Cellular mechanisms underlying the pharmacological induction of phosphenes
- 1 February 2007
- journal article
- review article
- Published by Wiley in British Journal of Pharmacology
- Vol. 150 (4), 383-390
- https://doi.org/10.1038/sj.bjp.0706998
Abstract
Visual sensations evoked by stimuli other than luminance changes are called phosphenes. Phosphenes may be an early symptom in a variety of diseases of the retina or of the visual pathways, but healthy individuals may perceive them as well. Phosphene-like phenomena are perhaps the most common side effect reported in clinical pharmacology. Ivabradine, a novel anti-anginal drug that reduces heart-rate by inhibiting the hyperpolarization activated current expressed in cardiac sinoatrial node cells (I(f)) induces phosphenes in some patients. One hypothesis is that ivabradine interacts with the visual system by inhibiting hyperpolarization-activated current in retinal cells (Ih). An Ih current with properties similar to cardiac I(f) has been reported in retinal neurones. Under normal circumstances most of the random fluctuations generated within the retinal circuits do not reach the level of conscious perception because they are filtered out. Presumably, filtering occurs mostly within the retina and one serious candidate for this action is the ability of Ih to act as a negative-feedback mechanism. Ih activation in the membrane of visual cells causes dampening of responses to slow noisy inputs thus tuning the visual system to perceptually more relevant signals of higher frequency. Ih inhibition, by altering at the retinal synapses the filtering of signals generated by thermal breakdown of rhodopsin or other fluctuations, is expected to increase the probability of phosphene occurrence. It is the purpose of the present paper to outline and discuss the features of the visual system and the pharmacological conditions relevant to phosphene perception.This publication has 110 references indexed in Scilit:
- RETINAL PROCESSING NEAR ABSOLUTE THRESHOLD: From Behavior to MechanismAnnual Review of Physiology, 2005
- Heart Rate Lowering by Specific and Selective If Current Inhibition with IvabradineDrugs, 2004
- HCN channels are expressed differentially in retinal bipolar cells and concentrated at synaptic terminalsEuropean Journal of Neuroscience, 2003
- Functional characterisation and subcellular localisation of HCN1 channels in rabbit retinal rod photoreceptorsThe Journal of Physiology, 2002
- Membrane current noise in dark‐adapted and light‐adapted isolated retinal rods of the larval tiger salamanderThe Journal of Physiology, 1998
- Characteristics of Migraine Visual AuraHeadache: The Journal of Head and Face Pain, 1997
- The Amateur ScientistScientific American, 1981
- Ferrier lecture - Functional architecture of macaque monkey visual cortexProceedings of the Royal Society of London. B. Biological Sciences, 1977
- Evoked Pressure Responses in the Rabbit EyeScience, 1967
- Optic Nerve Impulses and Weber's LawCold Spring Harbor Symposia on Quantitative Biology, 1965