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Biomedical subjects

G F Wilson

Publications and source records attributed to G F Wilson.

53 records · Page 3Linked to original sources
PubMed1988

Sensitivity of auditory cortical neurons of kittens to monaural and binaural high frequency sound.

The experiments reported here describe the abilities of young auditory cortical neurons to encode information about tone bursts having frequencies above 2.5 kHz. The studies were carried out in anesthetized kittens ranging from 8 to 44 days of age. At all ages studied, stimulation of the contralateral ear was most effective in evoking spikes. Typically the response was confined to stimulus onset. Thresholds were comparatively high and response latencies were comparatively long in the youngest kittens studied. The time course of threshold development was very similar to that of the auditory nerve and cochlear nuclei indicating that most, if not all, age related thresholds and threshold changes at the cortical level are accounted for by mechanisms operating at the level of the cochlea and auditory nerve. Response latency shortened progressively over the first month of postnatal life and while the absolute change in response latency differed considerably from that of cells in the cochlear nuclei the proportional changes were very similar. These data indicate that the comparatively long response latency and latency changes recorded at the cortex are imposed by underdeveloped central auditory processes. Response areas of kitten cortical neurons resembled those of the adult. At all ages studied, binaural interactions were robust and similar in kind to those recorded in adult cats. We conclude that cortical neurons of kittens preserve the results of interactions occurring at lower brainstem levels and that the development of the circuits of which these neurons are a part develop as a functional unit.

Age Factors↗
PubMed1988

Importance of body tissues as sources of nutrients for milk synthesis in the cow, using 13C as a marker.

1. The proportions of carbon in individual milk constituents derived from feed and body tissues in dairy cows, were estimated by taking advantage of the natural variations which occur in the ratio, 13C:12C present in C3- and C4-plant species. 2. Four cows, which had previously grazed C3 plants (ryegrass (Lolium spp.) and white clover (Trifolium repens)), were accustomed to indoor feeding on a ration of C3-plant material (cut pastures and barley meal). The ration was then changed abruptly to one of C4-plant material (paspalum (Paspalum dilatatum) hay, maize silage and meal) for a period of 8 or 9 d in early and again in late lactation. 3. During early lactation it was estimated that 54% of the C in milk fat was derived from the body fat reserves of high genetic merit cows. Corresponding values for casein and lactose were 34 and 24% respectively, if it is assumed they were derived from body protein reserves. In contrast steam-volatile fatty acids in milk fat were almost entirely derived from dietary sources. 4. The proportional contribution of body-tissue C to individual milk constituents varied considerably between animals, possibly associated with genetic merit or the size of the body reserves available for mobilization. 5. In late lactation, when cows were close to energy and protein balance, contributions of body-tissue C to milk fat, casein and lactose ranged up to 19, 19 and 8% respectively. 6. Estimates of endogenous losses of C in faeces averaged 12 and 9% in early and late lactation respectively, and corresponding values for endogenous urinary C were 23 and 15%.

Animal Feed↗
PubMed1988

Hemispheric asymmetries in phonological processing assessed with probe evoked magnetic fields.

Auditory Evoked Magnetic Fields (EFs) to tonal stimuli were recorded at homotopic maxima over the left and right auditory areas in nine subjects. Recordings were made during two conditions, both involving simultaneous presentation of the probe tone stimuli and a set of tape-recorded verbal material. During the control condition subjects were instructed to attend to the tones and ignore the verbal material. In the phonological processing condition they were instructed to ignore the tones and attempt to identify a phonological target item which was embedded in the verbal material. EFs obtained during both conditions were characterized by an early N1m and a later P2m component corresponding to the N1 and P2 components of auditory evoked potentials (EPs). During the phonological condition, the amplitude of the N1m was significantly reduced in both hemispheres symmetrically whereas the amplitude of the P2m was attenuated to a significantly greater degree in the left hemisphere. These data are in agreement with previous EP evidence of greater interference of linguistic processing with processing of irrelevant probe stimuli in the left hemisphere, indicative of greater left hemisphere involvement in language tasks.

Acoustic Stimulation↗
PubMed1985

Neurons in the cat's primary auditory cortex distinguished by their responses to tones and wide-spectrum noise.

In the cortex of barbiturate-anesthetized cats, area AI was identified by its tonotopic organization, and single neurons in that field were examined with regard to the shapes of their spike count-versus-intensity functions, the organization of their frequency-intensity response areas, and their responses to wide-spectrum noise, using calibrated sealed stimulating systems. Neurons whose pure tone rate intensity functions were monotonic in shape displayed V-shaped response areas that were open-ended at high tone intensities. In contrast, cells displaying nonmonotonic tone intensity functions tended to have circumscribed response areas; these cells were responsive to tones over limited ranges of both frequency and intensity. Monotonic neurons almost always responded to wide-spectrum noise stimuli, while nonmonotonic neurons often did not. The mean minimum latent period of monotonic cells (14.0 ms) was significantly shorter than that for nonmonotonic neurons (19.1 ms). For those cells that responded to both tones and noise, minimum latent periods for the two stimuli were similar or identical. Monotonic neurons tended to be horizontally segregated from nonmonotonic neurons across AI's middle cortical layers. The implications of these data for the nature of some neural mechanisms underlying the stimulus selectivity of cortical cells are discussed.

Anesthesia, General↗
PubMed1984

Dexamethasone in electroconvulsive therapy: efficacy for depression and post-ECT amnesia.

Dexamethasone, compared to placebo in a double-blind study, failed to prevent the memory deficiency that typically accompanies electroconvulsive therapy (ECT) (n = 48 patients treated for DSM-III diagnosed major depressive disorder). Rather, the administration of the drug was associated with attention (p less than 0.02) and short-term memory (p less than 0.0003) difficulties in both bilateral and unilateral ECT patients. Bilateral ECT plus dexamethasone patients had significantly less improvement (p less than 0.05) in their depression (measured by the Hamilton Depression Scale) compared to bilateral ECT plus placebo patients. These depression differences were not seen among unilateral ECT patients.

Amnesia↗
PubMed1973

Some Physiological Effects of Viviparous Genes vp(1) and vp(5) on Developing Maize Kernels.

The effects of two viviparous genes, vp(1) and vp(5), on development of the maize (Zea mays L.) embryo and endosperm were investigated. Differences between viviparous and normal embryos first appeared at 25 to 30 days after pollination. Increases in fresh weights indicated that viviparous began to grow more rapidly than normal embryos at that time. Amino acids and ethanol-soluble carbohydrates also accumulated more rapidly in viviparous, but a reserve material (lipid) was lower in viviparous than in normal embryos.The fresh and dry weights and total nitrogen content of endosperms from viviparous resembled those of normal seeds until about 30 days after pollination, but were all lower in viviparous after that time. Pronounced differences in alpha-amylase activity were not observed until late in development (40 days after pollination) when the enzyme increased in viviparous seeds only. Developmental changes in viviparous seeds generally resemble those of normally germinating seeds.

Journal Article↗
PubMedDate not supplied

Gd-DTPA: an alternative contrast medium for CT.

OBJECTIVE: The purpose of this study was to demonstrate that gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) could be used as a contrast medium in CT as an alternative to iodine-based compounds. MATERIALS AND METHODS: Solutions of different concentrations of Gd-DTPA and iopromide were scanned in a tissue equivalent phantom and it was shown that Gd-DTPA caused 2.5 times the attenuation of an equimolar solution of iopromide. From these in vitro studies an in vivo dose of 0.5 mmol/kg Gd-DTPA was calculated to be equivalent to 50 ml iopromide 300. RESULTS: Pre- and postenhancement CT was performed in a volunteer using Gd-DTPA intravenously, and adequate enhancement occurred in intracranial vessels. CONCLUSION: Gd-DTPA can be used to provide enhancement during CT and might be of value in iodine-sensitive patients.

Brain↗