Intracerebroventricular injection of ghrelin decreases wheel running activity in rats

Chronic food restriction in mice and increased systemic ghrelin induce preference for running wheel activity

OBJECTIVES

In eating disorders, particularly anorexia nervosa (AN), patients exhibit intense physical activity which is inappropriate regarding food restriction and chronic undernutrition, and exacerbates weight loss and energy deprivation. Rodent models of food restriction exhibit increased running wheel activity in the food anticipation period, also known as Food Anticipatory Activity (FAA). FAA probably has various physiological and/or neurobiological origins. Plasma concentrations of the orexigenic hormone ghrelin are, for example, increased during FAA. We hypothesize that the drive for physical activity in chronic food restriction is triggered by metabolic factors but also relies on motivational aspects that we aim to decipher in this study.

METHODS

Young female C57Bl6/J mice were exposed to a paradigm based on a progressive 50% quantitative food restriction alone (FR) or associated with running wheel activity (Food Restriction Wheel: FRW) in their home-cage during 15 days. We measured preference for running wheel in a three-chamber apparatus in which animals could choose to explore either a known running wheel or a novel object. Testing took place either during resting or during FAA. We calculated the time spent in each compartment and the activity in running wheels. After progressive refeeding over 10 days, mice were tested again when refed. Plasma levels of both ghrelin isoforms were measured with selective immunoassays.

RESULTS

When tested during FAA period, food restricted mice displayed increased preference for the running wheel compared to ad libitum fed controls. Both FR and FRW mice exhibited increased running time and distance in the wheel and running distance was correlated with ghrelin levels. Similar preference and behavior were found when testing took place during the resting period. Animals housed without an active wheel also exhibited active running. Progressive refeeding resulted in body weight restoration, a decrease in FAA and completely abolished preference for the running wheel. Refed animals displayed similar behavior as ad libitum fed controls.

CONCLUSIONS

These data provide evidence that food restriction-induced physical activity is closely correlated with metabolic adaptations to nutritional status implicating ghrelin in the quantity of physical activity.

Gene-expression profile reveals the genetic and acquired phenotypes of hyperactive mutant SPORTS rat

Spontaneously Running Tokushima Shikoku (SPORTS) rat is a hyperactive rat strain. However, the causative mutation of this phenotype has not yet been identified. To investigate the molecular basis for the unique phenotype of SPORTS rats, we examined gene-expression profiles by microarray analyses. Among adenylate kinase isozymes that maintain the homeostasis of cellular adenine nucleotide composition in the cell, only adenylate kinase 1 is highly up-regulated in both exercised and sedentary SPORTS rats compared with wild-type (WT) rats, 5.5-fold and 3.3-fold, respectively. Further comparative analyses revealed that genes involved in glucose metabolism were up-regulated in skeletal muscle tissue of exercised SPORTS rats compared with sedentary mutants, whereas genes related to extracellular matrix or region were down-regulated compared with WT rats. In brain tissue of sedentary SPORTS rats, genes associated with defense and catecholamine metabolism were highly expressed compared with WT rats. These findings suggest that genetic mutation(s) in SPORTS rat remodels metabolic demands through differentially regulating gene expression regardless of exercise. Therefore, the SPORTS rats are useful animal model not only for further examining the effects of exercise on metabolism but also for deeply studying the molecular basis how mutation affect the psychological motivation with spontaneous voluntary exercise phenotype. J. Med. Invest. 67 : 51-61, February, 2020.

Ghrelin regulates sepsis‑induced rat acute gastric injury

Ghrelin, a peptide expressed in the gastric mucosa, has an essential role in sustaining the normal function of the digestive system. Sepsis is one of the primary causes of mortality in intensive care units and can lead to multiple organ dysfunction, especially in the gastrointestinal system. The aim of the present study was to explore the effect of ghrelin on gastric blood flow in a rat model of sepsis, as well as the effect of ghrelin on the expression of the apoptotic markers, B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax), in gastric tissues. The sepsis model was established using cecal ligation and puncture (CLP). The expression levels of apoptosis-related factors in gastric epithelial cell were determined by immunohistochemistry, reverse transcription quantitative-PCR and western blotting. Collectively, the present results suggested that ghrelin administration attenuated sepsis symptoms induced by CLP. Blood flow in the stomach greater curvature was significantly higher in the CLP-induced sepsis group rats (284.3±95.7 perfusion units) compared with the sham operation group (317.8±5.2 perfusion units; P<0.05), whereas there was no difference between the CLP group treated with ghrelin (377.8±99.0 perfusion units) and the sham rats. Ghrelin administration also reduced the secretion of pro-inflammatory cytokines compared with the CLP-induced sepsis group rats. In addition, CLP significantly reduced the expression of Bcl-2 and enhanced the expression of the pro-apoptotic proteins, Bax and cleaved caspase-3; whereas, ghrelin application reversed the effects of CLP on these apoptosis-associated proteins. In conclusion, the present study revealed that ghrelin has the ability to increase blood flow in the gastrointestinal tract in a sepsis model and can also regulate the expressions of apoptosis-associated factors in gastric tissues. These results suggest that ghrelin could be a novel treatment for sepsis-induced gastric injury.