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Biomedical subjects

V B Meyer-Rochow

Publications and source records attributed to V B Meyer-Rochow.

At least 37 records · Page 2Linked to original sources
PubMed1999

Coming to grips with a slippery issue: human waste disposal in cold climates.

Problems associated with sewage treatment and human wastes at high latitudes are briefly reviewed. In view of the fact that E. coli and other faecal bacteria can survive in the snow and the coastal waters of polar regions, several methods of how to deal with sewage outfalls in the Arctic and Antarctic are compared and discussed. Some consequences of raw sewage on the health of captive populations of a variety of Antarctic invertebrates and fish are described. Locomotion and respiration appear to be most affected. However, gaps, both in understanding the biological impact of human sewage on polar ecosystems and in finding optimal solutions for the disposal and treatment of the wastes generated by people who live in polar settlements, unfortunately still remain.

Antarctic Regions↗
PubMed1998

Possible natural circaseptan rhythm in the beach beetle Chaerodes trachyscelides white.

Activity rhythms in groups of captive beach beetles (Chaerodes trachyscelides White) have been recorded in an actograph over a period of 29 days. Under constant illumination and when no sand was provided for the beetles to burrow in abnormal behaviour occurred. With sand and in constant darkness a strictly nocturnal activity period with apparently circaseptan components superimposed was observed. The beetles in their natural habitat are confined to the debris zone where they feed on washed up seaweed and this debris zone moves up and down depending on the heights of the tides. Circaseptan elements in the beetles' activity may act as adaptations to the weekly alternations between spring- and neap-tides.

Animals↗
PubMed1997

Absolute and spectral sensitivities in dark- and light-adapted Pagothenia borchgrevinki, an Antarctic nototheniid fish.

Functional properties of the retina of Pagothenia borchgrevinki, an Antarctic nototheniid fish that lives beneath the 2.5-3 m thick sea-ice in water of -1.8 degrees C temperature, were analyzed electrophysiologically at Scott Base (77 degrees 50'S; 166 degrees 45'E). The waveform of the ERG was monophasic in the dark-adapted state and showed an off-response of opposite polarity in the light-adapted condition. Responses of the light-adapted retina were smaller than those of the dark-adapted eye, although both photopic and scotopic components were observed. Spectral sensitivity measured by monochromatic photostimulation at 14 different wavelengths across the 400-700-nm range showed a single maximum at 490 nm. The spectral sensitivity curve is consistent with a rhodopsin photopigment. The dark-adapted retina exhibited a photon flux density threshold of approximately 2 x 10(9) photons cm-2 s-1) when monochromatic flashes of 500 nm wavelength and 250 ms duration were used. When the stimulus consisted of 1 s white light, a minimum energy flux density of approx. 2 x 10(-4) microW/cm2 was necessary to elicit a detectable response. It was concluded that the visual system of P. borchgrevinki was in tune with the dominant downwelling spectral irradiance and that, due to retinal thermal noise reduction in the cold environment, no great need for particular anatomical adaptations to further enhance sensitivity existed.

Acclimatization↗
PubMed1997

Thermally-induced changes in the metabolism of the eye of the crayfish Paranephrops planifrons: respiration and substrate utilization at three distinct temperatures.

The effect of temperature on the metabolism of 10 isolated eyes taken from 5 lake-dwelling specimens of the crayfish Paranephrops planifrons was examined by measuring oxygen uptake and carbon dioxide production at 3 temperatures. The mean values for oxygen utilization at 3 degrees C, 13 degrees C, and 23 degrees C, expressed in microM O2 g-1 min-1, were 15.40 +/- 1.36, 21.91 +/- 1.20, and 22.52 +/- 2.47, respectively. The resulting Q10 values for respiration rate were 1.43 +/- 0.05 for the 3-13 degrees C range and 1.03 +/- 0.07 for the environmental range of 13-23 degrees C, indicating immediate compensation within the definition presented by Hazel and Prosser (16). The ability of this tissue to undergo immediate thermal compensation reflects the physiological adaptations of intertidal invertebrates, and is significant in terms of the feeding strategy that this animal adopts. Calculations of respiratory quotients for the 3 measurement temperatures indicate a switching in substrate utilization: at 13 degrees C lipid or lipid/protein oxidation and, at the extremes of 3 degrees C and 23 degrees C, carbohydrates or a carbohydrate/protein mixture.

Animals↗
PubMed1996

Review of larval and postlarval eye ultrastructure in the lamprey (Cyclostomata) with special emphasis on Geotria australis (Gray).

The literature dealing with the lateral eye in lampreys is briefly reviewed here. While there appears to be no longer much doubt that the short and long photoreceptor cells in the lamprey eye correspond to rods and cones, questions of dark/light adaptational changes, the nature of visual pigments, and the roles of retinal serotonin and melatonin need to be re-addressed. Eyes of the larval and postlarval ("macrophthalmia") stages of the lamprey Geotria australis were examined by electron microscopy and it was found that the larval retina is largely undifferentiated except for a small central zone surrounding the optic nerve head. The retina of the postlarval stage is fully differentiated and the photoreceptor outer segments undergo renewal, which appears to involve the retinal pigment epithelium (RPE). The distribution of larval RPE and choroidal pigments, postlarval ganglion cells, and the orientation of scleral collagen are unusual for vertebrates. No obvious positional or size differences of any retinal cell type were apparent between day- and night-fixed specimens.

Animals↗
PubMed1995

Electron microscopy in Jamaica: applications and techniques.

Although the electron microscope was developed about 60 years ago in Germany, its arrival and subsequent use in Jamaica are of considerably more recent date. In this paper, the principles of scanning and transmission electron microscopy (SEM & TEM) are briefly explained, and examples are given of the research done with the electron microscopes at the University of the West Indies (UWI), Mona Campus, Jamaica, especially over the last three years. Detailed descriptions of specimen preparation are provided for both SEM and TEM and particular emphasis is placed on the methodology used in our laboratory, as it sometimes differs from the routine followed in electron microscopy units of temperate countries.

Animals↗
PubMed1993

Red-white muscle distribution and fibre growth dynamics: a comparison between lacustrine and riverine populations of the southern smelt Retropinna retropinna Richardson.

The myotomal musculature of the common New Zealand smelt Retropinna retropinna from a lacustrine and a riverine population was investigated in an attempt to correlate differences in the fish's maximum body size and migratory habits with differences in muscle morphology and growth dynamics of their component muscle fibres. Based on measurements of cross sections through the fish at 70% fork length, a significant increase in red muscle percentage is recorded between pre- and post-migratory stages in the riverine population. Although lacustrine and pre-migratory riverine smelt possess similar white: red muscle ratios, the red muscle increase in post-migratory, riverine smelt is explained by the requirement for sustained swimming during upstream migration. The growth dynamics of red fibres also appear to be related to functional requirements such as sustained swimming. The slower rates of growth and smaller maximum size (dwarfing) exhibited by lacustrine smelt of basically riverine stock in comparison with diadromous, riverine smelt, are attributed to differences in white fibre growth dynamics. The recruitment of new fibres into the growing muscle mass ceases to be of significance at a shorter fork length in the dwarfed lacustrine form of smelt, with the subsequent result of larger mean diameters of white fibres at all fork lengths compared with those of the riverine form. Hypertrophy of white fibres gradually diminishes in both forms as the mean diameters of white fibres approach 100 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

A system of regular ridges instead of nipples on a compound eye that has to operate near the diffraction limit.

A system of regular, radial ridges, spaced approx. 250 nm apart, is reported from the outer corneal surface of the eye of the tiny moth Leucoptera coffeella. Antireflective coatings in larger insects with flatter facets often take the form of corneal nipples. However, evidence is presented that in an insect whose eyes have to operate near the lower diffraction limit and possess strongly convexly-curved corneae a radial arrangement of microridges is just as effective as nipples--and simpler to construct.

Animals↗
PubMed1992

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis.

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

Animals↗
PubMed1992

Observations on an accidental case of raw sewage pollution in Antarctica.

The effects of an accidental exposure to saltwater polluted by human wastes on aquarium populations of a variety of Antarctic organisms are described. Only the giant Antarctic slater Glyptonotus antarcticus survived the exposure to the contaminated water unharmed. A comparative analysis of water qualities revealed that total nitrogen and phosphorus levels of the contaminated sample were 15 and 19.5 times higher than those of the control and that the contaminated sample contained high amounts of coliform bacteria, whereas the latter were not identified in the control. Considering the widespread practice in Antarctica of disposing of raw sewage into the sea, the dearth of knowledge concerning the biological impact of such behaviour is seen as worrysome.

Accidents↗
PubMed1991

Nephroblastoma in the clawed frog Xenopus laevis.

One 2.5-3 year old female clawed frog (Xenopus laevis), out of a consignment of 4,000 frogs, was found to have an abnormal abdominal growth, weighing 7.9 g. The growth was examined histologically and on the basis of the abundant stroma and serially-arranged tubules nephroblastoma was diagnosed. The growth is not considered to be transmissible.

Animals↗
PubMed1990

Fine structure of regenerating caudal spinal cord in adult tuatara (Sphenodon punctatus).

A report on the presence of cerebrospinal fluid contacting neurons (CSFCN) inside the regenerating caudal spinal cord of adult specimens of the tuatara Sphenodon punctatus is given. The cells in question are easily distinguished from amongst ependymal tanicytes of the regenerating cord. Large granules of high electron density are particularly common in these neural cells which generally show clear cytoplasm of low electron density. The ultrastructural findings strongly support the idea of a secretory activity of these neurons directed toward the central canal.

Animals↗
PubMed1990

ERG-determined spectral and absolute sensitivities in relation to age and size in the halfcrab Petrolisthes elongatus (Crustacea; Decapoda; Anomura).

The electroretinogram (ERG) waveform of Petrolisthes elongatus is biphasic and transient and does not change with age (monitored as carapace length and weight of the individual). Though there was a very slight decrease in sensitivity with age (R2 = 0.008), spectral peaks and curves remained virtually unchanged. A shift of 2.2 log units in threshold sensitivity, however, was observed in relation to the different adaptational states. The greatest difference, not unexpectedly, occurred between dark-adapted eyes, tested at night, and light-adapted eyes tested during the day at a background illumination of 250 1x. The gradient of the V/LogI curve (n) in light-adapted animals increased, which means a smaller increase in intensity is required to produce an increase in response compared to a dark-adapted animal, but there was no difference in n with regard to the different age-groups. Also, no significant difference was noticed between dark-adapted eyes tested during day and night. It is concluded that the intensity range over which vision in P. elongatus is maximally sensitive to contrast (the dynamic range) is 2.5-3.0 log units. Since there is apparently little or no alteration in the photic environment and the behaviour of P. elongatus as it ages, there is no advantage in fundamentally altering the parameters of the absolute and spectral sensitivity function with age. Our observations suggest that the eyes are able to adjust within 30 min to changing ambient light levels irrespective of whether or not a circadian activity rhythm operates.

Age Factors↗
PubMed1990

Growth patterns in the eye of Petrolisthes elongatus (Crustacea; Decapoda; Anomura).

The eye of Petrolisthes elongatus is of the reflecting superposition type. The facets are square and the dioptric apparatus consists of a crystalline cone and a conestalk, each made up of four identical radially arranged units. The rhabdom has an elonagated (2-3 microns diameter) distal segment and a much thicker (6-16 microns diameter) proximal section. The distribution of screening pigments alters dramatically in a migration associated with changes in adaptational state. The following trends with increasing age, monitored as carapace length, were found: (1) increasing number of facets; (2) increasing size of eye and eye-stalk; (3) increasing length of eye-stalk in proportion to eye length; (4) increasing breadth of eye-stalk in proportion to eye breadth; (5) increasing breadth of eye-stalk and eye in proportion to length of eye-stalk and eye; (6) increase in volume of both retinal and dioptric structures; (7) slight increase in rhabdom width; (8) increase in crystalline cone length and breadth and (9) increase in focal length. The results of these trends were presumed to be, firstly, an increase in absolute sensitivity of single ommatidia; secondly, an increase in sensitivity to point sources of light and, thirdly, an increase in angular visual field of the whole eye.

Adaptation, Physiological↗