Biomedical subjects

M L Graydon

Publications and source records attributed to M L Graydon.

3 recordsLinked to original sources

PubMed1987

Retinal wholemounts: a simple method for precise mapping.

A simple and inexpensive method to analyse retinal wholemounts is described. It allows the definition of regularly spaced sites to map regional specializations of the retina under light microscopy. After attaching a piece of translucent millimetre graph paper behind the slide holding the preparation, the two grid patterns of the graph paper and of the eye-piece grid are used in combination for the definition of sites for analysis and the return to specific areas as small as 50-100 microns2. The present method is simpler and offers several advantages when compared to others based on X-Y movements of the microscope stage or on photographic montage.

Evaluation Studies as Topic↗

PubMed1984

Topography of the retinal ganglion cell layer of Xenopus.

Cell distribution in the retinal ganglion cell layer of Xenopus laevis was studied by electron microscopy and the retinal wholemount method. Unlike the familiar stratification of the retina, the ganglion cell perikarya and their axons were localised in the same layer, but strictly segregated in alternate rows converging in a radial pattern on the optic disc. Rows of perikarya (retinal cords) were two to ten cells wide and clearly defined for a little more than half the distance between the optic disc and the ora serrata. Detailed analysis of 25% of the retinal surface showed higher cell density (about 3500 cells/mm2) in the centrodorsal region than in the periphery (about 2000 cells/mm2). The higher density regions represent a weak visual streak having no nasotemporal asymmetry. After staining with cresyl violet, the majority of cells appeared to be small (10 micron diameter) with very little Nissl substance. The cytoplasm was scant; this was confirmed by electron microscopy. The difference between the total cell count (68470 +/- 7360) and the total axon count in the optic nerve (Wilson, 1971) suggests a population of 15% non-ganglionic cells (glia and amacrine cells) in the retinal ganglion cell layer. Retinal ganglion cell topography in Xenopus may have relevance to studies on retinal growth and retinotopy. The functional significance of the weak visual streak in Xenopus is consistent with a limited need for visual acuity.

Animals↗

PubMedDate not supplied

A variant of the mammalian somatotopic map in a bat.

Two ordered representations of the body surface, S-I and S-II, have been described on the cortical surface of the brains of a variety of mammals; additional separate topographical maps have been found in the somatosensory cortex of the cat and monkey. Except for minor variations in the placement of the body parts, the basic somatotopy of the maps is remarkably consistent across species. As the reasons for this consistency and the minor variations are unclear, we examined the somatotopy of the bat, whose body plan has been modified extensively so that the forelimb can be used for flight. We report here that in both S-I and S-II of the grey-headed flying fox, not only is the representation of the distal forelimb displaced from its usual position on the map, but the digits are directed caudally instead of rostrally as they are in all other mammals studied. The variant somatotopy appears to reflect the postural differences between flying and walking mammals, supporting the notion that topographical maps may have functional significance apart from their point-to-point connections with the sensory periphery.

Animals↗