Impact of negative energy balance on the reward brain system via leptin signaling

Layman Summary

The major scope of this study is to provide further knowledge on the role of neurons that are sensitive to a fat-derived hormone called leptin, on those hyperactive behaviours that are typical of patients suffering from Anorexia Nervosa (AN). The hormone leptin is involved in the

regulation of energy balance. These behaviours emerge from a negative energy balance in which the amount of energy intake of AN patients (i.e. eating) is less than the amount of energy

expenditure (i.e. Hyperactive behaviours). Thus, there is a reduced energy intake relative to energy expenditure. In order to study the role of leptin in a laboratory setting, we will mimic the negative energy balance typical of AN patients in a mouse model of Anorexia, called Activity Based Anorexia Model (ABA). When rodents are fed a one-timed meal a day and allowed to run on an activity wheel, they reduce food intake concomitantly with a paradoxical increase in wheel activity leading to negative energy balance and starvation to death if not stopped.

This study aims at assessing whether and how pharmacologic treatment with leptin can suppress or prevent the development of anorectic behaviours in ABA such as Food anticipatory activity (i.e. excessive running before the delivery of the one-timed meal a day ). Moreover, we will attempt to define whether selective manipulation via chemogenetic tools, of a specific leptin- sensitive neuronal population within the Lateral Hypothalamus of the mouse, can also be effective to modulate energy balance.

To this end, in our first experiments, we will determine how systemic leptin treatment can impact the negative energy balance of the ABA rodent. Furthermore, we will use genetically modified mice that have neurons that express receptors sensitive to leptin, for the same purpose. We will then Chemogenetically inhibit the cellular activity of these specific neurons (i.e. LHLepR neurons) that express artificially engineered receptors (DREADD), via injection of Clozapine-N-Oxide (CNO), an activating ligand that directly acts on such receptors. Hence, we will express inhibitory hM3Di(Gi) DREADD receptors in LHLepR neurons of mice exposed to the ABA protocol.

What emerged from our results is that following systemic and chronic leptin treatment, both aspects of energy balance (i.e. energy expenditure, and energy intake) decrease. Additionally, chronic and systemic leptin treatment, once AN-like symptoms had already developed, can prevent a drop in food intake as well as an increase in energy expenditure. Finally, from the last series of experiments, we observed that chemogenetic manipulation of hM3Di(Gi) receptors in LHLepR neurons does not lead to reduced FAA or impact on Body weight or Food intake. Thus, it is unlikely that this neuronal population is strongly responsible for these symptoms. Although no significant differences emerged, we can conclude that selective stimulation of LHLepR hM3DGi neurons can be considered a potential target for further investigations of the underlying

mechanisms involved in the regulation of AN-like symptoms in an ABA model.