Kimberly S. Topp

Microtubule disorientation and axonal swelling in unmyelinated sensory axons during vincristine-induced painful neuropathy in rat

Neuropathic pain accompanies peripheral nerve injury following a variety of insults including metabolic disorders, traumatic injury, and exposure to neurotoxins such as vincristine and taxol. Vincristine, a microtubule depolymerizing drug, produces a peripheral neuropathy in humans that is accompanied by painful paresthesias and dysesthesias (Sandler et al., [1969] Neurology 19:367–374; Holland et al. [1973] Cancer Res. 33:1258–1264). The recent development of an animal model of vincristine‐induced neuropathy provides an opportunity to investigate mechanisms underlying this form of neuropathic pain. Systemic vincristine (100 μg/kg) produces hyperalgesia to mechanical stimuli during the second week of administration, which persists for more than a week (Aley et al. [1996] Neuroscience 73:259–265). To test the hypothesis that changes in microtubule structure in nociceptive sensory neurons accompany vincristine‐induced hyperalgesia, we analyzed unmyelinated axons in saphenous nerves of vincristine‐treated rats. This study constitutes the first quantitative ultrastructural analysis of the cytoskeleton of unmyelinated axons in peripheral nerve during neuropathic hyperalgesia. There was no evidence of unmyelinated fiber loss or a decrease in the number of microtubules per axons. There was, however, a significant decrease in microtubule density in unmyelinated axons from vincristine‐treated rats. This decrease in microtubule density was due to a significant increase in the cross‐sectional area of unmyelinated axons, suggesting swelling of axons. In addition, vincristine‐treated axons had significantly fewer microtubules cut in cross‐section and significantly more tangentially oriented microtubules per axon compared to controls. These results suggest that vincristine causes disorganization of the axonal microtubule cytoskeleton, as well as an increase in the caliber of unmyelinated sensory axons. J. Comp. Neurol. 395:481–492, 1998.

Damage to the cytoskeleton of large diameter sensory neurons and myelinated axons in vincristine-induced painful peripheral neuropathy in the rat

Vincristine, along with other antimitotic chemotherapeutic drugs, produces a peripheral neuropathy in humans that is accompanied by painful paresthesias, dysesthesias, and occasionally hypoesthesia, and by hyporeflexia (Holland et al. [ 1973 ] Cancer Res. 33:1258–1264; McLeod and Penny [ 1969 ] J Neurol Neurosurg Psychiatry 32:297–304; Postma et al. [1993] J Neurooncol. 15:23–27; Sandler et al. [ 1969 ] Neurology 19:367–374). Systemic administration of vincristine causes swelling of unmyelinated axons and disorientation of axonal microtubules (Tanner et al. [ 1998a 1998a] J Comp Neurol. 395:481–492) at a time when it also produces allodynia and mechanical hyperalgesia (Aley et al. [ 1996 ] Neuroscience 73:259–265; Authier et al. [1999] Neuroreport 10:965–968) and enhanced responsiveness in C‐fibers in the rat (Tanner et al. [ 1998b ] J Neurosci. 18:6480–6491). Because slowing of A‐fiber conduction velocities had also been demonstrated (Tanner et al. [ 1998b ] J Neurosci. 18:6480–6491), and mechanical hyperalgesia can occur secondary to damage to large diameter sensory afferents (Basbaum et al. [ 1991 ] Can J Physiol Pharmacol. 69:647–651; Coggeshall et al. [ 1993 ] Pain 52:233–242; Woolf and Mannion [ 1999 ] Lancet 353:1959–1964), we sought to determine whether vincristine also induced ultrastructural changes in myelinated A‐fibers. Moreover, since systemic treatment with vincristine did not cause profound microtubule depolymerization in the unmyelinated axons of the peripheral nerve, we hypothesized that the drugs effects may be more extensive in the cell body, because in the spinal ganglion, the blood‐nerve barrier is less restrictive. We used quantitative ultrastructural methods to analyze the microtubule cytoskeleton in myelinated axons in the mid‐shaft of the saphenous nerve and in the sensory ganglion cells. Vincristine induced swelling of the whole nerve and an increase in the cross‐sectional areas of myelinated axons but no loss of myelinated axons. There was a significant decrease in axonal microtubules, as well as microtubule disorganization, in myelinated fibers from vincristine‐treated rats. In the spinal ganglion, vincristine induced swelling of large diameter sensory neurons and a build‐up of neurofilaments in the cell bodies and proximal axons, suggestive of impaired anterograde axonal transport. J. Comp. Neurol. 424:563–576, 2000.

Upper extremity impairments in women with or without lymphedema following breast cancer treatment

IntroductionBreast-cancer-related lymphedema affects ∼25% of breast cancer (BC) survivors and may impact use of the upper limb during activity. The purpose of this study is to compare upper extremity (UE) impairment and activity between women with and without lymphedema after BC treatment.Methods144 women post BC treatment completed demographic, symptom, and Disability of Arm-Shoulder-Hand (DASH) questionnaires. Objective measures included Purdue pegboard, finger-tapper, Semmes-Weinstein monofilaments, vibration perception threshold, strength, range of motion (ROM), and volume.ResultsWomen with lymphedema had more lymph nodes removed (p < .001), more UE symptoms (p < .001), higher BMI (p = .041), and higher DASH scores (greater limitation) (p < .001). For all participants there was less strength (elbow flexion, wrist flexion, grip), less shoulder ROM, and decreased sensation at the medial upper arm (p < .05) in the affected UE. These differences were greater in women with lymphedema, particularly in shoulder abduction ROM (p < .05). Women with lymphedema had bilaterally less elbow flexion strength and shoulder ROM (p < .05). Past diagnosis of lymphedema, grip strength, shoulder abduction ROM, and number of comorbidities contributed to the variance in DASH scores (R2 of 0.463, p < .001).Implications for cancer survivorsUE impairments are found in women following treatment for BC. Women with lymphedema have greater UE impairment and limitation in activities than women without. Many of these impairments are amenable to prevention measures or treatment, so early detection by health care providers is essential.

Mechanosensitivity of the lower extremity nervous system during straight-leg raise neurodynamic testing in healthy individuals.

STUDY DESIGN Cross-sectional, observational study. OBJECTIVES To explore how ankle position affects lower extremity neurodynamic testing. BACKGROUND Upper extremity limb movements that increase neural loading create a protective muscle action of the upper trapezius, resulting in shoulder girdle elevation during neurodynamic testing. A similar mechanism has been suggested in the lower extremities. METHODS Twenty healthy subjects without low back pain participated in this study. Hip flexion angle and surface electromyographic measures were taken and compared at the onset of symptoms (P1) and at the point of maximally tolerated symptoms (P2) during straight-leg raise tests performed with ankle dorsiflexion (DF-SLR) and plantar flexion (PF-SLR). RESULTS Hip flexion was reduced during DF-SLR by a mean +/- SD of 5.5 degrees +/- 6.6 degrees at P1 (P = .001) and 10.1 degrees +/- 9.7 degrees at P2 (P<.001), compared to PF-SLR. DF-SLR induced distal muscle activation and broader proximal muscle contractions at P1 compared to PF-SLR. CONCLUSION These findings support the hypothesis that addition of ankle dorsiflexion during straight-leg raise testing induces earlier distal muscle activation and reduces hip flexion motion. The straight-leg test, performed to the onset of symptoms (P1) and with sensitizing maneuvers, allows for identification of meaningful differences in test outcomes and is an appropriate end point for lower extremity neurodynamic testing.

Factors that contribute to the transneuronal spread of herpes simplex virus.

In viral encephalitis and retinal necrosis, different herpes simplex virus (HSV) strains spread between neurons in the central nervous system (CNS) by distinctly different routes. The steps of viral infection and spread in a single neuron type and nearby glial cells in vivo have been determined for three different strains of HSV (F, H129, and McIntyre‐B). The corneas of mice were inoculated with equivalent titers of the strains. Two to 5 days later, the animals were killed. The spread of viral proteins within trigeminal cells was examined using immuno‐ and electron microscopy and Western blots with anti‐HSV polyclonal antiserum. McIntyre‐B virus infection resulted in fewer labeled ganglion cells, possibly as a result of reduced viral production in the corneal epithelium or trigeminal ganglion cells. Although the McIntyre‐B strain was at least as, if not more efficient, at retrograde transport than the other strains, the amount of McIntyre‐B virus that was transported in the trigeminal roots in an anterograde direction was significantly less than the other strains. Uptake by ganglionic satellite cells was qualitatively similar for the three strains, but maturation and release of virus from satellite cells to other neurons were reduced in the McIntyre‐B strain. These characteristics may account for the preferential retrograde transneuronal spread of McIntyre‐B strain. J. Neurosci. Res. 49:485–496, 1997.

Naturally Occurring Disk Herniation in Dogs: An Opportunity for Pre-Clinical Spinal Cord Injury Research

Traumatic spinal cord injuries represent a significant source of morbidity in humans. Despite decades of research using experimental models of spinal cord injury to identify candidate therapeutics, there has been only limited progress toward translating beneficial findings to human spinal cord injury. Thoracolumbar intervertebral disk herniation is a naturally occurring disease that affects dogs and results in compressive/contusive spinal cord injury. Here we discuss aspects of this disease that are analogous to human spinal cord injury, including injury mechanisms, pathology, and metrics for determining outcomes. We address both the strengths and weaknesses of conducting pre-clinical research in these dogs, and include a review of studies that have utilized these animals to assess efficacy of candidate therapeutics. Finally, we consider a two-species approach to pre-clinical data acquisition, beginning with a reproducible model of spinal cord injury in the rodent as a tool for discovery with validation in pet dogs with intervertebral disk herniation.

Validation of a hip-worn accelerometer in measuring sleep time in children

This study compared measures of sleep from an accelerometer worn on the hip to measures obtained from an accelerometer worn on the wrist, the gold standard measure of sleep behavior in community research. The accelerometer worn on the hip provides a measure of total sleep time in 10- to 11-year-old children comparable to the wrist-worn unit. We provide an alternate method to ascertain bedtime and final wake time when diary data are missing. A hip-worn accelerometer may provide a cost-effective means of gathering physical activity and sleep data simultaneously in large samples of children with or without an accompanying sleep diary.

Centripetal transport of herpes simplex virus in human retinal pigment epithelial cells in vitro

Herpes simplex virus displays tropism for neurons and other polarized epithelial cells. We have grown human retinal pigment epithelial cells in culture to study potential mechanisms whereby herpes simplex virus (type I) is transported from the plasma membrane of the cell to the nucleus. The cells were highly polarized as determined by a variety of criteria. They were tightly coupled by junctional complexes, as determined by electron microscopy, immunofluorescent staining of tight junctions and measurements of transepithelial electrical resistances > 200 omega cm2. Immunofluorescence and confocal microscopy were used to visualize microtubule orientation. The microtubules were arranged (i) in a single apical cilium, (ii) in a meshwork beneath the apical membrane and (iii) in longitudinally arranged bundles near the lateral membranes and nucleus. The latter microtubules were primarily oriented with their plus ends directed toward the basal surface of the cells. We infected retinal pigment epithelial cells at the apical surface with virus and assayed the uptake and transport of virus to the nucleus by quantitative immunoblot and immunocytochemical staining for the viral immediate early gene product, infected cell protein 4. The antigen first appeared in retinal pigment epithelial cells 2 h after infection. Treatment of the cells with 33 microM nocodazole, a microtubule-destabilizing drug, delayed the appearance of the viral antigen by 1 h. The effect of nocodazole treatment on microtubule integrity was confirmed by immunofluorescent staining and immunoblots of tubulin. Both cytoplasmic dynein and the ubiquitous form of kinesin were identified in the cells using immunoblots. These novel data indicate that human retinal pigment epithelial cells, like neurons, are susceptible to infection by herpes simplex virus and that the centripetal transport of virus to the nucleus in both cell types is facilitated by microtubules. The orientation of microtubules in retinal pigment epithelial cells suggests that the transport of herpes simplex virus from the apical surface is mediated by a microtubule-activated motor enzyme, possibly kinesin.

Case Report: Painful Peripheral Neuropathy Following Treatment With Docetaxel for Breast Cancer

Peripheral neuropathy is a common side effect of many chemotherapy agents. As many as 60% of patients receiving taxane therapy report symptoms such as numbness, tingling, burning, pain, and, in severe cases, weakness in a stocking and glove pattern. These symptoms are associated with problems in physical mobility and decreased quality of life, yet few articles in the literature discuss collaborative interdisciplinary assessment and treatment of this population. This article describes the care of a patient with diabetes and docetaxel-induced, painful peripheral neuropathy by a multidisciplinary team of nurses, physicians, and physical therapists. Because nurses are often the first clinicians to recognize symptoms of chemotherapy-induced peripheral neuropathy, they provide the essential coordination of care by appropriate medical and rehabilitative services. This case also raises important questions about the relationship between diabetes mellitus and persistent, painful peripheral neuropathy.

Peripheral Nerve: From the Microscopic Functional Unit of the Axon to the Biomechanically Loaded Macroscopic Structure

Peripheral nerves are composed of motor and sensory axons, associated ensheathing Schwann cells, and organized layers of connective tissues that are in continuity with the tissues of the central nervous system. Nerve fiber anatomy facilitates conduction of electrical impulses to convey information over a distance, and the length of these polarized cells necessitates regulated axonal transport of organelles and structural proteins for normal cell function. Nerve connective tissues serve a protective function as the limb is subjected to the stresses of myriad limb positions and postures. Thus, the tissues are uniquely arranged to control the local nerve fiber environment and modulate physical stresses. In this brief review, we describe the microscopic anatomy and physiology of peripheral nerve and the biomechanical properties that enable nerve to withstand the physical stresses of everyday life.