Comparative multielectrode recording studies on retinal development in the chick Tanja Ugniwenko*, Christiane Ziegler, Axel Blau Department of Physics and Biophysics, University of Kaiserslautern, Kaiserslautern, Germany * Corresponding author. E-mail address: [email protected]

Much is known about the maturation of the vertebrate, especially the mammalian retinal network, including developmentally regulated activity waves as well as the progression of photosensitivity. In contrast, information on developmental features of the chick primary visual system is less consistent and there is little information on robust strategies for directly probing the electrophysiology of the retinal layers during development. We present a comparative multielectrode recording approach based on acutely dissected retinas of the embryonic chicken at different developmental stages to examine and characterize the light perceiving structures as well as spontaneous network activity in more detail.

1 Purpose The maturation of the vertebrate retina comprises the refinement of retinal connectivity, provided by periodic waves of spontaneous activity, and the acquirement of photosensitivity, born by image forming as well as non-image-forming photoreceptor cells [14]. We applied multielectrode recordings on acute retinal slices of the embryonic chicken to investigate the progression of these events, especially the photoreceptivity of non-image-forming neurons that is based on the photopigment melanopsin [4,5].

2 Experimental procedures Retinas from embryonic chicken were dissected at different embryonic stages. 4-5mm squares from the central region were prepared. The retinal slices were placed ganglion cell layer down onto planar microelectrode arrays (30/200 MEAs, Multichannelsystems, Reutlingen, Germany) and held in place by a platinum grid, allowing the recording of retinal ganglion cell activity. Retinas were permanently held in carbogen gassed Ringer solution. An adequate perfusion set-up was established to ensure constant conditions during recording experiments. Thus, it was possible to record from one slice for up to 8 hours. Drugs were applied via the perfusion system to test various synapse blockers. For closer examination of non image forming light responses, kynurenic acid was applied to silence potential rod or cone photoreceptor actions as well as the periodical burst waves that inhibited light responses. MEA recordings were performed using a MEA60-1System (Multichannelsystems, Reutlingen, Germany). Light pulses were applied by a white LED that was positioned over the centre of the array delivering diffused light.

3 Results and discussion Using MEA technology, earliy maturation of the so-called intrinsically photosensitive retinal ganglion cells (ipRGCs) has already been described for the mammalian retina [6]. Alike, periodical retinal waves as well as light evoked activity could be recorded from several regions of the retinal network of embryonic chicken. Non-image forming photosensitive ganglion cells were found to display light evoked activity from the first embryonic stage (E) tested (E13). That is much earlier than E18, when their image forming complements start to respond to light [7,8]. The characteristics of the light responses varied between cells as well as between different developmental stages (Fig.1). Periodic burst activity of the retinal network could be observed for all examined stages (E13 to E17). Application of drugs delivered obvious variations in wave characteristics for the different drugs and developmental stages, indicating the driving connections responsible for wave generation, expansion and modulation that are shifting during retinal network maturation (Fig. 2) [9-11]. Acknowledgement We are grateful to the Landesgraduiertenförderung for financial support. References [1] [2] [3] [4]

Wong, R. O. Retinal waves and visual system development. Annu Rev Neurosci. 1999; 22:29-47. Katz, L. C. and Shatz, C. J. Synaptic activity and the construction of cortical circuits. Science. 1996; 274:1133-1138. Foster, R. G. and Hankins, M. W. Non-rod, non-cone photoreception in the vertebrates. Prog Retin Eye Res. 2002; 21:507527. Fu, Y., Liao, H. W., Do, M. T. and Yau, K. W. Non-imageforming ocular photoreception in vertebrates. Curr Opin Neurobiol. 2005; 15:415-422.

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Tomonari, S., Takagi, A., Akamatsu, S., Noji, S. and Ohuchi, H. A non-canonical photopigment, melanopsin, is expressed in the differentiating ganglion, horizontal, and bipolar cells of the chicken retina. Dev Dyn. 2005; 234:783-790. Sekaran, S., Lupi, D., Jones, S. L., Sheely, C. J., Hattar, S., Yau, K. W., Lucas, R. J., Foster, R. G. and Hankins, M. W. Melanopsin-dependent photoreception provides earliest light detection in the mammalian retina. Curr Biol. 2005; 15:10991107. Peters, J. J., Vonderahe, A. R. and Powers, T. H. Electrical studies of functional development of the eye and optic lobes in the chick embryo. J Exp Zool 1958; 139:459-468.

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Witkovsky, P. An Ontogenetic Study Of Retinal Function In The Chick. Vision Res. 1963; 61:341-355. [9] Sernagor, E., Eglen, S. J. and O'Donovan, M. J. Differential effects of acetylcholine and glutamate blockade on the spatiotemporal dynamics of retinal waves. J Neurosci. 2000; 20:RC56. [10] Catsicas, M., Bonness, V., Becker, D. and Mobbs, P. Spontaneous Ca2+ transients and their transmission in the developing chick retina. Curr Biol. 1998; 8:283-286. [11] Wong, W. T., Sanes, J. R. and Wong, R. O. Developmentally regulated spontaneous activity in the embryonic chick retina. J Neurosci. 1998; 18:8839-8852

Fig. 1 Perievent histograms from 6 photosensitive ganglion cells stimulated by 1sec at 0.1 Hz frequency light pulses indicated by light bars. The histograms on the left display light responses from an E13, on the right from an E17 retina. The number of evoked spikes per 25 ms bin was summed for 30 successive light responses.

Fig. 2 Mean firing rate histograms displaying periodical wave activity of the E13/14 (top) and the E16 retina (bottom) after application of kynurenic acid, a non-selective antagonsist for NMDA and AMPA/kainite receptors, and dihydro-ß-erythroidine (DHßE), a nicotinic receptor antagonist. The number of evoked spikes was summed within 500 ms bins

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