Activation of Kappa Opioid Receptor Regulates the Hypothermic Response to Calorie Restriction and Limits Body Weight Loss

Abstract

Mammals maintain a nearly constant core body temperature (T_b) by balancing heat production and heat dissipation. This comes at a high metabolic cost that is sustainable if adequate calorie intake is maintained. When nutrients are scarce or experimentally reduced such as during calorie restriction (CR), endotherms can reduce energy expenditure by lowering T_b [1-6]. This adaptive response conserves energy, limiting the loss of body weight due to low calorie intake [7-10]. Here we show that this response is regulated by the kappa opioid receptor (KOR). CR is associated with increased hypothalamic levels of the endogenous opioid Leu-enkephalin, which is derived from the KOR agonist precursor dynorphin [11]. Pharmacological inhibition of KOR, but not of the delta or the mu opioid receptor subtypes, fully blocked CR-induced hypothermia and increased weight loss during CR independent of calorie intake. Similar results were seen with DIO mice subjected to CR. In contrast, inhibiting KOR did not change T_b in animals fed ad libitum (AL). Chemogenetic inhibition of KOR neurons in the hypothalamic preoptic area reduced the CR-induced hypothermia, whereas chemogenetic activation of prodynorphin-expressing neurons in the arcuate or the parabrachial nucleus lowered T_b. These data indicate that KOR signaling is a pivotal regulator of energy homeostasis and can affect body weight during dieting by modulating T_b and energy expenditure.

Keywords: body temperature; body weight; calorie restriction; dieting; dynorphin; energy expenditure; energy homeostasis; hypothermia; kappa opioid receptor.