Anna O'Brien

Nitric oxide synthase is localized predominantly in the Golgi apparatus and cytoplasmic vesicles of vascular endothelial cells.

The localization of nitric oxide synthase (NOS) in vascular endothelial cells of submucosal blood vessels from the guinea-pig ileum was examined using NADPH diaphorase histochemistry at the light microscopic level, and endothelial NOS immunohistochemistry at the light and electron microscopic level. The pattern of staining observed following NADPH diaphorase histochemistry and endothelial NOS immunohistochemistry was identical. Endothelial cells of the arterioles, capillaries and venules showed small patches of intense, perinuclear staining. Under the electron microscope, endothelial NOS immunoreactivity was found predominantly in association with the Golgi apparatus and with the membranes of some vesicles. Small regions of the plasma membrane and the rough endoplasmic reticulum also showed some immunoreactivity. The presence of NOS in the Golgi apparatus and in vesicles raises the possibility that NOS may be exteriorized by endothelial cells, and hence that nitric oxide is synthesized extracellularly.

Relationships between NADPH diaphorase staining and neuronal, endothelial, and inducible nitric oxide synthase and cytochrome P450 reductase immunoreactivities in guinea-pig tissues

Abstract The presence of NADPH diaphorase staining was compared with the immunohistochemical localization of four NADPH-dependent enzymes – neuronal (type I), inducible (type II), and endothelial (type III) nitric oxide synthase (NOS) and cytochrome P450 reductase. Cell types that were immunoreactive for the NADPH-dependent enzymes were also stained for NADPH diaphorase, suggesting that endothelial and neuronal NOS and cytochrome P450 reductase all show NADPH diaphorase activity in formaldehyde-fixed tissue. However, in some tissues, the presence of NADPH diaphorase staining did not coincide with the presence of any of the NADPH-dependent enzymes we examined. In vascular endothelial cells, the punctate pattern of staining observed with NADPH diaphorase histochemistry was identical to that seen following immunohistochemistry using antibodies to endothelial NOS. In enteric and pancreatic neurons and in skeletal muscle, the presence of NADPH diaphorase staining correlated with the presence of neuronal NOS. In the liver, sebaceous glands of the skin, ciliated epithelium, and a subpopulation of the cells in the subserosal glands of the trachea, zona glomerulosa of the adrenal cortex, and epithelial cells of the lacrimal and salivary glands, the presence of NADPH diaphorase staining coincided with the presence of cytochrome P450 reductase immunoreactivity. In epithelial cells of the renal tubules and zona fasciculata and zona reticularis of the adrenal cortex, NADPH diaphorase staining was observed that did not coincide with the presence of any of the enzymes. Inducible NOS was not observed in any tissue. Thus, while tissues that demonstrate immunoreactivity for neuronal and endothelial NOS also stain positively for NADPH diaphorase activity, the presence of NADPH diaphorase staining does not reliably or specifically indicate the presence of one or more NOS isoforms.

The effect of frequency-dependent microphone directionality on horizontal localization performance in hearing-aid users.

Abstract Frequency-dependent microphone directionality alters the spectral shape of sound as a function of arrival azimuth. The influence of this on horizontal-plane localization performance was investigated. Using a 360° loudspeaker array and five stimuli with different spectral characteristics, localization performance was measured on 21 hearing-impaired listeners when wearing no hearing aids and aided with no directionality, partial (from 1 and 2 kHz) directionality, and full directionality. The test schemes were also evaluated in everyday life. Without hearing aids, localization accuracy was significantly poorer than normative data. Due to inaudibility of high-frequency energy, front/back reversals were prominent. Front/back reversals remained prominent when aided with omnidirectional microphones. For stimuli with low-frequency emphasis, directionality had no further effect on localization. For stimuli with sufficient mid- and high-frequency information, full directionality had a small positive effect on front/back localization but a negative effect on left/right localization. Partial directionality further improved front/back localization and had no significant effect on left/right localization. The field test revealed no significant effects. The alternative spectral cues provided by frequency-dependent directionality improve front/back localization in hearing-aid users. Sumario La direccionalidad de un micrófono frecuencia-dependiente altera la configuración espectral del sonido como función del azimuth de llegada. Se investigó la influencia de esto en el desempeño para la localización en el plano horizontal. Usando un sistema de altoparlante 360° y cinco estímulos con diferentes características espectrales, se midió el desempeño para la localización en 21 hipoacúsicos, sin usar auxiliares auditivos y con el apoyo de no direccionalidad, de direccionalidad parcial (de 1 y 2 kHz) y con direccionalidad total. Los esquemas de la prueba también se evaluaron en la vida cotidiana. Sin auxiliares auditivos, la precisión para localizar fue significativamente más pobre que los datos normativos. Debido a la inaudibilidad de la energía de altas frecuencias, las inversiones frente/atrás fueron prominentes. Las inversiones frente/atrás permanecieron prominentes cuando hubo apoyo con micrófonos omnidireccionales. Para estímulos con énfasis en frecuencias graves, la direccionalidad no tuvo un efecto adicional en la localización. Con estímulos cuya información de frecuencias medias y altas fue suficiente, la direccionalidad total tuvo un pequeño efecto positivo para la localización frente/atrás, pero un efecto negativo en la localización izquierda/derecha. La direccionalidad parcial mejoró adicionalmente la localización frente/atrás pero no tuvo un efecto significativo en la localización izquierda/derecha. La prueba de campo no mostró efectos significativos. Las claves espectrales alternativas proporcionadas por la direccionalidad frecuencia-dependiente, mejoraron la localización frente/atrás en usuarios de auxiliares auditivos.

Variation in preferred gain with experience for hearing-aid users

This study aimed to determine whether gain adaptation occurs, and at which frequency bands, among new hearing aid (HA) users. Fifty new and 26 experienced HA users were fitted with three listening programs (NAL-NL1 and NAL-NL1 with low- and high-frequency cuts) in the same hearing instrument family. Real-life gain preferences and comfortable loudness levels were measured one, four, and 13 months post-fitting for the new HA users, and one month post-fitting for the experienced HA users. Relative to experienced HA users, new HA users preferred progressively less overall gain than prescribed as the hearing loss became more severe. Gain adaptation occurred in new HA users with greater hearing loss, but was not complete 13 months post-fitting, and was not explained by changes in loudness perception. Preferences for a high-frequency gain cut by half of all study participants could not be predicted from audiological data. Gain adaptation management is recommended for new HA users with more than a mild hearing loss.

Validity and reliability of in-situ air conduction thresholds measured through hearing aids coupled to closed and open instant-fit tips

Abstract Audiometric measurements through a hearing aid (‘in-situ’) may facilitate provision of hearing services where these are limited. This study investigated the validity and reliability of in-situ air conduction hearing thresholds measured with closed and open domes relative to thresholds measured with insert earphones, and explored sources of variability in the measures. Twenty-four adults with sensorineural hearing impairment attended two sessions in which thresholds and real-ear-to-dial-difference (REDD) values were measured. Without correction, significantly higher low-frequency thresholds in dB HL were measured in-situ than with insert earphones. Differences were due predominantly to differences in ear canal SPL, as measured with the REDD, which were attributed to leaking low-frequency energy. Test-retest data yielded higher variability with the closed dome coupling due to inconsistent seals achieved with this tip. For all three conditions, inter-participant variability in the REDD values was greater than intra-participant variability. Overall, in-situ audiometry is as valid and reliable as conventional audiometry provided appropriate REDD corrections are made and ambient sound in the test environment is controlled. Sumario Las mediciones audiométricas a través de un auxiliar auditivo (‘in-situ’) pueden facilitar la prestación de servicios auditivos donde éstos son limitados. Este estudio investigó la validez y confiabilidad de los umbrales auditivos por conducción aérea in-situ, medidos con domos abiertos y cerrados, en relación a umbrales medidos con auriculares de inserción, y exploró las fuentes de variabilidad en la medición. Veinticuatro adultos con hipoacusia sensorineural asistieron a dos sesiones donde se midieron los valores de los umbrales y de la diferencia de oído real a marcación (REDD). Sin corrección, se midieron umbrales en dB HL para las bajas frecuencias significativamente más altos in-situ que con los auriculares de inserción. Las diferencias se debieron predominantemente a diferencias en la SPL del canal auditivo, conforme se midieron con el REDD, y se atribuyeron a fuga de energía en las bajas frecuencias. Los datos de test-retest rindieron una mayor variabilidad con el acoplamiento de domos cerrados, debido al sello inconsistente que se obtuvo con esta punta. Para las tres condiciones, la variabilidad entre los participantes en los valores REDD, fue mayor que la variabilidad intra-participantes. Globalmente, la audiometría in-situ es tan válida y confiable como la audiometría convencional, en la medida que se realicen correcciones REDD apropiadas y que haya control de sonido en el ambiente de evaluación.

Bilateral cochlear implants in long-term and short-term deafness.

Abstract This case is of a 70-year-old man with single-sided deafness (SSD) in the right ear since childhood, who developed a sudden severe hearing loss in the left ear at the age of 63. Eventually, after he received cochlear implants in both ears, he started to present behavioural auditory processing skills associated with binaural hearing, such as improved ability to understand speech in the presence of background noise, and sound localization. Outcomes were measured using cortical auditory evoked potentials, speech perception in noise, sound localization tests, and a self-rating questionnaire. The results suggest that even after more than 50 years of unilateral deafness it was possible to develop binaural interaction and sound localization as a result of electric auditory stimulation.