Ontogeny of white matter, toll‐like receptor expression, and motor skills in the neonatal ferret

Abstract

Inflammation caused by perinatal infection, superimposed with hypoxia and/or hyperoxia, appears to be important in the pathogenesis of preterm neonatal encephalopathy, with white matter particularly vulnerable during the third trimester. The associated inflammatory response is at least partly mediated through Toll-like receptor (TLR)-dependent mechanisms. Immunohistochemistry, gene expression, and behavioral studies were used to characterize white matter development and determine TLR3 and TLR4 expression and accumulation in the neonatal ferret brain. Expression of markers of white matter development increased significantly between postnatal day (P)1 and P10 (NG2, PDGFRα) or P15 (Olig2), and either remained elevated (NG2), or decreased again at P40 (PDGFRα, Olig2). Olig2 immunostaining within the internal capsule was also greatest at P15. Myelin basic protein (MBP) immunostaining and mRNA expression increased markedly from P15 to P40 and into adulthood, which correlated with increasing performance on behavioral tests (negative geotaxis, cliff aversion, righting reflex, and catwalk gait analysis). TLR4 and TLR3 positive staining was low at all ages, but TLR3 and TLR4 mRNA expression both increased significantly from P1 to P40. Following lipopolysaccharide (LPS) and hypoxia/hyperoxia exposure at P10, meningeal and parenchymal inflammation was seen, including an increase in TLR4 positive cells. These data suggest that the neuroinflammation associated with prematurity could be modeled in the newborn ferret.

Key roles of glial cells in the encephalopathy of prematurity

“…Similar to findings in immune activation models of EoP, in a model of hypoxic‐ischemic EoP microglial reactivity and recruitment in the white matter correlated with a decrease in the number of oligodendrocyte progenitors (Falahati et al, 2013 ). Across models of the different facets of EoP not only is there an immediate and robust immune‐reactivity, but reactivity can persist into young adulthood (Galinsky, van de Looij, et al, 2020 ; Gussenhoven et al, 2018 ; Jinnai et al, 2020 ; Morin et al, 2022 ; Romantsik et al, 2022 ; Snyder et al, 2018 ; Vaes et al, 2021 ). Transcriptomics analyses have shown that microglia involved in immune‐reactive or inflammatory processes disengage from their developmental functions (Krishnan et al, 2017 ; Matcovitch‐Natan et al, 2016 ).…”

Inhibition of immunoproteasome subunit low molecular mass polypeptide 7 with ONX-0914 improves hypoxic-ischemic brain damage via PI3K/Akt signaling

“…Three physiological reflexes of newborn rats, including the cliff aversion, negative geotaxis, and righting reflexes, were tested 1 day after model establishment (PND8) [13]. The cliff aversion reaction was used to assess the ability of rodents to respond to adverse environments.…”

“…Rats were placed supine, and the time taken to move into the prone position with the front and back paws on the ground was recorded. If the time taken for the cliff aversion or negative geotaxis reflexes exceeded 20 s, the results were excluded [13].…”

Evaluating Neuroprotective Effects of Uridine, Erythropoietin, and Therapeutic Hypothermia in a Ferret Model of Inflammation-Sensitized Hypoxic-Ischemic Encephalopathy

“…The ferret is an ideal animal model to examine the long-term effects of injury on brain development and response to treatment in prematurity and asphyxia-related disease states [ 7 , 8 ]. Postnatal ferret brain development is histologically similar to the rapid brain maturation that occurs in the second half of human gestation [ 9 , 10 ]. Our group recently published a protocol utilizing lipopolysaccharide (LPS) inflammation presensitized hypoxia-ischemia plus hyperoxia (HIH) to model hypoxic-ischemic (HI) brain injury in the near-term (P17) ferret [ 11 ].…”