A single administration of 'microbial' D-alanine to healthy volunteers augments reaction to negative emotions: A comparison with D-serine.

BACKGROUND: Activation of the glutamate N-methyl-D-aspartate receptor with its co-agonist D-serine has been shown to improve subjective mood in healthy volunteers. D-alanine is another potent N-methyl-D-aspartate receptor co-agonist which arises from the natural breakdown of host gut microbes, and is predominantly sequestered in the pituitary. This may suggest that D-alanine influences the neuroendocrine stress response which may then impact on emotion. AIMS: The current study explored the effects of D-serine and D-alanine on emotional processing, cognition and the levels of the stress hormone cortisol in healthy volunteers. METHODS: In a double-blind, placebo-controlled randomised study, participants (n=63) received a single oral dose of either D-serine, D-alanine (60 mg/kg) or placebo and then performed the Emotional Test Battery and N-back task (two hours post-administration) and provided saliva samples at fixed intervals. RESULTS: Subjects administered with D-alanine were faster at identifying facial expressions of fear, surprise and anger, and at categorising negative self-referential words. Participants on D-alanine also showed a trend to recall more words than placebo in a memory task. D-serine did not have any meaningful effects in any of the tasks. Neither amino acid had a significant effect on salivary cortisol or working memory. CONCLUSION: This study is the first to suggest that D-alanine can modulate emotional cognitive processing after a single dose. The lack of findings for D-serine nevertheless contrasts a previous study, emphasising a need for further investigation to clarify discrepancies. A better understanding of the physiological actions of D-amino acids would be beneficial in evaluating their therapeutic potential.

Prebiotic supplementation does not affect reading and cognitive performance in children: A randomised placebo-controlled study.

Based on the emerging interest in the effects of gut microbiota on cognition, this proof-of-concept study assessed how children aged 7 to 9 with low reading scores responded to the ingestion of a 3-month prebiotic supplement versus a placebo. As a secondary aim, the effects of the prebiotic on cognition, sleep, behaviour, mood, anxiety, and cortisol were assessed. In this sample, the prebiotic did not affect any of the outcome measures.

Prebiotic reduction of brain histone deacetylase (HDAC) activity and olanzapine-mediated weight gain in rats, are acetate independent.

The intestinal microbiome is emerging as a novel therapeutic target owing to the wide range of potential health benefits that could result by manipulating the microbiota composition through relatively simple interventions. Ingestion of the prebiotic Bimuno™ galacto-oligosaccharide (B-GOS®) is one such intervention that has been shown to attenuate olanzapine-induced weight gain and improve cognitive flexibility in rats, potentially through mechanisms involving acetate, the major short-chain fatty acid (SCFA) that is produced by B-GOS® fermentation. The present study investigated the individual influences of B-GOS® and sodium acetate intake on brain histone acetyltransferase (HAT) and histone deacetylase (HDAC) activities, cortical and hippocampal expression of HDAC1-4 and N-methyl-d-aspartate receptor subunits in saline or olanzapine injected female rats. The effect of sodium acetate on olanzapine-induced weight gain was also investigated. Daily ingestion of B-GOS® for 21 days, reduced HDAC activity and hippocampal HDAC-4, and elevated levels of cortical HDAC-1 and HDAC-3 mRNAs. Sodium acetate supplementation significantly decreased HAT, but not HDAC, activity and increased hippocampal HDAC-3 and HDAC-4 mRNAs. Olanzapine-induced weight gain and fourteen genera of intestinal bacteria, were not influenced by sodium acetate intake. Together these data suggests the effects of B-GOS® in rats cannot be replicated by acetate ingestion, and that mechanisms beyond the production of this SCFA are likely to underlie the psychotropic and metabolic actions of this prebiotic.