Antenatal dexamethasone after asphyxia increases neural injury in preterm fetal sheep.

BACKGROUND AND PURPOSE: Maternal glucocorticoid treatment for threatened premature delivery dramatically improves neonatal survival and short-term morbidity; however, its effects on neurodevelopmental outcome are variable. We investigated the effect of maternal glucocorticoid exposure after acute asphyxia on injury in the preterm brain. METHODS: Chronically instrumented singleton fetal sheep at 0.7 of gestation received asphyxia induced by complete umbilical cord occlusion for 25 minutes. 15 minutes after release of occlusion, ewes received a 3 ml i.m. injection of either dexamethasone (12 mg, n = 10) or saline (n = 10). Sheep were killed after 7 days recovery; survival of neurons in the hippocampus and basal ganglia, and oligodendrocytes in periventricular white matter were assessed using an unbiased stereological approach. RESULTS: Maternal dexamethasone after asphyxia was associated with more severe loss of neurons in the hippocampus (CA3 regions, 290 ± 76 vs 484 ± 98 neurons/mm(2), mean ± SEM, P<0.05) and basal ganglia (putamen, 538 ± 112 vs 814 ± 34 neurons/mm(2), P<0.05) compared to asphyxia-saline, and with greater loss of both total (913 ± 77 vs 1201 ± 75/mm(2), P<0.05) and immature/mature myelinating oligodendrocytes in periventricular white matter (66 ± 8 vs 114 ± 12/mm(2), P<0.05, vs sham controls 165 ± 10/mm(2), P<0.001). This was associated with transient hyperglycemia (peak 3.5 ± 0.2 vs. 1.4 ± 0.2 mmol/L at 6 h, P<0.05) and reduced suppression of EEG power in the first 24 h after occlusion (maximum -1.5 ± 1.2 dB vs. -5.0 ± 1.4 dB in saline controls, P<0.01), but later onset and fewer overt seizures. CONCLUSIONS: In preterm fetal sheep, exposure to maternal dexamethasone during recovery from asphyxia exacerbated brain damage

Examples of EEG patterns in preterm fetal sheep.

<p>Panel A shows an example of normal EEG activity prior to asphyxia, showing the normal mixed EEG amplitude and frequency. Panel B shows an example from the asphyxia-saline group, 4 hours after asphyxia, showing significant suppression of EEG amplitude and the presence of repetitive sharp and fast wave transients <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077480#pone.0077480-Bennet2" target="_blank">[39]</a>. Panel C shows an example from the asphyxia-DEX group, 4 hours after asphyxia, showing the presence of interictal high amplitude slow-waves and fast waves. Panel D shows an example of a seizure-like event in the asphyxia-DEX group, 3 hours after asphyxia, characterised as slow-wave activity ending in a high amplitude burst. All figures are continuous raw data from individual animals.</p

Time course of changes in% time/h of prolonged slow wave activity after asphyxia-saline (open circles) and asphyxia-DEX (closed circles).

<p>Data are one hour means ± SEM up to 24 h then 24 h averages until the end of experiment. *P&lt;0.01 asphyxia-DEX vs. asphyxia-saline.</p

Photomicrographs showing examples of immunohistochemically stained neurons (NeuN) in the Caudate Nucleus (A-C), and in the CA3 region of the hippocampus (D-F).

<p>In Plates G to R show photomicrographs from periventricular white matter (PVWM), including all oligodendrocytes (Olig-2, G-I), immature to mature oligodendrocytes (CNPase, J-L), proliferating cells (Ki-67, M-O) and microglia (Iba-1, P-R) from sham-control, asphyxia-saline and asphyxia-DEX fetuses. Arrows show examples of labelled cells. Note the reduction in number of neurons and oligodendrocytes after asphyxia and further loss with DEX treatment, and marked induction of microglia in the PVWM. Scale bar is 40 µm.</p

Time course of changes in mean arterial blood pressure (MAP, mmHg), and EEG power (dB) from 24 hours before, until 7 days after occlusion (occlusion data not shown) in the asphyxia-saline (open circles) and asphyxia-DEX (closed circles) groups.

<p>Data are one hour means ± SEM. *P&lt;0.05 asphyxia-DEX vs. asphyxia-saline, # P&lt;0.05, both occlusion groups vs. baseline.</p

Photomicrographs of coronal sections of a preterm fetal sheep brain showing the fields used for analysis.

<p>Left panel: periventricular white matter (1) and Caudate (2) and putamen (3). Right panel: CA1-2 (1) and CA3 (2) regions of the hippocampus. Scale bars = 2.5 mm.</p