EFFECTS OF DIETARY PREFERENCE AND GALANIN ADMINISTRATION IN THE PARAVENTRICULAR OR AMYGDALOID NUCLEUS ON DIET SELF-SELECTION

Microinjection of galanin into the paraventricular nucleus (PVN) of th e hypothalamus has been reported to predominantly increase dietary fat consumption during the light or late dark periods, However, there hav e been no studies of the macronutrient-specific effects of galanin adm inistered into the amygdala (AMY), We used male Sprague-Dawley rats to test the effect of galanin administered into the PVN or central nucle us of the AMY on diet selection using two different protocols: the two -choice composite diet (10% or 55% energy as fat) (Study 1) or the thr ee-choice macronutrient diet (Study 2). In the first study, total food intake was significantly increased 60 min after galanin injection (0. 3 nmol) into either the PVN or AMY, but there was no difference in int ake between the low- and high-fat diets. In Study 2, using the three-c hoice macronutrient diet, the feeding stimulation produced by galanin in the PVN also was not diet-dependent. In the AMY, there was a signif icant effect of diet on the feeding response to galanin, due primarily to the lack of stimulation of protein intake, whereas the intakes of fat and carbohydrate were not significantly different. In summary, the re was no difference in the effect of galanin on fat versus carbohydra te intake for either nuclei, whether animals were injected during the light or the late-dark phase. Because rats often display preferences w hen allowed to choose among individual macronutrient sources, we also examined the relationship between baseline macronutrient preference an d the feeding response to galanin in groups of highly fat-preferring a nd carbohydrate-preferring rats (Study 3). After PVN galanin injection , fat-preferring rats demonstrated significant increases in their cons umption of both carbohydrate and fat, whereas carbohydrate-preferring rats responded by eating carbohydrate almost exclusively. There were s ignificant positive associations between baseline macronutrient intake and galanin-induced intake. The results of these studies combined sug gest that the effect of galanin on macronutrient selection is not spec ific for fat and that underlying macronutrient preferences are importa nt in determining the feeding response to galanin.