UNCORRECTED PROOF Correlation of the electrical and intrinsic optical signals in the chicken spreading depression phenomenon N.L.V. Peixoto a, * , V.M. Fernandes de Lima b , W. Hanke c a Microelectronics Laboratory, University of Sa Äo Paulo-USP, Esc. Politecnica, AvenueProfessor Luciano Gualberto, 158, Trav.3, CEP 05508-900, Sa Äo Paulo, SP, Brazil b Department of Neuroscience, FUNREI, Sa Ä o Joa Äo del Rey, MG, Brazil c Institute of Zoophysiology, Hohenheim University, Stuttgart, Germany Received 11 October 2000; received in revised form 14 December 2000; accepted 18 December 2000 Abstract This paper presents some results on the correlation between the electrophysiological and intrinsic optical signals (IOS) of spreading depression waves in chicken retinae. We ®rst show that the peak of the time derivative of the electrophy- siological wave occurs precisely when the optical signal reaches the electrode tip. Second, by comparing bath applica- tions of propranolol and glycerol it can be shown that the slow potential shift is not directly correlated to the intrinsic optical signal. Propranolol depresses the amplitude of the electrical wave, although the intrinsic optical signal continues being visible. On the other hand, we observe total absence of the IOS under glycerol, while the electrical wave is always present. Correlations of this kind are relevant for a deeper understanding of the underlying mechanisms of the spreading depression phenomenon. q 2001 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Retina; Spreading depression; Chicken retinae; Propranolol; Glycerol; Intrinsic optical signals The spreading depression (SD) phenomenon was discov- ered by A. Lea Äo in 1944 [8]. Since then, SD waves have been investigated and successfully elicited in all regions of the gray matter, including the retina, which constitutes its most accessible part. Intrinsic optical signal (IOS) percept- ibility of SD is made possible due to transient changes mainly in the extracellular osmolarity, which is a side effect of the massive motion of ions between extra and intracel- lular spaces. Translocation of ions also yields an electrical pro®le, which is present in all retinal layers during SD waves [2,3]. Despite the fact that they may share the trigger- ing event, IOS and electrophysiological signals may be separately accessed and individually in¯uenced, as we show here. We have simultaneously measured optical (re¯ected light) and electrophysiological signals of SD waves, and their synchronism has been investigated in control experi- ments as well as under bath application of drugs. The begin- ning of the brightness pro®le obtained from IOS is concomitant with the peak of the time derivative of the slow potential shift in all cases. Analysis of IOS and electrophysiological pro®les was performed by treating retinae with propranolol and glycerol. These drugs are found to in¯uence the behavior of SD waves in different ways [12,13], but their form of action and consequences to the retinal tissue are still subject of debate. Experiments are carried out on 6±12-day-old chickens [5]. Immediately after the chick being decapitated, the eyeball is dissected, cut at the equatorial plane, and the vitreous humour is removed. The eyecup is immersed in a Petri dish perfused at a rate of 4 ml/min with Ringer solution (pH 7.4), containing 0.1 M NaCl, 6 mM KCl, 1 mM MgCl 2 , 1 mM NaH 2 PO 4 , 1 mM CaCl 2 , 30 mM NaHCO 3 , 30 mM glucose and 5 mM Tris. In experiments with propranolol (0.5 mM) and glycerol (5%), drugs are added to the Ringer solution. Temperature is maintained at 298C(^18C). Waves are elicited chemically with 0.1 M KCl (approx. 50 ml applied by means of a micropipette) at the eyecup border every 15 min. Electrophysiological measurements are performed using glass electrodes ®lled with 1 M KCl (10 mm tip diameter) positioned in the inner plexiform layer. The reference electrode is a silver chloride pellet electrode, positioned in the bath surrounding the eyecup. Electrical signals are low-pass ®ltered at 10 Hz, and digitally recorded. Neuroscience Letters xx (2001) xxx±xxx NSL 17555 0304-3940/01/$ - see front matter q 2001 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3940(01)01501-4 www.elsevier.com/locate/neulet * Corresponding author. Tel: 155-11-3765-1378; fax. 155-11- 3818-5585. E-mail address: nathalia@lme.usp.br (N.L.V. Peixoto).