Behavioral response to fiber feedingis cohort-dependent and associated with gut microbiota composition in mice.

Recent data has supported a role for the gut microbiota in improving cognition and shaping behavior. Here, we assessed whether pectin, a soluble, fermentable fiber, could enhance learning and memory in mice. Two cohorts of young male C57Bl/6 J mice, C1 (n = 20) and C2 (n = 20), were obtained from Jackson Laboratory and randomized to semi-purified AIN-93 M diets containing 5% pectin (n = 10) or cellulose (n = 10). After 16 weeks, learning and memory was assessed by Morris Water Maze (MWM) and microbiota composition was analyzed by 16S rRNA sequencing. Despite identical treatment, we observed differences in learning and memory abilities between cohorts, along with distinct microbiotas. In C1, pectin-fed mice spent a higher percentage of time in the target quadrant at the 24-h probe trial of the MWM versus cellulose-fed mice; in C2, no effect of pectin was observed. In both cohorts, UniFrac distance revealed significant differences in gut microbial communities between cellulose-fed and pectin-fed mice. UniFrac analysis also revealed significantly different bacterial communities between cohorts. Further analysis demonstrated that the microbial genera Oscillospira, Bilophila, and Peptostreptococcoceae were more abundant in C1 versus C2, and positively associated with distance from the platform during the 24-h probe test. These data support previous findings that differences in the gut microbiota may play a role in host response to a dietary intervention and could partly explain irreproducibility in psychological and behavioral experiments. Further research is needed to determine if a causal relationship exists.

Long-term supplementation with EGCG and beta-alanine decreases mortality but does not affect cognitive or muscle function in aged mice.

We have previously shown that 6weeks of a diet containing epigallocatechin gallate (EGCG) and beta-alanine (B-ALA) was not effective in improving either cognitive or muscle function in aged (18month) mice (Gibbons et al. Behav Brain Res 2014). However, diet reduced oxidative stress in the brain, and previous studies using longer-term interventions have documented beneficial effects in cognitive, but not muscle, function. Therefore, we investigated the effect of 6months of feeding on measures of cognitive and muscle function in mice. Mice (12months, N=15/group) were fed AIN-93M containing 0.15% EGCG and 0.34% B-ALA or standard AIN-93M for 6months, then underwent a battery of tests for cognitive and muscle function at 18months. Interestingly, a higher percentage of mice receiving EGCG and B-ALA (E+B, 80%) survived to study end compared to control (Ctrl, 40%) mice (p=0.02). E+B did not affect arm preference in the Y-maze test (p=0.74, novel arm) and did not alter performance in an active avoidance test (p=0.16, avoidances per 50 trials). E+B increased rotarod performance (p=0.03), did not affect grip strength (p=0.91), and decreased time to exhaustion in a treadmill fatigue test (p=0.02) compared to Ctrl. In conclusion, E+B reduced mortality, had no effect on cognitive function and variable effects on muscle function.

Dose-dependent decrease in mortality with no cognitive or muscle function improvements due to dietary EGCG supplementation in aged mice.

We have previously shown that a diet containing epigallocatechin gallate (EGCG) and beta-alanine is not effective in improving either cognitive or muscle function in aged (18 month) mice (Gibbons et al., Behav. Brain Res., 2014, 272:131-140; Pence et al., Appl. Physiol. Nutr. Metab., 2016, 41(2): 181-190). However, this diet reduced oxidative stress in the brain, and previous studies using longer term interventions and other doses have documented beneficial effects in cognitive and muscle function, especially with EGCG. Here we hypothesized that a different dose of EGCG or longer feeding period would be more efficacious in improving cognition. Aged (21-25 mo) Balb/cByJ male mice underwent 63 days of feeding with EGCG at 0, 0.091, or 3.67 mg/g AIN-93M diet and were then subjected to a battery of cognitive and muscle function tests. EGCG feeding at either of the 2 doses did not alter preference for novel versus familiar arm in the Y-maze test (p = 0.29) and did not affect learning in the active avoidance test (p = 0.76). Similarly, EGCG did not affect preference for novel versus familiar mice in a social discrimination test (p = 0.17). Likewise, there was no effect of EGCG on muscle function by grip strength (p = 0.16), rotarod (p = 0.18), or treadmill test to exhaustion (p = 0.25). EGCG reduced mortality in a dose-dependent fashion (p = 0.05, log-rank test for trend), with 91% of high EGCG, 72% of low EGCG, and 55% of control mice surviving to the end of the study. In conclusion, EGCG improves survival in aged mice but does not affect cognitive or muscle function.

Experience Modulates the Effects of Histone Deacetylase Inhibitors on Gene and Protein Expression in the Hippocampus: Impaired Plasticity in Aging.

The therapeutic potential of histone deacetylase inhibitor (HDACi) treatment has attracted considerable attention in the emerging area of cognitive neuroepigenetics. The possibility that ongoing cognitive experience importantly regulates the cell biological effects of HDACi administration, however, has not been systematically examined. In an initial experiment addressing this issue, we tested whether water maze training influences the gene expression response to acute systemic HDACi administration in the young adult rat hippocampus. Training powerfully modulated the response to HDACi treatment, increasing the total number of genes regulated to nearly 3000, including many not typically linked to neural plasticity, compared with <300 following HDACi administration alone. Although water maze training itself also regulated nearly 1800 genes, the specific mRNAs, gene networks, and biological pathways involved were largely distinct when the same experience was provided together with HDACi administration. Next, we tested whether the synaptic protein response to HDACi treatment is similarly dependent on recent cognitive experience, and whether this plasticity is altered in aged rats with memory impairment. Whereas synaptic protein labeling in the young hippocampus was selectively increased when HDACi administration was provided in conjunction with water maze training, combined treatment had no effect on synaptic proteins in the aged hippocampus. Our findings indicate that ongoing experience potently regulates the molecular consequences of HDACi treatment and that the interaction of recent cognitive experience with histone acetylation dynamics is disrupted in the aged hippocampus. SIGNIFICANCE STATEMENT: The possibility that interventions targeting epigenetic regulation could be effective in treating a range of neurodegenerative disorders has attracted considerable interest. Here we demonstrate in the rat hippocampus that ongoing experience powerfully modifies the molecular response to one such intervention, histone deacetylase inhibitor (HDACi) administration. A single learning episode dramatically shifts the gene expression profile induced by acute HDACi treatment, yielding a qualitatively distinct hippocampal transcriptome compared with the influence of behavioral training alone. The downstream synaptic protein response to HDACi administration is similarly experience-dependent, and we report that this plasticity is disrupted in the aged hippocampus. The findings highlight that accommodating the modulatory influence of ongoing experience represents a challenge for therapeutic development in the area of cognitive neuroepigenetics.

Proactive and reactive inhibitory control in rats.

Inhibiting actions inappropriate for the behavioral context, or inhibitory control, is essential for survival and involves both reactively stopping the current prepared action and proactively adjusting behavioral tendencies to increase future performance. A powerful paradigm widely used in basic and clinical research to study inhibitory control is the stop signal task (SST). Recent years have seen a surging interest in translating the SST to rodents to study the neural mechanisms underlying inhibitory control. However, significant differences in task designs and behavioral strategies between rodent and primate studies have made it difficult to directly compare the two literatures. In this study, we developed a rodent-appropriate SST and characterized both reactive and proactive control in rats. For reactive inhibitory control, we found that, unlike in primates, incorrect stop trials in rodents result from two independent types of errors: an initial failure-to-stop error or, after successful stopping, a subsequent failure-to-wait error. Conflating failure-to-stop and failure-to-wait errors systematically overestimates the covert latency of reactive inhibition, the stop signal reaction time (SSRT). To correctly estimate SSRT, we developed and validated a new method that provides an unbiased SSRT estimate independent of the ability to wait. For proactive inhibitory control, we found that rodents adjust both their reaction time and the ability to stop following failure-to-wait errors and successful stop trials, but not after failure-to-stop errors. Together, these results establish a valid rodent model that utilizes proactive and reactive inhibitory control strategies similar to primates, and highlight the importance of dissociating initial stopping from subsequent waiting in studying mechanisms of inhibitory control using rodents.

Effects of perinatal bisphenol A exposure during early development on radial arm maze behavior in adult male and female rats.

Previous work has shown that exposure to bisphenol A (BPA) can affect anxiety behavior. However, no studies have examined whether administration of this endocrine disruptor during the perinatal period has the potential to induce alterations in cognitive behavior in both adult males and females as assessed in an appetitive task. The goal of the current study was to determine whether exposure to different doses of BPA during early development alters performance on the 17-arm radial maze in adulthood in Long-Evans rats. Oral administration of corn oil (vehicle), 4 µg/kg, 40 µg/kg, or 400 µg/kg BPA to the dams occurred daily throughout pregnancy, and the pups received direct oral administration of BPA between postnatal days 1-9. Blood was collected from offspring at weaning age to determine levels of several hormones (thyroxine, thyroid stimulating hormone, follicle stimulating hormone, luteinizing hormone). One male and one female from each litter were evaluated on the 17-arm radial maze, a working/reference memory task, in adulthood. Results indicated that after exposure to BPA at both 4 and 400 µg/kg/day, rats of both sexes had decreased levels of FSH at weaning. There were no significant effects of BPA on performance on the radial arm maze in males or females. In conclusion, exposure to BPA during early development had modest effects on circulating hormones but did not affect performance on a spatial learning and memory task.