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Biomedical subjects

D W Shucard

Publications and source records attributed to D W Shucard.

At least 37 records · Page 2Linked to original sources
PubMed1987

Pentobarbital-induced changes in the mouse brainstem auditory evoked potential as a function of click repetition rate and time postdrug.

The effects of pentobarbital (80 mg/kg, i.p.) and saline injections on the BAEP were studied in 10 adult female BDF1 mice. Pentobarbital anesthesia induced statistically significant increases in the amplitudes and latencies of various BAEP components relative to preinjection and saline control values. These pentobarbital-induced changes were maximal shortly after drug administration and dissipated over time in a pattern similar to a drug elimination curve. Since pentobarbital and fast stimulus repetition rates are considered to be 'synaptic stressors', it was predicted that pentobarbital anesthesia and click repetition rate would have combined effects on the BAEP. This prediction was partially supported in that pentobarbital-induced changes in P4 amplitude and latency were significantly dependent on click repetition rate. The pentobarbital-induced effects on earlier BAEP components, however, proved to be largely independent of click rate. Pentobarbital-associated changes in the BAEP were not due to such factors as core temperature changes, circadian variations, and stress. The importance of anesthetic-induced changes in the BAEP for clinical and experimental studies is discussed.

Acoustic Stimulation↗
PubMed1987

Auditory event-related potentials in waking infants and adults: a developmental perspective.

Auditory event-related potentials (AERPs) were recorded in waking 1 month olds, 3 month olds, 6 month olds and adults in order to study the morphology and development of the wave form in the waking subject. Previous data were generally obtained in sleeping or drowsy infants. The findings indicated that there were 3 quantitative changes in the AERP over the first 6 months of life in waking infants: an increase in the latency of peaks, an increase in peak amplitude, and a decrease in intersubject variability. Adult peak latencies were generally shorter than those for 3 month olds and 6 month olds. Further, latencies of earlier AERP peaks for 1 and 6 month olds, in the present study, were comparable to those reported in previous investigations with sleeping infants. However, latencies of later AERP peaks differed from those of previous reports and were closer to those reported for waking adults. With respect to the amplitude, the 6 month olds, in general, had the highest amplitudes, the 1 month olds the lowest, and the 3 month olds and adults fell in between the two groups. Some differences were present between early and late components. The findings of this study are significant in that the AERPs were quantitatively different from those reported in earlier work with sleeping or drowsy infants. If cognitive and perceptual development is to be studied, it is necessary to obtain data on waking subjects. The data presented in this report are consistent with behavioral studies of biobehavioral shifts that are associated with changes in responsivity of the organism to stimuli during the first 6 months of life.

Adult↗
PubMed1987

Brain-reactive autoantibody levels in the sera of ageing autoimmune mice.

Brain-reactive autoantibodies are thought to play an important role in mediating central nervous system (CNS) disorders in systemic lupus erythematosus (SLE). In this paper the developmental occurrence of these antibodies in the sera of autoimmune mice, i.e. NZB, NZB/W, MRL/l and BXSB mice were examined. All murine strains tested, whether autoimmune or not, showed some degree of serum reactivity toward brain antigens. Autoimmune mice, however, displayed higher levels of serum brain-reactive antibodies, and at earlier ages, than non-autoimmune mice. Immunofluorescence assays against brain sections and adsorption assays, with both neural and non-neural tissue, indicated a heterogeneity in the specificity of the populations of brain-reactive antibodies present. These studies provide an important step in characterizing the appearance and diversity of brain-reactive autoantibodies, with the goal of better understanding their significance and potential role in mediating CNS dysfunction in SLE.

Aging↗
PubMed1986

Age-related hearing loss in BDF1 mice as evidenced by the brainstem auditory evoked potential.

Age-related hearing loss was studied in unanesthetized female BDF1 mice using brainstem auditory evoked potential (BAEP) latency-intensity (L-I) profiles and BAEP thresholds. The mice were divided into 5 age-related groups: 3-4 months, 5.5-7 months, 9-10 months, 12 months and 18 months. Relative to the youngest group, BAEP threshold data indicated shifts in auditory sensitivity ranging from +6 dB for the 5.5- to 7-month-old group to +71 dB for the 18-month-old group. The BAEP L-I profiles of older mice were consistent with recruitment-type sensorineural (cochlear) hearing losses. No evidence of retrocochlear involvement was observed.

Aging↗
PubMed1985

A method for chronically recording brain-stem and cortical auditory evoked potentials from unanesthetized mice.

Anesthetizing or sedating animals affords control over movement artifact during electrophysiological recording. However, the use of chemical restraint leads to unwanted side effects such as drug-induced hypothermia. Hypothermia is problematic because BAEP amplitudes and latencies are affected significantly by core temperature changes. Moreover, several recent studies have indicated that anesthetics and sedatives may significantly alter the BAEP and CAEP even in thermoregulated subjects. There is a need, therefore, to develop a practical technique for obtaining chronic BAEPs and CAEPs in restrained, unanesthetized animals. The present report describes a technique that permits the gathering of consistent, reliable evoked potential recordings over time in unanesthetized mice. The preparation is useful for studying the CNS effects of pharmacological agents, pathological conditions, aging and development in the mouse and could be adapted for use with other small animals as well.

Anesthesia↗
PubMed1985

The neuropsychological phenotype in Turner syndrome.

Numerous studies have demonstrated a significant depression in performance IQ (PIQ) in Turner Syndrome (TS) females, but the neuropsychological interpretation of this finding remains unclear. The present study addressed the following questions regarding the neuropsychological phenotype in TS: Are TS women neuropsychologically impaired? Is the impairment lateralized and How consistent is the neuropsychological phenotype across TS individuals? Unlike previous studies, the present study utilized both normal and brain damaged female controls. All subjects were given an extended Halstead-Reitan neuropsychological battery. The TS females were significantly worse than normals but not significantly different from brain damaged females in their overall level of neuropsychological functioning. However, their impairment was not lateralized. Their pattern of lateralizing findings was similar to that found in the Diffuse and Normal groups, but significantly different from either the right or left unilateral lesion groups. Fairly consistent deficits were found on tests of visuospatial skills and long term memory, but there was considerable variability in all the other test findings among TS individuals. The results are discussed in relation to the recent findings (Inglis and Lawson, 1981) that verbal-performance IQ discrepancies may be unreliable indicators of lateralized cerebral dysfunction in females. Hence the depressed PIQ in TS appears not to indicate predominantly right hemisphere dysfunction and may not even indicate a consistent underlying neuropsychological phenotype.

Dominance, Cerebral↗
PubMed1985

Effects of impeded breathing on auditory brainstem responses in conscious man.

Auditory brainstem responses (ABR) recorded in two groups of 10 normal volunteers were compared under conditions of impeded and unimpeded breathing. Impedance to breathing was accomplished by adding inspiratory flow-resistive loads of varying magnitude. Loaded breathing selectively augmented the amplitude of ABR components generated in the vicinity of the pontomidbrain junction. Peak latencies and other peak amplitudes of the ABR were unaffected. These findings suggest that the ABR procedure may serve as a direct noninvasive approach to the assessment of brainstem respiratory functions in conscious humans.

Adult↗
PubMed1985

Central nervous system effects of antiasthma medication--an EEG study.

The relationship between electroencephalographic (EEG) abnormalities (in particular paroxysmal activity) and theophylline alone or in combination with corticosteroids and/or ephedrine was examined in 161 adult and 93 pediatric patients. For each patient, total theophylline dosage was calculated and a theophylline blood level was obtained at the time of EEG recording. The major findings indicated: The presence of EEG paroxysmal activity in a greater percentage of the population studied than that which has been reported in a group of nonhospitalized individuals of similar age in the general population. There is a greater probability of EEG paroxysmal activity among patients with higher theophylline blood levels or total dosages than among those with lower blood levels or total dosages. There is an increase in EEG abnormalities with the addition of ephedrine. There is a possible protective effect of steroids against theophylline-related central nervous system disturbances.

Adrenal Cortex Hormones↗
PubMed1984

Event-related brain potentials differentiate normal and disabled readers.

Auditory event-related potentials (AERPs) recorded to irrelevant tone pairs while subjects performed visual, reading-related cognitive tasks differed significantly between normal and disabled readers. Disabled readers as compared with normal readers showed significantly lower amplitude right hemisphere AERP responses during tasks that involved visual-phonemic transfer of information and simple pattern recognition. Disabled readers as compared with normal readers also showed significantly higher amplitude left hemisphere responses during the visual-phonemic task. In both experimental conditions the reading-disabled subjects showed significantly lower amplitude right than left hemisphere AERP responses. Task-related strategies did not differ between groups. The pattern of AERP amplitude asymmetry found for disabled readers, which was opposite to that found for normal readers, suggests that the same reading-related tasks activated different cerebral processes in the two groups studied.

Adolescent↗
PubMed1983

The use of a control or baseline condition in electrophysiological studies of hemispheric specialization of function.

Asymmetries in event-related potential (ERP) measures between the two cerebral hemispheres in humans may not be apparent when the absolute values of left and right hemisphere recordings are only considered within the context of one experimental condition. ERP asymmetries may only emerge when results obtained during experimental conditions designed to differentially activate the two cerebral hemispheres are compared to a baseline or control condition involving low-level cognitive demands. Both theoretical and empirical considerations of such a baseline condition are discussed.

Adult↗
PubMed1983

Changes in patterns of hemispheric electrophysiological activity as a function of instructional set.

Investigations of differential hemispheric functioning which have used auditory event-related potentials (AERPs) typically employ paradigms in which two or more conditions are used. In these paradigms, conditions typically differ from each other with respect to both the physical aspects of the stimuli and the operations the subject must perform on these stimuli. Because both the subject's task and the physical properties of the stimuli change from one condition to another, it is unclear whether different patterns of AERP cerebral asymmetries obtained between conditions are primarily a function of differences in the stimuli (e.g., verbal vs. musical stimuli) or of endogenous factors such as the subject's cognitive approach to the processing of the stimuli. In the present study, two conditions with identical stimuli were employed but different instructions were given about how to process these stimuli. Music and paired tones were simultaneously presented in both conditions. In the Music Condition, subjects performed a task which involved attending to the music and ignoring the tones. In the Tones Sequence Condition, subjects counted specified sequences of tones and ignored the music. The results indicated that there were different patterns of left-right hemispheric AERP relationships between the two conditions. These findings support the hypothesis that endogeneous factors play a significant role in differential hemispheric functioning and that the AERP technique employed in this paradigm is a sensitive index of changes in electrophysiological activity associated with these endogeneous factors.

Acoustic Stimulation↗
PubMed1983

Permeability of the blood cerebrospinal fluid barrier during acute immune complex disease.

Changes in the permeability of the blood-brain barrier (BBB) and blood-cerebrospinal fluid (blood-CSF) barrier in rabbits were assessed by using a sensitive double isotope technique at different times after the induction of acute immune complex disease (AICD). Induction of AICD was done with a single large dose of bovine serum albumin, whereas controls received only saline. Animals were sacrificed 6, 9, 12, 15, and 18 days after induction. Extravasation of protein was measured by injecting rabbits i.v. with 131I-rabbit serum albumin (RSA) 24 hr before sacrifice. In order to correct for intravascular blood volume, 125I-RSA was injected 5 min before sacrifice. Extravascular blood equivalents (EVBE), a measure of barrier permeability, were elevated in the CSF of rabbits sacrificed on days 12 and 15. None of the brain regions from any of the animal groups showed any changes or significant differences from controls in EVBE values on these days. These results indicate that there was an increase in the permeability of the blood-CSF barrier to radiolabeled albumin but not in the BBB proper during the time that CSF IgG levels were elevated in AICD. The potential significance of these findings for the mechanisms mediating central nervous system involvement in systemic lupus erythematosus is discussed.

Acute Disease↗
PubMed1982

Suppression of water intake by immune complex formation in the hypothalamus. Implications for systemic lupus erythematosus.

Immune complex formation in the perifornical region of the hypothalamus resulted in depressed water consumption in rats, but did not consistently alter body temperature. The antibody with an unrelated antigen did not affect water consumption or body temperature. These results support the notion that immune complex reactions within the central nervous system can alter behavior.

Animals↗
PubMed1981

Evoked potentials to auditory probes as indices of cerebral specialization of function--replication and extension.

This study was an attempt to replicate findings from previous work in our laboratory as well as to study the relationship between vertex-referenced and linked mastoid-referenced responses under conditions purported to produce differential hemispheric activation. Auditory evoked potentials were recorded between T4-Cz, T3-Cz, T4-A1A2, and T3-A1A2 to task-irrelevant tone pips superimposed on a baseline condition and on two experimental conditions (verbal and music) hypothesized to differentially activate areas of the left and right cerebral hemispheres. Significant AEP amplitude asymmetries were obtained as a function of the ongoing tasks, replicating our previous findings. Higher amplitude AEPs were recorded from temporal-to-vertex leads from the hemisphere thought to be most involved in the ongoing task. In addition, temporal-linked mastoids placements showed an effect opposite to that seen for the vertex-referenced leads with lower amplitude AEPs occurring from the hemisphere purported to be most activated by the task. Mastoid-referenced placements were also less sensitive to task effects than vertex-referenced placements.

Adult↗
PubMed1981

Semantic comprehension in infancy: a signal detection analysis.

The purpose of this study was to validate a paradigm by which an infant's comprehension of concrete nouns could be assessed while controlling for (a) response bias, (b) stimulus preference, and (c) maternal cuing. More specifically, we sought to determine whether 11- and 13-month-old infants directed their eye fixations to the referent of an object word said by the mother and to determine whether there was a developmental shift in responding to object words at these 2 ages, as some previous research suggests. Duration of looking at each of 4 corners of an apparatus was measured while the mother (unable to see what the child was doing) uttered a word she felt the infant knew, 1 she felt he/she did not know, and a nonsense word. Analyses based on signal detection theory using "known" words as signal trials and nonsense words as noise revealed that 13-month-olds directed their looking time significantly longer at the referent of the known word when that word was uttered than when the nonsense word was uttered. At neither age did looking at the referent of the unknown word exceed control values. No significant effects were obtained at 11 months of age, nor were there any sex effects.

Discrimination Learning↗