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Dinan T.G. Mind-altering microorganisms: The impact of the gut microbiota on brain and behaviour.

2 Foster J.A.

Neufeld K.A.M. Gut-brain: How the microbiome influences anxiety and depression.

3 Collins S.M.

Surette M.

Bercik P. The interplay between the intestinal microbiota and the brain.

4 Mayer E.A.

Knight R.

Mazmanian S.K.

Cryan J.F.

Tillisch K. Gut microbes and the brain: Paradigm shift in neuroscience.

1 Cryan J.F.

Dinan T.G. Mind-altering microorganisms: The impact of the gut microbiota on brain and behaviour.

4 Mayer E.A.

Knight R.

Mazmanian S.K.

Cryan J.F.

Tillisch K. Gut microbes and the brain: Paradigm shift in neuroscience.

5 Hsiao E.Y.

McBride S.W.

Hsien S.

Sharon G.

Hyde E.R.

McCue T.

et al. Microbiota modulate behavioral and physiological abnormalities associated with neurodevelopmental disorders.

6 Gareau M.G.

Wine E.

Rodrigues D.M.

Cho J.H.

Whary M.T.

Philpott D.J.

et al. Bacterial infection causes stress-induced memory dysfunction in mice.

7 Miller B.R.

Hen R. The current state of the neurogenic theory of depression and anxiety.

8 Marin-Burgin A.

Schinder A.F. Requirement of adult-born neurons for hippocampus-dependent learning.

9 Snyder J.S.

Soumier A.

Brewer M.

Pickel J.

Cameron H.A. Adult hippocampal neurogenesis buffers stress responses and depressive behaviour.

6 Gareau M.G.

Wine E.

Rodrigues D.M.

Cho J.H.

Whary M.T.

Philpott D.J.

et al. Bacterial infection causes stress-induced memory dysfunction in mice.

10 Sudo N.

Chida Y.

Aiba Y.

Sonoda J.

Oyama N.

Yu X.N.

et al. Postnatal microbial colonization programs the hypothalamic-pituitary-adrenal system for stress response in mice.

2 Foster J.A.

Neufeld K.A.M. Gut-brain: How the microbiome influences anxiety and depression.

11 Clarke G.

Grenham S.

Scully P.

Fitzgerald P.

Moloney R.D.

Shanahan F.

et al. The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner.

Accumulating evidence suggests that the microbiota plays a key role in the brain and behavior (). Alterations in the gut microbiota-brain axis have been implicated in stress-related disorders such as depression and anxiety, in neurodevelopmental disorders such as autism, and in cognitive functioning (). Neurogenesis, the birth of new neurons, in the adult hippocampus is thought to play an important role in learning and memory and responses to stress and antidepressant drugs (). Germ-free (GF) mice have grown up without having ever been exposed to microorganisms and are an excellent tool to probe the role of the microbiota in health and disease. Several studies have suggested that some brain processes that are regulated by adult hippocampal neurogenesis are also affected in GF mice (), and altered concentrations of substrates known to influence adult hippocampal neurogenesis, such as corticosterone, serotonin, brain-derived neurotrophic factor, and proinflammatory cytokines, have been reported in these mice (). However, whether adult hippocampal neurogenesis is altered in GF mice has not yet been reported.