Neuronal activity‐dependent regulation of retinal blood flow

Abstract

Blood flow in the retina is intrinsically regulated to meet the metabolic demands of its constituent cells. Flickering light or stationary contrast reversals induce an increase in blood flow within seconds of the stimulus onset. This phenomenon is thought to compensate for an increase in ganglion cell activity and energy consumption. Ganglion cell activity is in turn dependent on signals from photoreceptors, bipolar cells, horizontal cells and amacrine cells. The physiological properties of these neurons determine how each type is affected by a particular light characteristic. Neuronal activity then triggers the release of signalling molecules that dilate local blood vessels and increase blood flow. Nitric oxide has been implicated as an important mediator, but metabolites of arachidonic acid may also be involved. Detailed elucidation of these mechanisms, together with advances in imaging technology, may facilitate the use of neurovascular tests to improve the detection of retinal damage in pathological conditions.

Optical Coherence Tomography Angiography in Neurodegenerative Disorders

“…In terms of the microvasculature, retinal and cerebral small blood vessels share many common features. Both cerebral and retinal microcirculation are high oxygen extraction systems whose flow is dependent on local neuronal activity [ 3 ]. In addition, they have mechanisms of autoregulation to maintain a relatively constant blood flow despite variation in perfusion pressure [ 4 , 5 ].…”

Pulsed Electrical Stimulation of the Human Eye Enhances Retinal Vessel Reaction to Flickering Light

“…Generally, the modulation of neuronal activity in the retina is associated with variations in local retinal blood flow (Falsini et al, 2002; Riva et al, 2004; Metea and Newman, 2006; Newman, 2015; Noonan et al, 2015), a functional connection known as neurovascular coupling (NVC) (Roy and Sherrington, 1890). In terms of NVC, an activation of retinal neurons results in an increased metabolic demand that is regulated by Müller cells.…”

“…The generation and control of retinal vascular tone is determined by intrinsic mechanisms (Newman, 2015). Several competing and simultaneously linked autoregulatory mechanisms are involved, including endothelial-mediated regulation (de Wit et al, 2006; Bharadwaj et al, 2013), myogenic mechanisms (Bayliss effect) (Bayliss, 1902; Blum et al, 1999), metabolic mechanisms (Delaey and van de Voorde, 2000; Pournaras et al, 2008), and NVC (Metea and Newman, 2006; Noonan et al, 2015). With our study it is not possible to clarify which of these mechanisms are affected by electrical stimulation.…”

The Retinal Relaxing Factor: Update on an Enigmatic Regulator of the Retinal Circulation

“…This neurovascular coupling means that when the neural activity increases, in this case by flickering light, the higher demand for nutrients and oxygen is compensated by an increased blood flow through release of retinal vasodilators. [38][39][40][41] The RRF could be one of these retinal vasodilators. Vasorelaxing substances can be released from two cell types of the retina: neurons and glial cells.…”