PROJECT SUMMARY/ABSTRACT
Obesity is a global public health crisis, and its prevalence continued to increase dramatically during the last three
decades. Although numerous factors influence on body weight, excessive consumption of palatable foods (e.g.,
high-fat diet, HFD) is a major risk factor leading to obesity. Notably, most of the individuals who achieved a
successful diet with withdrawal from such foods show high rates of relapse to HFD overconsumption. Given that
this process is highly associated with the increased preference for palatable foods, understanding neural circuit
mechanisms leading to HFD overconsumption after abstinence is arguably the core issue in therapeutic
strategies for the long-term treatment of obesity. However, neither the specific neural circuit pathway nor the
molecular mechanisms underlying this process are well understood. Leptin, an adipose tissue-derived hormone,
exerts its anorexic effects by acting on its receptors in the hypothalamus. Activation of long leptin receptor (LepR)
stimulates multiple signal transduction pathways to suppress food intake and weight gain. While a decrease in
hypothalamic tissue sensitivity to leptin is characterized by a disturbance in the ability of LepR to activate
downstream effectors or impairment in LepR expression, we do not understand critical issues concerning primary
brain circuit that develops leptin insensitivity which can subserve relapse to HFD overconsumption. Thus, in this
proposal we aim to propose an interdisciplinary approach to understand the circuit-specific role of leptin
sensitivity in driving HFD overconsumption following abstinence from such foods. We will primarily focus on the
leptin-responsive circuit that connects the lateral hypothalamus (LH) to the ventrolateral periaqueductal gray
(vlPAG) and functionally probe its neural adaptation after HFD exposure. The central objective of this proposal
is to determine the neural dysfunction of LepR-expressing LH (LepR LH) neurons projecting to the vlPAG using
the intermittent access schedule of HFD to better understand the neural mechanisms underlying HFD
overconsumption when the food becomes more salient. To achieve our objective, we will first characterize in
vivo activity of target-specific LepR LH neurons during HFD consumption at different food stages. We will
examine whether the vlPAG-projecting LepR LH neurons are engaged in post-abstinence HFD overconsumption
(Aim 1). Secondly, using molecular profiling methods, we will examine how HFD abstinence induces circuit-
specific neural adaptation in the LepR signaling associated with HFD overconsumption (Aim 2). Third, we will
determine how LepR knockdown-induced leptin insensitivity in the LepR LH neurons regulates HFD consumption
and body weight with a circuit-specific manner (Aim 3). The significance of this study is substantial because it
represents the first steps towards understanding how leptin-responsive LH-vlPAG circuitry controls HFD
consumption that is exacerbated by abstinence. The contribution is innovative because it will provide, for the first
time, a framework for studying the circuit-specific role of leptin sensitivity in relapse to HFD overconsumption,
and in developing targeted therapies for the treatment of pathological symptoms in eating disorders and obesity.