Synchrony of the Rat Medial Prefrontal Cortex Network During Isoflurane Anaesthesia

摘要

In the anaesthetized rat, the membrane potential of the prefrontal cortex (PFC) fluctuates between two states of polarization: the up- and down-states. The PFC network strongly governs activity in its target areas such as various basal ganglia structures. The influence of anaesthesia on network dynamics in the prelimbic cortex will therefore have direct consequences for the activity profile of the output structures. In order to investigate the effects of isoflurane anaesthesia on network activity ofthe PFC, rats were anaesthetized with isoflurane of which the concentration was varied between 1.25 and 2.25%. Local EEG and single-unit activity were recorded simultaneously. At baseline levels (1.75%), isoflurane anaesthesia induced up-state transitions in the prelimbic cortex visible in the local EEG signal. The up-state deflections in the EEG were determined as reflections of clustered firing of individual prelimbic neurons. 2.25% isoflurane strongly reduced the up-state frequency whereas 1.25% isoflurane allowed the network to shift to a continuous activity mode. These results show that neuronal activity in the medal PFC and therefore its target structures is highly dependent on the level of isoflurane anaesthesia. Considering the similarity between the synaptic targets of isoflurane by which surgical anaesthesia is maintained and the mechanisms involved in initiation, maintenance and cessation of up-states, the up- and down-state fluctuations are a direct result of anaesthesia.