Sex-Dependent Wheel Running Effects on High Fat Diet Preference, Metabolic Outcomes, and Performance on the Barnes Maze in Rats

Exercise recovers weight gain, but not increased impulsive choice, caused by a high-fat diet

A high-fat diet has negative effects on physical, neurological, and behavioral outcomes. One consistent finding is that a diet high in fat increases impulsive choice behavior-behavior that is linked to a wide range of other negative health behaviors. While the mechanism for this increase in impulsive choice is not well understood, exercise, with its well-known and many benefits, may serve as an effective and accessible way to combat increased impulsive choice associated with a high-fat diet. The goal of this work was to test this possibility. Rats were divided into four groups in a two-by-two factorial design: exercise and control diet, sedentary and control diet, exercise and high-fat diet, sedentary and high-fat diet. Rats in the exercise groups engaged in 30-min of forced, moderate intensity wheel-running exercise five days per week. Rats in the high-fat diet groups ate a diet high in fat. Impulsive choice was measured using a delay discounting task. Exercise prevented weight gain associated with the high-fat diet. Exercise also preserved relative motivation for food reinforcement. However, exercise did not prevent increases in impulsive choice observed for rats that consumed a high-fat diet relative to the rats that consumed the control diet. This work rules out several possible mechanisms by which a high-fat diet may increase impulsive choice behavior. It makes clear that exercise alone may not stave off increases in impulsive choice caused by a high-fat diet. Future work is necessary to uncover the underlying mechanism for this effect and discover interventions, perhaps ones that combine both physically and cognitively demanding activities, to improve health and behavior as it relates to decision making processes.

Role of the CB2 Cannabinoid Receptor in the Regulation of Food Intake: A Systematic Review

The CB2 cannabinoid receptor has been found in brain areas that are part of the reward system and has been shown to play a role in food intake regulation. Herein, we conducted a systematic review of studies assessing the role of the CB2 receptor in food intake regulation. Records from the PubMed, Scopus, and EBSCO databases were screened, resulting in 13 studies that were used in the present systematic review, following the PRISMA guidelines. A risk of bias assessment was carried out using the tool of the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE). The studies analyzed used two main strategies: (1) the intraperitoneal or intracerebroventricular administration of a CB2 agonist/antagonist; and (2) depletion of CB2 receptors via knockout in mice. Both strategies are useful in identifying the role of the CB2 receptor in food intake in standard and palatable diets. The conclusions derived from animal models showed that CB2 receptors are necessary for modulating food intake and mediating energy balance.

An updated Barnes maze protocol for assessing the outcome of controlled cortical impact mouse models of traumatic brain injury

BACKGROUND

The Barnes Maze (BM) is a common method of testing cognitive deficits in rodents. Adapting BM protocols for specific neurological disorders could potentially aid in more effective testing, reduce research time, and help decrease variability between studies.

NEW METHOD

We tested differences an updated, shortened BM consisting of 6 days, 3 trials per day, only covering the equivalent of the spatial acquisition week BM protocol and a probe trial day consisting of one trial (7 total days).

RESULTS

Kaplan-Meier plots of escape percentage as a function of total latency showed a significant difference between control and CCI mice in the updated protocol on days 3 through 6. Additionally, probe trial data showed significant differences in primary latency, primary errors, and returns to goal.

COMPARISON WITH EXISTING METHODS

We tested differences between a traditional 5 days per week, 2 trials per day, spatial acquisition and reversal weeks BM protocol (12 total days with probe trials) with an updated 6-day BM protocol (7 total days with probe trial). In the probe trial, the updated protocol control mice showed an over 5-fold decrease in primary latency and primary errors and a 4.6-fold increase in returns to goal compared to the traditional protocol. Additionally, mice in both protocols performed similarly on a trial-by-trial basis suggesting that the changes made for the updated protocol increased learning and memory and was not simply an easier task.

CONCLUSION

The updated BM protocol showed an improved ability to distinguish between control and CCI mice and promoted improved and more consistent learning for both the control and CCI groups.

Outrunning a bad diet: interactions between exercise and a Western-style diet for adolescent mental health, metabolism and microbes

Adolescence is a period of biological, psychological and social changes, and the peak time for the emergence of mental health problems. During this life stage, brain plasticity including hippocampal neurogenesis is increased, which is crucial for cognitive functions and regulation of emotional responses. The hippocampus is especially susceptible to environmental and lifestyle influences, mediated by changes in physiological systems, resulting in enhanced brain plasticity but also an elevated risk for developing mental health problems. Indeed, adolescence is accompanied by increased activation of the maturing hypothalamic-pituitary-adrenal axis, sensitivity to metabolic changes due to increased nutritional needs and hormonal changes, and gut microbiota maturation. Importantly, dietary habits and levels of physical activity significantly impact these systems. In this review, the interactions between exercise and Western-style diets, which are high in fat and sugar, on adolescent stress susceptibility, metabolism and the gut microbiota are explored. We provide an overview of current knowledge on implications of these interactions for hippocampal function and adolescent mental health, and speculate on potential mechanisms which require further investigation.

The Aging Human Liver: The Weal and Woe of Evolutionary Legacy

Aging is characterized by the progressive decline of biological integrity and its compensatory mechanisms as well as immunological dysregulation. This goes along with an increasing risk of frailty and disease. Against this background, we here specifically focus on the aging of the human liver. For the first time, we shed light on the intertwining evolutionary underpinnings of the liver's declining regenerative capacity, the phenomenon of inflammaging, and the biotransformation capacity in the process of aging. In addition, we discuss how aging influences the risk for developing nonalcoholic fatty liver disease, hepatocellular carcinoma, and/or autoimmune hepatitis, and we describe chronic diseases as accelerators of biological aging.

Maternal High-Energy Diet during Pregnancy and Lactation Impairs Neurogenesis and Alters the Behavior of Adult Offspring in a Phenotype-Dependent Manner

Obesity is one of the biggest and most costly health challenges the modern world encounters. Substantial evidence suggests that the risk of metabolic syndrome or obesity formation may be affected at a very early stage of development, in particular through fetal and/or neonatal overfeeding. Outcomes from epidemiological studies indicate that maternal nutrition during pregnancy and lactation has a profound impact on adult neurogenesis in the offspring. In the present study, an intergenerational dietary model employing overfeeding of experimental mice during prenatal and early postnatal development was applied to acquire mice with various body conditions. We investigated the impact of the maternal high-energy diet during pregnancy and lactation on adult neurogenesis in the olfactory neurogenic region involving the subventricular zone (SVZ) and the rostral migratory stream (RMS) and some behavioral tasks including memory, anxiety and nociception. Our findings show that a maternal high-energy diet administered during pregnancy and lactation modifies proliferation and differentiation, and induced degeneration of cells in the SVZ/RMS of offspring, but only in mice where extreme phenotype, such as significant overweight/adiposity or obesity is manifested. Thereafter, a maternal high-energy diet enhances anxiety-related behavior in offspring regardless of its body condition and impairs learning and memory in offspring with an extreme phenotype.

Morris water maze: a versatile and pertinent tool for assessing spatial learning and memory

Since its development about 40 years ago (1981–2021), Morris water maze has turned into a very popular tool for assessing spatial learning and memory. Its many advantages have ensured its pertinence to date. These include its effectiveness in evaluating hippocampal-dependent learning and memory, exemption from motivational differences across diverse experimental manipulations, reliability in various cross-species studies, and adaptability to many experimental conditions with various test protocols. Nonetheless, throughout its establishment, several experimental and analysis loopholes have galvanized researchers to assess ways in which it could be improved and adapted to fill this gap. Therefore, in this review, we briefly summarize these developments since the early years of its establishment through to the most recent advancements in computerized analysis, offering more comprehensive analysis paradigms. In addition, we discuss the adaptability of the Morris water maze across different test versions and analysis paradigms, providing suggestions with regard to the best paradigms for particular experimental conditions. Hence, the proper selection of the experimental protocols, analysis paradigms, and consideration of the assay’s limitations should be carefully considered. Given that appropriate measures are taken, with various adaptations made, the Morris water maze will likely remain a relevant tool to assess the mechanisms of spatial learning and memory.

Wheel running leads to sex-specific effects on Western diet-associated glucose homeostasis and brain insulin signaling without altering food-related impulsive choice

OBJECTIVES

There is a clear association between obesity and impulsivity. While exercise can suppress weight gain and decrease impulsive choice (IC), the relationship between impulsivity, the consumption of palatable, energy dense diets, and exercise is unclear. We examined IC before and after Western diet (WD) exposure in rats of both sexes and whether exercise would rescue any diet-mediated increases in IC. Our hypotheses were twofold: first, increased impulsivity would be associated with higher WD preference in a positive feedback loop and second, increased WD consumption would impair both peripheral and central insulin signaling, both of which exercise would attenuate.

METHODS

Following baseline assessment of IC through a delay discounting task, rats were divided into naïve, sedentary (Sed), or wheel running (WR) groups for a 5-week WR and two-diet choice period after which rats underwent an oral glucose (OGTT) and insulin tolerance test (ITT) in addition to a re-test of IC. Insulin induced Akt-GSK3β signaling in the brain was examined using western blot.

RESULTS

All Sed rats preferred the WD diet, and all WR rats initially avoided the WD but subsequently reversed their avoidance to preference with females reversing earlier than males. Exercise suppressed weight gain and adiposity to a greater extent in males than females. Only WR males showed improved glucose clearance during OGTT, but both male and female WR rats had a faster recovery of hypoglycemia during ITT. Furthermore, WR rescued WD-induced deficits in hypothalamic Akt-GSK3β signaling in males but not females. In the prefrontal cortex, however, WD and WR both reduced Akt-GSK3β signaling in males but not females. There were no sex differences in IC at baseline, and all rats made more impulsive choices during the re-test independent of diet, sex, or exercise.

DISCUSSION

The results suggest that while exercise may have a greater efficacy at attenuating diet-mediated metabolic dysregulation in males, it has some beneficial effects for females and highlights the need to develop sex-specific interventions for restoring energy balance.

Building Resilience with Aerobic Exercise: Role of FKBP5

Both preclinical and clinical studies have pointed that aerobic exercise, at moderate doses, is beneficial at all stages of life by promoting a range of physiological and neuroplastic adaptations that reduce the anxiety response. Previous research about this topic has repeatedly described how the regular practice of aerobic exercise induces a positive regulation of neuroplasticity and neurogenesis-related genes, as well as a better control of the HPA axis function. However, limited progress has been carried out in the integration of neuroendocrine and neuroplastic changes, as well as in introducing new factors to understand how aerobic exercise can promote resilience to future stressful conditions. Resilience is defined as the ability to adapt to stress while maintaining healthy mental and physical performance. Consistent findings point to an important role of FKBP5, the gene expressing FK506-binding protein 51 (FKBP51), as a strong inhibitor of the glucocorticoid receptor (GR), and thus, an important regulator of the stress response. We propose that aerobic exercise could contribute to modulate FKBP5 activity acting as a potential therapeutic approach for mood disorders. In this sense, aerobic exercise is well known for increasing the growth factor BDNF, which by downstream pathways could affect the FKBP5 activity. Therefore, our manuscript has the aim of analyzing how FKBP5 could constitute a promising target of aerobic exercise promoting resilient-related phenotypes.