From mother to adult: timing-dependent effects of Lactiplantibacillus plantarum on gut, brain and behaviour in mice

Exposure to immune challenges during sensitive developmental windows, such as pregnancy or early postnatal life, is widely recognized as a significant risk factor for neurodevelopmental disorders, including autism spectrum disorder. These early immune perturbations are often associated with long-lasting alterations in behavioural and brain development, frequently accompanied by gut inflammation and microbiota dysbiosis. In this context, the present study investigated whether selected strains of Lactiplantibacillus plantarum (Lpb), characterized by anti-inflammatory and microbiota-modulating properties, could mitigate adult behavioural and neurobiological consequences induced by early-life immune activation.We employed three mouse models of early immune activation: (i) prenatal maternal immune activation (MIA), in which pregnant dams were treated with the viral mimetic Poly(I:C) at gestational day 12; (ii) postnatal immune activation (PIA), in which pups received bacterial Lipopolysaccharide (LPS) at postnatal day 9; and (iii) a combined prenatal plus postnatal exposure model (EIA). Thus, we evaluated whether the timing of probiotic intervention differentially affects gut-brain communication and behavioural outcomes. Two supplementation strategies, both lasting 5 weeks, were applied: indirect maternal exposure during gestation and lactation, and direct post-weaning administration, enabling comparison between early-life and adult interventions.

Behavioural assessments at adulthood included locomotor activity, anxiety-like behaviour, fear conditioning, sociability, social communication (including ultrasonic vocalizations (USVs)). In parallel, neuroinflammatory markers, gut inflammatory status and permeability, and microbiota composition were analysed. Statistical analyses were performed using ANOVA (p < 0.05). In addition, multivariate analyses were conducted using principal coordinates analysis (PCoA), followed by permutational multivariate analysis of variance (PERMANOVA) to assess group differences, and beta-dispersion analysis to evaluate within-group variability.

PCoA showed that early-life immune activation induced persistent alterations in EIA males, detectable from the juvenile stage and maintained into adulthood. These changes included reduced hippocampal BDNF levels and increased IL-6 expression compared to controls. Behaviourally, adult EIA males showed elevated USVs, increased locomotor activity, and greater time spent in the central area, indicating altered emotional and exploratory profiles. Importantly, these abnormalities were normalized following adult Lpb treatmentat both molecular and behavioural levels. Across both supplementation strategies, Lactiplantibacillus plantarum produced consistent pro-social effects in males, increasing sociability and USVs. Fear memory performance was also enhanced in both males and females regardless of timing, indicating a robust effect on emotional memory across sexes. When administered postweaning, Lpb further increased hippocampal BDNF in males, whereas in females primarily affected exploratory (locomotor activity, time spent in the central area) parameters, and body weight.

A comparison between the two time-windows of Lpb exposure revealed no major behavioural differences in males, as both maternal and adult Lpb exposure produced comparable outcomes. By contrast, in female’s adult supplementation primarily influenced anxiety-like behaviour and fear memory, whereas maternal exposure was more strongly associated with social responsiveness.

Overall, Lpb exerts beneficial effects across neuro-inflammation, emotional memory, sociability, and social communication in models of early-life immune challenge, with different effects in the two sexes.

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