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Biomedical subjects

R L Cooper

Publications and source records attributed to R L Cooper.

At least 19 recordsLinked to original sources
PubMed1992

Anterograde and retrograde effects of synapse formation on calcium currents and neurite outgrowth in cultured leech neurons.

The aim of our experiments has been to analyse how formation of chemical synapses affects the distribution of calcium (Ca2+) currents and neurite outgrowth of leech Retzius cells. Previous results showed that Ca2+ currents measured in the initial process or 'stump' of postsynaptic cells were significantly smaller than those in corresponding sites on presynaptic neurons. In the present experiments, neurons were plated together in close apposition as pairs or as triads, with the tip of one Retzius cell touching the soma of another. Ca2+ currents from selected areas of the neuronal surfaces were measured by loose-patch recording before and after the formation of chemically mediated synaptic connections, which developed in about 8 h. With three cells arranged in a row, the last of the series, which was purely postsynaptic (i.e. with no target), also showed a dramatic reduction in Ca2+ currents in its initial segment, compared with the currents seen in either the first cell (purely presynaptic) or the second cell of the chain (which was both postsynaptic to the first cell and presynaptic to the third). This suggests that retrograde as well as anterograde effects on Ca2+ currents occurred as a result of synapse formation: the Ca2+ currents in the middle cell did not decrease although a synapse had been formed on it. To test for additional consequences of synapse formation, neurite outgrowth was measured in postsynaptic cells and in single cells plated on an extract of extracellular matrix containing laminin (ECM-laminin). After 48 h, the total length of neuritic outgrowth in postsynaptic cells was only about one third of that in single cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Developmental study of chondroitin-6-sulphate in normal and dystrophic rat retina.

The RCS rat is a widely studied model of human retinal dystrophies including retinitis pigmentosa. Chondroitin-6-sulphate (C6S) in the interphotoreceptor matrix was localised immunocytochemically in both the normal congenic and dystrophic strains of the RCS rat up to 65 days postnatally. From postnatal days 5 to 15 the distribution of C6S in both strains was similar, being localised in the interstices of developing inner and outer segments and adjacent to the RPE surface. In the normal rats, the distribution of C6S did not change with age. In the RCS rats, however, at postnatal days 20 to 35 staining was observed as a dense band at the junction of inner and outer segments and no staining was observed adjacent to the surface of the RPE. At postnatal day 45 onwards there was a decrease and a complete absence of C6S staining in these rats. This change in the pattern of staining correlated with the morphological observation of the progressive degeneration of photoreceptor cells suggesting that C6S may be important in photoreceptor degeneration in the RCS rat.

Aging↗
PubMed1992

Correlations between densitometry of red-free photographs and reflectometry with the scanning laser ophthalmoscope in normal subjects and glaucoma patients.

OBJECTIVE: To compare image measurements of the retina produced by scanning laser ophthalmoscopy with those from red-free photographs (RFP) of the nerve fibre layer. SUBJECTS: The left eyes of 23 subjects (10 normal, 7 glaucoma suspect and 6 glaucomatous) were included in this study. METHOD: All the eyes were photographed using standard red-free photography, and images of the retina were digitised directly from the SLO. RESULTS: The correlation coefficient for all except three subjects was > 0.45, and the probability (p) that R = 0 was < 0.05 in all but 5 eyes. CONCLUSIONS: The data indicate that variations in retinal surface reflectivity as measured by the SLO are similar to those recorded on negative film during RFP. This further suggests that the SLO can be useful for making objective measurements of the RNFL, without the intermediate and variable steps of photography.

Densitometry↗
PubMed1992

Effect of inhaled methanol on pituitary and testicular hormones in chamber acclimated and non-acclimated rats.

Two experiments were conducted in which the acute effects of inhaled methanol on serum hormones associated with reproductive function in the male rat were evaluated. In the first experiment, rats exposed to methanol (0, 200, 5000 and 10,000 ppm) for 6 h were killed at the end of the exposure period (6 h) or the following morning (24 h). Also, because the process of exposure itself could modify neuroendocrine function, the effect of the handling associated with placing the rat in the exposure chamber was evaluated further by dividing the exposed animals into acclimated (2 weeks of prior handling) and non-acclimated groups. At 6 h, an effect of prior handling was noted in the sham-exposed rats, with serum luteinizing hormone (LH) of the non-acclimated group being greater than that of the acclimated group. Serum LH concentrations were altered by methanol exposure, but the direction of change and the exposure level at which an effect was noted differed between the acclimated and non-acclimated rats. Methanol (5000 ppm) reduced serum LH in the non-acclimated animals, while 10,000 ppm increased LH in the acclimated rats. Follicle stimulating hormone (FSH) and testosterone were unchanged by methanol in rats killed at 6 h. Thus, this experiment did not confirm earlier reports that exposure to 200 ppm for 6 h reduced serum testosterone. At 24 h, an effect of prior handling was still present in the hormonal measures, with serum and interstitial fluid testosterone concentrations being greater in the non-acclimated rats. Also, there was a dose x handling interaction with methanol exposure inducing an increase in serum testosterone in the non-acclimated rats (up to 5000 ppm) and a decrease in the acclimated rats (up to 10,000 ppm). In the second experiment, groups of acclimated and non-acclimated rats were exposed to 0 or 5000 ppm methanol for 1, 2 and 6 h and killed immediately after removal from the chamber. Serum LH, testosterone and FSH values were not different in sham- vs methanol-exposed rats at any time point. As in experiment 1, an effect of prior handling was noted. In general, the concentrations of these hormones and serum prolactin in the non-acclimated rats were greater than those observed for acclimated rats. Methanol exposure resulted in increased prolactin concentrations under both handling conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗
PubMed1992

Laser microsclerostomy for primary open angle glaucoma: a review of laser mechanisms and delivery systems.

A number of different lasers and delivery systems are currently used in experimental sclerostomy procedures. These are discussed with reference to their performance in terms of cutting accuracy and trauma to the adjacent tissues. Lasers emitting wavelengths close to the absorption peaks of water in the mid-infrared region and organic polymers in the far ultraviolet region have a short absorption pathlength in the sclera and produce the least adjacent thermal tissue trauma. These ablating lasers cannot be delivered gonioscopically, and contact endoscopic techniques trap hot expanding gases within the forming sclerostomy channel causing secondary thermal and mechanical damage. Optimal results should be obtained using an ablating laser delivered either through an open mask or a modified endoscopic system incorporating an adequate exhaust mechanism.

Endoscopy↗
PubMed1992

Use of unsharp masks with high-contrast retinal nerve fibre layer photographs.

Retinal nerve fibre layer (RNFL) photography is an established and integral tool in the management of ocular hypertensives and glaucoma suspects, and in assessing the management of glaucoma in an ophthalmic practice. When RNFL negatives are viewed for analysis, high-contrast negatives yield the most information. When positive prints are subsequently requested, the RNFL negatives are difficult to print. The use of an unsharp mask facilitates the transfer of all the high-contrast negative density range to the print. The use of an unsharp mask has been simplified so that it is quick and efficient and can be adapted for high-contrast negatives other than RNFL images.

Glaucoma↗
PubMed1991

"Black prosthesis" revisited: a study of epinephrine-induced pigment deposits on poly(methyl methacrylate).

To investigate in detail the "black prosthesis" syndrome, experimental production of melanin from epinephrine was performed both in bulk and onto the surface of a common prosthetic material, poly(methyl methacrylate) (PMMA). The study by ultraviolet/visible spectrometry showed that the radiation-absorptive properties of PMMA were significantly enhanced; a sample treated for 20 days in epinephrine absorbed all ultraviolet radiation up to a 344-nm wavelength and transmitted only 4.9% from the ultraviolet spectrum at 400 nm and 16.2% from the visible spectrum at 500 nm. Transmission electron microscopy studies suggest that melanogenesis occurs on the surface of PMMA, and the pigment does not penetrate the polymer. Using infrared spectrometry, it was confirmed that the pigmentation is caused by a melanin formed through the oxidative polymerization of epinephrine.

Epinephrine↗
PubMed1991

Influence of chlordimeform on alpha-adrenergic receptor-associated mechanisms of hormonal regulation in the rat: pituitary and adrenocortical secretion.

The acaricide chlordimeform (CDF) has been reported to have effects on the central nervous system that appear to involve an interaction with alpha-adrenergic receptor-mediated mechanisms of neurotransmission. The present study examined the effects of CDF on adrenocortical and pituitary prolactin secretion, which are known to involve central adrenergic receptors. Male Long-Evans rats were injected i.p. with 20 or 50 mg/kg CDF and killed after 1, 4, 8 or 24 h. Both noninjected and saline-injected controls were included. Dosing was structured so that trunk blood could be collected during the morning nadir of circulating corticosterone (CORT). Assays for plasma adrenocorticotropic hormone (ACTH), CORT and prolactin (PRL) showed that with 50 mg/kg, all three hormones rose sharply by 1 h. CORT increased in a dose-dependent fashion and declined over the ensuing 8 h. Other rats were treated with the alpha-adrenergic antagonist phenoxybenzamine (PBZ, 20 mg/kg) or the alpha-agonist clonidine (CLON, 0.6 mg/kg) 40 min before and killed 1 h after CDF (25 mg/kg) injection. CLON was found to completely suppress the CDF-induced rise in CORT, while PBZ enhanced the CORT/ACTH response to CDF. CLON also significantly elevated PRL, an alteration not seen in the CLON-pretreated CDF rats. Dexamethasone was able to block the CDF-induced rise in CORT and significantly suppressed PRL levels in both saline- and CDF-treated groups. These effects indicate that CDF is interfering with a regulatory signal mediated by alpha-adrenergic receptor-associated activity.

Adrenocorticotropic Hormone↗
PubMed1991

A novel dialysing seton: short-term biocompatibility.

A novel dialysing seton made from haemodialysis tubes was implanted into eleven rabbit eyes to establish its biocompatibility. The animals were observed for up to 67 days after implantation. The cannulae were well tolerated clinically. Tissue obtained at seven different time periods was studied by light and electron microscopy and showed only a mild inflammatory reaction of the same grade as or less than that surrounding nylon sutures used to close the scleral trapdoors. The eye containing the seton had consistently lower intraocular pressure compared to the sham-operated fellow eye for up to 24 days. This effect declined over the ensuing five weeks.

Animals↗
PubMed1991

Antineutrophil cytoplasmic antibody in uveitis and scleritis.

We report a case where the detection of antineutrophil cytoplasmic antibody (ANCA) at the time of diagnosis of a case of sclero-uveitis predicted the later development of systemic features and prompted an early and definitive diagnosis of systemic vasculitis.

Autoantibodies↗
PubMed1991

Suppression of the luteinizing hormone surge by chlordimeform in ovariectomized, steroid-primed female rats.

The midcycle surge of luteinizing hormone (LH) from the pituitary provides the physiological trigger in the mammalian female for the process of ovulation. Accordingly, any agent that compromises the LH surge could function as a reproductive toxicant. Since ovariectomized (OVX) rats implanted with oestradiol capsules will exhibit daily afternoon surges, such animals can serve as a useful model for the investigation of toxicant-induced alterations in this functional hormonal event. The acaricide chlordimeform (CDF) has previously been found to decrease serum LH, probably by altering the hypothalamic noradrenergic transmitter control of LH secretion. Consequently, the present study focused on the effect of acute CDF administration on the appearance of the induced LH surge. Single intraperitoneal injections of CDF (0, 10, 25, 50 mg/kg) in OVX, oestradiol-implanted female Long-Evans rats approximately 5 hr prior to the expected surge caused a complete suppression at 25 and 50 mg/kg. Ten mg/kg had no effect on surge amplitude, but advanced the LH peak by 2 hr. The observed suppression did not persist beyond the day of CDF administration. Earlier dosing at 11 or 18 hr prior to the surge was without effect. Since CDF has been found to elevate serum corticosterone (CORT), 10 mg CORT/rat were given at different times prior to the surge. Twenty hr after administration only a partial lowering was seen; 5 hr exposure were ineffective. This indicates that an indirect adrenal effect was not the principal route, but may accompany an action of CDF on the hypothalamic mechanisms regulating the surge and becomes evident after more prolonged exposure.

Animals↗
PubMed1991

IL-4 suppresses IL-1 beta, TNF-alpha and PGE2 production by human peritoneal macrophages.

Human interleukin-4 (IL-4) down-regulates IL-1 and tumour necrosis factor-alpha (TNF-alpha) production by monocytes stimulated in vitro. In contrast, in studies of activation of murine macrophages, both stimulatory and inhibitory functions of murine IL-4 have been documented. To investigate whether opposing activities of IL-4 reflect a difference in the target cell studied, due either to cell maturation or the site from which the cells were isolated, we examined the effect of IL-4 on human peritoneal macrophage production of IL-1 beta, TNF-alpha and prostaglandin E2 (PGE2). Human peritoneal macrophages stimulated with lipopolysaccharide (LPS) produced levels of these mediators that were at least as great as those previously reported for monocytes. Similarly, IL-4 was inhibitory for peritoneal macrophage mediator production after in vitro stimulation. Thus, IL-4 has effects on human peritoneal macrophages similar to those on blood monocytes. In addition, as it down-regulates mediator production by cells that have left the circulation, it may be important in controlling the immune response in tissues.

Ascitic Fluid↗
PubMed1990

Chlordimeform-induced alterations in endocrine regulation within the male rat reproductive system.

The acaricide chlordimeform has been reported to have adverse effects in mammals that may be mediated by an interaction with alpha-adrenergic receptors. Since the hormonal signals involved in the regulation of reproductive function are themselves under hypothalamic adrenergic control, the present study was designed to investigate the effects of acute exposure to this compound on the hypothalamic-pituitary-testicular axis. Male rats given two intraperitoneal injections of chlordimeform-HCl (20 or 50 mg/kg) spaced 12 hr apart showed 24-hr declines in serum gonadotropins at 50 mg/kg that were paralleled by a drop in testosterone. These changes returned to control levels by 96 hr. Thyroid-stimulating hormone exhibited a dose-response decline that was accompanied by a similar decrease in serum thyroid hormone levels. The norepinephrine-stimulated secretion in vitro of gonadotropin-releasing hormone from hypothalamic explants was suppressed at the higher dose, while LH release from pituitary fragments in culture was unaffected. Although measurements of the in vitro release of other pituitary hormones suggest that there could be some direct pituitary effects of the compound, it appears likely that chlordimeform is able to influence endocrine regulation adversely within the reproductive system by interfering with hypothalamic alpha-adrenergic activity.

Amidines↗
PubMed1990

Simplification of unsharp masking in retinal nerve fibre layer photography.

Fundus photography is now an established tool for showing early changes in the retinal nerve fibre layer (RNFL). RNFL defects may precede glaucomatous visual field defects by up to five years and any improvement in photography should aid RNFL defect analysis. We have found that the use of an unsharp mask has helped to visualise the RNFL and by using readily available darkroom materials the process of unsharp mask preparation has been simplified.

Densitometry↗
PubMed1990

Blind registrations in Western Australia: a five-year study.

This paper reports the annual blind certification by the Association for the Blind, Western Australia, for five consecutive years, to December 1988. The data are analysed with a view to obtaining minimum figures for incidence of the major causes of blindness in this state.

Adolescent↗
PubMed1990

A study of variance in densitometry of retinal nerve fiber layer photographs in normals and glaucoma suspects.

The main object of this research was to develop a reliable method of screening glaucoma suspects and patients for early loss of or changes in the retinal nerve fiber layer (RNFL). This study quantifies the variances due to photography, digitizing, and analysis of red-free photographs of the RNFL. The influence of pupil size, optic disc position and eye movements, film processing, digitizing, and intra- and interphotographic-session and intra- and interoperator variances were established. It was found that pupils needed to be dilated to at least 6 mm, that the optic disc had to be positioned in a standardized area in the negative, that the head of the subject had to remain still during photography, and that film processing and digitizing of the negative needed to be strictly controlled to minimize the variance in collection of densitometry data from RNFL red-free photographs. It was established that focusing of the negatives during digitization was not crucial. Criteria were defined for acceptable negatives. Interphotographic-session and intraoperator variances were not significant in most cases when negatives were digitized to these criteria. Analysis of interphotographic-session variance showed that there were still some factors in photography, film processing, and/or image digitizing that were not sufficiently controlled for long-term follow-up without normalization of the data. Densitometry data gathered using the established protocol, from negatives of 71 subjects were analyzed; best sensitivity and specificity rates of 80% and 100%, respectively, were achieved for the diagnosis of glaucoma.

Adult↗