| Abstract No.: | A-B1042 |
| Country: | Canada |
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| Title: | ALTERATIONS IN GAMMA EEG ACTIVITY AND THALAMOCORTICAL EVOKED RESPONSES IN THE RAT BARREL CORTEX DURING ISOFLURANE ANESTHESIA. |
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| Authors/Affiliations: | 1 Sean Reed*; 2 Gilles Plourde; 2 Porlier Chantale; 1 Christine Werk; 1 Andrew Chapman;
1 Concordia University, Montreal, QC, Canada; 2 McGill University, Montreal, QC, Canada
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| Content: | Objective: Gamma-frequency (40-80 Hz) EEG rhythms reflect a functional state associated with consciousness and may contribute to the integration of sensory representations. We have shown previously that anesthetic-induced unconsciousness in humans is associated with a marked reduction of gamma activity evoked by auditory stimuli. In the present study, we have investigated alterations in gamma oscillations in the barrel cortex of the rat to determine how spontaneous and evoked gamma rhythms are altered by precisely controlled concentrations of isoflurane, and how these alterations are related to reductions in thalamocortical evoked synaptic responses. Materials and Methods: Bipolar stimulating electrodes were chronically implanted under electrophysiological control in the ventroposteromedial (VPM) thalamic nucleus, and in the ipsilateral barrel cortex. Rats were placed in an air-tight chamber for exposure to isoflurane concentrations of 0, 0.7, 1.1, 1.5 vol% (measured with a gas analyzer; 20 min. equilibration). The righting reflex was assessed and recordings of spontaneous EEG and field EPSPs evoked by thalamic stimulation (50 to 500 μA; single pulses or short 10 and 40 Hz trains) were recorded at each concentration. Results: The 1.1 and 1.5% isoflurane levels were associated with loss of righting reflex and with reductions in synaptic responses to thalamic stimulation. The EEG at these concentrations revealed a reduction in low-amplitude gamma-frequency activity. This activity was suppressed during slow surface-negative deflections that may reflect widespread neuronal hyperpolarization. At the 1.5% concentration, the spontaneous EEG also showed brief periods of large-amplitude irregular activity that contained a clear gamma component. Conclusions: These results show disruptions of gamma oscillations during isoflurane anesthesia in vivo, and suggest that there is concurrent modulation of inputs to barrel cortex mediated by thalamocortical alterations. |
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