[Show abstract][Hide abstract] ABSTRACT: Dendritic signals play an essential role in processing visual information in the retina. To study them in neurites too small for electrical recording, we developed an instrument that combines a multi−photon (MP) microscope with a through−the−objective high−resolution visual stimulator. An upright microscope was designed that uses the objective lens for both MP imaging and delivery of visual stimuli to functionally intact retinal explants or eyecup preparations. The stimulator consists of a miniature liquid−crystal−on−silicon display coupled into the optical path of an infrared−excitation laser−scanning microscope. A pair of custom−made dichroic filters allows light from the excitation laser and three spectral bands (‘colors') from the stimulator to reach the retina, leaving two intermediate bands for fluorescence imaging. Special optics allow displacement of the stimulator focus relative to the imaging focus. Spatially resolved changes in calcium−indicator fluorescence in response to visual stimuli were recorded in dendrites of different types of mammalian retinal neurons.
Pflügers Archiv - European Journal of Physiology 01/2009; · 4.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is essential for the visual system to detect image motion and to compute its direction and speed. Information on local motion is needed to predict the trajectory of moving objects, whereas information on global motion provides important feedback about body and head movement relative to the environment. That the computation of image motion starts in the retina was discovered more than 40 years ago: when Barlow and his colleagues recorded from retinal ganglion cells in the rabbit, they found a subset of cells that fired vigorously when an object moved in a certain (preferred) direction across their receptive fields but remained silent when the object moved in the opposite (null) direction. This chapter provides an overview of these direction−selective ganglion cells and the neuronal circuitry that underlies direction selectivity in the vertebrate retina.
A. I. Basbaum, A. Kaneko, G. M. Shepherd, G. Westheimer: The Senses − A Comprehensive Reference, 413-422 (2008). 01/2008;
[Show abstract][Hide abstract] ABSTRACT: Detection of image motion direction begins in the retina, with starburst amacrine cells (SACs) playing a major role. SACs generate larger dendritic Ca(2+) signals when motion is from their somata towards their dendritic tips than for motion in the opposite direction. To study the mechanisms underlying the computation of direction selectivity (DS) in SAC dendrites, electrical responses to expanding and contracting circular wave visual stimuli were measured via somatic whole-cell recordings and quantified using Fourier analysis. Fundamental and, especially, harmonic frequency components were larger for expanding stimuli. This DS persists in the presence of GABA and glycine receptor antagonists, suggesting that inhibitory network interactions are not essential. The presence of harmonics indicates nonlinearity, which, as the relationship between harmonic amplitudes and holding potential indicates, is likely due to the activation of voltage-gated channels. [Ca(2+)] changes in SAC dendrites evoked by voltage steps and monitored by two-photon microscopy suggest that the distal dendrite is tonically depolarized relative to the soma, due in part to resting currents mediated by tonic glutamatergic synaptic input, and that high-voltage-activated Ca(2+) channels are active at rest. Supported by compartmental modeling, we conclude that dendritic DS in SACs can be computed by the dendrites themselves, relying on voltage-gated channels and a dendritic voltage gradient, which provides the spatial asymmetry necessary for direction discrimination.
[Show abstract][Hide abstract] ABSTRACT: In goldfish, the retinal pathways involved in motion coding have been demonstrated to have an L-cone dominated action spectrum (S. Schaerer, C. Neumeyer, Motion detection in goldfish investigated with the optomotor response is "color blind", Vision Res. 36 (1996) 4025-4034). The neurotransmitters involved in retinal motion coding mechanisms, and the relevance of these retinal motion coding mechanisms for motion perception, are little investigated in fish. In this study, the optomotor response was used to investigate the effect of antagonists on different receptor types for acetylcholine (ACh), GABA, for the dopamine D2-receptor (D2-R) - which is known to modulate the action spectrum in motion coding (C. Mora-Ferrer, K. Behrend, Dopaminergic modulation of photopic temporal transfer properties in goldfish retina investigated with the ERG, Vision Res. 44 (2004) 2067-2081) - and of an agonist for against the mGluR6-receptor (mGluR6) on goldfish motion vision in the photopic range. Blockade of nicotinic ACh-R, GABAa-R and both GABAa- and GABAc-R eliminated the optomotor response completely. Neither a muscarinic ACH-R antagonist, a D2-R antagonist or a mGluR6-agonist affected goldfish motion vision. The pharmacological profile of the goldfish optomotor response resembles the pharmacological profile of direction-selective ganglion cells (DS-GC) described for vertebrate retinas in electrophysiological experiments, e.g. (S. Weng, W. Sun, S. He, Identification of ON-OFF direction-selective ganglion cells in the mouse retina, J. Physiol. 562 (2005) 915-923). This indicates that cells with direction-selective receptive field properties exist in the goldfish retina. It is proposed that these cells provide the input for the full field motion perception in goldfish.
Brain research 11/2005; 1058(1-2):17-29. · 2.46 Impact Factor