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Alterations in pain thresholds and avoidance conditioning in rats with septal lesions
Neuropsychologia, 1971, Vot. 9, pin. 325 to 330. Pergamon Press. Printed in England
ALTERATIONS IN CONDITIONING
PAIN THRESHOLDS AND IN RATS WITH SEPTAL
AVOIDANCE LESIONS*
BARBARA A. DOT'," and MARY R. FORKNER North Central College, Naperville, Illinois 60540, U.S.A. (Received 26 October 1970)
Almtraet--Rats with septal ablations displayed lower jump thresholds for pain than shamoperated controls, but did not differ in open-field activity. Septal rats were poor two-way avoidance learners with a moderately strong UCS intensity on both a simpleand a discriminated avoidance task. Septal lesions may affect avoidance performance by increasing the rat's responsiveness to painful stimuli, thereby disrupting behavior associated with an intense fear drive. LESIONS in the septal region consistently enhance performance on two-way shuttle-box avoidance tasks in rats [1]. Superior performance was seen both immediately after surgery and several months postoperatively [2-5]. Hyperactivity' or inability to inhibit motor responses seemingly cannot account for the superior avoidance performance of animals with septal lesions, since these preparations do not differ from controls in intertrial-interval retracings which are punished by shock. Paradoxically, rats with septal damage are inferior to controls in the acquisition of 3-compartment shuttle-box avoidances, and they typically perform very poorly on simpler, one-way avoidance tasks as well as on passive avoidance tasks [1, 6-8]. These findings are sometimes attributed to a lesion-produced reduction in fear motivation or in the strength of responses such as crouching or freezing which normally compete with appropriate avoidance responding, or both [1, 9]. This interpretation is weakened by findings of excessive freezing in rats wittl septal lesions during one-way avoidance training and in the open field [10, 11]. An alternative explanation of these findings is that septal lesions alter the subject's responsiveness to painful stimuli. This approach is suggested by findings of SCI-IWARTZaAUM and SPIETH [12] that septal subjects accepted more shocks than controls during passive avoidance training. More to the point, animals with septal lesions were totally unresponsive to increases in shock intensity. They persisted in seeking food at shock levels which completely inhibited the approach responses of controls. While these results are consistent with an hypothesis that damage to the septal area leads to a loss in inhibition, they do not concur with the findings of HARVEY et aL [13] regarding the effects of septal lesions on P U N performance (the discriminated suppression of lever pressing by punishment). Rats with septal ablations showed less response suppression than controls only with intermediate intensities of punishing shock. Very weak shocks had no consistent effects on response suppression by animals with septal area ablations. In contradiction to the findings of * This research was supported by NSF-URP grant GY-346. 325
326
BARBARAA. DOTYand MARY R. FORKNER
SCHWARTZBAUM a n d SPIETH, these p r e p a r a t i o n s d e m o n s t r a t e d considerable response suppression, and, in fact, did n o t differ f r o m controls. However, these a u t h o r s reported that septal a n d s h a m - o p e r a t e d rats did n o t differ in latencies of responses to r a d i a n t heat. Nevertheless, research cited in the study by HARVEY et al. [13] implies that rats with septal lesions display increased sensitivity to electric shock. In addition, electrical s t i m u l a t i o n of the septal area appears to elevate p a i n thresholds [14]. The present study was u n d e r t a k e n to determine whether septal a b l a t i o n s alter responsiveness to painful electric shock, a n d to clarify a n y possible relationship between painresponse thresholds a n d two-way avoidance p e r f o r m a n c e in rats with septal damage. A n y l e s i o n - p r o d u c e d alterations in pain thresholds might be expected to p r o d u c e parallel " changes in avoidance performance. METHODS The subjects were 31, 90 day-old Long-Evans hooded rats. Of these animals, 16 received electrolytic lesions in the septal area and 15 received sham operations in which the skulls were opened but no electrode penetration occurred. The lesions were produced stereotaxically at the bregma, 4.5 mm below the skull surface. The incisor bar was about 3 mm below the level of the ear bars so that the skull was level in the region of the bregrna and lambda. A 2-mA d.c. current was passed through a 0.01-in. monopolar electrode for 20 sec. The anode of the current generator (Leheigh Valley lesioner) was attached to the electrode and the cathode was connected to the scalp at the edge of the incision. At the end of the experiment the rats were perfused with saline and 10~o formalin in saline and serial frozen sections were made. Every fourth section was stained with cresyl violet acetate and luxol "fast" blue MBS. Representative lesions are illustrated in Fig. 1.
Flo. 1. Reconstruction of coronal brain sections through the area of the smallest and largest lesions. The area of septal damage is shown in black. Ac=anterior commissure; Cc=corpus caliosum; Cd=caudate nucleus; Vc=ventricle; Gc=cingulate gyms.
Animals were allowed to recover for two weeks postoperatively after which time they were tested for activity in the open field, pain-response thresholds, and conditioned-avoidance performance, in that order. Open-field observations were made by placing each rat individually in the center of a 36-in. square field marked off in black and white 3-in. squares. Animals were observed by two independent raters for one three-minute interval. Squares entered and boluses excreted were recorded. Rats were handled for two weeks preoperatively and two weeks postoperatively to reduce the hyperreactivity normally seen after septal ablations. Handling consisted of stroking by the experimenters at least 10 minutes daily. On the day preceding pain-response testing, all animals were rated for emotionality by means of Krso's [15] procedures.
ALTERATIONS IN PAIN THRESHOLDS AND AVOIDANCE CONDITIONING
327
Pain-response thresholds were determined by placing each rat individually in a circular metal chamber, 16 in. high and 12 in. in dia., placed on an electrified grid and covered with a Plexiglass lid. This method was used instead of measuring tail-flick responses because the 2 methods produce similar results in studies of analgesic drug effects [16], and the former method provides for finer discriminations among responses to painful stimuli. The test procedures were similar to those of EvANs [16]. Animals were allowed to explore the enclosure until coming to rest and were then exposed to five series of 10-ft shock intensifies of 0.05 to 1.00 mA. Stimulus intensities were presented in a different random order on each series. Shocks were presented five seconds apart and one minute elapsed between each series. Responses to each current application were categorized by two independent, pretrained experimenters as no response, flinch (body twitch or withdrawal of front feet from the grid), or jump (withdrawal of hind feet, complete body withdrawal or running). The jump response was treated as the major index of pain-response thresholds. Avoidance training was conducted in a metal, five-compartment shuttle-box type of apparatus mounted on an electrified grid. The apparatus has been described in detail in a previous publication [12]. Septal rats and sham operates were randomly assigned to one of four avoidance conditioning groups and ran 90 training trials on either a simple, or a light-dark discriminated avoidance task with either a mild UCS (0.3 mA, footshock intensity) or a strong UCS (1.0 mA). These UCS levels were selected on the basis of the preceding pain-response threshold tests which indicated that the at lower intensity (0.3 mA), almost no controls responded by jumping while all controls jumped at the higher intensity. On the simple avoidance task, animals were required to enter either of two compartments to avoid the UCS, shock to the feet. The discriminated avoidance task was similar except that animals ran to the lighted member of the pair of opposite compartments to prevent the shock. Rats ran thirty trials a day for three consecutive days. RESULTS
Open-field behavior N u m b e r s o f squares entered and boluses excreted in the open-field by animals with septal, and those with sham operations were analyzed by M a n n - W h i t n e y U tests. The two groups differed significantly (two-tailed tests) on neither measure. T h e m e d i a n n u m b e r o f squares entered by septals was 89.5 a n d by controls was 83.6. M e d i a n boluses d r o p p e d was 1.8 for animals with septal damage, and 2.1 for those with s h a m operations.
Emotionality Rats with septal ablations did not differ f r o m sham-operated controls o n postoperative emotionality ratings. B o t h groups received relatively low median ratings c o m p a r a b l e to those reported for n o r m a l h o o d e d rats [18, 19]. These findings imply a dissociation between emotionality scores a n d pain-response thresholds.
Pain-response thresholds Frequencies o f j u m p responses and c o m b i n e d flinch and response failure at each stimulus intensity were averaged over the five-shock series. These averaged values were analyzed by means o f separate chi-square for each stimulus intensity. Significant chi-square values (df= I, p < 0.01, one-tailed tests) were o b t a i n e d for the comparisons between groups at all shock intensities between 0.30 and 1.00 m A . A higher p r o p o r t i o n o f septal operates than controls j u m p e d at all stimulus intensities except those below 0.30 mA. The relatively high frequency o f j u m p s by septals relative to s h a m operates is particularly striking at the higher stimulus intensities. These trends can be seen in Fig. 2. Similar chi-square analyses o f flinch responses failed to reveal any significant differences between groups at any stimulus intensity a l t h o u g h animals with septal operations tended to flinch m o r e than controls at very low intensities.
Avoidance conditioning Instances o f successful avoidance were analyzed by a 2 × 2 x 2 factorial analysis o f variance to test main effects o f operative treatment, shock intensity and task difficulty, as well as the interactions a m o n g them. The significance o f m e a n differences a m o n g groups
328
BARBARAA. DOTYand MARYR. FORKNER
was tested by application of Duncan's Multiple Range Tests. The means of the successful avoidance performed by all subjects are presented in Table 1. IOO
/---;
-
-
Sham
operates
/
/
9oi Septals
------
/
80
/
7o
40
/
/
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/
/I ii////
"
n
20-io
-
/ii I 005
010
020
I
I
F
I
I
I
I
0.30 0.40 0 5 0 0.60 070 0.80 0.90 IO0 mA
F]G. 2. Averaged proportions of jump responses of septal and control rats on all shock series. Table 1. Mean shuttle-box avoidances performed by all rats Avoidance Treatment group Shock intensity
0.3 mA 1.0 mA
Task 0.3 mA 1.0 mA
Septal animals
63.8*
61.3
54.3*
38.2
Sham operates
44.3
76.6*
32.6
56.4*
* Significantly larger than other column mean (p < 0.01). Significant F values, all with 1/30 df were obtained for the main effects of task difficulty ( F = 15.68, p = < 0.01) and shock intensity ( F = 10.72), task difficulty × shock ( F = 11.54). Both treatment groups made more correct responses on the simple avoidance task, confirming that the two problems do represent different levels of difficulty. Changes in shock intensity affected the performance of both septal-and sham-operates but in opposite directions. Septal animals made significantly more successful instances of simple and discriminated avoidances than controls with a mild UCS level. The reverse was true at the stronger level of shock. The simple avoidance performance of animals with septal damage was not affected by an increase in UCS intensity but their performance on the more complex discriminated avoidance task was very definitely disrupted by a stronger punishing shock. In other words, the avoidance performance of septal operates was impaired either when training was conducted with a strong UCS, or when the learning task was relatively difficult, and these effects appear to be additive.
ALTERATIONS IN PAIN THRESHOLDS AND AVOIDANCE CONDITIONING
329
DISCUSSION These analyses make it clear that the effects of septal lesions on avoidance performance vary considerably as a function of the UCS intensity associated with the learning task. Animals with septal operations are poor two-way avoidance performers when a relatively strong level of punishment shock is employed. Witha mild level of shock, septal rats avoid much more efficiently than do controls. This finding is partly a function of the fact that sham-operates perform inadequately on avoidance tasks associated with mild UCS levels. These data suggest that septals perform more capably than controls with minimallypunishing stimuli. A basis for these findings is suggested by the pain-response threshold data. Septal animals had substantially lower thresholds of jump responses to punishing shock than did controls. Since rats with septal lesion were as active as controls in the open-field, these findings cannot be easily explained in terms of septal lesion effects on general motor activity. The lowered pain-response thresholds of septal rats probably do not reflect a heightened emotional state, since these animals behaved similarly to controls on an independent test of emotionality. Since the performance of septal rats varied as a function of task difficulty and shock intensity, the present data do not support TRAFTON'S [5] proposal that septal lesions enhance avoidance learning by increasing the probabilities of running rather than freezing in the shuttle-box, An alternative explanation is that septal lesions affect avoidance performance by enhancing the animal's sensitivity to painful stimuli. Any lesion-produced increase in sensitivity to punishment might be associated with a heightened fear drive. The animal with septal damage, therefore, might perform very poorly on some avoidance tasks because he is "over-aroused" by painful stimuli and is characterized by a fear drive which is so strong as to disrupt normal behavioral organization. Conversely, this preparation may perform very efficiently on two-way avoidance tasks with mild shock levels which are difficult for normal rats because the latter are less responsive to the motivational requirements of the tasks. These data fit well with Lints' findings ofincreasedresponsiveness among rats with septal operations to painful stimuli (cited by HARVEY et al. [13]). They are not in agreement with evidence suggesting that septal ablations reduce fear motivation [1]. Obviously, these comments are highly speculative since pain sensitivity per se has never been investigated. Nevertheless, other evidence also implies a septal role in the mediation of pain sensitivity. FISHERand Cotmv [20] pointed out that electrical or cholinergic stimulation of the same neural circuit produces increased food or water intake, hyperirritability, sexual arousal, and high response rates for electrical brain stimulation. This circuit which has been outlined by NAUTA [21] includes the dorsomedial hippocampus, septal area, reuniosmesial thalamic area, prefornical and preoptic regions, lateral-hypothalamusmedial forebrain bundle, mammillary interpeduncular areas, anterodorsal and anteroventral thalamic nuclei, and the cingulate cortex. These connections may well provide an integrated neural substrate underlying a variety of motivational states. REFERENCES 1. I~NYON,J. and KRIErmAus,E. E. Decrementsin one-wayavoidancelearningfollowingseptal lesions in rats. Psychonora. Sci. 3, 113-114, 1965. 2. KEt,rgON,J. Unpublisheddoctoral dissertation, MeGillUniver., 1962. 3. KINa,F. A. and MEYER,P. M. Effectsof amygdaloidlesions upon septal hyperemotionalityin the rat. Science 128, 655-656, 1958. 4. KRmKHAUS,E. E., StMMONS,M. J., T~tOM^S,E. J. and KENYON,J. Septallesionsenhanceshock avoidance behavior in the rat. Exp. Neurol. 9, 107-113, 1964.
330
BARBARAA. DOTY and MARY R. FORKNER
5. TRAFTON,C. L. Effects on lesions in the septal area and cingulate cortex areas on conditioned suppression of activity and avoidance behavior in rats. J. comp. PhysioL Psychol. 63, 191-197, 1967. 6. McNEw, J. J. and THOMPSON,R. Role of the limbic septum in active and passive avoidance conditioning in the rat. J. comp. physiol. Psychol. 61, 173-180, 1966. 7. MCCLEARY,R. Response specificity in the behavioral effects oflimbic system lesions in the rat. J. comp. physiol. Psychol. 54, 605-613, 1961. 8. VANDERWOLF,C. H. Effects of combined medial thalamic and septal lesions on active-avoidance behavior. J. comp. physiol. Psychol. 58, 31-37, 1964. 9. KENYON,J. and KRIEKHAUS,E. E. Enhanced avoidance behavior following septal lesions in the rat as a function of lesion size and spontaneous activity. J. comp. physiol. PsychoL 59, 446--468, 1955a. 10. LIss, P. H. Unpublished doctoral dissertation, McGill University, 1964. 11. SCHWARTZBAUM,J. S. and GAY, P. E. Interacting behavioral effects of septal and amygdaloid lesions in the rat. J. comp. physiol. Psychol. 61, 59-65, 1966. 12. SCnWAgrZnAtrM, J. S. and SPtErn, T. M. Analysis of the response-inhibition concept of septat functions in "passive-avoidance" behavior. Psychonom. Sci. 1, 145-146, 1964. 13. HARVEY,J. A., LiterS, C. E., JACOBSON,L. E. and HUNT, H. F. Effects of lesions in the septal area on conditioned fear and discriminated instrumental punishment in the albino rat. J. comp.physiol. Psychol. 59, 37--48, 1965. 14. ANDY, J. J. In Reticular Formation of the Brain, H. H. JASeER, et al., (Editors), p. 722. Little, Brown, Boston, 1958. 15. IONO, F. A. Effects of septal and amygdaloid lesions on emotional behavior and conditioned avoidance responses in the rat. J. nerv. merit. Dis. i26, 57-63, 1958. 16. EVANS, W. D. A technique for the investigation of some effects of spychotropic and anlgesic drugs on reflexive behavior in the rat. U.S. Army Med Res. Develop. Command Rept. No. 476, 1961. 17. Dory, B.A. and DOTY, L. A. Facilitative effects of amphetamine on avoidance conditioning in relation to age and problem difficulty. Psychomarcologia 9, 242, 247, 1966. 18. KaNO, F. A. Relationship of the "septal syndrome" to genetic differences in emotionality in rats. PsychoL Rep. 5, 11-17, 1959. 19. YUTSEY,D. A., MEYER,P. M. and MEYER,D. R. Emotionatity changes following septal and neocortical ablations in rats. J. comp. physioL PsychoL 58, 463-465, 1964. 20. FISHER, A. E. and COORY, J. M. Cholinergic tracing of a central neural circuit underlying the thirst drive. Science 138, 691-693, 1962. 21. NAUTA,W. J. H. In Advances in Neuroendocrinology, A. V. NALBANSOU,(Editors), p. 5. University of Illinois, Urbana, 1963. R6sum&---Chez des rats avec ablations septales les seuils de saut/t la douleur dtaient inf6rieurs /t ceux des contr61es ayant subi une pseudo-opdration, mais l'activitd en champ ouvert des deux groupes n'6tait pas diffdrente. Les rats ~tldsion septale apprenaient real un 6vitement /t deux voies avec une intensitd mod6rdment forte du choc dlectrique, que la tgtche d'dvitement ff~t simple ou qu'elle comport~t une discrimination. Les 16sions septales pouvaient affecter les performances d'6vitement en augmentant la sensitivitd aux stimuli douloureux, et par l~t eta d6sorgaulsant le comportement normalement associd/t une peur tr~s intense. Zusammenfassuagea--Trtigt man bei Ratten das Septum ab, so zeigen sie erniedrigte Sprungschwellen fiir Schmerz, und zwar im Gegensatz zu scheinoperierten Kontrolltieren. In der freien Feldaktivit/it zeigen sic abet keine Unterschiede. "Septalratten" erlemten eine Zweiwegvermeidung (mit 20ffnungen) schlecht, dies sowohl bei einer m~Big strengen unkonditionierten Reizintensitiit als auch im Rahmen einer unterscheidenden Vermeidungsaufgabe. Septale Liisionen k6nnen infolge sttirkerer Antworten yon Ratten auf schmerzvolle Stimuli Vermeidungsreaktionen hervorrufen. Das Verhalten wird dadurch gespalten und geht mit einer sehr starken Angst einher.
ALTERATIONS IN CONDITIONING
PAIN THRESHOLDS AND IN RATS WITH SEPTAL
AVOIDANCE LESIONS*
BARBARA A. DOT'," and MARY R. FORKNER North Central College, Naperville, Illinois 60540, U.S.A. (Received 26 October 1970)
Almtraet--Rats with septal ablations displayed lower jump thresholds for pain than shamoperated controls, but did not differ in open-field activity. Septal rats were poor two-way avoidance learners with a moderately strong UCS intensity on both a simpleand a discriminated avoidance task. Septal lesions may affect avoidance performance by increasing the rat's responsiveness to painful stimuli, thereby disrupting behavior associated with an intense fear drive. LESIONS in the septal region consistently enhance performance on two-way shuttle-box avoidance tasks in rats [1]. Superior performance was seen both immediately after surgery and several months postoperatively [2-5]. Hyperactivity' or inability to inhibit motor responses seemingly cannot account for the superior avoidance performance of animals with septal lesions, since these preparations do not differ from controls in intertrial-interval retracings which are punished by shock. Paradoxically, rats with septal damage are inferior to controls in the acquisition of 3-compartment shuttle-box avoidances, and they typically perform very poorly on simpler, one-way avoidance tasks as well as on passive avoidance tasks [1, 6-8]. These findings are sometimes attributed to a lesion-produced reduction in fear motivation or in the strength of responses such as crouching or freezing which normally compete with appropriate avoidance responding, or both [1, 9]. This interpretation is weakened by findings of excessive freezing in rats wittl septal lesions during one-way avoidance training and in the open field [10, 11]. An alternative explanation of these findings is that septal lesions alter the subject's responsiveness to painful stimuli. This approach is suggested by findings of SCI-IWARTZaAUM and SPIETH [12] that septal subjects accepted more shocks than controls during passive avoidance training. More to the point, animals with septal lesions were totally unresponsive to increases in shock intensity. They persisted in seeking food at shock levels which completely inhibited the approach responses of controls. While these results are consistent with an hypothesis that damage to the septal area leads to a loss in inhibition, they do not concur with the findings of HARVEY et aL [13] regarding the effects of septal lesions on P U N performance (the discriminated suppression of lever pressing by punishment). Rats with septal ablations showed less response suppression than controls only with intermediate intensities of punishing shock. Very weak shocks had no consistent effects on response suppression by animals with septal area ablations. In contradiction to the findings of * This research was supported by NSF-URP grant GY-346. 325
326
BARBARAA. DOTYand MARY R. FORKNER
SCHWARTZBAUM a n d SPIETH, these p r e p a r a t i o n s d e m o n s t r a t e d considerable response suppression, and, in fact, did n o t differ f r o m controls. However, these a u t h o r s reported that septal a n d s h a m - o p e r a t e d rats did n o t differ in latencies of responses to r a d i a n t heat. Nevertheless, research cited in the study by HARVEY et al. [13] implies that rats with septal lesions display increased sensitivity to electric shock. In addition, electrical s t i m u l a t i o n of the septal area appears to elevate p a i n thresholds [14]. The present study was u n d e r t a k e n to determine whether septal a b l a t i o n s alter responsiveness to painful electric shock, a n d to clarify a n y possible relationship between painresponse thresholds a n d two-way avoidance p e r f o r m a n c e in rats with septal damage. A n y l e s i o n - p r o d u c e d alterations in pain thresholds might be expected to p r o d u c e parallel " changes in avoidance performance. METHODS The subjects were 31, 90 day-old Long-Evans hooded rats. Of these animals, 16 received electrolytic lesions in the septal area and 15 received sham operations in which the skulls were opened but no electrode penetration occurred. The lesions were produced stereotaxically at the bregma, 4.5 mm below the skull surface. The incisor bar was about 3 mm below the level of the ear bars so that the skull was level in the region of the bregrna and lambda. A 2-mA d.c. current was passed through a 0.01-in. monopolar electrode for 20 sec. The anode of the current generator (Leheigh Valley lesioner) was attached to the electrode and the cathode was connected to the scalp at the edge of the incision. At the end of the experiment the rats were perfused with saline and 10~o formalin in saline and serial frozen sections were made. Every fourth section was stained with cresyl violet acetate and luxol "fast" blue MBS. Representative lesions are illustrated in Fig. 1.
Flo. 1. Reconstruction of coronal brain sections through the area of the smallest and largest lesions. The area of septal damage is shown in black. Ac=anterior commissure; Cc=corpus caliosum; Cd=caudate nucleus; Vc=ventricle; Gc=cingulate gyms.
Animals were allowed to recover for two weeks postoperatively after which time they were tested for activity in the open field, pain-response thresholds, and conditioned-avoidance performance, in that order. Open-field observations were made by placing each rat individually in the center of a 36-in. square field marked off in black and white 3-in. squares. Animals were observed by two independent raters for one three-minute interval. Squares entered and boluses excreted were recorded. Rats were handled for two weeks preoperatively and two weeks postoperatively to reduce the hyperreactivity normally seen after septal ablations. Handling consisted of stroking by the experimenters at least 10 minutes daily. On the day preceding pain-response testing, all animals were rated for emotionality by means of Krso's [15] procedures.
ALTERATIONS IN PAIN THRESHOLDS AND AVOIDANCE CONDITIONING
327
Pain-response thresholds were determined by placing each rat individually in a circular metal chamber, 16 in. high and 12 in. in dia., placed on an electrified grid and covered with a Plexiglass lid. This method was used instead of measuring tail-flick responses because the 2 methods produce similar results in studies of analgesic drug effects [16], and the former method provides for finer discriminations among responses to painful stimuli. The test procedures were similar to those of EvANs [16]. Animals were allowed to explore the enclosure until coming to rest and were then exposed to five series of 10-ft shock intensifies of 0.05 to 1.00 mA. Stimulus intensities were presented in a different random order on each series. Shocks were presented five seconds apart and one minute elapsed between each series. Responses to each current application were categorized by two independent, pretrained experimenters as no response, flinch (body twitch or withdrawal of front feet from the grid), or jump (withdrawal of hind feet, complete body withdrawal or running). The jump response was treated as the major index of pain-response thresholds. Avoidance training was conducted in a metal, five-compartment shuttle-box type of apparatus mounted on an electrified grid. The apparatus has been described in detail in a previous publication [12]. Septal rats and sham operates were randomly assigned to one of four avoidance conditioning groups and ran 90 training trials on either a simple, or a light-dark discriminated avoidance task with either a mild UCS (0.3 mA, footshock intensity) or a strong UCS (1.0 mA). These UCS levels were selected on the basis of the preceding pain-response threshold tests which indicated that the at lower intensity (0.3 mA), almost no controls responded by jumping while all controls jumped at the higher intensity. On the simple avoidance task, animals were required to enter either of two compartments to avoid the UCS, shock to the feet. The discriminated avoidance task was similar except that animals ran to the lighted member of the pair of opposite compartments to prevent the shock. Rats ran thirty trials a day for three consecutive days. RESULTS
Open-field behavior N u m b e r s o f squares entered and boluses excreted in the open-field by animals with septal, and those with sham operations were analyzed by M a n n - W h i t n e y U tests. The two groups differed significantly (two-tailed tests) on neither measure. T h e m e d i a n n u m b e r o f squares entered by septals was 89.5 a n d by controls was 83.6. M e d i a n boluses d r o p p e d was 1.8 for animals with septal damage, and 2.1 for those with s h a m operations.
Emotionality Rats with septal ablations did not differ f r o m sham-operated controls o n postoperative emotionality ratings. B o t h groups received relatively low median ratings c o m p a r a b l e to those reported for n o r m a l h o o d e d rats [18, 19]. These findings imply a dissociation between emotionality scores a n d pain-response thresholds.
Pain-response thresholds Frequencies o f j u m p responses and c o m b i n e d flinch and response failure at each stimulus intensity were averaged over the five-shock series. These averaged values were analyzed by means o f separate chi-square for each stimulus intensity. Significant chi-square values (df= I, p < 0.01, one-tailed tests) were o b t a i n e d for the comparisons between groups at all shock intensities between 0.30 and 1.00 m A . A higher p r o p o r t i o n o f septal operates than controls j u m p e d at all stimulus intensities except those below 0.30 mA. The relatively high frequency o f j u m p s by septals relative to s h a m operates is particularly striking at the higher stimulus intensities. These trends can be seen in Fig. 2. Similar chi-square analyses o f flinch responses failed to reveal any significant differences between groups at any stimulus intensity a l t h o u g h animals with septal operations tended to flinch m o r e than controls at very low intensities.
Avoidance conditioning Instances o f successful avoidance were analyzed by a 2 × 2 x 2 factorial analysis o f variance to test main effects o f operative treatment, shock intensity and task difficulty, as well as the interactions a m o n g them. The significance o f m e a n differences a m o n g groups
328
BARBARAA. DOTYand MARYR. FORKNER
was tested by application of Duncan's Multiple Range Tests. The means of the successful avoidance performed by all subjects are presented in Table 1. IOO
/---;
-
-
Sham
operates
/
/
9oi Septals
------
/
80
/
7o
40
/
/
..~~o 50 E .O
/
/I ii////
"
n
20-io
-
/ii I 005
010
020
I
I
F
I
I
I
I
0.30 0.40 0 5 0 0.60 070 0.80 0.90 IO0 mA
F]G. 2. Averaged proportions of jump responses of septal and control rats on all shock series. Table 1. Mean shuttle-box avoidances performed by all rats Avoidance Treatment group Shock intensity
0.3 mA 1.0 mA
Task 0.3 mA 1.0 mA
Septal animals
63.8*
61.3
54.3*
38.2
Sham operates
44.3
76.6*
32.6
56.4*
* Significantly larger than other column mean (p < 0.01). Significant F values, all with 1/30 df were obtained for the main effects of task difficulty ( F = 15.68, p = < 0.01) and shock intensity ( F = 10.72), task difficulty × shock ( F = 11.54). Both treatment groups made more correct responses on the simple avoidance task, confirming that the two problems do represent different levels of difficulty. Changes in shock intensity affected the performance of both septal-and sham-operates but in opposite directions. Septal animals made significantly more successful instances of simple and discriminated avoidances than controls with a mild UCS level. The reverse was true at the stronger level of shock. The simple avoidance performance of animals with septal damage was not affected by an increase in UCS intensity but their performance on the more complex discriminated avoidance task was very definitely disrupted by a stronger punishing shock. In other words, the avoidance performance of septal operates was impaired either when training was conducted with a strong UCS, or when the learning task was relatively difficult, and these effects appear to be additive.
ALTERATIONS IN PAIN THRESHOLDS AND AVOIDANCE CONDITIONING
329
DISCUSSION These analyses make it clear that the effects of septal lesions on avoidance performance vary considerably as a function of the UCS intensity associated with the learning task. Animals with septal operations are poor two-way avoidance performers when a relatively strong level of punishment shock is employed. Witha mild level of shock, septal rats avoid much more efficiently than do controls. This finding is partly a function of the fact that sham-operates perform inadequately on avoidance tasks associated with mild UCS levels. These data suggest that septals perform more capably than controls with minimallypunishing stimuli. A basis for these findings is suggested by the pain-response threshold data. Septal animals had substantially lower thresholds of jump responses to punishing shock than did controls. Since rats with septal lesion were as active as controls in the open-field, these findings cannot be easily explained in terms of septal lesion effects on general motor activity. The lowered pain-response thresholds of septal rats probably do not reflect a heightened emotional state, since these animals behaved similarly to controls on an independent test of emotionality. Since the performance of septal rats varied as a function of task difficulty and shock intensity, the present data do not support TRAFTON'S [5] proposal that septal lesions enhance avoidance learning by increasing the probabilities of running rather than freezing in the shuttle-box, An alternative explanation is that septal lesions affect avoidance performance by enhancing the animal's sensitivity to painful stimuli. Any lesion-produced increase in sensitivity to punishment might be associated with a heightened fear drive. The animal with septal damage, therefore, might perform very poorly on some avoidance tasks because he is "over-aroused" by painful stimuli and is characterized by a fear drive which is so strong as to disrupt normal behavioral organization. Conversely, this preparation may perform very efficiently on two-way avoidance tasks with mild shock levels which are difficult for normal rats because the latter are less responsive to the motivational requirements of the tasks. These data fit well with Lints' findings ofincreasedresponsiveness among rats with septal operations to painful stimuli (cited by HARVEY et al. [13]). They are not in agreement with evidence suggesting that septal ablations reduce fear motivation [1]. Obviously, these comments are highly speculative since pain sensitivity per se has never been investigated. Nevertheless, other evidence also implies a septal role in the mediation of pain sensitivity. FISHERand Cotmv [20] pointed out that electrical or cholinergic stimulation of the same neural circuit produces increased food or water intake, hyperirritability, sexual arousal, and high response rates for electrical brain stimulation. This circuit which has been outlined by NAUTA [21] includes the dorsomedial hippocampus, septal area, reuniosmesial thalamic area, prefornical and preoptic regions, lateral-hypothalamusmedial forebrain bundle, mammillary interpeduncular areas, anterodorsal and anteroventral thalamic nuclei, and the cingulate cortex. These connections may well provide an integrated neural substrate underlying a variety of motivational states. REFERENCES 1. I~NYON,J. and KRIErmAus,E. E. Decrementsin one-wayavoidancelearningfollowingseptal lesions in rats. Psychonora. Sci. 3, 113-114, 1965. 2. KEt,rgON,J. Unpublisheddoctoral dissertation, MeGillUniver., 1962. 3. KINa,F. A. and MEYER,P. M. Effectsof amygdaloidlesions upon septal hyperemotionalityin the rat. Science 128, 655-656, 1958. 4. KRmKHAUS,E. E., StMMONS,M. J., T~tOM^S,E. J. and KENYON,J. Septallesionsenhanceshock avoidance behavior in the rat. Exp. Neurol. 9, 107-113, 1964.
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5. TRAFTON,C. L. Effects on lesions in the septal area and cingulate cortex areas on conditioned suppression of activity and avoidance behavior in rats. J. comp. PhysioL Psychol. 63, 191-197, 1967. 6. McNEw, J. J. and THOMPSON,R. Role of the limbic septum in active and passive avoidance conditioning in the rat. J. comp. physiol. Psychol. 61, 173-180, 1966. 7. MCCLEARY,R. Response specificity in the behavioral effects oflimbic system lesions in the rat. J. comp. physiol. Psychol. 54, 605-613, 1961. 8. VANDERWOLF,C. H. Effects of combined medial thalamic and septal lesions on active-avoidance behavior. J. comp. physiol. Psychol. 58, 31-37, 1964. 9. KENYON,J. and KRIEKHAUS,E. E. Enhanced avoidance behavior following septal lesions in the rat as a function of lesion size and spontaneous activity. J. comp. physiol. PsychoL 59, 446--468, 1955a. 10. LIss, P. H. Unpublished doctoral dissertation, McGill University, 1964. 11. SCHWARTZBAUM,J. S. and GAY, P. E. Interacting behavioral effects of septal and amygdaloid lesions in the rat. J. comp. physiol. Psychol. 61, 59-65, 1966. 12. SCnWAgrZnAtrM, J. S. and SPtErn, T. M. Analysis of the response-inhibition concept of septat functions in "passive-avoidance" behavior. Psychonom. Sci. 1, 145-146, 1964. 13. HARVEY,J. A., LiterS, C. E., JACOBSON,L. E. and HUNT, H. F. Effects of lesions in the septal area on conditioned fear and discriminated instrumental punishment in the albino rat. J. comp.physiol. Psychol. 59, 37--48, 1965. 14. ANDY, J. J. In Reticular Formation of the Brain, H. H. JASeER, et al., (Editors), p. 722. Little, Brown, Boston, 1958. 15. IONO, F. A. Effects of septal and amygdaloid lesions on emotional behavior and conditioned avoidance responses in the rat. J. nerv. merit. Dis. i26, 57-63, 1958. 16. EVANS, W. D. A technique for the investigation of some effects of spychotropic and anlgesic drugs on reflexive behavior in the rat. U.S. Army Med Res. Develop. Command Rept. No. 476, 1961. 17. Dory, B.A. and DOTY, L. A. Facilitative effects of amphetamine on avoidance conditioning in relation to age and problem difficulty. Psychomarcologia 9, 242, 247, 1966. 18. KaNO, F. A. Relationship of the "septal syndrome" to genetic differences in emotionality in rats. PsychoL Rep. 5, 11-17, 1959. 19. YUTSEY,D. A., MEYER,P. M. and MEYER,D. R. Emotionatity changes following septal and neocortical ablations in rats. J. comp. physioL PsychoL 58, 463-465, 1964. 20. FISHER, A. E. and COORY, J. M. Cholinergic tracing of a central neural circuit underlying the thirst drive. Science 138, 691-693, 1962. 21. NAUTA,W. J. H. In Advances in Neuroendocrinology, A. V. NALBANSOU,(Editors), p. 5. University of Illinois, Urbana, 1963. R6sum&---Chez des rats avec ablations septales les seuils de saut/t la douleur dtaient inf6rieurs /t ceux des contr61es ayant subi une pseudo-opdration, mais l'activitd en champ ouvert des deux groupes n'6tait pas diffdrente. Les rats ~tldsion septale apprenaient real un 6vitement /t deux voies avec une intensitd mod6rdment forte du choc dlectrique, que la tgtche d'dvitement ff~t simple ou qu'elle comport~t une discrimination. Les 16sions septales pouvaient affecter les performances d'6vitement en augmentant la sensitivitd aux stimuli douloureux, et par l~t eta d6sorgaulsant le comportement normalement associd/t une peur tr~s intense. Zusammenfassuagea--Trtigt man bei Ratten das Septum ab, so zeigen sie erniedrigte Sprungschwellen fiir Schmerz, und zwar im Gegensatz zu scheinoperierten Kontrolltieren. In der freien Feldaktivit/it zeigen sic abet keine Unterschiede. "Septalratten" erlemten eine Zweiwegvermeidung (mit 20ffnungen) schlecht, dies sowohl bei einer m~Big strengen unkonditionierten Reizintensitiit als auch im Rahmen einer unterscheidenden Vermeidungsaufgabe. Septale Liisionen k6nnen infolge sttirkerer Antworten yon Ratten auf schmerzvolle Stimuli Vermeidungsreaktionen hervorrufen. Das Verhalten wird dadurch gespalten und geht mit einer sehr starken Angst einher.