Loss of interneurons and disruption of perineuronal nets in the cerebral cortex following hypoxia-ischaemia in near-term fetal sheep

Tania M Fowke,Justin M Dean,Robert Galinsky,Joanne O Davidson,Jaya D Prasad,Laura Bennet,Alistair J Gunn,Rashika N Karunasinghe,Guido Wassink

doi:10.1038/s41598-018-36083-y

Tania M Fowke, Justin M Dean + Show 7 more

Open Access

https://doi.org/10.1038/s41598-018-36083-y

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Abstract

Hypoxia-ischaemia (HI) in term infants is a common cause of brain injury and neurodevelopmental impairment. Development of gamma-aminobutyric acid (GABA)ergic circuitry in the cerebral cortex is a critical event in perinatal brain development. Perineuronal nets (PNNs) are specialised extracellular matrix structures that surround GABAergic interneurons, and are important for their function. Herein, we hypothesised that HI would reduce survival of cortical interneurons and disrupt PNNs in a near-term fetal sheep model of global cerebral ischaemia. Fetal sheep (0.85 gestation) received sham occlusion (n = 5) or 30 min of reversible cerebral ischaemia (HI group; n = 5), and were recovered for 7 days. Expression of interneurons (glutamate decarboxylase [GAD]+; parvalbumin [PV]+) and PNNs (Wisteria floribunda agglutinin, WFA) was assessed in the parasagittal cortex by immunohistochemistry. HI was associated with marked loss of both GAD+ and PV+ cortical interneurons (all layers of the parasagittal cortex and layer 6) and PNNs (layer 6). The expression and integrity of PNNs was also reduced on surviving GAD+ interneurons. There was a trend towards a linear correlation of the proportion of GAD+ neurons that were WFA+ with seizure burden (r2 = 0.76, p = 0.0534). Overall, these data indicate that HI may cause deficits in the cortical GABAergic system involving loss of interneurons and disruption of PNNs, which may contribute to the range of adverse neurological outcomes following perinatal brain injury.

Highlights

Perinatal hypoxic-ischemia (HI) is a common trigger of brain injury in term infants, being responsible for approximately 1–3 cases of moderate to severe encephalopathy per 1,000 live births, and is associated with a high risk of death or disability[1]
Disrupted GABAergic signalling in the cerebral cortex is thought to contribute to the neurophysiological and cognitive impairments observed in numerous neurodevelopmental disorders, and there is limited preclinical and human evidence of damage to cortical GABAergic interneurons after perinatal brain injury[24,25,26,27]
These data suggest that perinatal HI may cause deficits in the cortical GABAergic system that involve, at least in part, disruption of Perineuronal nets (PNNs) that are important for cortical inhibitory network function and regulation of CNS plasticity

Summary

Introduction

Perinatal hypoxic-ischemia (HI) is a common trigger of brain injury in term infants, being responsible for approximately 1–3 cases of moderate to severe encephalopathy per 1,000 live births, and is associated with a high risk of death or disability[1]. A major neuropathology observed following HI at term involves parasagittal watershed zone injury with neuronal loss, and damage to the underlying subcortical white matter[2,3,4,5,6,7,8,9]. This pattern of injury is strongly associated with adverse neurological outcomes, including cerebral palsy, cognitive delay, and epilepsy[10,11,12,13,14]. In the present study we tested the hypothesis that cortical PNNs are associated with interneurons in the near-term fetal sheep, and that global cerebral ischaemia is associated with loss of both cortical interneurons and PNNs

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