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Biomedical subjects

K A Martin

Publications and source records attributed to K A Martin.

143 records · Page 8Linked to original sources
PubMed1982

Treating monocularly deprived lambs with 4-aminopyridine produces rapid changes in ocular dominance only after short periods of deprivation.

Lambs of various ages (4-30 days) were monocularly deprived for periods ranging from 4 to 51 days after which they were prepared for conventional electrophysiological recording from the striate cortex. Sufficient units were sampled to obtain a representative ocular dominance (OD) histogram. A second sample of units was then obtained after the lambs had been given an i.v. dose of 4-aminopyridine (4-AP; 0.5-5.3 mg/kg) which increases synaptic transmission. For four out of five lambs in which the deprivation had been of 4-5 days duration there was a significant increase in responsiveness of the deprived eye to stimulation after the 4-AP had been given. By contrast, only one out of four lambs which had been deprived for 19-51 days showed a significant recovery after 4-AP treatment. The results suggest that during the initial stages of monocular deprivation the deprived eye remains connected to, but is less effective in driving, cortical cells. One explanation of the failure to reactivate the deprived eye after long periods of deprivation is that the deprived eye becomes anatomically disconnected from cortical cells.

4-Aminopyridine↗
PubMed1982

Some determinants of optic terminal localization and retinotopic polarity within fibre populations in the tectum of goldfish.

1. The reorganization of the retinotectal projection which results after partial ablation of tectal tissue was examined in goldfish using electrophysiological methods. 2. Regardless of the size of a unilateral ablation of caudal tectum, an orderly and virtually complete, 'compressed', visual projection re-formed on the remaining tectum after crushing the optic nerve and allowing it to regenerate. 3. If the optic nerve was left intact after ablations of caudal tectum, compressed projections were only found when the ablations were small. Large caudal ablations involving half or more of the dorsal tectum resulted in the cut fibres transposing onto the remaining tectum and forming an overlaid, 'duplicate', projection on the remaining intact projection. 4. In approximately one third of cases the duplicate projection lay in a reversed polarity along the rostrocaudal axis of the tectum. In the remaining cases the polarity of the duplicate projection was normal. 5. Transposed projections of reversed rostrocaudal polarity could be consistently obtained by ablating temporal retina and caudal tectum, leaving an intact strip of fibres terminals along the caudal edge of the tectal remnant. 6. Compression and duplication occurred in the same way if fish were maintained in constant light. 7. After ablations of lateral tectum, leaving the optic nerve intact, compression and some disorderly duplications were found. 8. Reversed projections could be induced across the mediolateral axis of dorsal tectum by denervating the medial tectum and ablating a strip of lateral tectum. 9. Projections of normal polarity were found after the optic nerve was allowed to regenerate into tecta which had previously supported reversed polarity projections.

Animals↗
PubMed1981

Half-life of 13,14-dihydro-15-keto prostaglandin f2 alpha in peripheral plasma of the pig.

The metabolite of prostaglandin F2 alpha (PGF2 alpha ) namely 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM), was administered as an intravenous bolus injection into five adult pigs. Concentrations of PGFM in blood collected periodically after injection indicated a biexponential decline suggesting a rapid distribution to the extracellular fluid and a slower elimination by metabolism. A mean half-life value of 14.97 +/- 1.33 (SD) minutes was calculated for the second component of the decline in PGFM concentration.

Animals↗
PubMed1978

Comparison of the transfer of 125I, 82Br, and 26Cl into the growing oocytes of the Japanese quail.

Laying Japanese quail were doubly-labeled with either 125I and 36Cl or 82Br and 36Cl. Eighteen-hour accumulations, expressed as percent of tracer doses, were: growing oocytes, 125I 48.2 vs. 36Cl 2.07, 82Br 4.01 vs. 36Cl 1.99; thyroids, 125I 10.6 vs. 36Cl .030, 82Br .027 vs. 36Cl .020. Concentrations (expressed as percent per gram) of the radionuclides in the growing oocytes and the thyroids as compared with concentrations in the plasma were: for oocytes, the mean 125I concentration was 199 times the mean plasma concentration, 82Br was .34 x and 36Cl was .13 x; for thyroids, 125I was 13,500 x, 82Br was .48 x, and 36Cl was .41 x the mean plasma concentration. Eight day totals for yolks of eggs laid were 125I 29% vs. 36Cl 3.7%.

Animals↗
PubMed1976

A study of solvent effects on the phosphorescence properties of flavins.

A combination of zero field triplet state techniques are used to study the excited electronic states of a series of flavin and flavin related molecules both in single crystals and glass matrices. Particular attention is given to the effects of solvent interaction on the triplet state properties of the flavin molecules. The total phosphorescence decay rate constants at 1.4 degrees K are reported for the flavin molecules in polar and nonpolar solvents. The rate constants are then correlated to the degree of solvent interaction. Results indicate possible complex formation between the isoalloxazine and adenine groups in FAD. Finally, the results and possible interpretation on the study of a flavoenzyme, L-amino acid oxidase are presented.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Form, function, and intracortical projections of neurons in the striate cortex of the monkey Macacus nemestrinus.

Single neurons were recorded in the striate visual cortex (area 17) of the old-world monkey Macacus nemestrinus. Eight pyramidal neurons, seven spiny stellate neurons, two basket cells, a clutch cell, and a chandelier cell were filled intracellularly with HRP. Their receptive fields were consistent with previous single-unit studies. Their axonal arbors were less elaborate than in equivalent neurons in the cat, but the laminar specificity of the boutons was very much more precise in the monkey than in the cat. Nevertheless, the basic cortical circuits in cat and monkey appear to be very similar.

Animals↗
PubMedDate not supplied

Estimates of the net excitatory currents evoked by visual stimulation of identified neurons in cat visual cortex.

The action potential discharge response of single neurons to both visual stimulation and injections of current were obtained during intracellular recordings in cat visual cortex in order to estimate the net excitatory current arriving at the soma during visual stimulation. Of 45 neurons recorded intracellularly, 19 pyramidal neurons and one basket cell were labelled with horseradish peroxidase. The discharge of all neurons adapted to constant current. For 40 neurons, a single exponential provided a good fit to the adapting discharge (r2 = 0.73 +/- 0.03) for all current intensities. Superficial layer neurons were significantly faster adapting [P < 0.001, mean (+/- SEM) time constant of adaptation = 11.5 +/- 1.3 ms; n = 20] than deep layer neurons (mean time constant of adaptation = 51.4 +/- 6.4 ms; n = 10). The percentage adaptation of the spike frequency, %(peak - adapted rate)/peak, was determined from the fitted exponential. Superficial layer neurons adapted significantly more strongly (P < 0.01, mean = 67 +/- 3%) than deep layer neurons (mean = 51 +/- 5%). The mean firing frequency in response to a current step of 320 ms duration had a linear relationship to the amplitude of the injected current (slope 66 spikes/s/nA; origin zero, mean r2 = 0.94; n = 33). This relationship provided a means of estimating the net peak excitatory current generated by visual stimuli. The estimated mean peak somatic current during the passage of a bar across the receptive field was 1.1 nA and the average current for the duration of the visually evoked discharge was 0.64 nA (n = 17). The transfer response of real and model neurons was obtained by differentiating the discharge response to a step input current and was then used to predict the output of the neuron following an arbitrary input. When these transfer responses were convolved with known input signals in model neurons, the predicted output was close to the simulated response of the model neuron to the same input waveforms. The transfer response was calculated for eight real neurons. Estimates of the net excitatory current arriving at the soma during visual stimulation was obtained by deconvolution. The mean peak somatic current for these neurons was 0.62 nA.

Action Potentials↗