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Victoria P Connaughton, Sabrina Jones, Katie DeCicco-Skinner, Terry Davidson, Cassie Gould; Assessing cognition and neurochemical changes in hyperglycemic zebrafish. Invest. Ophthalmol. Vis. Sci. 2018;59(9):3564.
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© ARVO (1962-2015); The Authors (2016-present)
To determine if one month of hyperglycemia induced by alternating glucose exposure causes cellular changes in brain and retinal neurochemistry and cognitive deficits in zebrafish.
Adult zebrafish were alternately exposed to either glucose (1-2%), mannitol (1-2%), or water in temperature-controlled containers for 4wks. At that time, blood glucose was measured prior to collection of brain and retinal tissue for protein analysis. Western Blots of retinal and brain homogenates were probed with antibodies to β-actin (housekeeping gene;1:1000), NFκB (RelA;1:1000), IκB (IKK;1:500), TOH (1:2000), GAD (1:1000), or GFAP (1:1000). To assess cognition, we used a 3-compartment chamber with a dark side, a light side, and a central neutral-colored compartment to introduced the fish. Animals underwent 2dy of group acclimation, followed by a 3rd dy of individual acclimation. Then, baseline preference for either the dark or light side was determined and reinforced with a food reward. Time to first decision and the order of correct/incorrect trials was assessed. We then tested if prolonged hyperglycemia (7wks) affects these acclimation and discrimination protocols.
Four wks of alternating glucose exposure significantly elevated mean blood sugar to 140-152mg/dL. Densitometry on Western Blots identified an increase in NFκB in both retinal (3.5x) and brain (1.6x) homogenates. Brain IKK levels were increased 1.5x and retinal GFAP levels were increased 1.4x. Retinal GAD and TOH levels were comparable to controls; whereas brain GAD levels increased 2x. When tested prior to glucose exposure, the time to 1st decision was decreased by half after of 4dy of assessment, with no differences across groups (p=0.7). However, when tested at 7wk of treatment, glucose-treated fish took longer to complete individual acclimation (N=4/group; p=0.06). There was no significant difference on percent accuracy after 4dy of discrimination (N=3/group; p=0.77).
Hyperglycemia elevated GFAP and NFκB in retinal tissue, and NFκB and IKK in brain tissue, indicating an inflammatory response. In contrast, retinal GAD and TOH levels were not changed, though brain GAD levels increased, suggesting these systems are less sensitive to hyperglycemic insult. Glucose-treated fish took a longer time to acclimate and have a reduced ability to discriminate, suggesting possible cognitive deficits.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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