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Journal of Experimental Biology 108,45-55 (1984)
Published by Company of Biologists 1984

A Comparison of Neuronal and Behavioural Thresholds in the Displacement-Sensitive Pathway of the Crayfish Procambarus

YOSHIO EBINA ¹ and KONRAD WIESE ²

¹ Yamaguchi University, Faculty of Electrical Engineering, UBE, 755 Japan
² Zoologisches Institut der Technischen Universität, Tierphysiologie, D-33 Braunschweig, Pockelstrasse 10a F.R.G.

1. Velocity thresholds of neurones in the displacement-sensitive pathway of the crayfish were investigated using a stimulus programme of ramp fluid movements, with a range of velocities from 0.01-55 cm s^-1 at the source (in both forward and backward directions).

2. The velocity of the stimulus was calculated to produce particle movements with velocities of between 0.001-1.0cms^-1 at the receptors of the telson.

3. The distribution of threshold values for afferents in the fourth root of the sixth abdominal ganglion and interneurones of abdominal 4-5 connectives was plotted. Thresholds were similar for afferents and interneurones, differing in absolute value from 0.001-1.0cms^-1. Although neurones had threshold values throughout this range, there were peaks in the distributions. For the sample of 143 interneurones these were at 0.002-0.004, 0.01-0.08, 0.1-0.4cms^-1. In the sample of 43 afferents the middle peak fell at 0.02-0.06cms^-1, but the other two were the same as those for the interneurones.

4. The threshold for a behaviour pattern which makes crayfish turn to face the water current was around 0.1 cms^-1 continuous fluid speed.

5. Escape behaviour elicited by pure displacement stimuli was observed in our experiments only in animals of 2-3 cm body length which responded to displacement amplitudes of 28 mm s^-1 and 6.7 cms^-1 maximum particle velocity.

6. Strongly phasic interneurones in the pathway obviously contribute significantly in triggering escape and need high acceleration transients to become fully active.

Note:

Present address: Zoologisches Institut der Universitat, Martin Luther King Plate 3, D-2 Hamburg 13, F. R. G.

Key words: Crayfish, displacement sensitivity, thresholds

Accepted on August 8, 1983