Abstract

Past research indicates that nutrients in the intestine affect feeding and increase neural activity in the medulla, midbrain, and forebrain. However, such observations only suggest that these areas constitute a specific feeding-control pathway. The current study is designed to demonstrate functional connections between these brain regions.

Rats received injections of the retrograde tracer, Fluorogold, in the paraventricular nucleus of the hypothalamus and the central nucleus of the amygdala prior to intestinal infusions of saline, linoleic acid (a lipid), amino acids, or glucose. Following removal and sectioning of brains, c-fos immunocytochemical labeling was used to identify activated neurons. Immuno-labeling of Fluorogold followed. Double labeling of neurons with both c-fos label and Fluorogold would suggest a functional pathway into forebrain regions.

The results, though limited by small sample sizes, reveal functional connections between the midbrain and forebrain. Results from linoleic acid infusions suggest that this lipidís potent effect on feeding may be due to strong signals or the large number of activated cells sending their axons to the paraventricular nucleus and the central nucleus of the amygdala. Few cells in the medulla contained Fluorogold, indicating that the tracer did not travel well or few connections exist between the medulla and forebrain.

Based on these and other results, neural pathways for nutrient-related signals may include a route from dorsomedial medulla through the lateral parabrachial nucleus and on to forebrain regions previously associated with feeding-behavior control.