Effects Of Propofol On Sensory Information Processing In Mouse Cerebellar Molecular Layer And Granule Cell Layer

[Purpose]Propofol is a global central nervous system depressant, which decreases information processing in the neocortex in a dose-dependent manner under in vivo conditions. However, the effects of propofol on the sensory information processing in cerebellar cortical molecular layer in living animals are currently unknown. In the present study, we examined the effects of propofol on sensory stimulation-evoked field potential responses in the cerebellar molecular layer of urethane-anesthetized mice by electrophysiological and pharmacological methods.[Methods]Adult （6-8-week old） ICR mice were anesthetized by intraperitoneal injection of urethane （1.3 g/kg body weight）, then tracheotomized to avoid respiratory obstruction, and fixed on a custom-made stereotaxic frame. After a watertight chamber was created, a 1-1.5 mm craniotomy was drilled to expose the cerebellar surface corresponding to Crus II （inferior semilunar lobule）. The surface of brain was constantly superfused with oxygenated ACSF at 0.4 ml/min with a peristaltic pump. The rectal temperature was monitored, and maintained at 37.0 ± 0.2℃. Local field potential recordings were performed with an Axopatch-200B amplifier （Molecular Devices, Foster City, CA）. The potentials were acquired through a Digidata 1440 series analog-to-digital interface on a personal computer using Clampex 10.3 software. Recording electrodes were filled with ACSF and with resistances of 3-5 MΩ. Propofol and gabazine were bought from Sigma-Aldrich （Shanghai, China）. All chemicals were applied to the cerebellar surface at 0.4 ml/min in ACSF. Electrophysiological data were analyzed using Clampfit 10.3 software. All data are expressed as the mean ± S.E.M. Differences between the mean values recorded under control and test conditions were evaluated with the Student’s paired t-test using SPSS （Chicago, IL） software. P values below 0.05 were considered to indicate a statistically significant difference between experimental groups.[Results]（1） Cerebellar surface perfusion of propofol （10-1000 μM） significantly inhibited sensory stimulation evoked GABAergic component （PI） of the response, which exhibited decreases in amplitude and area under the curve （AUC）, but increases the rising time and the decay time of P1.（2） Administration of propofol significantly enhanced the sensory stimulation evoked excitatory component （N1）, which exhibited increases in the amplitude and AUC, and accompanied with increases in the rising time and the decay time.（3） In the presence of GABAa receptor antagonist, gabazine （20 μM）, propofol significantly increased the amplitude and the AUC of the excitatory postsynaptic component （N2）.[Conclusion]Our results indicate that propofol modulates GABAA receptor activity, which induces a competitive inhibition of the sensory stimulation evoked GABAergic response and an enhancement of PF excitatory response in cerebellar molecular layer in cerebellar cortex in vivo in mice.[Purpose]Propofol is a central nervous system depressant, which decreases neuronal activity via activation of GABAa and glycine receptors. We recently found that propofol induced an inhibition of facial stimulation evoked GABAergic response, but facilitated the parallel fiber excitatory inputs in cerebellar molecular layer and onto Purkinje cells（PCs） in vivo in mice, suggesting that propofol modulated granule cell laryer transfer sensory information in living animals. Therefore, we here examined the effects of propofol on facial stimulation-evoked field potential responses in the cerebellar granule cell layer in urethane-anesthetized mice by electrophysiological and pharmacological methods.[Methods]Adult（6-8-week old） ICR mice were anesthetized by intraperitoneal injection of urethane（1.3 g/kg body weight）, then tracheotomized to avoid respiratory obstruction, and fixed on a custom-made stereotaxic frame. After a watertight chamber was created, a 1-1.5 mm craniotomy was drilled to expose the cerebellar surface corresponding to Crus II （inferior semilunar lobule）. The surface of brain was constantly superfused with oxygenated ACSF at 0.4 ml/min with a peristaltic pump.The rectal temperature was monitored, and maintained at 37.0 ± 0.2°C. Local field potential recordings were performed with an Axopatch-200 B amplifier（Molecular Devices, Foster City, CA）. The potentials were acquired through a Digidata 1440 series analog-to-digital interface on a personal computer using Clampex 10.3 software.Recording electrodes were filled with ACSF and with resistances of 3-5 MΩ. Propofol and gabazine were bought from ISigma-Aldrich（Shanghai, China）. All chemicals were applied to the cerebellar surface at 0.4 ml/min in ACSF. Electrophysiological data were analyzed using Clampfit 10.3 software. All data are expressed as the mean ±S.E.M. Differences between the mean values recorded under control and test conditions were evaluated with the Studenf s paired t-test using SPSS（Chicago, IL）software. P values below 0.05 were considered to indicate a statistically significant difference between experimental groups.[Results]（1） Cerebellar surface perfusion of propofol (50-1000 μM。significantly facilitated the air-puff stimuladon（60 ms, 60 psi） on ipsilateral whisker pad evoked field potential Ksponses in mouse cerebellar granule cell layer, which exhibited increases in half-width and area under the curve（AUG） of stimulus onset responses（Ron）, but without significantly changed the amplitude and rise tau of Ron.（2） Propofbl also induced significant increases in amplitude of stimulus offset response（Roaf） and the value of R_off/H_on. The propofol-induced increase in AUC of facial stimulation-evoked Ron was dose-dependent with the 50% effective concentration(EC₅₀) was 242.4 mM.（3） Application of GABAa receptor antagonist, gabazine （20 μM） induced significant increases in amplitude, half-width, rise tau and AUC of Ron, which were further increased by additional application of propofol （300μM）.（4） Application of N-methykD-aspartate（NMDA） receptor blocker,D-APV （250μM） not only significantly attenuated half-width, AUC of R_on and amplitxide of R_off,but also abolished the propofo-induced enhancetnent of facial stimulation evoked responses.In addition, blocking NMDA receptors activity did not chang the amplitude of Ron.[Conclusion]These resuits indicate that propofol modulates NMDA receptor activity,resulting in an enhancement of facial stimulation-evoked responses in cerebellar granule cell layer, These results explained the tnechanisms of facial stimulation induced an enhancement of parallel fiber excitatory inputs in cerebellar molecular layer and onto PCs in vivo in mice.