Electron microscopy of severed motor fibers in the crayfish

Summary Cut and crushed crayfish claw nerves were examined with the electron microscope at intervals up to 6 months after lesion. In sections 1 centimeter distal to the lesion there were no signs of degeneration among the giant motor axons even after many months. Swelling of glial wrappings was observed within 48 hours of nerve severance and was particularly notable in the innermost glial layer, the adaxonal layer. Golgi elements, rough endoplasmic reticulum, and mitochondria accumulated in the glia. These changes were perhaps indicative of a greater supportive role required by the severed axons. Regeneration from the proximal stumps of the giant axons began within one week and had proceeded across the lesion gap by 4 weeks. Axon sprouts appeared to travel toward the terminals within the glial sheaths of the distal giant axon segments. Before regeneration was complete, as determined by a simple behaviour test, the regenerating axons occupied increasing proportions of the sheath space. After regeneration was complete occasional degenerations were seen among the sprouts. These degenerations may have occurred in regenerating axons which had grown to the incorrect muscles. The original distal giant axons probably degenerated, as well, after regeneration was complete. There was no evidence of rehealing of proximal and distal segments of the axons.This work was supported by NIH postdoctoral fellowship number 1F2 NB 32, 723 N RB awarded to RHN and grants in aid from the Multiple Sclerosis Society, The American Cancer Society and The National Institutes of Health.     

Regeneration of motor axons in crayfish limbs: Distal stump activation followed by synaptic reformation

Summary Servered distal stumps of limb motor axons in the crayfish Procambarus clarkii remain ultrastructurally intact for at least 2–3 ms after being severed from their cell body. Initial regeneration of a motor axon is associated with the appearance of up to 200 small profiles (satellite axons) having no glial sheath adjacent to the large surviving stump for about 1 cm distal to the lesion at 4–5 wks postoperatively. These satellite axons are seen 2–4 cm distally at the target muscles 3–4 ms postoperatively. By 14–15 ms postoperative, the motor sheaths from the lesion site to the target muscles contain small axonal processes having thick glial sheaths. Behavioral tests show that some axons that are reconnected to the CNS at 4–5 wks may not be connected at 14–15 ms, whereas other axons not connected by 3–4 ms may be connected at 14–15 ms when the original distal stumps have degenerated.We suggest that all these data can best be explained by the view that motor axons in crayfish limbs initially regenerate via activation of the surviving distal stump by satellite axons which grow out from proximal stump. In most cases, these satellite axons continue to activate the surviving distal stump as they slowly grow to the target muscle. Eventually the satellite axons reform synapses on the target muscle and the original distal stump degenerates.This work was supported by NSF grants BNS 77-27678 and 80-22248 and an NIH RCDA 00070 to GDB. The authors would like to thank Mr. Martis Ballinger, Mr. Robert Reiss, and Mrs. Mary Raymond for their excellent technical assistance. We would also like to thank Dr. Wesley Thompson and Mr. Douglas Baxter for helpful discussions.     

Long Term Survival of Severed Distal Axonal Stumps in Vertebrates and Invertebrates

SYNOPSIS. Severed distal stumps of nerve axons have now beenreported to survive for months to years in both vertebrate andinvertebrate nervous systems While low (>15°C) temperaturesmay increase survival times in some preparations such as unmyelinatedgarfish olfactory axons, temperature between 15 and 25°Cis not the only significant factor determining the time courseof survival in goldfish Mauthner axons and for many invertebrateaxons For example when different axons in a crayfish are allstudied at the same temperature, long term survival differsin different axons In some cases these differences appear tobe due to differences in the nature of the ghal reaction orthe presence of synaptic contacts. The possible cellular mechanisms for long term survival fallinto three general cate gories slow degradation of axonal proteinsde novo axoplasmic protein synthesis, and transfer of proteinsfrom adjacent cells to severed axonal stumps In crayfish andsquid giant axons, there is evidence that proteins are indeedtransferred intact from glia to axons or from axon to axon,possibly via exocytotic/endocytotic processes However cellularmechanisms for long term survival may well differ in differentaxons of the same organism, much less between axons in organismsfrom different phyla In particular the ghal sheaths of myehnatedvertebrate axons which demonstrate long term survival mightbe expected to impede ghal/axonal or axonal/axonal protein transfer. The study of long term survival of severed distal stumps isimportant for studies of axonal regeneration because axons inorganisms having long survival times often show functional reconnectionmuch more rapidly and with higher specificity than do axonsin organisms lacking long survival times The study of long termsurvival is also important to cell biologists for an understandingof the molecular mechanisms which allow a piece of cytoplasmseparated from direct cytoplasmic contact with any nucleus toremain morphologically intact and functionally competent formonths to years.     

Chemical degeneration of indolamine axons in rat brain by 5,6-dihydroxytryptamine

Summary Evidence has been obtained by electron microscopy of a direct cytotoxic effect of intraventricularly administered 5,6-dihydroxytryptamine (5,6-DHT) on unmyelinated axons in the rat brain. Ultrastructural signs of axonal damage were observed in areas rich in indolamine nerve terminals as early as 2 hrs after injection. By 6–24 hrs, characteristic and more dramatic signs of degeneration developed, involving coalescence of all axonal constituents—often in combination with a uniform osmiophilic impregnation of the axoplasm—accompanied by engulfment of the dystrophic structures by glial processes. During the next five days, the degenerating axons and axon terminals appeared to be removed by glial cell phagocytosis, whose equivalents were the inclusion of axonal residues into membrane-bound lysosome-like bodies. Concomitantly, there was a progressively increasing number of extremely large and dilated axons in all regions analysed. These axonal swellings, which have an ultramorphology similar to that of dilated stumps of mechanically severed monoamine axons, correspond most probably to proximal, dilated portions of drug-damaged axons.The present results, in combination with biochemical and fluorescence microscopical data, indicate that within a proper dose range the 5,6-DHT-induced degeneration is largely restricted to indolamine axons and axon terminals. However, unselective effects on other unmyelinated axons, on myelin, and on glial cells were observed in narrow subependymal zones close to the lateral ventricles, i.e. close to the injection cannula.Supported by grants from the Deutsche Forschungsgemeinschaft.Supported by grants from the National Institutes of Health, USPHS (NS-06701-06) and from the Swedish Medical Research Council (grants No. B72-14X-712-07B and B72-14X-56-08B).     

Propagation failure of action potentials at the bifurcation point of the slow axon innervating the extensor tibiae muscle ofDecticus albifrons (Orthoptera)

Summary Failure of conduction of nerve impulses has been observed at the bifurcation point of the metathoracic slow extensor tibiae motor axon (SETi) ofDecticus albifrons. Records from the region proximal and distal to the bifurcation point of the axon showed that during prolonged and repetitive stimulation and after a certain number of stimuli, proportional to the stimulating frequency, some SETi action potentials failed to cross this point (Fig. 1).Cross-sections of the metathoracic extensor motor nerve ofD. albifrons show that at the region of axonal bifurcation, both the neural lamella and the layer of glial cells (the sheath) around the SETi axons became thinner than the region proximal and distal to the bifurcation (Fig. 2).The possible role of the conduction block in the neuronal control of the muscle has been discussed.Abbreviations ETi extensor tibiae - SETi slow extensor tibiae - PE proximal electrode - DE distal electrode - SE stimulating electrode     

Degeneration and Regeneration in Crustacean Neuromuscular Systems

Crayfish motor neurons seem to repair damage to peripheral axonsby selective fusion of outgrowing proximal stumps with severeddistal processes that can survive morphologically and physiologicallyintact for over 200 days. Survival of isolated motor and CNSgiant axons is associated with much hypertrophy of their glialsheath. The severed stumps of peripheral sensory neurons oftendegenerate within 21 days and their glial sheath does not hypertrophy.Denervation and immobilization produce relatively little changein the morphology and physiology of the opener muscle, whereastenotomy produces much atrophy within 30-60 days. Crayfish motor and CNS giant neurons show no capability forregenerating ablated cell bodies, whereas peripheral sensorysomata regenerate after limb autotomy. An entire opener musclecan be replaced after limb autotomy but the organism shows littleor no ability to redifferentiate an entire muscle in the absenceof body part regeneration. However, a few opener muscle fiberscan be regenerated if the bulk of the muscle mass remains intact.The significance of all these findings are interpreted withrespect to the developmental capabilities and environmentaladaptations of the crayfish together with the evolution of regenerativeabilities in anthropods and vertebrates.     

Axonal degeneration within the tympanal nerve of Schistocerca gregaria

This study describes time course and ultrastructural changes during axonal degeneration of different neurones within the tympanal nerve of the locust Schistocerca gregaria. The tympanal nerve innervates the tergit and pleurit of the first abdominal segment and contains the axons of both sensory and motor neurones. The majority of axons (approx. 97%) belong to several types of sensory neurones: mechano- and chemosensitive hair sensilla, multipolar neurones, campaniform sensilla and sensory cells of a scolopidial organ, the auditory organ. Axons of campaniform sensilla, of auditory sensory cells and of motor neurones are wrapped by glial cell processes. In contrast, the very small and numerous axons (diameter <1 microm) of multipolar neurones and hair sensilla are not separated individually by glia sheets. Distal parts of sensory and motor axons show different reactions to axotomy: 1 week after separation from their somata, distal parts of motor axons are invaded by glial cell processes. This results in fascicles of small axon bundles. In contrast, distal parts of most sensory axons degenerate rapidly after being lesioned. The time to onset of degeneration depends on distance from the lesion site and on the type of sensory neurone. In axons of auditory sensory neurones, ultrastructural signs of degeneration can be found as soon as 2 days after lesion. After complete lysis of distal parts of axons, glial cell processes invade the space formerly occupied by sensory axons. The rapid degeneration of distal auditory axon parts allows it to be excluded that they provide a structure that leads regenerating axons to their targets. Proximal parts of severed axons do not degenerate.     

Retrograde axoplasmic transport of neurosecretory material

The axonal transport of neurosecretory material was studied in neurosecretory axons of the supraoptico-posthypophyseal system after in-situ transection of the median eminence. Two hours, 8 h, and 18 h after the lesion, both vasopressin and oxytocin antibodies revealed progressive accumulations of immunoreactive material not only in the proximal but also in the distal stumps of the transected axons. The electron-microscopic examination of these axonal portions revealed that such intense immunopositive labelings could be correlated, in both stumps, to a conspicuous accumulation of neurosecretory granules. It is concluded that, under normal physiological conditions, a significant amount of axoplasmic neurosecretory material is transported in retrograde direction and that such a retrograde transport mainly involves neurosecretory granules.     

Cellular migration and axonal outgrowth from adult mammalian peripheral nerves in vitro

It is known that following peripheral nerve transections, sheath cells proliferate and migrate to form a bridge between nerve stumps, which may facilitate axonal regeneration. In the present investigations, cellular migration and axonal outgrowth from nerves of adult mice were studied in vitro using collagen gels. During the first 3 days in culture, profuse migration of fibroblasts and macrophages occurred from the ends of sciatic nerve segments, which had been lesioned in situ a few days prior to explanation, but not from segments of normal nerves. The mechanism of cellular activation in the lesioned nerves was not determined, but migration was blocked by suramin, which inhibits the actions of several growth factors. The migrating cells, which form the bridge tissue, may promote axonal regeneration in two ways. Firstly, axonal outgrowth from isolated intercostal nerves was significantly increased in co-cultures with bridges from lesioned sciatic nerves. This stimulatory effect was inhibited by antibodies to 2.5S nerve growth factor. Secondly, the segments of bridge tissue contracted when removed from animals. It is possible that fibroblasts within the bridge exert traction that would tend to pull the lesioned stumps of peripheral nerve together, as in the healing of skin wounds. The traction may also influence deposition of extracellular matrix materials, such as collagen fibrils, which could orient the growth of the regenerating axons toward the distal nerve stump. © 1996 John Wiley & Sons, Inc.     

The fine structure of the ocelli of Triatoma infestans (Hemiptera: Reduviidae)

The morphology and fine structure of the ocelli of Triatoma infestans have been analyzed by means of light and electron microscopy. The two dorsal ocelli of this species are located behind the compound eyes, looking dorsally and frontally. Externally, the ocelli are marked by the corneal lenses virtually spherical in form and limited internally by a cuticular apodeme. The lens focuses the incoming rays beyond the retina. A single layer of corneagen cells lies below the cuticular lens. The corneagen cells and photoreceptors are arranged in a cup-like fashion beneath the cuticular lens. A distal retinal zone comprises the rhabdoms, which are laterally connected in an hexagonal meshwork. A middle retinal zone comprises the receptor cell segment free of rhabdom, and a proximal zone their axons. In the middle zone, the oviform nuclei and spheroids are located. Screening pigment granules are present within the retinal cell. Spherical mitochondria are homogeneously distributed in the cytoplasm of the cell body. In the axonal zone, mitochondria are found in the peripheral region. Axons from receptor cells extend into the ocellar neuropile at the base of the ocelli, to synapse with second order neurons. The large axons of second order neurons are bundled by glial cells. The ocellar plexus exhibits a high diversity of synaptic unions (i.e. axo-dendritic, axo-axonic, dendro-axonic, and dendro-dendritic).     

Visualizing Peripheral Nerve Regeneration by Whole Mount Staining

Peripheral nerve trauma triggers a well characterised sequence of events both proximal and distal to the site of injury. Axons distal to the injury degenerate, Schwann cells convert to a repair supportive phenotype and macrophages enter the nerve to clear myelin and axonal debris. Following these events, axons must regrow through the distal part of the nerve, re-innervate and finally are re-myelinated by Schwann cells. For nerve crush injuries (axonotmesis), in which the integrity of the nerve is maintained, repair may be relatively effective whereas for nerve transection (neurotmesis) repair will likely be very poor as few axons may be able to cross between the two parts of the severed nerve, across the newly generated nerve bridge, to enter the distal stump and regenerate. Analysing axon growth and the cell-cell interactions that occur following both nerve crush and cut injuries has largely been carried out by staining sections of nerve tissue, but this has the obvious disadvantage that it is not possible to follow the paths of regenerating axons in three dimensions within the nerve trunk or nerve bridge. To try and solve this problem, we describe the development and use of a novel whole mount staining protocol that allows the analysis of axonal regeneration, Schwann cell-axon interaction and re-vascularisation of the repairing nerve following nerve cut and crush injuries.     

Glial Cells in Abdominal Ganglia of Crayfish

Glial cells of abdominal ganglia of crayfish have been studied by transmission electron microscopy. Four cell types can be defined: (1) perivascular glial cells, close to the vascular spaces; (2) perineuronal glial cells, the processes of which ensheathe neuron perikarya; (3) adaxonal glial cells ensheathing axons; (4) neuropilar glial cells, associated with synapsing terminals in the neuropile. Neuropilar glia, adaxonal glia and the system formed by perineuronal and perivascular glia separate different functional zones of the neurons from the hemolymph or the electron dense extracellular matrix. These glial arrangements could play a similar role in hemato-neuronal transport. Gap-like junctions between glia and neuron cell bodies are frequent and could be involved in direct triggering of glial activities related to neurons.     

Using fluorescence photoablation to study the regeneration of singly cut leech axons

The regeneration of the axons of leech Retzius cells was compared following two different methods of axonal severing: (1) a crush of the whole connective that includes the Retzius axon; and (2) photoablation of a small segment of only the Retzius axon. The photoablation was carried out after filling the Retzius cell with Lucifer Yellow (LY). Several tests were carried out to determine whether the photoablation actually severed the axon. These included (1) using the lipophilic membrane probe DiI as an indicator of membrane severance (2) electron microscopic examination of the photoablated axon after filling it with horseradish peroxidase (HRP); and (3) filling the Retzius cell first with HRP, then photoablating, and looking for the disappearance of the HRP in the photoablated region. These and other observations indicated that the photoablated axon was actually severed. Two differences were seen in the regeneration of the Retzius axon after crush versus after photoablation. First, the sprouting following crush was far more disorganized, and included significantly more lateral spread. Second, after photoablation, over 70% of the axons, upon refilling with LY after 3 days or more, showed the newly introduced LY suddenly extending far down the distal segment, indicating that the proximal and distal segments had become reconnected. This was never seen following a crush. The photoablated axons did not pass HRP into the distal segment, suggesting that the reconnection was not by fusion, but perhaps by a gap junction. The results show that axonal regeneration can take a dramatically different form than it does following a standard crush procedure if, instead, the axon is severed in a way that preserves the structural integrity of the surrounding tissue.     

Acetylcholinesterase Distribution in Axotomized Frog Motoneurons

Abstract: The distribution of acetylcholinesterase (AChE; EC 3.1.1.7) activity was examined in the perikarya and proximal axonal stumps of frog motoneurons injured by ventral root transection. Based upon measurements of net AChE accumulation in the proximal stumps of transected ventral roots, and upon orthograde clearances of AChE reported by others, it was determined that an amount of AChE equivalent to at least 0.7–2 times the perikaryal content of this enzyme enters the motor axon each day. A progressive decrease in the rate of AChE accumulation in transected axons during the first 3 days after ventral rhizotomy raised the possibility that excess enzyme might accumulate elsewhere within the axotomized motoneurons. However, AChE accumulation was detected only near the cut ends of the ventral roots and was not appreciably increased within injured motoneuronal cell bodies and proximal dendrites, which were isolated by a new method combining bulk and single-cell isolation techniques. These data suggest that AChE turnover is altered rapidly in response to axonal injury, thereby avoiding large perikaryal accumulations of this enzyme.     

Structure of the intramural nerves of the rat bladder

The bladder of adult female rats receives ～16,000 axons (i.e., is the target of that many ganglion neurons) of which at least half are sensory. In nerves containing between 40 and 1200 axons cross-sectional area is proportional to number of axons; >99% of axons are unmyelinated. A capsule forms a seal around nerves and ends abruptly where nerves, after branching, contain ～10 axons. A single blood vessel is present in many of the large nerves but never in nerves of <600 axons. The number of glial cells was estimated through the number of their nuclei. There is a glial nucleus profile every 76 axonal profiles. Each glial cell is associated with many axons and collectively covers ～1,000 μm of axonal length. In all nerves a few axonal profiles contain large clusters of vesicles independent of microtubules. The axons do not branch; they alter their relative position along the nerve; they vary in size along their length; none has a circular profile. All the axons are fully wrapped by glial cells and never contact each other. The volume of axons is larger than that of glial cells (55%–45%), while the surface of glial cell is twice as extensive as that of axons; there are ～2.27 m² of axolemma and ～4.60 m² of glial cell membrane per gram of nerve. Of the mitochondria of a nerve ～3/4 are in axons and ～1/4 in glial cells.     

Cell-to-cell transfer of glial proteins to the squid giant axon: The glia- neuron protein transfer hypothesis

The hypothesis that glial cells synthesize proteins which are transferred to adjacent neurons was evaluated in the giant fiber of the squid (Loligo pealei). When giant fibers are separated from their neuron cell bodies and incubated in the presence of radioactive amino acids, labeled proteins appear in the glial cells and axoplasm. Labeled axonal proteins were detected by three methods: extrusion of the axoplasm from the giant fiber, autoradiography, and perfusion of the giant fiber. This protein synthesis is completely inhibited by puromycin but is not affected by chloramphenicol. The following evidence indicates that the labeled axonal proteins are not synthesized within the axon itself. (a) The axon does not contain a significant amount of ribosomes or ribosomal RNA. (b) Isolated axoplasm did not incorporate [(3)H]leucine into proteins. (c) Injection of Rnase into the giant axon did not reduce the appearance of newly synthesized proteins in the axoplasm of the giant fiber. These findings, coupled with other evidence, have led us to conclude that the adaxonal glial cells synthesize a class of proteins which are transferred to the giant axon. Analysis of the kinetics of this phenomenon indicates that some proteins are transferred to the axon within minutes of their synthesis in the glial cells. One or more of the steps in the transfer process appear to involve Ca++, since replacement of extracellular Ca++ by either Mg++ or Co++ significantly reduces the appearance of labeled proteins in the axon. A substantial fraction of newly synthesized glial proteins, possibly as much as 40 percent, are transferred to the giant axon. These proteins are heterogeneous and range in size from 12,000 to greater than 200,000 daltons. Comparisons of the amount of amino acid incorporation in glia cells and neuron cell bodies raise the possibility that the adaxonal glial cells may provide an important source of axonal proteins which is supplemental to that provided by axonal transport from the cell body. These findings are discussed with reference to a possible trophic effect of glia on neurons and metabolic cooperation between adaxonal glia and the axon.     

Ultrastructural changes at gap junctions between lesioned crayfish axons

Summary In crayfish, the severed distal segment of single lateral giant axon (SLGA) often survives for at least 10 months after lesioning if this segment retains a septal region of apposition with an adjacent, intact SLGA. In control (unsevered) SLGAs, this septal region usually contains gap junctions and 50–60 nm vesicles near the axolemma of both SLGAs. From 1–14 days after lesioning, the distal segment of a severed SLGA undergoes obvious ultrastructural changes in mitochondria and neurotubular organization compared to control SLGAs or to adjacent, intact SLGAs in the same animal. Gap junctions are very difficult to locate in severed SLGAs within 24 h after lesioning. From two weeks to ten months after lesioning, the surviving stumps of severed SLGAs often appear remarkably normal except that structures normally associated with the presence of gap junctions remain very difficult to find.These and other data suggest that SLGA distal segments receive trophic support from adjacent, intact SLGAs. The mechanism of this support probably could not be via diffusion across gap junctions between intact and severed SLGAs since gap junctions largely disappear after lesioning. However, trophic maintenance could occur via the exocytotic — pinocytotic action of 50–60 nm vesicles which are always present on both sides of the septum between an intact SLGA and a severed SLGA distal segment.This work was supported by NIH research grant NS-14412 and and RCDA 00070 to G.D.B.     

Morphology and distribution of Müller cells in the retina of the toad Bufo marinus

We have previously shown that an antibody against neuron-specific enolase (NSE) selectively labels Müller cells (MCs) in the anuran retina (Wilhelm et al. 1992). In the present study the light- and electron-microscopic morphology of MCs and their distribution were described in the retina of the toad, Bufo marinus, using the above antibody. The somata of MCs were located in the proximal part of the inner nuclear layer and were interconnected with each other by their processes. The MCs were uniformly distributed across the retina with an average density of 1500 cells/mm². Processes of MCs encircled the somata of photoreceptor cells isolating them from each other by glial sheath, except for those of the double cones. Some of the photoreceptor pedicles remained free of glial sheath. Electron-microscopic observations confirmed that MC processes provide an extensive scaffolding across the neural retina. At the outer border of the ganglion cell layer these processes formed a non-continuous sheath. The MC processes traversed through the ganglion cell layer and spread beneath it between the neuronal somata and the underlying optic axons. These processes formed a continuous inner limiting membrane separating the optic fibre layer from the vitreous tissue. Neither astrocytic nor oligodendrocytic elements were found in the optic fibre layer. The significance of the uniform MC distribution and the functional implications of the observed pattern of MC scaffolding are discussed.     

A novel Drosophila model of nerve injury reveals an essential role of Nmnat in maintaining axonal integrity

Axons damaged by acute injury, toxic insults, or during neurodegenerative diseases undergo Wallerian or Wallerian-like degeneration, which is an active and orderly cellular process, but the underlying mechanisms are poorly understood. Drosophila has been proven to be a successful system for modeling human neurodegenerative diseases. In this study, we established a novel in vivo model of axon injury using the adult fly wing. The wing nerve highlighted by fluorescent protein markers can be directly visualized in living animals and be precisely severed by a simple wing cut, making it highly suitable for large-scale screening. Using this model, we confirmed an axonal protective function of Wld(S) and nicotinamide mononucleotide adenylyltransferase (Nmnat). We further revealed that knockdown of endogenous Nmnat triggered spontaneous, dying-back axon degeneration in vivo. Intriguingly, axonal mitochondria were rapidly depleted upon axotomy or downregulation of Nmnat. The injury-induced mitochondrial loss was dramatically suppressed by upregulation of Nmnat, which also protected severed axons from degeneration. However, when mitochondria were genetically eliminated from axons, upregulation of Nmnat was no longer effective to suppress axon degeneration. Together, these findings demonstrate an essential role of endogenous Nmnat in maintaining axonal integrity that may rely on and function by stabilizing mitochondria.     

Uptake of lipoproteins for axonal growth of sympathetic neurons

Lipoproteins originating from axon and myelin breakdown in injured peripheral nerves are believed to supply cholesterol to regenerating axons. We have used compartmented cultures of rat sympathetic neurons to investigate the utilization of lipids from lipoproteins for axon elongation. Lipids and proteins from human low density lipoproteins (LDL) and high density lipoproteins (HDL) were taken up by distal axons and transported to cell bodies, whereas cell bodies/proximal axons internalized these components from only LDL, not HDL. Consistent with these observations, the impairment of axonal growth, induced by inhibition of cholesterol synthesis, was reversed when LDL or HDL were added to distal axons or when LDL, but not HDL, were added to cell bodies. LDL receptors (LDLRs) and LR7/8B (apoER2) were present in cell bodies/proximal axons and distal axons, with LDLRs being more abundant in the former. Inhibition of cholesterol biosynthesis increased LDLR expression in cell bodies/proximal axons but not distal axons. LR11 (SorLA) was restricted to cell bodies/proximal axons and was undetectable in distal axons. Neither the LDL receptor-related protein nor the HDL receptor, SR-B1, was detected in sympathetic neurons. These studies demonstrate for the first time that lipids are taken up from lipoproteins by sympathetic neurons for use in axonal regeneration.