Biomedical subjects

G Yates

Publications and source records attributed to G Yates.

13 recordsLinked to original sources

PubMed1999

Coding of sound pressure level in the barn owl's auditory nerve.

Rate-intensity functions, i.e., the relation between discharge rate and sound pressure level, were recorded from single auditory nerve fibers in the barn owl. Differences in sound pressure level between the owl's two ears are known to be an important cue in sound localization. One objective was therefore to quantify the discharge rates of auditory nerve fibers, as a basis for higher-order processing of sound pressure level. The second aim was to investigate the rate-intensity functions for cues to the underlying cochlear mechanisms, using a model developed in mammals. Rate-intensity functions at the most sensitive frequency mostly showed a well-defined breakpoint between an initial steep segment and a progressively flattening segment. This shape has, in mammals, been convincingly traced to a compressive nonlinearity in the cochlear mechanics, which in turn is a reflection of the cochlear amplifier enhancing low-level stimuli. The similarity of the rate-intensity functions of the barn owl is thus further evidence for a similar mechanism in birds. An interesting difference from mammalian data was that this compressive nonlinearity was not shared among fibers of similar characteristic frequency, suggesting a different mechanism with a more locally differentiated operation than in mammals. In all fibers, the steepest change in discharge rate with rising sound pressure level occurred within 10-20 dB of their respective thresholds. Because the range of neural thresholds at any one characteristic frequency is small in the owl, auditory nerve fibers were collectively most sensitive for changes in sound pressure level within approximately 30 dB of the best thresholds. Fibers most sensitive to high frequencies (>6-7 kHz) showed a smaller increase of rate above spontaneous discharge rate than did lower-frequency fibers.

Acoustic Stimulation↗

PubMed1999

Role of L-type Ca(2+) channels in transmitter release from mammalian inner hair cells I. Gross sound-evoked potentials.

Intracochlear perfusion and gross potential recording of sound-evoked neural and hair cell responses were used to study the site of action of the L-type Ca(2+) channel blocker nimodipine in the guinea pig inner ear. In agreement with previous work nimodipine (1-10 microM) caused changes in both the compound auditory nerve action potential (CAP) and the DC component of the hair cell receptor potential (summating potential, or SP) in normal cochleae. For 20-kHz stimulation, the effect of nimodipine on the CAP threshold was markedly greater than the effect on the threshold of the negative SP. This latter result was consistent with a dominant action of nimodipine at the final output stage of cochlear transduction: either the release of transmitter from inner hair cells (IHCs) or the postsynaptic spike generation process. In animals in which the outer hair cells (OHCs) had been destroyed by prior administration of kanamycin, nimodipine still caused a large change in the 20-kHz CAP threshold, but even less change was observed in the negative SP threshold than in normal cochleae. When any neural contamination of the SP recording in kanamycin-treated animals was removed by prior intracochlear perfusion with TTX, nimodipine caused no significant change in SP threshold. Some features of the data also suggest a separate involvement of nimodipine-sensitive channels in OHC function. Perfusion of the cochlea with solutions containing Ni(2+) (100 microM) caused no measurable change in either CAP or SP. These results are consistent with, but do not prove, the notion that L-type channels are directly involved in controlling transmitter release from the IHCs and that T-type Ca(2+) channels are not involved at any stage of cochlear transduction.

Acoustic Stimulation↗

PubMed1998

Relationship between oversizing of self-expanding stents and late loss index in carotid stenting.

Stenting of the internal carotid artery is facilitated by stenting across the carotid bifurcation and sizing the diameter of a self-expanding stent to the large common carotid segment. This usually results in marked oversizing of the self-expanding stent in the internal carotid segment. This study was done to determine the relationship between stent oversizing and late luminal loss index after stenting of the internal carotid artery. Between September 1995 and March 1997, there were 165 patients (189 vessels) who underwent successful carotid stenting with self-expanding stents. Fifty-nine patients (63 vessels) had six-month follow-up carotid angiograms and on-line quantitative angiographic analysis. The mean reference diameter of the internal carotid arteries was 4.93+/-1.31 mm. Nominal stent size was 5 mm in 4 patients, 6 mm in 6 patients, 8 mm in 106 patients, 10 mm in 77 patients, and 12 mm in 1 patient. The average stent/patient was 1.03+/-0.16. There were three patients who had more than 50% diameter renarrowing at follow-up. The mean late loss index was 0.25+/-0.41. By linear regression analysis, there was no clear linear relationship between stent oversizing and late loss index after stenting (correlation coefficient = -0.21, P = 0.09). When analysis of variance with linear contrast was used to analyze six groups of different stent/artery ratios (from 1.4 to > or = 2), late loss indexes are significantly lower in the groups of high stent/artery ratio than the groups of low stent/artery ratio (P = 0.01). The process of oversizing of self-expanding stents deployed in the internal carotid artery does not appear to be associated with late restenosis and high stent/artery ratio seems to be associated with low late loss index.

Adult↗

PubMed1997

Intraduodenal vaccination of brushtail possums with bacille Calmette-Guérin enhances immune responses and protection against Mycobacterium bovis infection.

SETTING: An effective oral bacille Calmette-Guérin (BCG) vaccine would have advantages for use in humans and as an oral bait vaccine for protecting wild-life against bovine tuberculosis. OBJECTIVE: To compare the level of protection against tuberculosis in intraduodenally BCG-vaccinated possums with those vaccinated intragastrically in order to determine whether degradation of BCG in the stomach lowers vaccine efficacy. DESIGN: Three groups of five possums were vaccinated with BCG by the intraduodenal, intragastric or subcutaneous routes, with a fourth group serving as unvaccinated controls. The animals were later challenged intratracheally with a low dose of virulent Mycobacterium bovis. RESULTS: Possums vaccinated intraduodenally with BCG had significantly greater lymphocyte blastogenic responses to bovine purified protein derivative (PPD) and lower lung bacterial counts in comparison with intragastrically vaccinated animals. In comparison with unvaccinated animals, all of the BCG-vaccinated groups had significant protection against M. bovis infection as assessed by changes in body weight, lung weight and reduction in numbers of mycobacteria and granulomas in the spleen. CONCLUSION: The enhanced immune responses and protection against bovine tuberculosis observed in the intraduodenally BCG-vaccinated possums indicated that if BCG vaccine is protected from degradation in the stomach its efficacy should improve.

Administration, Oral↗

PubMed1992

Hippocampal lesions impair navigational learning in experienced homing pigeons.

Adult experienced homing pigeons from Maryland were subjected to hippocampal lesion and then transferred to a new loft in Ohio to examine what effect such treatment may have on learning to navigate to a new home loft. When subsequently released from an unfamiliar site, the hippocampal lesioned birds were impaired in taking up a vanishing bearing toward their new Ohio loft. This deficit is interpreted as an impairment in hippocampal-lesioned birds learning a new navigational map. Together with a previous study, the results suggest that an intact hippocampus is necessary if young naive or adult experienced homing pigeons are to learn a navigational map.

Animals↗

PubMed1991

Social isolation effects on the "behavioral despair" forced swimming test: effect of age and duration of testing.

Social loss is considered to be one of the major precipitants of depression. Prior work with the Porsolt forced swimming test (FST) has failed to demonstrate increases in despair-like immobility as a result of prior social isolation in adult animals. In the present work, increased immobility was observed in young Swiss Webster mice that had been socially isolated for 24 h prior to a 15-minute FST. The effect was not apparent until after the first five minutes of testing. The increase in immobility as a result of social isolation was apparent in 17-21-day-old animals but not in 26-30-day-old ones. Control experiments indicated that the increase in immobility was not due to the slightly higher weight loss of the socially isolated animals. Administration of reserpine (0.25 mg/kg) induced a marginal increase in immobility in the youngest animals but decreased immobility at later ages. These data suggest that the mouse only exhibits a short period of time during early development where social isolation can promote despair-like immobility in the FST and suggest that analyses of depressive processes which result from social variables may be best studied during a limited age range in this species.

Aging↗

PubMed1985