- Email: [email protected]
Locomotor and avoidance behavior in rats with partial or total hippocampal perforant paths sections
Physiology & Behavior, Vol. 15, pp. 217--224. Pergamon Press and Brain Research Publ., 1975. Printed in the U.S.A.
Locomotor and Avoidance Behavior in Rats with Partial or Total Hippocampal Perforant Paths Sections TROND MYHRER
Institute o f Neurophysiology, University o f Oslo, Oslo, Norway
(Received 12 November 1974) MYHRER, T. Locomotor and avoidance behavior in rats with partial or total hippocampal perforant paths sections. PHYSIOL. BEHAV. 15(2) 217-224, 1975. - Bilateral partial damage to the hippocampal perforant paths in rats produced impaired two-way active avoidance performance, while the behavior in open field, passive and one-way active avoidance remained unchanged. Total disruption of the perforant path projection resulted in increased open field activity and impaired one-way active avoidance, but normal passive avoidance behavior. The results are discussed in terms of reduced sensory information to the hippocampal formation. Perforant paths
Rats
Open field
Passiveand active avoidance
Anatomical evidence has been presented to show that the entorhinal cortex in primates may receive polymodal sensory information from neocortical fields [30]. In view of the striking neuroanatomical uniformity across animal species, similar neocortical connections may be expected to exist in the rat. Since the entorhinal cortex projects massively to the fascia dentata and the hippocampus, transection of the perforant paths in rats may reduce sensory information to the hippocampus, perhaps resulting in behavioral changes similar to those which are seen after hippocampectomy. Inasmuch as large hippocampal lesions often produce increased open field activity, passive avoidance deficit, improved two-way active avoidance and impaired one-way active avoidance behavior (cf., [ 1, 9, 18]), these tests were used in the present study. Because a functional distinction between the dorsal and the ventral hippocampus has been made in several test situations (e.g., [ 11, 16, 17, 23, 24, 28 ] ) another object of this study was to investigate whether subdivisions of the perforant paths may subserve different functions. In one group of rats the perforant paths to both the dorsal and ventral hippocampus were transected, and in another group the perforant paths to only the dorsal hippocampus were divided. The present study consists of two experiments. In Experiment 1, effects of partial perforant paths lesions were tested in open field, passive avoidance, shuttle-box and jump avoidance test. In Experiment 2, effects of total perforant paths lesions were assessed in all tests but the shuttle-box.
INCREASED locomotor activity in rats has been demonstrated after selective disruption of the hippocampal CA1 output [23]. Furthermore, changes in locomotor, avoidance and alternation behavior have been seen after interruption of the hippocampal CA3 output [23]. In order to gain further information about hippocampal function it would be of interest to test behavioral effects of damage to the major hippocampal input system. The hippocampus and the fascia dentata receive their major extrinsic fiber input from the entorhinal area through the perforant path [5, 8, 20, 25, 26]. It has recently been shown in the rat that this pathway is composed of at least two distinct fiber systems, each of which has fields of termination along the whole axial extent of the hippocampus and fascia dentata. The medial perforant path arises in the medial part of the entorhinal area and terminates in the middle of the dentate molecular layer and in the deep part of the stratum lacunosum-moleculare of the hippocampal subfield CA3 [ 15]. The lateral perforant path arises from the lateral portion of the entorhinal area and projects to a superficial zone in the dentate molecular layer and to the superficial portion of the stratum lacunosum-moleculare of CA3 [14] (see Fig. 1). The perforant path is a powerful excitatory i n p u t t o the hippocampus. Electrical stimulation of regions containing medial perforant path fibers activates the granule cells of the fascia dentata [3, 21, 22]. The mossy fibers which originate from these neurons excite the pyramidal cells of CA3, which in turn activate the CA1 pyramids through the Schaffer collaterals (e.g., [2] ).
This research was supported by the Norwegian Research Council for Science and the Humanities. 217
218
MYHRER EXPERIMENT 1 METHOD
Animals Thirty-three male albino rats of the commercially supplied M/511-Wistar strain, weighing 2 5 0 - 3 0 0 g at the time of surgery, were used. They were randomly assigned to four groups: 9 animals received bilateral transection of both the dorsal and the ventral portions of the perforant paths, 8 received section of only the dorsal portion of the perforant paths, 8 received control lesions, and 8 rats served as normal controls and had only the scalp reflected. The rats were housed in groups of 3 and fed commercial rat pellets and water ad lib, except when deprived. Animals from different groups were housed together, and their group assignment was not known during testing. The rats were maintained on a 12 hr reversed day/night cycle.
Procedure Surgery. The animals were anesthetized with pentobarbital sodium (60 mg/kg) and placed in a stereotaxic instrument with skull flat. Lesions were carried out mechanically with the sharp edges of cannulas which were provided with small adjustable collars. The cannula to be used was mounted on a syringe. After a small hole was made in the skull, a cannula was inserted to the depth permitted by the placement of the collar. Care was taken to avoid disruption of the posterior cerebral artery located near the area of the parasubiculum-presubiculum and the hippocampal stem artery located in the subiculum close to the hippocampal fissure. In one group of rats, the perforant paths to both the dorsal and the ventral fascia dentata were transected (designated the DVPP group). The point of cannula insertion for this lesion was 9 mm behind the bregma and 5 mm lateral to the midline. The cannula was inserted into the brain in a position deviating 20 ° from the vertical in the sagittal plane. From this position the syringe was moved along an approximate septo-occipital axis, making a cut about 1 mm wide separating the subiculum from the entorhinal area. The depth from the surface of the skull to the tip of the cannula was 6 mm for the dorsal section and 9 mm for the ventral section. The dorso-ventral lesion was performed in two stages. The tip of the cannula used for the ventral section was somewhat curved in order to follow the curvature of the ventral hippocampus. A second group of rats (designated DPP) received only a dorsal transection as described above. Animals assigned to a lesioned control group were treated in the same way as the experimental animals, except that the cannula was lowered only 4 mm into the brain. The normal control rats were only given an incision in the scalp. Open field. A Hebb-Williams closed field maze, described elsewhere [ 19] was used in the open field testing. In short, the field consisted of a square floor (96 cm) divided in 36 equal squares. The entire apparatus was covered by a 73 cm high pyramidal-shaped enclosure with observation windows. A 40 W bulb was located in the apex of the pyramid. A start box (22 X 14 X 9 cm) was placed in one corner. The floor and the inside of the enclosure were painted white and all other components were black. The rats were tested individually for 2 rain each day for 4 successive days beginning 12 days after the operation. The animals were placed in a start box, and latency of entering the field was measured. The pattern of running was
traced on a section paper and the number of squares traversed was used as a measure of activity. The number of fecal boluses dropped in the field and the start box was recorded. Passive avoidance. A wooden box (50 × 52 X 23 cm), previously described in detail [23] was supplied with a grid floor wired to one terminal of a weak electric source. The other terminal of the current source was connected to a water dish. When a rat drank from the dish, it closed the circuit and received a shock of 0.35 mA. The rats were deprived of water for 48 hr and tested once individually from Postoperative Day 22. In order to assess their motivational level the animals were weighed immediately before testing and again after testing, 1 hr after having free access to water in their home cage. During testing, the rat was first permitted to drink from the water dish for 2 min. It was then placed in the opposite corner from the dish, which then became electrified for a test period of 20 min. The total number of shocks accepted by the rats was recorded. Shuttle-box. A hand operated apparatus which has previously been described [23], consisted of a wooden box (40 × 22 × 20 cm) provided with a buzzer (CS) located on the middle of the Plexiglas roof. The compartment grids could be independently electrified by a shocker-scrambler adjusted to 0.5 mA. No door or hurdle separated the two compartments that were painted black. The rats were individually trained in the shuttle-box in the following manner. On the first day they were permitted to explore the box for 5 min. Following this, 20 trials were given daily for 3 consecutive days. The CS was a continuously sounded buzzer. The CS-US interval was 10 sec, and both buzzer and shock stayed on until the rat escaped to the other side, but no longer than 20 sec. The intertrial interval was 35 sec. Crossings during the intertrial interval were recorded, but no shock was applied. The testing started from Postoperative Day 33. Jump avoidance. The apparatus consisted of a 30 × 30 X 28 cm black plywood box placed on a grid, which could be electrified with 0.35 mA. A plywood shelf, 6 cm wide, was located around the outside of the box 1.3 cm below the upper edge. The rats could jump out of the box, catch the raised edge with their forepaws, and pull themselves up onto the outside shelf. Training was started, on Postoperative Day 56, by allowing a rat to explore the box for 5 min. On the succeeding training trials the rat was placed on the grid and given shocks (to a maximum of 5 sec) after 10 sec had elapsed. Intertrial interval was 1 min. Training continued each day until the occurrence of one correct avoidance response. On the second day the total latency until avoidance occurred was recorded. RESULTS
Histology Upon completion of testing the brains were removed, fixed in Formalin and embedded in paraffin. The brains were sectioned horizontally at 16 u. Every twentieth section was stained with a method for combined staining of myelin sheaths [32] and cell elements (cresyl violet). Bilateral transections, approximately parallel to the Layer IV of Lorente de N6 [20] in the entorhinal area, were observed in all 9 animals assigned to the DVPP group
PERFORANT PATHS AND BEHAVIOR
219 medial entorhinal area, most notably in the medial portion of Layer I. It was somewhat difficult to identify the intended sections in the lesioned control animals. In experimental animals, no damage other than that described above was observed.
medial ento
Open Field
fibres from lateral ento ~sion
A Model I analysis of variance [13] revealed no significant treatment effects among the groups in latency, activity or defecation (Table 1). Passive Avoidance Analysis of variance showed no reliable differences in number of shocks accepted among the groups (Fig. 2).
sub Sh u ttle-box Both experimental groups displayed poor shuttle-box acquisition (Fig. 3A). The lesioned and the normal control groups did not differ and they were treated as a single control group. Analysis of variance based on the total number of avoidance responses yielded a reliable treatment effect, F(2,30) = 3.67, p<0.05. All comparisons involving two groups used two-tailed t test in the present study, Mean comparisons revealed that the DVPP group made significantly fewer avoidance responses than the combined control group (t = 2.46, p<0.05). However, the DPP group did not differ significantly from the control group (t = 1.79, p
Jump Avoidance One rat from the DVPP group which appeared unable to learn the jumping task, was discarded. The jump avoidance response was otherwise relatively quickly learned by all other animals. On Day 2 of training the avoidance response occurred within 4 trials. The DVPP group tended to be slightly later in this respect, but analysis of variance revealed no significant differences (Fig. 4). In no tests used in the present study was it possible to find any behavioral correlation between bilateral transection of both the medial and the lateral perforant paths and destruction of the medial path alone. DISCUSSION Transection of both ventral and dorsal aspects of the perforant paths resulted in a somewhat stronger impairment of shuttle-box acquisition than the section of only the dorsal part. However, open field, passive avoidance and oneway jump avoidance behavior was unaffected b y either lesion. These results are different from those which often follow hippocampectomy. Lesions of the dorsal perforant path or of the dorsal and ventral part of the perforant paths gave similar results, indicating that the two parts may have similar functions.
220
MYHRER TABLE 1 MEANS AND STANDARD ERRORS OF OPEN FIELD MEASURES BASED ON AVERAGE SCORES FOR 4 DAYS IN EXPERIMENT 1
Group
N
DVPP DPP LCont Normal
9 8 8 8
Start Box Exit Latency in Sec
56.0 36.1 45.3 24.3
14
± 36.1 +_24.6 ± 35.3 ± 17.4
Number of Squares Traversed in Entire Field
7.2 9.0 7.7 15.3
Number of Squares Traversed in Interior Field
-+ 12.5 ± 9.8 ± 9.6 ± 12.4
0.0 0.4 0.1 0.5
m
A
_
± 0.0 ± 0.7 ± 0.4 ± 0.8
u) 12
Number of Fecal Boluses
3.7 2.0 2.5 2.6
± 1.6 ± 1.5 ± 1.7 ± 2.1
DVPP (N9)
-
tel
I0 U 0
i
6
< 4
(/3
!
2
I
I
u
DVPP
(N9)
DPP (NS)
LCont (NS)
Norm (N8)
FIG. 2. Mean number of shock responses in passive avoidance test in Experiment 1. Bars represent ± S. E. M. Abbreviations for this and following figures: L Cont = lesioned control; Norm = normal.
Present results suggest a mass a c t i o n e f f e c t ; i.e., t h e g r e a t e r the n u m b e r of fibers t r a n s e c t e d , t h e m o r e p r o n o u n c e d t h e b e h a v i o r a l effects. T h e r e was also n o i n d i c a t i o n t h a t t h e m e d i a l a n d t h e lateral c o m p o n e n t s o f t h e p e r f o r a n t p a t h subserve d i f f e r e n t f u n c t i o n s . N a t u r a l l y , test s i t u a t i o n s o t h e r t h a n t h o s e used in t h e p r e s e n t e x p e r i m e n t m a y reveal d i f f e r e n t i a t i o n in t e r m s o f a n a t o m y . A s s u m i n g a possible r e d u c t i o n in s e n s o r y i n f o r m a t i o n to t h e h i p p o c a m p u s caused b y p e r f o r a n t p a t h s s e c t i o n , o n e m i g h t have e x p e c t e d m o r e general a n d e x t e n s i v e b e h a v i o r a l changes t h a n were o b s e r v e d . I n s t e a d , a r a t h e r specific effect was revealed in t h e p r e s e n t s t u d y . I m p a i r e d s h u t t l e - b o x p e r f o r m a n c e m a y also b e seen a f t e r e n t o r h i n a l lesions [ 2 7 ] . H o w e v e r , in a n o t h e r s t u d y e n t o r h i n a l lesions have b e e n r e p o r t e d t o p r o d u c e i m p r o v e d s h u t t l e - b o x a c q u i s i t i o n [31 ], a result w h i c h o t h e r w i s e follows w h e n a n u n c u e d p a r a d i g m is used [ 2 7 ] . D a m a g e to t h e e n t o r h i n a l area results in increased o p e n field activity [ 1 0 , 2 7 ] , passive a v o i d a n c e
m
i 5 -- 3 o
I I I
1 2 DAYS
I 3
FIG. 3. Mean number of active avoidance responses (A) and intertrial crossings (B) in Experiment 1. deficit [ 10, 27, 31] a n d i m p a i r e d o n e - w a y active a v o i d a n c e b e h a v i o r [ 2 7 ] . T h e lack o f effect in t h e o p e n field, passive a v o i d a n c e a n d j u m p a v o i d a n c e test in t h e p r e s e n t experim e n t m a y b e due to t h e i n c o m p l e t e t r a n s e c t i o n s o f t h e p e r f o r a n t p a t h s , since t h e latter m a k e u p t h e m a i n o u t p u t of t h e e n t o r h i n a l area.
PERFORANT PATHS AND BEHAVIOR
221 in three stages with the following depths of the cannula insertions: 4, 6 and 9 mm. The cuts, about 1.5 mm wide, were made in the frontal plane. The experimental group was designated TPP (section of the total perforant paths). Open field. Apparatus and procedure were the same as used in Experiment 1. The testing started 4 days postoperatively. Passive avoidance. Apparatus and procedure were the same as described in Experiment 1. The testing was carried out on Postoperative Day 10. Jump avoidance. Apparatus and procedure were the same as described in Experiment 1. The training started 1 1 days after surgery.
B
25O) r~
Z
l
o 15 0
LcJ
5
RESULTS
Histology
DVPP (Na)
DPP (Na)
LCont (N8)
Norm (NS)
FIG. 4. Mean and ± S. E. M. of jump avoidance latency in Experiment 1. The impaired shuttle-box acquisition seen in the present experiment is in contrast to the superior performance of hippocampectomized rats in this test situation (e.g., [1, 9, 18]). Reduced species-specific freezing response has been suggested as one major effect of extensive hippocampal damage [6]. One interpretation of impaired shuttle-box acquisition in the present study is that the lesions increase freezing behavior, since it reduces input of sensory information. An alternative explanation, like altered sensitivity to painful stimuli, is not likely to account for the findings, since the experimental animals displayed normal passive avoidance behavior. An explanation in terms of either increased or decreased fear is not in accord with the open field results, particularly the lack of differences in defecation scores. EXPERIMENT 2 Since partial damage to the perforant paths produced only some of the effects seen after entorhinal lesions (Experiment 1), Experiment 2 was undertaken to test what may follow transection of the entire perforant path projection. The tests used were open field, passive avoidance and jump avoidance. METHOD
Animals Twenty male albino rats of the M6ll-Wistar strain weighing 2 5 0 - 3 0 0 g at the time of surgery were randomly assigned to two groups: 10 rats received bilateral sections of the perforant paths and 10 served as intact controls and were given an incision in the scalp only. The subjects were treated as described for Experiment 1.
Procedure Surgery. Lesions were made as described in Experiment 1, with the following modifications: the point of cannula insertion was 8.5 mm behind bregrna. Sections were made
The brains were treated as described for Experiment 1. In 7 rats the entire perforant paths were lesioned bilaterally. In 3 animals 8 0 - 9 0 percent of the projection systems were destroyed bilaterally. The sections, being about 1.5 mm in length, were made through the angular bundle, usually near the hippocampal fissure (Fig. 5). At the level of the hippocampal flexure the subiculum was damaged bilaterally in 5 cases and unilaterally in 3 instances. In 8 animals the temporal tip of the hippocampus was destroyed bilaterally, probably due to interference with the blood supply.
Open Field The TPP rats displayed more locomotor activity than the control subjects (Table 2). The difference was a significant one (t = 2.11, p<0.05). However, no reliable differences were revealed in activity outside the perimeter, start box exit latency, or defecation scores (Table 2).
Passive Avoidance The groups did not differ significantly in the number of shocks accepted (Fig. 6).
Jump Avoidance One control rat which appeared unable to learn the jumping task, was discarded. The TPP group exhibited longer latency than the control group (Fig. 7). The difference was a reliable one (t = 2.79, p< 0.02). DISCUSSION Destruction of the entire perforant path systems resulted in increased locomotor activity in the open field and impaired jump avoidance performance. The lesions had no effect on passive avoidance learning. The results substantiate the findings of Experiment I, indicating that the larger the lesions of the perforant paths, the stronger the behavioral effects. The results of the present two experiments are in accord with the effects of entorhinal lesions. This was not unexpected, since the perforant paths represent the major entorhinal output. Damage to the perforant paths produced increased open field activity and impaired two-way and one-way active avoidance. These results are also seen after entorhinal lesions in the rat [27]. However, a passive avoidance deficit which follows entorhinal abla-
222
MYHRER
6 01
o 4 O i
O1
2
TPP (NIO)
Norm (NIO)
FIG. 6. Mean number of shock responses in passive avoidance in Experiment 2. Bars represent +_ S. E. M.
FIG. 5. Diagram of a horizontal section from the level of the hippocampal flexure showing example of lesion in Experiment 2. For abbreviations see Fig. 1. tions [10, 27, 31] was n o t revealed in t h e p r e s e n t s t u d y . This c o n t r a d i c t i o n m i g h t be due t o b o t h s i t u a t i o n a l a n d p r o c e d u r a l differences. F o r i n s t a n c e , t h e animals were p r e t r a i n e d for several days in t h e t h r e e studies r e f e r r e d to above, whereas n o p r e t r a i n i n g was given in the p r e s e n t study. E n t o r h i n a l lesions m i g h t p e r h a p s i n t e r f e r e w i t h t h e e x t i n c t i o n of well e s t a b l i s h e d responses.
T h e p r e s e n t results in the o p e n field test a n d t h e oneway active a v o i d a n c e test are similar to t h o s e seen a f t e r h i p p o c a m p e c t o m y (see I n t r o d u c t i o n o f E x p e r i m e n t 1). However, t h e r e are differences b e t w e e n t h e p r e s e n t results a n d t h o s e seen a f t e r c o m p l e t e s e c t i o n o f t h e f i m b r i a [ 2 3 ] . T h e l a t t e r lesion causes b o t h i m p r o v e d passive a v o i d a n c e a n d s h u t t l e - b o x p e r f o r m a n c e , whereas p e r f o r a n t p a t h s lesions h a d n o effect o n passive a v o i d a n c e a n d r e d u c e d s h u t t l e - b o x learning. B o t h p r o c e d u r e s b r i n g a b o u t increased o p e n field activity. F u r t h e r m o r e , t h e effects of f i m b r i a l lesions are m o r e p o w e r f u l [23] t h a n t h e effects o f perfor a n t p a t h lesions. As seen f r o m t h e I n t r o d u c t i o n of E x p e r i m e n t 1, t h e neural connection between the perforant path input and t h e f i m b r i a l CA3 o u t p u t is m a d e up b y the granule cells a n d t h e m o s s y fibers. T h e fact t h a t lesions e f f e c t i n g h i p p o -
TABLE 2 MEANS AND STANDARD ERRORS OF OPEN FIELD MEASURES BASED ON AVERAGE SCORES FOR 4 DAYS IN EXPERIMENT :2
Number of Squares Traversed in Entire Field
Number of Squares Traversed in Interior Field
Number of Fecal Boluses
Group
N
Start Box Exit Latency in Sec
TPP
10
43.0 +- 33.5
10.4 -+ 10.7
0.6 -+ 0.8
2.5 +- 1.9
Normal
10
55.0 -+ 26.5
3.1 -+ 2.3
0.4 +- 0.5
1.9 +- 1.5
P E R F O R A N T PATHS AND BEHAVIOR
223
25
Z
I
0 15 0
w
5 TPP (NIO)
Norm (N9)
FIG. 7. Mean and +- S. E. M. of jump avoidance latency in Experiment 2. campal input and output produce different behavioral results implies that fascia dentata has a highly integrative function, in which the granules may play a crucial role. Such a view is reconcilable with the findings that selective interference with the granule cells by means of an x-ray technique results in behavioral changes closely resembling those observed following hippocampectomy [4,12]. The impaired jump avoidance performance among the experimental animals gives further support to the assump-
tion of increased freezing following perforant paths section. In the jump avoidance test, the rats have to make a sudden thrust of the hind legs in order to reach the edge of the box. Consequently, a tendency to freeze will most likely delay the jump response. It has been suggested that the hippocampus forms part of a trigger mechanism involved in the guidance of m o t o r performance which can be classified as higher order or " v o l u n t a r y " in nature [7,29]. When such a trigger mechanism is disrupted, perhaps following transection of the perforant paths, a reduced ability to initiate and maintain avoidance responses in the shuttle-box and the jump avoidance test may occur. The hippocampal de-afferentation caused by perforant paths section may block sensory input, which in turn reduces the rat's ability to organize m o t o r performance in a strongly fear-provoking situation. The increased l o c o m o t o r activity in the open field may be associated with reduced sensory information also. One may hypothesize that the experimental rats tried to compensate for their lack of sensory information by exploring more in their environment. Augmented open field activity and increased freezing may appear somewhat contradictory. However, fear probably must reach a certain level, as in the avoidance tests, before freezing behavior becomes evident (for discussion of this matter see [23]). This critical level may not be reached in open field testing. The assumption of increased freezing associated with perforant paths lesions predicts no behavior deficit in passive avoidance testing, a prediction confirmed in the present study. In view of the anatomical findings of Van Hoesen e t al. [30] and of the present results, it might be suggested that the hippocampus represents an important gateway to limbic structures for sensory information of neocortical origin. There is a marked difference in open field activity between the normal animals in Experiments 1 and 2 (Tables 1 and 2). Such a tendency is frequently seen among M611Wistar rats (cf., [231), when the rats used in separate experiments come in separate shipments. However, the reasons for the differences in basic activity level between rats in various deliveries are unknown.
REFERENCES
1. Altman, J., R. L. Brunner and S. A. Bayer. The hippocampus and maturation. Behav. Biol. 8: 557-596, 1973. 2. Andersen, P., T. V. P. Bliss and K. K. Skrede. LameUar organization of hippocampal excitatory pathways. Expl Brain Res. 13: 222-238, 1971. 3. Andersen, P., B. Holmqvist and P. E. Voorhoeve. Excitatory synapses on hippocampal apical dendrites activated by entorhinal stimulation. Acta physiol, scand. 66: 461--472, 1966. 4. Bayer, S. A., R. L. Brunner, R. Hine and J. Airman. Behavioural effects of interference with the postnatal acquisition of hippocampal granule ceils. Nature new Biol. 242: 222-224, 1973. 5. Blackstad, T. W. On the termination of some afferents to the hippocampus and fascia dentata. An experimental study in the rat. Acta Anat. 35: 202-214, 1958. 6. Blanchard, R. J. and D. C. Blanchard. Effects of hippocampal lesions on the rat's reaction to a cat. J. comp. physiol. Psychol. 78: 77-82, 1972. 7. Bland, B. H. and C. H. Vanderwolf. Diencephalic and hippocampal mechanisms of motor activity in the rat: Effects of posterior hypothalamic stimulation on behavior and hippocampal slow wave activity. Brain Res. 43: 67-88, 1972.
8. Cajal, S. Rarn6n y. Histologie du Systbme Nerveux de l'Homme et des Vertdbrds. T. 2, Paris: A. Maloine, 1911. 9. Douglas, R. J. The hippocampus and behavior. Psychol. Bull. 67: 416-442, 1967. 10. Entingh, D. Perseverative responding and hyperphagia following entorhinal lesions in cats. J. comp. physiol. Psychol. 75: 50-58, 1971. 11. Grant, L. D. and L. E. Jarrard. Functional dissociation within hippocampus. Brain Res. 10: 392-401, 1968. 12. Haggbloom, S. J., R. L. Brunner and S. A. Bayer. Effects of hippocampal granule-cell agenesis on acquisition of escape from fear and one-way active-avoidance responses. J. comp. physiol. Psychol. 86: 447-457, 1974. 13. Hays, W. L. Statistics. New York: Rinehart and Winston, 1963, pp. 356-412. 14. Hjorth-Simonsen, A. Projection of the lateral part of the entorhinal area to the hippocampus and fascia dentata. J.. comp. Neurol. 146: 219-231, 1972. 15. Hjorth-Simonsen, A. and B. Jeune. Origin and termination of the hippocampal perforant path in the rat studied by silver impregnation. J. comp. Neurol. 144: 215-231, 1972.
224 16. Holdstock, T. L. Dissociation of function within the hippocampus. Physiol. Behav. 8: 6 5 9 - 6 6 7 , 1972. 17. Hughes, K. R. Dorsal and ventral hippocampus lesions and maze learning: influence of preoperative environment. Can. Z Psychol. 19: 3 2 5 - 3 3 2 , 1965. 18. Kimble, D. P. Hippocampus and internal inh~ition. Psychol. Bull. 70: 2 8 5 - 2 9 5 , 1968. 19. Kveim, O., J. Setekleiv and B. R. Kaada. Differential effects of hippocampal lesions on maze and passive avoidance learning in rats. Expl Neurol. 9: 5 9 - 7 2 , 1964. 20. Lorente de N6, R. Studies on the structure of the cerebral cortex. II. Continuation of the study of the Ammonic system. J. Psychol. Neurol., Lpz. 46: 1 1 3 - 1 7 7 , 1934. 21. L~bmo, T. Patterns of activation in a monosynaptic cortical pathway: The perforant path input to the dentate area of the hippocampal formation. Expl Brain Res. 12: 1 8 - 4 5 , 1971. 22. L~bmo, T. Potentiation of monosynpatic EPSPs in the pertorant path - dentate granule cell synapse. Expl Brain Res. 12: 4 6 - 6 3 , 1971. 23. Myhrer, T. Locomotor, avoidance and maze behavior in rats with selective disruption of hippocampal output. J. comp. physiol. Psychol., in press. 24. Nadel, L. Dorsal and ventral hippocampal lesions and behavior. Physiol. Behav. 3: 8 9 1 - 9 0 0 , 1968.
MYHRER 25. Nafstad, P. H. J. An electron microscope study on the termination of the perforant path fibres in the hippocampus and the fascia dentata. Z. Zellforsch. 76: 5 3 2 - 5 4 2 , 1967. 26. Raisman, G., W. M. Cowan and T. P. S. PoweU. The extrinsic afferent, commissural and association fibres of the hippocampus. Brain 88: 9 6 3 - 9 9 6 , 1965. 27. Ross, J. F., L. L. Walsh and S. P. Grossman. Some behavioral effects of entorhinal cortex lesions in the albino rat. J. comp. physiol. Psychol. 85: 7 0 - 8 1 , 1973. 28. Siegel, A. and J. P. Flynn. Differential effects of electrical stimulation and lesions of the hippocampus and adjacent regions upon attack behavior in cats. Brain Res. 7: 2 5 2 - 2 6 7 , 1968. 29. Vanderwolf, C. H. Limbic-diencephalic mechanisms of voluntary movement. Psychol. Rev. 78: 8 3 - 1 1 3 , 1971. 30. Van Hoesen, G. W., D. N. Pandya and N. Butters. Cortical afferents to the entorhinal cortex of the rhesus monkey. Science 175: 1 4 7 1 - t 4 7 3 , 1972. 31. Van Hoesen, G. W., L. M. Wilson, J. M. MacDougaU and J. C. Mitchell. Selective hippocampal complex deafferentation and deefferentation and avoidance behavior in rats. Physiol. Behav. 8: 8 7 3 - 8 7 9 , 1972. 32. Woelcke, M. Eine neue Methode der Markscheidenf/irbung. J. Psychol. Neurol., Lpz. 51: 199-202, 1942.
Locomotor and Avoidance Behavior in Rats with Partial or Total Hippocampal Perforant Paths Sections TROND MYHRER
Institute o f Neurophysiology, University o f Oslo, Oslo, Norway
(Received 12 November 1974) MYHRER, T. Locomotor and avoidance behavior in rats with partial or total hippocampal perforant paths sections. PHYSIOL. BEHAV. 15(2) 217-224, 1975. - Bilateral partial damage to the hippocampal perforant paths in rats produced impaired two-way active avoidance performance, while the behavior in open field, passive and one-way active avoidance remained unchanged. Total disruption of the perforant path projection resulted in increased open field activity and impaired one-way active avoidance, but normal passive avoidance behavior. The results are discussed in terms of reduced sensory information to the hippocampal formation. Perforant paths
Rats
Open field
Passiveand active avoidance
Anatomical evidence has been presented to show that the entorhinal cortex in primates may receive polymodal sensory information from neocortical fields [30]. In view of the striking neuroanatomical uniformity across animal species, similar neocortical connections may be expected to exist in the rat. Since the entorhinal cortex projects massively to the fascia dentata and the hippocampus, transection of the perforant paths in rats may reduce sensory information to the hippocampus, perhaps resulting in behavioral changes similar to those which are seen after hippocampectomy. Inasmuch as large hippocampal lesions often produce increased open field activity, passive avoidance deficit, improved two-way active avoidance and impaired one-way active avoidance behavior (cf., [ 1, 9, 18]), these tests were used in the present study. Because a functional distinction between the dorsal and the ventral hippocampus has been made in several test situations (e.g., [ 11, 16, 17, 23, 24, 28 ] ) another object of this study was to investigate whether subdivisions of the perforant paths may subserve different functions. In one group of rats the perforant paths to both the dorsal and ventral hippocampus were transected, and in another group the perforant paths to only the dorsal hippocampus were divided. The present study consists of two experiments. In Experiment 1, effects of partial perforant paths lesions were tested in open field, passive avoidance, shuttle-box and jump avoidance test. In Experiment 2, effects of total perforant paths lesions were assessed in all tests but the shuttle-box.
INCREASED locomotor activity in rats has been demonstrated after selective disruption of the hippocampal CA1 output [23]. Furthermore, changes in locomotor, avoidance and alternation behavior have been seen after interruption of the hippocampal CA3 output [23]. In order to gain further information about hippocampal function it would be of interest to test behavioral effects of damage to the major hippocampal input system. The hippocampus and the fascia dentata receive their major extrinsic fiber input from the entorhinal area through the perforant path [5, 8, 20, 25, 26]. It has recently been shown in the rat that this pathway is composed of at least two distinct fiber systems, each of which has fields of termination along the whole axial extent of the hippocampus and fascia dentata. The medial perforant path arises in the medial part of the entorhinal area and terminates in the middle of the dentate molecular layer and in the deep part of the stratum lacunosum-moleculare of the hippocampal subfield CA3 [ 15]. The lateral perforant path arises from the lateral portion of the entorhinal area and projects to a superficial zone in the dentate molecular layer and to the superficial portion of the stratum lacunosum-moleculare of CA3 [14] (see Fig. 1). The perforant path is a powerful excitatory i n p u t t o the hippocampus. Electrical stimulation of regions containing medial perforant path fibers activates the granule cells of the fascia dentata [3, 21, 22]. The mossy fibers which originate from these neurons excite the pyramidal cells of CA3, which in turn activate the CA1 pyramids through the Schaffer collaterals (e.g., [2] ).
This research was supported by the Norwegian Research Council for Science and the Humanities. 217
218
MYHRER EXPERIMENT 1 METHOD
Animals Thirty-three male albino rats of the commercially supplied M/511-Wistar strain, weighing 2 5 0 - 3 0 0 g at the time of surgery, were used. They were randomly assigned to four groups: 9 animals received bilateral transection of both the dorsal and the ventral portions of the perforant paths, 8 received section of only the dorsal portion of the perforant paths, 8 received control lesions, and 8 rats served as normal controls and had only the scalp reflected. The rats were housed in groups of 3 and fed commercial rat pellets and water ad lib, except when deprived. Animals from different groups were housed together, and their group assignment was not known during testing. The rats were maintained on a 12 hr reversed day/night cycle.
Procedure Surgery. The animals were anesthetized with pentobarbital sodium (60 mg/kg) and placed in a stereotaxic instrument with skull flat. Lesions were carried out mechanically with the sharp edges of cannulas which were provided with small adjustable collars. The cannula to be used was mounted on a syringe. After a small hole was made in the skull, a cannula was inserted to the depth permitted by the placement of the collar. Care was taken to avoid disruption of the posterior cerebral artery located near the area of the parasubiculum-presubiculum and the hippocampal stem artery located in the subiculum close to the hippocampal fissure. In one group of rats, the perforant paths to both the dorsal and the ventral fascia dentata were transected (designated the DVPP group). The point of cannula insertion for this lesion was 9 mm behind the bregma and 5 mm lateral to the midline. The cannula was inserted into the brain in a position deviating 20 ° from the vertical in the sagittal plane. From this position the syringe was moved along an approximate septo-occipital axis, making a cut about 1 mm wide separating the subiculum from the entorhinal area. The depth from the surface of the skull to the tip of the cannula was 6 mm for the dorsal section and 9 mm for the ventral section. The dorso-ventral lesion was performed in two stages. The tip of the cannula used for the ventral section was somewhat curved in order to follow the curvature of the ventral hippocampus. A second group of rats (designated DPP) received only a dorsal transection as described above. Animals assigned to a lesioned control group were treated in the same way as the experimental animals, except that the cannula was lowered only 4 mm into the brain. The normal control rats were only given an incision in the scalp. Open field. A Hebb-Williams closed field maze, described elsewhere [ 19] was used in the open field testing. In short, the field consisted of a square floor (96 cm) divided in 36 equal squares. The entire apparatus was covered by a 73 cm high pyramidal-shaped enclosure with observation windows. A 40 W bulb was located in the apex of the pyramid. A start box (22 X 14 X 9 cm) was placed in one corner. The floor and the inside of the enclosure were painted white and all other components were black. The rats were tested individually for 2 rain each day for 4 successive days beginning 12 days after the operation. The animals were placed in a start box, and latency of entering the field was measured. The pattern of running was
traced on a section paper and the number of squares traversed was used as a measure of activity. The number of fecal boluses dropped in the field and the start box was recorded. Passive avoidance. A wooden box (50 × 52 X 23 cm), previously described in detail [23] was supplied with a grid floor wired to one terminal of a weak electric source. The other terminal of the current source was connected to a water dish. When a rat drank from the dish, it closed the circuit and received a shock of 0.35 mA. The rats were deprived of water for 48 hr and tested once individually from Postoperative Day 22. In order to assess their motivational level the animals were weighed immediately before testing and again after testing, 1 hr after having free access to water in their home cage. During testing, the rat was first permitted to drink from the water dish for 2 min. It was then placed in the opposite corner from the dish, which then became electrified for a test period of 20 min. The total number of shocks accepted by the rats was recorded. Shuttle-box. A hand operated apparatus which has previously been described [23], consisted of a wooden box (40 × 22 × 20 cm) provided with a buzzer (CS) located on the middle of the Plexiglas roof. The compartment grids could be independently electrified by a shocker-scrambler adjusted to 0.5 mA. No door or hurdle separated the two compartments that were painted black. The rats were individually trained in the shuttle-box in the following manner. On the first day they were permitted to explore the box for 5 min. Following this, 20 trials were given daily for 3 consecutive days. The CS was a continuously sounded buzzer. The CS-US interval was 10 sec, and both buzzer and shock stayed on until the rat escaped to the other side, but no longer than 20 sec. The intertrial interval was 35 sec. Crossings during the intertrial interval were recorded, but no shock was applied. The testing started from Postoperative Day 33. Jump avoidance. The apparatus consisted of a 30 × 30 X 28 cm black plywood box placed on a grid, which could be electrified with 0.35 mA. A plywood shelf, 6 cm wide, was located around the outside of the box 1.3 cm below the upper edge. The rats could jump out of the box, catch the raised edge with their forepaws, and pull themselves up onto the outside shelf. Training was started, on Postoperative Day 56, by allowing a rat to explore the box for 5 min. On the succeeding training trials the rat was placed on the grid and given shocks (to a maximum of 5 sec) after 10 sec had elapsed. Intertrial interval was 1 min. Training continued each day until the occurrence of one correct avoidance response. On the second day the total latency until avoidance occurred was recorded. RESULTS
Histology Upon completion of testing the brains were removed, fixed in Formalin and embedded in paraffin. The brains were sectioned horizontally at 16 u. Every twentieth section was stained with a method for combined staining of myelin sheaths [32] and cell elements (cresyl violet). Bilateral transections, approximately parallel to the Layer IV of Lorente de N6 [20] in the entorhinal area, were observed in all 9 animals assigned to the DVPP group
PERFORANT PATHS AND BEHAVIOR
219 medial entorhinal area, most notably in the medial portion of Layer I. It was somewhat difficult to identify the intended sections in the lesioned control animals. In experimental animals, no damage other than that described above was observed.
medial ento
Open Field
fibres from lateral ento ~sion
A Model I analysis of variance [13] revealed no significant treatment effects among the groups in latency, activity or defecation (Table 1). Passive Avoidance Analysis of variance showed no reliable differences in number of shocks accepted among the groups (Fig. 2).
sub Sh u ttle-box Both experimental groups displayed poor shuttle-box acquisition (Fig. 3A). The lesioned and the normal control groups did not differ and they were treated as a single control group. Analysis of variance based on the total number of avoidance responses yielded a reliable treatment effect, F(2,30) = 3.67, p<0.05. All comparisons involving two groups used two-tailed t test in the present study, Mean comparisons revealed that the DVPP group made significantly fewer avoidance responses than the combined control group (t = 2.46, p<0.05). However, the DPP group did not differ significantly from the control group (t = 1.79, p
Jump Avoidance One rat from the DVPP group which appeared unable to learn the jumping task, was discarded. The jump avoidance response was otherwise relatively quickly learned by all other animals. On Day 2 of training the avoidance response occurred within 4 trials. The DVPP group tended to be slightly later in this respect, but analysis of variance revealed no significant differences (Fig. 4). In no tests used in the present study was it possible to find any behavioral correlation between bilateral transection of both the medial and the lateral perforant paths and destruction of the medial path alone. DISCUSSION Transection of both ventral and dorsal aspects of the perforant paths resulted in a somewhat stronger impairment of shuttle-box acquisition than the section of only the dorsal part. However, open field, passive avoidance and oneway jump avoidance behavior was unaffected b y either lesion. These results are different from those which often follow hippocampectomy. Lesions of the dorsal perforant path or of the dorsal and ventral part of the perforant paths gave similar results, indicating that the two parts may have similar functions.
220
MYHRER TABLE 1 MEANS AND STANDARD ERRORS OF OPEN FIELD MEASURES BASED ON AVERAGE SCORES FOR 4 DAYS IN EXPERIMENT 1
Group
N
DVPP DPP LCont Normal
9 8 8 8
Start Box Exit Latency in Sec
56.0 36.1 45.3 24.3
14
± 36.1 +_24.6 ± 35.3 ± 17.4
Number of Squares Traversed in Entire Field
7.2 9.0 7.7 15.3
Number of Squares Traversed in Interior Field
-+ 12.5 ± 9.8 ± 9.6 ± 12.4
0.0 0.4 0.1 0.5
m
A
_
± 0.0 ± 0.7 ± 0.4 ± 0.8
u) 12
Number of Fecal Boluses
3.7 2.0 2.5 2.6
± 1.6 ± 1.5 ± 1.7 ± 2.1
DVPP (N9)
-
tel
I0 U 0
i
6
< 4
(/3
!
2
I
I
u
DVPP
(N9)
DPP (NS)
LCont (NS)
Norm (N8)
FIG. 2. Mean number of shock responses in passive avoidance test in Experiment 1. Bars represent ± S. E. M. Abbreviations for this and following figures: L Cont = lesioned control; Norm = normal.
Present results suggest a mass a c t i o n e f f e c t ; i.e., t h e g r e a t e r the n u m b e r of fibers t r a n s e c t e d , t h e m o r e p r o n o u n c e d t h e b e h a v i o r a l effects. T h e r e was also n o i n d i c a t i o n t h a t t h e m e d i a l a n d t h e lateral c o m p o n e n t s o f t h e p e r f o r a n t p a t h subserve d i f f e r e n t f u n c t i o n s . N a t u r a l l y , test s i t u a t i o n s o t h e r t h a n t h o s e used in t h e p r e s e n t e x p e r i m e n t m a y reveal d i f f e r e n t i a t i o n in t e r m s o f a n a t o m y . A s s u m i n g a possible r e d u c t i o n in s e n s o r y i n f o r m a t i o n to t h e h i p p o c a m p u s caused b y p e r f o r a n t p a t h s s e c t i o n , o n e m i g h t have e x p e c t e d m o r e general a n d e x t e n s i v e b e h a v i o r a l changes t h a n were o b s e r v e d . I n s t e a d , a r a t h e r specific effect was revealed in t h e p r e s e n t s t u d y . I m p a i r e d s h u t t l e - b o x p e r f o r m a n c e m a y also b e seen a f t e r e n t o r h i n a l lesions [ 2 7 ] . H o w e v e r , in a n o t h e r s t u d y e n t o r h i n a l lesions have b e e n r e p o r t e d t o p r o d u c e i m p r o v e d s h u t t l e - b o x a c q u i s i t i o n [31 ], a result w h i c h o t h e r w i s e follows w h e n a n u n c u e d p a r a d i g m is used [ 2 7 ] . D a m a g e to t h e e n t o r h i n a l area results in increased o p e n field activity [ 1 0 , 2 7 ] , passive a v o i d a n c e
m
i 5 -- 3 o
I I I
1 2 DAYS
I 3
FIG. 3. Mean number of active avoidance responses (A) and intertrial crossings (B) in Experiment 1. deficit [ 10, 27, 31] a n d i m p a i r e d o n e - w a y active a v o i d a n c e b e h a v i o r [ 2 7 ] . T h e lack o f effect in t h e o p e n field, passive a v o i d a n c e a n d j u m p a v o i d a n c e test in t h e p r e s e n t experim e n t m a y b e due to t h e i n c o m p l e t e t r a n s e c t i o n s o f t h e p e r f o r a n t p a t h s , since t h e latter m a k e u p t h e m a i n o u t p u t of t h e e n t o r h i n a l area.
PERFORANT PATHS AND BEHAVIOR
221 in three stages with the following depths of the cannula insertions: 4, 6 and 9 mm. The cuts, about 1.5 mm wide, were made in the frontal plane. The experimental group was designated TPP (section of the total perforant paths). Open field. Apparatus and procedure were the same as used in Experiment 1. The testing started 4 days postoperatively. Passive avoidance. Apparatus and procedure were the same as described in Experiment 1. The testing was carried out on Postoperative Day 10. Jump avoidance. Apparatus and procedure were the same as described in Experiment 1. The training started 1 1 days after surgery.
B
25O) r~
Z
l
o 15 0
LcJ
5
RESULTS
Histology
DVPP (Na)
DPP (Na)
LCont (N8)
Norm (NS)
FIG. 4. Mean and ± S. E. M. of jump avoidance latency in Experiment 1. The impaired shuttle-box acquisition seen in the present experiment is in contrast to the superior performance of hippocampectomized rats in this test situation (e.g., [1, 9, 18]). Reduced species-specific freezing response has been suggested as one major effect of extensive hippocampal damage [6]. One interpretation of impaired shuttle-box acquisition in the present study is that the lesions increase freezing behavior, since it reduces input of sensory information. An alternative explanation, like altered sensitivity to painful stimuli, is not likely to account for the findings, since the experimental animals displayed normal passive avoidance behavior. An explanation in terms of either increased or decreased fear is not in accord with the open field results, particularly the lack of differences in defecation scores. EXPERIMENT 2 Since partial damage to the perforant paths produced only some of the effects seen after entorhinal lesions (Experiment 1), Experiment 2 was undertaken to test what may follow transection of the entire perforant path projection. The tests used were open field, passive avoidance and jump avoidance. METHOD
Animals Twenty male albino rats of the M6ll-Wistar strain weighing 2 5 0 - 3 0 0 g at the time of surgery were randomly assigned to two groups: 10 rats received bilateral sections of the perforant paths and 10 served as intact controls and were given an incision in the scalp only. The subjects were treated as described for Experiment 1.
Procedure Surgery. Lesions were made as described in Experiment 1, with the following modifications: the point of cannula insertion was 8.5 mm behind bregrna. Sections were made
The brains were treated as described for Experiment 1. In 7 rats the entire perforant paths were lesioned bilaterally. In 3 animals 8 0 - 9 0 percent of the projection systems were destroyed bilaterally. The sections, being about 1.5 mm in length, were made through the angular bundle, usually near the hippocampal fissure (Fig. 5). At the level of the hippocampal flexure the subiculum was damaged bilaterally in 5 cases and unilaterally in 3 instances. In 8 animals the temporal tip of the hippocampus was destroyed bilaterally, probably due to interference with the blood supply.
Open Field The TPP rats displayed more locomotor activity than the control subjects (Table 2). The difference was a significant one (t = 2.11, p<0.05). However, no reliable differences were revealed in activity outside the perimeter, start box exit latency, or defecation scores (Table 2).
Passive Avoidance The groups did not differ significantly in the number of shocks accepted (Fig. 6).
Jump Avoidance One control rat which appeared unable to learn the jumping task, was discarded. The TPP group exhibited longer latency than the control group (Fig. 7). The difference was a reliable one (t = 2.79, p< 0.02). DISCUSSION Destruction of the entire perforant path systems resulted in increased locomotor activity in the open field and impaired jump avoidance performance. The lesions had no effect on passive avoidance learning. The results substantiate the findings of Experiment I, indicating that the larger the lesions of the perforant paths, the stronger the behavioral effects. The results of the present two experiments are in accord with the effects of entorhinal lesions. This was not unexpected, since the perforant paths represent the major entorhinal output. Damage to the perforant paths produced increased open field activity and impaired two-way and one-way active avoidance. These results are also seen after entorhinal lesions in the rat [27]. However, a passive avoidance deficit which follows entorhinal abla-
222
MYHRER
6 01
o 4 O i
O1
2
TPP (NIO)
Norm (NIO)
FIG. 6. Mean number of shock responses in passive avoidance in Experiment 2. Bars represent +_ S. E. M.
FIG. 5. Diagram of a horizontal section from the level of the hippocampal flexure showing example of lesion in Experiment 2. For abbreviations see Fig. 1. tions [10, 27, 31] was n o t revealed in t h e p r e s e n t s t u d y . This c o n t r a d i c t i o n m i g h t be due t o b o t h s i t u a t i o n a l a n d p r o c e d u r a l differences. F o r i n s t a n c e , t h e animals were p r e t r a i n e d for several days in t h e t h r e e studies r e f e r r e d to above, whereas n o p r e t r a i n i n g was given in the p r e s e n t study. E n t o r h i n a l lesions m i g h t p e r h a p s i n t e r f e r e w i t h t h e e x t i n c t i o n of well e s t a b l i s h e d responses.
T h e p r e s e n t results in the o p e n field test a n d t h e oneway active a v o i d a n c e test are similar to t h o s e seen a f t e r h i p p o c a m p e c t o m y (see I n t r o d u c t i o n o f E x p e r i m e n t 1). However, t h e r e are differences b e t w e e n t h e p r e s e n t results a n d t h o s e seen a f t e r c o m p l e t e s e c t i o n o f t h e f i m b r i a [ 2 3 ] . T h e l a t t e r lesion causes b o t h i m p r o v e d passive a v o i d a n c e a n d s h u t t l e - b o x p e r f o r m a n c e , whereas p e r f o r a n t p a t h s lesions h a d n o effect o n passive a v o i d a n c e a n d r e d u c e d s h u t t l e - b o x learning. B o t h p r o c e d u r e s b r i n g a b o u t increased o p e n field activity. F u r t h e r m o r e , t h e effects of f i m b r i a l lesions are m o r e p o w e r f u l [23] t h a n t h e effects o f perfor a n t p a t h lesions. As seen f r o m t h e I n t r o d u c t i o n of E x p e r i m e n t 1, t h e neural connection between the perforant path input and t h e f i m b r i a l CA3 o u t p u t is m a d e up b y the granule cells a n d t h e m o s s y fibers. T h e fact t h a t lesions e f f e c t i n g h i p p o -
TABLE 2 MEANS AND STANDARD ERRORS OF OPEN FIELD MEASURES BASED ON AVERAGE SCORES FOR 4 DAYS IN EXPERIMENT :2
Number of Squares Traversed in Entire Field
Number of Squares Traversed in Interior Field
Number of Fecal Boluses
Group
N
Start Box Exit Latency in Sec
TPP
10
43.0 +- 33.5
10.4 -+ 10.7
0.6 -+ 0.8
2.5 +- 1.9
Normal
10
55.0 -+ 26.5
3.1 -+ 2.3
0.4 +- 0.5
1.9 +- 1.5
P E R F O R A N T PATHS AND BEHAVIOR
223
25
Z
I
0 15 0
w
5 TPP (NIO)
Norm (N9)
FIG. 7. Mean and +- S. E. M. of jump avoidance latency in Experiment 2. campal input and output produce different behavioral results implies that fascia dentata has a highly integrative function, in which the granules may play a crucial role. Such a view is reconcilable with the findings that selective interference with the granule cells by means of an x-ray technique results in behavioral changes closely resembling those observed following hippocampectomy [4,12]. The impaired jump avoidance performance among the experimental animals gives further support to the assump-
tion of increased freezing following perforant paths section. In the jump avoidance test, the rats have to make a sudden thrust of the hind legs in order to reach the edge of the box. Consequently, a tendency to freeze will most likely delay the jump response. It has been suggested that the hippocampus forms part of a trigger mechanism involved in the guidance of m o t o r performance which can be classified as higher order or " v o l u n t a r y " in nature [7,29]. When such a trigger mechanism is disrupted, perhaps following transection of the perforant paths, a reduced ability to initiate and maintain avoidance responses in the shuttle-box and the jump avoidance test may occur. The hippocampal de-afferentation caused by perforant paths section may block sensory input, which in turn reduces the rat's ability to organize m o t o r performance in a strongly fear-provoking situation. The increased l o c o m o t o r activity in the open field may be associated with reduced sensory information also. One may hypothesize that the experimental rats tried to compensate for their lack of sensory information by exploring more in their environment. Augmented open field activity and increased freezing may appear somewhat contradictory. However, fear probably must reach a certain level, as in the avoidance tests, before freezing behavior becomes evident (for discussion of this matter see [23]). This critical level may not be reached in open field testing. The assumption of increased freezing associated with perforant paths lesions predicts no behavior deficit in passive avoidance testing, a prediction confirmed in the present study. In view of the anatomical findings of Van Hoesen e t al. [30] and of the present results, it might be suggested that the hippocampus represents an important gateway to limbic structures for sensory information of neocortical origin. There is a marked difference in open field activity between the normal animals in Experiments 1 and 2 (Tables 1 and 2). Such a tendency is frequently seen among M611Wistar rats (cf., [231), when the rats used in separate experiments come in separate shipments. However, the reasons for the differences in basic activity level between rats in various deliveries are unknown.
REFERENCES
1. Altman, J., R. L. Brunner and S. A. Bayer. The hippocampus and maturation. Behav. Biol. 8: 557-596, 1973. 2. Andersen, P., T. V. P. Bliss and K. K. Skrede. LameUar organization of hippocampal excitatory pathways. Expl Brain Res. 13: 222-238, 1971. 3. Andersen, P., B. Holmqvist and P. E. Voorhoeve. Excitatory synapses on hippocampal apical dendrites activated by entorhinal stimulation. Acta physiol, scand. 66: 461--472, 1966. 4. Bayer, S. A., R. L. Brunner, R. Hine and J. Airman. Behavioural effects of interference with the postnatal acquisition of hippocampal granule ceils. Nature new Biol. 242: 222-224, 1973. 5. Blackstad, T. W. On the termination of some afferents to the hippocampus and fascia dentata. An experimental study in the rat. Acta Anat. 35: 202-214, 1958. 6. Blanchard, R. J. and D. C. Blanchard. Effects of hippocampal lesions on the rat's reaction to a cat. J. comp. physiol. Psychol. 78: 77-82, 1972. 7. Bland, B. H. and C. H. Vanderwolf. Diencephalic and hippocampal mechanisms of motor activity in the rat: Effects of posterior hypothalamic stimulation on behavior and hippocampal slow wave activity. Brain Res. 43: 67-88, 1972.
8. Cajal, S. Rarn6n y. Histologie du Systbme Nerveux de l'Homme et des Vertdbrds. T. 2, Paris: A. Maloine, 1911. 9. Douglas, R. J. The hippocampus and behavior. Psychol. Bull. 67: 416-442, 1967. 10. Entingh, D. Perseverative responding and hyperphagia following entorhinal lesions in cats. J. comp. physiol. Psychol. 75: 50-58, 1971. 11. Grant, L. D. and L. E. Jarrard. Functional dissociation within hippocampus. Brain Res. 10: 392-401, 1968. 12. Haggbloom, S. J., R. L. Brunner and S. A. Bayer. Effects of hippocampal granule-cell agenesis on acquisition of escape from fear and one-way active-avoidance responses. J. comp. physiol. Psychol. 86: 447-457, 1974. 13. Hays, W. L. Statistics. New York: Rinehart and Winston, 1963, pp. 356-412. 14. Hjorth-Simonsen, A. Projection of the lateral part of the entorhinal area to the hippocampus and fascia dentata. J.. comp. Neurol. 146: 219-231, 1972. 15. Hjorth-Simonsen, A. and B. Jeune. Origin and termination of the hippocampal perforant path in the rat studied by silver impregnation. J. comp. Neurol. 144: 215-231, 1972.
224 16. Holdstock, T. L. Dissociation of function within the hippocampus. Physiol. Behav. 8: 6 5 9 - 6 6 7 , 1972. 17. Hughes, K. R. Dorsal and ventral hippocampus lesions and maze learning: influence of preoperative environment. Can. Z Psychol. 19: 3 2 5 - 3 3 2 , 1965. 18. Kimble, D. P. Hippocampus and internal inh~ition. Psychol. Bull. 70: 2 8 5 - 2 9 5 , 1968. 19. Kveim, O., J. Setekleiv and B. R. Kaada. Differential effects of hippocampal lesions on maze and passive avoidance learning in rats. Expl Neurol. 9: 5 9 - 7 2 , 1964. 20. Lorente de N6, R. Studies on the structure of the cerebral cortex. II. Continuation of the study of the Ammonic system. J. Psychol. Neurol., Lpz. 46: 1 1 3 - 1 7 7 , 1934. 21. L~bmo, T. Patterns of activation in a monosynaptic cortical pathway: The perforant path input to the dentate area of the hippocampal formation. Expl Brain Res. 12: 1 8 - 4 5 , 1971. 22. L~bmo, T. Potentiation of monosynpatic EPSPs in the pertorant path - dentate granule cell synapse. Expl Brain Res. 12: 4 6 - 6 3 , 1971. 23. Myhrer, T. Locomotor, avoidance and maze behavior in rats with selective disruption of hippocampal output. J. comp. physiol. Psychol., in press. 24. Nadel, L. Dorsal and ventral hippocampal lesions and behavior. Physiol. Behav. 3: 8 9 1 - 9 0 0 , 1968.
MYHRER 25. Nafstad, P. H. J. An electron microscope study on the termination of the perforant path fibres in the hippocampus and the fascia dentata. Z. Zellforsch. 76: 5 3 2 - 5 4 2 , 1967. 26. Raisman, G., W. M. Cowan and T. P. S. PoweU. The extrinsic afferent, commissural and association fibres of the hippocampus. Brain 88: 9 6 3 - 9 9 6 , 1965. 27. Ross, J. F., L. L. Walsh and S. P. Grossman. Some behavioral effects of entorhinal cortex lesions in the albino rat. J. comp. physiol. Psychol. 85: 7 0 - 8 1 , 1973. 28. Siegel, A. and J. P. Flynn. Differential effects of electrical stimulation and lesions of the hippocampus and adjacent regions upon attack behavior in cats. Brain Res. 7: 2 5 2 - 2 6 7 , 1968. 29. Vanderwolf, C. H. Limbic-diencephalic mechanisms of voluntary movement. Psychol. Rev. 78: 8 3 - 1 1 3 , 1971. 30. Van Hoesen, G. W., D. N. Pandya and N. Butters. Cortical afferents to the entorhinal cortex of the rhesus monkey. Science 175: 1 4 7 1 - t 4 7 3 , 1972. 31. Van Hoesen, G. W., L. M. Wilson, J. M. MacDougaU and J. C. Mitchell. Selective hippocampal complex deafferentation and deefferentation and avoidance behavior in rats. Physiol. Behav. 8: 8 7 3 - 8 7 9 , 1972. 32. Woelcke, M. Eine neue Methode der Markscheidenf/irbung. J. Psychol. Neurol., Lpz. 51: 199-202, 1942.