Rat model of influenza-associated encephalopathy (IAE): studies of electroencephalogram (EEG) in vivo

Influenza-associated encephalopathy (IAE) is characterized by severe neurological complications during high-grade fever with high morbidity and mortality in children. The major neurological complications during high-grade fever include convulsive seizures, loss of consciousness, neuropsychiatric behavior (hallucination, meaningless speech, disorientation, laughing alone); high voltage amplitude slow waves and the occurrence of theta oscillation are depicted on the electroencephalogram (EEG) in the IAE patients. At the early phase of the disease, the cytokines levels increase in severe cases. To understand the neuronal properties in the CNS leading to these neurological complications in IAE patients, we recorded EEG signals from the hippocampus and cortex of rats infected with influenza A/WSN/33 H1N1 virus (IAV) strain. Abnormal EEG activities were observed in all infected rats under anesthesia, including high voltage EEG burst amplitude and increased EEG spikes in the early phase (8 h-day 2) of infection, and these increases at the early phase were in parallel with a significant increase level of interleukin-6 (IL-6) in the serum. When the infected rats were heat-stressed by elevating the rat body core temperature to 39-41 degrees C, these abnormal EEG activities were enhanced, and the oscillation pattern shifted in most of rats from slow bursting waves (<1 Hz) to theta oscillation (3-6 Hz). These results indicate that the abnormal EEG activities in IAE patients could be well reproduced in anesthetized IAV infected rats under hyperthermia, hence this animal model will be useful for further understandings the mechanism of neuronal complications in IAE patient during high-grade fever.