2026 ECNP Congress

PS04-4016

Prenatal microglial depletion alters neurodevelopmental trajectories following early immune activation in mice

Naomi Ciano Albanese — M.I. Marino, M.A. Ajmone-Cat, R. De Simone, L. Ricceri · Istituto Superiore di Sanità, Centre for Behavioral Science and Mental Health, Rome, Italy

2026 ECNP Congress

Introduction

Brain developmental trajectories are highly sensitive to early immune stimulations [1,2], and in preclinical settings, early immune activation (EIA), consisting of both a prenatal and postnatal immune challenge, leads to behavioral abnormalities and a higher risk of neurodevelopmental disorders, also mediated by microglia dysfunction [3]. We previously showed that adolescent male mice have an increased vulnerability not only to the long-term behavioural (i.e. social novelty impairment) and neuroinflammatory effects of the EIA condition but also to postweaning microglial depletion [4]. Therefore, we further hypothesized that microglial depletion in earlier phases of development could more deeply modulate offspring’s neurodevelopmental trajectories and outcomes in EIA model.

Aims

This study aimed to assess, in a double-hit model combining prenatal and early postnatal immune challenges (EIA), the effects of prenatal microglia depletion on behavioral and neuroinflammatory profiles of the offspring.

Methods

Pregnant C57BL/6J mice were exposed to both polyinosinic:polycytidylic acid (Poly I:C) on gestational day (GD) 12.5, and a diet containing the Colony Stimulating Factor-1 receptor inhibitor (PLX5622) to deplete maternal and fetal microglia, from GD 11 to GD 15; a Poly(I:C) only and a Saline group, fed with standard diet, were used as controls. On postnatal day (PND) 9, offspring were subjected to a second immune challenge with lipopolysaccharide (LPS). Physiological parameters and home-cage locomotor activity were monitored in pregnant dams. In the offspring, we evaluated somatic growth profiles, spontaneous motor behavior, and ultrasonic vocalizations (USVs) on PNDs 3, 6, and 9, and discrimination of nest olfactory cues (Homing test) on PND 15 in both male and female offspring. All data were analyzed with two-way ANOVA, and post-hoc comparisons were performed using Tukey’s test.

Results

In the offspring, maternal and fetal microglial depletion modulated the effects of immune stimulations: pups from Poly(I:C)+PLX dams showed higher body weight than Poly only (p<0.001) up to PND9 and also displayed a deficit in motor coordination (p<0.05). On PND15, male offspring exposed to both EIA condition and prenatal microglia depletion, differently from controls (p<0.05), did not discriminate between familiar and novel olfactory cues. In females, combined microglia depletion and EIA condition increased the number of USVs (p<0.05). Only in males, EIA condition alone induces distinct behavioural alterations, decreasing general locomotor activity levels (p<0.05) and increasing grooming response (p<0.05).

Conclusions

Prenatal microglial depletion modulates offspring body weight gain and spontaneous activity in mice also exposed to prenatal immune stimulation. Following postnatal immune challenge, the previous microglial depletion induces detrimental effects (particularly in males) in recognition of familiar nest olfactory cues, underscoring the critical role of maternal and fetal microglia in shaping early neurodevelopmental trajectories. Interestingly, since adolescent microglia depletion impaired male discrimination between novel and familiar social stimuli, altogether these data suggest that microglia depletion during developmental phases selectively targets male preference towards social cues. Ongoing studies are evaluating the long-term effects of prenatal microglia depletion in adult offspring, considering peripheral and neurobehavioural endpoints.

References

  1. . Butera, A., et al., Effects of a gut-selective integrin-targeted therapy in male mice exposed to early immune activation, a model for the study of autism spectrum disorder. Brain Behav Immun, 2024. 115: p. 89-100.
  2. . Carlezon, W.A., Jr., et al., Maternal and early postnatal immune activation produce sex-specific effects on autism-like behaviors and neuroimmune function in mice. Sci Rep, 2019. 9(1): p. 16928.
  3. . Zengeler, K.E. and J.R. Lukens, Innate immunity at the crossroads of healthy brain maturation and neurodevelopmental disorders. Nat Rev Immunol, 2021. 21(7): p. 454-468.
  4. . Ciano Albanese N., et al., Microglia depletion in a mouse model of prenatal and postnatal immune activation. Brain Behav Immun, 2025. 129: p. 935-947.