Adolescent food insecurity in female rodents and susceptibility to diet-induced obesity

Mai O Spaulding, Jessica R Hoffman, Grace C Madu, Magen N Lord, Caroline Soares Iizuka, Kevin P Myers, Emily E Noble (Physiol Behav 2024 Jan 1:273:114416.doi: 10.1016/j.physbeh.2023.114416)

Food insecurity is defined as having limited or uncertain access to nutritious foods, and adolescent food insecurity is associated with obesity and disordered eating behaviors in humans. We developed a rodent model of adolescent food insecurity to determine whether adolescent food insecurity per se promotes increased susceptibility to diet-induced obesity and altered eating behaviors during adulthood. Female juvenile Wistar rats were singly housed and assigned to three experimental diets: food-secure with standard chow (CHOW), food-secure with a high-fat/sugar Western diet (WD), and food-insecure with WD (WD-FI). Food-secure rats (CHOW and WD) received meals at fixed feeding times (9:00, 13:00, and 16:00). WD-FI rats received meals at unpredictable intervals of the above-mentioned feeding times but had isocaloric amounts of food to WD. We investigated the impact of adolescent food insecurity on motivation for sucrose (Progressive Ratio), approach-avoidance behavior for palatable high-fat food (Approach-Avoidance task), and susceptibility to weight gain and hyperphagia when given an obesogenic choice diet. Secondary outcomes were the effects of food insecurity during development on anxiety-like behaviors (Open Field and Elevated Plus Maze) and learning and memory function (Novel Location Recognition task). Rodents with adolescent food insecurity showed a greater trend of weight gain and significantly increased fat mass and liver fat accumulation on an obesogenic diet in adulthood, despite no increases in motivation for sucrose or high-fat food. These data suggest that adolescent unpredictable food access increases susceptibility to diet-induced fat gain without impacting food motivation or food intake in female rodents. These findings are among a small group of recent studies modeling food insecurity in rodents and suggest that adolescent food insecurity in females may have long-term implications for metabolic physiology later in life.

Sexually Dimorphic Effects of a Western Diet on Brain Mitochondrial Bioenergetics and Neurocognitive Function

Magen N Lord, Jun-Won Heo, Albino G Schifino, Jessica R Hoffman, Kristen N Donohue, Jarrod A Call, Emily E Noble. (Nutrients, 2021, Nov 24;13(12):4222. doi: 10.3390/nu13124222)

We sought to determine whether a WD alters behavior and metabolic outcomes in male and female rodents through impacting hippocampal and hypothalamic mitochondrial bioenergetics. Results revealed a sexually dimorphic macronutrient preference, where males on the WD consumed a greater percentage of calories from fat/protein and females consumed a greater percentage of calories from a sugar-sweetened beverage. Both males and females on a WD gained body fat and showed impaired glucose tolerance when compared to same-sex controls. Males on a WD demonstrated impaired hippocampal functioning and an elevated tendency toward a high membrane potential in hippocampal mitochondria. Comprehensive bioenergetics analysis of WD effects in the hypothalamus revealed a tissue-specific adaption, where males on the WD oxidized more fat, and females oxidized more fat and carbohydrates at peak energy demand.

Gut microbial taxa elevated by dietary sugar disrupt memory function

Emily E Noble, Christine A Olson, Elizabeth Davis, Linda Tsan, Yen-Wei Chen, Ruth Schade , Clarissa Liu, Andrea Suarez, Roshonda B Jones, Claire de La Serre, Xia Yang, Elaine Y Hsiao, and Scott E Kanoski. (Translational Psychiatry, 2021 Mar 31;11(1):194. doi: 10.1038/s41398-021-01309-7)

Emerging evidence highlights a critical relationship between gut microbiota and neurocognitive development. Excessive consumption of sugar and other unhealthy dietary factors during early life developmental periods yields changes in the gut microbiome as well as neurocognitive impairments. However, it is unclear whether these two outcomes are functionally connected. Here we explore whether excessive early life consumption of added sugars negatively impacts memory function via the gut microbiome.

Hypothalamus-hippocampus circuitry regulates impulsivity via melanin-concentrating hormone

Noble EE, Wang Z, Liu CM, Davis EA, Suarez AN, Stein LM, Tsan L, Terrill SJ, Hsu TM, Jung AH, Raycraft LM, Hahn JD, Darvas M, Cortella AM, Schier LA, Johnson AW, Hayes MR, Holschneider DP, Kanoski SE (Nat Commun. (Nature Communications, 2019 Oct 29;10(1):4923. doi: 10.1038/s41467-019-12895-y))

Behavioral impulsivity is common in various psychiatric and metabolic disorders. Here we identify a hypothalamus to telencephalon neural pathway for regulating impulsivity involving communication from melanin-concentrating hormone (MCH)-expressing lateral hypothalamic neurons to the ventral hippocampus subregion (vHP). Results show that both site-specific upregulation (pharmacological or chemogenetic) and chronic downregulation (RNA interference) of MCH communication to the vHP increases impulsive responding in rats, indicating that perturbing this system in either direction elevates impulsivity. Furthermore, these effects are not secondary to either impaired timing accuracy, altered activity, or increased food motivation, consistent with a specific role for vHP MCH signaling in the regulation of impulse control. Results from additional functional connectivity and neural pathway tracing analyses implicate the nucleus accumbens as a putative downstream target of vHP MCH1 receptor-expressing neurons. Collectively, these data reveal a specific neural circuit that regulates impulsivity and provide evidence of a novel function for MCH on behavior.

Control of feeding behavior by cerebral ventricular volume transmission of melanin-concentrating hormone

Noble EE, Hahn JD, Konanur VR, Hsu TM, Page SJ, Cortella AM, Liu CM, Song MY, Suarez AN, Szujewski CC, Rider D, Clarke JE, Darvas M, Appleyard SM, Kanoski SE (Cell Metabolism. 2018; 28(1): 55-68

Traditional textbook knowledge indicates that the cerebral spinal fluid (CSF) acts primarily as [1] a buffer/barrier protecting the brain from mechanical impact with the skull, and/or [2] a medium for flushing metabolic waste from the brain’s cellular tissue. Here we show that the CSF is an active pathway for biological communication by providing evidence for CSF-mediated “volume transmission” of melanin-concentrating hormone (MCH) in the control of feeding behavior. These findings suggest that humoral-like signaling of neuropeptides in the cerebral ventricles may be a common biological pathway in the control of fundamental behaviors.

Early-life sugar consumption has long-term negative effects on memory function in male rats

Noble EE, Hsu TM, Liang J, Kanoski SE (Nutr Neurosci. 2019 Apr;22(4):273-283)

OBJECTIVES: Added dietary sugars contribute substantially to the diet of children and adolescents in the USA, and recent evidence suggests that consuming sugar-sweetened beverages (SSBs) during early life has deleterious effects on hippocampal-dependent memory function. Here, we test whether the effects of early-life sugar consumption on hippocampal function persist into adulthood when access to sugar is restricted to the juvenile/adolescent phase of development.

METHODS: Male rats were given ad libitum access to an 11% weight-by-volume sugar solution (made with high fructose corn syrup-55) throughout the adolescent phase of development (post-natal day (PN) 26-56). The control group received a second bottle of water instead, and both groups received ad libitum standard laboratory chow and water access throughout the study. At PN 56 sugar solutions were removed and at PN 175 rats were subjected to behavioral testing for hippocampal-dependent episodic contextual memory in the novel object in context (NOIC) task, for anxiety-like behavior in the Zero maze, and were given an intraperitoneal glucose tolerance test.

RESULTS: Early-life exposure to SSBs conferred long-lasting impairments in hippocampal-dependent memory function later in life- yet had no effect on body weight, anxiety-like behavior, or glucose tolerance. A second experiment demonstrated that NOIC performance was impaired at PN 175 even when SSB access was limited to 2 hours daily from PN 26-56.

DISCUSSION: Our data suggest that even modest SSB consumption throughout early life may have long-term negative consequences on memory function during adulthood.

Early-Life  Sugar  Consumption  Affects  the  Rat  Microbiome  Independently of Obesity

Noble EE, Hsu TM, Jones RB, Fodor AA, Goran MI, Kanoski SE (J Nutr. 2017 Jan;147(1):20-28)

BACKGROUND: The gut microbiome has been implicated in various metabolic and neurocognitive disorders and is heavily influenced by dietary factors, but there is a paucity of research on the effects of added sugars on the gut microbiome.

OBJECTIVE: With the use of a rodent model, our goal was to determine how added-sugar consumption during the juvenile and adolescent phase of development affects the gut microbiome.

METHODS: Forty-two juvenile male Sprague-Dawley rats [postnatal day (PND) 26; 50-70 g] were given access to 1 of 3 different 11%-carbohydrate solutions designed to model a range of monosaccharide ratios commonly consumed in sugar-sweetened beverages: 1) 35% fructose:65% glucose, 2) 50% fructose:50% glucose, 3) 65% fructose:35% glucose, and 4) control (no sugar). After ad libitum access to the respective solutions for the juvenile and adolescent period (PND 26-80), fecal samples were collected for next-generation 16S ribosomal RNA sequencing and multivariate microbial composition analyses. Energy intake, weight change, and adiposity index were analyzed in relation to sugar consumption and the microbiota.

RESULTS: Body weight, adiposity index, and total caloric intake did not differ as a result of sugar consumption. However, sugar consumption altered the gut microbiome independently of anthropometric measures and caloric intake. At the genus level, Prevotella [linear discriminant analysis (LDA) score = -4.62; P < 0.001] and Lachnospiraceae incertae sedis (LDA score = -3.01; P = 0.03) were reduced, whereas Bacteroides (LDA score = 4.19; P < 0.001), Alistipes (LDA score = 3.88; P < 0.001), Lactobacillus (LDA score = 3.78; P < 0.001), Clostridium sensu stricto (LDA score = 3.77; P < 0.001), Bifidobacteriaceae (LDA score = 3.59; P = 0.001), and Parasutterella (LDA score = 3.79; P = 0.004) were elevated by sugar consumption. No overall pattern could be attributable to monosaccharide ratio.

CONCLUSIONS: Early-life sugar consumption affects the gut microbiome in rats independently of caloric intake, body weight, or adiposity index; these effects are robust across a range of fructose-to-glucose ratios.

Oxytocin in the ventromedial  hypothalamic  nucleus  reduces  feeding  and  acutely  increases  energy expenditure

Noble EE, Billington CJ, Kotz CM, Wang C (Am J Physiol Regul Integr Comp Physiol. 2014 Sep 15;307(6):R737-45)

Central oxytocin reduces food intake and increases energy expenditure. The ventromedial hypothalamic nucleus (VMN) is associated with energy balance and contains a high density of oxytocin receptors. We hypothesized that oxytocin in the VMN is a negative regulator of energy balance acting to reduce feeding and increase energy expenditure. To test this idea, oxytocin or vehicle was injected directly into the VMN of Sprague-Dawley rats during fasted and nonfasted conditions. Energy expenditure (via indirect calorimetry) and spontaneous physical activity (SPA) were recorded simultaneously. Animals were also exposed to a conditioned taste aversion test, to determine whether oxytocin's effects on food intake were associated with malaise. When food was available during testing, oxytocin-induced elevations in energy expenditure lasted for 1 h, after which overall energy expenditure was reduced. In the absence of food during the testing period, oxytocin similarly increased energy expenditure during the first hour, but differences in 12-h energy expenditure were eliminated, implying that the differences may have been due to the thermic effects of feeding (digestion, absorption, and metabolic processing). Oxytocin acutely elevated SPA and reduced feeding at doses that did not cause a conditioned taste aversion during both the fed and fasted states. Together, these data suggest that oxytocin in the VMN promotes satiety and acutely elevates energy expenditure and SPA and implicates the VMN as a relevant site for the antiobesity effects of oxytocin.

Exercise reduces diet-induced cognitive decline and increases hippocampal brain-derived neurotrophic factor in CA3 neurons

Noble EE, Mavanji V, Little MR, Billington CJ, Kotz CM, Wang C (Neurobiol Learn Mem. 2014 Oct;114:40-50)

BACKGROUND: Previous studies have shown that a western diet impairs, whereas physical exercise enhances hippocampus-dependent learning and memory. Both diet and exercise influence expression of hippocampal brain-derived neurotrophic factor (BDNF), which is associated with improved cognition. We hypothesized that exercise reverses diet-induced cognitive decline while increasing hippocampal BDNF.

METHODS: To test the effects of exercise on hippocampal-dependent memory, we compared cognitive scores of Sprague-Dawley rats exercised by voluntary running wheel (RW) access or forced treadmill (TM) to sedentary (Sed) animals. Memory was tested by two-way active avoidance test (TWAA), in which animals are exposed to a brief shock in a specific chamber area. When an animal avoids, escapes or has reduced latency to do either, this is considered a measure of memory. In a second experiment, rats were fed either a high-fat diet or control diet for 16 weeks, then randomly assigned to running wheel access or sedentary condition, and TWAA memory was tested once a week for 7 weeks of exercise intervention.

RESULTS: Both groups of exercised animals had improved memory as indicated by reduced latency to avoid and escape shock, and increased avoid and escape episodes (p<0.05). Exposure to a high-fat diet resulted in poor performance during both the acquisition and retrieval phases of the memory test as compared to controls. Exercise reversed high-fat diet-induced memory impairment, and increased brain-derived neurotrophic factor (BDNF) in neurons of the hippocampal CA3 region.

CONCLUSIONS: These data suggest that exercise improves memory retrieval, particularly with respect to avoiding aversive stimuli, and may be beneficial in protecting against diet induced cognitive decline, likely via elevated BDNF in neurons of the CA3 region.