Slamin, M. M. | Search bioRxiv

bioRxiv2026

Cx3cr1-BAC-CRE-mediated knockout of toll-like receptor 4 alters mouse communicative behaviors, microglial morphology, and engulfment of synaptic material

Microglia, the tissue resident immune cells of the central nervous system, are critical regulators of postnatal neural circuit refinement. Innate immune receptors on microglia such as toll-like receptor 4 (TLR4) are best characterized in the context of inflammation, however, endogenous TLR4 ligands are generated during typical developmental processes. Here, we investigated whether TLR4 signaling in CX3CR1-expressing myeloid cells contributes to microglial morphology, synaptic engulfment, and behavioral development in mice under basal conditions. TLR4 conditional knockout altered maternal separation-induced ultrasonic vocalizations without impacting social preference or anxiety-like behaviors. Conditional TLR4 knockout in CX3CR1-expressing myeloid cells markedly increased microglial ramification and cell volume within the paraventricular nucleus (PVN) of the hypothalamus. TLR4 conditional knockout also reduced microglial engulfment of vGlut2-positive presynaptic material, while overall excitatory synapse numbers remained unchanged. Together, these findings demonstrate that TLR4 signaling in CX3CR1-expressing myeloid cells contributes to microglial morphology, presynaptic engulfment, and neonatal communicative behavior under basal conditions.

neuroscience↗

bioRxiv2025

Where's my mom? Resilient maternal preference in post-weaning male and female mice within a multi-chamber social behavior task

One of the earliest and most critical social bonds for many mammals is formed with their mother, who provides essential benefits for offspring development and survival. Growing evidence suggests that this social bond is retained even when animals gain independence, such as during the juvenile period immediately post-weaning. Here, we investigated whether juvenile (postnatal day (P)26) mice retain the ability to recognize and prefer their mothers post-weaning. We further investigated the strength of this bond using an acute immune activator. On P26, male and female C57BL/6J mice were intraperitoneally injected with the endotoxin lipopolysaccharide (LPS) or saline control (0.5 mg/kg). Four hours later, mice were subject to a five-chamber social preference task (the AGORA) containing their biological mother, a sex-matched novel mouse, a sex-matched sibling, a novel object, and an empty chamber. Our findings reveal that juvenile mice exhibit a strong maternal preference, significantly greater than chance and higher compared to any other social or non-social stimuli. While LPS exposure reduced the time spent investigating all stimuli, juvenile maternal preference was not significantly altered by LPS exposure. These effects were especially pronounced in females, while subtle shifts towards novel exploration began to emerge in males by P26. These results suggest that juvenile mice have a robust social preference for their mother that is resilient to early-life immune activation. Moreover, the novel multi-chamber task employed in the present study offered a more nuanced understanding of how social bonds evolve and vary across sex.

animal behavior and cognition↗