Fasting alters p75NTR and AgRP mRNA expression in rat olfactory bulb and hippocampus

Abstract

Classic non-homeostatic structures involved in food intake regulation are reciprocally influenced by metabolic signals. Orexigenic peptides expressed in the olfactory bulb (OB) and hippocampus (HP) modulate olfactory processing and memory, respectively. Hypothalamic circuits also modulate feeding behavior by activating and releasing Agouti-related peptide (AgRP) in response to orexigenic signals. An adequate response to fasting requires the expression of p75 neurotrophin receptor (p75NTR) in AgRP neurons. The present study aimed to determine whether there is a role for p75NTR and AgRP in the OB and HP on the feeding behavior of fasted rats. A group of fasted rats (FG) was confronted with a decision-making paradigm in a T-maze containing a standard chow pellet (CP), and the same pellet coated with a phenolic-rich avocado paste extract (AVO) on either end; their OB and HP were then analyzed with histological and molecular tools. FG rats had briefer feeding latencies, as compared to control rats fed ad libitum (median latencies: 55.4 vs 191.7 min, p = 0.032). They also had reduced cell counts in both brain structures, as compared to satiated rats. AgRP mRNA was not expressed in the HP of either group, however, it was found in the OB. p75NTR mRNA was expressed in both brain structures of FG rats. These results suggest that contrasting metabolic states (fasted or satiated) motivate different feeding responses, which are influenced by p75NTR and AgRP mRNA expression in non-homeostatic food intake brain structures.