Enflurane-induced burst firing of hippocampal CA 1 neurones. In vitro studies using a brain slice preparation

Enflurane can produce seizure activity in the cortical EEG, in vivo, at concentrations associated with surgical anaesthesia. The present study was designed to determine whether this seizure-like burst activity could occur in isolated cortical neurones. Enflurane altered synaptic transmission in the in vitro rat hippocampal slice preparation and produced seizure-like burst discharges of CA 1 neurones, at vapour concentrations equivalent to those obtained during anaesthesia (2-6 vol%; 0.5-1.5 mmol litre-1). Burst discharges occurred both spontaneously and in response to stimulation of stratum radiatum fibres in the CA 1 pyramidal region, but not in the dentate area. Low concentrations of enflurane (approx. 0.75 mmol litre-1), decreased the field potential responses of CA 1 neurones; however, dentate granule neurone responses were increased. Input/output analyses of field excitatory post-synaptic potential (EPSP) and population spike amplitudes revealed that the enflurane-induced depression of field potential responses was associated with decreases in synaptic input, whereas burst activity resulted from a decrease in the threshold of CA 1 neurones.