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Biomedical subjects

D Henderson

Publications and source records attributed to D Henderson.

At least 145 records · Page 8Linked to original sources
PubMed1993

Memory for source after traumatic brain injury.

A fame judgment task was used to distinguish subjects' ability to recognize previously presented information from their ability to recognize the source of that information. Traumatic brain injured (TBI) subjects were impaired relative to controls with respect to verbal recall and recognition as well as memory for source. However, memory for source was demonstrated to be independent of explicit indices of recall and recognition ability. It was also found to be an extremely sensitive index of coma duration in the TBI subjects. The anticipated relationship between source memory and a putative index of frontal function (Wisconsin Card Sorting Test) was modest relative to the relationship between source memory and subjects' performance on a complex visual pattern matching task (Benton Facial Recognition), raising questions about hypothesized cognitive and neurophysiological mechanisms underlying memory for source.

Accidents, Traffic↗
PubMed1993

Cyclic GMP-activated channels of the chick pineal gland: effects of divalent cations, pH, and cyclic AMP.

Chick pineal cells maintained in dissociated cell culture express an intrinsic photosensitive circadian oscillator, but the mechanisms of phototransduction in avian pinealocytes are not fully understood. In this study, we have used inside-out patches to examine the characteristics of cyclic GMP-activated channels of chick pinealocytes in more detail, concentrating on the effects of factors known to modulate the secretion of melatonin and/or the function of circadian pacemakers. In most patches, the predominant conductance state was 19 pS in symmetrical 145 mM NaCl. But in some patches, a second cyclic GMP-activated channel with a unitary conductance of 29 pS was also present. The current flowing through cyclic GMP-activated channels was not affected by application of salines containing 1 microM Ca2+ to the cytoplasmic face of the patch membrane. By contrast, application of 1 mM Ca2+ caused a partial reduction in cyclic GMP-activated current at all membrane potentials. Application of 1-5 mM Mg2+ ions caused a virtually complete blockade of current at positive membrane potentials, but caused only a small decrease in current at negative membrane potentials. No obvious differences in the gating of cyclic GMP-activated channels were observed in pH 8.2, 7.4 or 6.2 salines. Application of salines containing 100 microM, 500 microM, or 1 mM cyclic AMP did not cause activation of the channels, but 5 mM cyclic AMP evoked a low level of channel activity. Application of 5 mM but not 100 microM cyclic AMP decreased the probability of channel activation caused by 20-100 microM cyclic GMP and also increased the percentage of openings to an 11 pS subconductance state. Thus, cyclic AMP acts as a weak partial agonist. Nevertheless, the gating of these channels does not seem to be controlled directly by physiologically relevant changes in intracellular Ca2+, pH, or cyclic AMP.

Animals↗
PubMed1993

Post-operative infection of Proplast facial implants.

Proplast is an ultra-porous composite material that has been used widely to augment the facial skeleton. In recent years, however, the popularity of this material has declined because of complications associated with its use. This paper presents a retrospective study of 36 cases treated with 88 Proplast implants at one unit over a nine-year period. The results suggest that infection of the implant is the most common post-operative complication. Infection may occur at any time following implantation and appears to be more likely when implantation is associated with an osteotomy procedure. In addition, the overall rate of infection in this study (16%) was higher than reported previously and the male-female ratio was 2:1. The possible factors involved in infection are discussed.

Anti-Bacterial Agents↗
PubMed1993

Protection from noise induced hearing loss: is prolonged 'conditioning' necessary?

The effect of prior 'conditioning' noise exposures on the protection from subsequent higher level exposures was studied using four groups of chinchillas. The three experimental groups were 'conditioned' using a 0.5 kHz octave band noise at 95 dB SPL for 6 h a day. The first group was exposed to the noise once and allowed to recover for nine days prior to the second exposure. The second and third groups were exposed for ten and twenty days respectively. The first group showed only small reductions in threshold shift (TS) following the second exposure. The other two groups showed significant reductions in TS with repeated exposures. Following the last 'conditioning' exposure, all three experimental groups were allowed to recover for five days before exposing them to the same noise at 106 dB SPL for 48 h. Threshold shifts recorded following the 106 dB exposure were compared against those recorded in a control group exposed only to the higher level. Each of the three experimental groups developed significantly less permanent threshold shifts than the control group. However, there were no significant differences among the three experimental groups and the differences in hair cell losses were insignificant.

Acoustic Stimulation↗
PubMed1993

Individual susceptibility to noise-induced hearing loss: an old topic revisited.

The wide range in susceptibility to noise-induced hearing loss has intrigued researchers and hearing conservationists alike. Some of these differences in variability have been attributed to various intrinsic factors such as eye color, gender, age, etc. However, a review of controlled research shows that the influence of these intrinsic variables is relatively small and cannot explain the wide range of hearing loss observed in demographic studies. Furthermore, uncontrolled variables or unrecognized drug and noise interaction may obscure the relation between noise exposure and hearing loss. With the growing understanding of the physiology of the auditory system, new possibilities are emerging that may explain the range of susceptibility. A review of the role of acoustic reflex effectiveness, cochlear efferent function, and history of noise exposure provide a perspective for future strategies in predicting susceptibility to noise-induced hearing loss.

Age Factors↗
PubMed1993

Effect of low-frequency "conditioning" on hearing loss from high-frequency exposure.

Recent research has revealed that repeated exposures to a low-frequency noise results in a progressive reduction in threshold shifts (TS). This reduction in TS is not restricted to the exposure frequency, but can be observed at frequencies up to 3 or 4 octaves higher. Such "conditioning" exposures have also been observed to protect the auditory system against hearing loss from exposures to the same noise at higher levels. The aim of this study was to determine if "conditioning" using low-frequency exposures protects the auditory system against hearing loss from a high-frequency exposure. Monaural chinchillas were exposed to a 0.5-kHz octave band noise (OBN) at 95 dB SPL for 6 h a day. The animals were allowed to recover for 5 days, following which they were exposed to a 4-kHz OBN at 100 dB SPL for 48 h. Hearing thresholds determined using evoked potential recordings, indicated significantly greater permanent threshold shifts in this group of animals when compared to a control group exposed only to the 4-kHz OBN. These results were confirmed by histological examination which revealed greater hair cell loss in the experimental group.

Acoustic Stimulation↗
PubMed1992

Voltage- and Ca(2+)-activated ionic currents in acutely dissociated cells of the chick pineal gland.

Previous research on cultured chick pineal cells suggests that melatonin production is modulated by Ca2+ influx through voltage-dependent Ca2+ channels. The possible existence of other ionic currents was investigated by means of whole-cell recordings from acutely isolated cells. Several different inward and outward currents were identified. Inward currents included L-type Ca2+ currents and voltage-activated tetrodotoxin (TTX)-sensitive Na+ currents. Sodium currents have not been reported previously in pineal cells of any species. These two inward currents were present in the majority of cells. Chick pineal cells also expressed several types of voltage-dependent and Ca(2+)-dependent K+ currents that differed in voltage dependence, kinetics, and pharmacology. These included two Ca(2+)-dependent outward currents which differed in sensitivity to tetraethylammonium chloride (TEA), and at least two distinct voltage-activated K+ currents. Considerable cell-to-cell variation in the amplitude and nature of the evoked outward currents was observed. These ionic currents may be important for the regulation of melatonin synthesis and the modulation of circadian rhythmicity.

Animals↗
PubMed1992

Ingestive behavior and body temperature of pigeons during long-term cold exposure.

Pigeons well adapted to living in 21 degrees C ambient temperature (T(a)) were continuously exposed to cold T(a) for 6 days (Experiment 1) or 30 days (Experiment 2). The pigeons lived on a 12:12 L:D cycle where they could obtain short access to food and water at any time in the light phase by making 12 keypeck responses. Across the two experiments, the levels of cold exposure were 6 degrees C, 1 degrees C, and 0.6 degrees C. In cold, total daily food intake increased gradually across the first few days of the exposure, and the new level of food intake was inversely related to T(a). The daily ratio of total water drunk to total food eaten averaged approximately 1.3 in 21 degrees C, fell to approximately 1.0 on day 1 of cold exposure, and remained at that level for as long as 30 days. The day-night cycle in core body temperature was not changed by cold exposure. The bimodal temporal pattern of feeding in the light phase, which is characteristic of pigeons in moderate T(a), was preserved in the cold although the absolute level of feeding activity was enhanced. An analysis of the ways individual pigeons achieved total daily food intake by combining a number of feeding episodes with an average amount eaten per episode revealed considerable variation between birds, but a relatively constant feeding style within bird over time. In the colder temperatures used, however, the pigeons all increased the number of feeding episodes per day. The results provide the first detailed analysis of cold-induced changes in ingestive behavior in the pigeon and raise several questions about the behavioral expression of cold-sensitive regulatory processes.

Animals↗
PubMed1992

The effect of 'conditioning' on hearing loss from a high frequency traumatic exposure.

The role of high frequency, low level 'conditioning' exposures as moderators of hearing loss from subsequent exposure to the same noise at a higher level was studied using monaural chinchillas. All the animals in the experimental groups were exposed to an octave band noise centered at 4 kHz at 85 dB SPL for 6 h a day for 10 days. One of the experimental groups was allowed to recover for 5 days and the other was allowed to recover for 18 h, prior to the higher level exposure at 100 dB for 48 h. A third group exposed only to the higher level constituted the control group. A comparison of threshold shifts and hair cell loss after 4 weeks of recovery across the three groups revealed: (a) the 5-day recovery group incurred greater threshold shifts than the other two groups; the hair cell loss in this group was greater than in the 18-h recovery group, but the same as in the control group and (b) the 18-h recovery group incurred considerably less threshold shift as well as hair cell loss than the other two groups. The results were also compared with the results from similar exposures using low frequency noise which indicated that the base vs. apex differences in the cochlea appear to extend to the effects of 'conditioning' exposures.

Animals↗
PubMed1992

Factors influencing adjustment in the families of autistic children.

This study investigated factors influencing the adjustment of families of 49 autistic children (38 boys, 11 girls) to the stress of raising an autistic child. Analysis indicated that the severity of the child's disorder (stress), mother's social support (resources), and mother's perceived locus of control (perception) were significant factors in family adjustment. In addition, evidence suggested that agency affiliation also was an unexpected, yet important factor.

Adaptation, Psychological↗
PubMed1991

A cyclic GMP-activated channel in dissociated cells of the chick pineal gland.

Phototransduction in the vertebrate retina is dependent in part on a cyclic GMP-activated ionic channel in the plasma membrane of rods and cones. But other vertebrate cells are also photosensitive. Cells of the chick pineal gland have a photosensitive circadian rhythm in melatonin secretion that persists in dissociated cell culture. Exposure to light causes inhibition of melatonin secretion, and entrainment of the intrinsic circadian oscillator. Chick pinealocytes express several 'retinal' proteins, including arrestin, transducin and a protein similar to the visual pigment rhodopsin. Pinealocytes of lower vertebrates display hyperpolarizing responses to brief pulses of light. Thus it is possible that some of the mechanisms of phototransduction are similar in retinal and pineal photoreceptors. We report here the first recordings of cyclic GMP-activated channels in an extraretinal photoreceptor. Application of GMP, but not cyclic AMP, to excised inside-out patches caused activation of a 15-25 pS cationic channel. These channels may be essential for phototransduction in the chick pineal gland.

Animals↗
PubMed1991

Two types of antiprogestins identified by their differential action in transcriptionally active extracts from T47D cells.

Transcriptionally active nuclear extracts from human breast carcinoma cells (T47D) were used to compare the action of progestins and several antiprogestins of the 11 beta-aryl substituted steroid series on the DNA-binding properties and the trans-activating potential of progesterone receptor (PR) in vitro. Using the gel-shift assay we identified a novel type of antiprogestin (ZK98299, type I), which in contrast to type II antiprogestins, including RU486, does not induce binding of PR to progesterone response elements (PREs). In competition experiments excess of type I antiprogestin inhibits induction of DNA binding of PR by progestins and type II antiprogestins suggesting that its binding to PR interferes with the formation of stable receptor dimers. Moreover, we demonstrate that the antagonistic action of ZK98299 can be fully mimicked in vitro by using cell-free nuclear extracts from T47D cells and a 'simple' test promoter. In contrast, type II antiprogestins known to induce certain promoters in vivo exert strong agonistic effects on in vitro transcription of the test template used.

Base Sequence↗