Mice fed a single daily meal at intervals within the circadian range exhibit food anticipatory activity. Previous investigations strongly suggest that this behaviour is regulated by a circadian pacemaker entrained to the timing of fasting/refeeding. The neural correlate(s) of this pacemaker, the food entrainable oscillator (FEO), whether found in a neural network or a single locus, remain unknown. This study used a canonical property of circadian pacemakers, the ability to continue oscillating after removal of the entraining stimulus, to isolate activation within the neural correlates of food entrainable oscillator from all other mechanisms driving food anticipatory activity. It was hypothesized that continued anticipatory activation of central nuclei, after restricted feeding and a return to ad libitum feeding, would elucidate a neural representation of the signaling circuits responsible for the timekeeping component of the food entrainable oscillator. Animals were entrained to a temporally constrained meal then placed back on ad libitum feeding for several days until food anticipatory activity was abolished. Activation of nuclei throughout the brain was quantified using stereological analysis of c-FOS expressing cells and compared against both ad libitum fed and food entrained controls. Several hypothalamic and brainstem nuclei remained activated at the previous time of food anticipation, implicating them in the timekeeping mechanism necessary to track previous meal presentation. This study also provides a proof of concept for an experimental paradigm useful to further investigate the anatomical and molecular substrates of the FEO.

No abstract

No abstract

Ghrelin is a peptide hormone involved in multiple physiological processes related to energy homeostasis. This hormone features a unique posttranslational serine octanoylation modification catalyzed by the enzyme ghrelin O-acyltransferase, with serine octanoylation essential for ghrelin to bind and activate its cognate receptor. Ghrelin deacylation rapidly occurs in circulation, with both ghrelin and desacyl ghrelin playing important roles in biological signaling. Understanding the regulation and physiological impact of ghrelin signaling requires the ability to rapidly protect ghrelin from deacylation in biological samples such as blood serum or cell lysates to preserve the relative concentrations of ghrelin and desacyl ghrelin. In in vitro ghrelin O-acyltransferase activity assays using insect microsomal protein fractions and mammalian cell lysate and blood serum, we demonstrate that alkyl fluorophosphonate treatment provides rapid, complete, and long-lasting protection of ghrelin acylation against serine ester hydrolysis without interference in enzyme assay or ELISA analysis. Our results support alkyl fluorophosphonate treatment as a general tool for stabilizing ghrelin and improving measurement of ghrelin and desacyl ghrelin concentrations in biochemical and clinical investigations and suggest current estimates for active ghrelin concentration and the ghrelin to desacyl ghrelin ratio in circulation may underestimate in vivo conditions.

Under chronic social stress conditions, mice show a preference for carbohydrates. In this present thesis we hypothesize that this behavior is critical for blunting the stress response and that ghrelin contributes to this change in preference. Using the chronic social defeat stress paradigm, we showed that stressed mice increase their total caloric intake, particularly the intake of carbohydrate rich diets and sucrose solutions over palatable high fat diets. Furthermore, mice that are prevented from increasing their caloric intake show exaggerated hormonal responses to the social stressor. Finally, mice with mutations to the ghrelin receptor gene (GHSR KO) do not show increased caloric intake and show more depressive like symptoms in spite of increasing their consumption of a sucrose solution. This data suggests that stress increases the intake of carbohydrate rich foods to attenuate the endocrine response to social stress and that ghrelin plays an important role in this process.iii