J Korean Neurosurg Soc.  2015 Jul;58(1):22-29. 10.3340/jkns.2015.58.1.22.

Cognitive Dysfunction and Hippocampal Damage Induced by Hypoxic-Ischemic Brain Injury and Prolonged Febrile Convulsions in Immature Rats

• Byeon JH
• Kim GH
• Kim JY
• Sun W
• Kim H
• Eun BL

• KMID: 2067100
• DOI: http://doi.org/10.3340/jkns.2015.58.1.22

Abstract

OBJECTIVE
Perinatal hypoxic-ischemic encephalopathy (HIE) and prolonged febrile seizures (pFS) are common neurologic problems that occur during childhood. However, there is insufficient evidence from experimental studies to conclude that pFS directly induces hippocampal injury. We studied cognitive function and histological changes in a rat model and investigated which among pFS, HIE, or a dual pathologic effect is most detrimental to the health of children.
METHODS
A rat model of HIE at postnatal day (PD) 7 and a pFS model at PD10 were used. Behavioral and cognitive functions were investigated by means of weekly open field tests from postnatal week (PW) 3 to PW7, and by daily testing with the Morris water maze test at PW8. Pathological changes in the hippocampus were observed in the control, pFS, HIE, and HIE+pFS groups at PW9.
RESULTS
The HIE priming group showed a seizure-prone state. The Morris water maze test revealed a decline in cognitive function in the HIE and HIE+pFS groups compared with the pFS and control groups. Additionally, the HIE and HIE+pFS groups showed significant hippocampal neuronal damage, astrogliosis, and volume loss, after maturation. The pFS alone induced minimal hippocampal neuronal damage without astrogliosis or volume loss.
CONCLUSION
Our findings suggest that pFS alone causes no considerable memory or behavioral impairment, or cellular change. In contrast, HIE results in lasting memory impairment and neuronal damage, gliosis, and tissue loss. These findings may contribute to the understanding of the developing brain concerning conditions caused by HIE or pFS.

Keyword

Hypoxic-ischemic encephalopathy; Febrile seizure; Epilepsy; Hippocampal injury

MeSH Terms

Animals
Brain Injuries*
Brain*
Child
Epilepsy
Gliosis
Hippocampus
Humans
Hypoxia-Ischemia, Brain
Memory
Models, Animal
Neurons
Rats*
Seizures, Febrile*

Figure

• 

  Fig. 1 Duration of seizures. The total seizure duration was significantly longer in the HIE+pFS group (*p<0.05; t-test, p=0.032) (A). In the HIE+ pFS group, all types of seizures occurred more frequently than in the pFS-only group; however, only rolling (Mann-Whitney test, p=0.009) and tonic flexion (Mann-Whitney test, p=0.009) had a statistically significant difference (B). Data are expressed as the mean±standard error of the mean. pFS : prolonged febrile seizures, HIE : hypoxic-ischemic encephalopathy, HLC : hind-limb clonus, GTC : generalized tonic clonic seizures.

• 

  Fig. 2 Whole traveled distance and central entries in the open field activities test. The whole traveled distance in the open field tests were not different between groups (A) (Kruskal-Wallis test, p>0.005). The entries into the central zone were identical between groups (B) (Kruskal-Wallis test, p>0.005). Cont : control, pFS : prolonged febrile seizures, HIE : hypoxic-ischemic encephalopathy.

• 

  Fig. 3 Morris water maze test (invisible test). On the first 2 days of testing, there was no difference in the escape latency periods between the groups; however, after day 2, there were distinct differences in the escape latency periods to the hidden platform between the different groups. The HIE and HIE+pFS groups showed poorer performances than the pFS and control groups (*p<0.05; Kruskal-Wallis test, third day p=0.002, fourth day p<0.001, fifth day p=0.005). Cont : control, pFS : prolonged febrile seizures, HIE : hypoxic-ischemic encephalopathy.

• 

  Fig. 4 Morphology of the ipsilateral hippocampus. Immunofluorescence of the ipsilateral rat hippocampus (20 µm thickness) at PW9. The nucleus is labeled with Hoechst (blue), astrocytes with GFAP (green), and neurons with NeuN (red). The ipsilateral hippocampus had shrunk and the NeuN signals decreased in the HIE and HIE+pFS groups (A). The size of the ipsilateral hippocampus was smaller in the HIE and HIE+pFS groups than in the control group (B) (*p<0.05; Kruskal-Wallis test : Cont vs. HIE, p=0.044; Cont vs. HIE+pFS, p=0.009). Cont : control, pFS : prolonged febrile seizures, HIE : hypoxic-ischemic encephalopathy, PW9 : postnatal week 9, GFAP : glial fibrillary acidic protein, NeuN : neuronal specific nuclear protein.

• 

  Fig. 5 Image of the ipsilateral hippocampus CA1. Images were immunostained with the following neuronal markers : NeuN/glial marker, GFAP/nucleus marker, Hoechst (A). The number of NeuN-positive cells decreased in the HIE and HIE+pFS groups compared with the pFS and control groups (B) (Kruskal-Wallis test : Cont vs. HIE, p=0.001; Cont vs. HIE+pFS, p=0.000; pFS vs. HIE, p=0.018; pFS vs. HIE+pFS, p=0.001). The number of GFAP-positive cells was markedly increased in the CA1 of the HIE and HIE+pFS groups (C) (*p<0.05; Kruskal-Wallis test : Cont vs. HIE+pFS, p=0.000; pFS vs. HIE+pFS, p=0.000; Cont vs. HIE, p=0.000; pFS vs. HIE, p=0.000). Cont : control, pFS : prolonged febrile seizures, HIE : hypoxic-ischemic encephalopathy, NeuN : neuronal specific nuclear protein, GFAP : glial fibrillary acidic protein.

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