Regulatory processes of hunger motivated behavior

Gut Hormones in Health and Obesity: The Upcoming Role of Short Chain Fatty Acids

We are currently facing an obesity pandemic, with worldwide obesity rates having tripled since 1975. Obesity is one of the main risk factors for the development of non-communicable diseases, which are now the leading cause of death worldwide. This calls for urgent action towards understanding the underlying mechanisms behind the development of obesity as well as developing more effective treatments and interventions. Appetite is carefully regulated in humans via the interaction between the central nervous system and peripheral hormones. This involves a delicate balance in external stimuli, circulating satiating and appetite stimulating hormones, and correct functioning of neuronal signals. Any changes in this equilibrium can lead to an imbalance in energy intake versus expenditure, which often leads to overeating, and potentially weight gain resulting in overweight or obesity. Several lines of research have shown imbalances in gut hormones are found in those who are overweight or obese, which may be contributing to their condition. Therefore, this review examines the evidence for targeting gut hormones in the treatment of obesity by discussing how their dysregulation influences food intake, the potential possibility of altering the circulating levels of these hormones for treating obesity, as well as the role of short chain fatty acids and protein as novel treatments.

The role of gut hormones in appetite regulation (review)

Eating process is an aggregate of complex and different forms of behavior. Its regulation is based on energy homeostasis and appetite control which includes two components: the homeostatic and the hedonistic control. Important signals in appetite regulation are gut-derived hormones. They are produced by enteroendocrine cells in response to nutrient and energy intake, and achieve their effects by influencing brain structures involved in food intake regulation. The key brain structure involved in this process is the hypothalamus. Gut hormones reach the hypothalamus from the circulation or by the vagal nerve via the nucleus of the solitary tract. Among gut peptides, ghrelin is the only orexigenic hormone, leading to an increase in food intake and body weight. All others, such as cholecystokinin, glucagon like peptide-1, oxyntomodulin, peptide tyrosine tyrosine or pancreatic polypeptide, are anorexigenic, leading to decrease in food intake. Also, gut-derived endocannabinoids exert orexigenic effect on appetite. Keeping in mind the growing problem of obesity, the crucial issue when considering gut derived peptides is to understand their mechanisms of acting because of potential role in clinical therapy, and discovering long-lasting gut peptides or their analogues, with no or minimal side effects.

Effects of individual glucose levels on the neuronal correlates of emotions

This study aimed to directly assess the effect of changes in blood glucose levels on the psychological processing of emotionally charged material. We used functional magnetic resonance imaging (fMRI) to evaluate the effect of blood glucose levels on three categories of visually presented emotional stimuli. Seventeen healthy young subjects participated in this study (eight females; nine males; body weight, 69.3 ± 14.9 kg; BMI, 22 ± 2.7; age, 24 ± 3 years), consisting of two functional MRI sessions: (1) after an overnight fast under resting conditions (before glucose administration); (2) after reaching the hyperglycemic state (after glucose administration). During each session, subjects were presented with visual stimuli featuring funny, neutral, and sad content. Single-subject ratings of the stimuli were used to verify the selection of stimuli for each category and were covariates for the fMRI analysis. Analysis of the interaction effect of the two sessions (eu- and hyperglycemia), and the emotional categories accounting for the single-subject glucose differences, revealed a single activation cluster in the hypothalamus. Analysis of the activation profile of the left amygdala corresponded to the three emotional conditions, and this profile was obtained for both sessions regardless of glucose level. Our results indicate that, in a hyperglycemic state, the hypothalamus can no longer respond to emotions. This study offers novel insight for the understanding of disease-related behavior associated with dysregulation of glucose and glucose availability, potentially offering improved diagnostic and novel therapeutic strategies in the future.

Taste reactivity alterations after streptozotocin microinjection into the mediodorsal prefrontal cortex

The mediodorsal prefrontal cortex (mdPFC), as an integrant part of the forebrain glucose-monitoring neural network, plays important roles in neural control of feeding. Previous studies suggested that streptozotocin (STZ) causes selective destruction of forebrain glucose-monitoring (GM) neurons leading to development of feeding disturbances. The goal of this research was to evaluate gustatory consequences of bilateral streptozotocin microinjection into the mediodorsal prefrontal cortex of male Wistar rats during conditioned taste avoidance (CTA) acquisition, as well as during taste reactivity tests. Bilateral streptozotocin microinjection failed to impair CTA learning, tested in a saccharin CTA paradigm. However, taste reactivity deficit was found by a modified version of the protocol introduced by Grill and Norgren. The streptozotocin treated animals displayed significantly poorer ingestive reactions to pleasant taste stimuli than did rats of the control group. The unpleasant taste stimuli elicited ingestive and rejective taste reactivity patterns in a comparable manner in rats of the STZ vs. vehicle microinjected groups. The glucose-monitoring neurons of the mdPFC and their distinct role in the gustatory perception may have particular significance in the adaptive control of feeding.