Carbonic anhydrase activity in myelin fractions from rat optic nerves

The response of regenerating peripheral neurites to a grafted optic nerve

Optic nerves, both viable (fresh or pre-degenerate) or non-viable (frozen-thawed) were grafted between the proximal and distal stumps of freshly transected sciatic nerves, using either 10/0 sutures or strips of nitrocellulose paper. The majority of regenerating peripheral neurites, always in association with Schwann cells, avoided the viable optic nerve grafts, growing along the outside of the grafts in well vascularized minifascicles until they gained the distal stumps. A very small number of axons entered the grafts and grew, for distances typically less than 2 mm, between layers of astrocyte processes. The number of axons entering was not increased by using predegenerate grafts or by blocking Schwann cell proliferation in the proximal stumps by pre-treating the latter with mitomycin C. There was no evidence of a continuous cellular-acellular partition between graft and host during the outgrowth phase of the neurites: it was concluded that axons failed to enter the grafts as a result of inhibitory interactions between Schwann cells and astrocytes. When grafts were rendered acellular, all structured debris, including recognizable components of the extracellular matrix, was rapidly removed and the space thus vacated was invaded by manifascicles of Schwann cells and regenerating neurites. Glial fibrillary acidic protein-positive astrocytes and carbonic anhydrase II-positive oligodendrocytes persisted within viable grafts for 17 months; they did not migrate into the surrounding nerve.

Ultrastructural cytochemical localization of carbonic anhydrase activity in rat peripheral sensory and motor nerves, dorsal root ganglia and dorsal column nuclei

Some of the myelinated axons in rat peripheral nerves possess marked axoplasmic carbonic anhydrase activity [Riley, Ellis and Bain (1982) J. Histochem. Cytochem. 30, 1275-1288; Riley and Lang (1984) J. Hand Surg. 9A, 112-120]. A mixture of reactive and nonreactive neurons was a general observation in cervical, thoracic and lumbar ganglia. Nonmyelinated axons in lumbar dorsal roots were nonreactive; this was consistent with the lack of carbonic anhydrase in small sensory neurons. The carbonic anhydrase cytochemical method marked the larger afferent or sensory neurons and distinguished them from the smaller sensory neurons which were devoid of carbonic anhydrase activity. Nonmyelinated axons in the lumbar ventral roots were also nonreactive. Examination of muscle spindle innervation revealed staining of the primary sensory and gamma motor endings. This was strongly suggestive that some of the reactive sensory neurons were primary afferents and a portion of the reactive ventral root axons were gamma motor. The reactive central processes of spinal neurons sent collaterals into the grey matter of the spinal cord, entered the dorsal funiculi, and terminated in synaptic glomeruli in the cuneate and gracilis nuclei. Oligodendroglial cells appeared to be the only intrinsic cellular elements of the brain stem and spinal cord that exhibited high carbonic anhydrase activity. Both oligodendroglial and Schwann cells exhibited intense carbonic anhydrase activity in thin pockets of cytoplasm internal to compact myelin. The subcellular distribution of reaction product within sensory neurons and oligodendroglial cells agreed with biochemical reports of cytosol and membrane-bound forms of carbonic anhydrase. A general staining of the cytoplasm was suggestive of soluble carbonic anhydrase fixed in situ by the glutaraldehyde. Clumps of reaction product on the cytoplasmic surface of the endoplasmic reticulum possibly represented membrane-bound enzyme. Most of the membrane-bound carbonic anhydrase was associated with the internal membranes rather than the axolemma or limiting plasma membrane of the axon. In contrast to biochemical reports, a small fraction of neuronal mitochondria exhibited staining in the intracristal spaces. We suggest that the association of carbonic anhydrase with endoplasmic reticulum and mitochondria implicates the enzyme in regulating intracellular calcium because both organelles are known to sequester calcium.

Biochemical characterization of the central nervous system myelin proteins of the rainbow trout, Salmo gairdneri

Central nervous system myelin isolated from the rainbow trout (Salmo gairdneri) displays a very low median density on zonal gradient centrifugation, banding at approximately 0.32 M sucrose. Its proteins consist of a 36 K (36,000 mol.wt.) component, two Concanavalin A-reactive intermediate proteins IP1 (23,000 mol.wt.) and IP2 (26,200 mol.wt.), and two basic proteins BP1 and BP2, of which the latter co-migrates with rat SBP while BP1 is of slightly smaller size. The trout myelin proteins electrofocus at pH positions similar to those of their mammalian counterparts. Immunoblotting shows that antibodies against rat PNS myelin P0 glycoprotein are bound by IP1 and IP2, but not by 36K. None of the trout myelin proteins react with anti-rat CNS myelin proteolipid protein (PLP) antiserum. The basic proteins BP1 and BP2 bind strongly to antibodies directed against human myelin basic protein. In vivo injection of tritiated fucose or palmitate leads to radiolabeling of IP1 and IP2. Under autolytic in situ conditions the appearance of a glycosylated 20,000 mol.wt. component (IP0) is noted, with parallel reduction of both IP1 and IP2, indicating sequence homologies between IP1 and IP2. The 36K protein is not affected by autolysis.

Investigations on myelination in vitro: IV. "Myelin-like" or premyelin structures in cultures of dissociated brain cells from 14--15-day-old embryonic mice

The present study reports ultrastructural and biochemical data characteristic of myelin-related structures in 30- to 41-day-old cultures of dissociated brain cells from 14- to 15-day-old embryonic mice. Multilayered membranous material was identified and displayed an alternation of electron-lucent and electron-dense lamellae with a periodicity of 102 A. In these membranes, typical myelin constituents like basic protein, cerebrosides, sulfatides, and CNPase could be identified. Although we are still unable to distinguish if these membranes are premyelin or compact myelin, which could be partly degraded, these results indicate that cultured mouse brain cells retain, to a certain extent, potential to produce myelin-related membranes.

Dissociation of myelin from its 'enzyme markers' during ontogeny

To avoid any loss of membranes, total particulate material prepared from the forebrain and spinal cord of rats of different ages was fractionated on linear sucrose gradients. Particle distribution, proteins and enzyme activities were measured. Beginning at early ages, optical density increases were observed around 0.60 M-sucrose, which corresponded to myelin deposition, and were expressed by the appearance of typical myelin proteins, which paralleled the peak activity of myelin-associated enzymes. During later development myelin proteins were found over a broad density range together with optical density shifts to higher (forebrain) and lower (spinal cord) values. In both regions myelin-associated enzymes shifted to heavier densities and were dissociated from the density region commonly considered to be compacted myelin.

Carbonic anhydrase: an ultrastructural study in rat cerebellum

The cellular and intracellular distribution of carbonic anhydrase isozyme II in rat cerebellum has been investigated with the electron microscope by the indirect antibody immunohistochemical technique. Unequivocal evidence is presented supporting the view that this enzyme is exclusively localized in oligodendrocytes. Myelin does not appear to contain detectable amounts of carbonic anhydrase though it is present in oligodendrocyte processes and in the layer of oligodendrocyte cytoplasm frequently seen to coat the external surface of myelinated fibres. The immune precipitate is found to be confined to the cytosol and the cytosolic surfaces of intracellular membranes. The data are discussed in relation to the possible function of the enzyme and the role of oligodendrocytes in the central nervous system.

Application of Bradford's protein assay to chick brain subcellular fractions

Protein content of different subcellular fractions from chick brain is compared by using Lowry, TCA-Lowry and Bradford assay methods. Caution is urged in application of Bradford's method to general assay for protein concentration in subcellular fractions.