Enzyme changes in axon, myelin, and Schwann cells in injured sciatic nerve

Four enzymes related to specific cell functions were assayed in rat sciatic nerve injury by crush (cr) or crush and ligation (cr-lig) after 2, 7, and 15 days in situ. Enzyme activities in segments of sciatic nerve proximal and distal to the injury were compared to those in corresponding segments of the contralateral nerve. Choline acetyltransferase (CAT) activity in the distal portion decreased by 65% for cr and almost to zero for cr-lig by day 7, while in the proximal portions CAT decreased to 70% of control values by 7 days and to 50% at 15 days after cr-lig. The activity of the Schwann cell-myelin-associated enzyme 2',3'-cyclic nucleotide phosphohydrolase (CNP) decreased slowly distal to the injury. Distal to both types of injury the lysosomal enzyme beta-glucuronidase (GLR) increased six- to eightfold by 15 days. Proximal to injury GLR also increased (P cr X 2.5, P cr-lig X 5) but the peak proximally was attained by day 7. Despite interruption of axonally transported enzymes, the activities of the metabolic enzyme creatine kinase (CK) increased distal to injury apparently reflecting changes in the functions of the Schwann cells. The loss of metabolic enzymes from the axonal compartment may be completely obscured by reciprocal changes in the non-neuronal compartments if the activity is present in both compartments.

Demonstration of 2',3'-cyclic nucleotide 3'-phosphohydrolase in cultured human Schwann cells

Schwann cell cultures were established from adult human sural nerve biopsies. 2'3'-Cyclic nucleotide 3'-phosphohydrolase (CNPase) activity was estimated in the homogenates of those cells by a sensitive isotope assay using [3H]2',3'-cyclic AMP as substrate. A high level of CNPase activity was observed in cultured Schwann cells, whereas cultured human muscle and skin fibroblasts contained negligible levels of CNPase activity. CNPase of human Schwann cells followed typical enzyme-substrate kinetics, with an apparent Km of 1.6 mM for 2',3'-cyclic AMP, and the enzyme was stimulated by detergents such as Triton X-100 and deoxycholate. It was inhibited by p-chloromercuricbenzoate and 2'-AMP. These properties are typical of CNPase isolated from adult brain and spinal cord. CNPase can serve as a new biochemical marker of normal cultured human Schwann cells and can be useful in analyzing the properties of cultured Schwann cells from patients with dysschwannian neuropathies.

Slow axonal transport of the molecular forms of butyrylcholinesterase in a peripheral nerve

Butyrylcholinesterase was found in chick sciatic nerve in four main molecular forms--G1, G2, G4 and A12--distinguishable by thier sedimentation coefficients in sucrose gradients (4.2S, 6.4S, 11.3S and 19S, respectively). Axonal transport of butyrylcholinesterase was studied by measuring the accumulation of its molecular forms on each side of a transected sciatic nerve. Twenty-four hours after transection, butyrylcholinesterase activity had risen by about 32% at the extremity of the proximal stump, and by 20% at the extremity of the distal stump. Proximal accumulation was due to a two-fold rise in G4 activity and to a six-fold rise in A12 activity, whereas distal accumulation was exclusively due to a 50% increase in G4 activity, accompanied by the complete loss of A12. The activities of G1 and G2 remained stable in both directions. Under our experimental conditions, the accumulation of butyrylcholinesterase activity cannot be attributable to local protein synthesis, cross-contamination with accumulated acetylcholinesterase or the presence of plasma butyrylcholinesterase. Hence we conclude that all A12 butyrylcholinesterase molecules were carried in the anterograde direction, moving at 11.6 +/- 4.2 mm/day, and that probably some of the G4 molecules were slowly transported in both directions. These findings suggest that some of the butyrylcholinesterase is located in the axonal mitochondria and/or axolemma.

Histochemical study of lamellar cell development of Meissner corpuscles

The development of the lamellar cells of mouse digital corpuscles (Meissner corpuscle) was studied by light and electron microscopic histochemistry for cholinesterase (ChE) The materials used were the hind limbs taken from fetuses at 14, 17 and 20 days of gestation, and from young mice at 1, 5, 7, 15 and 20 days after birth. Embryonal Schwann cells had non-specific ChE activity in the cisternae of the rough endoplasmic reticulum and the nuclear envelope, suggesting that they had the ability of synthesizing the enzyme. After birth, such ability gradually decreased and by five days of age non-specific ChE activity was no longer demonstrable in Schwann cells at the time when myelin sheath formation began. However, Schwann cells which were associated with the axonal tips penetrating into the epidermis still had an intense non-specific ChE activity. Such Schwann cells surrounded the axons in gradually increasing numbers of cytoplasmic processes, which later became the lamellae around the axon terminals; thus by 20 days after birth they had differentiated into mature lamellar cells of Meissner corpuscles. These lamellar cells had, as in the embryonal Schwann cells, an intense ChE activity in the cytoplasm. These findings indicate that the lamellar cell is a specialized form of Schwann cell which still retains the embryonal characteristics for synthesizing non-specific ChE.

Ubiquitous presence of the tailed, asymmetric forms of acetylcholinesterase in the peripheral and central nervous systems of the frog (Rana temporaria)

Five molecular forms of acetylcholinesterase can be solubilized from the peripheral and central nervous systems of the frog: they will be referred to as the 3.6, 6, 10.5, 14 and 18 S forms. They seem to be analogous to the forms present in endplate-rich and endplate-free regions of frog skeletal muscle. In particular the 18 and 14 S forms represent the collagen-tailed forms of frog acetylcholinesterase. These heavy forms are found in all peripheral and central tissues examined, including whole brain or regions of brain: cerebellum, telencephalon, optic tectum, spinal cord, spinal ventral and dorsal roots and sciatic nerve, as well as in glial or Schwann cellrich tissues devoid of neuronal elements, such as the filum terminale or the severed stump of the nerve, several weeks after section. The 18 S form may represent up to 30% of total acetylcholinesterase activity. It thus seems that the 14 S and 18 S forms are very widely distributed throughout most neuronal and non-neuronal tissues in amphibians.

Lysosomal abnormalities in cultured schwann cells from a patient with peripheral neuropathy and continuous muscle fiber activity

Schwann cell cultures were established from a sural nerve containing large membrane-bound vacuoles in its Schwann cells, obtained from a patient with neuropathy and continuous muscle fiber activity. Cultured Schwann cells contained many large membrane-bound vacuoles, presumably lysosomes, resembling those present in the biopsied nerve. The acid phosphatase reaction was excessive in the patient's cultured Schwann cells but practically negative in normal cultured Schwann cells. This study indicates that the patient's neuropathy is primary dysschwannian with abnormal lysosomes as a major abnormality.

Neurochemical and morphological studies on the myelin of peripheral nervous system from Shiverer mutant mice: absence of basic proteins common to central nervous system

Shiverer mouse is characterized by poor lamella formation and absence of major dense line in the CNS myelin. PNS of the Shiverer was normal with regard to myelin lamellar formation, immunohistochemical staining of the Schwann cells by S-100 protein, and the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase. Analysis of the purified myelin by SDS-polyacrylamide gel electrophoresis revealed that P1 and Pr, which are common to BP in CNS, and PM protein were missing, while P0 and P2 proteins were of the same level as the control.

Enzymes of phospholipid synthesis: axonal versus Schwann cell distribution

Using quantitative EM autoradiography to localize sites of incorporation of tritiated inositol and choline into mouse sciatic nerve, we observed a substantial axon-based phosphatidylinositol synthesis, but no axonal phosphatidylcholine synthesis. In the present communication we provide biochemical evidence for the axonal transport of CDP-diglyceride:inositol transferase (EC 2.7.8.11), the terminal enzyme in de novo phosphatidylinositol biosynthesis. Axonal transport of 1,2-diacyl-glycerol:CDP-choline choline phosphotransferase (EC 2.7.8.2), required for de novo phosphatidylcholine synthesis, was not apparent in these studies. During subcellular fractionation activities for the synthesis of phosphatidylinositol by inositol transferase (IT) and phosphatidylcholine by choline phosphotransferase (CPT) were recovered in crude microsomal fraction of rat sciatic nerve. However, CPT was much more highly enriched in the microsome fraction than IT, which may be an indication of the different subcellular localizations of these enzymes. Following ligation, we detected localized increases in the activities of both enzymes in 5 (and 3) mm segments taken immediately proximal and distal to the ligature. Both activities increased in a linear fashion in the proximal segments over the ensuing 72 h period. It took about 40 h (IT) and 56 h (CPT) for the activities in the segments proximal to the ligature to double compared to unligated contralateral (control) nerves. The time-dependent accumulation of IT was primarily due to axonal transport, while that of CPT was largely a result of increased enzyme activity in local Schwann cells. Evidence came from double ligation studies, where a proximal ligature, acting to restrict orthograde axonal transport, reduced accumulation in a distal ligature by 80% for IT, but only 28% for CPT. Conversely, blockage of the Schwann cell response with actinomycin D, reduced accumulation of CPT by 83% and IT by only 36%. Finally, light microscopic autoradiography was used to show that in the segment proximal to the ligature, tritiated inositol incorporation into lipid was primarily axonal, whereas that of tritiated choline remained primarily associated with Schwann cells.

Adenosine triphosphatase activity of cutaneous nerve fibers

The histochemical study of Mg++-activated adenosine triphosphatase (Mg++-ATPase) activity was carried out on the peripheral nerves of mouse digital skin by light and electron microscopy. Under the light microscope, the ATPase activity was clearly demonstrated on the nerve fibers as a fine network in the subepidermal regions. Under the electron microscope, the reaction product of enzyme activity was located in the interspace between axolemma and the surrounding Schwann cells of the unmyelinated nerve fibers. No reaction product was observed in the space between the axolemma and the Schwann cells associated with myelinated nerve fibers. Demonstrable activity was absent at the nodes of Ranvier as well as on the para- and internodal regions of these myelinated axons. The part of the axolemma lacking a Schwann cell sheath failed to show a reaction product. The perineural epithelial cells surrounding the nerve fibers displayed reaction product in the caveolae. These results suggest a functional difference in the axon-Schwann interface of myelinated as compared to unmyelinated nerve fibers. The function of the perineural epithelial cell would be expected to be a regulatory one in transferring materials across the epithelium to keep the proper humoral environment around nerve fibers.

Pre- and postnatal development of catecholamine-containing and cholinesterase-positive nerves of the rat cornea and iris

Glyoxylic acid-induced fluorescence technique and a copper thiocholine method were used to investigate the ontogenesis of the catecholamine-containing and cholinesterase-positive nerves of the rat iris and cornea. First fluorescent nerve fibres appeared in the iris on the 18th gestation day and in the cornea on the 19th day. A rapid increase in the density of the adrenergic nerve fibres of the iris continued to the age of three weeks, while the number of such fibres were small in the cornea. Acetylcholinesterase-positive fibres appeared both in the cornea and in the iris on the 19th gestation day. Their density increased more rapidly in the iris, especially in the sphincter muscle, than in the cornea. Non-specific cholinesterase activity was localized in the Schwann cells and the reaction was more intense during development than in the nerves of the cornea of adult rats.

Electron microscope localization of acetylcholinesterase and butyrylcholinesterase in the superior cervical ganglion of the cat. I. Normal ganglion

The distributions of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the superior cervical ganglion (SCG) of the cat were determined by electron microscopy (EM) with the bis-(thioacetoxy)aurate (I), or Au(TA)2, method. Before the infusion of fixative, one of the enzymes was selectively, irreversibly inactivated in vivo, as confirmed by light microscope (LM) examination of sections of the stellate ganglion stained by the more specific copper thiocholine method. Physostigmine-treated controls, for inhibition of AChE or BuChE, were stained concomitantly with tissue for enzyme localization by the Au(TA)2 method for EM examination in each experiment. It was concluded that most of the AChE of the cat SCG is present in the plasma membranes of the preganglionic axons and their terminals, and in the dendritic and perikaryonal plasma membranes of the postsynaptic ganglion cells. BuChE is confined largely to the postsynaptic neuronal plasma membranes. Reasons for the discrepancies between the localizations found by the present direct EM observations and those deduced earlier from LM comparisons of normal and denervated SCG are discussed. It is proposed that a trophic factor released by the preganglionic terminals is probably required for the synthesis of postsynaptic neuronal AChE, and that BuChE may serve as a precursor of AChE at that site.

Study on the ultrastructure and acetylcholinesterase activity in von Recklinghausen's neurofibromatosis

The cutaneous nodules obtained from seven patients with von Recklinghausen's neurofibromatosis were investigated by electron microscopy, and ultrastructural localization of acetylcholinesterase activity was demonstrated in the nerve fibers of this tumor for the first time using Karnovsky's thiocholine method. The enzymatic activity was mainly found in unmyelinated fibers, exactly associated with their axonal membranes, the interspace between the apposing axonal and Schwann cell membrane, and some different mesaxons, which indicated their cholinergic nature. Almost all myelinated fibers and some unmyelinated fibers did not possess the activity. The relationship between axon and Schwann cell was quite similar to that of normal peripheral nervous system, but two striking alterations of the nerves existed: One is the dissociation of unmyelinated fibers, and the other is the degenerative changes of the axon and the myelin sheath. As the evidence of schwannian proliferation, onion bulb formations and collagen pockets were observed. Some signs of fibroblastic proliferation were also found. From the present study and the review of the literature, the probable histogenesis of this disease was discussed.

Early changes in the Schwann cells in experimental allergic neuritis

Experimental allergic neuritis (EAN) was induced in guinea-pigs by intradermal injection of rabbit peripheral nerve emulsified in Freund's adjuvant. Both sciatic nerves were obtained between 12--24 hr after clinical symptoms were evident. Several fascicles from each nerve were isolated for histochemical studies with NADH-diaphorase (NADH) and acid phosphatase (AP) applied to teased nerve fibres. Small pieces were processed for electron microscopy, and a fascicle was teased after staining with osmium tetroxide. In isolated nerve fibres stained with histochemical techniques myelin lesions of segmental character were found closely related to inflammatory cells; Schwann cell cytoplasm in contact with mononuclear cells showing a heavy enzymatic activity (NADH and AP). Under polarized light, the underliying myelin showed focal loss of birefringence. Some electron-microscopic pictures suggested active myelin breakdown by mononuclear cells. The possibility of primary Schwann cell damage by mononuclear cells with subsequent demyelination is discussed.

Observations on the functional cytochemistry of pars intermedia of the rat hypophysis

Light and electron microscopic histochemical reactions were studied in the cells of pars intermedia of the rat. The possible correlations between enzymatic reactions and endocrine functions of these cells were discussed. By combined formaldehyde and chloral vapour treatment the cells of the pars intermedia exhibited a strong yellow fluorescence suggesting the presence of a peptide or peptides with NH2-terminal tryptophan. Masked metachromasia after acid hydrolysis was probably due to these peptides. Only a weak or no alpha-glycerophosphate dehydrogenase and nonspecific esterase activity was observed in the cells of pars intermedia compared to the cells of pars distalis suggesting low production rate of hormone synthesis. Specific and non-specific cholinesterases were demonstrated light and electron microscopically constantly in the cells bordering the lobules. These cells probably represent a certain type of glial cells. In the other cells the enzymatic activities varied markedly in intensity and distribution showing different ultrastructural localizations. Thus cholinesterase activities in the cells of pars intermedia reflect possibly different functional stages of the cells in their hormone production, storage and secretion processes.

Lysosomal hydrolases in the trigeminal ganglion of mice afflicted with an hereditary sensory neuropathy (dystonia musculorum)

Selected lysosomal hydrolases have been investigated in the trigeminal ganglion of mice afflicted with an hereditary sensory neuropathy (dystonia musculorum). This was done using direct enzyme histochemistry. Correlative electron microscopy was also used to further elucidate perikaryal changes. The earlies observed lesion in the trigeminal ganglion of afflicted mice was numerous axon swellings containing intense lysosomal hydrolase activity. Subsequent to this observation, numerous neurones showed central chromatolysis, eccentric nucleus and increased lysosomal hydrolase activity. As various neurones throughout the ganglion underwent the classical chromatolytic reaction, the Golgi apparatus moved to a juxtanuclear location, and there was a focal juxtanuclear accumulation of lysosomes. During the later stages of the disease, a striking decrease in neuronal hydrolase activity characteristic of neuronal atrophy was observed. These results are consistent with earlier suggestions that loss of sensation in the disease could be due to an interruption of axonal transport in primary sensory of neurones.

The intrinsic innervation of the pancreas of the grass-snake (Natrix n. natrix L.), with particular reference to acetylcholinesterase activity in the islets of Langerhans

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Ultrastructural localization of phospholipid synthesis in the rat trigeminal nerve during myelination

A method for the ultrastructural localization of acyltransferase enzymes involved in phospholipid metabolism has been applied to the developing rat trigeminal nerve. Determination of acyltransferase levels in the nerve indicated that a peak of activity occurs at the 8th day after birth with gradual declines of activity up to 15 days. Morphological surveys and determinations of cholesterol levels suggested that heavy myelin formation occurs in the nerve during this latter period. Fixed nerves incubated in a medium for localization of acyltransferases indicated deposition of reaction product associated with Golgi cisternae, intracellular smooth vesicles, and the plasma membrane of the Schwann cell in the incipient stages of myelin formation. Golgi-derived vesicles appeared to move toward the Schwann cell surface and fuse with the plasma membrane. Activity continued to be detectable in the plasma membrane of the internal mesaxon as long as cytoplasm was evident and mature myelin membrane was not yet formed. Cells in which myelin formation appeared advanced showed little or no enzyme marker. Consistent with cytochemical observations were biochemical determinations of acyltransferases which showed high levels of the enzymes in microsomes, while no activity could be detected in the myelin fraction. Acyltransferase reaction product was also observed in the Golgi apparatus of ganglion cell bodies, axoplasmic smooth vesicles, and the axolemma. Localization of acyltransferase enzymes in Schwann cells, ganglion cell bodies, and axons during development of the nerve is discussed in relation to membrane biogenesis in the nervous system.

Biochemically differentiated neoplastic clone of Schwann cells

Four clonal lines have been established in tissue culture from a transplantable tumor of cervical nerve-root induced transplacentally with ethylnitrosourea in an inbred BD-IX rat strain. One clone (RN-2) has several biochemical properties of the nervous system that led to its classification as a Schwann cell line, namely (a) the synthesis of the nervous system specific protein S-100, (b) a high specific activity of 2',3'-cyclic nucleotide-3'-phosphohydrolase, an enzyme present in high specific activity only in glial cells, and (c) the presence of a basic protein related by immunological crossreaction, molecular size, and amino-acid composition to the encephalitogenic protein from beef brain myelin. Clone RN-2 has a high plating efficiency, a doubling time of about 20 hr, and a mean of 43 chromosomes of normal morphology. Clone RN-2 has also been inoculated subcutaneously into syngeneic rats and grown as a clonal tumor with good growth properties.

The appearance of acetylcholinesterase in the myotome of the embryonic rabbit. An electron microscope cytochemical and biochemical study

Acetylcholinesterase (AChE) activity has been studied in the myoblast of skeletal muscle of the 9-13 day fetal rabbit. Cytochemical activity is present in the nuclear envelope and the endoplasmic reticulum, including its derivatives the subsurface reticulum and the sarcoplasmic reticulum. End product is also found in the Golgi complex of the more differentiated myoblasts. The formation of reticulum-bound acetylcholinesterase in the myoblast appears to be independent of nerve-muscle contact, since the enzyme is present before the outgrowth of the spinal nerve. The nerve lacks cytochemical end product until the myoblast is well differentiated. Possible mechanisms of spontaneous muscle contraction have been discussed. A second type of myotomal cell, which exhibits a poorly localized end product of AChE activity, has been described. The ready solubility of the enzyme or diffusibility of its end product suggests that the enzyme may be a lyoesterase. This cell may be the precursor of the morphologically undifferentiated cell which is closely apposed to the myotubes in later stages of skeletal muscle development. Biochemical studies show a significant increase in AChE activity in the dermomyotome by day 12, when many of the myoblasts are well differentiated and the second type of myotomal cell is prominent. Cytochemical studies have indicated that many of the cells in the sample lack reaction product of enzymic activity, whereas others are very active. Biochemical values, therefore, reflect the amount of enzyme in the dermomyotome as a whole, but give little information on the enzymic content of individual cells.

Fine structural localization of cholinesterase activity in the rat submandibular gland

The innervation of the rat submandibular gland was investigated by means of electron microscopy and cytochemical techniques. Axonal swellings partially depleted of their Schwann cell investment were observed in relationship to myoepithelial cells, acinar cells, ducts, capillaries and smooth muscle cells of arterioles. No direct contacts were found to exist between these elements and the nerve fibers. Axonal swellings containing mitochondria and vesicles fell into two distinct types: those characterized by small agranular vesicles and larger vesicles with pale cores and those characterized by small agranular vesicles and small vesicles with dense cores. Reaction product due to acetylcholinesterase activity was observed to be associated with the axolemma and the Schwann cell membrane at the axon-Schwann cell interface of many unmyelinated nerves found in relationship to both the vascular and parenchymal elements of the gland. Activity was found in association with the surface pits and vesicles of myoepithelial cells and arteriolar smooth muscle cells and with the rough endoplasmic reticulum and the nuclear envelope of the myoepithelial cells. Axonal swellings devoid of activity were observed particularly in relationship to arterioles. Reaction product was found only at the axon-Schwann cell interface when sections were incubated in medium for the demonstration of butyrylcholinesterase activity, while no reaction product was found upon addition of eserine sulfate to any of the media. The possibility that the reaction product due to acetylcholinesterase activity observed in association with the axolemma and the surface vesicles and pits of the myoepithelial cells and the arteriolar smooth muscle cells may define the autonomic cholinergic junction in the rat submandibular gland was explored.

A neuropathy in goats caused by experimental coyotiool (Karwinskia humboldtiana) poisoning. II. Lesions in the peripheral nervous system--teased fiber and acid phosphatase studies

The sequential development of the lesions in the peripheral nervous systems of 22 goats poisoned with daily oral doses of ground coyotillo fruits was studied. Studies of teased fibers revealed swelling of Schwann cells, clefts in the myelin sheath, segmental demyelination, remyelination, Wallerian degeneration, and regeneration. A few fibers had a large globular or ovoid swelling in a transitional zone between a region undergoing segmental demyelination at one end and Wallerian degeneration at the other end. These distended transitional zones were the sites of intense acid phosphatase activity in axons.

These histologic studies indicate that the primary lesion occurred in Schwann cells and resulted in swelling of Schwann cells, clefts in the myelin sheath, and segmental demyclination. The sequence of development of the lesions suggests that axonal degeneration were secondary to Schwann-cell injury.

The appearance of acetylcholinesterase in the dorsal root neuroblast of the rabbit embryo. A study by electron microscope cytochemistry and microgasometric analysis with the magnetic diver

In the nine day old embryo, acetylcholinesterase (AChE) is found in the reticulum, i.e. the nuclear envelope, endoplasmic reticulum, and Golgi complex, of a few cells in the neural crest. When the neurite first enters the neural tube, reticulum-bound enzyme is present also in the varicosity of the growth cone of the bipolar neuroblast. At later stages, AChE in the neuroblast has a dual distribution; in addition to the reticulum, activity also appears at the axolemmal surface. The axolemmal activity is found initially on the distal portions of axons in the posterior fasciculus and then progressively appears along the nerve roots in a distal to proximal direction. Very little reticulum-bound enzyme is present within the axon proper. After the 13th day the levels of AChE activity in the posterior fasciculus greatly exceed those in the dorsal root or in the ganglion. Enzymatic activity in the dorsal root equals or exceeds that in the posterior fasciculus by day 16, and both areas are considerably more active than the ganglion.

A cholinergic component in the innervation of the longitudinal smooth muscle of the guinea pig vas deferens. The fine structural localization of acetylcholinesterase

Acetylcholinesterase (AChE) has been detected on the plasma membrane of about 25% of the axons in the longitudinal smooth muscle tissue of guinea pig vas deferens. These axons are presumably cholinergic. No enzyme was detected in the remaining 75% of axons. These axons are presumably adrenergic. The plasma membrane of the Schwann cells associated with the cholinergic axons also stained for AChE. Some axon bundles contained only cholinergic or adrenergic axons while others contained both types of axon. When a cholinergic axon approached within 1100 A of a smooth muscle cell, there was a patch of AChE activity on the muscle membrane adjacent to the axon. It is suggested that these approaches are the points of effective transmission from cholinergic axons to smooth muscle cells. Butyrylcholinesterase activity was detected on the plasma membranes of all axons and smooth muscle cells in this tissue.

Adenosine triphosphatase activity in the membranes of the squid nerve fiber

This investigation deals with the localization of sites of ATPase activity, especially of transport ATPase, in nerve fibers of the squid Doryteuthis plei, at the subcellular level. Splitting of ATP liberates inorganic phosphate which reacts with lead to form a precipitate in the tissue. The reaction was made on nerve fibers fixed with glutaraldehyde. Frozen slices were incubated in Wachstein-Meisel medium containing ATP and Pb(NO(3))(2). Deposits of reaction product were found in the axolemma (towards its axoplasmic side), Schwann cell membranes (mainly at the channels crossing the layer), and mitochondria. Control experiments revealed that no deposits were observed in nerve fibers fixed in osmium tetroxide prior to incubation in the medium containing ATP, or in nerve fibers incubated without substrate or with adenosine monophosphate, adenosine diphosphate, glycerophosphate, or guanosine triphosphate as substrate. For evaluation of transport ATPase activity, these findings were compared with results obtained with nerve fibers treated with G-strophanthin or K-strophanthoside before or after glutaraldehyde fixation. The cardiac glycosides produced a disappearance or diminution of the deposits. The largest inhibitory effect was observed in the axolemma. The findings indicate that the highest ATPase activity is localized in the axolemma and may be due primarily to transport ATPase.

The sorbitol pathway. Enzyme localization and content in normal and diabetic nerve and cord

The enzymes of the sorbitol pathway, aldose reductase and sorbitol dehydrogenase, were investigated in sciatic nerve and spinal cord. The substrate specificities of spinal cord aldose reductase indicates that it is a variant of TPN L-hexonate dehydrogenase which possesses poor polyol forming ability. In contrast, the cauda equina and sciatic nerve aldose reductase have a true aldose reductase with considerable polyol forming ability. The distribution of the latter enzyme is associated with the presence of Schwann cells. Wallerian degeneration experiments are compatible with the localization of true aldose reductase in the Schwann cell and sorbitol dehydrogenase in the axon. There was no change in the levels of sorbitol dehydrogenase in diabetic nerves, a 30 per cent decrease occurred in the aldose reductase content. This decrease suggests a metabolic abnormality of the Sehwann cell, possibly resulting from alrered cellular integrity, which may have important implication for the otiology of diabetic neuropathy.