Investigating addictive/compulsive feeding behavior

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To determine the impact of chronic activation of AGRP or POMC on addictive or compulsive feeding behavior. Hypothesis: Chronic activation of AGRPARC will result in compulsive feeding behavior, and chronic POMCARC activation will result in chronically reduced feeding behavior. Rationale: Studies have demonstrated that acute optogenetic-activation of AGRP neurons drives feeding behavior over the course of an hour (Aponte et al., 2011). While chronic photo-stimulation has not been reported, a 5-day DREADD-mediated activation of AGRP neurons has been shown to promote weight gain and fat mass due to hyperphagia (Krashes et al., 2011). Furthermore, chronic 24 hr activation of POMC neurons led to significant weight loss due to hypophagia (Aponte et al., 2011). Using the available optogenetic tools and transgenic Cre-expressing animals, we will assess the permanent behavior changes after chronic activation of AGRPARC or POMCARC neurons over a prolonged period of time. Approach: Both AGRP-ires-Cre and POMC-Cre mouse lines will be bilaterally injected with ChR2 in the hypothalamic ARC. After a 3-week transduction period, the animals will be subjected to chronic stimulation of either AGRPARC or POMCARC neurons over the course of a month (photostimulation every other hour; 12 hours a day). Food intake will be monitored and controlled for the duration of this stimulation month to ensure matching daily food intake as the control littermates. This is imperative as AGRP-stimulated mice will continually eat more food and POMC-stimulated mice will continually eat less food than littermate controls and body weights need to be matched for accuracy, as obese mice eat more and lean mice consume less food. Following a month of the stimulation protocol, animals will be given ad libitum food access while feeding parameters (quantity of food consumed, duration of meals, feeding bouts), as well as locomotor activity and foraging behavior are measured and compared to controls. Additionally, these animals will be assessed for their willingness to work for food using a nose poke assay described above. Predictions, interpretations & Future Experiments: We do not anticipate any problems with these experiments, as these studies are very straightforward to perform given our access to the necessary mice, viral reagents and equipment. We predict that chronic activation of hunger-promoting AGRP circuitry will lead to permanent increases in feeding-related behaviors, while chronic activation of satiety-promoting POMC circuitry will lead to permanent decreases in feeding-related behaviors. If as we predict, we detect changes in feeding behavior, we will perform additional experiments to assess both the downstream signaling pathways (for example, simultaneously stimulate or inhibit MC4RPVN neurons to occlude the effects of chronic AGRP or POMC activation, respectively). If we obtain negative results and eating behavior is not altered following a month-long stimulation, we can look at the effects of either direct chronic stimulation or inhibition of the neurons identified as sitting downstream from AGRPARC and POMCARC neurons.