Transduction and Adaptation in Spider Slit Sense Organ Mechanoreceptors. Juusola, Mikko and Andrew S. French. Department of Physiology and Biophysics, Dalhousie Univesity, Halifax, Nova Scotia B3H 4H7, Canada.
APStracts 2:0234N, 1995.
SUMMARY AND CONCLUSIONS
1. Mechanoreceptor neurons in spider (Cupiennius salei) slit sense organ were examined by intracellular current- and voltage-clamp recordings. Steps and pseudorandomly modulated displacement stimuli were delivered to the mechanosensitive cuticular slits. The resulting responses were used to determine the response dynamics and signal-to-noise ratio (SNR) of mechanoelectrical transduction. 2. Neurons were separated into two groups that, in terms of their afferent discharges, displayed different adaptations to displacement stimuli. Both responded at the onset of the step, but then adapted fully, either immediately or within 10-200 ms. Voltage-clamp recordings showed only small differences in the receptor currents of the two groups. 3. Displacement of the slit caused a large inward current that decayed in seconds to a steady level of about 10-25 % of the initial transient. When adapted to a steady displacement, the neurons responded to superimposed displacements in the same direction with additional transient currents, whose decay could be fitted by two exponentials with time constants of about 10 and 100 ms. In contrast, displacement in the opposite direction caused small "outward" currents without obvious adaptation. This behaviour persisted with increasing background displacements, suggesting a shift in the displacement- response curve along the displacement axis. 4. White-noise stimulation supported the step data and confirmed that the receptor's sensitivity was independent of mean slit membrane displacement. When the relative displacement of the stimulus (i.e. strain) was held constant at different maintained backgrounds, the SNR of the neurons remained fairly constant at about 2-10 over the frequency range from 4-450 Hz. The receptor current frequency responses showed high-pass characteristics, with a 2-7-fold enhancement of the response amplitude and a phase lag relative to the stimulus of 90 o at 300 Hz. Low coherence values in the frequency range 0.5-125 Hz were explained by nonlinear adaptation. 5. We conclude that, by rapidly adapting to the mean displacement of the slit membrane, slit-organ mechanoreceptor neurons maintain a high sensitivity and SNR that allow the detection of small and rapid changes in cuticular strain. 

Received 21 March 1995; accepted in final form 1 August 1995.
APS Manuscript Number J188-5
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.