Single Fascicles Research Articles

Nerve ultrasound follow‐up in a child with Guillain‐Barré syndrome

Nerve ultrasound has been used increasingly in neurophysiology laboratories, but data on Guillain-Barré syndrome (GBS) are still limited, and no follow-up studies are available. An 8-year-old boy was admitted with severe demyelinating GBS. Serial neurophysiological evaluations were performed initially and in follow-up. Ultrasound studies showed diffuse and heterogeneous nerve swelling and focal enlargement of single fascicles inside the nerve. Together with clinical and electrophysiological improvement, progressive normalization of ultrasound changes was seen. Ultrasound demonstrated structural nerve abnormalities in GBS. These changes normalized as the patient improved clinically and electrophysiologically. Further studies are needed to elucidate the diagnostic and prognostic value of ultrasound in GBS.

Fascicle-Scale Loading and Failure Behavior of the Achilles Tendon

Although the overall bulk properties of the Achilles tendon have been measured, there is little information detailing the properties of individual fascicles or their interactions. The knowledge of biomechanical properties at the fascicle-scale is critical in understanding the biomechanical behavior of tendons and for the construction of accurate and detailed computational models. Seven tissue samples (approximately 15x4x1 mm(3)) harvested from four freshly thawed human (all male) tendons, each sample having four to six fascicles, were tested in uniaxial tension. A sequential sectioning protocol was used to isolate interaction effects between adjacent fascicles and to obtain the loading response for a single fascicle. The specimen deformation was measured directly using a novel polarized light imaging system with digital image correlation (DIC) for marker-free deformation measurement. The modulus of the single fascicle was significantly higher compared with the intact fascicle group (single: 226 MPa (SD 179), group: 68 MPa (SD 33)). The interaction effect between the adjacent fascicles was less than 10% of the applied load and evidence of sub- and postfailure fascicle sliding was clearly visible. The DIC direct deformation measurements revealed that the modulus of single fascicles could be as much as three to four times the intact specimen. The consistently higher moduli values of the single (strongest) fascicle indicate that the overall response of the tendon may be dominated by a subset of "strongest" fascicles. Also, fascicle-to-fascicle interactions were small, which was <10% of the overall response. This knowledge is useful for developing computational models representing single fascicle and/or fascicle group mechanical behavior and provides valuable insights into fascicle-scale Achilles tendon material properties.

Corticosteroid administration alters the mechanical properties of isolated collagen fascicles in rat‐tail tendon

Overload tendon injuries are frequent in recreational and elite sports. The optimal treatment strategy remains unknown, but local administration of corticosteroids is one common treatment option. The direct effects of the corticosteroid administration on the tissue are not fully understood. The present study examined the biomechanical effects of intratendinous corticosteroid injections on healthy rat-tail tendon collagen fascicles. A total of 24 Wistar male rats were divided into (A) a corticosteroid group where the animals were injected in the tail tendon with methylprednisolone acetate, 1.0 mL of 40 mg/mL mixed with 1.0 mL 9% saline (n=12), and (B) a control group that was injected with 9% saline (n=12). Three days after the injections, the animals were sacrificed and single individual collagen fascicles were collected and underwent displacement to failure. Corticosteroid administration significantly reduced tensile fascicle yield strength by 16% and Young's modulus by 14% compared with sham treatment (10.5+/-0.8 vs 12.4+/-0.5 MPa, P< or =0.05, and 537+/-27 vs 641+/-30 MPa, P<0.05, respectively), while the strain properties were unaffected. Peak stress was similar between the two groups. There was no difference in fascicle diameter between the two groups.

DrosophilaNeurexin IV stabilizes neuron-glia interactions at the CNS midline by binding to Wrapper

Ensheathment of axons by glial membranes is a key feature of complex nervous systems ensuring the separation of single axons or axonal fascicles. Nevertheless, the molecules that mediate the recognition and specific adhesion of glial and axonal membranes are largely unknown. We use the Drosophila midline of the embryonic central nervous system as a model to investigate these neuron glia interactions. During development, the midline glial cells acquire close contact to commissural axons and eventually extend processes into the commissures to wrap individual axon fascicles. Here, we show that this wrapping of axons depends on the interaction of the neuronal transmembrane protein Neurexin IV with the glial Ig-domain protein Wrapper. Although Neurexin IV has been previously described to be an essential component of epithelial septate junctions (SJ), we show that its function in mediating glial wrapping at the CNS midline is independent of SJ formation. Moreover, differential splicing generates two different Neurexin IV isoforms. One mRNA is enriched in septate junction-forming tissues, whereas the other mRNA is expressed by neurons and recruited to the midline by Wrapper. Although both Neurexin IV isoforms are able to bind Wrapper, the neuronal isoform has a higher affinity for Wrapper. We conclude that Neurexin IV can mediate different adhesive cell-cell contacts depending on the isoforms expressed and the context of its interaction partners.

MRT in der erweiterten Diagnostik des Kubitaltunnelsyndroms

The T(2)-weighted contrast of peripheral nerve lesions and denervated muscles is the most important diagnostic criterion in neuromuscular MRI. By exactly determining the anatomic denervation pattern of muscles and with a particularly high spatial resolution for peripheral nerves by visualising single fascicles, MRI enables the exact localisation of ulnar nerve lesions in the cubital tunnel or at other sites. Furthermore, the extent of the lesion and the degree of its severity can be evaluated already during the early course of disease. Obviously, MRI is the method of choice for the direct visualisation of causative mass lesions such as ganglion cysts or lipoma, for example, before surgical exploration. Thus, it is a valuable diagnostic tool and supplement to conventional clinical and electrodiagnostic studies of the cubital tunnel syndrome (CuTS). The contribution of MRI to the preoperative selection of patients for either short- or long-segment decompression has to be clarified by further studies.

The internal innervation and morphology of the human female levator ani muscle

The purpose of this study was to describe the microinnervation of the human the female levator ani muscle complex. Detailed microdissection of 10 fresh female levator ani muscles was performed. Specimens were processed by modified Sihler's staining technique. A composite drawing of the levator ani nerve (LAN) distribution was created. Six hemi-levator ani muscles were stained and digitally reconstructed. The LAN traveled perpendicular to major muscular bundles while progressively branching into finer nerves that eventually entered single muscle fascicles. The LAN continued its course through the iliococcygeous muscle to innervate the puborectalis, puboperinealis, and puboanalis muscles. There was no distinct separation between pubovisceralis and iliococcygeous fibers. There were muscle fibers that could be best described as coccygeoperinealis. The utilized staining technique enabled us to visualize the LAN microinnervation of the levator ani muscle that extends to puboperinealis and puboanalis muscles. A blueprint for LAN and levator ani morphology was created.

The Normal and Neoplastic Perineurium

Peripheral nerves consist of 3 layers with differing characteristics: the endoneurium, perineurium, and epineurium. The perineurium represents a continuum with the pia-arachnoid from the central nervous system and extends distally with the sheath of capsular cells of peripheral sensorial organs and propioceptive receptors. It is made of layers of flattened cells surrounded by a basement membrane and collagen fibers, forming concentrically laminated structures around single nerve fascicles. Functionally, the perineurium modulates external stretching forces (that could be potentially harmful for nerve fibers), and along with endoneurial vessels, forms the blood-nerve barrier. Multiple pathologic conditions associated with the perineurium have been described. Perineurial invasion is considered an important prognostic factor in several malignant neoplasms. Perineuriomas are true benign infrequent perineurial cell neoplasms that have been divided in 2 categories: those with intraneural localization and a more common extraneural (soft tissue) group, including sclerosing and reticular variants. Sporadic cases of malignant perineuromas have been reported. Interestingly, neurofibromas and malignant peripheral nerve sheath tumors may also display perineurial cell differentiation. The histologic appearance of perineuriomas may overlap with other soft tissue spindle cell neoplasms. Immunohistochemistry is imperative for the diagnosis, although in certain cases ultrastructural studies may be needed. Typical perineuriomas are positive for epithelial membrane antigen, glucose transporter-1-1, and claudin-1, and negative for S-100 protein and neurofilaments. Perineuriomas have mostly simple karyotypes, with one or few chromosomal rearrangements or numerical changes and it seems that specific cytogenetic aberrations may correlate with perineurioma subtype.

Immunohistochemical detection of matrix metalloproteinase-1 in the periodontal ligament of equine cheek teeth

The hypsodont equine cheek tooth erupts continuously throughout life. The collagen fibers of the periodontal ligament (PDL) have to remodel constantly to allow the tooth to move in an occlusal direction. Remodeling of the collagen fiber bundles needs to be well-coordinated in order to maintain functional tooth support. The aim of this study was to examine the role of matrix metalloproteinase-1 (MMP-1) in the collagen remodeling of the equine PDL under physiological conditions. Specimens containing the PDL interposed between the dental cementum and the alveolar bone were taken from nine Warmblood horses at three designated horizontal levels: subgingival, middle, and apical. The expression of MMP-1 was detected immunohistochemically. MMP-1 was found to be present in the specimens of all horses. Immunopositive fibroblasts/fibrocytes were accumulated within individual single collagen fascicles. Our results suggest that MMP-1 induced collagen degradation plays a central role in the physiological remodeling of the equine PDL. The distribution of MMP-1 positive fascicles indicates well-directed remodeling which occurs as an asynchronous process, so that only single collagen fascicles are remodeled at the same time. Due to this remodeling of one fascicle at a time, the overall anchorage of the tooth is preserved at all times.

Innervation of the triangular fibrocartilage complex of the human wrist: Quantitative immunohistochemical study

The distribution of neural elements in the triangular fibrocartilage complex (TFCC) of the human wrists was studied via immunohistochemical staining of protein gene product (PGP) 9.5 and calcitonin gene-related peptide (CGRP). Articular branches projecting to the TFCC arose from the dorsal branch of the ulnar nerve in all wrists examined. The TFCC is subdivided into the following six regions: the articular disc proper (ADP), meniscus homolog (MH), radio-ulnar ligament (RUL), loose part of ulnar collateral ligament (lUCL), dense part of ulnar collateral ligament (dUCL), and internal portion (IP). The IP consists of a mixture of dense and loose connective tissues enclosed by the ADP, MH, RUL, and UCL, and resides deep in the prestyloid recess, which is a pit in the MH. The densities of PGP 9.5-positive neural elements, including free nerve endings, single nerve fibers, nerve fascicles, and perivascular neural nets, were significantly higher in the IP than in other regions. Some of the neural elements except for the perivascular neural nets were positive for CGRP. The high density of neural elements in the IP suggests that sensory nerves projecting to the TFCC enter into the IP and from there distribute to adjacent regions such as the MH and RUL. Free nerve endings are responsible for pain transmission. The high density of free nerve endings in the IP suggests that the IP is a source of ulnar side wrist pain.

(1623) Proposal to conserve the name Saussurea piptathera against S. indica (Compositae)

Saussurea piptathera Edgew. was originally described by Augustin Pyramus De Candolle (Prodr. 6: 541. 1838) as Aplotaxis discolor DC. It is a well-known, widespread alpine species in the western and central Himalaya in India (Himachal Pradesh, Uttar Pradesh), Sikkim and Nepal. In 1846, Michael P. Edgeworth and Carl Heinrich Schultz both independently found that most species of the genus Aplotaxis belonged to the genus Saussurea. Consequently, Edgeworth (in Trans. Linn. Soc. London 20: 76. 1846) made the new combination S. obvallata (DC.) Edgew., based on A. obvallata DC., and chose a nomen novum, S. piptathera Edgew., for A. discolor DC., since the name Saussurea discolor (Willd.) DC. (in Ann. Mus. Natl. Hist. Nat. 16: 199. 1810) was already in use for a different taxon from the European Alps. For the same reason, Schultz (in Linnaea 19: 330-331. 1846) placed all the then known species of Aplotaxis in Saussurea, validating the appropriate new combinations including S. obvallata (DC.) Sch. Bip. and renaming A. discolor DC. as S. indica Sch. Bip. For a long period of time, it was not clear if Schultz's publication preceded Edgeworth's article or not. While most recent authors, for example Lipschitz (in Bot. Zhurn. 52: 660. 1967, Rod (Saussurea: 58. 1979), Chater & Kitamura (in Hara & al., Enum. Fl. Pl. Nepal 3: 40. 1982), Wu (Index Fl. Yunnan. 2: 1417. 1984) and Hajra (Brahmakamal and its allies: 64-65. 1988) stated that Edgeworth's publication had been in August, whereas Schultz's had been in September (which is in accordance with Stafleu in Regnum Veg. 52: 421. 1967), some authors as Kitamura (in Acta Phytotax. Geobot. 24: 7. 1969), Stewart (in Nasir & Ali, Fl. West Pakistan: 776. 1972) and Liu (in Wu, Fl. Xizang. 4: 868. 1985) still cited Schultz Bipontinus as the author of Saussurea obvallata. The publication date of the relevant issue of the Transactions of the Linnean Society of London has been recisely ascertained by S. Raphael (in Biol. J. Linn. Soc. 2: 68, 75. 1970) as the day of 29 August 1846, whereas the exact publication date of Linnaea 19 (3) has hitherto not been clarified with similar accuracy. Kuntze (Revis. Gen. Pl. 3 (2): 158. 1898) gave the exact publication dates, as printed on the back covers of the single fascicles (Hefte), of volume 19 of Linnaea, unfortunately with the exception of Heft 3. Later contributions concerning publication dates of Linnaea (Stearn & SteenisKruseman in Steenis, Fl. Males., ser. I, 4 (5): cxcviii. 1954; Foster in J. Arnold Arbor. 43: 403. 1962; Moore & Wood in J. Arnold Arbor. 46: 68. 1965) could not give the date of volume 19 Heft 3, either. Stafleu, having consulted the correspondence of Linnaea's editor Schlechtendal (in Wentia 16: 90-91. 1966), came apparently to the conclusion that Linnaea 19 (3) was published in September 1846 (Stafleu in Regnum Veg. 52: 421. 1967). However, Stafleu and Cowan (in Regnum Veg. 112: 194. 1985) later corrected some of the publication dates of Linnaea, giving now July 1846 for Heft 3, but without any indication of their sources. After I have searched in vain in

Vorteile einer Nervenchirurgie mit intraoperativer Elektrodiagnostik

To date in most cases of high-grade nerve injuries only partial recovery is achieved and the prognosis is still poor for some types of lesions. Neurophysiological methods are implemented improve the outcome by assessing the condition of nerve fibres at any location and at any point of time during the course of surgery. Monitoring is utilised prevent inadvertent injury during surgical procedures. Free-running EMG signals are recorded from muscles targeted by a nerve at risk. Motor unit activity is initiated when dissecting instruments approach and contact the nerve. Bursts and neurotonic discharges arise and increase with tension or pressure exerted on the nerve. Acoustic feedback warns of imminent damage. Evoked muscle and cerebral potentials are applied reveal impairment of the nerve excitability and conductivity by mechanical and metabolic stress. Under normal conditions nerve action potential (NAP) recording from the exposed nerve reflects the integrity of the nerve by high amplitude, steep rise and normal temporal dispersion. Under pathological conditions the reduced density of nerve fibres, thickening of nerve sheaths, endoneurial cell proliferation and many other influences enhance the amplitude reduction of the NAP and may cause overestimation of nerve malfunction. However, this enhancement facilitates the detection of the location and the extension of the lesion. In nerve tumour surgery NAP recording identifies affected and unaffected nerve fascicles and the border of healthy In traumatology following closed nerve injuries early revision and evaluation with the aid of NAP recording has proved be the best possible procedure. When the nerve is found in continuity, the appearance of the nerve does not reliably reflect the grade of the lesion and the prognosis. Resection of low-grade injuries, capable of spontaneous regeneration downgrades the outcome. If a high-grade lesion without potential of regeneration is not resected and repaired, recovery is not possible. To avoid inadequate measures, nerve surgery is frequently delayed awaiting muscle reinnervation. However, this loss of time has the most adverse impact on final outcome when repair is necessary. Neurography detects the presence or absence of significant nerve regeneration in the early months following the injury. Where the lesion is found in continuity after 3-4 months and NAPs are recorded across the lesion, neurolysis is done in order promote nerve regeneration. Where NAPs are not recordable, resection and repair are required. In the same way NAP recording is used judge single fascicles. Split nerve repair is done if some fascicles are conductive and others are not. When nerve repair is indicated, the proximal stump has be sectioned back to healthy tissue. However, as intraoperative nerve evaluation by gross inspection and magnification does not reliably reflect the availability and viability of nerve fibres, NAP recording is recommended as an additional criterion for choosing an appropriate proximal coaptation site for reconstruction. Intraoperative nerve function assessment is essential for brachial plexus surgery. As nerve repair is useless in the presence of preganglionic lesion, SEPs are applied assess the integrity of the dorsal root. NAPs with high amplitude in the absence of nerve function are also useful tools identify preganglionic lesions.

Three-dimensional analysis of the arrangement and length distribution of fascicles in the triceps muscle of Galea musteloides (Rodentia, Cavimorpha)

Non-uniformity of fascicle parameters (fascicle lengths and orientation) within one skeletal muscle is well known. These parameters have an effect on the physiological cross-sectional area and lengthening rate of the skeletal muscle. Using a binocular microscope with a table driver (q- and p-axes) and vertical drive (v-axis) as a tool for reconstruction of the spatial orientation of single muscle fascicles, we developed an approach for three-dimensional analysis of the arrangement and length distribution in the skeletal muscle of small mammals. Two subunits of the triceps brachii muscle of the Galea musteloides forelimb, triceps longum and triceps laterale, were quantified and compared. Our data show that in the triceps laterale the fascicles are significantly longer (10.23 mm, SD=1.19, n=41) than those in the triceps longum (6.58 mm, SD=2.88, n=39). In the triceps laterale, the fascicle orientation is more or less uniform, whereas, in the triceps longum, there are two areas with different orientation of fascicles: anterior and posterior ones. Different inner architecture of the subunits can be interpreted as an adaptation to the main locomotory function of the triceps muscle, namely production of propulsive force during limb transfer phase and keeping dynamic stability during stance phase. Comparison of our data on the fascicle length and geometry with our previous histochemical results on G. musteloides, shows that the anterior region of the triceps longum, which differs in the fascicle orientation, also contains a significantly larger percent of slow muscle fibres. It is hypothesised here that this small region is involved in keeping posture.

Proportions of slow myosin heavy chain-positive fibers in muscle spindles and adjoining extrafusal fascicles, and the positioning of spindles relative to these fascicles

Chicken leg muscles were examined to calculate the percentages of slow myosin heavy chain (MHC)-positive fibers in spindles and in adjacent extrafusal fascicles, and to clarify how the encapsulated portions of muscle spindles are positioned relative to these fascicles. Unlike mammals, in chicken leg muscles slow-twitch MHC and slow-tonic MHC are expressed in intrafusal fibers and in extrafusal fibers, suggesting a close developmental connection between the two fiber populations. In 8-week-old muscles the proportions of slow MHC-positive extrafusal fibers that ringed muscle spindles ranged from 0-100%. In contrast, proportions of slow MHC-positive intrafusal fibers in spindles ranged from 0-57%. Similar proportions in fiber type composition between intrafusal fibers and surrounding extrafusal fibers were apparent at embryonic days 15 and 16, demonstrating early divergence of extrafusal and intrafusal fibers. Muscle spindles were rarely located within single fascicles. Instead, they were commonly placed where several fascicles converged. The frequent extrafascicular location of spindles suggests migration of intrafusal myoblasts from developing clusters of extrafusal fibers toward the interstitium, perhaps along a neurotrophic gradient established by sensory axons that are advancing in the connective tissue matrix that separates adjoining fascicles.

Clinical neurophysiology laboratory tests to assess the nociceptive system in humans.

This paper presents some currently available neurophysiological tools that are helpful in the clinical setting to evaluate and document neuropathic disturbances that may be associated with pain. The specific tests described in this discussion are quantitative sensory tests (QSTs), autonomic tests (ATs), microneurography (MCNG), and laser evoked potentials (LEPs). Quantitative sensory testing of the nociceptive system includes the thermal stimulation (TST) and current perception threshold (CPT) tests. The ATs applicable to some patients with pain are sudomotor and vasomotor tests. The quantitative sudomotor axon reflex test (QSART), resting sweat output (RSO), and sympathetic skin response (SSR) are the tests for sudomotor involvement. The vasomotor system is tested by measuring skin temperature (surface thermistor or thermography) at rest and, in some cases, after provocative maneuvers. In addition, MCNG (intraneural recording of single nerve fibers or fascicles of nerves) allows examiners to look directly at muscle and skin sympathetic efferent output in normal subjects without pain or with experimental pain and in patients with neuropathic pain. This technique also provides a means of studying the physiology of primary afferent fibers in persons with neurogenic pain. Recent development of LEPs that incorporate the use of painful infrared laser-induced stimuli allow selective study of the nociceptive system, both the central and peripheral portions.

The interaction of human fetal neurons and epidermal cells in vitro.

The interaction of autologous human fetal neurons with epidermal cells was studied by culturing fetal dorsal root ganglia (DRG) in the center of a dual chamber system with epidermal explants in the outer chamber. The two chambers were separated by two concentric stainless steel annular rings adherent to the substratum by silicon grease and agarose. Axons from the DRG penetrated the agarose barrier, growing into the exterior chamber by 10 d in vitro (DIV) and extended past sparse peripheral fibroblasts to interact specifically with epidermal cells by 12 to 16 DIV. Scanning electron microscopy (SEM) showed single or multiple neuronal fascicles terminating on epidermal cells with spatular, veillike or bulbous axon termini. Transmission electron microscopy (TEM) showed fine axonal termini between epidermal cells, separated by an intercellular gap. The specificity of axonal targeting for epidermal cells rather than fibroblasts was also demonstrated by infecting the DRG with Herpes simplex virus type-1 (HSV-1). Specific anterograde transport of HSV-1 along axons to keratin-expressing epidermal cells was demonstrated by immunofluorescence and immunoperoxidase staining using monoclonal antibodies to viral glycoprotein D. This model allows the study of the mechanism of the specific interactions between neurons and epidermal cells analogous to those in fetal development and after cutaneous nerve regeneration.

Reduced fatigue in electrically stimulated muscle using dual channel intrafascicular electrodes with interleaved stimulation.

Pairs of intrafascicular electrodes were implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. Measurements were made of fatigue induced in the muscle by single and dual channel tetanic stimulation. The level and rate of fatigue induced by concurrent dual channel stimulation (pulses presented simultaneously to the two electrodes) did not differ significantly from that induced by single channel stimulation. However, a significant reduction in the level and rate of muscle fatigue was found with interleaved dual channel stimulation. The extent of reduction in fatigue was found to be inversely related to the amount of overlap in the axonal populations activated by each of the two electrodes.

Selective stimulation of peripheral nerve fibers using dual intrafascicular electrodes

We have studied activation of nerve fibers by pairs of Pt-Ir wire electrodes implanted within single fascicles of the nerve innervating the gastrocnemius muscle in cats. The purpose of this study was to determine if these intrafascicular electrodes can activate nerve fibers in different fascicles independently of each other and if they can also be used to activate separate subsets of axonal populations within a single fascicle. The average overlap of activated nerve fiber populations was 5.5% between fascicles and 27% within a fascicle, indicating that such selective activation is possible with these electrodes.

Growth cone distribution patterns in the optic nerve of fetal monkeys: implications for mechanisms of axon guidance

The distribution of growth cones was studied in the optic nerve of monkeys during the first half of prenatal development using quantitative electron microscopic methods. Our aim was to test the hypothesis that ganglion cell growth cones extend predominantly along the surfaces of the nerve, just beneath the pia mater. A complete census of growth cones in cross sections of the nerve during the early phase of axon ingrowth, from embryonic day 39 (E39) to E41, demonstrates that growth cones are scattered within the majority of fascicles, even those located far from the surface of the nerve. By E45, growth cones are concentrated around the nasal, dorsal, and ventral edge of the optic nerve. They are less concentrated in the core and around the temporal edge. However, even as late as E49, virtually all fascicles in the nerve, whether deep or superficial, contain growth cones. Growth cones are dispersed within single fascicles and are often located far from glia. Thus, the newest fibers penetrate deep parts of the pathway and push through centers of densely packed bundles of older axons. This finding is consistent with the vagrant paths of growing axons reported in previous work on embryonic monkey optic nerve (Williams and Rakic, 1985). Our data challenge the hypotheses that growth cones extend selectively along the basal lamina, the pia mater, or glial end feet. Gradients found at later stages of development in the nerve are not due to a particular affinity of growth cones for non-neuronal substrata. The pattern we observed is much more likely to result from central-to-peripheral gradients in ganglion cell generation and possible associations between growth cones originating from the same regions of the retina.

Regeneration of axons from the adult rat optic nerve: influence of fetal brain grafts, laminin, and artificial basement membrane.

After transection of the optic nerve of adult rats, most of the axons in the proximal stump die and the surviving ones are unable to regenerate into the distal optic nerve. Since the fetal brain has an inherent capacity to regenerate axons, we investigated whether fetal (E16) target regions of optic axons (thalamus and tectum) transplanted to the completely transected optic nerve of adult rats would promote axon regeneration. In control operated rats, axon growth beyond the site of transection was restricted to a few fibers that grew irregularly within the connective tissue scar. By contrast, in grafted animals directed outgrowth of optic axons toward the transplant started at 6 days postoperation (p.o.) and reached its maximum 15 days p.o. and later, when numerous single optic fibers and small axon fascicles had grown toward and into the graft, where they formed arborizations and terminal varicosities. Regenerating optic axons were further advanced than GFAP-positive strands of astroglia that emanated from the proximal optic nerve stump. Laminin immunoreactivity appeared at 6 days p.o. in the zone of reactive astroglia in the terminal part of the optic nerve stump. Later it showed a distribution complementary to the pattern of GFAP immunoreactivity, which it seemd to circumscribe. There was no unequivocal codistribution of laminin immunoreactivity with regenerating axons. In further experiments, target regions from different ontogenetic stages (E14 to neonate and adult) and nontarget regions (E16, cerebral cortex or spinal cord) were grafted to the optic nerve stump. With the exception of the adult grafts, all transplants had effects on axon regeneration comparable to those of E16 target regions. In order to test the effects of extracellular matrix molecules on axon regeneration, a basement membrane gel reconstituted from individual components of the Engelbreth-Holm-Sarcoma (EHS) sarcoma was implanted between proximal and distal optic nerve stumps. No axons were induced to regenerate by this matrix. Likewise, laminin adsorbed to nitrocellulose paper and implanted at the lesion site did not stimulate axon growth from the proximal optic nerve stump. These results indicate that fetal brain is able to induce and direct regrowth of axons from the optic nerve toward the graft across a substrate that is not composed of astroglia or basement membrane components like laminin. The directed growth of axons in the absence of a preformed substrate implies a chemotactic growth response along a concentration gradient mediated by neurotropic molecules released from the graft.

An immunohistochemical and fine-structural analysis of peptidergic hypothalamic neurosecretory axon regeneration into the leptomeninges of the rat

Regeneration of severed hypothalamic peptidergic neurosecretory axons into the ventral pia-arachnoid was observed in rats at the light microscopic and fine-structural levels. A temporal increase occurred in the number of neurophysin-positive axons regenerating into the leptomeninges for distances up to 3.3 mm by 40 days post-lesioning. A consistent pattern of parallel, meshed and clustered axons, occuring either singly or in bundles, was present within the connective tissue, while plexus and bundles were observed in association with leptomeningeal blood vessels. Axons were characterized by preterminal and terminal dilatations. Neurosecretory granulated vesicles occurred throughout axons. The presence of microvesicles at contact points with basal lamina suggests the possibility of hormone release. Most axons were arranged as fascicles associated closely with basal lamina-bounded support cells whose thin lamellar processes wrapped single axons or fascicles of axons. We conclude, therefore, that cellular and intercellular leptomeningeal microenvironments support and sustain the growth and regeneration of transected neurosecretory axons.