A8 MICROBIAL ACTIVATION OF INTESTINAL DENDRITIC CELLS IS CRITICAL FOR THE ESTABLISHMENT OF NORMAL BEHAVIOR

Background

Accumulating evidence suggests that gut microbiota affects brain development and its function. It is well known that compared with conventional mice (SPF), germ-free (GF) mice display higher exploratory behavior, which normalizes after bacterial colonization. However, little is known about the underlying mechanisms and first critical steps initiating microbiota-gut-brain communication, which lead to establishment of normal behavior.

Purpose

To investigate the role of immune system in the establishment of normal behavior after bacterial colonization.

Method

We assessed behavior in GF mice before and after colonization with SPF microbiota, Altered Schaedler Flora (ASF) or the single bacterial strain E. coli JM83, and compared them to SPF mice, using the light-dark preference and tail suspension tests. Levels of brain-derived neurotrophic factor (BDNF) and c-Fos expression were measured by immunofluorescence in the hippocampus and amygdala. Colonic and brain gene expression were assessed using a NanoString technology. The immunodeficient MyD88-/- Ticam1- and SCID mice were used to study the role of the innate and adaptive immune systems. To demonstrate the role of the dendritic cells (DCs), we measured behavior before and after mono-colonization with E. coli JM83 in GF mice treated with cosalane and fingolimod, that inhibit DCs activation and migration, respectively. Brain levels of CD11b, CD11c and CD103 as DCs markers was assessed by immunofluorescence.

Result(s)

Compared to SPF mice, GF mice showed higher exploratory and less depressive-like behavior. The ex-germ-free mice colonized with ASF microbiota, or mono-colonized with E. coli JM83 showed similar normalization of behavior as those colonized with SPF microbiota. Mono-colonization with E. coli reduced both BDNF and c-fos levels in the hippocampus and amygdala. While colonization of GF SCID mice induced same change in behavior as in wild-type mice, GF MyD88-/-Ticam1-/- mice did not alter their behavior. Mono-colonization affected multiple genes in the colon and the brain, associated with innate immunity and neural plasticity. Treatment with both cosalane and fingolimod prevented behavioral changes after colonization, which was paralleled by absence of CD11b+CD103+CD11c+ cells in the brain, otherwise found in high numbers in control mono-colonized mice and absent in germ-free mice.

Conclusion(s)

The innate immune system, through activation and migration of intestinal dendritic cells into the brain, initiates the neuro-immune signaling within the gut-brain axis and leads to normalization of behavior after bacterial colonization. Our findings may impact several psychiatric conditions, in which altered innate immune signaling has been implicated.

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CIHR, Other

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Balsam Family Foundation

Disclosure of Interest

None Declared

A14 THE INTESTINAL MICROBIOTA CONTRIBUTES TO AGE-RELATED MEMORY DECLINE

Background

Age-related deterioration of cognitive function and memory capacity occur in both humans and rodents. For example, significant memory deficits have been reported in conventionally raised (SPF) old mice compared to conventionally raised young mice submitted to a spatial memory task (Prevot et al., 2019, Mol Neuropsychiatry 5, 84–97). Microbiota-to-brain signaling is now well established in mice and humans, but the extent to which it influences age-associated memory decline is unknown.

Aims

Our study examines whether the intestinal microbiota contributes to age-associated changes in brain function. We address the specific hypothesis that age-associated cognitive decline is attenuated in the absence of the intestinal microbiota.

Methods

We assessed anxiety-like and depressive-like behavior, locomotor activity and spatial memory performance in young germ-free (GF) mice (2–3 months of age, n=24) and senescent GF mice (13–27 months old, n=22) maintained in axenic conditions, and compared them to conventionally raised (SPF) mice of the same age. Anxiety-like behavior, locomotor activity and depressive-like behavior were measured using the light-dark preference, open-field, and tail suspension tests. We also used the Y-maze test based on a spontaneous alternation task to assess cognition, with the alternation rate as a proxy of spatial working memory. The age-associated inflammation was assessed with IL-6 cytokine plasma concentrations measured by ELISA.

Results

Anxiety-like behavior and depressive-like behavior did not change with the age regardless of the microbial status. However, old SPF mice traveled less distance (866.8 cm) than young SPF mice (1375 cm, p < 0.01) in the open-field. Similarly, old GF mice also traveled less distance (458.9 cm) than young GF mice (875.7 cm, p < 0.0001). In contrast to old SPF mice, old GF mice did not show memory impairment in the spatial memory task. Indeed, old SPF mice displayed lower alternation rate of 58.3%, compared to that found in young SPF mice (76.9%, p < 0.05) while both old and young GF mice had an identical alternation rate of 73.3% ( p > 0.05). In addition, IL-6 plasma levels revealed that old GF mice did not show signs of age-associated inflammation that was evident in old SPF mice (3.68 vs. 13.93 pg/ml, p < 0.05).

Conclusions

We conclude that the absence of age-related memory deficit in old germ-free mice is consistent with a role for the microbiota in age-related cognitive decline, likely mediated via the immune system, as suggested by the absence of age-associated inflammation in germ-free mice. We propose that novel microbiota-targeted therapeutic strategies may prevent or delay the cognitive decline of aging.

Funding Agencies

CIHRBalsam Family Foundation

A238 ABSENCE OF AGE-RELATED MEMORY DECLINE IN GERM-FREE MICE

Background

Age-associated deterioration of cognitive function and memory capacity occur in a variety of mammals, from humans to rodents. For example, significant memory deficits have been reported in conventionally raised (SPF) old mice compared to conventionally raised young mice submitted to a spatial memory task (Prevot et al., Mol Neuropsychiatry 2019). Microbiota to brain signaling is now well established in mice, but the extent to which this influences age-related memory decline is unknown.

Aims

Our project aims to determine whether the intestinal microbiota contributes to age-related changes in brain function. We address the hypothesis that age-related cognitive decline is attenuated in the absence of the intestinal microbiota.

Methods

We studied locomotor behavior and spatial memory performance in young germ-free (GF) mice (2–3 months of age, n=24) and senescent GF mice (13–27 months old, n=22) maintained in axenic conditions, and compared them to conventionally raised (SPF) mice. We used the Y-maze test based on a spontaneous alternations task to assess cognition, with alternation rate as a proxy of spatial working memory performance. The locomotor activity was measured using the open-field test.

Results

GF old mice traveled less distance (458.9 cm) than GF young mice (875.7 cm, p &lt; 0.001) but these differences in locomotor activity did not influence spatial memory performance. Indeed, both GF old and GF young mice had an identical alternation rate of 73.3% (p &gt; 0.05). This contrasted with the memory impairment found in old SPF mice that displayed lower alternation rate of 58.3%, compared to that found in young SPF mice (76.2%, p = 0.13).

Conclusions

We conclude that the absence of age-related memory decline in germ-free mice is consistent with a role for the microbiota in the cognitive decline associated with aging, likely through action on the immune system, well documented in SPF mice (Thevaranjan et al., Cell Host & Microbe 2017). We propose that novel microbiota-targeted therapeutic strategies may delay or prevent the cognitive decline of aging.

Funding Agencies

CIHRBalsam Family Foundation

Effects of tryptophan and probiotic supplementation on growth and behavior in quail

In laying hens, a diet supplemented with tryptophan (Trp) has been shown to affect their pecking behavior. However, unlike this positive effect, Trp is also involved in negative effects on behavior and stress through indolic pathways. Indole production can be reduced by probiotics (Pro), thus we hypothesized that Pro may prevent negative effects of Trp and increase beneficial effects on behavior in birds. Combined effects of Pro and Trp were also expected. To investigate the effects on behavior in birds of supplementing with a high level of Trp with or without Pro, Japanese quail were used because their behavior can be influenced by Pediococcus acidilactici, and they can be highly aggressive. Quails (n = 120) were assigned to 4 groups in a 2 × 2 factorial design for 55 d: C-C (control diet with usual Trp level, 0.3%; without Pro; n = 30), Trp-C (Trp: 2%; without Pro; n = 30), C-Pro (control diet; with Pro: 1 x 10⁹ CFU/L P. acidilactici in drinking water; n = 30), and Trp-Pro (Trp 2%; with Pro; n = 30). Body weight was measured every week, and different tests were conducted to investigate behavioral characteristics of each quail. Contrary to our hypothesis, there was almost no interaction between Trp and Pro treatments. Tryptophan supplementation significantly (P < 0.05) reduced live weight up to 27 d, whereas Pro treatment had no effect. There was no significant difference between groups for tonic immobility variables (P > 0.05). The birds fed the high Trp diet spent significantly less time in the periphery of the open field than those fed the control diet and moved less in the arena during the social isolation test. Interindividual distances were significantly lower in males fed with Trp 2% than with the control diet, whereas Trp and Pro supplements interacted in females. The treatments did not affect sexual motivation in males. These results indicate that a high level of Trp reduced growth and appeared to enhance emotional reactivity in quails and that supplementing with Pro did not reduce these effects. In conclusion, feeding high Trp for 55 d cannot be recommended as a strategy to improve social behavior unlike effects observed in laying hens.