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Appetitive behavior of rats in a T-maze following unilateral hypothalamic lesions
Physiology& Behavior. Vol. 22, pp. i-5. PergamonPress and Brain Research Publ.. 1979. Printed in the U.S.A.
Appetitive Behavior of Rats in a T-Maze Following Unilateral Hypothalamic Lesions J O S E P H G. YORI, ''~ D A V I D A S D O U R I A N A N D K A T H L E E N
A. D A R K
Department o f Psychology, Wayne State University, Detroit, MI 48202 ( R e c e i v e d 21 June 1978) YORI, J. G., D. ASDOURIAN AND K. A. DARK. Appetitive behavior of rats in a T-maze following unilateral hypothalamic lesions. PHYSIOL. BEHAV. 22(1) 1-5, 1979.m Rea~luhition of position responses in a T-rna~ are significantly disrupted following unilateral lateral hypothaiamic lesions ira response is required contrelateral to the side of the lesion. This disruption is more severe in animals trained on a shock motivated task than in those trained oll a water acquisition task. Animals trained to turn ipsilateral to the lesioned side on water acquisition showed no such deficits, suggesting disruption of sensory-motor mechanisms rather than specific interference with memory or relearning. Evidence indicates that the differential responding of thirst and shock motivated animals was not due to differences in response strategies. Lateral hypothalamic lesions
Water acquisition
IN A previous study in this laboratory [3] rats with unilateral lateral hypothalamic (LH) area lesions were shown to be deficient in their ability to acquire escape responses in a T-maze when shock termination was contingent upon a response contralaterai to the side of the lelmm. When rats in that study were required to escape shock in the T-maze by turning ipsilateral to the side of the lesion, they performed as well as (and even slightly better than) normal animals. This result showed that the unilateral lesion interfered only with the making of contralaterai responses and not with escape learning generally. In another study [1], rats with unilateral LH lesions were unable to maintain two-way avoidance responses that they had acquired prior to surgery. Post surgically, these animals oriented to a flashing CS, but their responses to foot shock were so disorganized they could not escape efficiently. The consequence of their inability to escape efficiently was that they were unable to make the transition to successful avoidance behavior. The rats in the two-way avoidance study regularly crossed the barrier that divided the test chamber during the 4 rain habituation period that preceded shock trials. It was only when these animals were shocked that they became unable to cross the barrier efficiently. Animals in the T-maze study were given 2 rain to habituate to the start box. During that 2 rain period although ipsiversive circling was predominent, contraversive turning was also observed; however, making a contraversive turn at the choice point to escape shock was very difficult for these animals. The results from both of these studies suggested to us that performance deficits following LH lesions are the result of
shock dependent sensory.motor disruptions rather than learning or memory deficits. The present study is based upon the assumption that electrical shock augments the characteristic bias to turn ipsilaterai to the side of an LH lesion and that animals with such lesions (which invade sensory and motor fiber systems) can be expected to have an especially difficult time turning contralateral to the lesion site while being shocked. We decided to compare the reacquisition of shock-escape performance of unilateral LH rats in a T-maze with the reacqulsition performance of a group of thirsty unilateral LH animals running the same T-maze for a water reward. We expected that when animals were required to turn contralateral to the side of the lesion, the performance of the thirsty animals would be significantly superior to that of the shock-escape animals because the thirsty animals would not be subjected to the disruptive effects of electrical shock.
METHOD
Animals Fifty female Spralue-Dawley albino rats weighing between 250 and 300 g were housed individually with Purina lab chow and tap water available as described below. The animal colony room was maintained on an 12:12 light-dark cycle.
Apparatus The T-maze was constructed of plywood and had a clear Plexiglas cover. The floor was made of brass rods (0.32 cm dia.) set 1.25 cm apart and connected to a Gra~an-Stadler
'Send reprint requests to Joseph G. Yori, 400 Old Main, Department of Psychology, Wayne State University, Detroit MI 48202. ~Joseph G. Yori was supported by NIMH Grant MH-14273-02. The authors wish to thank Robin Tianen for typing the manuscript.
C o p y r i g h t ¢ 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79/010001-05502.00/0
2 (Model EI064GS) constant current shock scramblergenerator. All alleys of the T-maze were 10 cm wide and 25 cm high. The start box, which was 25 cm long, was separated by a clear Plexigias guillotine door from the main alley that measured 70 cm in length. A door at the end of the main alley was used to separate this alley from both goal boxes. Each goal box was 55 cm long and could be individually isolated from the main alley and other goal box with a clear Plexiglas door.
Sltrgery The animals that underwent surgery were anesthetized with sodium pentobarbitoi (50 mg/kg) and given atropine sulphate (0.2 cc) to alleviate postoperative congestion. With their heads held level in a David Kopf stereotaxic instrument, unilateral electrolytic lesions were produced in the far lateral hypothalamus (LH) by passing lmA through an anodal electrode (a No. 1 stainless steel insect pin insulated except for 0.5 mm at the tip) for 45 sec. The side of the lesion depended upon the experimental group to which an animal was assigned (see below). In a group that received sham lesions, the electrode was lowered to the same locus as for the LH groups, but no current was passed. Approximately 24, 48, and 72 hr following surgery, animals were scored for sensorimotor deficits with a test derived from tests described elsewhere [7, 8, 9]. Only those animals with good responsivity on the side ipsilaterai to the lesion and a serious deficit on the side contralateral to the lesion on all 3 days of sensorimotor testing were used in the study. Animals that were eliminated from the study because they failed to meet this criterion were replaced so that each of the groups described below contained 10 animals at the termination of the experiment.
Pretraining Prior to surgery, 5 groups of animals containing 10 animals per group learned to make either a left or a right turn in the T-maze. Half of the animals in each group were run to the left and half to the right. Four of the groups were waterdeprived and ran for a water reward. The fifth group was not water-deprived and ran to escape foot-sbock. Animals in the water-deprived grou,~s were put on a 23 hr water deprivation schedule lasting 7 days. During each of these 7 days every animal was handled for 5 rain. On Days 8 and 9 they were placed into the start box 2 at a time, After a 2 rain waiting period the guillotine door of the start box was raised and both animals were free to explore the maze. Both arms of the maze contained water. Each pair of rats was given 5 min during which time they had free access to water in both goal boxes. On Days 10-14 the water-deprived animals were run singly for 10 trials per day. On the first trial of each of these 5 pre-training days each rat was placed into the start box and forced to wait for 2 min. The guillotine door was then raised. When an animal entered either the right or left arm of the maze the door separating the stem from the arms was lowered to prevent retracing. A correction procedure was used. When an animal entered the correct arm of the maze, the door sealing off that arm was lowered and the animal was allowed to drink for approximately 5 sec. Animals were then removed from the goal box and put back into the start box without a delay. Trials 2-10 began with a 15 sec waiting period in the start box. Half of the animals in each group were run with water available in the right arm and the
YORI, ASDOURIAN AND DARK other half with water available in the left arm. The number of correct responses, and the latency to entry into the correct arm were recorded. If an animal failed to make 9 correct responses out of 10 trials on at least 1 of the 5 days of pretraining, it was eliminated from the study and replaced. The 10 shock-escape animals were maintained in their home cages for 9 days and were not given the 2 days of habituation prior to the first day of data acquisition. On each of the 5 consecutive days of escape pretraining the following procedure was followed. On the first trial of each day animals were placed in the start box for 2 rain. The guillotine door was then opened and a 1.0 mA shock commenced simultaneously. A response was defined as an animal's first turn at the choice-point. The number of correct responses and the latency to shock termination were recorded. Shock remained on until the correct goal box was entered. Half of the animals were run to the left, and the other half to the right. If an animal did not enter the designated arm within 60 sec, shock was turned offand the trial terminated. Following entry into the correct arm, animals were given a 10 sec time-out and then placed in the start box without further delay. During Trials 2-10 the waiting period in the start-box was 15 sec.
Testing The animals in the 4 water-deprived groups and the shock motivated group were exposed to the following experimental procedures. Normal Water.-Animals were kept on a 23 hr deprivation schedule in their home cages for 4 days after pretraining. On the fourth day after pretraining they were given 5 days of retraining following the procedures used during the 5 days of pretraining described above. Sham Water.-In these animals, electrodes were lowered to the target area (as described above) on the side contralaterai to the correct turn in the T-maze. Thus if an animal had been trained to turn left during pretraining, the lesion was placed on the right side. These rats were allowed 3 days of post-operative recovery. On the third post-operative day (which, as for the normal group, was 4 days following pretraining) they were given 5 days of retraining following the procedures used during the 5 days of pretraining described above. lpsi Water.-Animals received electrolytic lesions ipsilateral to the correct turn in the T-maze and then run on the same schedule and in the same way as the rats in the sham group. Contra Water.-Animals received electrolytic lesions contralateral to the correct turn in the T-maze and then run on the same schedule and in the same way as the rats in the sham group. Contra Shock.-Animals received electrolytic lesions contralateral to the correct turn in the T-maze and then run on the same schedule as the sham group following the procedures described above for the 5 days of shock-escape pretraining.
Histology Following the last day of testing, the animals were sacrificed with an overdose of anhydrous ether and sodium pentobarbitol. They were perfused with 0.9% saline followed by 10% Formalin. Frozen frontal sections were cut every 40/z and stained with cresyl violet. Localization of lesions was
APPETITIVE BEHAVIOR AND HYPOTHALAMIC LESIONS determined by referring to the K6nig and Klippel atlas 16] as a reference. RESULTS
Figure I shows the daily mean percent of correct responses made by each of the groups in this experiment both during pretraining and following surgery. A oue-way analysis of variance on the percentages for the last day of pretraining was significant, F(4)=4.25, p<0.01. Figure 1 shows that the major contribution to this significant effect was the score achieved by the superior performance of the shock group. The right half of Fig. I shows that following surgery the contralateral shock group suffered a complete reversal in its level of performance having been best prior to surgery and worst following surgery. The effect of the surgery on the contralateral water group was that its performance fell below that of the other 3 water groups but was significantly better than the performance of the contralateral shock group. That the contralateral water group, the other 3 water groups, and the shock group yielded scores that made up 3 separate populations of means is shown in Fig. 1 where there is no overlap of the mean scores of 3 populations of animals. PRE
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FIG. 1. Pre- and post-surgical mean percent correct responses as a function of day of testing. NC=normal controls, SC=sham lesion controls, lLH=group run ipsilateral to the lesion, CLH-W=group run contralateral to lesion to water reward, CLH-S--group run contralateral to lesion motivated by foot shock. It should be noted that animals that were run ipsilateral to their LH lesions suffered no performance decrement whatsoever.
The separation of the groups seen in Fig. 1 was reflected in highly significant F values when a 2 factor repeated measures analysis of variance was performed on the 5 days of scores following surgery. The results of the analysis were that there was a significant group effect, F(4,45)--13.53, p<0.001, a significant time effect F(4,16)= 13.14, p<0.001, and a significant interaction F(4,180)=3.84, p<0.001. A comparison of the response iatencies of the 4 water groups on the last day prior to surgery revealed no significant differences, F(3)=2.83. A two-factor repeated measures analysis of variance on the mean latencies of the water groups following surgery yielded a significant group effect, F(3,36)=4.14, p<0.025, a significant time effect
3
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FIG. 2. Pre- and post-surgical mean response latency as a function of day of testing. NC--normal controls, ,~C=sham lesion controls, ILH=group run ipsilateral to the lesion, CLH-W=lproop run contralateral to water reward, CLH-S-group run contralateral to lesion motivated by foot shock.
Since there is no legitimate basis for comparing shockmotivated iatencies with thirst-motivated I~encies, no attempt was made to carry out that statistical analysis. The mean shock-motivated latencies are shown in Fig. 2 simply as a matter of record. As in a previous study from this laboratory [3], trials during which an animal entered the correct arm of the maze only after having turned toward the incorrect side (but without having entered it) were recorded and named positive prime scores. Since positive prime behavior was seen only in the contralateral water and contndateral shock groups, a 2 factor repeated measures analysis of variance was done comparing these groups on this measure. The results showed that the group effect F(1,18)=0.44, and time effect F(4,72)= 1.5 were both insignificant. Although the contralateral LH w ~ r and contralaIeral LH shock groups did not differ in the number of psoitive prime scores recorded, there were considerable individual differences. Only 5 contralaZeraJ shock animals showed any improvement in entering the correct arm over days. For 3 of these animals improvement was exclusively in the form of an increased number of positive prime scores. The other shock animals improved by increasing the number of conrect turns (positive scores). Thus the contralateral turn was sufficiently difficult for shock motivated animals to require an altered response strategy (positive prime responding) to account for a large propo~ion of the improvement observed in these animals. All but one of the contralateral LH water animals increased contralatend turning from Days I to 5, so that an altered response strategy was not as important a factor in correct responding as for shock animals. In the one case where a water animal did not recover contralateral turning the same strategy, i.e., positive prime responding, was used as in the shock group. Figure 3 shows the total number of correct responses made on the first trial of the first day following surgery for all of the groups. A one-way analysis of variance showed that
4
YORI. ASDOURIAN AND DARK
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GROUP FIG. 3. Total number of correct responses on the first trial of the first day following surgery.
there was a significant effect, F(3)=26.9, p<0.001. A Newman Kuels post hoc test comparing the first trial totals of each group with every other group confirmed what seems to be the case from an inspection of Figure 3, i.e., that both of the contralateral groups differed significantly from the control groups and the ipsilateral group, that there were no significant differences among the control groups and the ipsilaterai group, and that there was no difference between the 2 contralateral groups. All of the significant effects were at the 0.001 level. An examination of the histological preparations showed that all of the animals receiving lesions sustained extensive damage to the lateral hypothalamic area and the medial forebrain bundle. To a greater or lesser extent most animals also sustained damage to the zona incerta, optic tract, Forel's Field (H~), and the internal capsule. Figure 4 shows the extent of one of these lesions. DISCUSSION
This study has shown that reacquisition of both thirst and shock motivated position responses in a T-maze are significantly disrupted following a unilateral lateral hypothalamic lesion if the correct response is contralateral to the side of the lesion. As predicted above, Fig. 1 shows that the disruption was more severe in the contra-shock group than in the contra-water group. The postsurgical superiority of the contra-water group over the contra-shock group is particu-
FIG. 4. A photomicrograph of a typical unilateral lateral hypothalamic lesion (notch indicates right side of brain).
APPETITIVE BEHAVIOR AND HYPOTHALAMIC LESIONS larly striking in view of the reversal it represents from the relative positions of these 2 groups prior to surgery. That the contra-water group showed a deficit at all in their ability to make correct turns attests to the powerful effect of the unilateral lesions. The fact that the ipsi-water group demonstrated no postsurgical deficits either in terms of correct responses or response latencies shows that the unilateral LH lesion does not interfere with memory or relearning per se, but does disrupt sensory-motor integrative mechanisms in such a way that ipsiversive turning becomes prepotent. This disruption is exacerbated when electrical shock is used resulting in severe performance deficits such as those seen in this, and other studies l l, 2, 3, 4, 6]. Positive prime measures were taken to check on the possibility that the postsurgical success of one contralateral group relative to the other might have been due to greater use by one of these groups of a strategy that resulted in the making of correct responses only after incorrect responses were aborted (i.e. after an animal turned to the incorrect arm, but then circled and entered the correct arm without having entered the wrong arm). Although the two contralaterai groups did not differ significantly on the positive prime measure, it was nevertheless true that for the majority of contralateral LH shock animals that improved postsurgically, this improvement was in the form of positive prime scores. It is thus apparent that for those animals that did not recover contralateral turning, an altered response strategy was instrumental in their ability to make the required response. This same strategy was also employed in the one contralateral LH water animal that did not recover contralateral turning.
5
The finding that the 2 contralateral groups were significantly poorer than the other 3 groups on the first trial of the fi~t day of reacquisition following surgery is a final indication that the deficit they suffered was the result of a strong bias toward ipsiversive turning. On that first postsurgical trial, none of the animals had had any relearning trials thus providing us with an ideal stage in the study to see the biasing effects of the surgery without the complications attending postsurgical reinforced and non-reinforced responses. The results of this study, and the other studies utilizing unilateral LH lesions in our laboratory [1,3] support the position that LH lesions do not have an effect on learning, but do disrupt performance. A major difference between our procedure and other procedures that have been used to study the role of the LH area in learning is that we have used unilateral lesions while investigators in other laboratories have used bilateral LH lesions (e.g. [2, 4, 6]). The unilateral lesion produces an asymmetry in the sensory-motor control system not seen following bilateral lesions, and we believe that it is this asymmetry that makes it difficult for our animals to perform adequately (in a two-way avoidance task as well as in a T-maze). Although the asymmetry that we see (i.e. a strong ipsiversive bias) is absent in animals with bilateral lesions, it clearly is not the case that with bilateral lesions, one lesion clears up the effects of the other. The effects of 2 lesions surely combine in some way to produce a sensorimotor loss more profound, and longer lasting than that suffered by our animals. Thus, we suspect that what might appear to be learning deficits following bilateral L H lesions are actually performance deficits.
REFERENCES !. Asdourian, D., J. G. Dark, L. A. Chiodo and P. S. Papich. Active avoidance in rats with unilateral hypothalamic and optic nerve lesions. Physiol. Behav. 19: 209-212, 1977. 2. Coscina, D. V. and S. Balagura. Avoidance and escape behavior of rats with aphagia produced by basal diencephalic lesions. Physiol. Behav. $: 651-657, 1970. 3. Dark, J. O., L. A. Chiodo, P. S. Papich, J. G. Yori and D. Asdonrian. Impairment in a T-maze task following unilateral lateral hypothalamic lesions. Physiol. Behav. 19: 365-370, 1977. 4. Fibiger, H. C., A. G. Phillips and A. P. Zis. Deficits in instrumental responding after 6-hydroxydopamine lesions of the nigro-neostriatal dopaminergic projection. Pharmac. Biochem. Behav. 2: 87-96, 1974.
5. K6nig, J. F. R. and R. A. Klippel. The Rat's Brain: A Stereotaxic Atlas of the Forebrain and Power Parts of the Brain System.
Baltimore: Williams and Wilkins, 1963. 6. Heybach, J. P. and G. D. Coover. Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats. J. comp. physiol. Psychol. 90:.491-504, 1976. 7. Marshall, J. F. and P. Teitelbaum. Further analysis of sensory inattention following lateral hypothalamic damage in rats. J. comp. physiol. Psychol. 86: 375-395, 1974. 8. Marshall, J. F., H. Turner and P. Teitelbaum. Sensory neglect produced by lateral hypothalarnic damage. Science 174: 523-525, 1971. 9. Turner, B. H. A sensorimotor syndrome produced by lesions of the amygdala and lateral hypothalamus. J. comp. physiol. Psychol. 82: 37-47, 1973.
Appetitive Behavior of Rats in a T-Maze Following Unilateral Hypothalamic Lesions J O S E P H G. YORI, ''~ D A V I D A S D O U R I A N A N D K A T H L E E N
A. D A R K
Department o f Psychology, Wayne State University, Detroit, MI 48202 ( R e c e i v e d 21 June 1978) YORI, J. G., D. ASDOURIAN AND K. A. DARK. Appetitive behavior of rats in a T-maze following unilateral hypothalamic lesions. PHYSIOL. BEHAV. 22(1) 1-5, 1979.m Rea~luhition of position responses in a T-rna~ are significantly disrupted following unilateral lateral hypothaiamic lesions ira response is required contrelateral to the side of the lesion. This disruption is more severe in animals trained on a shock motivated task than in those trained oll a water acquisition task. Animals trained to turn ipsilateral to the lesioned side on water acquisition showed no such deficits, suggesting disruption of sensory-motor mechanisms rather than specific interference with memory or relearning. Evidence indicates that the differential responding of thirst and shock motivated animals was not due to differences in response strategies. Lateral hypothalamic lesions
Water acquisition
IN A previous study in this laboratory [3] rats with unilateral lateral hypothalamic (LH) area lesions were shown to be deficient in their ability to acquire escape responses in a T-maze when shock termination was contingent upon a response contralaterai to the side of the lelmm. When rats in that study were required to escape shock in the T-maze by turning ipsilateral to the side of the lesion, they performed as well as (and even slightly better than) normal animals. This result showed that the unilateral lesion interfered only with the making of contralaterai responses and not with escape learning generally. In another study [1], rats with unilateral LH lesions were unable to maintain two-way avoidance responses that they had acquired prior to surgery. Post surgically, these animals oriented to a flashing CS, but their responses to foot shock were so disorganized they could not escape efficiently. The consequence of their inability to escape efficiently was that they were unable to make the transition to successful avoidance behavior. The rats in the two-way avoidance study regularly crossed the barrier that divided the test chamber during the 4 rain habituation period that preceded shock trials. It was only when these animals were shocked that they became unable to cross the barrier efficiently. Animals in the T-maze study were given 2 rain to habituate to the start box. During that 2 rain period although ipsiversive circling was predominent, contraversive turning was also observed; however, making a contraversive turn at the choice point to escape shock was very difficult for these animals. The results from both of these studies suggested to us that performance deficits following LH lesions are the result of
shock dependent sensory.motor disruptions rather than learning or memory deficits. The present study is based upon the assumption that electrical shock augments the characteristic bias to turn ipsilaterai to the side of an LH lesion and that animals with such lesions (which invade sensory and motor fiber systems) can be expected to have an especially difficult time turning contralateral to the lesion site while being shocked. We decided to compare the reacquisition of shock-escape performance of unilateral LH rats in a T-maze with the reacqulsition performance of a group of thirsty unilateral LH animals running the same T-maze for a water reward. We expected that when animals were required to turn contralateral to the side of the lesion, the performance of the thirsty animals would be significantly superior to that of the shock-escape animals because the thirsty animals would not be subjected to the disruptive effects of electrical shock.
METHOD
Animals Fifty female Spralue-Dawley albino rats weighing between 250 and 300 g were housed individually with Purina lab chow and tap water available as described below. The animal colony room was maintained on an 12:12 light-dark cycle.
Apparatus The T-maze was constructed of plywood and had a clear Plexiglas cover. The floor was made of brass rods (0.32 cm dia.) set 1.25 cm apart and connected to a Gra~an-Stadler
'Send reprint requests to Joseph G. Yori, 400 Old Main, Department of Psychology, Wayne State University, Detroit MI 48202. ~Joseph G. Yori was supported by NIMH Grant MH-14273-02. The authors wish to thank Robin Tianen for typing the manuscript.
C o p y r i g h t ¢ 1979 Brain R e s e a r c h Publications Inc.--0031-9384/79/010001-05502.00/0
2 (Model EI064GS) constant current shock scramblergenerator. All alleys of the T-maze were 10 cm wide and 25 cm high. The start box, which was 25 cm long, was separated by a clear Plexigias guillotine door from the main alley that measured 70 cm in length. A door at the end of the main alley was used to separate this alley from both goal boxes. Each goal box was 55 cm long and could be individually isolated from the main alley and other goal box with a clear Plexiglas door.
Sltrgery The animals that underwent surgery were anesthetized with sodium pentobarbitoi (50 mg/kg) and given atropine sulphate (0.2 cc) to alleviate postoperative congestion. With their heads held level in a David Kopf stereotaxic instrument, unilateral electrolytic lesions were produced in the far lateral hypothalamus (LH) by passing lmA through an anodal electrode (a No. 1 stainless steel insect pin insulated except for 0.5 mm at the tip) for 45 sec. The side of the lesion depended upon the experimental group to which an animal was assigned (see below). In a group that received sham lesions, the electrode was lowered to the same locus as for the LH groups, but no current was passed. Approximately 24, 48, and 72 hr following surgery, animals were scored for sensorimotor deficits with a test derived from tests described elsewhere [7, 8, 9]. Only those animals with good responsivity on the side ipsilaterai to the lesion and a serious deficit on the side contralateral to the lesion on all 3 days of sensorimotor testing were used in the study. Animals that were eliminated from the study because they failed to meet this criterion were replaced so that each of the groups described below contained 10 animals at the termination of the experiment.
Pretraining Prior to surgery, 5 groups of animals containing 10 animals per group learned to make either a left or a right turn in the T-maze. Half of the animals in each group were run to the left and half to the right. Four of the groups were waterdeprived and ran for a water reward. The fifth group was not water-deprived and ran to escape foot-sbock. Animals in the water-deprived grou,~s were put on a 23 hr water deprivation schedule lasting 7 days. During each of these 7 days every animal was handled for 5 rain. On Days 8 and 9 they were placed into the start box 2 at a time, After a 2 rain waiting period the guillotine door of the start box was raised and both animals were free to explore the maze. Both arms of the maze contained water. Each pair of rats was given 5 min during which time they had free access to water in both goal boxes. On Days 10-14 the water-deprived animals were run singly for 10 trials per day. On the first trial of each of these 5 pre-training days each rat was placed into the start box and forced to wait for 2 min. The guillotine door was then raised. When an animal entered either the right or left arm of the maze the door separating the stem from the arms was lowered to prevent retracing. A correction procedure was used. When an animal entered the correct arm of the maze, the door sealing off that arm was lowered and the animal was allowed to drink for approximately 5 sec. Animals were then removed from the goal box and put back into the start box without a delay. Trials 2-10 began with a 15 sec waiting period in the start box. Half of the animals in each group were run with water available in the right arm and the
YORI, ASDOURIAN AND DARK other half with water available in the left arm. The number of correct responses, and the latency to entry into the correct arm were recorded. If an animal failed to make 9 correct responses out of 10 trials on at least 1 of the 5 days of pretraining, it was eliminated from the study and replaced. The 10 shock-escape animals were maintained in their home cages for 9 days and were not given the 2 days of habituation prior to the first day of data acquisition. On each of the 5 consecutive days of escape pretraining the following procedure was followed. On the first trial of each day animals were placed in the start box for 2 rain. The guillotine door was then opened and a 1.0 mA shock commenced simultaneously. A response was defined as an animal's first turn at the choice-point. The number of correct responses and the latency to shock termination were recorded. Shock remained on until the correct goal box was entered. Half of the animals were run to the left, and the other half to the right. If an animal did not enter the designated arm within 60 sec, shock was turned offand the trial terminated. Following entry into the correct arm, animals were given a 10 sec time-out and then placed in the start box without further delay. During Trials 2-10 the waiting period in the start-box was 15 sec.
Testing The animals in the 4 water-deprived groups and the shock motivated group were exposed to the following experimental procedures. Normal Water.-Animals were kept on a 23 hr deprivation schedule in their home cages for 4 days after pretraining. On the fourth day after pretraining they were given 5 days of retraining following the procedures used during the 5 days of pretraining described above. Sham Water.-In these animals, electrodes were lowered to the target area (as described above) on the side contralaterai to the correct turn in the T-maze. Thus if an animal had been trained to turn left during pretraining, the lesion was placed on the right side. These rats were allowed 3 days of post-operative recovery. On the third post-operative day (which, as for the normal group, was 4 days following pretraining) they were given 5 days of retraining following the procedures used during the 5 days of pretraining described above. lpsi Water.-Animals received electrolytic lesions ipsilateral to the correct turn in the T-maze and then run on the same schedule and in the same way as the rats in the sham group. Contra Water.-Animals received electrolytic lesions contralateral to the correct turn in the T-maze and then run on the same schedule and in the same way as the rats in the sham group. Contra Shock.-Animals received electrolytic lesions contralateral to the correct turn in the T-maze and then run on the same schedule as the sham group following the procedures described above for the 5 days of shock-escape pretraining.
Histology Following the last day of testing, the animals were sacrificed with an overdose of anhydrous ether and sodium pentobarbitol. They were perfused with 0.9% saline followed by 10% Formalin. Frozen frontal sections were cut every 40/z and stained with cresyl violet. Localization of lesions was
APPETITIVE BEHAVIOR AND HYPOTHALAMIC LESIONS determined by referring to the K6nig and Klippel atlas 16] as a reference. RESULTS
Figure I shows the daily mean percent of correct responses made by each of the groups in this experiment both during pretraining and following surgery. A oue-way analysis of variance on the percentages for the last day of pretraining was significant, F(4)=4.25, p<0.01. Figure 1 shows that the major contribution to this significant effect was the score achieved by the superior performance of the shock group. The right half of Fig. I shows that following surgery the contralateral shock group suffered a complete reversal in its level of performance having been best prior to surgery and worst following surgery. The effect of the surgery on the contralateral water group was that its performance fell below that of the other 3 water groups but was significantly better than the performance of the contralateral shock group. That the contralateral water group, the other 3 water groups, and the shock group yielded scores that made up 3 separate populations of means is shown in Fig. 1 where there is no overlap of the mean scores of 3 populations of animals. PRE
SURGERY
POST
IOC
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FIG. 1. Pre- and post-surgical mean percent correct responses as a function of day of testing. NC=normal controls, SC=sham lesion controls, lLH=group run ipsilateral to the lesion, CLH-W=group run contralateral to lesion to water reward, CLH-S--group run contralateral to lesion motivated by foot shock. It should be noted that animals that were run ipsilateral to their LH lesions suffered no performance decrement whatsoever.
The separation of the groups seen in Fig. 1 was reflected in highly significant F values when a 2 factor repeated measures analysis of variance was performed on the 5 days of scores following surgery. The results of the analysis were that there was a significant group effect, F(4,45)--13.53, p<0.001, a significant time effect F(4,16)= 13.14, p<0.001, and a significant interaction F(4,180)=3.84, p<0.001. A comparison of the response iatencies of the 4 water groups on the last day prior to surgery revealed no significant differences, F(3)=2.83. A two-factor repeated measures analysis of variance on the mean latencies of the water groups following surgery yielded a significant group effect, F(3,36)=4.14, p<0.025, a significant time effect
3
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FIG. 2. Pre- and post-surgical mean response latency as a function of day of testing. NC--normal controls, ,~C=sham lesion controls, ILH=group run ipsilateral to the lesion, CLH-W=lproop run contralateral to water reward, CLH-S-group run contralateral to lesion motivated by foot shock.
Since there is no legitimate basis for comparing shockmotivated iatencies with thirst-motivated I~encies, no attempt was made to carry out that statistical analysis. The mean shock-motivated latencies are shown in Fig. 2 simply as a matter of record. As in a previous study from this laboratory [3], trials during which an animal entered the correct arm of the maze only after having turned toward the incorrect side (but without having entered it) were recorded and named positive prime scores. Since positive prime behavior was seen only in the contralateral water and contndateral shock groups, a 2 factor repeated measures analysis of variance was done comparing these groups on this measure. The results showed that the group effect F(1,18)=0.44, and time effect F(4,72)= 1.5 were both insignificant. Although the contralateral LH w ~ r and contralaIeral LH shock groups did not differ in the number of psoitive prime scores recorded, there were considerable individual differences. Only 5 contralaZeraJ shock animals showed any improvement in entering the correct arm over days. For 3 of these animals improvement was exclusively in the form of an increased number of positive prime scores. The other shock animals improved by increasing the number of conrect turns (positive scores). Thus the contralateral turn was sufficiently difficult for shock motivated animals to require an altered response strategy (positive prime responding) to account for a large propo~ion of the improvement observed in these animals. All but one of the contralateral LH water animals increased contralatend turning from Days I to 5, so that an altered response strategy was not as important a factor in correct responding as for shock animals. In the one case where a water animal did not recover contralateral turning the same strategy, i.e., positive prime responding, was used as in the shock group. Figure 3 shows the total number of correct responses made on the first trial of the first day following surgery for all of the groups. A one-way analysis of variance showed that
4
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GROUP FIG. 3. Total number of correct responses on the first trial of the first day following surgery.
there was a significant effect, F(3)=26.9, p<0.001. A Newman Kuels post hoc test comparing the first trial totals of each group with every other group confirmed what seems to be the case from an inspection of Figure 3, i.e., that both of the contralateral groups differed significantly from the control groups and the ipsilateral group, that there were no significant differences among the control groups and the ipsilaterai group, and that there was no difference between the 2 contralateral groups. All of the significant effects were at the 0.001 level. An examination of the histological preparations showed that all of the animals receiving lesions sustained extensive damage to the lateral hypothalamic area and the medial forebrain bundle. To a greater or lesser extent most animals also sustained damage to the zona incerta, optic tract, Forel's Field (H~), and the internal capsule. Figure 4 shows the extent of one of these lesions. DISCUSSION
This study has shown that reacquisition of both thirst and shock motivated position responses in a T-maze are significantly disrupted following a unilateral lateral hypothalamic lesion if the correct response is contralateral to the side of the lesion. As predicted above, Fig. 1 shows that the disruption was more severe in the contra-shock group than in the contra-water group. The postsurgical superiority of the contra-water group over the contra-shock group is particu-
FIG. 4. A photomicrograph of a typical unilateral lateral hypothalamic lesion (notch indicates right side of brain).
APPETITIVE BEHAVIOR AND HYPOTHALAMIC LESIONS larly striking in view of the reversal it represents from the relative positions of these 2 groups prior to surgery. That the contra-water group showed a deficit at all in their ability to make correct turns attests to the powerful effect of the unilateral lesions. The fact that the ipsi-water group demonstrated no postsurgical deficits either in terms of correct responses or response latencies shows that the unilateral LH lesion does not interfere with memory or relearning per se, but does disrupt sensory-motor integrative mechanisms in such a way that ipsiversive turning becomes prepotent. This disruption is exacerbated when electrical shock is used resulting in severe performance deficits such as those seen in this, and other studies l l, 2, 3, 4, 6]. Positive prime measures were taken to check on the possibility that the postsurgical success of one contralateral group relative to the other might have been due to greater use by one of these groups of a strategy that resulted in the making of correct responses only after incorrect responses were aborted (i.e. after an animal turned to the incorrect arm, but then circled and entered the correct arm without having entered the wrong arm). Although the two contralaterai groups did not differ significantly on the positive prime measure, it was nevertheless true that for the majority of contralateral LH shock animals that improved postsurgically, this improvement was in the form of positive prime scores. It is thus apparent that for those animals that did not recover contralateral turning, an altered response strategy was instrumental in their ability to make the required response. This same strategy was also employed in the one contralateral LH water animal that did not recover contralateral turning.
5
The finding that the 2 contralateral groups were significantly poorer than the other 3 groups on the first trial of the fi~t day of reacquisition following surgery is a final indication that the deficit they suffered was the result of a strong bias toward ipsiversive turning. On that first postsurgical trial, none of the animals had had any relearning trials thus providing us with an ideal stage in the study to see the biasing effects of the surgery without the complications attending postsurgical reinforced and non-reinforced responses. The results of this study, and the other studies utilizing unilateral LH lesions in our laboratory [1,3] support the position that LH lesions do not have an effect on learning, but do disrupt performance. A major difference between our procedure and other procedures that have been used to study the role of the LH area in learning is that we have used unilateral lesions while investigators in other laboratories have used bilateral LH lesions (e.g. [2, 4, 6]). The unilateral lesion produces an asymmetry in the sensory-motor control system not seen following bilateral lesions, and we believe that it is this asymmetry that makes it difficult for our animals to perform adequately (in a two-way avoidance task as well as in a T-maze). Although the asymmetry that we see (i.e. a strong ipsiversive bias) is absent in animals with bilateral lesions, it clearly is not the case that with bilateral lesions, one lesion clears up the effects of the other. The effects of 2 lesions surely combine in some way to produce a sensorimotor loss more profound, and longer lasting than that suffered by our animals. Thus, we suspect that what might appear to be learning deficits following bilateral L H lesions are actually performance deficits.
REFERENCES !. Asdourian, D., J. G. Dark, L. A. Chiodo and P. S. Papich. Active avoidance in rats with unilateral hypothalamic and optic nerve lesions. Physiol. Behav. 19: 209-212, 1977. 2. Coscina, D. V. and S. Balagura. Avoidance and escape behavior of rats with aphagia produced by basal diencephalic lesions. Physiol. Behav. $: 651-657, 1970. 3. Dark, J. O., L. A. Chiodo, P. S. Papich, J. G. Yori and D. Asdonrian. Impairment in a T-maze task following unilateral lateral hypothalamic lesions. Physiol. Behav. 19: 365-370, 1977. 4. Fibiger, H. C., A. G. Phillips and A. P. Zis. Deficits in instrumental responding after 6-hydroxydopamine lesions of the nigro-neostriatal dopaminergic projection. Pharmac. Biochem. Behav. 2: 87-96, 1974.
5. K6nig, J. F. R. and R. A. Klippel. The Rat's Brain: A Stereotaxic Atlas of the Forebrain and Power Parts of the Brain System.
Baltimore: Williams and Wilkins, 1963. 6. Heybach, J. P. and G. D. Coover. Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats. J. comp. physiol. Psychol. 90:.491-504, 1976. 7. Marshall, J. F. and P. Teitelbaum. Further analysis of sensory inattention following lateral hypothalamic damage in rats. J. comp. physiol. Psychol. 86: 375-395, 1974. 8. Marshall, J. F., H. Turner and P. Teitelbaum. Sensory neglect produced by lateral hypothalarnic damage. Science 174: 523-525, 1971. 9. Turner, B. H. A sensorimotor syndrome produced by lesions of the amygdala and lateral hypothalamus. J. comp. physiol. Psychol. 82: 37-47, 1973.