# The Ovine Brain as a Model for Human Neurodevelopment: Immunohistochemical Profiling of Brain Maturation Markers in Preterm Lambs

## TL;DR

This study shows that lamb brain development mirrors human patterns, making lambs a useful model for studying the effects of preterm birth on neurodevelopment.

## Contribution

The study provides a detailed immunohistochemical comparison of brain maturation in preterm and term lambs, supporting their use as a model for human neurodevelopment.

## Key findings

- 140-day preterm lambs showed higher positivity for interneurons, synaptic vesicles, and myelin compared to 100-day lambs.
- Cerebellar neurons were more developed in 140-day lambs, suggesting antero-posterior brain maturation similar to humans.
- No significant differences in microglia were observed between the two preterm groups.

## Abstract

Preterm birth is known to severely impact the neurological development of newborns with long‐lasting complications and higher risks of neurological disorders. Sheep (Ovis aries) is well known as a pre‐clinical model in therapeutic studies, such as extra‐uterine support. The aim of our study was to investigate the relevance of the lamb as a pre‐clinical model for preterm birth when cortical maturation of preterm and term lamb is addressed. Cesarean sections were performed on time‐dated pregnant ewes to obtain 13 lambs at 100 days and 140 days of pregnancy each (corresponding to 24 and 36 weeks of pregnancy in humans, respectively). Brains were collected and separated in frontal lobe, temporo‐parietal lobe, occipital lobe, and cerebellum. Immunohistochemistry staining was used for each brain area by targeting neurons, interneurons, synaptic vesicles, oligodendrocytes, myelin, astrocytes, and microglia. Quantifications were normalized by the surface area of analysis. Overall, 140‐days late preterm lambs have significantly higher mean positivity for interneurons, synaptic vesicles, oligodendrocytes, astrocytes, and myelin than 100‐days extremely preterm lambs. Similarly, significantly higher mean positivity for neurons was found in the cerebellum of 140‐days term lambs. No significant difference was observed regarding microglia. Based on the cellular and structural markers used in this study, brain development in lamb seems to follow an antero–posterior direction similarly to what was reported in humans. Further studies with more specific markers and in‐depth analysis will allow for a more accurate and exhaustive description of brain development in lamb.

Prematurity negatively impacts brain development, especially at early stage of gestation. We provide a characterization and comparisons of the neurodevelopment of extreme and late preterm lamb through immunohistochemistry of targets known to be impacted by prematurity. Our results found similarity between human and lamb brain development in the context of prematurity, supporting the lamb as a valid model for neurodevelopmental studies.