Alterations in long-term seizure susceptibility and the complex of PSD-95 with NMDA receptor from animals previously exposed to perinatal hypoxia.
OBJECTIVE
Perinatal hypoxia is an important cause of brain injury in the newborn and has consequences that are potentially devastating and life-long, such as an increased risk of epilepsy in later life. The postsynaptic density (PSD) is a cytoskeletal specialization involved in the anchoring of neurotransmitter receptors and in regulating the response of postsynaptic neurons to synaptic stimulation. The postsynaptic protein PSD-95 binds to the N-methyl-D-aspartate receptor (NMDAR) subunit, and hence activates cascades of NMDAR-mediated events, such as cyclic adenosine monophosphate (cAMP)-responsive element binding protein phosphorylation at serine-133 (pCREB(Serine-133)). Here we studied the effect of perinatal hypoxia on protein interactions involving PSD-95 and the NMDAR, as well as pCREB(Ser-133) expression at an age when the animals show increased seizure susceptibility.


METHODS
Rats were assigned randomly to the control rats or the rats exposed to transient global hypoxia at postnatal day 10 (P10). At P45, some rats from both groups were treated with pentylenetetrazol (PTZ) intraperitoneally to test the seizure threshold, and others were studied for neuronal loss, pCREB(Serine-133), PSD-95, and NMDAR expressions in the midbrain, temporal cortex, and hippocampal CA1 subfield by using immunohistochemistry, co-immunoprecipitation, and immunoblotting techniques, respectively.


RESULTS
The rats with prior exposure to perinatal hypoxia exhibited increased seizure susceptibility to PTZ, compared with the control rats. Associated with this long-term change in seizure susceptibility, selective neuronal loss was observed in the midbrain region while pCREB(Ser-133) expression was reduced in the midbrain, temporal cortex, and hippocampal CA1 subfield. Perinatal hypoxia led to a decrease in PSD-95 expression in the both midbrain and hippocampal CA1 subfield, with the exception of temporal cortex. Furthermore, the association between PSD-95 and NMDAR subunits (NR1, NR2A, and NR2B) in the hippocampal CA1 was also markedly altered by perinatal hypoxia.


CONCLUSIONS
This study demonstrates that the decrease in several protein complexes that are essential components of the postsynaptic apparatus is associated with the observed increase in seizure susceptibility in adult rats with prior exposure to perinatal hypoxia. The results indicate that reductions in PSD-95 expression, PSD-95 binding of NMDAR subunits, and subsequent NMDAR-mediated CREB phosphorylation, particularly in hippocampal CA1, are long-term consequences of perinatal hypoxia and may, at least in part, contribute to perinatal hypoxia-induced reduction in seizure threshold.
Chen
Wu-Fu
WF
Graduate Institute of Medical Sciences, National Defense Medical Center, Taipei, Taiwan.
Chang
Hong
H
Huang
Li-Tung
LT
Lai
Ming-Chi
MC
Yang
Chun-Hwa
CH
Wan
Tz-Hisung
TH
Yang
San-Nan
SN
D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D004195:Disease Models, Animal; D004198:Disease Susceptibility; D000076122:Disks Large Homolog 4 Protein; D006624:Hippocampus / Q000378:metabolism; D002534:Hypoxia, Brain / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology; D015151:Immunoblotting; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism* / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D008636:Mesencephalon / Q000378:metabolism; D010433:Pentylenetetrazole; D010766:Phosphorylation; D011485:Protein Binding; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism* / Q000502:physiology; D012307:Risk Factors; D012640:Seizures / Q000139:chemically induced / Q000209:etiology* / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013702:Temporal Lobe / Q000378:metabolism
D017362:Cyclic AMP Response Element-Binding Protein; D000076122:Disks Large Homolog 4 Protein; C501449:Dlg4 protein, rat; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D016194:Receptors, N-Methyl-D-Aspartate; D012694:Serine; D000242:Cyclic AMP; D010433:Pentylenetetrazole