Equipo de Espectrometría de Absorción Atómica

Table 1 Brotz Case Ringer’s Solution pH 7.2

Chemical Mol. Weight Concentration Supplier

Glucose 180.16 g/mol 13.9 nM Sucrose 342.30 g/mol 73.7 nM NaHCO3 84.01 g/mol 20 nM NaCl 58.44 g/mol 110 nM KCl 74.55 g/mol 5.4 nM CaCl2-2H2O 147.02 g/mol 1.9 nM Merck KGaA, Darmstadt, DE TRIS/HCL 121.14 g/mol 15 nM Fructose 180.2 g/mol 23 nM Sigma-Aldrich Chemie GmbH, Steinheim, DE

Table 1 Constituents used for Case Ringers solution. New solution was made fresh approximately every 2-3 months using the above components. The Ringer’s was then sterile filtered and kept at 4 O_{C until needed.}

Table 2 Electrophysiology Equipment Specifications

Name Properties

Microscope Eye pieces 8x, f = 100 mm Tungsten Electrodes 1 MΩ impedance

Glass Capillary tubes 1 mm outer diameter

Micropipette Puller Heat 479, Pull 180, Pressure 500, Velocity 100, Time 200 Visual Monitor 200 Hz refresh rate, 13 x 9.8 cm, P15 Phosphor, dot size

0.25 mm

Amplifier 3000 and 100 times

Band-pass filter range 500-10,000 Hz and again 300-3,000 Hz Table 2 Specifications of the electrophysiological equipment used.

Table 3 Equipment suppliers

Object Company

Micromanipulators Narishige Japan, assembled partly by MPI- Neurobiology, Martinsried, DE

Microscope Carl Zeiss, DE

Tungsten Electrodes World Precision Instruments Inc., Florida, USA

Glass Capillary tubes Science Products GMbH, Hofheimer, DE Brown-Flaming micropipette puller (P-97) Sutter Instruments, California, USA Air Table and accessories Newport Corporation, California, USA Tektronix TDS 2002 Digital Oscilloscope Tektronix, Oregon, USA

Audio Monitor Grass Medical Instruments, Massachusetts, USA

Analog electronic amplification and filtering equipment

Designed by the Max-Planck Institute of biological Cybernetics, Tübingen, DE

DAS16 I/O AD/DA Board Metrabyte; Measurement Computing Co. CRT Monitor, model 608, or 604 Tektronix, Oregon, USA

Picasso Image Synthesizer Innisfree Inc., Massachusetts, USA Bullmess stimulation and data acquisition

software

Privately designed in Delphi (Borland) by Dr. Jürgen Haag

Dell Personal Computer Pentium II, Intel Corporation, California, USA Matlab versions 6.5-7.1 Mathworks Inc., Massachusetts, USA

IDL version 5.0-6.0 Research Systems Inc. Colorado, USA Table 3 Suppliers for the electrophysiological equipment and programming software.

H1-cell response adaptation was tested under three experimental conditions. First, the overall magnitude and shape of the H1-cell input-output function was tested in response to the velocity standard deviation and time constant using a sinusoidal grating and a low-pass filtered Gaussian white noise velocity signal. Second, the effect of the visual pattern was tested by using the same velocity signals as in the first set of experiments but in addition to the sinus grating, a square wave grating was introduced. Lastly, the speed at which the H1- cell adapted was tested by switching either the standard deviation or the time constant of the velocity signal during the experiment. The results for each of the experimental conditions were then compared with simulations of the Reichardt detector in response to the same stimuli.

3

Results

The H1-cell adapted its stimulus-response function to the entire set stimulus conditions tested. The slope of the stimulus-response function decreased as the velocity standard deviation increased and increased with increasing velocity time constant. The speed at which the cell responded to the stimulus also increased as the velocity standard deviation increased. The square wave visual pattern increased the dynamic gain for all of the velocity standard deviations and time constants tested compared to a sine wave grating. The H1-cell adapted quickly to the new stimulus condition after the velocity standard deviation or time constant was switched. This suggests that the mechanism behind the adaptation also occurs on a fast time scale.

The same changes in the slope of the stimulus-response function were found in the Reichardt motion detector without any change in the model parameters. It was an automatic function of the motion detector itself. The slope of the stimulus-response function in the Reichardt detector decreased as the velocity standard deviation increased and increased with increasing velocity time constant. The Reichardt detector changed its stimulus-response function very rapidly in response to a switch in either velocity standard deviation or time constant. The only discrepancy between the experiment and the model was in the response to the square wave grating. The model adapted its slope of the stimulus-response function less for a square wave

pattern compared to a sine wave pattern. The experiments showed exactly the opposite effect. This is likely due to saturation in the firing rate that is not accounted for in the model.

In the following section I often substituted Greek letters for the different stimulus parameters that I used or for the time constants of the Reichardt detector model. These letters consistently stand for the same property throughout this work. The standard deviation of the Gaussian colored noise velocity profile is represented by the lower case Greek letter sigma (σ), and the low-pass filter time constant of the Gaussian colored noise velocity profile as the lower case Greek letter tau with subscript zero (τ0). The first order low-pass time constant of the Reichardt detector is represented by the Greek letter tau with subscript L (τL) and the first order high-pass filter with the Greek letter tau with a subscript H (τH).