Alterations in Long‐term Seizure Susceptibility and the Complex of PSD‐95 with NMDA Receptor from Animals Previously Exposed to Perinatal Hypoxia

Abstract

Summary:Purpose: 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 ). Here we studied the effect of perinatal hypoxia on protein interactions involving PSD-95 and the NM-DAR, 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. Key Words: CREB-Longterm encephalopathy-NMDA receptor-PentylenetetrazolPerinatal hypoxia-PSD-95.Hypoxic encephalopathy is the most common cause of neonatal seizures and is associated with an increased risk of epilepsy in the later life (1). Neonatal rats exposed to transient global hypoxia on postnatal days 10-12 (P10-12) exhibited spontaneous electrographic and behavioral seizures that resulted in ...

Learning and memory disabilities in IUGR babies: Functional and molecular analysis in a rat model

“…Abnormally reduced PSD95 expression impairs activity‐dependent synaptic stabilization (Ehrlich, Klein, Rumpel, & Malinow, 2007), whereas PSD95 overexpression increases the excitatory to inhibitory synapses ratio and alters dendritic arbor development (Bustos et al., 2014; Prange, Wong, Gerrow, Wang, & El‐Husseini, 2004). PSD95 was dramatically reduced in the hippocampus of IUGR rats, similar to what has been described in animals exposed to perinatal hypoxia which also displayed impaired hippocampal maturation and deficits in spatial learning and memory (Chen et al., 2006, 2007). Abnormal PSD95 expression has also been associated with autism spectrum disorders in humans and animal models (Keith & El‐Husseini, 2008; Tsai et al., 2012), and these disorders have also been related to IUGR (Leonard et al., 2008; Walker et al., 2015).…”

“…Synaptophysin is a presynaptic protein involved in synaptic vesicle biogenesis and trafficking that increases in parallel with the formation of synapses and is frequently used as an indicator of total synaptic vesicles pools (Valtorta et al., 2004). It is known that positive stimuli such as physical exercise and environmental enrichment increase synaptic proteins expression and normalize interneuron development, and are associated with improved synaptic plasticity and cognitive function (Abel & Rissman, 2013; Chen, Chen, Lei, & Wang, 1998; Chen et al., 2006; Hu, Ying, Gomez‐Pinilla, & Frautschy, 2009; Komitova et al., 2013). Therefore, it is possible that exercise inherent to water maze training might account for the synaptophysin normalization in IUGR rats after training such as what was observed in this study, and suggests that environmental management might reverse some of the synaptic changes associated with prenatal growth restriction postnatally.…”

Granulocyte-Colony Stimulating Factor Alleviates Perinatal Hypoxia-Induced Decreases in Hippocampal Synaptic Efficacy and Neurogenesis in the Neonatal Rat Brain

“…Previously, we reported that, using an animal model, experimentally perinatal hypoxia decreased pCREB and PSD-95 expression within the hippocampus (9,13). Thus, it highlights the possibility that such decreased expression could be a tentative therapeutic target for an alleviation of long-term neurological dysfunctions.…”

“…On postnatal day 9 (P9), the animals were divided into four experimental groups as follows: vehicle-control, G-CSF alone, perinatal hypoxia, and G-CSF plus perinatal hypoxia rats, respectively. The procedures for inducing perinatal hypoxia were as described previously (9,13,25). It is generally accepted that rat pups of P10 to P12 roughly correspond to a term human infant (26).…”

“…On P17, hippocampal slices (400 m) were collected and were immediately transferred to artificial cerebrospinal fluid (ACSF) in an incubating chamber featuring a humidified 95% O 2 /5% CO 2 gas at 34.0 Ϯ 0.5°C for an equilibrium period of at least 1 h (9,13,25). To obtain hippocampal CA1 region tissue, a hippocampal slice was incubated with ice-cold oxygenated ACSF and was then cut into a tissue block (0.1 ϫ 0.5 cm) within 15 s of tissue slicing.…”