Interocular effect of intravitreal injection of 6-hydroxydopamine and dopamine on spinule formation in teleost retina

Abstract

Terminal dendrites of cone horizontal cells (HCs) in teleost retinas show numerous spine-like protrusions named spinules, which are invaginated into the cone pedicles during light-adaptation, but retracted during dark-adaptation. Somata of HC show nematosomes whose size decreases as the number of spinules increases. Mechanisms regulating these changes in nematosomes and spinules are only partially understood, being an area of controversy in retinal cell biology. It has been suggested that efferent fibres from the brain to the retina might be involved in the control of spinule formation. Moreover, we have reported that actin depolymerization has an interocular effect on spinule formation, which could be mediated by these fibres. In the present report, we show an interocular effect on spinule dynamics: the monocular intravitreal injection of dopamine (DA) and 6-hydroxydopamine (6-OHDA), two drugs that affect the spinule formation, produces the same effects in the contralateral, untreated eye as in the injected eye. Our results reinforce the idea of an interocular central control of this phenomenon of synaptic plasticity. Dopamine-dependent events in the retina appear to be necessary to forge the afferent signals eliciting this interocular effect.