Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Neuropathic pain is a common and dose-limiting adverse effect of several cancer chemotherapeutic agents including paclitaxel. Current treatments for chemotherapy-induced peripheral neuropathy (CIPN) are largely ineffective and the pain can persist long after the cessation of the chemotherapy regimen. Whilst the specific underlying mechanisms are not fully understood, oxidative stress and mitochondrial damage are thought to be involved in the development of CIPN. Antioxidants which protect mitochondria may inhibit oxidative stress and protect mitochondrial function more effectively than antioxidants which do not specifically act within mitochondria, and may attenuate CIPN. The overall aim of the study was therefore to determine the effects of mitochondrial-targeted antioxidants on CIPN. This was addressed in two main parts. Firstly, in vitro studies aimed to determine the effects of paclitaxel alone and in combination with mitochondrial-targeted antioxidants melatonin and MitoVitE, and a non-targeted antioxidant, Trolox, on oxidative stress and mitochondrial function in cells. In vivo studies aimed to determine the effects of melatonin, MitoVitE and Trolox in a preclinical rat model of paclitaxel neuropathic pain. In vitro studies used a dorsal root ganglion (DRG) cell line (50B11). Cells were cultured with a range of concentrations of paclitaxel, with or without the addition of melatonin, MitoVitE or Trolox. Several measures of oxidative stress including free radical production, and glutathione levels, and measures of mitochondrial function, including mitochondrial metabolic rate, membrane potential, mitochondrial pore opening and ATP production were made. In vivo studies used a rat model of paclitaxel-CIPN, and assessed the effects of melatonin, MitoVitE and Trolox on behavioural measures of pain. In vitro studies showed that paclitaxel induced oxidative stress and caused mitochondrial damage in the DRG cell line. Compared to paclitaxel alone, cells co-treated with melatonin and MitoVitE had reduced oxidative stress and mitochondrial damage. Co-treatment of cells with paclitaxel and Trolox did not differ from conditions with paclitaxel only. In vivo studies demonstrated that melatonin and MitoVitE attenuated paclitaxel-induced mechanical hypersensitivity, whilst Trolox did not affect behavioural measures of CIPN. These studies suggest that mitochondrial-targeted antioxidants may be useful as a potential treatment strategy for CIPN.

Since the discovery of peripheral nerve regeneration nearly a century ago, the mechanisms that guide this regeneration have been elusive. This project aimed to describe how an axon is able to traverse the environment of the body and precisely reinnervate its target cell. Using a novel technique of combining light and electron microscopy, I observed reinnervating axons in transgenic mice to answer the questions of whether Schwann cells are an important guidance cue for the motor neuron and whether the outgrowing axon is fully developed or the process is a step-wise process of activation. The data suggests that Schwann cell contact is important for the tip of the regenerating axon to guide the axon back to its synapse on the muscle fiber. Further, it seems that the tip of the axon is not capable of synaptic transmission as it lacks active zones, suggesting that reinnervation is a step-wise process. / Department of Physiology and Health Science

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Bibliography : leaves 175-184. / Ph.D.

Injuries to the peripheral nervous system rank among the most common causes of chronic neuropathic pain. Afflicting millions of people for months or even years, symptoms of this condition have proven difficult to treat clinically. A thorough understanding of the pathophysiological changes induced by such nerve lesions is essential to the development of more efficient therapeutic options. Peripheral nerve injury induces a robust and tightly regulated innate immune response in the dorsal horn of the spinal cord. The precise molecular mechanisms regulating the spatiotemporal dynamics and functional impact of the response remain incompletely understood. Preclinical evidence suggests mitigating this immune response can have a significant therapeutic benefit in the treatment of neuropathic pain, however these findings have yet to be clinically validated. To elucidate the mechanisms regulating the spinal immune response, we used a mouse model of partial sciatic nerve injury exclusively in male adult (2-3-month-old) mice. The spared nerve injury (SNI) model employed throughout our studies induces robust, persistent neuropathic pain-like behavior. We established a time course for the spinal immune response to SNI and used mRNA extracted from the ipsilateral dorsal horn of lumbar spinal cord segments L4 and L5 to analyze changes in the transcriptome at the peak of the immune reaction 7 days after nerve lesion. We discovered upregulation of multiple elements of the triggering receptor expressed on myeloid cells 2 (Trem2) pathway. Trem2 is considered a regulator of toll-like receptor signaling in innate immune cells. It also promotes microglia-mediated phagocytosis in the central nervous system. Recent work from our lab has established neuronal apoptosis in the ipsilateral dorsal horn after SNI as an essential mechanism leading to the development of chronic neuropathic pain-like behavior. We used TUNEL staining of L4 spinal cord sections to compare the clearance of apoptotic cell profiles in Trem2-/- mice to wild-type littermates and discovered a key role for Trem2 in the clearance of apoptotic cells after SNI. We further used genetic deletion of Trem2 as well as administration of a Trem2 agonist in C57Bl/6 mice to assess the impact of Trem2 signaling on both the spinal immune response and neuropathic pain-like behavior after SNI. Neither removal nor augmentation of Trem2 signaling significantly affected the development of neuropathic pain-like behavior. Utilizing flow cytometry, we also evaluated the cellular composition of the spinal immune response. We found no evidence that monocytes from the peripheral circulation invade the spinal cord after SNI, as has been previously suggested. These findings were corroborated by immunohistochemical analysis of spinal cord sections from transgenic mice that express distinct fluorescent proteins in their monocyte and microglia cell populations. To better understand the different mechanisms modulating the spinal immune response, we further examined several transcriptionally regulated signaling pathways. We achieved the greatest reduction of mechanical allodynia in nerve-lesioned mice treated with a P2x4r antagonist. Surprisingly, the removal of fractalkine (Cx3cl1) signaling, another prominent chemokine signaling pathway in microglia, had no significant impact on either the spinal immune response or mechanical allodynia after SNI. Reducing the number of spinal microglia by blocking Csf1r activation did not prevent the development of mechanical allodynia after SNI either. Our findings reveal a more nuanced concept of microglial activation after nerve injury. The impact on neuropathic pain-like behavior and phagocytosis appear to be regulated by pathways that differ from those controlling immune cell recruitment and global activation. These findings provide a greater understanding of the complex mechanisms governing microglial function and offer new insight into molecular targets essential to the development of more efficient treatment options for neuropathic pain.

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Medical Sciences

Not available / text

published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy

In standard anatomical textbooks, the formation of the cervical plexus is well defined; however the accurate differentiation into superficial and deep plexuses, their emerging patterns, and gross anatomical relations are not documented as expansively. In order to obtain detailed anatomical knowledge of the superficial and deep cervical plexuses, the investigation aimed to clarify the anatomy and variations of these plexuses, define possible anatomical landmarks, and record the relationship of the external jugular vein and muscles of the posterior triangle of neck to the branches of the superficial cervical plexus, and the relationship of the common carotid artery, internal jugular vein, sympathetic chain, cervical verterbrae, and vertebral artery to the deep cervical plexus. The studies utilized the gross anatomical dissection, morphological and statistical analyses of forty fetal and fifteen adult cadaveric, formalinized specimens. The branches of the superficial cervical plexus emerged from the posterior border of the sternocleidomastoid muscle at the great auricular point (situated in the middle third of the muscle) and was described as ascending (lesser occipital, great auricular, transverse cervical nerves) and descending (supraclavicular nerves). Further, these branches were recorded according to their branching patterns, relations to the external jugular vein and variations. The branching patterns are described as single, duplicate and triplicate. The external jugular vein was constantly located inferior to the great auricular nerve, superior to the transverse cervical nerve and intertwined with the branches of the supraclavicular nerves. Variations of the branches of the superficial cervical plexus were observed only in fetuses and classified according to their course, branching patterns and communications. The emerging point of the branches of the superficial cervical plexus on the sternocleidomastoid muscle, were determined according to the seven types of “emerging pattern” classification by Kim et al., (2002). In order to record the deep cervical plexus, the sternocleidomastoid muscle was reflected with the following observation: the ventral rami of the second and third cervical nerves emerged between the scalenus anterior and scalenus medius muscles, and the third and fourth cervical nerves was located at the lateral edge of scalenus medius muscle. The deep cervical plexus was described as communicating, muscular, ansa cervicalis, and phrenic nerves. The superior cervical ganglion constantly communicated with the ventral rami of the cervical nerves; and the hypoglossal communicated with the superior root of the ansa cervicalis. The muscular branches were observed to the scalenus anterior and scalenus medius muscles with an anomalous branch to the sternocleidomastoid muscle. The ansa cervicalis demonstrated a degree of variation with regard to its origin, course and formation of the loops. The phrenic nerve arose from the ventral rami of the third, fourth and fifth cervical nerves and descended on the lateral border of the scalenus anterior muscle. The precise understanding of the anatomy of the superficial and deep cervical plexuses together with variations may assist anesthetists and surgeons to accurately identify the vascular, neural and muscular structures and reduce the risks of complications when performing neural blocks in regional anesthesia, facial rejuvenation surgery and parotidectomies. / Thesis (M.Med.Sc.)-University of KwaZulu-Natal, Westville, 2010.