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Biomedical subjects

R H Douglas

Publications and source records attributed to R H Douglas.

At least 19 recordsLinked to original sources
PubMed1992

Kynurenine identified as the short-wave absorbing lens pigment in the deep-sea fish Stylephorus chordatus.

A number of deep-sea fish have bright yellow lenses whose coloration is attributable to a variety of largely unidentified short-wave absorbing pigments. Here the pigment of the deep-sea fish Stylephorus chordatus has been isolated and identified by NMR and mass spectroscopy as kynurenine; a pigment also found in the human lens. The degree of this pigmentation is greater in older animals. The fact that the lenses of both a deep-sea fish and man contain the same pigment is of interest, given the vastly different light environments they inhabit.

Animals↗
PubMed1992

Endocrine abnormalities and hormonal therapy.

Routine measurement of estrogens, testosterone, T4, insulin, FSH, and LH at least four times per year (e.g., during each of the four seasons) may improve the efficiency of stallion management. Benefits may not be realized in the short term but will provide valuable historical data on individual stallions that, when added to other data, will improve ability of management personnel to initiate early treatment and delay or slow declining fertility. This ability will be greatly improved as more data and products become available. There appears to be a relationship between low total estrogen concentration/high FSH concentration and subfertility. This condition is associated with high average breedings per pregnancy. A decrease in concentration of estrogen and an increase in FSH concentration often precede a decline in fertility associated with oligospermia. Hypogonadotropic stallions have not been reported. This condition is not likely to be a cause of declining fertility in stallions and greatly limits the potential efficacy of GnRH therapy in subfertile stallions. Much research must be done to elucidate the etiology of testicular degeneration associated with increased FSH concentrations and decreased estrogen concentrations in stallions. At present, no reliable hormonal therapeutic protocols exist that will improve fertility in subfertile stallions.

Animals↗
PubMed1991

Ultraviolet-sensitive cones in the goldfish.

Goldfish have been shown behaviourally to have ultraviolet sensitivity. We have now identified by microspectrophotometry a population of small single cones in the goldfish retina that contain a visual pigment maximally sensitive around 355-360 nm.

Animals↗
PubMed1990

Retinal dopamine.

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Adaptation, Ocular↗
PubMed1990

Dopamine in the cerebrospinal fluid of prepubertal and adult horses.

Catecholamine concentrations (pg/ml) in the cerebrospinal fluid (CSF) of prepubertal (n = 9) and adult (n = 18) horses were determined by radioenzymatic assay. Norepinephrine was low or non detectable in all CSF samples. In contrast, measurable CSF dopamine concentrations were effected by age, reproductive status and exogenous steroid treatments. The concentration of dopamine in the CSF of prepubertal females (733 +/- 92) was greater (p less than 0.05) than the concentration in the CSF of prepubertal males (117 +/- 67). Prepubertal male horses which were treated with testosterone for 5 days (50 mg/day) had elevated (p less than 0.05) dopamine concentrations (2,533 +/- 1,160) in the CSF compared to control males. In adult mares, dopamine was lower (p less than 0.05) in the ovulatory season (25 +/- 10) than during the anovulatory season (200 +/- 101). Daily intramuscular estradiol-17 beta (5 mg/day) injections had no effect (p less than 0.05) on dopamine concentrations in the CSF of seasonally anovulatory mares (250 +/- 35). Further, concentrations of dopamine in the CSF of long-term ovariectomized mares (80 +/- 21) were not influenced (p less than .05) by season. These results suggest that age, sex and gonadal steroids may effect dopamine, but not norepinephrine, concentrations in the brain ventricular system of the equine species. Further, seasonal effects on CSF dopamine concentrations are dependent upon the presence of the ovaries.

Animals↗
PubMed1990

Time course of cerebra; magnetic resonance changes after electroconvulsive therapy.

Nuclear magnetic resonance images of the non-dominant cerebral hemisphere were obtained in 20 unipolar depressed patients immediately before and 25 minutes after electroconvulsive therapy (ECT). T1 values rose about 1%. Repeated scanning up to 24 hours after ECT was carried out in 13 of these patients. The greatest change in magnetic resonance images was two hours after ECT, and thereafter images gradually returned to baseline values. There was no correlation between magnetic resonance changes and the time taken to become reorientated after ECT.

Adult↗
PubMed1989

Rods trigger light adaptive retinomotor movements in all spectral cone types of a teleost fish.

Action spectra for light induced cone contraction are described for the two spectral cone types of a dichromatic (red/green) cichlid species (Aequidens pulcher). Criterion response thresholds (50% of maximal response amplitude) were determined for seven wavelengths. After correcting for absorption by cornea and lens, the resulting action spectra were compared with the absorption spectra of the rod and cone visual pigments. We find (i) that the action spectra of red and green sensitive cones are almost identical and (ii) matched most closely the absorption spectrum of the rod visual pigment. We therefore conclude that light adaptive cone contraction is triggered by light absorption in rods, which in the dark adapted state are located next to the external limiting membrane and are therefore in an optimal position to capture the incident light during early dawn. Possible mechanisms of signal transfer from rods to cones are discussed.

Adaptation, Ocular↗
PubMed1989

The spectral transmission of the lens and cornea of the brown trout (Salmo trutta) and goldfish (Carassius auratus)--effect of age and implications for ultraviolet vision.

This study reports spectral transmission curves (250-700 nm) for the lenses and corneas of two teleost species known to be u.v. sensitive; brown trout (Salmo trutta) aged 0-3 yr, and goldfish (Carassius auratus) aged 0-4 yr. In both cases there is a decrease in lenticular short-wave transmission with increased age which cannot be explained by an increase in lens size alone. Corneas of goldfish go through a similar ageing process while those of the trout do not. An orange pigmentation located in the dorsal cornea of goldfish is also described.

Aging↗
PubMed1989

The spectral transmission of freshwater teleost ocular media--an interspecific comparison and a guide to potential ultraviolet sensitivity.

Based on their spectral transmission, the lenses of 50 teleost species can be classified into three categories: "type 1" colourless lenses with 50% transmission points between 315 and 354 nm, "type 2" lenses which also appear colourless but have 50% cut-off points around 362-405 nm, and "type 3" lenses which are visibly yellow (50% transmission 425-450 nm). Most corneas transmit all wavelengths down to around 300 nm, with only 3 species showing a distinct yellow colouration. This distribution of ocular media transmission is related both to the phylogenetic group of the fish and to their photic environment.

Animals↗
PubMed1989

Effect of general anaesthesia on the magnetic resonance imaging signal from the brain.

Magnetic resonance images of the brain were obtained in 10 female patients before and 2-6 h after a standard general anaesthetic. The longitudinal magnetic relaxation times (T1) showed a non-significant decrease, whereas the transverse magnetic relaxation times (T2) increased in all scans, with significant increases in the pons and corpus callosum. This suggests that general anaesthesia may be associated with structural changes in the brain at a molecular level.

Adult↗
PubMed1989

Magnetic resonance imaging of the brain in alcoholics: cerebral atrophy, lifetime alcohol consumption, and cognitive deficits.

Magnetic resonance imaging of the brain in 69 detoxified alcoholics revealed that relaxation time (T1) in whole brain and in grey matter and parietal white matter was greater than in age-matched controls. In 48 patients, data on cognitive function and lifetime alcohol consumption were available. With age-controlled, lifetime consumption, and impairment on performance in the cognitive test (a Category Sorting Test) correlated positively with T1 whole brain and in selected regions. Impairment in the cognitive test correlated with increased T1 in whole brain and white matter independently of cerebral atrophy. Alcohol consumption patterns in the following 6 months were unrelated to changes in T1. The excess water implied by the elevated T1 values may be intra- or extracellular. It is uncertain whether or not T1 elevation in alcoholics is a marker of neuronal damage. T1 elevation appears to be a marker of one type of alcohol-related cognitive impairment.

Adult↗
PubMed1988

Size constancy in goldfish (Carassius auratus).

This study examines whether fish are able to judge the real size of objects taking distance into account, or if size judgements are based purely on the angle objects subtend on the retina. Goldfish were trained to discriminate between 2 targets which differed from one another only in their diameters (5 cm and 10 cm), presented initially equidistantly from the fish. A choice of the correct target was rewarded either by food or by access to other fish. Following successful training, the targets were shifted so that they both subtended the same visual angle. The fish continued to choose the target to which they had been trained, showing that they display size constancy. This ability was present in both monocular and binocular animals.

Animals↗
PubMed1988

Brain hydration during alcohol withdrawal in alcoholics measured by magnetic resonance imaging.

Twenty-seven patients had a first Magnetic Resonance Imaging (MRI) scan 1-3 days after stopping drinking and a second approximately 2 weeks later with no change in whole brain T1 or T1 in selected brain areas. Six patients whose first scan was over 36 h after the last drink underwent an increase in whole brain T1 in the interval to the second scan. The later the first scan was performed the greater was the increase in T1. These results are compatible with a very early fall in brain water immediately on cessation of drinking (perhaps due to a rebound increase of vasopressin activity) with a return to 'baseline' after two weeks. A third scan after discharge from hospital in 23 individuals who had abstained from alcohol or drank very little did not reveal any further significant change in brain T1.

Adult↗
PubMed1988

Magnetic resonance imaging in pre-senile dementia of the Alzheimer-type, multi-infarct dementia and Korsakoff's syndrome.

Magnetic resonance imaging T1 values in Alzheimer's disease (ATD) were similar to age-matched controls although frontal T1 values tended to increase intraindividually with progression of the dementia. T1 values were raised, in both cortical grey and white matter, in Korsakoff's syndrome and multi-infarct dementia. T1 values appear of little value in studying the neuropathological changes in ATD in relationship to the neuropsychological deficits, but can assist in the differential diagnosis of pre-senile dementia.

Aged↗