Oxytocin Reduces Reward-Driven Food Intake in Humans

Experiments in animals suggest that the neuropeptide oxytocin acts as an anorexigenic signal in the central nervous control of food intake. In humans, however, research has almost exclusively focused on the involvement of oxytocin in the regulation of social behavior. We investigated the effect of intranasal oxytocin on ingestion and metabolic function in healthy men. Food intake in the fasted state was examined 45 min after neuropeptide administration, followed by the assessment of olfaction and reward-driven snack intake in the absence of hunger. Energy expenditure was registered by indirect calorimetry, and blood was repeatedly sampled to determine concentrations of blood glucose and hormones. Oxytocin markedly reduced snack consumption, restraining, in particular, the intake of chocolate cookies by 25%. Oxytocin, moreover, attenuated basal and postprandial levels of adrenocorticotropic hormone and cortisol and curbed the meal-related rise in plasma glucose. Energy expenditure and hunger-driven food intake as well as olfactory function were not affected. Our results indicate that oxytocin, beyond its role in social bonding, regulates nonhomeostatic, reward-related energy intake, hypothalamic-pituitary-adrenal axis activity, and the glucoregulatory response to food intake in humans. These effects can be assumed to converge with the psychosocial function of oxytocin and imply possible applications in the treatment of metabolic disorders.The hypothalamic nonapeptide oxytocin is released into the circulation by axonal terminals in the posterior pituitary and, moreover, acts directly on central nervous receptors. Oxytocin, which has been highly preserved during mammalian evolution, regulates physiological functions related to reproduction and mother-infant interaction, such as lactation, and in recent years, has been shown to modulate affiliative behavior (1). Research in humans has almost exclusively focused on the role of oxytocin in the regulation of prosocial behavior, including trust, attachment, and sexual behavior (2–5), largely ignoring potential effects of the neuropeptide on ingestive behavior and metabolism. In fact, evidence from rodent studies indicates that the neuropeptide acts as a strong inhibitor of food intake and affects energy expenditure and glucose homeostasis (6–9). Oxytocinergic neurons in the hypothalamic paraventricular nucleus are assumed to mediate the food intake–limiting effect of leptin, an adipokine that provides the brain with negative feedback on body fat stores and sensitizes caudal brainstem nuclei to satiety factors such as cholecystokinin (10). Hypothalamic oxytocin signaling, moreover, mediates anorexigenic effects of the satiety factor nesfatin-1 in a leptin-independent manner (11). Importantly, oxytocin reduces food intake not only in normal-weight rodents but also in animals with diet-induced obesity (8,12,13), so oxytocinergic pathways might be a promising target of clinical interventions in obese patients.The direct manipulation of neuropeptidergic central nervous signaling pathways can be achieved via the intranasal administration of peptides, which is known to bypass the blood–brain barrier and result in significant cerebrospinal fluid elevations in substance levels within 40 min, without the need for systemic infusion (14,15). This approach has been validated, among others, for vasopressin, a close homolog of oxytocin (14), and intranasal oxytocin administration has been shown to reliably modulate neuropsychological functions in a series of studies (2–5) in the absence of relevant side effects (16). Surprisingly, however, the effect of intranasal oxytocin on energy metabolism, including ingestive behavior, has not been investigated in humans so far. The assessment of respective effects of intravenous oxytocin (17) is hampered because peripheral oxytocin is not readily transported across the blood–brain barrier (18).In the present experiments, we studied the contribution of oxytocin signaling to the control of ingestive behavior and energy expenditure in normal-weight, healthy men, with a particular view to endocrine regulators of metabolism, such as ghrelin and insulin, as well as hypothalamic-pituitary-adrenal (HPA) axis secretory activity. Ingestive behavior is not only regulated homeostatically (i.e., by central nervous pathways that respond to energy depletion) but also by nonhomeostatic brain circuits that process the reward-related, “hedonic” qualities of food intake (19). Therefore, we applied a twofold assessment of food intake that relied, on the one hand, on a large breakfast buffet after an overnight fast to investigate homeostatic, primarily hunger-driven energy intake (20–22), and on the other hand, on a collection of snacks of varying palatability offered after breakfast intake for the measurement of reward-driven food intake (22–24).     

Identification of a Vibration Regime Favorable for Bone Healing and Muscle in Estrogen-Deficient Rats

Numerous whole-body vibration (WBV) devices of various forces are available on the market, although their influence on the musculoskeletal system is not yet understood. The effect of different WBVs on bone healing and muscle function was evaluated in rats ovariectomized at 3 months of age. 2 months after ovariectomy, bilateral metaphyseal tibia osteotomy and T-plate osteosynthesis were performed. Rats were divided into groups: intact, OVX, and OVX exposed to vertical WBVs of 35, 50, 70, or 90 Hz (experiment 1) or horizontal WBVs of 30, 50, 70, or 90 Hz (experiment 2) 5 days after osteotomy (0.5 mm, 15 min/day for 30 days). The tibia and gastrocnemius and soleus muscles were collected. Vertical vibrations (>35 Hz) improved cortical and callus densities, enlarged callus area and width, suppressed the tartrate-resistant acid phosphatase gene, enhanced citrate synthase activity, accelerated osteotomy bridging (35 and 50 Hz), upregulated the osteocalcin (Oc) gene (70 Hz), and increased relative muscle weight (50 Hz). Horizontal vibrations reduced cortical width (<90 Hz) and callus density (30 Hz), enhanced alkaline phosphatase (Alp) gene expression (50 Hz), decreased the size of oxidative fibers (35 and 70 Hz), and increased capillary density (70, 90 Hz). Biomechanical data; serum Oc, Alp, and creatine kinase activities; body weight; and food intake did not change after WBVs. Vertical WBVs of 35 and 50 Hz produced more favorable results than the higher frequencies. Horizontal WBV showed no positive or negative effects. Further studies are needed to elucidate the effects of WBV on different physiological systems, and precautions must be taken when implementing WBV in the treatment of patients.     

Acute Effects of Glucocorticoids on Serum Markers of Osteoclasts, Osteoblasts, and Osteocytes

The aim of this study was to investigate the acute effects of oral glucocorticoids in doses used in clinical practice on biochemical indices of the function of osteoclasts, osteoblasts, and osteocytes. In 17 adult patients suffering from various medical pathologies requiring systemic steroid therapy that were never before treated with glucocorticoids, glucocorticoid treatment was initiated (mean prednisolone equivalent dose of 23.1 ± 12.7 mg/day, range 10–50). Fasting morning serum concentrations of osteocalcin (OC), amino-terminal propeptide of type I procollagen (PINP), type 1 collagen cross-linked C-telopeptide (βCTX), soluble receptor activator of nuclear factor kappaB ligand (sRANKL), osteoprotegerin (OPG), sclerostin, Dickkopf-1 (Dkk-1), and high-sensitivity C-reactive protein (hsCRP) were measured at baseline and on three consecutive days. Significant reductions in serum OC, PINP, OPG, sclerostin, and hsCRP were observed during 96 h of glucocorticoid administration, while serum βCTX showed a significant percentual increase. A significant positive correlation was found between serum concentrations of Dkk-1 and βCTX after 96 h of treatment with glucocorticoids. A significant drop in serum sclerostin, OPG, and OC observed in this study may reflect the rapid glucocorticoid-induced apoptosis of osteocytes.     

WNT Signaling and Cartilage: Of Mice and Men

In adult articular cartilage, the extracellular matrix is maintained by a balance between the degradation and the synthesis of matrix components. Chondrocytes that sparsely reside in the matrix and rarely proliferate are the key cellular mediators for cartilage homeostasis. There are indications for the involvement of the WNT signaling pathway in maintaining articular cartilage. Various WNTs are involved in the subsequent stages of chondrocyte differentiation during development, and deregulation of WNT signaling was observed in cartilage degeneration. Even though gene expression and protein synthesis can be activated upon injury, articular cartilage has a limited ability of self-repair and efforts to regenerate articular cartilage have so far not been successful. Because WNT signaling was found to be involved in the development and maintenance of cartilage as well as in the degeneration of cartilage, interfering with this pathway might contribute to improving cartilage regeneration. However, most of the studies on elucidating the role of WNT signaling in these processes were conducted using in vitro or in vivo animal models. Discrepancies have been found in the role of WNT signaling between chondrocytes of mouse and human origin, and extrapolation of results from mouse models to the human situation remains a challenge. Elucidation of detailed WNT signaling functions will provide knowledge to improve cartilage regeneration.     

Operator Independent Focused High Frequency ISM Band for Fat Reduction: Porcine Model

Background

Selective fat reduction has been clearly shown for various methods and energy modalities including cryolipolysis and high intensity focused thermal ultrasound. Mathematical modeling of focused high frequency of the EM spectrum has indicated that selective heating of fat is possible using wavelengths not previous explored. The purpose of this study was to demonstrate in the porcine model that selective heating of fat is possible with a non‐contact, operator independent device.

Methods

High frequencies of the Industrial, Scientific and Medical (ISM) RF band were utilized to reduce abdominal fat in a porcine model. Practical application of mathematical modeling allowed an auto‐feedback loop to be developed to allow operator independent adjustment of energy to maintain subcutaneous fat at 45–46°C while overlying skin remained at 40–41°C.

Results

Treatments of three Vietnamese pigs were performed under anesthesia in a certified veterinary facility. Gross and microscopic histologic results demonstrated a marked reduction in adipocytes of the treated area after 4 treatments of a total of 30 minutes each, with incremental fat diminution after each treatment. A final 70% reduction of the abdominal fat layer was seen in the treated areas. Duplex ultrasound revealed a reduction of fat layer from 7.6 to 2.9 mm. Histologic evaluation revealed that epidermis, dermis, and adnexal structures such as hair follicles were unaffected by the treatment, while adipocytes were significantly affected.

Conclusion

A new model of fat reduction using high frequency RF has been successfully achieved in a porcine model. This has very positive implications in the development of an operator independent, contact free device for reduction of fat in clinical practice. Lasers Surg. Med. © 2013 Wiley Periodicals, Inc.