On axoplasmic flow

The spatiotemporal localization of JAM-C following sciatic nerve crush in adult rats

JAM-C is a junctional adhesion molecule, enriched at tight junctions on endothelial and epithelial cells, and also localized to Schwann cells at junctions between adjoining myelin end loops. The role of JAM-C following peripheral nerve injury (PNI) is currently unknown. We examined the localization of JAM-C after sciatic nerve crush injury in adult rats. JAM-C immunoreactivity was present in paranodes and incisures in sham surgery control nerve, but distal to the crush injury significantly decreased at three and 14 days. JAM-C was re-expressed at 28 days and, by 56 days, was significantly increased in the distal nerve compared to controls. In a 7-mm length of sciatic nerve sampled distal to the crush site, the densities of JAM-C immunoreactive paranodes increased in the distal direction. Conversely, the densities of JAM-C immunoreactive incisures were highest immediately distal to the crush site and decreased in the more distal direction. Further analysis revealed a strong correlation between JAM-C localization and remyelination. Fifty-six days after crush injury, greater densities of JAM-C paranodes were seen compared to the nodal marker jacalin, suggesting that paranodal JAM-C precedes node formation. Our data are the first to demonstrate a potential role of JAM-C in remyelination after PNI.

The progressive nature of Wallerian degeneration in wild-type and slow Wallerian degeneration (WldS) nerves

BACKGROUND

The progressive nature of Wallerian degeneration has long been controversial. Conflicting reports that distal stumps of injured axons degenerate anterogradely, retrogradely, or simultaneously are based on statistical observations at discontinuous locations within the nerve, without observing any single axon at two distant points. As axon degeneration is asynchronous, there are clear advantages to longitudinal studies of individual degenerating axons. We recently validated the study of Wallerian degeneration using yellow fluorescent protein (YFP) in a small, representative population of axons, which greatly improves longitudinal imaging. Here, we apply this method to study the progressive nature of Wallerian degeneration in both wild-type and slow Wallerian degeneration (WldS) mutant mice.

RESULTS

In wild-type nerves, we directly observed partially fragmented axons (average 5.3%) among a majority of fully intact or degenerated axons 37-42 h after transection and 40-44 h after crush injury. Axons exist in this state only transiently, probably for less than one hour. Surprisingly, axons degenerated anterogradely after transection but retrogradely after a crush, but in both cases a sharp boundary separated intact and fragmented regions of individual axons, indicating that Wallerian degeneration progresses as a wave sequentially affecting adjacent regions of the axon. In contrast, most or all WldS axons were partially fragmented 15-25 days after nerve lesion, WldS axons degenerated anterogradely independent of lesion type, and signs of degeneration increased gradually along the nerve instead of abruptly. Furthermore, the first signs of degeneration were short constrictions, not complete breaks.

CONCLUSIONS

We conclude that Wallerian degeneration progresses rapidly along individual wild-type axons after a heterogeneous latent phase. The speed of progression and its ability to travel in either direction challenges earlier models in which clearance of trophic or regulatory factors by axonal transport triggers degeneration. WldS axons, once they finally degenerate, do so by a fundamentally different mechanism, indicated by differences in the rate, direction and abruptness of progression, and by different early morphological signs of degeneration. These observations suggest that WldS axons undergo a slow anterograde decay as axonal components are gradually depleted, and do not simply follow the degeneration pathway of wild-type axons at a slower rate.

Cardiac vagal effects in the toad are attenuated by repetitive vagal stimulation

The neuropeptide, somatostatin is co-localised with acetylcholine and galanin in cardiac vagal nerve fibres in the toad, Bufo marinus. Cardiac responses attributed to the release of somatostatin are profound bradycardia, and potentiation of cardiac vagal action by increased acetylcholine release. Cardiac slowing in response to a standard electrical stimulus applied to the vagus (1-2 Hz for 10 s) was potentiated after a 2 min high frequency stimulation (10 Hz). This potentiation of cardiac vagal action was abolished after a 1-hour period of repetitive vagal stimulation. In the presence of atropine, increases in pulse interval recorded in response to vagal stimulation at various frequencies for 2 min each, were significantly reduced after the hour of repetitive stimulation. Potentiation of cardiac vagal action and increases in baseline pulse interval were recorded also in response to intravenous injection of exogenous somatostatin. These responses were not significantly different after the hour of repetitive stimulation. It is concluded that attenuation of the cardiac responses described after the hour of repetitive stimulation is due to depletion of the stores of the neuropeptide somatostatin in the vagal nerve endings.

Comparative study of laser and scalpel nerve transections

This investigation was designed to compare standard scalpel transections of the tibial branch of the rat sciatic nerve with those performed using either a milliwatt carbon dioxide (CO2) or a potassium titanyl phosphate (KTP/532) laser. Four transection groups consisted of nerves sectioned with (1) scalpel (control), (2) milliwatt CO2 laser, (3) KTP/532 with microscope attachment, and (4) KTP/532 laser with 400-microns bare fiber. Each laser was used with the same parameters: 10 watts, 0.4-mm spot size, and continuous-wave mode. Horseradish peroxidase (HRP) was applied to the proximal stump for 30 min, and the animals were sacrificed 24 h later. Horseradish peroxidase (HRP)-labeled motoneuron cell bodies in the lumbar spinal cord were then counted. The average numbers of labeled neurons in each group were as follows: group I (n = 14) 518, group II (n = 8) 424, group III (n = 8) 351, and group IV (n = 8) 283. The standard deviations were quite large, however. When all laser transections were pooled and compared with paired scalpel transections, we found a significant difference, both by the paired t-test (P = 0.016) and by the Wilcoxon matched-paired test (P = 0.02). We conclude that laser transection significantly diminishes the number of neurons labeled by the retrograde transport of HRP.

Temporal relationship between nerve-stump-length-dependent changes in the autophosphorylation of a cyclic AMP-dependent protein kinase and the acetylcholine receptor content in skeletal muscle

The acetylcholine receptor (AChR) content and the autophosphorylation of the regulatory subunit of cyclic AMP-dependent protein kinase type II (R-II) were evaluated in rats soleus muscles at 24, 30 and 66 hr after surgical denervation by cutting the nerve at a short distance (short-nerve-stump) and at a long distance (long-nerve-stump) from the muscle. AChR content was based on the specific binding of [125I]alpha-bungarotoxin (BUTX); changes in the autophosphorylation of R-II were based upon the predominant in vitro 32P-phosphorylation of a 56-Kd soluble protein in cytosolic fractions of solei. The AChR content and the 32P-autophosphorylation of R-II were increased in samples from short-nerve-stump solei, but not from long-nerve-stump solei, after a denervation-time of 30 hr. This nerve-stump-length dependency indicates that the two denervation effects are not related to the immediate halt of impulse-evoked muscle contractility. Furthermore, the results show that alterations in the 32P-autophosphorylation of R-II occurred before, as well as whenever, increases in the AChR content were found. Speculatively, this temporal relationship may be significant with respect to the potential role of R-II in gene expression.

Dystrophic symptoms prevented by phenobarbital in avian muscular dystrophy

New Hampshire normal (line 412) and dystrophic (line 413) chickens were treated with central stimulants and central depressants, respectively, once a day from the 2nd to the 10th day after hatching, and effects of the treatment were examined on a number of muscle fibers, areas of muscle fibers, and the coefficient of variation of a muscle on the 13th day. Central depressants, especially phenobarbital, effectively prevented development of the dystrophic symptoms, whereas central stimulants made normal chickens "dystrophic". The righting ability of the dystrophic chickens was normal after treatment with 10 mg/kg of phenobarbital during the early postnatal period from the 2nd to the 28th day after hatching.

Rapid axoplasmic transport of insulin-like growth factor I in the sciatic nerve of adult rats

Somatomedin C (Sm-C; insulin-like growth factor I; IGF-I) is a polypeptide (Mr 7649), often dependent on growth hormone (GH), with trophic effects on several different tissues. Monospecific IGF-I antisera were used to investigate its localization in the sciatic nerve and corresponding nerve cells, as well as its possible axoplasmic transport in the adult rat. IGF-I-like immunoreactivity was demonstrated in anterior horn motor nerve cells in the spinal cord and in spinal- and autonomic ganglion nerve cells. Faint IGF-I immunoreactivity was under normal conditions observed in axons of the sciatic nerve and in the Schwann cells. Using crush technique, accumulation of IGF-I immunoreactivity was seen in dilated axons within 2 h, both proximal and distal to the crush. However, only a small fraction of the anterogradely transported IGF-I immunoreactive material could be demonstrated to be transported in retrograde direction. Colchicine injected proximal to a crush prevented accumulation of IGF-I immunoreactivity proximal to the crush, but not distal to it. IGF-I-immunoreactive material is synthesized in the cell bodies of peripheral sensory and motor nerve cells. It is transported at rapid rates in the axoplasm of the sciatic nerve of adult rats both in anterograde and retrograde directions. We propose that axonally transported IGF-I may be released and exert trophic influence on innervated cells, tissues and organs.

The kinematics of turnaround and retrograde axonal transport

Rapid axonal transport of a pulse of 35S-methionine-labelled material was studied in vitro in the sensory neurons of amphibian sciatic nerve using a position-sensitive detector. For 10 nerves studied at 23.0 +/- 0.2 degrees C it was found that a pulse moved in the anterograde direction characterized by front edge, peak, and trailing edge transport rates of (mm/d) 180.8 +/- 2.2 (+/- SEM), 176.6 +/- 2.3, and 153.7 +/- 3.0, respectively. Following its arrival at a distal ligature, a smaller pulse was observed to move in the retrograde direction characterized by front edge and peak transport rates of 158.0 +/- 7.3 and 110.3 +/- 3.5, respectively, indicating that retrograde transport proceeds at a rate of 0.88 +/- 0.04 that of anterograde. The retrograde pulse was observed to disperse at a rate greater than the anterograde. Reversal of radiolabel at the distal ligature began 1.49 +/- 0.15 h following arrival of the first radiolabel. Considerable variation was seen between preparations in the way radiolabel accumulated in the end (ligature) regions of the nerve. Although a retrograde pulse was seen in all preparations, in 7 of 10 preparations there was no evidence of this pulse accumulating within less than 2-3 mm of a proximal ligature; however, accumulation was observed within less than 5 mm in all preparations.

Retrograde cell changes in medial septum and diagonal band following fimbria-fornix transection: quantitative temporal analysis

Complete unilateral fimbria-fornix transections, including the overlying cingulate cortex, were administered to female rats. At time points from 1 day to 6 weeks, the septal-diagonal band region was examined using acetylcholinesterase histochemistry, Cresyl Violet cell staining, and choline acetyltransferase biochemistry. As early as 1 day following the transection a decrease in acetylcholinesterase positive cell body staining was observed in the medial septum; however, no loss of Nissl-stained neurons was measured in Cresyl Violet stained sections until 1 week after the lesion. Maximal loss of acetylcholinesterase-positive cells, as visualized after irreversible acetylcholinesterase inhibition, was measured at 1 week, and no further change was observed at time points up to 6 weeks after operation. The loss of acetyltransferase-positive cells was greatest in the medial septal area (-65%) and the vertical limb of the diagonal band (-55%). Little cell loss was measured in the horizontal limb of the diagonal band. This is consistent with the known projections of these cell bodies. Remaining acetylcholinesterase-positive cell bodies in the medial septum had shrunk by about 20% (measured as the diameter along the major axis). A marked neuronal cell loss (about 50%) was demonstrable in the medial septum and vertical limb of the diagonal band in the Cresyl Violet-stained sections, too. A pile-up of acetylcholinesterase-stained material was observed in the dorsal-lateral quadrant of the septal area just proximal to the lesion at 1 day following transection. This pile-up occurred in the medial septum and diagonal band area up to 1 week following the transection, and had nearly disappeared by 2 weeks post-transection. Choline acetyltransferase biochemical activity, measured in samples of whole septum, decreased significantly at 1 day but subsequently returned to control levels. By 2 weeks following transection, an increase in acetylcholinesterase-positive stained fibers was observed in the dorsal-lateral quadrant of the septum, ipsilateral to the lesion relative to the contralateral septum. This response, which was interpreted as sprouting from the lesioned axons proximal to the transection, probably accounted for the rise in choline acetyltransferase biochemical activity in the whole septum following the reduction on the first day.

Axoplasmic transport of thioredoxin and thioredoxin reductase in rat sciatic nerve

Thioredoxin and thioredoxin reductase were localized immunohistochemically in the rat sciatic nerve by immunofluorescence using specific rabbit antisera. Both proteins showed strong immunoreactivity in the cytoplasm of Schwann cells and at the nodes of Ranvier. The axoplasm of myelinated axons also showed a low, evenly distributed immunoreactivity for both proteins. A single or double crush of the nerve caused accumulation of immunoreactivity in dilatated axons both proximally and distally to the crush for up to 8 h. Local cooling of the nerve or subepineural injection of either colchicine or vinblastine prevented the accumulation indicating a role of microtubules. The results showed that thioredoxin and thioredoxin reductase are synthesized in nerve cell bodies and rapidly transported in axons both in anterograde and retrograde directions.

Axonal microtubules: a computer-linked quantitative analysis

Employing current computer-aided morphometric techniques, axonal microtubule density was determined for the rat sural nerve. Analysis of extensive data showed that while microtubule number increases with axon size, the increase is not directly proportional. Thus the relationship between microtubule density and axonal size is inversely related, so that microtubule density is greater in smaller axons than in larger axons. When a proximal and distal site, separated by 2 cm, were compared for microtubule density there was no significant difference, using pooled data for all fibre diameters. The results are interpreted in terms of our present knowledge of axonal-microtubule quantitative relationships, which is reviewed.

Neurochemical basis of auditory fatigue: a new hypothesis

Neuroactive polypeptides such as substance P and enkephalin have recently been demonstrated in the neuronal elements of the inner ear. It has been suggested that the same neuropeptides have a transmitter role in various sensory systems. Transmitter roles for the neuropeptides in the cochlear processes could provide new explanations for many physiological phenomena of hearing. The neuropeptides are particularly well suited to explain such a noise-induced auditory overloading condition as temporary threshold shift.

Effects of dorsal rhizotomy on the several types of primary afferent terminals in laminae I-III of the rat spinal cord. An electron microscope study

After cervical dorsal rhizotomy, small dark central terminals (C1) of glomeruli underwent electron dense changes at 8 h and were all degenerated at 36 h; their number persisted, though slightly diminished, up to 15 days, glial engulfment being negligible. Light large central terminals without neurofilaments (CIIa) showed electron-lucent or electron-dense degeneration from 14 to 36 h, while those with neurofilaments (CIIb) exhibited increased neurofilamentous areas, with depletion and presynaptic concentration of synaptic vesicles as in the electron-lucent change, at the 8-36 h postrhizotomy periods. Both CII-varieties were all degenerated at 36 h and became electron dense at 48 h; glial phagocytosis was intense and no terminals were present after 4 days. It is concluded that in the rat the 3 types of central glomerular terminals are primary axons, and that each type undergoes a different pattern of degeneration which points to a separate primary afferent origin. Numerous nonglomerular axodendritic endings began showing electron-dense degeneration at 8 h which rapidly masked their normal structure, although most appeared to contain round agranular vesicles, and some of them dense-cored vesicles (in lamina I). A few endings exhibited electron-lucent degeneration. Labeling methods seem preferable for studying the primary origin of nonglomerular terminals, due to the difficulty in recognizing the normal predegenerative structure of these profiles.

Regulation of nerve growth factor synthesis and release in organ cultures of rat iris

We studied the synthesis and release of nerve growth factor (NGF) in cultured rat iris with a two-site enzyme immunoassay by measuring the time course of NGF levels remaining in the iris and relased into the medium up to 72 h. For up to 3 h, the NGF levels in the iris did not change significantly. After that, they increased to a maximal level of 350 +/- 30 pg NGF/iris at 19 h, which is 200 times higher than the in vivo content. Between 20 and 72 h in culture, the NGF level decreased to 130 +/- 10 pg NGF/iris, whereas general protein synthesis did not change during that time period. Maximal rate of NGF production (203 pg NGF/h/iris) was seen between 9 and 12 h in culture. In the medium, NGF levels were first detectable after 6 h. Levels then increased with a time course similar to that seen within the iris, reaching a maximal level of 1,180 +/- 180 pg after 19 h in vitro, and then did not significantly change for up to 48 h. The NGF production of the densely sympathetically innervated dilator was three times higher than that of the predominantly cholinergically innervated sphincter. The NGF production was blocked by inhibitors of messenger RNA synthesis (actinomycin D) and of polyadenylation (9-beta-D-arabinofuranosyladenine) as well as by inhibitors of translation (cycloheximide). Monensin, which interferes with the transport of proteins through the Golgi apparatus, decreased NGF levels to 8-12% of controls in the medium, suggesting that the Golgi apparatus is involved in the intracellular processing of NGF.

Axoplasmic transport of somatostatin and substance P in the vagus nerve of the rat, guinea pig and cat

The axoplasmic transport of somatostatin (SS) and substance P (SP) in the cervical vagus nerve was studied in the rat, guinea pig and cat. In preliminary studies, neuropeptide immunoreactivity (IR-SS and IR-SP) was evaluated in extracts of nodose ganglion and vagus nerve using gel and reverse-phase high-performance liquid chromatography (HPLC). In each species, a single immunoreactive form of SP co-eluted with the synthetic undecapeptide on a Bio-Gel P-10 column. More than 95% of transported vagal IR-SS co-eluted with synthetic SS-14. A small percentage in each species co-eluted with SS-28. No larger form, corresponding to a prosomatostatin, was identified in any of the 3 species. On HPLC, IR-SP and IR-SS co-eluted with their synthetic forms. To quantify neuropeptide transport, the vagus nerve was ligated distal to the nodose ganglion. 24 h later in each species, the content of IR-SS and IR-SP was more than 6 times greater in a 3-mm segment of nerve proximal to the ligature than in equal length segments distal to ligature or in the unligated contralateral nerve. In the proximal segment, the net content of IR-SP (pg/3-mm segment, mean +/- S.E.M.) was 366 +/- 45 in the rat, 2038 +/- 184 in the guinea pig, and 912 +/- 108 in the cat. The content of IR-SS in the same segment was 36 +/- 4, 66 +/- 13, and 575 +/- 59 pg/3-mm, respectively. The apparent transport velocities were similar for each peptide and among species. The contribution of the nodose ganglion to transported neuropeptide was estimated by crushing the vagus above the nodose ganglion and simultaneously ligating the nerve distal to the ganglion. The percent contribution of the ganglion to transported IR-SS following this procedure was 50% in the rat, 73% in the guinea pig, and 16% in the cat. Nodose ganglion contribution to IR-SP transport was 31%, 50% and 74%, respectively. Estimated turnover of IR-SS and IR-SP within the ganglion ranged from 4.1 to 6.8 times per 24 h in each species.(ABSTRACT TRUNCATED AT 400 WORDS)

Decreased G4 (10S) acetylcholinesterase content in motor nerves to fast muscles of dystrophic 129/ReJ mice: lack of a specific compartment of nerve acetylcholinesterase?

Acetylcholinesterase (AChE; EC 3.1.1.7) activity and the distribution of its molecular forms were studied in the nervous system of normal and dystrophic 129/ReJ mice, including the sciatic-tibial nerve trunk and motor nerves to slow- and fast-twitch muscles. In normal mice, motor nerves to the slow-twitch soleus exhibited a low AChE activity together with a low level of G4 (10S form) as compared with nerves of the predominantly fast-twitch plantaris and extensor digitorum longus. In contrast, in dystrophic mice, the AChE activity as well as the G4 content of nerves to the fast-twitch muscles were low, displaying an AChE content similar to that of the nerve of the soleus muscle. In the sciatic-tibial nerve trunk, the AChE activity decreased along the nerve in an exponential mode, at rates that were similar in both conditions. However, in dystrophic mice, the AChE activity was reduced throughout the nerve length by a constant value of approximately 180 nmol/h/mg protein. Further analyses indicated that AChE in this nerve trunk was distributed among two compartments, a decaying and a constant one. The decay involved exclusively the globular forms. The activity of A12 (16S form) remained constant along the nerve and was similar in both normal and dystrophic mice. In addition, according to the equation describing the decay of AChE, the reduction in enzymatic activity observed in the dystrophic mice affected mainly G4 in the constant compartment. Brain, spinal cord, sympathetic ganglia, and serum, which were also examined, showed no remarkable differences between the two conditions in their G4 content. The AChE abnormalities that we found in nervous tissues of 129/ReJ dystrophic mice were confined to the motor system.

The distribution of Thy-1 antigen in the P.N.S. of the adult rat

The distribution of the cell surface glycoprotein Thy-1 in the P.N.S. of adult rats was examined using immunohistochemical and experimental techniques. In the hypoglossal nerve the pattern of Thy-1 labelling suggested the antigen was on the plasma membrane of all axons, not only in their major myelinated course but also on their fine terminal branches and at the motor end plate itself. Similarly in other peripheral nerves examined [phrenic and vagus nerves, dorsal and ventral roots, and both the preganglionic and postganglionic trunks of the superior cervical ganglion (SCG) and the submandibular ganglion] Thy-1 was always associated with axons, but the resolution obtained with immunohistochemical techniques was not in itself sufficient to exclude the possibility that the antigen was on the surface of the ensheathing Schwann cell where it apposed the axons. However, in the hypoglossal nerve the antigen was found to accumulate proximal to a ligation of the nerve, suggesting it was made by the neurons and transported down the nerve by axoplasmic flow. This impression was supported by examining neuronal cell bodies in the SCG, dorsal root ganglia and submandibular ganglion, all of which contain readily detectable cytoplasmic Thy-1. In the SCG this cytoplasmic antigen was shown to include the pool of newly synthesized Thy-1. It was increased by treatment of the ganglion with colchicine, and decreased by cycloheximide. Conversely, treatment of hypoglossal nerve trunk with colchicine did not lead to the appearance of the antigen around the non-neuronal perikarya. It is therefore concluded that in those parts of the adult rat P.N.S. examined, Thy-1 is made by neurons and occurs generally on the plasma membrane of axons.

Morphometry of nuclei, nuclear envelopes and nucleoli in aging hamster cerebrum

The neuronal nucleus and nucleolus undergo extensive dimensional and configurational changes during maturation and aging, as shown in this study of pyramidal cells of the hamster motor cortex. With maturation, the increase in nuclear perimeter length per unit nuclear area was associated with an increased amount of nuclear invaginations. With maturation and aging, there was a change in nuclear caliper shape, from spherical to very nonspherical. The number of nucleoli containing microbodies peaked first at 15 days and again at 600 days. It is concluded that area, perimeter and form factor relate to nuclear caliper shape and the presence of nucleolar microbodies. The correlated changes in these parameters appear to differentially reflect stage-specific metabolic conditions related to two critical phases: (1) an early phase (10-15 days) at the inception of configurational changes leading to maturity, and (2) a late phase (600-700 days) at the inception of configurational changes leading to old age.

Proximodistal degeneration of C-fibers detached from their perikarya

Degeneration was followed in the garfish olfactory nerve after removal of the mucosa containing the cell bodies. Degeneration, as measured by a decrease in the weight of consecutive 3-mm nerve segments, spreads at constant velocity from the site of injury toward the synaptic area. The proximodistal degeneration is temperature dependent and progresses from 0.3 mm/d at 10 degrees C to 13.0 mm/d at 35 degrees C. Between 14 and 35 degrees C, the velocity increases linearly with temperature. At all the temperatures investigated, these proximodistal degeneration velocities are identical to the rates of slow intraaxonal flow measured in axons detached from their cell bodies, or to the rates measured in regenerating fibers, and, except at 10 degrees C, are 3.3 times faster than the rate of slow flow in intact nerves. These results were confirmed by light and electron microscopy. We hypothesize that the collapse and subsequent degeneration of the axons is the result of a proximodistal depletion of cytoskeletal elements no longer provided by the cell body to the axon by slow intraaxonal flow. A significant number of axons disappeared rapidly from the nerve before the arrival of the slow degenerative wave. From studies by other groups, this rapid degeneration may be the result of a lack of rapidly transported, mainly membranous components.

Axonal transport involvement in long-lasting synaptic modifications in Blatta orientalis

To determine whether axonal transport plays a role in the establishment of long-lasting changes in synaptic transmission, the effects of colchicine on transport and on synaptic modifications induced by hyperactivity were studied in the nerve cord of the cockroach Blatta orientalis. Application of a lead weight on the insect's dorsum, and the consequent exaggerated use of antigravity reflexes, facilitated synaptic transmission along a particular nervous pathway in the metathoracic ganglion. Application of colchicine in the prothoracic ganglion reversibly blocked such synaptic facilitation and temporarily interfered with the transport of proteins along the cord. Five components of axonal transport, moving at 2, 10, 25, 75, and 150 mm/day, were altered by colchicine treatment with a temporal course that coincided with the reversible inhibition of synaptic facilitation. These results were brought about by colchicine acting directly on axonal transport at the level of the prothoracic ganglion, rather than on synaptic transmission measured at the metathoracic ganglion. The temporal correlation observed between the effects of colchicine on axonal transport and on synaptic facilitation strongly suggest that the transport process is essential for long-lasting synaptic modifications to take place.

Axonal transport dysfunction in dystrophia myotonica

Axonal transport of acetylcholinesterase (AChE) was measured in the median and sural nerves of a subject who suffered from dystrophia myotonica and in a control subject. It was found that the basal activity of AChE was increased in myotonic nerves while its proximodistal transport was inhibited.

Ultrastructure of a new microtubule-neurofilament coupler in nerves

A new structure associated with the surfaces of neuronal microtubules is described which connects microtubules to neurofilaments in the axonal processes of cultured chick sensory ganglia. These couplers consist of a spherical core particle (15 nm in diameter) from which radiate several thin filaments (4 nm in diameter). Connection of adjacent microtubules and neurofilaments is achieved by thin filaments radiating from core particles positioned between these cytoskeletal elements. Couplers are most conspicuous in regions of axonal processes containing widely separated microtubules and neurofilaments. The structure and distribution of these couplers suggests that they are directly involved in intra-axonal organelle movements, possibly by modulating the spatial separation of adjacent microtubules and neurofilaments, thereby allowing the passage of transported organelles.

Cytofluorimetric scanning: a tool for studying axonal transport in monoaminergic neurons

A new technique is described which makes it possible to measure several substances and parameters related to axonal transport in peripheral nerves. The technique is based on histofluorescent techniques and measures accumulated amounts of fluorescent substances, e.g. proximal to a crush or local cooling of the nerve. Sections from nerves, treated according to the FIF method for visualization of catecholamines or for immunofluorescence, are placed in a cytofluorimeter (Leitz MPV 2). The nerve sections are passed under a measuring slit by a motor-driven cross-table and the fluorescence intensity is continuously registered via a recorder with integrator which gives a graphical "nerve-accumulation profile." Comparisons between accumulation curves obtained with the cytofluorimetric scanning technique and biochemically determined accumulation curves of noradrenaline, dopamine-beta-hydroxylase and tyrosine-hydroxylase in the sciatic nerve following crush operations, demonstrated a striking similarity. With this technique it is possible to semiquantify the accumulated amount of a fluorescent substance, study morphology, perform morphometry and photographical documentation in the same section. This scanning technique may prove useful, since the accumulation and distribution of several substances in consecutive sections, along the length of a nerve, can be demonstrated graphically using superimposed curves.

High voltage electron microscopy studies of axoplasmic transport in neurons: a possible regulatory role for divalent cations

Light and high voltage electron microscopy (HVEM) procedures have been employed to examine the processes regulating saltatory motion in neurons. Light microscope studies demonstrate that organelle transport occurs by rapid bidirectional saltations along linear pathways in cultured neuroblastoma cells. HVEM stereo images of axons reveal that microtubules (Mts) and organelles are suspended in a continuous latticework of fine microtrabecular filaments and that the Mts and lattice constitute a basic cytoskeletal structure mediating the motion of particles along axons. We propose that particle transport depends on dynamic properties of nonstatic microtrabecular lattice components. EXperiments were initiated to determine the effects of changes in divalent cation concentrations (Ca2+ and Mg2+) on: (a)the continuation of transport and (b) the corresponding structural properties of the microtrabecular lattice. We discovered that transport continues or is stimulated to a limited extent in cells exposed to small amounts of exogenously supplied Ca2+ and Mg2+ ions (less than 0.1 mM). Exposure of neurons to increased dosages of Ca2+ and Mg2+ (0.2-1.0 mM) stimulates transport for 2-4 min at 37 degrees C, but after a 5- to 20-min exposure the saltatory movements of organelles are observed gradually to become shorter in duration and rate particle motion ceases to occur. HVEM observations demonstrated that Ca2+ - and with the cessation of motion. Ca2+-containing solutions produced contractions of the microtrabecular filaments, whereas Mg2+-containing solutions had the opposing effect of stimulating an elongation and assembly (expansion) of microtrabeculae. On the basis of these observations we hypothesize that cycles of Ca2+/Mg2+-coupled contractions and expansions of the microtrabecular lattice probably regulate organelle motion in nerve cells.

Axonal transport of adenylate cyclase activity in normal and axotomized frog sciatic nerve

Adenylate cyclase activity accumulated proximal to a constriction placed around the frog sciatic nerve. The rate of accumulation was linear between 8 and 24 h following placement of the constriction; accumulation rate declined substantially after 24 h. Accumulation of activity distal to the constriction in normal nerve was not significantly different from control for the first 72 h, but increased at 5 days. These data are interpreted as indicating that adenylate cyclase is transported from the cell body to the nerve terminals in normal frog nerve, but not in the reverse direction. Following axon transection, anterograde transport of adenylate cyclase activity declined, but a transient retrograde transport of adenylate cyclase activity appeared. In addition, adenylate cyclase activity accumulated in the proximal transected nerve stump during the period when Schwann cell proliferation and the initiation of nerve regeneration both appear. The pattern of response of adenylate cyclase activity to nerve injury suggests that the adenylate cyclase: cAMP system could play some role in peripheral nerve regeneration.

Polarity orientation of axonal microtubules

The polarity orientation of cellular microtubules is widely regarded to be important in understanding the control of microtubule assembly and microtubule-based motility in vivo. We have used a modification of the method of Heidemann and McIntosh (Nature (Lond.). 286:517-519) to determine the polarity orientation of axonal microtubules in postganglionic sympathetic fibers of the cat. In fibers from three cats we were able to visualize the polarity of 68% of the axonal microtubules; of these, 96% showed the same polarity orientation. Our interpretation is that the rapidly growing end of all axonal microtubules is distal to the cell body. We support Kirschner's hypothesis on microtubule organizing centers. (J. Cell Biol. 86:330-334), although this interpretation raises questions about the continuity of axonal microtubules. Our results are inconsistent with a number of models for axonal transport based on force production on the surface of microtubules in which the direction of force is determined by the polarity of microtubules.

Axonal transport in transplanted frog sciatic nerve

Axonal transport was studied in transplanted frog sciatic nerves-dorsal ganglia for periods up to three months. The ganglia were either labeled prior to, or after varying periods of transplantation and the distribution of labeled proteins compared. The survival of the preparations was assessed by studying their ability to transmit compound action potentials, to maintain axonal transport and by their ultrastructural appearance. The sensory neurons retained their fast axonal transport and excitability during the transplantation periods. Morphologically about 30% of the axons appeared normal after one month of transplantation. The amount and distribution of protein incorporated radioactivity in the ganglia and the nerve changed with time but the decrease in the ganglia was not accompanied by a corresponding increase in the nerve. There was no evidence for a distinct slow phase of transport in spite of a functional fast transport system. The results indicate that either slow transport stops when the normal balance between release, degradation and recirculation is distributed by the presence of a ligature or that there is a continuous change in the composition of transported material with the time after labeling which is not reflected in altered transport characteristics.

An increase in smooth endoplasmic reticulum and a decrease in Golgi apparatus occur with ionic conditions that block initiation of fast axonal transport

The ultrastructure of bullfrog spinal ganglia was analyzed after incubation in media containing concentrations of calcium and cobalt known to inhibit export of proteins from the soma to the axon. Although most somal organelles were morphologically unchanged by the various incubation media, striking changes were seen in the smooth endoplasmic reticulum (SER) and the Golgi apparatus (GA). In order of effect, calcium-free medium (CFM), normal medium supplemented with cobalt (NM--Co), and CFM supplemented with cobalt (CFM--Co) produced increasing amounts of SER coupled with decreasing densities of GA stacks. In the extreme case, CFM--Co incubation resulted in a nearly 10-fold increase in SER volume as well as in a virtually complete depletion of GA stacks. Axons originating within the ganglion were also examined and showed little change after the various incubations. The rank order of the altered incubation media in producing morphological changes was the same as the relative effectiveness of the media in depressing the fast axonal transport of [3H]protein within the dorsal root ganglion neurons. The morphological and biochemical results are discussed with respect to establishing the localization of the calcium-dependent step(s) that has been proposed to occur in the neuronal soma during the initiation of axonal transport.

Peripheral nerve repair

The neuron is remarkable as a cell with a prolonged process, the axon. Various substances and organelles are transported up and down the axon. Axotomy profoundly affects this axonal transport. The proximal stump of the axon seals off and organelles accumulate. Terminal sprouts appear and move towards the distal stump. Soon after reinnervation neurotransmission reappears. Initially polyneuronal innervation occurs but this is then eliminated. Somatopetal axonal transport has been studied using tracer macromolecules in the mouse facial neuron model. Transport was blocked by axotomy from terminals in muscle but persisted at the injured axonal membrane. This stopped when the axonal membrane grew over the stump. Transport returned after reinnervation. Such transport may carry the signals that govern neuronal response to axotomy.

Axonal transport of the molecular forms of acetylcholinesterase in chick sciatic nerve

Acetylcholinesterase (AChE) polymorphism was studied in the sciatic nerve of 4-week-old Leghorn chicks, by sucrose gradient sedimentation analysis. Four main AChE molecular forms were found with sedimentation coefficients of 5S, 7.5S, 11.5S and 20S respectively. Axonal transport of each of these forms was investigated on the basis of the enzyme accumulation kinetics measured on both sides of nerve transections and of the enzyme redistribution kinetics in nerve segments isolated in vivo. After nerve transection, 11.5S and 20S forms accumulated faster in the anterograde than in the retrograde direction and also much faster than 5S and 7.5S forms in the anterograde direction. Retrograde accumulations of 5S and 7.5S were faint or negligible. In addition, 1 h after nerve cutting, the accumulation rates for 11.5S and 20S forms (but not for 5S and 7.5S) fell, in both directions, to about one-third of their initial values, probably owing to reversal of axonal transport at the axotomy site. Local protein synthesis inhibition by cycloheximide did not affect the accumulation of 11.5S and 20S in front of a transection, at least during the first hours, but reduced that of 5S and 7.5S by about 40%. In isolated nerve segments in vivo, the rapidly mobile fraction of AChE was estimated to constitute 23% of the total enzyme activity present in the nerve, 14% of it moving in an anterograde and 9% in a retrograde direction. A small amount of 11.5S molecules (approx. 20%) was in rapid transit (two-thirds in the anterograde and one-third in the retrograde direction), whereas almost all the 20S--about 90%--migrated rapidly (two-thirds forwards and one-third backwards). Anterograde velocities of 408 +/- 94 and 411 +/- 161 mm/day respectively were estimated for the 11.5S and 20S forms. Their respective retrograde velocities were 175 +/- 85 and 145 +/- 107 mm/day. Assuming that the totality of 5S and 7.5S molecules are moving in the anterograde direction, their accumulation rates were consistent with the average anterograde velocities of 2.9 +/- 1.3 and 5.1 +/- 1.4 mm/day, respectively.

Opioid receptors undergo axonal flow

Previous studies have indicated the presence of opiate receptors on axons of the rat vagus nerve and on other small diameter fibers. In examinations of the effect of ligation on the distribution of receptors in the vagus nerve by in vitro labeling light microscopic autoradiography, a large buildup of receptors was found proximal to the ligature. This result indicates an axonal flow of receptors.

Rapid effect of nerve injury upon axonal transport of phospholipids

1. Axonal transport of phospholipids labelled by lumbosacral spinal cord injection of [3H]choline has been studied in normal and injured sciatic nerves of the rat. 2. The appearance of labelled material in progressively increasing amounts in the sciatic nerve following spinal cord injection was consistent with a maximum velocity of axonal transport of about 20 mm/hr. There was also evidence of substantial amounts of labelled phospholipids being transported at much slower velocities. 3. In sciatic nerves injured by crushing there was an accumulation of labelled phospholipid immediately proximal to the crush. The accumulation was progressive with time. There was also an increase of labelled phospholipid in all the more proximal segments of the crushed nerves; this reached a maximum of about twice that in uncrushed nerves at 10 hr. after spinal cord injection. 4. The labelled phospholipid was shown to be about 80-90% phosphatidylcholine both in uncrushed and crushed nerves. 5. The nature of the mechanism of this very rapid response of neurones to peripheral injury did not appear to be due to loss of 'information' from the periphery or action potentials initiated at the site of injury. The phenomenon has been further investigated by injection of drugs into the injured or control nerves. KCl injected at (but not proximal to) the site of injury was effective in blocking the injury response providing it was injected between a few minutes before or up to 30 min after the time of injury. Injection of either tetrodotoxin or local anaesthetic was as effective as injury in increasing the amount of labelled phospholipid transport. 6. These results suggest that the occurrence of an injury in a distant process of a neuron can be signalled retrogradely to the cell body by a mechanism involving a signal velocity of at least 140 mm/hr.

The movement of membranous organelles in axons. Electron microscopic identification of anterogradely and retrogradely transported organelles

To identify the structures to be rapidly transported through the axons, we developed a new method to permit local cooling of mouse saphenous nerves in situ without exposing them. By this method, both anterograde and retrograde transport were successfully interrupted, while the structural integrity of the nerves was well preserved. Using radioactive tracers, anterogradely transported proteins were shown to accumulate just proximal to the cooled site, and retrogradely transported proteins just distal to the cooled site. Where the anterogradely transported proteins accumulated, the vesiculotubular membranous structures increased in amount inside both myelinated and unmyelinated axons. Such accumulated membranous structures showed a relatively uniform diameter of 50--80 nm, and some of them seemed to be continuous with the axonal smooth endoplasmic reticulum (SER). Thick sections of nerves selectively stained for the axonal membranous structures revealed that the network of the axonal SER was also packed inside axons proximal to the cooled site. In contrast, large membranous bodies of varying sizes accumulated inside axons just distal to the cooled site, where the retrogradely transported proteins accumulated. These bodies were composed mainly of multivesicular bodies and lamellated membranous structures. When horseradish peroxidase was administered in the distal end of the nerve, membranous bodies showing this activity accumulated, together with unstained membranous bodies. Hence, we are led to propose that, besides mitochondria, the membranous components in the axon can be classified into two systems from the viewpoint of axonal transport: "axonal SER and vesiculotubular structures" in the anterograde direction and "large membranous bodies" in the retrograde direction.