Mapping Functional Activity in Rodent Cortex Using Optical Intrinsic Signals

We have investigated the dynamic response of rodent posteromedialbarrel subfield (PMBSF) cortex to mechanical whisker deflection,using optical intrinsic signal imaging. While electrophysiologicresponse in barrel cortex has been well studied, dynamic metabolicchanges affecting activity-related perfusion or oxidative enzymesare not well understood. Male Sprague-Dawley rats were anesthetized. Contralateral singleand multiple vibrissae were deflected while images of somatosensorycortex were acquired with a charge-coupled-device camera. Intrinsicsignals were observed over PMBSF as stimulus-related reflectancedecreases (10^–3 of baseline) comprising two distinct spatiotemporalcomponents. At 610 nm the first, diffuse, component begins 0.5–1sec after stimulus onset, peaks at 2.5–3 sec, and returnsto baseline by 4–5 sec. The second component is macrovascular,beginning at 1–1.5 sec, peaking at 3 sec, and dissipatingby 5–6 sec. Similar patterns were observed at 550 nm and850 nm. Signal size and location varied with the stimulus. Evokedpotentials were found to have maximal amplitude in the regionof maximal optical signals, diminishing toward the optical periphery. We have demonstrated PMBSF response to vibrissal deflectionusing optical reflectance methods. These intrinsic signals overlieregions of maximal electrophysiologic response, but commence,peak, and extinguish over a time scale of seconds from stimulusonset. They most likely indicate activity-related microvascularrecruitment and chromophore redox changes.     

Burst Activation of the Cerebral Cortex by Flash Stimuli during Isoflurane Anesthesia in Rats

Background: The degree of suppression of sensory functions during general anesthesia is controversial. Here, the authors investigated whether discrete flash stimuli induced cortical field potential responses at an isoflurane concentration producing burst suppression and compared the spatiotemporal properties and frequency spectra of flash-induced burst responses with those occurring spontaneously.

Methods: Rats were equipped with multiple epidural and intracortical electrodes to record cortical field potentials in the right hemisphere at several locations along the anterior-posterior axis. At isoflurane concentrations of 1.1, 1.4, and 1.8%, discrete light flashes were delivered to the left eye while cortical field potentials were continuously recorded.

Results: Isoflurane at 1.4-1.8% produced burst suppression. Each flash produced a visual evoked potential in the primary visual cortex followed by secondary bursting activity in more anterior regions. The average latency and duration of these bursts were 220 and 810 ms, respectively. The spontaneous and flash-induced bursts were similar in frequency, duration, and spatial distribution. They had maximum power in the frontal (primary motor) cortex with a dominant frequency of 10 Hz.     

Signal Verification of Middle Latency Auditory Evoked Potentials by Automated Detection of the Brainstem Response

Background: The midlatency components of auditory evoked potentials (AEPs) are gradually suppressed with increasing concentrations of anesthetics. Thus, they have been proposed as a monitor of anesthetic depth. However, undetected malfunction or disconnection of headphones and undetected hearing loss also result in suppressed midlatency AEPs that in turn may be misinterpreted as signs of deep anesthesia. As the brainstem component of the AEP is minimally influenced by anesthetics, its presence or absence can be used to verify that the recorded signal is a true AEP rather than an artifact. In this study, an online-capable procedure for detection of the brainstem component of the AEP was developed.

Methods: One hundred and ninety perioperatively recorded AEPs (binaural stimuli, 500 sweeps) were selected from a database with electroencephalographic and concomitant AEP stimulus information. Identical electroencephalogram regions were used to produce nonstimulus synchronized averaged signals (500 sweeps, "non-AEP"). The 190 AEPs and 190 "non-AEPs" were used to develop a detector of the brainstem component of AEPs. AEPs and "non-AEPs" were wavelet transformed (discrete wavelet decomposition, biorthogonal 2.2 mother-wavelet), and the coefficient with the best separation of the two classes of signals was selected. Receiver operating characteristic curve analysis was performed to determine the optimum threshold value for this coefficient.

Results: The third coefficient of the third level was selected. In AEP signals, retransform of this coefficient produces a peak that resembles peak V of the brainstem response. The developed detector of the brainstem component of AEP had a sensitivity of 97.90% and a specificity of 99.48%.     

Activation of Human Prefrontal Cortex during Spatial and Nonspatial Working Memory Tasks Measured by Functional MRI

Separate working memory domains for spatial location, and forobjects, faces, and patterns, have been identified in the prefrontalcortex (PFC) of nonhuman primates. We have used functional magneticresonance imaging to examine whether spatial and nonspatialvisual working memory processes are similarly dissociable inhuman PFC. Subjects performed tasks which required them to remembereither the location or shape of successive visual stimuli. Wefound that the mnemonic component of the working memory tasksaffected the hemispheric pattern of PFC activation. The spatial(LOCATION) working memory task preferentially activated themiddle frontal gyrus (MFG) in the right hemisphere, while thenonspatial (SHAPE) working memory task activated the NIFG inboth hemispheres. Furthermore, the area of activation in theleft hemisphere extended into the inferior frontal gyrus forthe nonspatial SHAPE task. A perceptual target (DOT) detectiontask also activated the MFG bilaterally, but at a level approximatelyhalf that of the working memory tasks. The activation in theMFG occurred within 3–6 s of task onset and declined followingtask offset. Time-course analysis revealed a different patternfor the cingulate gyrus, in which activation occurred upon taskcompletion. Cingulate activation was greatest following theSHAPE task and was greater in the left hemisphere. The presentresults support the prominent role of the PFC and, specifically,the MFG in working memory, and indicate that the mnemonic contentof the task affects the relative weighting of hemispheric activation.     

Modulation of γ-Aminobutyric Acid Type A Receptor-mediated Spontaneous Inhibitory Postsynaptic Currents in Auditory Cortex by Midazolam and Isoflurane

Background: Anesthetic agents that target [gamma]-aminobutyric acid type A (GABAA) receptors modulate cortical auditory evoked responses in vivo, but the cellular targets involved are unidentified. Also, for agents with multiple protein targets, the relative contribution of modulation of GABAA receptors to effects on cortical physiology is unclear. The authors compared effects of the GABAA receptor-specific drug midazolam with the volatile anesthetic isoflurane on spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal cells of auditory cortex.

Methods: Whole cell recordings were obtained in murine brain slices at 34[degrees]C. GABAA sIPSCs were isolated by blocking ionotropic glutamate receptors. Effects of midazolam and isoflurane on time course, amplitude, and frequency of sIPSCs were measured.

Results: The authors detected no effect of midazolam at 0.01 [mu]m on sIPSCs, whereas midazolam at 0.1 and 1 [mu]m prolonged the decay of sIPSCs by approximately 25 and 70%, respectively. Isoflurane at 0.1, 0.25, and 0.5 mm prolonged sIPSCs by approximately 45, 150, and 240%, respectively. No drug-specific effects were observed on rise time or frequency of sIPSCs. Isoflurane at 0.5 mm caused a significant decrease in sIPSC amplitude.     

CaN和CaMK Ⅱ在单核细胞活化信号传导中的作用

目的：观察CaN和CaMKⅡ在LPS诱导人单核细胞活化的细胞内信号传导过程中的作用。方法：以CaN抑制剂CsA或CaMKⅡ抑制剂KN93预处理已经分化的人单核细胞系U937后，再用LPS刺激，采用Western 印迹法检测细胞内IκB-α水平及胞核内NF-κB水平的变化，并用MTT法测定上清液中TNF-α水平变化。结果：CsA和KN93均可明显抑制LPS刺激U937细胞后胞核内NF-κB水平及上清液中TNF-α水平的升高。结论：CaN和CaMKⅡ在LPS诱导人单核细胞活化的信号传导过程中均起重要作用。     

Imaging Human Cerebral Pain Modulation by Dose-dependent Opioid Analgesia: A Positron Emission Tomography Activation Study Using Remifentanil

Background: Previous imaging studies have demonstrated a number of cortical and subcortical brain structures to be activated during noxious stimulation and infusion of narcotic analgesics. This study used 15O-water and positron emission tomography to investigate dose-dependent effects of the short-acting [mu]-selective opioid agonist remifentanil on regional cerebral blood flow during experimentally induced painful heat stimulation in healthy male volunteers.

Methods: Positron emission tomography measurements were performed with injection of 7 mCi 15O-water during nonpainful heat and painful heat stimulation of the volar forearm. Three experimental conditions were used during both sensory stimuli: saline, 0.05 [mu]g [middle dot] kg-1 [middle dot] min-1 remifentanil, and 0.15 [mu]g [middle dot] kg-1 [middle dot] min-1 remifentanil. Cardiovascular and respiratory parameters were monitored noninvasively. Across the three conditions, dose-dependent effects of remifentanil on regional cerebral blood flow were analyzed on a pixel-wise basis using a statistical parametric mapping approach.

Results: During saline infusion, regional cerebral blood flow increased in response to noxious thermal stimulation in a number of brain regions as previously reported. There was a reduction in pain-related activations with increasing doses of remifentanil in the thalamus, insula, and anterior and posterior cingulate cortex. Increasing activation occurred in the cingulofrontal cortex (including the perigenual anterior cingulate cortex) and the periaqueductal gray.     

Feasibility of the Optical Imaging of Thrombus Formation in a Rotary Blood Pump by Near‐Infrared Light

Blood coagulation is one of the primary concerns when using mechanical circulatory support devices such as blood pumps. Noninvasive detection and imaging of thrombus formation is useful not only for the development of more hemocompatible devices but also for the management of blood coagulation to avoid risk of infarction. The objective of this study is to investigate the use of near‐infrared light for imaging of thrombus formation in a rotary blood pump. The optical properties of a thrombus at wavelengths ranging from 600 to 750 nm were analyzed using a hyperspectral imaging (HSI) system. A specially designed hydrodynamically levitated centrifugal blood pump with a visible bottom area was used. In vitro antithrombogenic testing was conducted five times with the pump using bovine whole blood in which the activated blood clotting time was adjusted to 200 s prior to the experiment. Two halogen lights were used for the light sources. The forward scattering through the pump and backward scattering on the pump bottom area were imaged using the HSI system. HSI showed an increase in forward scattering at wavelengths ranging from 670 to 750 nm in the location of thrombus formation. The time at which the thrombus began to form in the impeller rotating at 2780 rpm could be detected. The spectral difference between the whole blood and the thrombus was utilized to image thrombus formation. The results indicate the feasibility of dynamically detecting and imaging thrombus formation in a rotary blood pump.     

Isoflurane Protects against Myocardial Infarction during Early Reperfusion by Activation of Phosphatidylinositol-3-Kinase Signal Transduction: Evidence for Anesthetic-induced Postconditioning in Rabbits

Background: Brief episodes of ischemia during early reperfusion after coronary occlusion reduce the extent of myocardial infarction. Phosphatidylinositol-3-kinase (PI3K) signaling has been implicated in this "postconditioning" phenomenon. The authors tested the hypothesis that isoflurane produces cardioprotection during early reperfusion after myocardial ischemia by a PI3K-dependent mechanism.

Methods: Pentobarbital-anesthetized rabbits (n = 80) subjected to a 30-min coronary occlusion followed by 3 h reperfusion were assigned to receive saline (control), three cycles of postconditioning ischemia (10 or 20 s each), isoflurane (0.5 or 1.0 minimum alveolar concentration), or the PI3K inhibitor wortmannin (0.6 mg/kg, intravenously) or its vehicle dimethyl sulfoxide. Additional groups of rabbits were exposed to combined postconditioning ischemia (10 s) and 0.5 minimum alveolar concentration isoflurane in the presence and absence of wortmannin. Phosphorylation of Akt, a downstream target of PI3K, was assessed by Western blotting.

Results: Postconditioning ischemia for 20 s, but not 10 s, reduced infarct size (P < 0.05) (triphenyltetrazolium staining; 20 +/- 3% and 34 +/- 3% of the left ventricular area at risk, respectively) as compared with control (41 +/- 2%). Exposure to 1.0, but not 0.5, minimum alveolar concentration isoflurane decreased infarct size (21 +/- 2% and 43 +/- 3%, respectively). Wortmannin abolished the protective effects of postconditioning (20 s) and 1.0 minimum alveolar concentration isoflurane. Combined postconditioning (10 s) and 0.5 minimum alveolar concentration isoflurane markedly reduced infarct size (17 +/- 5%). This action was also abolished by wortmannin (44 +/- 2%). Isoflurane (1.0 minimum alveolar concentration) increased Akt phosphorylation after ischemia (32 +/- 6%), and this action was blocked by wortmannin.