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Effect of the lesion of the mammillary bodies on the performance in the open field
Physiology and Behavior, Vol. 9, pp. 501-504, Brain Research Publications Inc., 1972. Printed in U.S.A.
Effect of the Lesion of the M ammillary Bodies on the Performance in the Open Field M. P. SANTACANA, R. ALVAREZ PELAEZ AND P. TEJEDOR
Departamento de BiofiSica, Institute Ca]al, C. S. I. C., Madrid, Spain
(Received 31 May 1972)
SANTACANA, M. P., R. ALVAREZ PELAEZ AND P. TEJEDOR. Effect of the lesion of the mammillary bodies on the performance in the open field. PHYSIOL. BEHAV. 9(4) 501-504, 1972.- Twenty rats were selected according to their emotivity: 10 highly emotive and 10 low emotive animals. In each group 5 rats were submitted to bilateral lesions of the mammiilary bodies (experimental rats) and 5 rats were submitted to a sham operation (control rats). General exploratory behavior in the open field and exploration of the central areas of the apparatus increased, while the number of boluses excreted during test periods decreased after the lesion of the mammillary bodies. No significant change appeared in the performance of the control group. From this it seems advisable to consider that lesions of the mammillary bodies produce a decrease of emotivity in the rat. MammiUarybodies
Emotivity
Open field
measure of exploratory behavior. This implies that animals which explore are not fearful. The results reported by Broadhurst [4], Denenberg [6] and Hayes [9] are in accord with this interpretation.
IN PREVIOUS experiments it was shown that a lesion of the mammillary bodies does not alter the retention of an active avoidance response [12]. It was even shown [11] that such a lesion actually enhanced the acquisition of that avoidance response in the shuttle box. Such a facilitatory effect has also been reported by Cardo [5]. A decrease in the acquisition of a C. E. R. was also found. Thus, a hypothesis was formulated that the facilitatory effect of the lesion of the mammiUary bodies might be due to some extent to a reduction in the emotivity of the animals [ 11 ]. Testing of this hypothesis is complicated by the probability that the effects of the lesion would depend upon the initial level of emotivity. Thus, in rats which are preoperatively non-emotive the effects of the lesion might be masked. That emotivity may act as a disturbing factor during performance in the shuttle box has indeed been suggested by Broadhurst [2]. This author reported that strains of low emotive (non-reactive) rats acquired an avoidance response in the shuttle box easier than strains of emotive (reactive) rats. The purpose of this paper is: (a) to confirm the decrease in emotivity after lesions of the mammillary bodies; and, (b) to test if the initial emotivity level plays any role in the effects of the lesion. The open field test was chosen for both purposes. By placing an animal in a brightly lit open field and recording the urination and defecation score of the rats, Hall [8] established that defecation and urination in a strange situation are valid measures of emotionality. Broadhurst used this test in a similar way to select strains of emotive and non-emotive animals [3]. The deambulation in the open field shown by rats has also been interpreted as a
METHOD
Animals In order to determine the effects of the lesion on emotivity, 40 male albino rats about 100 days old were used initially, to select among them a group of 10 rats with a high emotivity level (high score of defecation in the open field) and a group of 10 rats showing a low emotivity level (no defecation in the open field). The 20 animals which presented intermediate values were discarded. These two groups were divided into two subgroups of 5 highly emotive rats and two subgroups of 5 lowly emotive rats. Within each group subgroups were statistically equivalent according to their emotivity level. In each group one subgroup was submitted to lesions of the mammillary bodies (experimental animals) and the other was submitted to a sham operation, including the penetration of the electrode, but without lesion (control animals).
Apparatus and Tests An open field, hexagonal in form, was used, the side of the hexagon measured 90 cm and its walls were 40 cm high. (See Fig. 1). The areas limited by the walls and the first hexagon were named outer areas or level A. The areas inside the first 501
502
SANTACANA, PELAI'Z, I I:'~.II~I)OR
b
90cm.
'
FIG. 1. Diagram of tile open field. White areas are named outer or external areas. Striped areas are named inner or central areas.
hexagon were named inner areas or level B. The existence of the different levels in our open field and the extension occupied by each is based on the behavior of the rats in the different parts of the apparatus. It is a well known fact that rats tend to move around the wails. Then, to explore the inner areas requires lower emotivity than is required to explore level A. In fact the exploration shown by rats during the first few days was almost restricted to the external areas. Tests were carried out individually in 4 daily sessions of 5 min each. In each test the following items were recorded: (a) the total number of areas entered by animals regardless of the level entered; (b) the number of inner areas explored by animals; and, (c) the number of boluses excreted during the test periods.
Surgical Operations and Postoperative Tests Under nembutal anesthesia the experimental groups received bilateral lesions in the mammillary bodies. A cathodal current (1,2 mA) was passed through the electrode which was stereotaxicaUy placed according to the atlas of Albe-Fessard [1]. Control groups were submitted to the same surgical procedures except that no current was passed through the electrode. A period of 6 days was allowed for recovery before the beginning of postoperative tests. These were carried out in the same way as the preoperative ones. After completion of the test the animals were sacrificed with an overdose of nembutal and perfused transcardiatly with a 10% formaline solution. The brains were removed, fixed in formaline, and frozen sections were made at 100u. The sections were stained by the Nissl method. (Fig. 2 shows an example of the lesions obtained).
RESULTS
Effects of the Lesion of the Mammillary Bodies on General Exploratory Behavior Lesioned rats, whether emotive or non-emotive, showed a significant increase in their general exploratory behavior (see Table 1, a). The number of areas explored by emotive experimental rats showed an increase from an average of 37.7 before to 65.8 after the lesion of the mammillary bodies. Low emotive rats explored, on average, 38.2 areas before the lesion was made and 78.1 after it. Non-emotive controls showed a small decrease after surgery. They explored 34.1 areas before and 28.8 after it. The analysis of variance revealed that there was a significant difference between preoperative and postoperative performance in the experimental groups and when compared with their controls (F = 8.19; p < 0.01).
Effects of the Lesion on the Exploratory Behavior in the Inner Areas Again, both experimental groups, whether emotive or non-emotive, showed an increase in the exploration of the central areas. (See Table 1, b). Emotive experimental animals explored, on average, 1.2 areas before the lesion; After it the number of areas entered was 8.6. A little variation (nonsignificant) was shown by animals in the control group. They explored 1.1 inner areas before surgery and 2.2 after it. Low emotive experimental animals explored 4.8 inner areas before lesion 17.1 after it was made. Non-emotive controls explored 2.9 areas before, and 0.97 after surgery. (The difference is not significant). The analysis of variance revealed that there was a
MAMMILLARY BODIES AND OPEN FIELD TEST.
503
FIG. 2. An example of maximum lesions in the mammillary bodies.
TABLE 1
GENERAL EXPLORATORY BEHAVIOR (a)
EXPLORATION OF INNER AREAS (b)
DEFECATION RATE (c)
Preoper.
Postoper,
Preo~r.
Postoper.
Preoper.
Postoper.
Highly emotive experimental rats
37.7
65.8
1.2
8.6
5.0
1.0
Highly emotive control rats
37.9
39.0
1.0
2.2
4.4
4.9
Low emotive experimental rats
38.2
78.1
4.8
17.1
0.7
0
Low emotive control rats
34.1
28.8
2.9
1.0
0.9
0
(a) Average number of open field areas entered. (b) Average number of inner areas entered. (c) Average of defecation rate. significant difference between preoperative and postoperative performance in experimental groups when compared with their control groups (F = 8.19; p < 0.01).
Effects of the Lesion of the Mammillary Bodies Upon the Defecation Rate The
lesion of
the
mammillary
bodies produced
a
decrease in the defecation rate in the high emotive lesioned rats. The average defecation rate was 5.0 before the lesion was made and 1.0 after surgery. No variation was shown by the control group of emotive rats. Their average defecation rate was 4.4 before surgery and 4.9 after it. The average defecation rate showed by low emotive experimental animals before lesion was 0.7, and the average for non-emotive controls was 0.9 before surgery. The score of
504
SANTACANA, PELAEZ, TEJEI)OR
defecation recorded for both the experimental and the control group after operation dropped to 0. No defecation was registered in any animal. (See Table 1, c). The analysis of variance shows that the decrease observed in the defecation rate of the experimental emotive group after the lesion of the mammillary bodies is significant when compared with their own preoperative rate and when compared with their controls (F = 13.19; p < 0.01). No significant difference was found for the low emotive experimental group when compared with their preoperative rate. DISCUSSION This experiment shows that the lesion of the mammillary bodies produces a decrease in emotivity, which is manifested simultaneously in three parameters of the open field test: (a) the general exploration; (b) the number of times that animals explore the inner areas; and, (c) the rate of defecations recorded. (a) The increase in the general exploratory behavior after the lesion of the mammillary bodies is evident. The experimental animals showed, after operation, an exploratory activity that was approximately twice its preoperative rate. This increase in the exploratory behavior may be interpreted, like the studies of Hall, Broadhurst, etc. suggest, as due, at least in part, to a decrease in emotivity of the animals. (b) Not only general exploratory behavior, which concerns mainly exploration along the walls was increased. Exploration on the inner areas increased in a major proportion. (More than 3 times the average showed
preoperatively). This fact is interesting because this kind of exploration may be considered as characteristic of low emotive animals. In fact, the large increase of exploration in central areas is not likely to be due to tile increase of general exploratory behavior, but to a decline in emotivity after operation. (c) The large decrease in the defecation rate in tile open field shown by animals previously selected because of their rate of defecations is the most convincing proof of the effect of the lesion upon emotivity. The control emotive animals showed no change in that respect, li is a well known fact [7] that defecations in experimental situations may be considered as due to the emotional reactions of animals. In previous experiments we had also observed a decrease in the number of defecations in the test situations following the lesion of the mammillary bodies. This last part of our experiment is specially relevant in that it tends to confirm that the increase in the exploratory behavior shown in parts (a) and (b) is to be explained in terms of emotivity as well. However, it is difficult to assert that the effects of the lesion were more conspicuous in the highly emotive than in the low emotive animals. The results show that in both groups the lesion of the mammillary bodies acts in the same direction, regardless of the initial emotivity level. Alterations of the emotivity evidenced after the lesion of the mammillary bodies is not a surprising event. In fact this structure belongs to the limbic system and was considered by Papez [10] as a structure playing a role in his proposed mechanism of emotion.
REFERENCES
l. Albe-Fessard, D., F. Stutinsky and S . Libouban. Atlas St~r~otaxique du dienc6phale du rat blanc. Ed. C.N.R.S. Paris, 1966. 2. Broadhurst, P. L. and S. Levine. Behavioural consistency in strains of rats selectively bred for emotional elimination. Br. J. Psychol. 54: 121-125, 1963. 3. Broadhurst, P. L. Applications of biometrical genetics to the inheritance of behaviour. In: Experiments in Personality, edited by H. J. Eysenck. Vol. 1. New York: Praeger, 1960. 4. Broadhurst, P. L. Determinants of emotionality in the rat: I. Situational factors. Br. J. Psychol. 48: 1-12, 1957. 5. Cardo, B. Rapports entre le niveau de vigilance et le conditionnement chez t'animal. J. Psysiol. Paris. 53: 1--212, 1961. 6. Denenberg, V. H. Critical periods, stimulus input and emotional reactivity. A theory of infantile stimulation. Psychol. Rev. 71: 335--351, 1964.
7. Gray, J. A. Psychology of the Fear and Stress. World Universitary Library. London: Weidenfeld and Nicolson, 1971. 8. Hall, C. S. Emotional behavior in the rat. I. Defecation and urination as measures of individual differences in emotionality. J. comp. Psychol. 18: 385-403, 1934. 9. Hayes, K. J. Exploration and fear. Pwchol. Rep. 6: 91-93, 1960. 10. Papez, J. W. A. A proposed mechanism of emotion. Archs. Neurol. Psychiat. 38: 725-743, 1937. 11. Santacana, M. P. and R. Alvarez. Effets, chez le rat, de la 16sion des corps mamillaires sur les aspects 6motionnels des conditionnements d6fensifs. C. r. Acad. Sci. Paris. 268: 721-724, 1969. 12. Santacana, M. P. and J. Delacour. Effets, chez le rat, des t~sions de la zona incerta et des corps mamillaires sur un conditionnement d6fensifs. Neuropsychologia 6: 115-124, 1968.
Effect of the Lesion of the M ammillary Bodies on the Performance in the Open Field M. P. SANTACANA, R. ALVAREZ PELAEZ AND P. TEJEDOR
Departamento de BiofiSica, Institute Ca]al, C. S. I. C., Madrid, Spain
(Received 31 May 1972)
SANTACANA, M. P., R. ALVAREZ PELAEZ AND P. TEJEDOR. Effect of the lesion of the mammillary bodies on the performance in the open field. PHYSIOL. BEHAV. 9(4) 501-504, 1972.- Twenty rats were selected according to their emotivity: 10 highly emotive and 10 low emotive animals. In each group 5 rats were submitted to bilateral lesions of the mammiilary bodies (experimental rats) and 5 rats were submitted to a sham operation (control rats). General exploratory behavior in the open field and exploration of the central areas of the apparatus increased, while the number of boluses excreted during test periods decreased after the lesion of the mammillary bodies. No significant change appeared in the performance of the control group. From this it seems advisable to consider that lesions of the mammillary bodies produce a decrease of emotivity in the rat. MammiUarybodies
Emotivity
Open field
measure of exploratory behavior. This implies that animals which explore are not fearful. The results reported by Broadhurst [4], Denenberg [6] and Hayes [9] are in accord with this interpretation.
IN PREVIOUS experiments it was shown that a lesion of the mammillary bodies does not alter the retention of an active avoidance response [12]. It was even shown [11] that such a lesion actually enhanced the acquisition of that avoidance response in the shuttle box. Such a facilitatory effect has also been reported by Cardo [5]. A decrease in the acquisition of a C. E. R. was also found. Thus, a hypothesis was formulated that the facilitatory effect of the lesion of the mammiUary bodies might be due to some extent to a reduction in the emotivity of the animals [ 11 ]. Testing of this hypothesis is complicated by the probability that the effects of the lesion would depend upon the initial level of emotivity. Thus, in rats which are preoperatively non-emotive the effects of the lesion might be masked. That emotivity may act as a disturbing factor during performance in the shuttle box has indeed been suggested by Broadhurst [2]. This author reported that strains of low emotive (non-reactive) rats acquired an avoidance response in the shuttle box easier than strains of emotive (reactive) rats. The purpose of this paper is: (a) to confirm the decrease in emotivity after lesions of the mammillary bodies; and, (b) to test if the initial emotivity level plays any role in the effects of the lesion. The open field test was chosen for both purposes. By placing an animal in a brightly lit open field and recording the urination and defecation score of the rats, Hall [8] established that defecation and urination in a strange situation are valid measures of emotionality. Broadhurst used this test in a similar way to select strains of emotive and non-emotive animals [3]. The deambulation in the open field shown by rats has also been interpreted as a
METHOD
Animals In order to determine the effects of the lesion on emotivity, 40 male albino rats about 100 days old were used initially, to select among them a group of 10 rats with a high emotivity level (high score of defecation in the open field) and a group of 10 rats showing a low emotivity level (no defecation in the open field). The 20 animals which presented intermediate values were discarded. These two groups were divided into two subgroups of 5 highly emotive rats and two subgroups of 5 lowly emotive rats. Within each group subgroups were statistically equivalent according to their emotivity level. In each group one subgroup was submitted to lesions of the mammillary bodies (experimental animals) and the other was submitted to a sham operation, including the penetration of the electrode, but without lesion (control animals).
Apparatus and Tests An open field, hexagonal in form, was used, the side of the hexagon measured 90 cm and its walls were 40 cm high. (See Fig. 1). The areas limited by the walls and the first hexagon were named outer areas or level A. The areas inside the first 501
502
SANTACANA, PELAI'Z, I I:'~.II~I)OR
b
90cm.
'
FIG. 1. Diagram of tile open field. White areas are named outer or external areas. Striped areas are named inner or central areas.
hexagon were named inner areas or level B. The existence of the different levels in our open field and the extension occupied by each is based on the behavior of the rats in the different parts of the apparatus. It is a well known fact that rats tend to move around the wails. Then, to explore the inner areas requires lower emotivity than is required to explore level A. In fact the exploration shown by rats during the first few days was almost restricted to the external areas. Tests were carried out individually in 4 daily sessions of 5 min each. In each test the following items were recorded: (a) the total number of areas entered by animals regardless of the level entered; (b) the number of inner areas explored by animals; and, (c) the number of boluses excreted during the test periods.
Surgical Operations and Postoperative Tests Under nembutal anesthesia the experimental groups received bilateral lesions in the mammillary bodies. A cathodal current (1,2 mA) was passed through the electrode which was stereotaxicaUy placed according to the atlas of Albe-Fessard [1]. Control groups were submitted to the same surgical procedures except that no current was passed through the electrode. A period of 6 days was allowed for recovery before the beginning of postoperative tests. These were carried out in the same way as the preoperative ones. After completion of the test the animals were sacrificed with an overdose of nembutal and perfused transcardiatly with a 10% formaline solution. The brains were removed, fixed in formaline, and frozen sections were made at 100u. The sections were stained by the Nissl method. (Fig. 2 shows an example of the lesions obtained).
RESULTS
Effects of the Lesion of the Mammillary Bodies on General Exploratory Behavior Lesioned rats, whether emotive or non-emotive, showed a significant increase in their general exploratory behavior (see Table 1, a). The number of areas explored by emotive experimental rats showed an increase from an average of 37.7 before to 65.8 after the lesion of the mammillary bodies. Low emotive rats explored, on average, 38.2 areas before the lesion was made and 78.1 after it. Non-emotive controls showed a small decrease after surgery. They explored 34.1 areas before and 28.8 after it. The analysis of variance revealed that there was a significant difference between preoperative and postoperative performance in the experimental groups and when compared with their controls (F = 8.19; p < 0.01).
Effects of the Lesion on the Exploratory Behavior in the Inner Areas Again, both experimental groups, whether emotive or non-emotive, showed an increase in the exploration of the central areas. (See Table 1, b). Emotive experimental animals explored, on average, 1.2 areas before the lesion; After it the number of areas entered was 8.6. A little variation (nonsignificant) was shown by animals in the control group. They explored 1.1 inner areas before surgery and 2.2 after it. Low emotive experimental animals explored 4.8 inner areas before lesion 17.1 after it was made. Non-emotive controls explored 2.9 areas before, and 0.97 after surgery. (The difference is not significant). The analysis of variance revealed that there was a
MAMMILLARY BODIES AND OPEN FIELD TEST.
503
FIG. 2. An example of maximum lesions in the mammillary bodies.
TABLE 1
GENERAL EXPLORATORY BEHAVIOR (a)
EXPLORATION OF INNER AREAS (b)
DEFECATION RATE (c)
Preoper.
Postoper,
Preo~r.
Postoper.
Preoper.
Postoper.
Highly emotive experimental rats
37.7
65.8
1.2
8.6
5.0
1.0
Highly emotive control rats
37.9
39.0
1.0
2.2
4.4
4.9
Low emotive experimental rats
38.2
78.1
4.8
17.1
0.7
0
Low emotive control rats
34.1
28.8
2.9
1.0
0.9
0
(a) Average number of open field areas entered. (b) Average number of inner areas entered. (c) Average of defecation rate. significant difference between preoperative and postoperative performance in experimental groups when compared with their control groups (F = 8.19; p < 0.01).
Effects of the Lesion of the Mammillary Bodies Upon the Defecation Rate The
lesion of
the
mammillary
bodies produced
a
decrease in the defecation rate in the high emotive lesioned rats. The average defecation rate was 5.0 before the lesion was made and 1.0 after surgery. No variation was shown by the control group of emotive rats. Their average defecation rate was 4.4 before surgery and 4.9 after it. The average defecation rate showed by low emotive experimental animals before lesion was 0.7, and the average for non-emotive controls was 0.9 before surgery. The score of
504
SANTACANA, PELAEZ, TEJEI)OR
defecation recorded for both the experimental and the control group after operation dropped to 0. No defecation was registered in any animal. (See Table 1, c). The analysis of variance shows that the decrease observed in the defecation rate of the experimental emotive group after the lesion of the mammillary bodies is significant when compared with their own preoperative rate and when compared with their controls (F = 13.19; p < 0.01). No significant difference was found for the low emotive experimental group when compared with their preoperative rate. DISCUSSION This experiment shows that the lesion of the mammillary bodies produces a decrease in emotivity, which is manifested simultaneously in three parameters of the open field test: (a) the general exploration; (b) the number of times that animals explore the inner areas; and, (c) the rate of defecations recorded. (a) The increase in the general exploratory behavior after the lesion of the mammillary bodies is evident. The experimental animals showed, after operation, an exploratory activity that was approximately twice its preoperative rate. This increase in the exploratory behavior may be interpreted, like the studies of Hall, Broadhurst, etc. suggest, as due, at least in part, to a decrease in emotivity of the animals. (b) Not only general exploratory behavior, which concerns mainly exploration along the walls was increased. Exploration on the inner areas increased in a major proportion. (More than 3 times the average showed
preoperatively). This fact is interesting because this kind of exploration may be considered as characteristic of low emotive animals. In fact, the large increase of exploration in central areas is not likely to be due to tile increase of general exploratory behavior, but to a decline in emotivity after operation. (c) The large decrease in the defecation rate in tile open field shown by animals previously selected because of their rate of defecations is the most convincing proof of the effect of the lesion upon emotivity. The control emotive animals showed no change in that respect, li is a well known fact [7] that defecations in experimental situations may be considered as due to the emotional reactions of animals. In previous experiments we had also observed a decrease in the number of defecations in the test situations following the lesion of the mammillary bodies. This last part of our experiment is specially relevant in that it tends to confirm that the increase in the exploratory behavior shown in parts (a) and (b) is to be explained in terms of emotivity as well. However, it is difficult to assert that the effects of the lesion were more conspicuous in the highly emotive than in the low emotive animals. The results show that in both groups the lesion of the mammillary bodies acts in the same direction, regardless of the initial emotivity level. Alterations of the emotivity evidenced after the lesion of the mammillary bodies is not a surprising event. In fact this structure belongs to the limbic system and was considered by Papez [10] as a structure playing a role in his proposed mechanism of emotion.
REFERENCES
l. Albe-Fessard, D., F. Stutinsky and S . Libouban. Atlas St~r~otaxique du dienc6phale du rat blanc. Ed. C.N.R.S. Paris, 1966. 2. Broadhurst, P. L. and S. Levine. Behavioural consistency in strains of rats selectively bred for emotional elimination. Br. J. Psychol. 54: 121-125, 1963. 3. Broadhurst, P. L. Applications of biometrical genetics to the inheritance of behaviour. In: Experiments in Personality, edited by H. J. Eysenck. Vol. 1. New York: Praeger, 1960. 4. Broadhurst, P. L. Determinants of emotionality in the rat: I. Situational factors. Br. J. Psychol. 48: 1-12, 1957. 5. Cardo, B. Rapports entre le niveau de vigilance et le conditionnement chez t'animal. J. Psysiol. Paris. 53: 1--212, 1961. 6. Denenberg, V. H. Critical periods, stimulus input and emotional reactivity. A theory of infantile stimulation. Psychol. Rev. 71: 335--351, 1964.
7. Gray, J. A. Psychology of the Fear and Stress. World Universitary Library. London: Weidenfeld and Nicolson, 1971. 8. Hall, C. S. Emotional behavior in the rat. I. Defecation and urination as measures of individual differences in emotionality. J. comp. Psychol. 18: 385-403, 1934. 9. Hayes, K. J. Exploration and fear. Pwchol. Rep. 6: 91-93, 1960. 10. Papez, J. W. A. A proposed mechanism of emotion. Archs. Neurol. Psychiat. 38: 725-743, 1937. 11. Santacana, M. P. and R. Alvarez. Effets, chez le rat, de la 16sion des corps mamillaires sur les aspects 6motionnels des conditionnements d6fensifs. C. r. Acad. Sci. Paris. 268: 721-724, 1969. 12. Santacana, M. P. and J. Delacour. Effets, chez le rat, des t~sions de la zona incerta et des corps mamillaires sur un conditionnement d6fensifs. Neuropsychologia 6: 115-124, 1968.