- Title
- Changes in intracranial pressure and cerebrospinal fluid circulation after ischaemic stroke in mice
- Creator
- Warren, Kirby Elizabeth
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2020
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Background: Our group has made a number of findings regarding intracranial pressure (ICP) elevation at 24 hours after ischaemic stroke. These findings challenge the existing dogma that only large hemispheric strokes result in ICP elevation by showing that rats and humans with mild-moderate strokes experience ICP elevation. Additionally, experimental studies show there is little oedema in the brains of these animals, suggesting a novel mechanism behind this ICP rise. Mechanistic studies are ongoing however there is evidence to suggest that changes in cerebrospinal fluid (CSF) dynamics are involved. This finding has not been demonstrated in mice. ICP monitoring methods in mice are largely limited to invasive locations such as the lateral ventricle or within the parenchyma which may be prone to causing brain damage which confounds recordings related to an experimental injury. Epidural ICP recordings are much less invasive and have been used extensively in rats. Development of a minimally invasive protocol for monitoring ICP from the epidural space in mice is necessary before determining if ICP is elevated after stroke in mice. This would be advantageous as mice offer additional methods for mechanistic studies such as genetic manipulation and glymphatic imaging. The glymphatic system may be closely linked to CSF outflow and may become dysfunctional under high ICP. Study of the glymphatic system has been conducted by many groups however there have been no studies to determine the most appropriate CSF tracer or when to assess glymphatic function after tracer has been administered. Changes in the glymphatic system may also contribute to chronic changes in the brain such as accumulation of neurotoxic proteins like amyloid beta which may in turn contribute to the occurrence of post-stroke cognitive impairment. Cognitive impairment may affect up to 80% of stroke patients. The CSF circulation system is thought by some to be dependent on aquaporin 4 (AQP4), a protein expressed on astrocyte end-feet. However, this apparent dependence comes from studies in mice where AQP4 is genetically knocked out. This most likely results in compensatory mechanisms for CSF dynamics in these animals and precludes the study of just the role of AQP4 in CSF circulation. Aims: The aims of this PhD were to 1. Develop a protocol for measuring ICP from the epidural space in mice. 2. Determine if ICP is elevated at 24 hours post-stroke in mice and the association of this rise, if any, with oedema volume. 3. Determine the most appropriate CSF tracer and time post-tracer administration for assessment of glymphatic function. 4. Determine if glymphatic function is altered at 24 hours and 2 weeks post-stroke. 5. Determine if acute inhibition of AQP4 in naïve, wild-type mice affects glymphatic function. Methods: Numerous techniques were assessed for their applicability in monitoring epidural ICP in mice. The developed method was used to monitor ICP at 24 hours after stroke. Oedema and infarct volumes were assessed in the same mice. Three commonly used dye conjugates were studied for their adherence to stroke tissue and applicability in tracing CSF. Using the optimal tracer, a time course study was performed to determine which time glymphatic function should be assessed following tracer administration into the CSF. This information was then used to assess glymphatic function at 24 hours and 2 weeks post-stroke as well as after administration of a pharmacological inhibitor of AQP4, TGN-020 (500µg/kg in 2% DMSO). Results: Epidural ICP was found to be most reliable and consistent when recorded from a burr hole in the occipital bone, under ketamine/xylazine anaesthesia with the first recording taken within an hour of stroke. ICP was significantly elevated at 24 hours post-stroke in 2 cohorts of mice. This rise was not correlated with oedema. Glymphatic function was found to be decreased in both the ipsilateral and contralateral hemispheres after stroke at 24 hours but not at 2 weeks post-stroke. Acute inhibition of AQP4 did not result in a change in glymphatic function compared to vehicle. Conclusions: ICP can be consistently and accurately recorded in the epidural space in mice, providing a minimally invasive alternative to the commonly used recording sites of the lateral ventricle or within the parenchyma. Using epidural ICP monitoring, it was found that ICP significantly increases at 24 hours following stroke and this is unrelated to oedema volume, suggesting an alternate mechanism. While mechanisms are unclear, this ICP rise may be related to the significant and global dysfunction of the glymphatic system at 24 hours post-stroke. This dysfunction is resolved by 2 weeks post-stroke. It is possible that glymphatic function is not dependent on AQP4 in wild-type naïve mice, suggesting other mechanisms may contribute to changes in glymphatic function seen in animals with genetic deletion of AQP4.
- Subject
- intracranial pressure (ICP); ischaemic stroke; epidural; mice
- Identifier
- http://hdl.handle.net/1959.13/1422020
- Identifier
- uon:37795
- Rights
- Copyright 2020 Kirby Elizabeth Warren
- Language
- eng
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| View Details Download | ATTACHMENT01 | Thesis | 12 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 286 KB | Adobe Acrobat PDF | View Details Download |