Multi-unit mapping of acoustic stimuli in gerbil inferior colliculus.

Multi-unit peristimulus time (MU-PST) histograms were recorded in the gerbil inferior colliculus (IC) in response to tone burst stimuli. Histograms were collected every 100 microns as the recording electrode was advanced along the tonotopic axis of the central nucleus of the IC. Space/time maps of neural activity were constructed from these data. In most of our sample the pattern of response changed systematically as the stimulating frequency was increased in octave steps. At low frequencies (< 500 Hz) the pattern of response was broadly distributed spatially and phase-locked to the stimulus frequency. At higher frequencies (> 1 kHz) the pattern of response was more localized and showed no evidence of phase locking. The location of the maximum response to tones from 1 to 32 kHz moved ventrally along the tonotopic axis at an approximate rate of 230 microns/stimulus octave. The patterns of response were localized near stimulus threshold and spread over a larger region as level increased. This method of collecting and displaying multi-unit response maps provides an overview of ensemble activity that allows concurrent observation of spatial and temporal variations in activity patterns. The quantitative analysis of components of MU-PST Maps are consistent with trends illustrated with single-unit tuning and level functions. This perspective of IC activity suggests potential processing mechanisms that are congruent with single-unit reconstructions.

Preferred hearing-aid frequency responses in simulated listening environments.

This study was designed to determine if an adaptive strategy could be used to select frequency/gain characteristics that would be considered appropriate across a variety of listening environments. In Experiment I, the test-retest reliability of the paired comparison procedure used in Experiment II was assessed in quiet for nine subjects and in speech noise for six subjects. For both conditions, results revealed mean standard deviations of < 3 dB from 200 through 4000 Hz. In Experiment II, four subjects selected frequency/gain characteristics for five different listening environments (quiet, speech noise, quiet conference room, reverberant lecture hall, and reverberant lecture hall in noise). In general, subjects did not tend to select different frequency/gain characteristics across the five simulated environments used in this study. When differences in frequency responses were observed, they tended to be alterations in overall gain rather than changes in relative frequency response. Findings support additional evaluation in more diverse listening environments, possibly with systems that incorporate nonlinear signal processing.

A comparison of speech discrimination with cochlear implants and tactile aids.

This study investigates patterns of speech discrimination in profoundly hearing-impaired children who have received cochlear implants or tactile aids. The change/no change procedure was used to assess speech discrimination in these children. Three groups of subjects were tested: the first group used 3M/House single-channel cochlear implants; the second group used Nucleus 22-channel cochlear implants; and the third group used two-channel Tactaid II+ vibrotactile aids. Nine contrasts were constructed that assessed discrimination of suprasegmental and segmental speech features. Subjects were presented with stimulus trials in which stimuli changed during the trial or in which stimuli remained the same. Hits, misses, false alarms, and correct rejections were tallied and d' values were calculated for individual subjects for each contrast. Results indicated that different patterns of speech discrimination are provided by the three sensory prosthetic devices. For all contrasts, mean discrimination performance with the Nucleus device was better than that observed for the other two devices, despite the shorter duration of subject experience with this cochlear implant. In addition, interactions between device and speech contrast were not observed. Examination of individual subject performance revealed that each device group had a distribution of good to poor performers. The results suggest that the change/no change procedure is able to provide information regarding speech perception through sensory prosthetic devices despite existing differences in vocabulary and language skills of subjects.

Improved development of rabbit one-cell embryos to the hatching blastocyst stage by culture in a defined, protein-free culture medium.

In Exp. 1, Medium 199 and Medium RD (RPMI-1640 and Dulbecco's MEM, 1:1 v/v) were compared in a 2 x 2 factorial design by supplementing each with 15 mg bovine serum albumin (BSA)/ml of 1 mg polyvinyl alcohol (PVA)/ml. All media contained 5 micrograms insulin/ml, 5 micrograms transferrin/ml, 5 ng selenium/ml (ITS), and 10 ng epidermal growth factor (EGF)/ml. One-cell embryos were cultured at 39 degrees C with 5% CO2 in air for 65 h and then stained with Hoechst 33342 to determine blastomere number. Embryos in Medium 199 developed poorly (P less than 0.001) when PVA was used instead of BSA (30 vs 76 cells/embryo), but developed rapidly in Medium RD with PVA or BSA (118 and 121 cells). Similar results were obtained in Exp. 2 in BSA- and PVA-free medium. In Exp. 3, the development of 1-cell embryos after 65 h in unsupplemented (protein-free) Medium RD (68% blastocysts, 117 cells) did not differ (P greater than 0.37) from that obtained using Medium RD with insulin, ITS or EGF alone. Culture in protein-free Medium RD for 96 h resulted in 82% of the 1-cell embryos forming blastocysts and 40% hatching through the zona pellucida. In a preliminary test of viability, 1-cell embryos cultured in this medium for 48 or 65 h and transferred to synchronous recipients resulted in 5/18 (28%) and 3/24 (12%) Day-15 viable fetuses. Cell counts of approximately 120 per blastocyst after culturing 1-cell embryos for 65 h in Medium RD indicated that cell division was more rapid than that obtained with all other media tested previously in this laboratory. This is the first report of rabbit embryo development from the 1-cell to the hatching blastocyst stage in a defined protein-free culture medium.

The interrelationship of thyroid hormones with vitamin A and zinc nutritional status in patients with chronic hepatic and gastrointestinal disorders.

To define the role of vitamin A, retinol binding protein, and zinc deficiency in producing the thyroid hormone abnormalities found in chronic illness, we studied 62 clinically stable patients with hepatic and gastrointestinal disorders. Serum triiodothyronine (T3) and free T3 index (FT3I) were depressed compared to controls (p less than 0.05) in the patients. Retinol binding protein and prealbumin levels correlated with both T3 and FT3I (p less than 0.01), whereas vitamin A levels did not. Vitamin A therapy in patients with documented vitamin A deficiency produced an increase in T3, thyroxine (T4), FT3I, FT4I, and free T3 by dialysis, with a concomitant increase in retinol binding protein and no alteration in prealbumin concentrations. Zinc-deficient patients had significantly depressed T3 and FT3I (p less than 0.001) and increased prolactin levels (p less than 0.01). Zinc supplementation failed to return any of these parameters to normal. Vitamin A therapy in normals produced a transient decrease in T3 and T4 after 1 wk of therapy, but after a further 2 wk, thyroid function returned to normal. Our data suggest a causal relationship between the pathogenesis of deranged vitamin A-retinol binding protein metabolism and the low T3 syndrome either by interfering with T4 entry into tissues or by directly affecting the enzymatic conversion of T4 to T3.

Vitamin-A reversal of abnormal dark adaptation in cirrhosis. Study of effects on the plasma retinol transport system.

Of 26 patients hospitalized with mild to moderate alcohol-associated cirrhosis, 14 had dark-adaptation abnormalities consistent with marginal vitamin-A status. The response of dark adaptation and the plasma retinol transport proteins, retinol-binding protein and prealbumin, was studied in 12 of these patients after daily oral vitamin-A supplements of 3300 microgram. Vitamin-A supplementation was associated with significant (p less than 0.05-0.005) improvement in dark adaptation and increased plasma concentrations of retinyl esters, retinol, and retinol-binding protein. Thus in patients with cirrhosis and marginal vitamin-A status, supplemental vitamin-A therapy appears to stimulate retinol-binding protein release from the liver. This enhancement of plasma retinol transport and delivery of retinol to peripheral tissues such as the retina is one of several factors that may serve to optimize vitamin-A nutritional status in patients with cirrhosis.