Proper regulation of blood flow is essential for the health and function of the retina. Flicker stimulation evokes increases in blood flow in the retina a response termed functional hyperemia. This response brings additional oxygen and glucose to active neurons. We have recently demonstrated that blood flow is differentially regulated within the three capillary layers in the retina. Flickering light evokes far greater increases in capillar diameter and blood flow in the intermediate capillary layer than in the deep and superficial layers. The goal of this project is to determine the mechanisms responsible for this differential control of blood flow and to establish whether this control is altered in diabetic retinopathy, where functional hyperemia is known to be disrupted.
The aims of the project are:
Aim 1. Test the hypothesis that selective dilation of intermediate layer capillaries is driven by the activity f nearby neurons. The large flicker-evoked responses of intermediate layer capillaries may arise because synaptic activity near these capillaries is greater than activity near the other capillary layers, leading to greater release of vasodilating agents. This hypothesis will be tested by using local Ca2+ signals within Mller glial cells as an indicator of nearby synaptic activity. Calcium signals will be imaged in different retinal layers using transgenic mice expressing the genetically encoded Ca2+ indicator GCaMP3 in Mller cells.
Aim 2. Test the hypothesis that flicker-evoked dilations of capillaries is mediated by production of arachidonic acid metabolites. Flicker-evoked capillary dilations will be monitored in the rat in vivo in the three capillary layers as the signaing of candidate vasodilators is blocked by intravitreal injection of synthesis inhibitors. Candidate vasodilators will also be injected into the vitreous humor and the resulting changes in capillary diameter in the three capillary layers will be monitored.
Aim 3. Test the hypothesis that dilation of intermediate layer capillaries is compromised in diabetic retinopathy. Capillary diameter in the three capillary layers will be measured at 0.5, 1, 3 and 6 months after diabetes induction by streptozotocin injection. The effect of aminoguanidine, which reverses the loss of arteriole dilation in the diabetic retina, on capillary dilation will be investigated.

Public Health Relevance

Layer-specific regulation of blood flow profoundly affects the delivery of oxygen and glucose to retinal neurons. Elucidating the mechanisms responsible for this hemodynamic response will aid in the development of therapies for treating pathologies of the microvasculature, including diabetic retinopathy. The proposed work will also help elucidate the cellular origins of functional brain imaging (BOLD-fMRI), which is an essential tool for clinicl diagnosis.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY026514-02
Application #
9233121
Study Section
Diseases and Pathophysiology of the Visual System Study Section (DPVS)
Program Officer
Shen, Grace L
Project Start
2016-03-01
Project End
2021-02-28
Budget Start
2017-03-01
Budget End
2018-02-28
Support Year
2
Fiscal Year
2017
Total Cost
$338,169
Indirect Cost
$113,169
Name
University of Minnesota Twin Cities
Department
Neurosciences
Type
Schools of Medicine
DUNS #
555917996
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
Nippert, Amy R; Biesecker, Kyle R; Newman, Eric A (2018) Mechanisms Mediating Functional Hyperemia in the Brain. Neuroscientist 24:73-83
Biesecker, Kyle R; Srienc, Anja I; Shimoda, Angela M et al. (2016) Glial Cell Calcium Signaling Mediates Capillary Regulation of Blood Flow in the Retina. J Neurosci 36:9435-45