Effect of stress on fasting-induced ghrelin, orexin and galanin secretion in male rats fed different levels of their energy requirement

Orexins (hypocretins): The intersection between homeostatic and hedonic feeding

Orexins are hypothalamic neuropeptides originally discovered to play a role in the regulation of feeding behaviour. The broad connections of orexin neurons to mesocorticolimbic circuitry suggest they may play a role in mediating reward-related behaviour beyond homeostatic feeding. Here, we review the role of orexin in a variety of eating-related behaviour, with a focus on reward and motivation, and the neural circuits driving these effects. One emerging finding is the involvement of orexins in hedonic and appetitive behaviour towards palatable food, in addition to their role in homeostatic feeding. This review discusses the brain circuitry and possible mechanisms underlying the role of orexins in these behaviours. Overall, there is a marked bias in the literature towards studies involving male subjects. As such, future work needs to be done to involve female subjects. In summary, orexins play an important role in driving motivation for high salient rewards such as highly palatable food and may serve as the intersection between homeostatic and hedonic feeding.

Neuropeptidergic Control of Feeding: Focus on the Galanin Family of Peptides

Obesity/overweight are important health problems due to metabolic complications. Dysregulation of peptides exerting orexigenic/anorexigenic effects must be investigated in-depth to understand the mechanisms involved in feeding behaviour. One of the most important and studied orexigenic peptides is galanin (GAL). The aim of this review is to update the mechanisms of action and physiological roles played by the GAL family of peptides (GAL, GAL-like peptide, GAL message-associated peptide, alarin) in the control of food intake and to review the involvement of these peptides in metabolic diseases and food intake disorders in experimental animal models and humans. The interaction between GAL and NPY in feeding and energy metabolism, the relationships between GAL and other substances involved in food intake mechanisms, the potential pharmacological strategies to treat food intake disorders and obesity and the possible clinical applications will be mentioned and discussed. Some research lines are suggested to be developed in the future, such as studies focused on GAL receptor/neuropeptide Y Y₁ receptor interactions in hypothalamic and extra-hypothalamic nuclei and sexual differences regarding the expression of GAL in feeding behaviour. It is also important to study the possible GAL resistance in obese individuals to better understand the molecular mechanisms by which GAL regulates insulin/glucose metabolism. GAL does not exert a pivotal role in weight regulation and food intake, but this role is crucial in fat intake and also exerts an important action by regulating the activity of other key compounds under conditions of stress/altered diet.

Bmal1 knockdown suppresses wake and increases immobility without altering orexin A, corticotrophin-releasing hormone, or glutamate decarboxylase

OBJECTIVE

To determine the effect of Bmal1 knockdown (KD) on sleep, activity, immobility, hypothalamic levels of orexin, corticotrophin-releasing hormone (CRH), and GABAergic glutamate decarboxylase (GAD).

METHODS

We used Bmal1 siRNA, or control siRNA intracerebroventricular (ICV) injection to knock down Bmal1 in C57BL/6 mice. Sleep polysomnography, wheel-running activity, and tail suspension test were performed. Polysomnographic (PSG) recordings in both groups were preceded by ICV injection made during both the light phase and the dark phase. We also measured brain orexin A and CRH using an ELISA and measured GAD using immunoblotting.

RESULTS

Compared with control group, Bmal1 KD group had reduced wheel activity and increased immobility. Compared with control, the Bmal1 KD group had reduced wheel activity and increased immobility. During the first 24 hours after treatment, we observed that control siRNA induced a much greater increase in sleep during the dark phase, which was associated with lower orexin levels. However, beginning 24 hours after treatment, we observed an increase in sleep and a decrease in time spent awake during the dark phase in the Bmal1 KD group. These changes were not associated with changes in brain levels of orexin A, CRH, or GAD.

CONCLUSION

Bmal1 KD led to reduced activity, increased immobility, and dramatic reduction in time spent awake as well as an increase in sleep during the dark phase. Early after injection, there was a slight change in sleep but brain levels of orexin, CRH, and GAD remain unchanged. Control siRNA also affected sleep associated with changes in orexin levels.

Plasma orexin-A level associated with physical activity in obese people

OBJECTIVE

To measure the amount of physical activity (PA) among obese adults, investigate the association between plasma orexin-A level and PA patterns, and explore the effect of orexin on the prevention and control of obesity.

METHODS

Interviews were conducted in 218 participants (106 obese; 73 overweight; and 39 normal) who ranged in age between 18 and 70 years using a survey that included sociodemographic variables. The International Physical Activity Questionnaire (IPAQ-long version) was used to measure PA. A total of 178 participants agreed to submit blood sample collections, and plasma orexin-A content was measured by ELISA testing.

RESULTS

The average level of orexin-A was 85.34 ± 42.85 ng/L in the obese group, 97.38 ± 36.72 ng/L in the overweight group, and 106.56 ± 52.09 ng/L in the control group, which was significantly different (P = 0.03). The concentration of plasma orexin-A correlated with the total PA (P = 0.000), moderate PA (obese = 0.007; overweight: P = 0.000; control: P = 0.000), and walking PA (P = 0.000) in all three groups. Working and domestic PAs were significantly associated with the plasma orexin-A level (P < 0.0001).

CONCLUSIONS

The plasma orexin-A level was associated with PA in obese and overweight people, including many aspects of daily life, such as working, domestic work, and walking especially.

High-protein breakfast promotes weight loss by suppressing subsequent food intake and regulating appetite hormones in obese Chinese adolescents

OBJECTIVE

A high-protein diet may decrease food intake through regulating satiety and appetite hormones and can be an effective strategy for weight loss. Few studies exist on obese Chinese adolescents.

METHODS AND MATERIALS

156 obese Chinese adolescents were enrolled and randomly assigned to one of two isoenergetic breakfasts, either with egg or steamed bread. Subsequent lunchtime food intake was recorded 4 h later. Appetite was assessed with a visual analog scale. Anorexigenic hormones peptide YY (PYY), glucagon-like peptide-1 (GLP-1) and orexigenic hormone ghrelin were determined with radioimmunoassay at 0, 30, and 180 min. Body weight was recorded. The tests were repeated 3 months later. Analysis was performed between two tests and then two groups. Pearson's correlation was used for association analysis.

RESULTS

Subsequent lunchtime food intake and body weight were decreased while satiety was increased in subjects on an egg breakfast, which is associated with an increase of serum PYY and GLP-1 (p < 0.001, respectively). There were strong correlations between weight loss, appetite, subsequent food intake and changes of appetite hormones.

CONCLUSION

A high-protein breakfast promotes weight loss in obese Chinese adolescents, possibly through its regulation of satiety, subsequent food intake and appetite hormones.

Spexin Enhances Bowel Movement through Activating L-type Voltage-dependent Calcium Channel via Galanin Receptor 2 in Mice

A novel neuropeptide spexin was found to be broadly expressed in various endocrine and nervous tissues while little is known about its functions. This study investigated the role of spexin in bowel movement and the underlying mechanisms. In functional constipation (FC) patients, serum spexin levels were significantly decreased. Consistently, in starved mice, the mRNA of spexin was significantly decreased in intestine and colon. Spexin injection increased the velocity of carbon powder propulsion in small intestine and decreased the glass beads expulsion time in distal colon in mice. Further, spexin dose-dependently stimulated the intestinal/colonic smooth muscle contraction. Galanin receptor 2 (GALR2) antagonist M871, but not Galanin receptor 3 (GALR3) antagonist SNAP37899, effectively suppressed the stimulatory effects of spexin on intestinal/colonic smooth muscle contraction, which could be eliminated by extracellular [Ca²⁺] removal and L-type voltage-dependentCa²⁺ channel (VDCC) inhibitor nifedipine. Besides, spexin dramatically increased the [Ca²⁺]i in isolated colonic smooth muscle cells. These data indicate that spexin can act on GALR2 receptor to regulate bowel motility by activating L-type VDCC. Our findings provide evidence for important physiological roles of spexin in GI functions. Selective action on spexin pathway might have therapeutic effects on GI diseases with motility disorders.