Inflammatory pain is a debilitating condition that can occur following tissue injury or inflammation and results in touch evoked pain (allodynia), exaggerated pain (hyperalgesia) and spontaneous pain, yet the neural plasticity underlying these symptoms is not fully understood. However, it is known that lamina I neurokinin 1 receptor expressing (NK1R+) spinal cord output neurons are crucial for the manifestation of inflammatory pain. There is also evidence that the afferent input to and the postsynaptic response of these neurons may be altered in inflammatory pain, which could be relevant for inflammatory pain hypersensitivity. Therefore, the aim of this thesis was to study inflammatory pain spinal plasticity mechanisms by investigating the synaptic input to lamina I NK1R+ neurons. In ex vivo spinal cord and dorsal root preparations from the rat, electrophysiological techniques were used to assess inflammation-induced changes in and pharmacological manipulation of the primary afferent drive to lamina I NK1R+ neurons. The excitatory input to lamina I NK1R+ neurons was examined and it was found that inflammation did not alter the relative distribution of the type of primary afferent input received and did not potentiate monosynaptic A δ or monosynaptic C-fibre input, the predominant input to these neurons. Spontaneous excitatory input was significantly elevated in the subset of neurons that received monosynaptic A δ-fibre input only, regardless of inflammation. It has recently been shown that the chemerin receptor 23 (ChemR23) represents a novel inflammatory pain target, whereby ChemR23 agonists can decrease inflammatory pain hypersensitivity, by a mechanism that involves the attenuation of potentiated spinal cord responses. This study has found that the ChemR23 agonist, chemerin, attenuated capsaicin potentiation of excitatory input to lamina I NK1R+ neurons and significantly reduced monosynaptic C-fibre input to a subset of these neurons in inflammatory pain. However, chemerin was without effect in non-potentiated conditions. In exploring potential inflammatory pain spinal plasticity mechanisms, I have investigated a phenomenon called activity-dependent slowing (ADS), whereby repetitive stimulation of C-fibres at frequencies of 1Hz or above results in a progressive slowing of action potential conduction velocity, which manifests as a progressive increase in response latency. This is proposed to limit nociceptive input to the spinal cord, thus regulating plasticity. Results demonstrate that inflammation significantly attenuated C-fibre ADS in isolated dorsal roots. Furthermore, ADS in monosynaptic C-fibre input to lamina I NK1R+ neurons was significantly reduced in inflammatory pain, which could facilitate nociceptive drive to these key spinal cord output neurons and promote inflammatory pain spinal cord plasticity. In conclusion, the major novel findings of this thesis are firstly, that chemerin can attenuate primary afferent input to lamina I NK1R+ neurons in potentiated conditions, which supports recent studies that suggest ChemR23 is a potential target for the development of new analgesics. Secondly, it was discovered that ADS in monosynaptic C-fibre inputs to lamina I NK1R+ neurons is altered in inflammatory pain, which could be relevant for inflammatory pain spinal plasticity. The findings presented in this thesis could contribute to the development of novel inflammatory pain treatments.

INTRODUCTION: HIV- associated neurocognitive disorder (HAND) and pathology are common manifestations of HIV-infection, and often persist in spite of controlled peripheral viremia. Severity of HAND can range from loss of concentration and psychological changes to frank dementia. Inflammatory host-immune responses and chemotaxis of immune cells into the CNS are thought to be integral to development of NeuroAIDS and HAND. OBJECTIVES: This studies' primary aim was to determine if significant differences existed between Substance P and NK1R expression in brain tissue samples of HIV-infected individuals with neurocognitive disorder or pathology. The secondary aim was to determine whether expression of HIV viral entry receptors CCR5 and CXCR4 correlate with expression of Substance P or NK1R. The tertiary aim of this study was to determine if age at death, CNS penetration-effectiveness of antiretroviral therapy, diagnosis before HAART, average plasma CD4, or abnormal alcohol or drug use increased prevalence of neurocognitive disease. STUDY DESIGN: Cross-sectional study of HIV-infected individuals (n=60) from the larger National NeuroAIDS Tissue Consortium Cohort. Pre-death demographic data, neurocognitive assessment, alcohol and drug use, ART regimens, date of diagnosis and death, and plasma CD4 levels, as well as pathology findings at autopsy and brain tissue samples were provided by the NNTC; expression levels of Substance P, NK1R, CCR5, and CXCR4 from brain samples were provided by Dr. Steven Douglas of The Children's Hospital of Philadelphia. RESULTS: In this sample of HIV-infected individuals, Substance P expression was significantly less in the cingulate cortex of individuals with (p=0.003). Within-subject expression patterns of CCR5 and truncated-NK1R in the cingulate cortex and cerebellum were both significantly altered by neuropathology and cannabis use; CCR5 expression was also significantly affected by opiate use. CCR5 and CXCR4 expression correlated strongly with truncated-NK1R expression. No between-subject factors significantly altered prevalence of neurocognitive impairment in this HIV-infected population. CONCLUSIONS: The study found significant changes in Substance P, NK1R, and CCR5 expression associated with neuropathology. Furthermore, in heterogeneous populations, expression patterns may be more important than overall level of expression in identifying risk factors for NeuroAIDS and other chronic diseases. / Epidemiology