Abstract

The questions this thesis aims to answer are: Are third order sensory neurons involved in the process of feeding inhibition in adult rats and is there a relationship between the type of nutrient ingested and the amount of neuronal activity of the rats?

Previous analysis involved first and second order sensory neurons and their relation to satiety in adult rats. In these tests it was observed that duodenal infusions of linoleic acid (1.5 kcal), an amino acid mixture (1.5 kcal) and glucose (4.5 kcal) suppressed sham feeding relative to control infusions and triggered Fos expression in the nucleus of the solitary tract and area postrema. Significant quantitative differences, but similar subnuclear distribution patterns of Fos-expressing neurons were seen for the three nutrients. Linoleic acid and glucose (at 3 times the caloric value) suppressed sham feeding and stimulated Fos expression similarly. The amino acids greatly suppressed sham feeding, yet showed relatively little Fos expression. This indicates that the potency of intake-suppression depends more on the type of macronutrient than the caloric value and that although amino acids highly induce satiety, they do so by a process differing from that of lipids and carbohydrates.

Present analysis uses the mid-brain portions of the same rats to observe cells, particularly in the parabrachial nucleus, for the presence of Fos-expression. It has been determined that the presence of linoleic acid (1.5 kcal/mol) or glucose (4.5 kcal/mol) in the duodenum results in significant c-Fos expression in the lateral parabrachial nucleus, especially in the external subnucleus, in comparison to the other infusions solutions. There was also a significant difference between the number of Fos-expressing cells in the rats that received the linoleic acid infusion and those that received the glucose. Using the previous observations on satiety it appears there is a connection between third order Fos expression and the suppression of feeding.