evaluation of the central serotonergic tonus

Hyperphagia in rats fed a cafeteria diet might be related to the palatability of the diet or to diet-induced changes in central neurotransmitters regulating the feeding behavior. In this study the central serotonergic tonus in adult male Wistar rats was evaluated in vivo after 6 weeks of feeding a cafeteria diet by the prolactin response to the administration of 5-hydroxytryptophan (5HTP), the immediate serotonin precursor. Blood was taken just before, 30, 60 and 90 min after the ip injection of 50 mg/kg 5HTP for the determination of prolactin by a standard RIA. Means (±SE) basal prolactin concentrations were comparable between cafeteria fed rats and control rats, fed normal laboratory chow (12.7±5.4 vs 7.7±4.5 ng/ml). The 5HTP-stimulated prolactin secretion in the cafeteria diet fed rats, determined by the peak value (95.8±17.2 vs 119.1 ±27.0 ng/ml) as well as by the integrated area under the curve (5478±774 vs 5916±2275 ng/ml. 90 min) was not significantly lower than in the control rats. In conclusion, our results did not show a significantly decreased 5HTP-induced prolactin release in cafeteria-fed rats, suggesting that a low hypothalamic serotonergic tonus is probably not involved in the overeating of this dietary-induced obesity model.