Hyposalivation Affecting Womens' Voice.

OBJECTIVES: Balanced hydration is crucial for optimal physiological function, whereas hypohydration may cause adverse effects. Like many other organs, the larynx is negatively affected by hypohydration, potentially affecting voice production. Therefore, the purpose of this study was to examine voice properties in women diagnosed with dry-mouth. METHODS: Twenty-four women diagnosed with hyposalivation and 24 age-matched controls were recruited. All participants underwent three sialometry tests for quantifying oral-dryness. These tests were conducted in three conditions: after 2-hour fasting, after gustatory salivary stimulation and after drinking water. After each sialometry, participants were recorded while producing the vowels /a/ and /i/, and during a standardized reading task. A basic set of acoustic measures was extracted from these recordings. Self-evaluation of voice was performed using the VHI-10 questionnaire; and listeners' perception of the voice was performed by five professional judges who rated the recordings perceptually, using the GRBAS scale. RESULTS: Significant group differences were found in fundamental frequency and jitter, but not in shimmer and noise-to-harmonic ratio (corrected P < 0.05). The participants in the hyposalivation group exhibited higher scores on the VHI-10 questionnaire compared to the control group (P = 0.002), and the judges perceptually rated their voices higher on the Grade and Roughness scales (0.03 ≤ P ≤ 0.04). In contrast with the significant group differences, no significant differences were found between the three study conditions. CONCLUSIONS: Women suffering from oral-dryness were shown to exhibit degradation in voice quality, evident in both acoustic, perceptual and self-evaluation measures. However, in this paradigm, short-term superficial hydration was not shown to elicit a significant improvement in voice properties. These findings highlight the importance of consistent oral-hydration for voice, especially among people suffering from hyposalivation.

Characterization of neuronal viability and network activity under microfluidic flow.

BACKGROUND: Microfluidics technology has the potential to allow precise control of the temporal and spatial aspects of solute concentration, making it highly relevant for the study of volume transmission mechanisms in neural tissue. However, full utilization of this technology depends on understanding how microfluidic flow at the rates needed for rapid solution exchange affects neuronal viability and network activity. NEW METHOD: We designed a tape-based pressurized microfluidic flow system that is simple to fabricate and can be attached to commercial microelectrode arrays. The device is multi-layered, allowing the inclusion of a porous polycarbonate membrane to isolate neuronal cultures from shear forces while maintaining diffusive exchange of solutes. We used this system to investigate how flow affected survival and spiking patterns of cultured hippocampal neurons. RESULTS: Viability and network activity of the cultures were reduced in proportion to flow rate. However, shear reduction measures did not improve survival or spiking activity; media conditioning in conjunction with culture age proved to be the critical factors for network stability. Diffusion simulations indicate that dilution of a small molecule accounts for the deleterious effects of flow on neuronal cultures. COMPARISON WITH EXISTING METHODS: This work establishes the experimental conditions for real time measurement of network activity during rapid solution exchange, using multi-layered chambers with reversible bonding that allow for reuse of microelectrode arrays. CONCLUSIONS: With correct media conditioning, the microfluidic flow system allows drug delivery on a subsecond timescale without disruption of network activity or viability, enabling in vitro reproduction of volume transmission mechanisms.

Glutamate mediated astrocytic filtering of neuronal activity.

Neuron-astrocyte communication is an important regulatory mechanism in various brain functions but its complexity and role are yet to be fully understood. In particular, the temporal pattern of astrocyte response to neuronal firing has not been fully characterized. Here, we used neuron-astrocyte cultures on multi-electrode arrays coupled to Ca2+ imaging and explored the range of neuronal stimulation frequencies while keeping constant the amount of stimulation. Our results reveal that astrocytes specifically respond to the frequency of neuronal stimulation by intracellular Ca2+ transients, with a clear onset of astrocytic activation at neuron firing rates around 3-5 Hz. The cell-to-cell heterogeneity of the astrocyte Ca2+ response was however large and increasing with stimulation frequency. Astrocytic activation by neurons was abolished with antagonists of type I metabotropic glutamate receptor, validating the glutamate-dependence of this neuron-to-astrocyte pathway. Using a realistic biophysical model of glutamate-based intracellular calcium signaling in astrocytes, we suggest that the stepwise response is due to the supralinear dynamics of intracellular IP3 and that the heterogeneity of the responses may be due to the heterogeneity of the astrocyte-to-astrocyte couplings via gap junction channels. Therefore our results present astrocyte intracellular Ca2+ activity as a nonlinear integrator of glutamate-dependent neuronal activity.

Optical validation of in vitro extra-cellular neuronal recordings.

Simultaneous calcium imaging and extra-cellular recordings from cultured cortical rat neurons were performed to directly map the efficacy of extra-cellular recordings with microelectrodes. For the first time, we can associate extra-cellular recordings with neuronal activity of specific neurons in the vicinity of the electrode. We demonstrate that recorded cells can be identified by correlating the electrical signals and the calcium response. Our data demonstrate that in sparse cultures, microelectrodes record exclusively from cells which reside at very close proximity to the recording electrode. Moreover, we show that recording appears to be limited to only a partial subset of the cells residing in this range. We further show that even in cases of strong neuron-electrode coupling, extra-cellular signals recorded from single, well-identified neurons vary in shape over time rendering spike sorting and network activity rate analysis incongruous. As multi-electrode array technology is becoming increasingly widespread, the visualization technique we report here will help users better understand the limits of this versatile and useful method.