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M McCulloch

Publications and source records attributed to M McCulloch.

22 records · Page 2Linked to original sources
PubMed1981

Shaking pups: a disorder of central myelination in the spaniel dog. II. Ultrastructural observations on the white matter of the cervical spinal cord.

The ultrastructure of the cervical cord is described in a new canine mutant with severe hypomyelination of the C.N.S. Axons were either non-myelinated or surrounded by a myelin sheath that was markedly reduced in both its thickness and length of internode. Myelinated and non-myelinated zones were present on a single axon. There was no paucity of oligodendrocytes but many of those present contained empty or granular vacuoles within the cytoplasm. Features suggesting immaturity of myelination were commonly found at paranodes and along the internode. Abnormal inter-relationships of oligodendrocytes and astrocytes were present at many paranodes. These observations suggest an intrinsic defect of oligodendrocyte metabolism such that they are incapable of normal extension of their plasma membranes, while the cytoplasmic vacuoles may represent breakdown of defective lipids.

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PubMed1981

Shaking pups: a disorder of central myelination in the Spaniel dog. Part 1. Clinical, genetic and light-microscopical observations.

A new disorder of central myelination has been recognised in male Springer Spaniel pups which is probably inherited in a sex-linked recessive mode. The affected animals were much reduced in weight an size and showed gross generalised tremor, particularly when aroused, at about 10-12 days of age. Affected pups were studied between 1 and 3 months of age. There was severe hypomyelination throughout the CNS which was more marked in the cerebrum and optic nerves than in the spinal cord. The amount of myelin at each location increased with age. Axonal calibre also increased and there was no difference between the axonal diameters of affected and age-matched normal pups. Axons were either naked or surrounded by a disproportionately thin layer of myelin. Myelinated internodes tended to be short and heminodes were frequent. Vacuoles were present adjacent to axons or within glia but there was no evidence of demyelination. Total glial numbers were not reduced and numerous oligodendroglial and astrocytic nuclei identified. Peripheral, cranial and autonomic nerves were myelinated normally. It is suggested that there is an abnormality of oligodendroglial metabolism such that they cannot form and maintain normal myelin. Consequently the radial and longitudinal extensions of their plasma membranes are reduced. The vacuoles may represent a breakdown of defective myelin lipids as suggested in certain murine mutants. This defect of myelination provides a further model in which normal and disordered myelinogenesis can be studied.

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PubMedDate not supplied

Further studies of the central nervous system in canine giant axonal neuropathy.

The CNS of three further cases of canine giant axonal neuropathy (GAN) were examined. The axonal swellings were present in the distal portions of the spinal long tracts and their terminations in the cerebellar vermis; in the distal optic pathways; the nuclei of the habenulo-interpeduncular tract; certain thalamic relay nuclei and the cerebral cortex. The swellings were present both paranodally and internodally with the myelin sheath being attenuated or even absent. Excessive numbers of disordered 10 nm neurofilaments were the main constituent although mitochondria, membranous bodies, glycogen bodies and amorphous electron dense material also accumulated, particularly in the fasciculus gracilis. The neurotubules tended to form small subaxolemmal or intra-axonal islands. Complex interdigitations of oligodendroglia and axolemma were found in the affected areas. A small number of fibres in the rostral fasciculus gracilis showed marked proliferation of the smooth endoplasmic reticulum which may represent abortive attempts at regeneration. A small proportion of astrocytic processes were markedly enlarged with excessive whorling of the glial filaments. The accumulation of these various organelles in the non-terminal axon in the absence of mechanical obstruction suggests a defect in axoplasmic transport which may result from an energy failure as suggested in toxic neuropathies. The significance and pathogenesis of the glial filamentous changes and those reported in other cells in human GAN is at present uncertain.

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