Copper binding at nodes of Ranvier: a new electron histochemical technique for the demonstration of polyanions

Enzyme histochemistry of cutaneous sensory nerve formations

The cutaneous sensory nerve formations belong to the structures which are studied intensely by the enzyme activity histochemistry since the early history of this technique. The histochemical localization of the activities of nonspecific cholinesterase, alkaline phosphatases, acid phosphatase, adenosine tri- and diphosphatases, adenylate cyclase, and dipeptidylpeptidase-IV in the cutaneous sensory nerve formations, mainly sensory corpuscles, is reviewed. The histochemical approach has brought new knowledge of both morphological building of these unique structures and their biochemical constituents. Taken together, the present results of enzyme histochemistry provide insight into the function of enzymes, and disclose new relationships between the sensory terminals and auxiliary structures in the cutaneous sensory nerve formations.

Ultrastructural and cytochemical evidence for single impulse initiation zones in vestibular macular nerve fibers of rat

Cupric ion-ferricyanide labeling methods and related ferrocyanide-stained tissues were used to locate and characterize, at the ultrastructural level, presumptive impulse initiation zones in the three types of vestibular macular nerve fibers. Large-diameter, M-type vestibular nerve fibers terminate in a calyx at the heminode, and labeling is coextensive with the base of the calyx. Intermediate, M/U-type nerve fibers have short, unmyelinated preterminal segments that sometimes bifurcate intramacularly, and small-diameter, U-type nerve fibers have long, unmyelinated preterminal axons and up to three branches. Preterminals of these nerve fibers display ultrastructural heterogeneity that is correlated with labeling patterns for sodium channels and/or associated polyanionic sites. They have a nodelike ultrastructure and label heavily from near the heminode to the base of the macula. Their intramacular branches, less organized ultrastructurally, label only slightly. Results indicate that vestibular nerve fibers have one impulse initiation zone, located near the heminode, that varies in length according to nerve fiber type. Structural heterogeneity may favor impulse conduction in the central direction, and length of the impulse initiation zone could influence nerve discharge patterns.

Electron microscopical study of non-specific cholinesterase activity in simple lamellar corpuscles of glabrous skin from cat rhinarium: a histochemical evidence for the presence of collagenase-sensitive molecular forms and their secretion

The distribution of nCHE activity was studied histochemically in simple lamellar corpuscles (SLCs) of glabrous skin from cat rhinarium. The Schwann cells forming myelin sheaths in preterminal part of SCLs exhibited no positive reaction for nCHE activity. Prevalent reaction product was localized extracellularly in the inne core enveloping terminal portion of unmyelinated sensory axon. A dot-like shaped reaction product was deposited in the basal lamina of the inner core cells and their cytoplasmic lamellae or was scattered in enlarged interlamellar spaces. Only small amount of fine end product was found to be associated with the plasma membrane of inner core lamellae. Fine reaction product for nCHE activity was consistently localized in perinuclear and rER cisternae and saccules of the Golgi apparatus of inner core cells. Some vesicles around rER and the Golgi apparatus, ones beneath the plasma membrane, and tubular-like cisternal profiles oriented towards the surface contained nCHE end product, as well. The intracellular and extracellular localization of nCHE reaction product suggests that this enzyme behaves in cat SLCs as a secreted rather than as an integral membrane protein. A large amount of dot-like reaction product in the interlamellar spaces disappeared if the skin sections were treated with collagenase before incubation in the medium for histochemical detection of nCHE activity. The decrease of nCHE end product in SLCs of the skin sections after collagenase digestion was corroborated by means of light microdensitometer and electrometrical measurement. The histochemical detection and electrometrical measurement revealed that the majority of the reaction product in the interlamellar spaces of inner core corresponds with the nCHE molecules sensitive to collagenase treatment and they are probably counted among asymmetrical molecular forms.

Cation-binding sites in trigeminal ganglia and maxillary nerve: unusual reactivity of perikarya, stem axons and satellite cells

We have used the cupric/ferrocyanide reaction to study cation-binding in trigeminal ganglia and maxillary nerve of adult rats. Unmyelinated axons did not react, whereas myelinated axons were stained at nodal, paranodal or cleft sites. At 'nodal' sites, metallic deposits were found in the axoplasm, along the axolemma, and at the extracellular interfaces of the paranodal myelin. At 'paranodal' sites, particles were concentrated in the paranodal axoplasm and in the intracellular spaces of the myelin loops. Most maxillary axons examined at successive sites had all nodal or all paranodal staining, but 13 of 51 had a mixture. In trigeminal ganglia there was no staining of perineurial sheath, endoneurial cells or mast cells. Satellite cells and their basal laminae were prominently stained, with those around small neurons more reactive than those of large neurons. Patches of neuronal membrane on cell bodies were stained, more often for small than large neurons. The axon hillock and proximal stem axon were not stained in some cases, but approximately half the neurons had staining of perikaryal cytoplasm at the axon hillock or a dense asymmetric band in the proximal stem axon. Strong intraaxonal staining was found at the junction between unmyelinated proximal and myelinated distal stem axon. In distal stem axons, staining was found at the first myelin segment and at each successively thicker myelin segment; staining was mostly weak and paranodal, with intensity proportional to myelin thickness. The T-junction between stem and main myelinated axon had nodal or paranodal patterns; unmyelinated T-junctions were not stained. The varied cation-binding patterns in trigeminal ganglia show unusual properties of satellite cells and important differences between stem and main axons. The results that the cell membrane of axon hillock and proximal stem regions of many sensory large and small neurons may have numerous sodium channels and could affect signal propagation.

Rapid alterations of the axon membrane in antibody-mediated demyelination

Alterations of nodal and paranodal axolemma of the rat sciatic nerve were investigated in antigalactocerebroside serum-induced demyelination. A ferric ion-ferrocyanide (FeFCN) stain that appears to stain the regions with a high sodium channel density in nerve fibers was applied. When acute conduction block was initiated 20 to 180 minutes after the antiserum injection, myelin terminal loops began to be detached from the paranodal axolemma and reaction product of FeFCN stain originally localized at the nodes decreased in density and extended to the paranodal axolemma. By the time that complete conduction block was established, 5 hours after the injection, FeFCN stain was barely detectable around the nodal area. The loss of staining was associated with detachment and vesiculovacuolar degeneration of the paranodal myelin. This rapid deterioration and disappearance of normal cytochemical characteristics of the axolemma in the presence of only modest paranodal demyelination could be a morphological correlate of the loss of excitability of the axon membrane.

Cytochemical staining characteristics of peripheral nodes of Ranvier in hexacarbon intoxication

Changes in the distribution of stainable gap substance and subaxolemmal density at peripheral nodes of Ranvier in hexacarbon-intoxicated rats have been studied by light and electron microscopy. Cupric ion binding to the nodal gap substance was seen in normal nodes as a discrete annulus by the formation with ferrocyanide of Hatchett's Brown reaction product. Staining of osmicated fibres with ferrocyanide ions alone gave a deposit of black reaction product at the subaxolemmal region at nodes of Ranvier. Paranodal distension by neurofilamentous masses and separation of the terminal myelin loops in the early phase of paranodal dilatation produced no change in the distribution of the two kinds of stainable material. Paranodal myelin retraction with increases both in nodal gap width and nodal axon diameter resulted in displacement and attenuation of both stained regions. Axonal protrusion at the nodal region tended only to displace the stained gap substance, but sometimes it resulted in its attenuation. Occasionally loss of subaxolemmal staining was found. The possible functional relevance of these abnormal findings is discussed in relation to changes in conduction in affected nerves.

The structural correlate of saltatory conduction along the Mauthner axon in the tench (Tinca tinca L.): identification of nodal equivalents at the axon collaterals

The spiny collaterals of the Mauthner axon were reinvestigated in the tench (Tinca tinca L.) with the electron microscope and special staining procedures. These collaterals, as demonstrated by intraaxonal labelling with lucifer yellow, are more or less regularly spaced (100-300 micrometers) and make synaptic contacts with processes of spinal motoneurons and interneurons. The unmyelinated tips of the collaterals are further characterized by the following structural features: (1) an electron-dense undercoating of the axolemma, (2) a positive Prussian blue reaction of the inner surface of the axolemma following ferric ion-ferrocyanide staining (Waxman and Quick, '78a), (3) expanded extracellular spaces which react specifically to inorganic phosphate, metallic ions, and diaminobenzidine. All these properties are known to be shared by the axolemma of central and peripheral nodes of Ranvier. Previous studies from this laboratory have shown that the nerve impulse is propagated along the Mauthner axon in a saltatory mode. Since classical nodal gaps could not be identified within the myelin sheath of this giant fiber, it is concluded on the basis of the present findings that the unmyelinated tips of the spiny collaterals represent nodal equivalents, and thus provide the morphological substrate for the saltatory propagation of the nerve impulse along the Mauthner axon. The typical latency steps, as demonstrated in the latency plot of the longitudinal current signals (Greeff and Yasargil, '80), and the distances between the identified membrane specializations at the axon collaterals are consistent with this conclusion.

Physiological and ultrastructural evidence for an extracellular anion matrix in the central nervous system of an insect (Periplaneta americana)

The efflux of radiocations (22Na, 2K and 45Ca) and of radiochloride occur as two-stage processes from intact cockroach nerve cords. It is suggested that the initial, fast fraction of efflux comes mainly from the superficial connective tissue layer, the neural lamella, and the clefts between the underlying layer of neuroglia, the perineurium. This is deduced from the lack of effect of a metabolic inhibitor and sodium-transport inhibitors on the fast component of 22Na efflux (which contrast with their effects both on the size an the half-time of the slow component) and from the typically extracellular ratios between the fast components of substantial increase in the fast fractions of 22Na and 45Ca efflux but only a small increase in 36Cl efflux: effects which would be expected if the addition to the fast fraction consisted of ions maintained in Donnan equilibrium with fixed anionic sites within the extracellular system. The presence of such anionic sites is also indicated by lanthanum-binding in the extracellular matrix and by the previous histochemical demonstration of hyaluronic acid in the matrix by Ashhurst and Costin. It is suggested that the anionic glycosaminoglycans provide an extracellular cation reservoir which could serve a role in short-term ionic homeostasis of the brain microenvironment.

Localization of hyaluronectin in the nervous system

The localization of hyaluronectin was determined by immunofluorescence and immunoperoxidase methods, in the rat, the sheep and the human. The study of the peripheral nervous system revealed the localization of this protein at the node of Ranvier. It was also present at this site in the central nervous system where the appearance was less characteristic than in the peripheral nervous system. The protein was also observed around about 10% of neurones in all of the regions studied. The subcellular structures labelled could not be precisely defined with the optical microscope.

Cation binding at the node of Ranvier: II. Redistribution of binding sites during electrical stimulation

The nodal and paranodal areas of mature myelinated axons are known to bind cations. To examine whether the cation binding substance may play a role in saltatory conduction, a combined electrophysiological and histochemical study was undertaken. The sciatic nerve of anesthetized or unanesthetized adult C57B1 mice was exposed and not stimulated (control) or stimulated with constant square-wave pulses at one of the following rates: 10/sec, 30/sec, 100/sec or 500/sec. Phosphate-buffered 2.5% glutaraldehyde was either dropped onto the nerve during stimulation until cessation of the compound action potential or the nerve was fixed after discontinuing stimulation. The nerve was excised and processed for the histochemical reaction of copper sulfate/potassium ferrocyanide (which forms an electron dense precipitate at areas of cation binding), dehydrated and infiltrated with SpurrR epoxy resin. Individual nerve fibers were microdissected and counts made of the numbers of paranodal and nodal areas exhibiting the reaction product. The percentage of nodes stained, with respect to the total numbers of nodes and paranodes stained, was calculated. There was no significant difference in percent of nodes stained between the simultaneously fixed, non-stimulated, anesthetized (43.1%), the non-stimulated unanesthetized (45.3%), the animals stimulated at 10/sec (45.9%) and the animals stimulated at 30/sec (50.2%) and 100/sec(46.0%), and fixed post-stimulation. However, all values at the higher frequencies and fixed during stimulation were significantly different both from the control and from each other (30/sec-59.3%; 100/sec-70.5%; and 500/sec-76.4%). The location of cation binding appears to change in response to electrical stimulation and correlates with the increased frequency of the inward movement of sodium ions.

Cation binding at the node of Ranvier: I. Localization of binding sites during development

Cations are known to bind to the node of Ranvier and the paranodal regions of myelinated fibers. The integrity of these specialized structures is essential for normal conduction. Sites of cation binding can be microscopically identified by the electrondense histochemical reaction product formed by the precipitate of copper sulfate/potassium ferrocyanide. This technique was used to study the distribution of cation binding during normal development of myelinating fibers. Sciatic nerves of C57B1 mice, at 1, 3, 5, 6, 7, 8, 9, 13, 16, 18, 24 and 30 days of age, were prepared for electron microscopy following fixation in phosphate-buffered 2.5% glutaraldehyde and 1% osmic acid, microdissection and incubation in phosphate-buffered 0.1 M cupric sulfate followed by 0.1 M potassium ferrocyanide. Localization of reaction product was studied by light and electron microscopy. By light microscopy, no reaction product was observed prior to 9 days of age. At 13 days, a few nodes and paranodes exhibited reaction product. This increased in frequency and intensity up to 30 days when almost all nodes or paranodes exhibited reaction product. Ultrastructurally, diffuse reaction product was first observed at 3 days of age in the axoplasm of the node, in the paranodal extracellular space of the terminal loops, in the Schwann cell proper and in the terminal loops of Schwann cell cytoplasm. When myelinated axons fulfilled the criteria for mature nodes, reaction product was no longer observed in the Schwann cell cytoplasm, while the intensity of reaction product in the nodal axoplasm and paranodal extracellular space of the terminal loops increased. Reaction product in the latter site appeared to be interrupted by the transverse bands. These results suggest that cation binding accompanies nodal maturity and that the Schwann cell may play a role in production or storage of the cation binding substance during myelinogenesis and development.

The localization of sodium and calcium to schwann cell paranodal loops at nodes of Ranvier and of calcium to compact myelin

High-voltage electron microscopy (HVEM) has been used to determine the distribution of cationic precipitates in myelinated axons resulting from the application of two cytochemical techniques: a direct osmium pyroantimonate treatment for precipitating Na+, Ca2+ and Mg2+; and a 5 mM Ca2+ inclusion procedure (Oschman & Wall) for imparting electron density to Ca2+ binding sites. Electron probe wavelength spectroscopy was then used on semi-thick tissue sections to identify the species of ions present in the following regions: Schwann cell paranodal loops, axoplasm at the node, compact myelin and extracellular matrix. With these combined procedures we were able to localize elevated concentrations of both Na+ and Ca2+ to cytoplasmic compartments of the Schwann cell paranodal loops, as well as to detect the presence of Ca2+ at elevated levels in compact myelin. The involvement of the Schwann cell paranodal loops in providing a source and/or sink for Na+ involved in impulse conduction is suggested by these results, and the significance of such a role is discussed. A role for Ca2+ in the formation and stabilization of myelin lamellae is also suggested.

Ferric ion, ferrocyanide, and inorganic phosphate as cytochemical reactants at peripheral nodes of Ranvier

Ferric ion (Fe3+) and ferrocyanide (Fe(CN)64-) were used under a variety of conditions to stain nodes of Ranvier in mammalian peripheral nerves. Principal findings are: 1. Ferric ion will bind to the extracellular nodal gap substance if nerves are pretreated with a phosphate buffer; or, it will bind to the cytoplasmic surface of the nodal axolemma if pretreatment is with cacodylate or veronal--acetate buffer. 2. Ferrocyanide will bind to the inner surface of the nodal axolemma, where it may react with ferric ion to form a blue stain, or with an osmium compound to form a black stain. 3. Ferric ion and ferrocyanide are bound to nodes as colloidal precipitates, and may migrate away from their sites of formation. 4. Not all nodes in a single piece of tissue, or in a single fibre have identical staining properties. It is concluded that ferric ion, ferrocyanide, and inorganic phosphate are valuable as cytochemical reactants for peripheral nodes of Ranvier, but they must be used in carefully controlled experimental situations in order to avoid spurious results.

Evidence for inorganic phosphate binding at nodes of Ranvier in peripheral nerves

Ferric ion is bound to different sites at nodes of Ranvier, depending on how the nerves are prepared. By immersing fresh, unfixed nerves in phosphate buffer, cacodylate buffer, or physiological saline prior to staining with ferric ion and ferrocyanide, it can be shown that binding of ferric ion to the extracellular nodal gap substance requires pretreatment with inorganic phosphate. This implies that phosphate anions are bound to the gap substance where they may then promote precipitation of ferric ion. These results call for a re-evaluation of data that depend on ferric ion binding to nodes of Ranvier. They also open the possibility that affinity for anions in general, or phosphate in particular, may be a significant feature of extracellular molecules present at nodes.

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.