Glutamatergic regulation of cognition and functional brain connectivity:insights from pharmacological, genetic and translational schizophrenia research

The pharmacological modulation of glutamatergic neurotransmission to improve cognitive function has been a focus of intensive research, particularly in relation to the cognitive deficits seen in schizophrenia. Despite this effort there has been little success in the clinical use of glutamatergic compounds as procognitive drugs. Here we review a selection of the drugs used to modulate glutamatergic signalling and how they impact on cognitive function in rodents and humans. We highlight how glutamatergic dysfunction, and NMDA receptor hypofunction in particular, is a key mechanism contributing to the cognitive deficits observed in schizophrenia, and outline some of the glutamatergic targets that have been tested as putative procognitive targets for the disorder. Using translational research in this area as a leading exemplar, namely models of NMDA receptor hypofunction, we discuss how the study of functional brain network connectivity can provide new insight into how the glutamatergic system impacts on cognitive function. Future studies characterising functional brain network connectivity will increase our understanding of how glutamatergic compounds regulate cognition and could contribute to the future success of glutamatergic drug validation

Dietary magnesium deficiency alters gut microbiota and leads to depressive-like behaviour

Objective: Gut microbiota (GM) has previously been associated with alterations in rodent behaviour, and since the GM is affected by the diet, the composition of the diet may be an important factor contributing to behavioural changes. Interestingly, a magnesium restricted diet has been shown to induce anxiety and depressive-like behaviour in humans and rodents, and it could be suggested that magnesium deficiency may mediate the effects through an altered GM. Methods: The present study therefore fed C57BL/6 mice with a standard diet or a magnesium deficient diet (MgD) for 6 weeks, followed by behavioural testing in the forced swim test (FST) to evaluate depressive-like behaviour. An intraperitoneal glucose tolerance test (GTT) was performed 2 day after the FST to assess metabolic alterations. Neuroinflammatory markers were analysed from hippocampus. GM composition was analysed and correlated to the behaviour and hippocampal markers. Results: It was found that mice exposed to MgD for 6 weeks were more immobile than control mice in the FST, suggesting an increased depressive-like behaviour. No significant difference was detected in the GTT. GM composition correlated positively with the behaviour of undisturbed C57BL/6 mice, feeding MgD diet altered the microbial composition. The altered GM correlated positively to the hippocampal interleukin-6. Conclusion: In conclusion, we hypothesise that imbalances of the microbiota–gut–brain axis induced by consuming a MgD diet, contributes to the development of depressive-like behaviou