Effects of propofol on nonlinear parameters of EEG in the rat
AIM:To investigate the effects of propofol on electroencephalogram (EEC) approximate entropy (ApEn) and correlation dimension (D2) in the rat. METHODS: Forty-eight male Sprague-Dawley rats were divided into 4 groups randomly (n = 12), whose EEGs were recorded bipolarly with pairs of epidural electrodes in the left and right parietal cortices, frontal cortices, occipital cortices and ventral posteromedial thalamic nucleus (VPM) respectively. Anesthetic concentration of propofol was started at 400 μg/(kg · min) and then rised in four increments to 900 μg/(kg · min) while the rats were breathing spontaneously. A 10 min period was allowed at each concentration level. Calculated and compared interhemispheric EEGs ApEn and D2 of different encephalic region at different concentration level. And in all the rats the loss of righting reflex and the loss of tail-clamped reflex as a function of anesthetic concentration was tested a week before the animals were subjected to be placed the epidural electrodes. RESULTS: EEG ApEn and D2 of parietal cortices, frontal cortices, occipital cortices and thalamic VPM dose-dependently decreased as propofol concentration increased. ApEn and D2 of all the encephalic region fell below the awake baseline at 600 μg/(kg · min) and 900 μg/(kg · min) anesthetic concentration that also abolished the righting reflex and the tail-clamped reflex respectively. CONCLUSION: Propofol dose-dependently decrease the functional states of parietal cortices, frontal cortices, occipital cortices and thalamic VPM, and ApEn and D2 are both sensitive correlates of different anesthetic effects of propofol.
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