Ablation of Oxytocin Neurons Causes a Deficit in Cold Stress Response

Abstract

The paraventricular nucleus (PVN) is a critical locus of energy balance control. Three sets of neurons in the PVN are involved in regulating energy balance: oxytocin-expressing neurons (OXT-neurons), thyrotropin-releasing hormone–expressing neurons, and corticotrophin-releasing hormone–expressing neurons. To examine the role of OXT-neurons in energy balance, we ablated these neurons in mice by injecting diphtheria toxin into mice possessing both the oxytocin promoter driving cre expression and a cre-inducible diphtheria toxin receptor. Immunohistochemistry and real-time reverse transcriptase polymerase chain reaction confirmed that this injection caused a significant decrease in PVN OXT-neurons and OXT-mRNA abundance. OXT-neuron ablation did not alter food intake, weight, or energy expenditure at room temperature on either chow or a high-fat diet. To further characterize OXT-neuron–ablated mice, we examined their response to 1) intraperitoneal cholecystokinin (CCK) injection and 2) thermogenic stress. OXT-neuron–ablated mice had a blunted decrease in feeding response to CCK. When exposed to the extreme cold (4°C) for 3 hours, OXT-neuron–ablated mice had significant decreases in both rectal and brown adipose tissue temperature relative to controls, which was rescued by OXT treatment. Thermographic imaging revealed that OXT-neuron–ablated mice had increased body surface temperature. Thus, we report that OXT-neuron ablation shows no role for OXT-neurons in energy homeostasis at neutral temperature but reveals a heretofore unappreciated role for OXT-neurons and oxytocin specifically in regulating the thermogenic stress response.

Role of oxytocin in the control of stress and food intake

“…26,146 Oestrogen treatment has also been reported to increase oxytocin mRNA and induce anorexia in rats. 147 Among these anorexigenic substances, oxytocin has been suggested to be downstream of some anorexigenic substances to induce anorexia, including CCK, [148][149][150] Consistent with the view that oxytocin neurones are activated after food intake, ghrelin, an orexigenic hormone that is released during fasting, has been reported to hyperpolarise the majority of oxytocin neurones in the hypothalamus, 155 although i.c.v. administration of ghrelin has been reported to induce Fos protein expression in some oxytocin neurones.…”

“…164 However, a meta-analysis revealed that the anorexigenic effect of oxytocin administration is not statistically significant in humans. 165 On the other hand, although oxytocin receptor-deficient male mice show late-onset mild obesity, 166 it has been reported that oxytocin receptor deficiency, 166 chemogenetic inhibition of hypothalamic paraventricular oxytocin neurones, 167 genetically targeted ablation of oxytocin neurones 152 and destruction of hypothalamic paraventricular oxytocin neurones 150 do not significantly change the total amounts of food intake in mice. 165 On the other hand, although oxytocin receptor-deficient male mice show late-onset mild obesity, 166 it has been reported that oxytocin receptor deficiency, 166 chemogenetic inhibition of hypothalamic paraventricular oxytocin neurones, 167 genetically targeted ablation of oxytocin neurones 152 and destruction of hypothalamic paraventricular oxytocin neurones 150 do not significantly change the total amounts of food intake in mice.…”

“…135 Oxytocin deficiency, 171 ablation of oxytocin neurones 150 and an oxytocin receptor antagonist 172 have been shown in mice to enhance intake of sucrose solutions but not intake of palatable liquid emulsions 173 or a high-fat diet, suggesting that oxytocin preferentially suppresses carbohydrate intake, although no significant preference has been reported in oxytocin receptor-deficient mice. Oxytocin has been shown to reduce preference for carbohydrates but not fat.…”

Convergent neuronal projections from paraventricular nucleus, parabrachial nucleus, and brainstem onto gastrocnemius muscle, white and brown adipose tissue in male rats

“…In the PBN, we instead determined the presence of CGRP (Alhadeff, Holland, Nelson, Grill, & De Jonghe, ; Campos et al, ) in PRV‐labeled cells. The immunogen used to raise each of the antibodies used in the neurochemical phenotyping are indicated (Table ), and their specificity for the peptides is supported by citations in the literature showing their reaction in negative and positive controls (Allison et al, ; Lee et al, ; Xi et al, ; Zhang et al, ). Thus, imaging the intrinsic fluorescence of the virally encoded GFPs, cells infected with PRV‐152 appeared, and are pseudocolored, as green, those infected with PRV‐614 appeared, and were pseudocolored as magenta, while those expressing the above peptides are pseudocolored as blue.…”

“…in gray, the percentage of the dual-labeled PRV neurons. ACTH, adrenocorticotropic hormone; AP, area postrema; DMNV, dorsal motor nucleus of the vagus; E, epinephrine; GiV, gigantocellular reticular nucleus, ventral part; IML, intermediolateral nucleus; LPGi, lateral paragigantocellular nucleus; M, skeletal muscle; mlf, medial longitudinal fasciculus; n, the average total number of neurons counted in each brain region; NE, norepinephrine; NTS, nucleus of the solitary tract; PBN, parabrachial nucleus; PVN, paraventricular nucleus of the hypothalamus; ROb, raphe obscurus nucleus; RPa, raphe pallidus nucleus; SG, sympathetic chain ganglia (Allison et al, 2015;Xi et al, 2017;Zhang et al, 2003). Thus, imaging the intrinsic fluorescence of the virally encoded GFPs, cells infected with PRV-152 appeared, and are pseudocolored, as green, those infected with PRV-614 appeared, and were pseudocolored as magenta, while those expressing the above peptides are pseudocolored as blue.…”