Neuropeptide and fasting control of food hoarding and foraging in Siberian hamsters (Phodopus sungorus)

Siberian hamsters decrease their lipid stores during fasting. Upon refeeding food hoarding, rather than food intake (FI), increases. Little is known about the neuropeptides causing this behavior. Neuropeptide Y (NPY) and agouti-related protein (AgRP) are colocalized in arcuate neurons. Each appears to be involved in stimulating FI because: (1) conditions that elicit increases in FI increase NPY and AgRP gene expression/content and (2) either peptide administered intracerebroventricularly (icv) markedly stimulates FI. We tested the effect of foraging-effort level on food hoarding, on fasting-induced increases in hoarding, and whether decreases in total body fat are associated with hoarding increases. We also tested whether ventricular administration of NPY, NPY receptor agonists and/or antagonists implicated in food intake (NPY Y1 and NPY Y5), or AgRP altered foraging, FI and hoarding by Siberian hamsters. Testing for tissue-specific responses, we injected NPY and NPY antagonists into the paraventricular nucleus (PVN). Hamsters were housed in a simulated burrow system where completion of a programmed number of wheel revolutions triggered food pellet delivery. Food hoard size increased with the availability of running wheels, and increased further with low foraging levels, but was abolished at the highest foraging level. Fasted-refed hamsters increased foraging and hoarding, especially at the lowest foraging effort, but not FI. Hoarding became progressively smaller as foraging effort increased. Hoarding increased more the FI with NPY ventricular and PVN administration. NPY Y5 agonist significantly increased FI. NPY Y5 antagonist decreased NPY-induced feeding. These changes were more pronounced when administered into the PVN rather than icv. NPY Y1 agonist significantly increased hoarding, whereas NPY Y1 antagonist significantly decreased hoarding. These changes were more pronounced when administered icv versus into the PVN. AgRP increased hoarding more than FI and exhibited long-term increase in hoarding and FI. AgRP also increased foraging. Collectively, these results demonstrate that body fat levels and food hoarding can be uncoupled with increases in foraging effort. The fasting-induced increases in hoarding may be triggered by an overall change in energy metabolism rather than by general decreases in lipid stores. NPY and AgRP appear to be involved with food hoarding in this species.