Host microbiota modulates development of social preference in mice

Abstract

Background: Mounting evidence indicates that the indigenous gut microbiota exerts long-lasting programming effects on brain function and behaviour.

Objective: In this study, we used the germ-free (GF) mouse model, devoid of any microbiota throughout development, to assess the influence of the indigenous microbiota on social preference and repetitive behaviours (e.g. self-grooming).

Methods and results: Using the three-chambered social approach task, we demonstrate that when adult GF mice were given a choice to spend time with a novel mouse or object, they spent significantly more time sniffing and interacting with the stimulus mouse compared to conventionally raised mice (specific pathogen-free, SPF). Time spent in repetitive self-grooming behaviour, however, did not differ between GF and SPF mice. Real-time PCR-based gene expression analysis of the amygdala, a key region that is part of the social brain network, revealed a significant reduction in the mRNA levels of total brain-derived neurotrophic factor (BDNF), BDNF exon I-, IV-, VI-, IX-containing transcripts, and NGFI-A (a signalling molecule downstream of BDNF) in GF mice compared to SPF mice.

Conclusion: These results suggest that differential regulation of BDNF exon transcripts in the amygdala by the indigenous microbes may contribute to the altered social development of GF mice.

Keywords: BDNF; amygdala; brain development; gene expression; germ-free mice; synaptic plasticity genes.

Fig. 1

Germ-free (GF) mice display increased sociability. (a) Bars show time (seconds) spent in the different chambers during the social approach session by specific pathogen-free (SPF) and GF mice. (b) Bars show time (seconds) spent interacting with the stimulus mouse or in close proximity to the novel object. (c) Bars show sociability indexes (percentage) of SPF and GF mice. (d) Bars show time (seconds) spent in self-grooming by SPF and GF mice. All data (a–d) are presented as means (±SEM; n=10 per group). *p<0.05, *p<0.01, ***p<0.001 compared with SPF mice.

Fig. 2

GF mice display increased spontaneous motor activity. (a) Average distance travelled (metres) measured in 15-min time bins across a 90-min session in an open-field box. (Inset) Bars show time (seconds) spent in the centre during the initial 15 min of testing. (b) Average number of rears measured in 15-min bins across a 90-min session in an open-field box. (c) Representative tracks of movement patterns of SPF and GF mice at the 0–15, 46–60, and 76–90-min intervals of the 90-min open-field test session; distance travelled and rearing activity are shown in dark red and blue, respectively. All data (a–b) are presented as means (±SEM; n=10 per group). *p<0.05, **p<0.01 compared with SPF mice.

Fig. 3

Differential promoter control of the BDNF gene by gut microbiota in the amygdala. Quantitative real-time polymerase chain reaction was used to examine expression levels of the common and exon-specific BDNF transcripts in the amygdala of GF and SPF mice. Expression level of each transcript examined was normalised to heat shock protein 90 (Hsp90) levels and expressed relative to the SPF group. Data are presented as means (±SEM; n=6 per group). *p<0.05, **p<0.01, ***p<0.001 compared with SPF mice.