1. The effect of thermal stimuli on the spontaneous spike-like receptor potential (RP) of the tuberous (Knollen) organ in Gnathonemus (Mormyridae, Pisces) was examined.
2. The frequency of the spike-like receptor potentials vanes from organ to organ even in the same fish; the mean frequency values observed lay between 162 and 1180 Hz.
3. The frequency of the RP discharge was related to steady temperature of the receptor site over a temperature range of 19° to 30° C. with a maximum at 24°-26° C. In some cases the frequency increased with increasing temperature over the whole range.
4. The receptor potential shows a temporary increase on cooling (paradoxical thermal response), followed by a decrease in frequency (normal thermal response); warming provokes opposite effects.
5. The amplitude of the paradoxical response depends on the rate of temperature change but its time course does not.
6. The time course of the dynamic component of the normal thermal response is related to the rate of temperature change. The static component of the normal thermal response depends on the absolute temperature value and displays positive and negative temperature coefficients in the ‘cold’ and the ‘warm’ temperature ranges respectively.
7. The receptor potential shows behaviour on temperature change similar to the mammalian cold fibre and the afferent fibres of several other sense organs. Thus, the results suggest that (within certain limits) the events occurring at the level of sensory cells could be responsible for the frequency behaviour of the action potential in the afferent nerves of sense organs.
8. The significance of the thermal effect under natural conditions is discussed.
Supported by research grant no. 659-535 from the Direction de Recherches et Moyens d'Essais (D.R.M.E.) to Dr T. Szabo.
Zoologisches Institut der Universität, München, Luisenstrasse 14, Germany.
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