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R J Clarke

Publications and source records attributed to R J Clarke.

At least 91 records · Page 5Linked to original sources
PubMed1987

Detection of trace levels of trichothecene mycotoxins in environmental residues and foodstuffs using gas chromatography with mass spectrometric or electron-capture detection.

Methods are described for the simultaneous detection of a wide range of trichothecenes, including the most polar ones and some macrocyclics, using either gas chromatography-mass spectrometry with selected ion monitoring, or gas chromatography with electron-capture detection. Trichothecenes were extracted directly from the various matrices, or from Clin Elut columns, and cleaned up on Florisil Sep-Pak cartridges. Macrocyclics and neosolaniol were detected after hydrolysis to verrucarol and T-2 tetraol respectively. For optimum sensitivity (0.5-10 ng per sample) over the range, trichothecenes were detected, both before and after hydrolysis of ester groups, as their heptafluorobutyrate derivatives using a quadrupole mass spectrometer and negative ion chemical ionisation. The use of a magnetic sector instrument with electron-impact ionisation gave comparable sensitivity for most trichothecenes, but was less useful for the simultaneous detection of verrucarol in the presence of other trichothecenes. The methods were used to detect the presence of scirpentriol, nivalenol and 15-monoacetoxyscirpendiol in sorghum from Thailand. Trichothecenes in less complex matrices could be detected, after hydrolysis, using gas chromatography with electron-capture detection.

Chemical Phenomena↗
PubMed1987

Opioid mechanisms involved in the slow potential change and neuronal refractoriness during cortical spreading depression.

The slow potential change (spc) accompanying spreading depression (SD) was studied in rats and in a seizure-sensitive strain of Mongolian gerbil under three different experimental paradigms, each involving the use of naloxone. Gerbils undergoing electroconvulsive shock treatment displayed SD during the post-ictal phase, which was blocked by the intraperitoneal (i.p.) administration of naloxone (20-50 mg kg-1). Topical application of naloxone to the exposed cortex of the anaesthetized gerbil and rat blocked the spc of SD evoked by KCl. Microiontophoretic ejection of naloxone during extracellular recordings reversed cell refractoriness following the spc, demonstrated by the observation of a maintained sensitivity to iontophoretic pulses of glutamate. The results suggest a possible involvement of naloxone-sensitive processes in the mechanism responsible for cortical SD.

Animals↗
PubMed1987

Distribution of motoneurones innervating extraocular muscles in the brain of the marmoset (Callithrix jacchus).

Extraocular muscle motoneurones were localised in the oculomotor nucleus (ON), trochlear nucleus (TN) and abducens nucleus (AN) in the marmoset brain using the horseradish peroxidase (HRP) retrograde labelling technique. HRP pellets injected into individual extraocular muscles revealed one or more groups of labelled neurones occupying discrete loci within these nuclei. Relatively little overlap of motoneurone pools was observed, except in the case of the inferior oblique and superior rectus muscles. Injections of HRP into the medial rectus muscle revealed three separate populations of labelled cells in the ipsilateral ON. Motoneurones innervating the inferior rectus muscle were mainly localised in the lateral somatic cell column of the ipsilateral ON. A second smaller grouping was observed in the medial longitudinal fasciculus. The inferior oblique muscle motoneurones were localised in the ipsilateral medial somatic cell column intermingled with motoneurones supplying the superior rectus muscle of the opposite eye. The superior oblique muscle motoneurones occupied the entire TN and the lateral rectus muscle motoneurones the AN. It was concluded that the organisation of nuclei and subnuclei responsible for controlling the extraocular muscles in the marmoset is broadly similar to that of other primates.

Abducens Nerve↗
PubMed1987

Unusual distribution of ganglion cells in the retina of the three-toed sloth (Bradypus variegatus).

1. The distribution and size of retinal ganglion cells labelled with horseradish peroxidase (HRP) were studied in flat-mounted retinas of three-toed sloths. 2. Massive injections of HRP solution were made throughout the thalamus and midbrain in anesthetized sloths in order to retrogradely label the retinal ganglion cell population. Twenty to thirty h later the eyes were excised and the retinas flat-mounted and reacted with phenylenediamine-HCl and H2O2 to label ganglion cells, thus distinguishing them from other cells in the same retinal layer. 3. Ganglion cell density gradually increased from about 500 cells/mm2 at the far periphery to a peak of about 1,500 cells/mm2 in an area, termed the area centralis, deep in the inferior temporal retina. The presence of a vertical visual streak was also noted. 4. The area centralis contained a higher frequency of small ganglion cells than the peripheral retina where large cells predominated. 5. The unusual position of the area centralis and visual streak in the retina can be explained by the sloth's unique ability to rotate its head 180 degrees while climbing upside-down along horizontal branches so that the head is right-side-up. If it is assumed that the branch directly above the sloth's head needs to be visualized for accurate claw placement then the branch would be imaged on the inferior temporal retina in an area corresponding to the maximum density region.

Animals↗
PubMed1986

Detection of trace levels of trichothecene mycotoxins in human urine by gas chromatography-mass spectrometry.

A method is described for the simultaneous detection of the trichothecene mycotoxins T-2, HT-2, T-2 tetraol, diacetoxyscirpenol, 15-monoacetoxyscirpendiol, scirpentriol, nivalenol and deoxynivalenol, in human urine. Samples were extracted from Clin Elut columns and cleaned up using reversed-phase Sep-Pak C18 cartridges. Trichothecenes were derivatised as their heptafluorobutyryl esters, and detected by gas chromatography-mass spectrometry-selected-ion monitoring using electron impact ionisation. The method was validated by the analysis of 22 urine samples, spiked and submitted "blind" for analysis by another laboratory. An alternative gas chromatography-mass spectrometry method using negative ion chemical ionisation is also described and a preliminary comparison of the two methods made. The methods enabled levels down to 1 ppb to be detected, with confirmation of identity at levels between 2 and 5 ppb, depending on the toxin.

Gas Chromatography-Mass Spectrometry↗
PubMed1985

Luminance and darkness detectors in the olivary and posterior pretectal nuclei and their relationship to the pupillary light reflex in the rat. I. Studies with steady luminance levels.

In order to identify the pretectal nucleus which contains pupillomotor cells in the rat, cells were sought which were sensitive to changes in luminance level at the eye. Two types were found: Luminance detectors which showed a graded increase in firing with increase in luminance, and darkness detectors which showed a graded increase in firing rate with graded dimming of luminance intensity. All luminance detectors were located in the olivary pretectal nucleus, whereas darkness detectors were located in the posterior pretectal nucleus. Consensual pupil responses were recorded in conscious normal and sympathectomised rats using an infra-red sensitive T.V. pupillometer. Pupil diameter varied 2mm in an approximately linear fashion over six log units range in luminance intensity. Sympathectomy produced a general constriction of the pupil, but the overall response to light was unaffected. The changes in pupil size occurred over the same range of luminance that the firing rates of both luminance and darkness detectors changed. The olivary pretectal nucleus may therefore be involved in pupilloconstruction in the light, and the posterior pretectal nucleus, with pupillodilation in the dark.

Animals↗
PubMed1985

Luminance detectors in the olivary pretectal nucleus and their relationship to the pupillary light reflex in the rat. II. Studies using sinusoidal light.

The luminance detectors in the olivary pretectal nucleus, which are likely candidates mediating the pupillary light reflex, responded to all frequencies of sinusoidally modulated light up to 12-25 Hz. At low frequencies (0.05-4.0 Hz) the luminance detectors responded with modulated firing to different stimulation rates. The modulation depth of the cell response increased with the increase in stimulation frequency up to 20 Hz, then rapidly fell. There was a delay between the peak intensity of the stimulus and the peak firing of cell response of about 30-40 ms. The amplitudes of the consensual pupil responses to the same sinusoidal stimulus, on the other hand, decreased with an increase in frequency and no discernible response was recorded above 2 Hz. The pupil responses were little affected by sympathectomy. The differences in the frequency response characteristics of luminance detectors and the pupil were attributed to the sluggish dynamic properties of the pupil muscles. This was demonstrated using an electronic model of the iris muscle which modified the responses of the luminance detectors giving output waveforms broadly resembling pupil responses to square and sinusoidally modulated lights.

Animals↗
PubMed1985

Distribution of parasympathetic motoneurones in the oculomotor complex innervating the ciliary ganglion in the marmoset (Callithrix jacchus).

Parasympathetic motoneurones in the oculomotor complex which innervate the ciliary ganglion were identified using the horseradish peroxidase (HRP) retrograde axonal tracer technique. The ciliary ganglion was located behind the eye by a lateral orbital approach and injected with HRP pellets mounted on the tips of microelectrodes. Most of the labelled cells were distributed throughout the whole Edinger-Westphal nucleus (EW). Outside the EW, only a small number of labelled cells were found, and most of these were located in the median zone ventral to the EW. There was no evidence of a division of the EW into rostral and posterior subnuclei, nor for separate cell populations in the EW and the anterior median nucleus (AM), respectively. At rostral levels labelled cells were confined to the EW with no overlap into the AM. In contrast to most previous studies no labelled cells were found in the AM. The possible physiological functions of the EW and the ventral components of the EW are discussed.

Animals↗
PubMed1985

Oculomotor areas involved in the parasympathetic control of accommodation and pupil size in the marmoset (Callithrix jacchus).

The motoneurons of the oculomotor complex responsible for controlling accommodation and pupil size of the marmoset were identified by injecting horseradish peroxidase (HRP) into the ciliary ganglion. The anatomical organization of accommodation and pupil constrictor motoneurons was determined using electrical stimulation techniques. HRP-labelled cells were found through the whole length of the Edinger-Westphal nucleus (EW) and also just ventral to this nucleus in caudal sections. A projection from the antero-median nucleus to the ciliary ganglion could not be demonstrated. Electrical stimulation data showed that currents of less than 1 microampere applied inside the EW evoked accommodation responses. Pupil constriction responses, on the other hand, were evoked with weak currents at sites ventral to those in the EW generating accommodation at caudal and central levels. It was concluded that the EW was responsible for accommodation and areas containing HRP-labelled cells ventral to the caudal part of the EW were responsible for pupil constriction.

Accommodation, Ocular↗
PubMed1984

Massive eosinophilic reaction to desipramine in conjunction with pneumonia.

The authors report on a female patient with bipolar affective disorder who presented with marked eosinophilia in conjunction with pneumonia five days after a medication change from amitriptyline to desipramine (for intolerable dry mouth). She improved with discontinuance of medications and supportive management, and her eosinophilia normalized. Reinstitution of desipramine was followed by prompt appearance of asymptomatic eosinophilia, which resolved with discontinuation of desipramine. A subsequent depression managed with amitriptyline was followed by no abnormal white blood count findings. Eosinophilia is occasionally encountered in imipramine or desipramine therapy and, although usually asymptomatic, appears to be manageable by switching to amitriptyline or nortriptyline.

Aged↗
PubMed1979

Aspects of the middle and external ear of early South African hominids.

A brief description of the exposed middle ear from two Swartkrans specimens demonstrates the feasibility of examining the inner auditory structures of existing fossil hominid material. These Swartkrans fossils provide the first clear view of the early hominid middle ear, and their structures appear to be morphologically distinct. The bony anatomy of the external ear of Australopithecus robustus is found to be unique among the South African hominids.

Animals↗
PubMed1976

The reactivity of canine cerebral arteries to O2 and CO2 in vitro.

The responses of canine middle cerebral arteries to changes in pCO2 and pO2 were tested in vitro. It was found that there was no response to changes in pCO2 from 38.1 mm. Hg to 26.6 mm. Hg, but there was some constriction of the vessels with lowering of the pCO2 below 26.6 mm. Hg and there was minimal dilatation of the vessels when the pCO2 was increased from 38.1 mm. Hg to 87.2 mm. Hg. There was no response to changes in pO2 from more than 55 mm. Hg to 59.6 mm. Hg, but when pO2 was lowered below 50 mm. Hg there was a sudden, massive constriction of the arteries tested. It is postulated that this constriction is due to build-up of a substance (substances) during a period of hypoxia (pO2 less than 50 mm. Hg). The significance of the results obtained are discussed.

Animals↗