Etomidate enhances cerebellar CF-PC synaptic plasticity through CB1 receptor/PKA cascade in vitro in mice.

Etomidate (ET) is a widely used intravenous imidazole general anesthetic, which depresses the cerebellar neuronal activity by modulating various receptors activity and synaptic transmission. In this study, we investigated the effects of ET on the cerebellar climbing fiber-Purkinje cells (CF-PC) plasticity in vitro in mice using whole-cell recording technique and pharmacological methods. Our results demonstrated that CF tetanic stimulation produced a mGluR1-dependent long-term depression (LTD) of CF-PC excitatory postsynaptic currents (EPSCs), which was enhanced by bath application of ET (10 µM). Blockade of mGluR1 receptor with JNJ16259685, ET triggered the tetanic stimulation to induce a CF-PC LTD accompanied with an increase in paired-pulse ratio (PPR). The ET-triggered CF-PC LTD was abolished by extracellular administration of an N-methyl-(D)-aspartate (NMDA) receptor antagonist, D-APV, as well as by intracellular blockade of NMDA receptors activity with MK801. Furthermore, blocking cannabinoids 1 (CB1) receptor with AM251 or chelating intracellular Ca2+ with BAPTA, ET failed to trigger the CF-PC LTD. Moreover, the ET-triggered CF-PC LTD was abolished by inhibition of protein kinase A (PKA), but not by inhibition of protein kinase C inhibiter. The present results suggest that ET acts on postsynaptic NMDA receptor resulting in an enhancement of the cerebellar CF-PC LTD through CB1 receptor/PKA cascade in vitro in mice. These results provide new evidence and possible mechanism for ET anesthesia to affect motor learning and motor coordination by regulating cerebellar CF-PC LTD.

Etomidate Modulates the Tactile Stimulation-Evoked Field Potential Responses in Cerebellar Granule Cell Layer in vivo in Mice.

Etomidate (ET) produces sedation by binding on the γ-aminobutyric acid type A (GABAA) receptors. We previously found that ET inhibited cerebellar Purkinje cells activity via both GABAA and glycine receptors in vivo in mice, suggesting that ET modulated sensory information synaptic transmission in cerebellar cortex. In this study, we investigated the effect of ET on the sensory stimulation-evoked responses in the cerebellar granule layer (GL) in urethane-anesthetized mice, using electrophysiological and pharmacological methods. Our results showed that cerebellar surface perfusion of ET (100 µmol/L) significantly decreased amplitude and area under the curve (AUC) of the sensory stimulation-evoked excitatory component (N1) in the cerebellar GL. Application of GABAA receptor antagonist, SR95531 (20 µmol/L) significantly attenuated, but not abolished the ET-induced decrease in amplitude and AUC of facial stimulation-evoked responses. However, application of a mixture of SR95531 (20 µmol/L) and cannabinoid 1 receptor (CB1) antagonist, AM-251 (5 µmol/L), completely blocked the ET-induced decrease in amplitude and AUC of facial stimulation-evoked responses. Furthermore, application of the CB1 receptor agonist, WIN55212-2, induced a decrease in amplitude and AUC of N1 in the absence of GABAA receptors activity, as well occluded the ET-induced depression of N1. Moreover, the ET-induced changes in amplitude and AUC of N1 in absence of GABAA receptors activity were abolished by a specific protein kinase A (PKA) inhibitor, KT5720. These results indicate that ET facilitates CB1 receptors in the absence of GABAA receptors activity, resulting in a depression of the sensory stimulation-evoked synaptic transmission via PKA signaling pathway in mouse cerebellar GL.

Propofol enhances facial stimulation-evoked responses in the cerebellar granule cell layer via NMDA receptor activation in mice in vivo.

We recently reported that propofol depressed facial stimulation-evoked gamma-aminobutyric acid (GABA) transmission at cerebellar molecular layer interneuron-Purkinje cell (PC) synapses in mice in vivo, but facilitated excitatory parallel fiber inputs onto PCs. Here, we examine the effects of propofol on cerebellar granule cell layer (GCL) responses to facial stimulation in urethane-anesthetized mice, using electrophysiological and pharmacological methods. Cerebellar surface perfusion of propofol (50-1000µM) facilitated field potentials evoked in the cerebellar GCL by air-puff stimulation of the ipsilateral whisker pad, shown by increases in the half-width and area under the curve (AUC) of the stimulus onset response (Ron). Propofol also significantly increased the amplitude of the stimulus offset response (Roff) and Roff/Ron ratio. The propofol-induced increase in Ron AUC was dose-dependent, with a 50% effective concentration (EC50) of 242.4µM. Application of the GABAA receptor antagonist gabazine (20µM) significantly increased the amplitude, half-width, rise tau and AUC of Ron, but these parameters were further increased by additional application of propofol (300µM). Notably, application of the N-methyl-d-aspartate (NMDA) receptor blocker D-APV (250µM) significantly attenuated the half-width and AUC of Ron and the amplitude of Roff, without significantly changing the amplitude of Ron. These results indicate that propofol enhanced facial stimulation-evoked responses in the cerebellar GCL via NMDA receptor activation, which resulted in the facilitation of excitatory parallel fiber inputs onto cerebellar PCs in mice in vivo.

Effects of Propofol on the Dynamic Properties of Sensory Information Processing in the Mouse Cerebellar Cortical Molecular Layer in vivo.

Propofol is a global central nervous system depressant that affects information processing in the central nervous system. However, the effects of propofol on sensory information processing in the cerebellar cortical molecular layer are unknown. In this study, we examined the effects of propofol on the dynamics of sensory stimulation-evoked responses in the cerebellar molecular layer in urethane-anesthetized mice, using electrophysiological and pharmacological methods. Our results showed that cerebellar surface perfusion of propofol (10-1,000 µmol/l) significantly decreased amplitude and area under the curve (AUC) of the sensory stimulation-evoked inhibitory component (P1) but increased the rise time and decay time of P1. In contrast, administration of propofol significantly enhanced the sensory stimulation-evoked excitatory component (N1), which exhibited increases in amplitude and AUC, as well as increases in rise time and decay time. By blocking the GABAA receptor activity, propofol failed to increase the amplitude and the AUC of the excitatory postsynaptic component (N2) of PCs. Our present results suggest that propofol modulates the dynamic properties of the sensory information processing in the cerebellar molecular layer through the modulation of GABAA receptors activity in the adult mouse.

Propofol facilitates excitatory inputs of cerebellar Purkinje cells by depressing molecular layer interneuron activity during sensory information processing in vivo in mice.

Propofol is a rapid-acting sedative-hypnotic medication that has been widely used for the induction and maintenance of anesthesia; it has specific actions on different areas of the brain, such as sensory information transmission in the somatosensory cortex. However, the effects of propofol on the properties of sensory stimulation-evoked responses in cerebellar Purkinje cells (PCs) are currently unclear. In the present study, we studied the effects of propofol on facial stimulation-evoked responses in cerebellar PCs and molecular level interneurons (MLIs) in urethane-anesthetized mice using electrophysiological and pharmacological methods. Our results showed that cerebellar surface perfusion with propofol induced a decrease in the amplitude of the gamma-aminobutyric acid (GABA)-ergic component (P1) in a dose-dependent manner, but induced a significant increase in the amplitude of the excitatory response (N1). The IC50 of propofol-induced inhibition of P1 was 217.3 µM. In contrast, propofol (100 µM) depressed the spontaneous activity and tactile-evoked responses in MLIs. In addition, blocking GABA(A) receptor activity abolished the propofol (300 µM)-induced inhibition of the tactile-evoked inhibitory response and the increase in the sensory stimulation-evoked spike firing rate of PCs. These results indicated that propofol depressed the tactile stimulation-evoked spike firing of MLIs, resulting in a decrease in the amplitude of the tactile-evoked inhibitory response and an increase in the amplitude of the excitatory response in the cerebellar PCs of mice. Our results suggest that propofol modulates sensory information processing in cerebellar cortical PCs and MLIs through the activation of GABA(A) receptors.

Propofol depresses cerebellar Purkinje cell activity via activation of GABA(A) and glycine receptors in vivo in mice.

Propofol is an intravenous sedative-hypnotic agen, which causes rapid and reliable loss of consciousness. Under in vitro conditions, propofol activates GABAA and glycine receptors in spinal cord, hippocampus and hypothalamus neurons. However, the effects of propofol on the cerebellar neuronal activity under in vivo conditions are currently unclear. In the present study, we examined the effects of propofol on the spontaneous activity of Purkinje cells (PCs) in urethane-anesthetized mice by cell-attached recording and pharmacological methods. Our results showed that cerebellar surface perfusion of propofol (10-1000 µM) induced depression of the PC simple spike (SS) firing rate in a dose-dependent manner, but without significantly changing the properties of complex spikes (CS). The IC50 of propofol for inhibiting SS firing of PCs was 144.5 µM. Application of GABAA receptor antagonist, SR95531 (40 µM) or GABAB receptor antagonist, saclofen (20 µM), as well as glycine receptor antagonist, strychnine (10 µM) alone failed to prevent the propofol-induced inhibition of PCs spontaneous activity. However, application the mixture of SR95531 (40 µM) and strychnine (10 µM) completely blocked the propofol-induced inhibition of PC SS firing. These data indicated that cerebellar surface application of propofol depressed PC SS firing rate via facilitation of GABAA and functional glycine receptors activity in adult cerebellar PCs under in vivo conditions. Our present results provide a new insight of the anesthetic action of propofol in cerebellar cortex, suggesting that propofol depresses the SS outputs of cerebellar PCs which is involved in both GABAA and glycine receptors activity.

Effect of gabazine on sensory stimulation train evoked response in mouse cerebellar Purkinje cells.

Cerebellar Purkinje cells (PCs) respond to sensory stimulation via climbing fiber and mossy fiber-granule cell pathways, and generate motor-related outputs according to internal rules of integration and computation. However, the dynamic properties of sensory information processed by PC in mouse cerebellar cortex are currently unclear. In the present study, we examined the effects of the gamma-aminobutyric acid receptor A (GABA(A)) antagonist, gabazine, on the stimulation train on the simple spike firing of PCs by electrophysiological recordings method. Our data showed that the output of cerebellar PCs could be significantly affected by all pulses of the low-frequency (0.25 -2 Hz) sensory stimulation train, but only by the 1st and 2nd pulses of the high-frequency (≥ 4 Hz) sensory stimulation train. In the presence of gabazine (20 µM), each pulse of 1 Hz facial stimulation evoked simple spike firing in the PCs, but only the 1st and 2nd pulses of 4 Hz stimulation induced an increase in simple spike firing of the PCs. These results indicated that GABAA receptor-mediated inhibition did not significantly affect the frequency properties of sensory stimulation evoked responses in the mouse cerebellar PCs.

Leptin's effect on accelerated fracture healing after traumatic brain injury.

OBJECTIVE: To investigate mechanisms behind the faster rehabilitation of limb fractures when associated with traumatic brain injury (TBI). METHODS: New Zealand rabbits were divided into TBI group and sham-operation group for four studies as follows: (1) blood and cerebrospinal fluid (CSF) were drawn on days 1, 3, and 7 to demonstrate changes in serum leptin, growth hormone (GH), insulin-like growth factor 1 (IGF-1), and CSF leptin; (2) bone defection was created by drilling in the tibial bone and either leptin or normal saline was injected into rabbit's cerebellomedullary cistern. X-ray was taken at 1 days, 2 weeks, and 5 weeks and evaluated by criteria to determine rate of bone healing; (3) FITC-labeled rabbit leptin was injected into TBI and sham-operation groups, and frozen sections of rabbit brain were observed to identify differences in central nervous system (CNS) leptin by fluorescence; (4) polymerase chain reaction (PCR) was used to evaluate the expression of leptin production by brain tissue. RESULTS: Serum and CSF leptin, GH, and IGF-1 concentrations were found to be higher in the TBI group than the sham-operation group at days 1, 3, and 7 (P<0·05). CSF leptin of the TBI group was positively correlated with serum leptin on day 1 (P<0·05), and positively correlated with GH and IGF-1 on days 3 and 7 (P<0·05). X-ray criteria demonstrated that leptin administration caused significantly faster healing calluses at 3 and 5 weeks as compared to control animals (P<0·05). FITC-labeled leptin study demonstrated that TBI animals had stronger expression of leptin in the brain than sham-operated animals. However, PCR of brain tissue leptin showed no significant differences between TBI and sham-operated animals in the expression of leptin. CONCLUSIONS: Our study suggests that increased CSF leptin, likely from blood-brain barrier breakdown, combined with elevated serum GH and IGF-1 after TBI, leads to accelerated fracture healing.

Effects of stresscopin on rat hypothalamic paraventricular nucleus neurons in vitro.

The effects of stresscopin (SCP) on rat paraventricular nucleus (PVN) neurons were examined using whole-cell patch-clamp recordings and single-cell reverse-transcription multiplex polymerase chain reaction (SC-RT-mPCR) techniques. Under current-clamp conditions, bath application of SCP (100 nM) induced inhibition in 35.2% (37/105) of putative magnocellular neurons and 24.7% (20/81) of putative parvocellular neurons, and excitation in 5.7% (6/105) of putative magnocellular neurons and 18.5% (15/81) of putative parvocellular neurons. SCP-induced inhibition persisted in the presence of a mixture of TTX, a voltage-gated Na+ channel blocker, CNQX, an AMPA/kainate receptor antagonist and bicuculline, a GABA(A) receptor antagonist, whereas SCP-induced excitation of PVN neurons was reversed by the mixture. The SCP-induced inhibition of PVN neurons was abolished by bath application of antisauvagine-30, a selective CRF receptor 2 (CRF-R2) antagonist. Under voltage-clamp conditions, SCP evoked outward currents at the holding potential (-60 mV), which reversed near the potassium equilibrium potential. The SCP-evoked membrane currents were completely blocked by bath application of tertiapin-Q, a selective blocker of G protein-activated inwardly rectifying potassium (GIRK) channels. SC-RT-mPCR analysis indicated that all the SCP-sensitive PVN neurons (57 SCP-inhibited neurons, 21 SCP-excited neurons) expressed CRF-R1 and CRF-R2 mRNAs. Among SCP-hyperpolarized PVN neurons, oxytocin (OT) mRNA was detected in 91.8% of putative magnocellular neurons and 45.0% of putative parvocellular neurons. OT mRNA was also detected in 26.6% of SCP-depolarized parvocellular neurons, but not in SCP-depolarized magnocellular neurons. These results indicate that SCP inhibits a subpopulation of PVN neurons, especially OTergic magnocellular neurons, by enhancing the activity of GIRK channels via CRF-R2.