Mean Number Of Axons Research Articles

(067) How Many Nerve Fibers Innervate the Human Glans Penis: A Histomorphometric Analysis of the Human Dorsal Nerve of the Penis

Abstract Introduction The mainstream media has frequently quoted that the penis has “half as many” nerve fibers as the human clitoris. Recent work has demonstrated that the number of nerve fibers in the dorsal nerve of clitoris was under-estimated, and no study has yet quantified the number of axons in the human dorsal nerve of the penis (DNP). Improving our understanding of penile innervation and sexual response has potential implications for fields of medical and surgical practice. Several nerve transfers have recently emerged targeting the DNP for re-innervation in order to restore penile sensation and/or erectile function, demonstrating variability in outcomes. Understanding the axon counts of the DNP at the anatomic level that these nerve transfers are performed may inform technical refinements and improve our understanding of current outcomes. Comparing DNP axon counts to the recently reported axon counts of the dorsal nerve of the clitoris may also inform techniques in transgender genital surgery, anticipate sensory outcomes in penile allotransplantation and further our understanding of sexual responses across genitalia. Objective The objective of this study is to quantify the number of axons in the human dorsal nerve of the penis. Methods Bilateral DNP samples were obtained from 5 fresh frozen cadavers. Samples were collected at the base of the penis at the level of the pubic symphysis, a location commonly targeted for coaptation in nerve transfers. Specimens were placed in 3% glutaraldehyde, post-fixed in 1% osmium tetroxide and serially dehydrated in ethanol and toluene. They were embedded in araldite, sectioned on ultramicrotome into 1 μm cross-sections and counter-stained with 1% toluidine blue. Histomorphometric evaluation was performed at 1000x magnification using Leitz Laborlux S microscope and image analysis software (Clemex Vision Professional, Longueuil, Quebec) to obtain nerve fiber counts from each specimen (Figure). Results 10 DNP samples were analyzed. The mean number of axons in the human dorsal nerve of penis was 3,844 +/- 1,238 (range 1,915 to 5,494). Accounting for the bilaterality of the DNP, the mean total number of axons innervating the human glans penis was 7,688 +/- 1,762. Conclusions This study is the first to report the number of axons in the human dorsal nerve of the penis and approximate the number of axons innervating the human glans penis. At the level of the pubic symphysis, axon counts of the dorsal nerve of penis varied significantly and averaged 3,844. The variation in axon counts at this anatomic level was greater than seen in prior reports on the DNC and may be one factor contributing to variations in outcomes following nerves transfers for penile sensation and erection. This variation could also reflect the anatomic level of sample collection or differences in specimen origin (cadaver vs. live person). DNP axon counts were less than or equal to recently reported axon counts of the human glans clitoris, despite the much larger size of the glans penis. This finding may be important when considering clitoral construction in transgender genital surgery, penile allotransplantation and different in sexual responsiveness across genitalia. Disclosure No.

Nerve to the Zygomaticus Major Muscle for Facial Reanimation Surgery: A Cadaveric Study for Branching Patterns and Axonal Count.

Background:In facial reanimation surgery, higher donor facial nerve axonal load yields a superior outcome. Nerves supplying the zygomaticus major muscle are primary donors for the grafting procedure; however, their topography has not been studied in detail. This study identified potential donor nerves by quantifying axon loads of the zygomaticus major muscle through histological analysis of cadaveric specimens.Materials and Methods:Forty-three hemifaces from 26 fresh human cadavers were studied. Branching patterns of nerves were classified according to their shapes. All branches of interest were sectioned and stained for an axon count. The potential donors were mapped into each tributary of nerves supplying the zygomaticus major.Results:Branching patterns were categorized into five types: Y-type (28%), X-type (28%), H-type (19%), E-type (14%), and F-type (11%). The mean number of axons in the most superiorly and proximally located main branches was 1387.33 ± 406.59 in Y-type, 1021.42 ± 187.79 in X-type, 1222.75 ± 193.82 in H-type, 1496.17 ± 364.567 in E-type, and 1353.40 ± 256.07 in F-type (P > 0.05). A topographic relation between facial nerves supplying the zygomaticus major muscle and their mean axonal load was illustrated. The zygomatic/buccal branches were found within 5 mm from Zuker's point in 100% of X-, Y-, H-, and E-type and 75% of F-type specimens.Conclusions:Most proximal facial nerve branches supplying the zygomaticus major, arising at the anterior border of a parotid gland, contained over 900 axons in all five branching types. The primary subbranches may be used in selected cases if donor weakness is a concern. Further, our study provides evidence that demonstrates the precision of Zuker's point.

Compte axonal du nerf des rhomboïdes dans le transfert vers le nerf suprascapulaire

Introduction Paralysis of the suprascapular nerve in upper brachial plexus injuries is most often treated by a nerve transfer from the spinal accessory nerve. We recently described a transfer of the nerve of the rhomboids, branch of the dorsal scapular nerve. An anatomical study proved the transfer was feasible and the diameter of the nerve of the rhomboid was macroscopically compatible with the suprascapular. We performed an histomorphic analysis with an optimal axonal count of the nerve of the rhomboids and compared our results with the literature about the suprascapular nerve, to microscopically verify our anatomical study. Methods We dissected 6 fresh frozen cadavers and harvested the nerve of the rhomboids. A 5 mm long section of the nerve was analyzed in a histopathological lab at the Institute Pasteur in Paris. After fixation in formalion and sections of the nerves, an axon count was manually performed with computer assistance. Review of the previously published axon counts on the suprascapular and spinal accessory nerve was performed and compared with our results. Results The average perineural surface was 0,1 mm2 and the average number of axons was 1568. This is above 74% of the mean number of axons of the spinal accessory nerve found in the previously published literature. Conclusion In nerve transfers to restore the function of the shoulder, an appropriate size match between donor and recipient nerves was proved to be a factor affecting success. We described a novel nerve transfer preserving the spinal accessory nerve, thus the function of the trapezius muscle and the shoulder, using the nerve of the rhomboid. Our histomorphic analysis show the axon count of this nerve was equivalent to the spinal accessory nerve, making this new transfer as likely to be successful as the gold standard technique.

A Study of Unmyelinated Afferent Axons in the Suburothelium in Women with Urinary Stress Incontinence.

Study objectiveTo study the nerve profile of unmyelinated axons beside the suburothelial myofibroblasts, as neuroeffectors, in comparison to the axons in other sites of the suburothelium.MethodsThis is a prospective study. Bladder biopsies were obtained using rigid cystoscopy from four patients with urinary stress incontinence. Suburothelial nerve bundles were studied at two sites: those adjacent to myofibroblasts (Nmyo) and those located within other sites of the suburothelium (Ns). Axonal contents of unmyelinated nerve bundles and Schwann cells within the suburothelium were studied using transmission electron microscopy.ResultsThe mean age of patients was 56 ±15 years. All patients had normal bladder function (maximum cytometric capacity: 554±57 mL). The total of 93 axons beside myofibroblasts and 118 axons in other sites of suburothelium were counted. The mean number of axons per nerve bundle was similar in both groups of nerve bundles (Nmyo: 3.03 vs Ns: 2.95). However, the mean number of large dense cored vesicles (LDCV) and small vesicles (SV) was higher in Nmyo group in comparison to the Ns group imageand imageThe values were (Nmyo:16 vs Ns:12.61) for LDCV and (Nmyo: 1.05 vs Ns: 0.79) for SV. The percentage of activated Schwann cells was higher in Nmyo in comparison to the Ns group (52% vs 32.5%).ConclusionThis study showed that the axonal contents of the nerve bundles adjacent to myofibroblasts had a higher amount of neurotransmitters within them, as compared to nerve bundles elsewhere. This supports the hypothesis that suburothelial myofibroblasts play a role in neuronal signalling.

Effects of Lewis lung carcinoma and B16 melanoma on the innervation of the mouse trachea

Cancer patients often suffer from dyspnea the pathogenesis of which is incompletely understood. Both dyspnea and pulmonary diseases are closely linked to airway innervation. Recently, it was shown that Lewis lung carcinoma induces cardiac hypoinnervation in the mouse. We hypothesized that airway innervation undergoes similar changes as myocardial innervation and that this effect occurs in different mouse models of cancer. C57Bl6 mice were randomly assigned to subcutaneous injection of Lewis lung carcinoma cells (LLC, n=6), B16 melanoma cells (B16, n=6), or saline (control group, C, n=10). After 16 or 21 days, respectively, the trachea was processed for light and electron microscopic design-based stereology and the volume, surface area and length of axons ramifying in the tracheal wall were estimated. Body weight was reduced both in LLC and B16 vs. C. Hypoinnervation was present in both tumor groups compared to controls as volume and surface area of axons were significantly reduced in LLC and B16. However, the total length of tracheal axons and the mean number of axons per nerve fiber were reduced only in LLC but not in B16 compared to C indicating a differentially pronounced effect of cancer on tracheal innervation. In conclusion, reduced innervation of the trachea was observed in two different murine tumor models. These findings add to the pathophysiological concepts explaining cancer-related dyspnea and open new perspectives of treating this symptom.

Animal Model for the Evaluation of Repair of Injured Inferior Alveolar Nerve with Nerve Growth Factor

Purpose: The inferior alveolar nerve (IAN) can be damaged as a result of minor oral surgical procedure such as third molar extraction or implant placement. Repair of the injured IAN involves difficulty of access, and research studies are limited to elucidating the process of regeneration by surgical methods. This study sought to establish the rabbit animal model to apply polymeric membrane functionalized with nerve growth factor after a crush lesion for the evaluation of nerve regeneration using the electrophysiologic method. Materials and Methods: The IAN of 2 adult male New Zealand white rabbits (4 nerves) were exposed bilaterally, and crush injury rendered by jeweler's forceps was applied. Nerve conduction velocity was examined electrophysiologically using electromyography before, after, and 4 weeks after the crush injury. To evaluate the regeneration, the pattern of action potential of IAN was recorded, and the characteristics of neurons were histologically observed. Result: After the crush injury, afferent activity decreased in the injured group. Electromyography could not be recorded after four weeks because tissues surrounding the injured nerve collapsed. Decrease in the mean number of axons was observed in the injured part with membrane. Conclusion: Despite the limited result, the present animal model study may provide a possible way to research on the methods of enhancing the recovery of nerve injuries in clinical situations. For clinically widespread acceptance, however, it should gain more consecutive and scientific evidences.

Allometry of left ventricular myocardial innervation.

Body mass (BM) of terrestrial mammalian species ranges from a few grams in the case of the Etruscan shrew to a few tonnes for an elephant. The mass-specific metabolic rate, as well as heart rate, decrease with increasing BM, whereas heart mass is proportional to BM. In the present study, we investigated the scaling behaviour of several compartments of the left ventricular myocardium, notably its innervation, capillaries and cardiomyocytes. Myocardial samples were taken from 10 mammalian species with BM between approximately 2 g and 900 kg. Samples were analysed by design-based stereology and electron microscopy and the resulting data were subjected to linear regression and correlation analyses. The total length of nerve fibres (axons) in the left ventricle increased from 0.017 km (0.020 km) in the shrew to 7237 km (13,938 km) in the horse. The innervation density was similar among species but the mean number of axons per nerve fibre profile increased with rising BM. The total length of capillaries increased from 0.119 km (shrew) to 10,897 km (horse). The volume of cardiomyocytes was 0.017 cm(3) in the shrew and 1818 cm(3) in the horse. Scaling of the data against BM indicated a higher degree of complexity of the axon tree in larger animals and an allometric relationship between total length of nerve fibres/axons and BM. In contrast, the density of nerve fibres is independent of BM. It seems that the structural components of the autonomic nervous system in the heart are related to BM and heart mass rather than to functional parameters such as metabolic rate.

Microneurosurgical Planning in Toe-to-Hand Transplantation: Axonal Population of Digital Nerves in the Fingers and Toes

Although toe-to-hand microvascular transplantation is now an accepted and successful reconstructive strategy for the thumb, there remains varying success in recovery of sensibility. The purpose of the present study was to provide an anatomic basis for analyzing neurotization of the great toe or the second toe with the digital nerves of the fingers and hand. Axon counts were obtained from donor and recipient nerves during reconstructive procedures. Sixty-seven upper- and eighty lower-extremity nerves were analyzed. No statistical difference was found between the mean number of axons between the thumb and the index finger; however, the thumb had significantly more (p < 0.001) axons than the middle or the ring finger. The great toe had significantly more axons than the second toe (p < 0.001). The common plantar digital nerve had significantly more axons than a digital nerve (p < 0.001). The thumb had significantly more axons than the great toe (p < 0.001). The thumb had significantly more axons than the second toe (p < 0.001). Numerical data are now available for strategic planning of toe transplantation, and direct neurotization from the dorsum of the hand to the digits.

The experimental toxicology of metallic mercury on the murine peripheral motor system: A novel method of assessing axon calibre spectra using the phrenic nerve

The toxicology of metallic mercury on motor neurons and their processes requires further work to resolve controversial implications in the aetiology of human motor neuron disease (MND). The assessment of experimental neurotoxicity in the peripheral motor system is, however, technically problematic and difficult to interpret. The mean number of axons in a nerve can vary considerably due to a high degree of biological variation. Atrophy of large axons can appear as loss when, in fact, their numbers appear in smaller diameter axonal categories. We addressed these quantitative problems using the murine phrenic nerve (MPN), a mono-fascicular, predominantly motor nerve as a model system. One micrometer transverse sections of gluteraldehyde/osmium tetroxide fixed MPNs were stained for myelin using a silver technique. Axon areas were measured from digital images of the nerve in cross-section (ImagePro Plus software) and transformed to circular diameter equivalents, then displayed as frequency distributions. We found a high biological variation in the mean axon number between paired nerves within experimental groups. Therefore, axon diameter data within individuals group was pooled. Theoretical simulation of axonal degeneration, atrophy and hypertrophy of larger myelinated axons (also affected in MND) were modelled by manipulating the original data set. With this model, by comparing normal distributions, it is possible to distinguish axonal atrophy, degenerative loss, and hypertrophy as distinct pathological processes in the large calibre axon subgroup that are selectively vulnerable to metallic toxins such as mercury.

Axonal regeneration in severed peripheral facial nerve of the rabbit: relation of the number of axonal regenerates to behavioral and evoked muscle activity.

The minimum number of regenerating facial nerve myelinated motor axons that are required to innervate and activate the mimetic musculature is not known. We compare rabbit facial nerve regeneration following complete transectional injuries of the buccal division to the evoked and behavioral muscle activities of the quadratus labii superioris muscle of the rabbit in three experimental models: end-to-end direct anastomosis (N = 4), 8-mm autologous nerve grafts (N = 8), and 10-mm silicone chamber implants (N = 40). Data are presented as total numbers of regenerating myelinated axons that traverse the surgical repair and innervate the fascicles of the transected distal nerve stump, as well as the percentage of regenerating neurites, as compared to the preoperative normal controls. Five weeks after neural repair, direct end-to-end anastomosis regained more myelinated axons across the reconstructed defect (2,632 +/- 1,232; 67%) than silicone tube implants (2,006 +/- 445; 51%) or autologous cable graft repairs (1,660 +/- 1,169; 42%). However, only a small percentage of myelinated fibers innervated the intrafascicular region of the distal transected neural stump in direct anastomosis (948 +/- 168; 24%), silicone tube implants (670 +/- 275; 17%), or autologous nerve grafts (445 +/- 120; 12%) in rabbits that regained evoked and behavioral mimetic muscle activity. All rabbits with direct anastomosis and neural cable grafts regained motor activity, despite the fact that 66% of regenerating motor neurites in cable graft repairs and 54% in direct anastomosis were collateral sprouts that did not contribute to effective muscle activity. In 17 rabbits with neural regenerates within the silicone tube implants that did not regain mimetic activity, the mean number of regenerating myelinated motor axons across the defect was 504 +/- 419 (13%), and the mean number of axons that innervated the distal transected nerve stump fascicles was 277 +/- 128 (7%). Therefore, the minimal number of motor axons that is required to activate the quadratus labii superioris muscle is 12% of the original motor axon population of the normal buccal nerve division.

Axonal Branching and Growth Cone Structure Depend on Target Cells

Growth cones provide crucial guidance to neurons in response to appropriate targets and other environmental cues. We have cocultured ciliary neurons with myotubes and utilized antibodies to GAP-43 (a neuron-specific, growth-associated phosphoprotein) and MAP-2 (a cytoskeletal marker for dendrites) together with immunofluorescence microscopy to characterize the changes in patterns and polarity that ciliary nerve growth cones undergo when they contact a "proper" target. Our results show that ciliary neurons plated alone or cocultured with fibroblasts have one or two axons, but, when cocultured with myotubes, most cells have 4 or 5 axons showing GAP-43 immunoreactivity. The mean number of axons per cell soma was 1.9 ± 0.1 μm 2 (SEM) when ciliary neurons were plated alone and 3.4 ± 0.1 when ciliary neurons were cocultured with myotubes. Differences in growth cone size were readily apparent in these two types of cultures. In coculture with myotubes the neuronal growth cone lamelopodia occupied 20-30 μm 2 with an average area of 25.0 ± 2.3 μm 2 (SEM) whereas those neurons plated alone or in the presence of fibroblasts occupied an average area of 56.3 μm 2 ± 4.1 μm 2 (SEM). The number of growth cone filopodia depended on culture condition. In nerve-muscle cocultures, the average number of filopodia per growth cone was 3.6 ± 0.2 (SEM), whereas in ciliary cultures plated in the absence of myotubes the number of filopodia was 6.8 ± 0.4 (SEM). These results indicate that muscle cells or the factors they release can regulate the growth and topography of axons and their growth cones.

MORPHOLOGICAL CHANGES IN UNMYELINATED NERVE FIBRES IN THE SURAL NERVE WITH AGE

Quantitative changes in unmyelinated nerve fibres in sural nerves obtained at autopsy were evaluated in 28 normal adults. The following conclusions were reached. (1) The density of unmyelinated axons showed no significant correlation with age, but the densities of (2) Schwann cell subunits with axons, (3) Schwann cell subunits without axons, (4) single protrusions of Schwann cells and (5) collagen pockets, and (6) the mean number of Schwann cell profiles per axon, all showed positive correlations with age. Additionally, (7) the percentage of subunits containing unmyelinated axons and (8) the mean number of axons in single axon-containing Schwann cell subunits demonstrated negative correlations with age. The density of Schwann cell nuclei related to unmyelinated fibres did not show a significant change with age. The age-dependent changes in unmyelinated nerve fibres thus mainly consist of an increased production of processes by Schwann cells in the absence of cell multiplication. A decrease in unmyelinated nerve fibre density or a compensatory increase of small unmyelinated axons did not occur in these normal adults. In terms of relative sensitivity for the detection of the earliest changes in unmyelinated fibres, the indices (6) and (7) are considered to be useful and superior to the conventional assessment of unmyelinated axon density and diameter distribution. These two indices are not influenced by postmortem swelling of the axons and Schwann cells. Measurements of unmyelinated axon density and size distribution will continue to be useful in the assessment of more advanced pathological conditions.

Regenerating afferent fibers stimulate the recovery of mauthner cell dendritic branching in the axolotl

In the medulla of the axolotl (Ambystoma mexicanum), Mauthner cells (M-cells) occur as a pair of large identifiable neurons at the level of entry of the vestibular nerve (nVIII). Each receives synapses from the ipsilateral nVIII; the terminals can be identified as club endings and are restricted to a specific set of M-cell dendritic branches. We have examined these branches for morphologic changes following long-term deafferentation in the presence and absence of nerve regeneration. Deafferentation was brought about in a group of young larvae by unilaterally severing nVIII. The nerve was allowed to regenerate in half of the larvae. In those remaining, the nVIII ganglion was damaged to preclude or limit nerve regeneration. The contralateral side served as control. After 3 months survival, the larvae were killed and the medullae prepared for microscopy. To estimate the extent of nerve regeneration, axons in the experimental nVIII tract were counted and compared with the number in the control. The mean number of axons in the nVIII tract ipsilateral to intact ganglia indicated that 69% of the fibers had regenerated. In contrast, only 31% regenerated in larvae with damaged ganglia. Electron microscopic analysis of selected sections revealed that the mean number of nVIII terminals per section through M-cells ipsilateral to destroyed ganglia was significantly less than the mean number in analogous sections through either control cells or cells ipsilateral to intact ganglia. Control and experimental M-cells were reconstructed from serial sections. Deprived M-cells had significantly reduced dendritic branching patterns in the region that normally receives nVIII input. On the other hand, the extent of branching on cells receiving regenerated afferents from intact ganglia was like that of their contralateral controls. The distribution of dendritic branches on many reinnervated M-cells, however, was broader than that on control cells. Electron microscopic examination of the displaced dendritic branches (those extending into adjacent tracts) revealed that they received vestibular synapses. Thus, in some animals, regenerated vestibular fibers were not restricted to the nVIII tract. Deafferentation of the M-cells results in a reduction of dendritic branches in the region deprived of vestibular contacts.(ABSTRACT TRUNCATED AT 400 WORDS)