Behavior of Stimulus Response Signals in a Rat Cortical Neuronal Network Under Xe Pressure.

Neurons cultured on a multi-electrode array show not only spontaneous firing, but also network-specific burst firing, the latter of which develops into synchronous bursting. Such synchronous bursting can be suppressed by exposure to xenon (Xe) gas. To better understand such suppression of bursting by Xe, we investigate here whether signal transmission between neurons is also suppressed under these conditions. In these experiments, we apply a pulse electrical-stimulus to one electrode and observe the response signals within 10 ms at other active electrodes. When put under a sufficient Xe pressure, some response signals become delayed or vanish after disappearance of synchronous-bursts, particularly signals passing through multiple synaptic bonds. Such bonds have a high probability of having delayed or vanishing signals when the Xe pressure is above 0.3 MPa. The pressure dependence of the response ratio to the stimulus suggests that Xe suppresses multiple points of action simultaneously when suppressing synaptic signal transduction, as observed in the suppression of the synchronized bursting. In addition, we find that the signal that transmits not via synaptic bonding (axon conduction) is also suppressed under Xe gas pressures over 0.3 MPa. Therefore, we conclude that Xe-induced suppression of synchronized bursting is caused mainly by a decrease in the apparent number of active neurons that contribute to the neuronal network, a decrease due to inhibition of signal transmission via synaptic connections.

Xenon-induced inhibition of synchronized bursts in a rat cortical neuronal network.

Xenon (Xe) and other inert gases produce anesthesia via an inhibitory mechanism in neuronal networks. To better understand this mechanism, we measured the electrical signals from cultured rat cortical neuronal networks in a multi-electrode array (MEA) under an applied Xe pressure. We used the MEA to measure the firing of the neuronal network with and without Xe gas pressurized to 0.3MPa. The MEA system monitored neuronal spikes on 16 electrodes (each 50×50µm(2)) at a sampling rate of 20kHz. The embryo rat cortical cells were first cultured on MEAs without Xe for approximately 3weeks, at which time they produced synchronized bursts that indicate maturity. Then, with an applied Xe pressure, the synchronized bursts quickly ceased, whereas single spikes continued. The Xe-induced inhibition-recovery of neuronal network firing was reversible: after purging Xe from the system, the synchronized bursts gradually resumed. Thus, Xe did not inhibit single neuron firing, yet reversibly inhibited the synaptic transmission. This finding agrees with the channel-blocker and a modified-hydrate hypothesis of anesthesia, but not the lipid-solubility hypothesis.

Minimum neuron density for synchronized bursts in a rat cortical culture on multi-electrode arrays.

To investigate the minimum neuron and neurite densities required for synchronized bursts, we cultured rat cortical neurons on planar multi-electrode arrays (MEAs) at five plating densities (2500, 1000, 500, 250, and 100 cells/mm(2)) using two culture media: Neuron Culture Medium and Dulbecco's Modified Eagle Medium supplemented with serum (DMEM/serum). Long-term recording of spontaneous electrical activity clarified that the cultures exhibiting synchronized bursts required an initial plating density of at least 250 cells/mm(2) for Neuron Culture Medium and 500 cells/mm(2) for DMEM/serum. Immediately after electrical recording, immunocytochemistry of microtubule-associated protein 2 (MAP2) and Neurofilament 200 kD (NF200) was performed directly on MEAs to investigate the actual densities of neurons and neurites forming the networks. Immunofluorescence observation revealed that the construction of complicated neuronal networks required the same initial plating density as for synchronized bursts, and that overly sparse cultures showed significant decreases of neurons and neurites. We also found that the final densities of surviving neurons at 1 month decreased greatly compared with the initial plating densities and became saturated in denser cultures. In addition, the area of neurites and the number of nuclei were saturated in denser cultures. By comparing both the results of electrophysiological recording and immunocytochemical observation, we revealed that there is a minimum threshold of neuron densities that must be met for the exhibition of synchronized bursts. Interestingly, these minimum densities of MAP2-positive final neurons did not differ between the two culture media; the density was approximately 50 neurons/mm(2). This value was obtained in the cultures with the initial plating densities of 250 cells/mm(2) for Neuron Culture Medium and 500 cells/mm(2) for DMEM/serum.

The assessment of methyl mercaptan, an important clinical marker for the diagnosis of oral malodor.

OBJECTIVE: This study aimed to determine the clinical assessment of volatile sulfur compound (VSCs) for the evaluation of noticeable oral malodor using gas chromatography (GC). METHODS: The oral malodor of 127 adult patients was investigated using the organoleptic test and GC, and the relation between the organoleptic evaluation and VSCs were analyzed. RESULTS: The optimum cut-off values of CH3SH, H2S and total VSC (CH3SH + H2S) to discriminate between the patients with and without noticeable oral malodor were obtained from ROC curves, and determined to be 0.44, 1.10 and 2.20 ng/10 ml, respectively. The logistic regression was analyzed for estimation of the association between an organoleptic evaluation greater than a slight level and the groups with CH3SH, H2S or total VSC with concentrations above the optimum cut-off value. Only CH3SH showed an independent association with noticeable oral malodor. CONCLUSIONS: It was evident that CH3SH was a more useful marker for the evaluation of oral malodor than H2S. Moreover, it appears CH3SH is the predominant causative factor of noticeable oral malodor.

A new automatic device for measuring the spinnbarkeit of saliva: the Neva Meter.

OBJECTIVES: We have recently developed a new device for measuring the spinnbarkeit of saliva called the Neva Meter. The purpose of this study was to evaluate this device and to measure spinnbarkeit as well as viscosity, another important property, in the resting saliva of 24 healthy adults. METHODS: We used polyvinyl alcohol (PVA) as a standard solution to establish the reproducibility of spinnbarkeit tests. We collected resting saliva from 24 employees of a business office (16 males and 8 females, average age: 37.8) and investigated the relationship between spinnbarkeit and viscosity. RESULTS: The spinnbarkeit of PVA increased along with the concentration of the solution, and the reproducibility of the values was acceptable. Spinnbarkeit of resting saliva showed a positive correlation with viscosity at a shear rate of 76.6 s(-1) (r = 0.55, P < 0.05) and 191.5 s(-1) (r = 0.59, p < 0.05). CONCLUSIONS: The newly developed Neva Meter was suitable for measuring the spinnbarkeit of saliva quickly and easily at the chair-side in the dental clinic. Results obtained using this new device may be important for understanding and evaluating the condition of the oral cavity.

The relationship between the presence of periodontopathogenic bacteria in saliva and halitosis.

OBJECTIVE: To evaluate the association between the presence of periodontal pathogenic bacteria in saliva and halitosis in mouth air. DESIGN: Cross-sectional microbiological and clinical oral examination of adult patients. SUBJECTS: 101 adult patients (25 males, 76 females) who attended the Preventive Dentistry and Breath Odour Clinic of Kyushu Dental College. Their average age was 50.0+/-13.5 years old (mean +/- SD). SETTING: The subjects were classified into three groups: halitosis subjects with a probing depth (PD) > or = 4mm (P group), halitosis subjects without PD > or = 4mm (H group), and non-halitosis subjects without PD > or = 4mm (C group). METHODS: All subjects received a periodontal examination. Volatile sulphur compounds (VSC: hydrogen sulphide and methyl mercaptan) were measured using gas chromatography. The presence of Bacteroides forsythus, Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans and Prevotella intermedia in the saliva was detected by polymerase chain reaction. RESULTS AND CONCLUSION: The presence of B. forsythus, P. gingivalis and P. intermedia influenced the production of VSC. Specifically, the presence of B. forsythus in subjects with periodontitis was strongly correlated to the concentration of VSC in mouth air.