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The effect of decreasing and increasing temperature on the frequency of the electric organ discharge in Eigenmannia sp
Comp. Biochem.Physiol., 1970, Vol. 37, pp. 601 to 603. PergamonPress.Printedin Great Britain
SHORT COMMUNICATION T H E EFFECT OF DECREASING AND INCREASING TEMPERATURE ON THE FREQUENCY OF THE ELECTRIC ORGAN DISCHARGE IN E I G E N M A N N I A SP* MICHEL BOUDINOT Laboratoire de Neurophysiologie Sensorielle Compar6e, Centre d'Etudes de Physiologic Nerveuse, 4 avenue Gordon Bennett, Paris 16bme, France (Received 8 June 1970) A b s t r a c t - - 1 . A device was designed for accurate and automatic measurement
of the frequency/temperature relationship of the electric discharge in a weakly electric fish, Eigenmannia sp. 2. The observed hysteresis for increasing and decreasing temperatures was in the range of 2-4 per cent, maximal 10 per cent. 3. The low values of hysteresis explains, in this respect, the negative results of Enger & Szabo (1968) who used measuring methods which were not sufficiently accurate. INTRODUCTION IT HAS been shown by several authors (Grundfest, 1957; Lissmann, 1958; Coates et al., 1954) that in many kinds of gymnotid fish the electric organ discharge (EOD) frequency is temperature dependent and that the discharge rate is constant at a given temperature. However, Lissmann (1958) observed in Gymnotus carapo that the EOD frequency is not exactly the same for a given temperature, depending on whether the latter is reached from a previously higher or lower temperature level; the maximal difference between decreasing and increasing temperature is about 25 per cent. The results of Enger & Szabo (1968), obtained on six other gymnotid species (Gymnotus carapo, Sternopygus, Sternarchorhynchus, Eigenmannia, Steatogenys, Sternarchus), indicate similar temperature dependency, but there is no difference between a decreasing and an increasing change of temperature. T h e authors suggest, however, that a hysteresis could be hidden by the insufficient accuracy (1-6 per cent) of reproducibility of their temperature tests. Indeed, Bullock (1958) observed in gymnotid fish a "small" hysteresis using accurate methods of measurement (frequency meter and thermistor thermometer). To clear up the contradictions which emerge from the results of these authors, a device was designed which permitted an accurate, automatic and simultaneous measurement of frequency and temperature. * This study was aided by grant No. 659,594 accorded to Dr. T. Szabo by the Direction de Recherches et Moyens d'Essais (D.R.M.E.). 601
602
MICHEL BOUDINOT MATERIALS AND METHODS
3/Ieasurement offrequency and temperature The analogical conversion of the EOD frequency is made by the integration of the electric organ pulses previously shaped in a uniform pulse. Each result represents the mean frequency of the considered sample. The temperature is measured by means of a thermistor connected through a Wheatstone bridge.
......
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I
aa
I ~(/bri heat dgestoneI
~
TEMPERATURE
Integrator[
t
FIc. 1. See explanation in the text. The results of temperature and frequency are recorded on the x-response y-axis of an oscilloscope, Tektronix 565. Each temperature/frequency value is photographed by a Grass Camera C4 electrically coupled to the measuring device. The sampling rate is performed by a timing switch (Chronoreptor). The results appear as a plotted curve on the film and can be utilized directly after development.
The experimentalprocedure Three Eigenmannia (Gymnotidae, Pisces) of the same species were used. The fish is maintained in a fretworked plastic tube, at the extremities of which are fixed the two carbon recording electrodes. T h e plastic tube which also contains the thermistor is placed in a water-filled plastic sac in which oxygen is continuously bubbled. Finally, the plastic sac is placed in a container with a thermostat regulated by the experimenter (or driven by the measuring device). T h e temperature was varied by steps of 0"6°C. Samples were taken twice at 5-rain intervals starting 5 minutes after each change of temperature; the small thermal capacity of the thermostatic container permitted it to reach an equilibrium (-0"2°C) after 3 min. T h e variation of the temperature was increasing-decreasing or vice versa. RESULTS AND DISCUSSION F o r a c h a n g e o f t e m p e r a t u r e o f 10°C in t h e r a n g e o f 2 0 - 3 0 ° C , t h e E O D freq u e n c y varies a b o u t 100 H z . A h y s t e r e s i s is o b s e r v e d for d e c r e a s i n g a n d i n c r e a s i n g t e m p e r a t u r e s . T h e values v a r y f r o m case to case b e t w e e n 2 - 4 p e r c e n t o f t h e m e a n f r e q u e n c y . I n Fig. 2, t h e h y s t e r e s i s r e a c h e s its m a x i m u m , 4 p e r c e n t o f t h e m e a n f r e q u e n c y o f 250 H z . T h e m a x i m a l v a l u e o f h y s t e r e s i s o b t a i n e d in o u r e x p e r i m e n t s was 10 p e r cent. U p to 20 m i n no a d a p t a t i o n occurs, i.e. t h e f r e q u e n c y r e m a i n s stable for 3 m i n after t h e c h a n g e of t e m p e r a t u r e .
EFFECT
OF
TEMPERATURE
ON
ELECTRIC
DISCHARGE
IN
E1GENM.4NNIA
SP
603
The weak values of the obtained hysteresis explain the omission of this phenomenon by Enger & Szabo (1968) due to their insufficient accuracy of measuring. 350
oo.O ~ g o o
300 o
'5
~ °e
°l
•
•
•
OO OO O
(5_
--
o
250
o
200
20
25
30
Temperature °C
FIG. 2. Variation of the electric organ discharge frequency in relation with the water temperature. Dots, increasing temperature; circles, decreasing temperature.
In these experiments the frequency values for increasing temperature were inferior to those for decreasing temperature. A similar hysteresis with respect to positive and negative temperature sequences was obtained by Burkhardt (1959) in stretch receptor of crayfish, while the direction of the loop of hysteresis was opposite for positive and negative mechanical variation (lengthening/shortening of the receptor). It is interesting to note in this connection that non-biological material, e.g. a piece of metal, shows identical hysteresis for mechanical as well as temperature effects, and is similar to that obtained for temperature in biological material. REFERENCES BULLOCK T. H. (1958) Personal communication. BURKHARDT I). (1959) Die Erregungsvorgiinge sensibler Ganglienzellen in Abh~ingigkeit v o n d e r Temperatur. Biol. Zentralbl. 78, 22-62. COATES C. W., ALTAMIRANOM. • GRUNDFEST H. (1954) Activity in electrogenic organs of knifefishes. Science 120, 845-846. ENGER S. & SZABO T. (1968) Effect of temperature on the discharge rates of the electric organ of some Gymnotids. Comp. Biochem. Physiol. 27, 625-627. GRUNDFEST I-{. (1957) The mechanism of discharge of the electric organs in relation to general and comparative electrophysiology. Progr. Biophys. 7, 1-86. LISSMANN H. W. (1958) On the function and evolution of electric organs in fish. J. exp. Biol. 35, 156-191.
Key Word Index--Temperature; sense organs; temperature receptors; electric organ; Eigenmannia.
SHORT COMMUNICATION T H E EFFECT OF DECREASING AND INCREASING TEMPERATURE ON THE FREQUENCY OF THE ELECTRIC ORGAN DISCHARGE IN E I G E N M A N N I A SP* MICHEL BOUDINOT Laboratoire de Neurophysiologie Sensorielle Compar6e, Centre d'Etudes de Physiologic Nerveuse, 4 avenue Gordon Bennett, Paris 16bme, France (Received 8 June 1970) A b s t r a c t - - 1 . A device was designed for accurate and automatic measurement
of the frequency/temperature relationship of the electric discharge in a weakly electric fish, Eigenmannia sp. 2. The observed hysteresis for increasing and decreasing temperatures was in the range of 2-4 per cent, maximal 10 per cent. 3. The low values of hysteresis explains, in this respect, the negative results of Enger & Szabo (1968) who used measuring methods which were not sufficiently accurate. INTRODUCTION IT HAS been shown by several authors (Grundfest, 1957; Lissmann, 1958; Coates et al., 1954) that in many kinds of gymnotid fish the electric organ discharge (EOD) frequency is temperature dependent and that the discharge rate is constant at a given temperature. However, Lissmann (1958) observed in Gymnotus carapo that the EOD frequency is not exactly the same for a given temperature, depending on whether the latter is reached from a previously higher or lower temperature level; the maximal difference between decreasing and increasing temperature is about 25 per cent. The results of Enger & Szabo (1968), obtained on six other gymnotid species (Gymnotus carapo, Sternopygus, Sternarchorhynchus, Eigenmannia, Steatogenys, Sternarchus), indicate similar temperature dependency, but there is no difference between a decreasing and an increasing change of temperature. T h e authors suggest, however, that a hysteresis could be hidden by the insufficient accuracy (1-6 per cent) of reproducibility of their temperature tests. Indeed, Bullock (1958) observed in gymnotid fish a "small" hysteresis using accurate methods of measurement (frequency meter and thermistor thermometer). To clear up the contradictions which emerge from the results of these authors, a device was designed which permitted an accurate, automatic and simultaneous measurement of frequency and temperature. * This study was aided by grant No. 659,594 accorded to Dr. T. Szabo by the Direction de Recherches et Moyens d'Essais (D.R.M.E.). 601
602
MICHEL BOUDINOT MATERIALS AND METHODS
3/Ieasurement offrequency and temperature The analogical conversion of the EOD frequency is made by the integration of the electric organ pulses previously shaped in a uniform pulse. Each result represents the mean frequency of the considered sample. The temperature is measured by means of a thermistor connected through a Wheatstone bridge.
......
~
I
aa
I ~(/bri heat dgestoneI
~
TEMPERATURE
Integrator[
t
FIc. 1. See explanation in the text. The results of temperature and frequency are recorded on the x-response y-axis of an oscilloscope, Tektronix 565. Each temperature/frequency value is photographed by a Grass Camera C4 electrically coupled to the measuring device. The sampling rate is performed by a timing switch (Chronoreptor). The results appear as a plotted curve on the film and can be utilized directly after development.
The experimentalprocedure Three Eigenmannia (Gymnotidae, Pisces) of the same species were used. The fish is maintained in a fretworked plastic tube, at the extremities of which are fixed the two carbon recording electrodes. T h e plastic tube which also contains the thermistor is placed in a water-filled plastic sac in which oxygen is continuously bubbled. Finally, the plastic sac is placed in a container with a thermostat regulated by the experimenter (or driven by the measuring device). T h e temperature was varied by steps of 0"6°C. Samples were taken twice at 5-rain intervals starting 5 minutes after each change of temperature; the small thermal capacity of the thermostatic container permitted it to reach an equilibrium (-0"2°C) after 3 min. T h e variation of the temperature was increasing-decreasing or vice versa. RESULTS AND DISCUSSION F o r a c h a n g e o f t e m p e r a t u r e o f 10°C in t h e r a n g e o f 2 0 - 3 0 ° C , t h e E O D freq u e n c y varies a b o u t 100 H z . A h y s t e r e s i s is o b s e r v e d for d e c r e a s i n g a n d i n c r e a s i n g t e m p e r a t u r e s . T h e values v a r y f r o m case to case b e t w e e n 2 - 4 p e r c e n t o f t h e m e a n f r e q u e n c y . I n Fig. 2, t h e h y s t e r e s i s r e a c h e s its m a x i m u m , 4 p e r c e n t o f t h e m e a n f r e q u e n c y o f 250 H z . T h e m a x i m a l v a l u e o f h y s t e r e s i s o b t a i n e d in o u r e x p e r i m e n t s was 10 p e r cent. U p to 20 m i n no a d a p t a t i o n occurs, i.e. t h e f r e q u e n c y r e m a i n s stable for 3 m i n after t h e c h a n g e of t e m p e r a t u r e .
EFFECT
OF
TEMPERATURE
ON
ELECTRIC
DISCHARGE
IN
E1GENM.4NNIA
SP
603
The weak values of the obtained hysteresis explain the omission of this phenomenon by Enger & Szabo (1968) due to their insufficient accuracy of measuring. 350
oo.O ~ g o o
300 o
'5
~ °e
°l
•
•
•
OO OO O
(5_
--
o
250
o
200
20
25
30
Temperature °C
FIG. 2. Variation of the electric organ discharge frequency in relation with the water temperature. Dots, increasing temperature; circles, decreasing temperature.
In these experiments the frequency values for increasing temperature were inferior to those for decreasing temperature. A similar hysteresis with respect to positive and negative temperature sequences was obtained by Burkhardt (1959) in stretch receptor of crayfish, while the direction of the loop of hysteresis was opposite for positive and negative mechanical variation (lengthening/shortening of the receptor). It is interesting to note in this connection that non-biological material, e.g. a piece of metal, shows identical hysteresis for mechanical as well as temperature effects, and is similar to that obtained for temperature in biological material. REFERENCES BULLOCK T. H. (1958) Personal communication. BURKHARDT I). (1959) Die Erregungsvorgiinge sensibler Ganglienzellen in Abh~ingigkeit v o n d e r Temperatur. Biol. Zentralbl. 78, 22-62. COATES C. W., ALTAMIRANOM. • GRUNDFEST H. (1954) Activity in electrogenic organs of knifefishes. Science 120, 845-846. ENGER S. & SZABO T. (1968) Effect of temperature on the discharge rates of the electric organ of some Gymnotids. Comp. Biochem. Physiol. 27, 625-627. GRUNDFEST I-{. (1957) The mechanism of discharge of the electric organs in relation to general and comparative electrophysiology. Progr. Biophys. 7, 1-86. LISSMANN H. W. (1958) On the function and evolution of electric organs in fish. J. exp. Biol. 35, 156-191.
Key Word Index--Temperature; sense organs; temperature receptors; electric organ; Eigenmannia.