Effects Of General Anesthetics On The Neural Activity In Mouse Hippocampus

Our study was to investigate effects of three general anesthetic agents, Pentobarbital sodium, Urethane, and Ketamine, on neuronal discharges of hippocampal CA1 region in mice by using the multi-channel recording technique. To study mechanisms of the anesthetic agents for the central neural system, we compared the local field potentials and the neuronal firing activities before and after injections.The results from Pentobarbital sodium showed that the amplitudes of local field potentials were obviously lower after injection than that in the normal state, and there were few rhythmic activities, suggested that local field potentials were intensively suppressed. Immediately after injection, firing of both pyramidal cells and interneurons was suppressed to some extent and even stopped. The firing rates did not rise to normal level until the mice recovered from the anesthetic state. During the deep anesthesia, mice lost consciousness, and there was no response to touch stimulations.After Urethane injection, local field potentials did not change significantly except that the amplitudes were suppressed slightly. Theta rhythms and ripple oscillations occurred alternately during anesthesia. Most of neuronal firing rates were suppressed, few were raised, and others did not change significantly. During deep anesthesia, mice remained immobile except for subtle movements, and there were weak responses to touch stimulations.After Ketamine injection, the activity local field potentials was enhanced, the high frequency component increased, and there were big rhythmic field potentials by turns at times. The effect of Ketamine on the firing rates was sophisticated, during deep anesthesia: some neurons increased their firing rates; whereas, some decreased. In earlier time of anesthetic, most mice showed self-motion with shaking heads. The extremities were titanic, and there was no response to touch stimulations.Our results suggested that Pentobarbital sodium inhibited neuronal firing through GABA_A receptors, therefore the local field potentials and neural firing rates were inhibited; Urethane acted on many kinds of receptors including inhibitory and excitory ones, so the local field potentials did not change significantly; however, because of the multiform receptors on the neurons, the changing of firing rates to different neurons were not the same; Ketamine mainly acted on the NMDA receptors, therefore the local field potentials and neural firing rates were enhanced, and most neural firing rates would be increased.In conclusion, there were different effects of three anesthetics on hippocampal neuronal firing rates and local field potentials, suggesting that Pentobarbital sodium, Urethane, and Ketamine had different mechanisms underlying neural firing activities.