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Up-hill avoidance: A new passive-avoidance task
Physiology & Behavior, Vol. 21, pp. 775--776. Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A.
Up-hill Avoidance: A New Passive-Avoidance Task URSULA
S T A U B L I A N D J O S E P H P. H U S T O N
Institute of Psychology, University of Diisseldorf, Lab. Comp. and Physiol. Psychology Universitiitsstr. 1, Diisseldorf, West-Germany and Institute of Pharmacology, University of Ziirich, Ziirich, Switzerland ( R e c e i v e d 12 M a y 1978) STAUBLI, U. AND J. P. HUSTON. Up-hill avoidance: A new passive-avoidance task. PHYSIOL. BEHAV. 22(4)
775-776, 1979.--Rodents and many other animal species orient and locomote up-hill when placed on a tilted surface. When placed with head facing downwards on an incline, rats turn around and climb up reliably within a few seconds. This behavior can be suppressed by a contingent tail-shock, and therefore is a suitable response for studying passive avoidance learning. The present report summarizes the effectiveness of various combinations of angle of incline and levels of tail-shock intensity on up-hill avoidance learning in rats. Passive-avoidance
Learning
Electric shock
Geotaxis
M A N Y animal species exhibit a negative geotaxis, i.e. the tendency to orient and locomote toward the top when placed on a slanted surface. When placed on a tilted platform with head facing down-hill, rats and mice invariably turn around and Iocomote up the incline reliably and with a short latency. This behavior, therefore, provides a potentially useful response for the study of passive avoidance learning. Passive avoidance learning involves learning to avoid noxious stimulation by non-performance of a high-probability response. The response should occur reliably with a short-latency, and be easily quantifiable. The present study was undertaken to determine whether the negative geotaxis would be a suitable response to study passive avoidance learning. F o r this purpose various combinations of tail-shock intensity and angles of tilt were examined. METHOD
Animals and Apparatus Animals were 48 male albino rats of the Sprague-Dawley strain. They weighed 280-320 g and were maintained in pairs under standard conditions. The experimental apparatus was a 50x50 cm box with 35 cm high gray plastic walls. The box could be inclined at a variable angle (see Fig. 1). The floor consisted of 10 mm dia. stainless steel grid bars placed 13 mm apart. To deliver a tail-shock, a tail-electrode was constructed, consisting of a wire clip (see Fig. 1) connected to a constant current shock source. The room was illuminated with dim fluorescent lighting.
Rats
Procedure The animal was first fitted with the tail-electrode and then placed onto the grid with its nose facing the bottom. In order to have the animal calm and inert during the critical moment of being released onto the grid, the rat was swung back and forth three times with wide arm movements of the experimenter. During baseline-trials the animal's latency to make a 180° turn and initiate the first climbing response was measured. Thereafter the animal was returned to its home cage. During the experimental trials the same latency was measured and additionally a tail-shock was administered contingent on the first climbing response after the 180° turn. Immediately after the shock the animal was placed into its home cage. Retest was measured 24 hr later. An animal was considered to have learned to inhibit the climbing response if it remained with its nose facing the bottom for 180 sec. An experiment was designed to investigate step-up avoidance learning under two conditions of degree of slope (20° and 30°) of the grid floor, comparing two intensities of tail-shock (1.5 and 2.0 mA). A total of 48 animals were assigned to 6 groups, including one control and two experimental groups run with the grid floor tilted at a 20° angle, and one control and two experimental groups tested with the angle set at 30° . The two experimental groups in each case received either 1.5 or 2.0 mA tail-shock. The control groups did not receive tail-shock, but were otherwise handled exactly as the experimental animals.
1Supported in part by Swiss National Science Foundation Grant No. 3.2270.77.
ZReprints obtainable from J. P. Huston at Dtisseldorf address above.
C o p y r i g h t © 1979 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/79AM0775-02502.00/0
776
STAUBLI AND HUSTON 50 cm 70.
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~ 15mA
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Controls 1
TRIALS
FIG. 2. Up-hill avoidance learning after two baseline trials as a function of degree of tilt of floor (A), and level of tail-shock (B). Graph (A) depicts mean latencies to ascend (and SEM) with groups separated according to angle of slope. Graph (B) shows performance with groups separated according to tall-shock current level. The controls did not receive tail-shocks and were run at either a 20° or 30° slope.
J
FIG. 1. Top: Up-hill avoidance learning task. Bottom: Schema of tail-shock clamp in place. RESULTS AND DISCUSSION Figure 2 summarizes the results in terms of latencies to ascend the tilted platform. During baseline trials the latencies to ascend were identical for all groups, ranging between 2 and 7 seconds across animals. This result shows that the response occurs with a high probability and reliably within a short period of time and, therefore, meets the basic requirements for a response to be suitable for the analysis of passive avoidance learning. The tail-electrode itself did not influence the latency to ascend, since pilot-studies showed no differences between animals with and without tail-electrodes in latency to ascend. Statistical comparisons between mean step-up latencies were performed with the two-tailed Randomization Test for Independent Samples [3]. Figure 2 shows that punishment of the ascending response with a contingent tail-shock considerably extended the time the animals spent on the grid floor with nose facing the bottom. Compared to the control animals (which received no tail-shock) all four experimental groups, independently of the kinds of procedural variables they were exposed to (i.e. tail-shock intensity and degree of incline of the grid floor), showed significantly higher latencies to ascend during the retest trial (in each case with p<0.01).
Figure 2A depicts the influence of the slope of the incline on learning irrespective of tail-shock intensity; conversely, Figure 2B shows the results of the different tail-shock intensities, pooled across inclines of the grid floor. Figure 2A shows that in the retest trial the rats tested at a 20° angle tilt learned to suppress the ascending response significantly better than animals tested at the 30° angle (p <0.02). Apparently, the strength of the negative geotaxis response covaries with increasing angle of tilt, and the stepup response accordingly becomes increasingly difficult to suppress with a tail-shock. Figure 2B indicates that even when pooled across angles of incline of the grid floor, the 2 mA tail-shock groups tended towards superior learning compared to the 1.5 mA shock. This difference approached significance with p <0.06 (two-tailed). As can be surmised from Fig. 2, the optimal combination for passive avoidance learning was a 2 mA tail-shock given with the floor tilted at a 20° angle. This, of course, does not preclude the possibility that other combinations of parameters not examined in the present study can lead to superior learning. The results also show that this task allows relatively simple control over extent of learning by manipulation of one or both of two obvious controlling parameters---shock intensity and angle of incline. Up-hill avoidance learning in terms of response latencies is comparable with performance of the same rat strain on the conventional step-down avoidance task [2]. The up-hill avoidance technique promises to provide a useful addition to the existing arsenal of passive avoidance methods [1]. Its most obvious advantage is that it can be administered to animals debilitated in sensory-motor coordination by pharmacological or surgical treatments that would preclude use of other passive avoidance tasks.
REFERENCES
1. Bureg, J., O. Buregovfi and J. P. Huston. Techniques and Basic Experiments for the Stud}' o f Brain and Behavior. Amsterdam: Elsevier/North-Holland Biomedical Press, 1976.
2. Huston J. P. and U. Staubli. Retrograde amnesia produced by posttrial injection of substance P into substantia nigra. Brain Res. 159: 468-472, 1978. 3. Siegel, S. Nonparametric Statistics for the Behavioral Sciences. New York: McGraw Hill, Inc., 1956.
Up-hill Avoidance: A New Passive-Avoidance Task URSULA
S T A U B L I A N D J O S E P H P. H U S T O N
Institute of Psychology, University of Diisseldorf, Lab. Comp. and Physiol. Psychology Universitiitsstr. 1, Diisseldorf, West-Germany and Institute of Pharmacology, University of Ziirich, Ziirich, Switzerland ( R e c e i v e d 12 M a y 1978) STAUBLI, U. AND J. P. HUSTON. Up-hill avoidance: A new passive-avoidance task. PHYSIOL. BEHAV. 22(4)
775-776, 1979.--Rodents and many other animal species orient and locomote up-hill when placed on a tilted surface. When placed with head facing downwards on an incline, rats turn around and climb up reliably within a few seconds. This behavior can be suppressed by a contingent tail-shock, and therefore is a suitable response for studying passive avoidance learning. The present report summarizes the effectiveness of various combinations of angle of incline and levels of tail-shock intensity on up-hill avoidance learning in rats. Passive-avoidance
Learning
Electric shock
Geotaxis
M A N Y animal species exhibit a negative geotaxis, i.e. the tendency to orient and locomote toward the top when placed on a slanted surface. When placed on a tilted platform with head facing down-hill, rats and mice invariably turn around and Iocomote up the incline reliably and with a short latency. This behavior, therefore, provides a potentially useful response for the study of passive avoidance learning. Passive avoidance learning involves learning to avoid noxious stimulation by non-performance of a high-probability response. The response should occur reliably with a short-latency, and be easily quantifiable. The present study was undertaken to determine whether the negative geotaxis would be a suitable response to study passive avoidance learning. F o r this purpose various combinations of tail-shock intensity and angles of tilt were examined. METHOD
Animals and Apparatus Animals were 48 male albino rats of the Sprague-Dawley strain. They weighed 280-320 g and were maintained in pairs under standard conditions. The experimental apparatus was a 50x50 cm box with 35 cm high gray plastic walls. The box could be inclined at a variable angle (see Fig. 1). The floor consisted of 10 mm dia. stainless steel grid bars placed 13 mm apart. To deliver a tail-shock, a tail-electrode was constructed, consisting of a wire clip (see Fig. 1) connected to a constant current shock source. The room was illuminated with dim fluorescent lighting.
Rats
Procedure The animal was first fitted with the tail-electrode and then placed onto the grid with its nose facing the bottom. In order to have the animal calm and inert during the critical moment of being released onto the grid, the rat was swung back and forth three times with wide arm movements of the experimenter. During baseline-trials the animal's latency to make a 180° turn and initiate the first climbing response was measured. Thereafter the animal was returned to its home cage. During the experimental trials the same latency was measured and additionally a tail-shock was administered contingent on the first climbing response after the 180° turn. Immediately after the shock the animal was placed into its home cage. Retest was measured 24 hr later. An animal was considered to have learned to inhibit the climbing response if it remained with its nose facing the bottom for 180 sec. An experiment was designed to investigate step-up avoidance learning under two conditions of degree of slope (20° and 30°) of the grid floor, comparing two intensities of tail-shock (1.5 and 2.0 mA). A total of 48 animals were assigned to 6 groups, including one control and two experimental groups run with the grid floor tilted at a 20° angle, and one control and two experimental groups tested with the angle set at 30° . The two experimental groups in each case received either 1.5 or 2.0 mA tail-shock. The control groups did not receive tail-shock, but were otherwise handled exactly as the experimental animals.
1Supported in part by Swiss National Science Foundation Grant No. 3.2270.77.
ZReprints obtainable from J. P. Huston at Dtisseldorf address above.
C o p y r i g h t © 1979 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/79AM0775-02502.00/0
776
STAUBLI AND HUSTON 50 cm 70.
--
60. 20 o
50.
i'
2rnA
/
/
/
40
it/
i / i
Z
~
/
i
/
i'
/
/ it
20
i /
i J
T 30 °
/
~ 15mA
10,
~ ,k
ntrols
';L TRIALS
;
~= BL
i • BL
Controls 1
TRIALS
FIG. 2. Up-hill avoidance learning after two baseline trials as a function of degree of tilt of floor (A), and level of tail-shock (B). Graph (A) depicts mean latencies to ascend (and SEM) with groups separated according to angle of slope. Graph (B) shows performance with groups separated according to tall-shock current level. The controls did not receive tail-shocks and were run at either a 20° or 30° slope.
J
FIG. 1. Top: Up-hill avoidance learning task. Bottom: Schema of tail-shock clamp in place. RESULTS AND DISCUSSION Figure 2 summarizes the results in terms of latencies to ascend the tilted platform. During baseline trials the latencies to ascend were identical for all groups, ranging between 2 and 7 seconds across animals. This result shows that the response occurs with a high probability and reliably within a short period of time and, therefore, meets the basic requirements for a response to be suitable for the analysis of passive avoidance learning. The tail-electrode itself did not influence the latency to ascend, since pilot-studies showed no differences between animals with and without tail-electrodes in latency to ascend. Statistical comparisons between mean step-up latencies were performed with the two-tailed Randomization Test for Independent Samples [3]. Figure 2 shows that punishment of the ascending response with a contingent tail-shock considerably extended the time the animals spent on the grid floor with nose facing the bottom. Compared to the control animals (which received no tail-shock) all four experimental groups, independently of the kinds of procedural variables they were exposed to (i.e. tail-shock intensity and degree of incline of the grid floor), showed significantly higher latencies to ascend during the retest trial (in each case with p<0.01).
Figure 2A depicts the influence of the slope of the incline on learning irrespective of tail-shock intensity; conversely, Figure 2B shows the results of the different tail-shock intensities, pooled across inclines of the grid floor. Figure 2A shows that in the retest trial the rats tested at a 20° angle tilt learned to suppress the ascending response significantly better than animals tested at the 30° angle (p <0.02). Apparently, the strength of the negative geotaxis response covaries with increasing angle of tilt, and the stepup response accordingly becomes increasingly difficult to suppress with a tail-shock. Figure 2B indicates that even when pooled across angles of incline of the grid floor, the 2 mA tail-shock groups tended towards superior learning compared to the 1.5 mA shock. This difference approached significance with p <0.06 (two-tailed). As can be surmised from Fig. 2, the optimal combination for passive avoidance learning was a 2 mA tail-shock given with the floor tilted at a 20° angle. This, of course, does not preclude the possibility that other combinations of parameters not examined in the present study can lead to superior learning. The results also show that this task allows relatively simple control over extent of learning by manipulation of one or both of two obvious controlling parameters---shock intensity and angle of incline. Up-hill avoidance learning in terms of response latencies is comparable with performance of the same rat strain on the conventional step-down avoidance task [2]. The up-hill avoidance technique promises to provide a useful addition to the existing arsenal of passive avoidance methods [1]. Its most obvious advantage is that it can be administered to animals debilitated in sensory-motor coordination by pharmacological or surgical treatments that would preclude use of other passive avoidance tasks.
REFERENCES
1. Bureg, J., O. Buregovfi and J. P. Huston. Techniques and Basic Experiments for the Stud}' o f Brain and Behavior. Amsterdam: Elsevier/North-Holland Biomedical Press, 1976.
2. Huston J. P. and U. Staubli. Retrograde amnesia produced by posttrial injection of substance P into substantia nigra. Brain Res. 159: 468-472, 1978. 3. Siegel, S. Nonparametric Statistics for the Behavioral Sciences. New York: McGraw Hill, Inc., 1956.