|Title:||Plasticity of spinal circuits underlying chronic visceral pain|
|Authors:||Arshi, Mehreen Sana|
|Publisher:||University of Sydney.|
Kolling Institute of Medical Research.
Northern Clinical School.
|Abstract:||Interstitial cystitis is a painful condition of bladder urgency and pain, often associated with inflammation with unknown etiology that commonly affects women. There are limited treatments available and no cure to date. This condition is known to affect two different pathways of the peripheral nervous system, the nociceptive pathway and the micturition reflex pathway. In this thesis, I have employed a key technique used to study somatosensory pain states to understand some of mechanisms underlying visceral pain by mimicking some primary symptoms of interstitial cystitis in rodents. In the somatosensory pain states, there is an increase in the release of the neurotransmitter SP in response to noxious stimulation of the sensory nociceptive terminals. The released SP binds to its receptor, the Neurokinin 1 receptor (NK1R) expressed on neurons in lamina I and outer lamina II of the lumbar spinal cord. The NK1R upon binding of its ligand shows internalisation in response to the noxious stimulation and thus identifies neurons that are activated. In this study we have applied this well-established methodology to a model of visceral pain to identify activated neurons in the sacral spinal cord in response to visceral noxious stimulation and inflammation. Adult Female Sprague Dawley rats were used in this study and spinal cords were harvested following intracardial perfusions. In previous studies NK1R expression has been shown in the dorsal horn (DH) projection neurons and in the intermediolateral (IML) column of neurons, an area containing interneurons and bladder projecting autonomic preganglionic parasympathetic neurons. We have used a combination of immunohistochemical techniques and confocal microscopy to investigate NK1R expression and internalisation in cryosections of the sacral spinal cord DH and IML neurons. In the first part of the thesis NK1R expression was quantified in the IML region. We found that a majority of autonomic preganglionic neurons in the IML express the NK1R. We next used capsaicin and mustard oil to induce noxious stimulation of the bladder afferent terminals. Capsaicin and mustard oil act on transient receptor potential vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) channels (respectively) and are known to be involved in nociceptive processing. These TRP channels are expressed on the bladder afferents and are activated in response to their ligand binding. NK1R internalisation was analysed in cryosections of the sacral spinal cord DH and IML neurons following TRPV1 and TRPA1 activation. We found that neurons in both nociceptive and micturition reflex pathways were activated in response to noxious stimulation of the bladder afferents after TRPV1 activation but only in the IML after TRPA1 activation. Next we proceeded to establish cyclophosphamide (CYP) induced acute and chronic inflammation of the bladder. Both acute and chronic inflammations of the bladder caused activation (NK1R internalisation) in the DH and IML neurons. Bladder function was also assessed by performing continuous cystometry in control and inflammation groups and NK1R internalisation was measured. Although we did not see a statistical difference in the cystometrograms between the control and CYP treated groups, an increase in NK1R internalisation levels was observed in both DH and IML regions following inflammation. This study has identified that the autonomic preganglionic neurons are a target of the bladder projecting peptidergic afferents. We have demonstrated that the NK1R internalisation technique established to study somatic inflammation can be used in a visceral model of inflammation. The lower levels of NK1R internalisation seen after visceral inflammation compared to somatic inflammation indicate that there may be a difference in the amount of neuropeptide (substance P) released from the two types of afferents. The sparse innervation of the viscera by visceral afferents may also account for this lower level of internalisation compared to the response observed in the somatic model. The results indicate that there is a difference in neuronal activity in DH and IML neurons after TRPV1 and TRPA1 activation. This suggests that both the nociceptive and micturition reflex pathways should be studied and bladder hyperactivity alone should not be used as a surrogate marker to study bladder pain. Furthermore we have shown that non-noxious stimulation of the bladder afferents (cystometry) leads to an increase in NK1R internalisation after acute and chronic inflammation. These results provide an insight into some of the mechanisms that underlie the characteristic symptoms of cystitis and provide a valuable tool to further probe these mechanisms and establish a better understanding of this disease.|
|Type of Work:||Masters Thesis|
|Type of Publication:||Master of Philosophy M.Phil|
|Appears in Collections:||Sydney Digital Theses (Open Access)|
|ARSHI Mehreen - Final thesis.pdf||Masters Thesis||12.71 MB||Adobe PDF|
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