Effects of hippocampal lesion on cardiovascular, adrenocortical and behavioral response patterns in mice

Physiology & Behavior, Vol. 18, pp. 1075-1083. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.

Effects of Hippocampal Lesion on Cardiovascular, Adrenocortical and Behavioral Response Patterns in Mice D A N I E L L. E L Y

Department o f Biology, The University o f Akron, Akron, OH 44325 E R N E S T G. G R E E N E

Department o f Psychology, University o f Southern California, Los Angeles, CA 90007 J A M E S P. H E N R Y

Department o f Physiology, University o f Southern California, Los Angeles, CA 90007 (Received 6 January 1977) ELY, D. L., E. G. GREENE AND J. P. HENRY. Effects of hippoeampal lesion on cardiovascular, adrenocortical and behavioral response patterns in mice. PHYSIOL. BEHAV. 18(6) 1075-1083, 1977. - It was found that animals with a hippocampal lesion developed high blood pressure, low heart rates, and high plasma corticosterone during social interaction in a territorial situation. However, hippocampal animals kept in a nonterritorial situation with minimal social interaction did not show significant cardiovascular or plasma corticosterone changes as compared to unoperated controls or cortically lesioned controls. The socially interacting hippocampal animals failed to develop a social hierarchy and did not respond aggressively to an intruder placed in the colony. The data suggests that the hippocampus is involved in the maintenance of social behavior which in turn may modulate autonomic nervous system activity. Hippocampal lesion Blood pressure Corticosterone Social hierarchy Autonomic nervous system

Social behavior

n o n s t r e s s f u l c o n d i t i o n s c o r t i c o s t e r o n e release was increased in the r a b b i t . Pfaff, Silva a n d Weiss [30] s h o w e d t h a t c o r t i c o s t e r o n e decreased h i p p o c a m p a l u n i t activity in the rat, a n d A C T H increased it. T o g e t h e r the evidence is suggestive t h a t t h e h i p p o c a m p u s is involved in cardiovascular and e n d o c r i n e responses w h e n the organism is in an aroused c o n d i t i o n . T h e r e f o r e , the aim of the p r e s e n t s t u d y was to m e a s u r e a u t o n o m i c n e r v o u s s y s t e m f u n c t i o n and a d r e n o c o r t i c a l f u n c t i o n in h i p p o c a m p a l animals u n d e r various social situations.

T H E R O L E of the h i p p o c a m p u s in a u t o n o m i c n e r v o u s system f u n c t i o n a n d its specific i n f l u e n c e o n c a r d i o v a s c u l a r a n d e n d o c r i n e s y s t e m s is n o t well defined. N u m e r o u s investigators have failed to find a n y e f f e c t of h i p p o c a m p a l s t i m u l a t i o n o n r e s p i r a t i o n or b l o o d pressure in t h e cat, dog, m o n k e y a n d r a b b i t [19, 20, 22, 29, 3 3 ] . H o w e v e r , V o t a w a n d L a u e r [34] f o u n d t h a t s t i m u l a t i o n of t h e h i p p o c a m p u s in the a n t e r i o r p o r t i o n s of t h e t e m p o r a l lobe o f m o n k e y r e d u c e d r e s p i r a t i o n a n d h e a r t rate w h i c h was later f o l l o w e d b y increases in b o t h measures. Torii arxd K a w a m u r a [ 3 2 ] f o u n d t h a t s t i m u l a t i o n of t h e a m y g d a l a , septal region, a n d p r e o p t i c area usually caused a fall in b l o o d pressure c o n c o m i t a n t with the a p p e a r a n c e of fast waves in t h e hippocampus, whereas posterior hypothalamic stimulation resulted in a rise in b l o o d pressure c o n c o m i t a n t w i t h h i p p o c a m p a l slow waves. Several studies have suggested h i p p o c a m p a l i n v o l v e m e n t in a d r e n o c o r t i c a l f u n c t i o n [25, 26, 3 0 ] . Moberg et al. [25] f o u n d a r e d u c e d c o r t i c o s t e r o n e circadian r h y t h m in fornix lesioned rats. K a w a k a m i et al. [ 21 ] s h o w e d t h a t u n d e r stressful c o n d i t i o n s s t i m u l a t i o n of the h i p p o c a m p u s i n h i b i t e d c o r t i c o s t e r o n e levels a n d u n d e r

METHOD

Animals All animals lived u n d e r the same level of i l l u m i n a t i o n and light-dark cycle (light, 0 6 0 0 - 1 8 0 0 h r ; dark, 1800-0600hr) and at a c o n s t a n t r o o m t e m p e r a t u r e of 6 8 - 7 2 F. All were reared w i t h t h e i r m o t h e r s u n t i l 3 weeks of age a n d t h e n w e a n e d , sexed a n d k e p t t o g e t h e r as siblings

1This research was supported by NIMH Grants: MH 19441, 17706 and 26155. The authors would like to acknowledge the technical assistance of Patricia Stephens for preparation of the figures. 1075

1076 in standard laboratory cages (23 x 11 x 11 cm) for 13 weeks. The thirty CBA/J males were then assigned to one of 6 groups according to surgical treatment and environmental treatment condition (5 males per group). Three surgical conditions existed which were: (1) unoperated controls (UC), (2) cortical lesioned controls (CL), and (3) hippocampal lesion (HL). Animals in each of the surgical conditions were then assigned to one of two environmental treatments: (1) a colony condition which enhanced territorial formation (CC), and included 8 females in addition to 5 males who socially interacted in a population cage (details under Behavioral Monitoring); (2) standard laboratory conditions (LC), which minimized territorial formation with 5 males housed together in a single standard laboratory cage. The animals remained in one of the two environmental conditions for a period of 81 days. Student's t-tests were used to determine statistical significance between groups.

Surgery All operations were performed in one stage using standard sterile surgical technique. A Gomco aspiration pump was used to produce the lesion with the aid of a Bausch and Lomb dissection-scope. The procedure followed that previously used by the authors [9]. The mice were allowed to recover for two weeks following surgery before being placed into one of the two environmental conditions.

ELY, GREENE AND HENRY duration we found physical appearance one of the best indicators of social position [9]. Aggressive behavior was measured between each resident male and an intruder male who were both placed in the food chamber for 20 min. The following measurements were made: latency to the first attack and the number of attacks (physical contact with biting by aggressor); number of escape attempts by the intruder; and successful escapes (retreat to area high upon the food basket which stopped fighting). Also each of the three groups of colony males was behaviorally tested in the intruder role by placing them into other colonies. The same indices of aggressive behavior were recorded with the exception that only 10 min was used for measurement instead of 20 rain to prevent physical damage to the experimental animals. All of the behavioral tests were performed between days 7 0 8 0 .

Physiological Measurement Systolic blood pressure was measured weekly during days 1 - 2 8 by tail plethysmography as previously described [14]. Heart rates were measured from the strip chart recordings of the tail pulsations. Also during the first month plasma corticosterone was fluorometrically assayed weekly at 1 2 0 0 - 1 3 0 0 hr. using a microtechnique [13]. Blood pressure and corticosterone measurements were separated by several days. Upon termination of the experiment, the preputial gland, adrenal gland and ventricles of the heart were removed, cleaned, and weighed to the nearest 0.1 mg on a torsion balance.

His t o logy At the end of the experiment, the hippocampal lesioned and cortical lesioned control animals were sacrificed with Nembutal, and perfused with a cold solution of 1% D M S O - 1 0 % glycerol. The brains were then removed, frozen and sectioned in an IEC cryostat to verify lesion placement. Slides were taken every 100u, beginning at the level of the fornix. The sections were fixed in 4% Formalin for a minimum of one day, then were washed and dehydrated through a sequence of ethyl alcohol and xylene. The sections were then rehydrated, stained in 0.5% cresyl violet, refixed in acetic Formalin, then were dehydrated in three charges of 95% ethanol, 100% ethanol, and xylene. The secretions were then mounted witb coverslips. Placement of the lesions were examined using a dissection scope.

Behavioral Monitoring The population cage for the colony situation consisted of eight boxes interconnected by 1 - 1 / 2 in. diameter plastic tubular runways seen in Fig. 1. This design is one we have used in earlier investigations [8,12]. Male social position was determined by a modified scoring method reported previously by Ely and Henry [8]. Basically, male social position was defined by physical appearance which was recorded 3 times per week for each male and averaged. More than 4 body scars was coded as a zero score, 3.1 4 scars coded as a score of 1, 2 . 1 - 3 . 0 scars coded as a score of 4, and 0 - 0 . 1 scars coded as a score of 5. The higher the coded score the higher the social rank of the animal. We have found that this is the best single indicator of rank as compared to the number of female associations each male had per week or as compared to the size of territory each male had [8]. Also in colonies of animals that we have behaviorally monitored with a minicomputer over 3 months

RESULTS

The size and placement of the lesions were virtually identical to those reported in a previous study by the authors [9]. Briefly, less cortex lateral to the hippocampus was removed, and this tissue was folded in against the thalamus, filling the space normally occupied by the hippocampus (Fig. 2). Dorsal hippocampus was removed entirely. There was some sparing of posterior hippocampus, and the ventral quarter of the hippocampus was commonly intact. Cingulate cortex, cingulum, thalamus, stria terminalis, and amygdala were not damaged. The amount of neocortex removed was comparable for the hippocampal lesion and for the cortical lesion control animals. Among the cortical control animals, it was common for the upper layer of the hippocampus to show the effects of abrasion against the skin covering the opening in the skull. The skull of the mouse is extremely thin, and at autopsy the exposed hippocampus appeared to be in contact with the skin. Damage to the hippocampus was not extensive but included loss of the superficial region of alveas and pyramidal layer in the dorsal quarter of the hippocampus. As seen in Fig. 3-A there was a significant increase in systolic blood pressure in the hippocampal animals socially interacting in the colony conditions (HLCC) as compared to the cortically lesioned controls in a colony situation (CLCC, p<0.02), or as compared to the unoperated controls (UCCC, p< 0.05) that were socially interacting in a colony situation. The significant HLCC blood pressure peaked on the 13th day and persisted throughout the remainder of the monitoring period (28 days). There was no significant difference found between the blood pressures of the two control groups (CLCC, UCCC). Also there were no significant blood pressure differences found in the

HIPPOCAMPUS AND AUTONOMIC NERVOUS SYSTEM

1077

FIG. l. Eight-box tubular population cage (for socially interacting territorial colonies).

hippocampal (HLC) and cortical lesioned controls (CLLC) or unoperated controls (UCLC) that were housed in the standard laboratory cage conditions (Fig. 3-B). An inverse relationship was observed between rising blood pressure and decreasing heart rate. As can be seen in Fig. 4-A there was a significant decrease in heart rate in the HLCC group after 7 days as compared to the CLCC group (p<0.05), or as compared to the UCCC group (p<0.01). This pattern persisted and was significant through Day 13. The trend, however, still remained in which the HLCC group had a slower rate than the control groups over the entire 28 day period and it failed to return to the group's initial rate. The same trend was evident in the three groups that were kept in the standard laboratory cage conditions. Figure 4-B shows these results in which the hippocampal animals had the slowest heart rate. However, it only reached statistical significance on Day 7 as compared to the CLCC group (p<0.05), and as compared to the UCCC group (p< 0.05). The plasma corticosterone response of the HLCC animals (Fig. 5-A) was significantly elevated above the two colony control groups (p<0.05). Also the HLCC group showed a significantly higher corticosterone level than the hippocampal control animals in laboratory cage conditions (Day 3: p<0.02, Days 1 1 - 1 4 : p<0.01, Day 20: p<0.001). Generally there were no significant differences in plasma

corticosterone levels between the three groups in the standard laboratory cage conditions (Fig. 5-B). Table 1 shows the behavioral responses of each group of colony animals to a single intruder placed into the colony for twenty min. It is evident that none of the hippocampal animals responded aggressively to the intruder. There were no attacks and, therefore, no intruder escapes. The cortical lesioned controls and the unoperated controls responded as is normal for CBA mice, exhibiting an attack within 1 0 - 1 4 min followed by a volley of several attacks. The intruder escaped from attack 9 0 - 1 0 0 % of the time. Table 2 shows the behavioral responses of the same three groups of colony animals when they each were acting as an intruder. There were no significant differences in the latency to the first attack among the groups. However, the hippocampal animals did not retreat when they were attacked, and therefore, received more attacks than the cortical lesioned controls (p<0.001) or the unoperated controls (p<0.001). The hippocampal animals' failure to retreat from attack by the resident aggressor is indicated by the fact that they escaped only 10% of the attacks, as compared to the cortical lesioned and unoperated controls who escaped 84% and 83% of the attacks, respectively (p< 0.02, p< 0.05). Table 3 shows the determination of male social position of the animals living in the socially interacting colony conditions. From previous studies it was found that with

1078

ELY, G R E E N E A N D H E N R Y

FIG. 2. Photomicrographs of a representative hippocampal lesion showing anterior and posterior locations (details in Results). Table 4 shows the tissue weights of the animals in the various groups. B e t w e e n group c o m p a r i s o n s of the animals tested u n d e r the territorial c o l o n y c o n d i t i o n shows t h a t h e a r t weight a m o n g the animals in the h i p p o c a m p a l g r o u p was significantly l o w e r t h a n the weight observed a m o n g cortical lesioned c o n t r o l s ( p < 0 . 0 0 1 ) or a m o n g the u n o p e r -

CBA males socially i n t e r a c t i n g in a c o l o n y c o n d i t i o n , physical a p p e a r a n c e scores are reliable i n d i c a t o r s of social p o s i t i o n [ 8 , 1 1 ] . T h e data s h o w e d an absence of social h i e r a r c h y f o r m a t i o n in the h i p p o c a m p a l group, w h i c h we have previously d o c u m e n t e d in h i p p o c a m p a l animals b y using a c o m p u t e r based b e h a v i o r a l m o n i t o r i n g system [91.

TABLE 1 BEHAVIORAL RESPONSES TO INTRUDER IN COLONY (TERRITORIAL) ANIMALS Initial Attack Latency (min)

Total Number of Attacks

Total Number of Intruder Escapes

Escapes Attacks (%)

Unoperated Controls

5.8 +--1.3"

13.6 ±2.6

13.6 ±2.8

100 ±0

Cortical Lesioned Controls

5.2 ±1.1

9.0 ±1.4

9.0 ±1.6

100 ±0

Group

Hippocampal Lesioned * = standard error of mean.

HIPPOCAMPUS AND AUTONOMIC NERVOUS SYSTEM

SYSTOLIC BLOOD PRESSURE mmHg 170-

1079 the two hippocampal groups (nonterritorial and territorial) were compared it was found that the territorial situation animals (HLCC) had a lower heart weight (p<0.02) and a higher preputial gland weight (p<0.05) than did the nonterritorial hippocampal animals (HLLC).

COLONY CONDITIONS

160-

DISCUSSION 150. 140130] 120-

0

® UNOPERATED CONTROLS(UCCC) 0 CORTICAL LESIONED CONTROLS (CLCC) • HIPPOCAMPAL LESIONED(HLCC) i

i

i

I

i

i

I

STANDARD LABORATORY CAGE CONDITIONS 150140-

130, 0 U~RATED CONTROLSkU ' CLC)

120-

CORTICAL LESIONED O CONTROLS(CLLC) • HIPPOCAMPAL LESIONED (HLLC)

oT DAYS

FIG. 3. Systolic blood pressure of the three groups of animals socially interacting in the territorial situation (A), and of the three groups living in the nonterritorial situation (standard laboratory cages - B). Day 0 represents the day before animal placement into the territorial colony conditions and the day before placement into the laboratory caging for the nonterritorial cage condition. The asterisks indicate levels of significance as compared to the controls, * = p<0.05, ** = p<0.001. ated controls (p<0.02). However, the hippocampals had larger preputial glands than did the cortically lesioned controls (p<0.02) or the unoperated controls (not significant). Among the nonterritorial groups there were no significant differences in any of the organ weights. When

There is some evidence suggesting hippocampal influence on autonomic nervous system activity in the hypothalamus [16,18]. Indeed, Anand and Duo [1] found that stimulating the anterior 1/3 of the hippocampus produced a slight drop and then an increase in blood pressure but posterior stimulation caused no change. Others have found both increases and decreases in blood pressure when the fimbria fibers from the hippocampus to specific regions in the hypothalamus were stimulated [6,7]. Nauta [27] suggested that some of the fibers of the ventral fimbria continued as the medial cortico-hypothalamic tract to the paraventricular zone of the anterior hypothalamus. Here then is a possible pathway for hippocampal influence on blood pressure. It may be that by removing the hippocampus the balance of autonomic nervous system reactivity was altered, and with the removal of septal influence on the hippocampus there was an increase in activity in the sympathetic nervous system. Holdstock's [ 17] data supports this concept since septal lesions produced less general autonomic reactivity with decreased sympathetic tone. The bradycardia observed in the hippocampals in the territorial stiuation most probably was a reflex response to the chronically elevated blood pressure. The low heart weight of these animals also suggested that the bradycardia was chronic and paralleled the high blood pressure. Since this group was so active in the colony one would predict higher or at least normal heart weights, but no decreased heart weights unless a pronounced bradycardia occurred. Supporting this interpretation are the data of Powell e t al. [31], which showed that stimulation of the septum and hypothalamus produced increased blood pressure and decreased heart rate which they suggested was a compensating reflex baroreceptor response. Our evidence further supports this idea since the hippocampal control animals (in standard lab cage) did not show an elevated blood pressure (mean: 139 mmHg) and their heart rate was near control values (522 bpm), whereas the territorial hippocampal animals showed increased blood pressure (mean: 160 m m H g ) a n d a reflex bradycardia (476 bpm).

TABLE 2 B E H A V I O R A L R E S P O N S E S AS AN I N T R U D E R IN T H E C O L O N Y (TERRITORIAL) A N I M A L S

Group Unoperated Controls Cortical Lesioned Controls Hippocampal Lesioned

Initial Attack Latency (min)

Total Number of Attacks Received

Total Number of Intruder Escapes

Escapes Attacks (%)

7.5 ± 1.8* 7.3 ± 1.4

6.0 --_1.7 7.6 ±0.6

5.0 -4-1.5 6.2 ±0.7

83 +--10 82 ---8

4.8 ±0.5

21.0 ___0.6

2.2 ___0.9

11 _+5

*= standard error of mean.

1080

ELY, GREENE

HEART RATE BEATS/min 700-

PLASMA CORTICOSTI !RONE .ug% 24-

COLONY C O N D I T I O N S

COLONY CONDITIONS

20--

600

AND HENRY

*"

16A 12 8

0

I

I

I

4-

CAGE

400-

CONTROLS (CLCC) • HIPPOCAMPAL LESIONED (HLCC) I I I

[

® UNOPERATEDCONTROLS(UCCC) CORTICAL LESIONED 0 CONTROLS (CLCC) • HIPPOCAMPAL LESIONED(HLCC)

o

S T A N D A R D L A B O R A T O R Y CAGE CONDITIONS

,2I ~ O'~ERAT~D CONTROLS(O~LC~

4-

o

o

(~ UNOFERATEDCONTROLS(UCLC) t~ CORTICAL LESIONED ~ CONTROLS (CLLC) • HIPPOCAMPAL LESIONED (HLLC)

0 I

~,

&

,~'

,;

2'0 ~4 2;

DAYS

FIG. 5. Plasma corticosterone of the three groups of animals in the territorial colony condition (A), and of the three groups in the nonterritorial condition (standard laboratory cages B). Day 0 represents the day before animal placement into the territorial colony conditions and the day before placement into the laboratory caging for the nonterritorial cage condition. The asterisks indicate levels of significance as compared to the controls * = p < 0 . 0 5 , ** p<0.01.

DAYS

FIG. 4. Heart rate of the three groups of animals in the territorial colony condition (A), and of the three groups in the nonterritorial condition (standard laboratory cages B). Day 0 represents the day before animal placement into the territorial colony conditions and the day before placement into the laboratory caging for the nonterritorial cage condition. The aserisks indicate levels o f significance as compared to the controls, * = p < 0 . 0 5 , ** = p < 0 . 0 1 . TABLE

3

SOCIAL STATUS DETERMINATION OF COLONY (TERRITORIAL) GROUPS

Animal Number

Actual Physical Appearance ( # Scars)

Physical Appearance Score

Unoperated Controls

11 20 30 10

0 1 3 3

5 4 2 2

Dominant Rival Subordinate Subordinate

Cortical Lesioned Controls

12 3 22 19 15

0 0 2 3 5

5 5 3 2 0

Dominant Dominant Subordinate Subordinate Subordinate

Hippocampal Lesioned

7 9 23 13 31

0 0 0 0 0

5 5 5 5 5

Dominant Dominant Dominant Dominant Dominant

Group

Social position

HIPPOCAMPUS AND AUTONOMIC NERVOUS SYSTEM

1081

TABLE 4 ABSOLUTEORGAN WEIGHTS (WET)

Group Standard Cage Conditions (nonterritorial) Unoperated Controls Cortical Lesioned Hippocampal Lesioned Colony Conditions (territorial) Unoperated Controls Cortical Lesioned Controls Hippocampal Lesioned

N

5 5 5

5 5

5

Body Weight (g)

Adrenal Gland (mg)

Ventricles (nag)

Preputial Gland (nag)

34.6 -+2.5* 34.9 ---2.5 34.7 -+2.2

5.3 -+0.4 4.9 ---0.9 3.15 -+1.5

150.0 -+15.0 159.4 -+10.0 154.0 -+17.0

54.4 -+20.0 59.5 -+20.0 58.3 -+29.0

28.3 ---3.5 32.7 -+1.7

4.9 -+2.4 4.4 -+0.7

147.0 -+7.0 161.0 -+8.9

57.0 -+24.0 59.0 -+17.0

28.6 • +2.0

3.7 +1.5

130.0 -+6.6

91.0 -+10.0

*=standard deviation. There is also evidence to suggest that the rise in plasma corticosterone in the territorial hippocampals was due to the altered social behavior. Kawakami etal. [21] showed that stimulation of the hippocampus in nonstressful conditions increased ACTH, but in stressful conditions it decreased it. This evidence suggests that under stressful conditions (such as those which exist in a colony) the hippocampus may normally inhibit the release of hypothalamic corticotrophic releasing factor, and thereby pituitary ACTH. However, without hippocampal control and in the presence of stressful conditions an increase in plasma corticosterone would be expected as was found in this study. Coover, Goldman and Levine [5] found contrary evidence showing that hippocampectomy abolished the pituitary-adrenal response normally occurring in rats during: extinction of an appetitive lever-pressing response, placement in a novel environment or ether anesthesia. However, the differences found in our results could be explained by the fact that we examined the pituitaryadrenal response under chronic social interaction which we propose utilizes different neural substrates than those pathways responsive in acute situations and when individuals are tested alone. It may be as Isaacson [ 18] has suggested that a balanced control over ergotrophic activity is essential to the continuation of normal social behavior and the hippocampus provides one means of providing this balance. Removal of this adjustment system may free the neural subsystems which control particular physiological responses and thereby produce disorganized patterns of autonomic activity during social interaction. In a previous report [9] the authors developed a case for hippocampal involvement in social behavior and showed a lack of aggressive activity as a key factor in the failure of

hippocampal animals to develop a social hierarchy. Nonneman and Kolb [28] likewise found that cats with hippocampal lesions were submissive and did not respond appropriately to threat, and they [23] noted a complete absence of aggression in rats with hippocampal lesions. In the present study a similar lack of aggressive behavior was noted which prompts the question: Are the physiological changes observed due to primary effects of the removal of the hippocampus or are these changes related to the effect on social behaviors? This question can be answered by analysis of the data of the two hippocampal groups. It can readily be seen that the control hippocampal animals (in lab cages) did not show any significant changes in blood pressure, heart rate or plasma corticosterone as compared to the other laboratory cage groups. Although these animals were housed together they could not compete for territory due to the restricted area, nor could they interact with females since none were present. If the hippocampus was directly involved in the control of physiological systems it is probable that an abnormal autonomic response pattern would have been detected in lesioned animals in both of the environmental test conditions. Since the blood pressure of the hippocampals in the lab cages was not significantly different from the control groups in lab cages it appeared that the hippocampal lesion did not cause a direct change in autonomic response level. However, if the hippocampus is involved in physiological control via a role in social behaviors, then changes should occur in these physiological response patterns when hippocampal animals are interacting in a highly social environment. Therefore, the disorganized social behavior found in the hippocampal colony animals produced altered physiological responses in the form of high blood pressure, reflex bradycardia and elevated plasma corticosterone. Independently, Henry (University of South-

1082

ELY, G R E E N E AND H E N R Y

ern California, personal c o m m u n i c a t i o n ) has f o u n d that fornix lesions in socially interacting CBA mice p r o d u c e d a significant elevation in b l o o d pressure and c o r t i c o s t e r o n e levels as c o m p a r e d to sham controls. This lends f u r t h e r evidence to the idea t h a t the h i p p o c a m p u s m a y influence a u t o n o m i c responses during social i n t e r a c t i o n . It is well established that mice with d i f f e r e n t social positions and behavior p a t t e r n s have d i f f e r e n t u n d e r l y i n g physiological r e s p o n s e p a t t e r n s [2, 3, 4, 2 4 ] . F u r t h e r evidence for this line of reasoning is derived f r o m previous studies from this l a b o r a t o r y [8, 10, 15] in which b l o o d pressure and c o r t i c o s t e r o n e changes were f o u n d to be d e p e n d e n t u p o n the animal's p o s i t i o n in the social hierarchy. The b l o o d pressure, l o c o m o t o r activity and tissue weight responses in the c o l o n y h i p p o c a m p a l s paralleled those o f a d o m i n a n t animal, but the c o r t i c o s t e r o n e levels and lack o f

behavioral responses to i n t r u d e r s paralleled those of a s u b o r d i n a t e animal. It, t h e r e f o r e , appears that the h i p p o c a m p u s is involved in the m a i n t e n a n c e o f social behavior, and alterations in behavior caused by its removal m a y p r o d u c e an imbalance b e t w e e n physiological response systems. The c o l o n y h i p p o campals did n o t a d o p t a typical d o m i n a n t or s u b o r d i n a t e m o d e of behavior but instead displayed a m i x e d m o d e with failure to develop a stable social system. It is i m p o r t a n t to n o t e that had we c o n f i n e d our observations to animals m o n i t o r e d in a standard l a b o r a t o r y cage (as do m o s t studies), we would have c o n c l u d e d that the h i p p o c a m p u s has no influence on physiological responses. It is necessary, t h e r e f o r e , to provide a semi-natural e n v i r o n m e n t for the animals if one is to study the i n v o l v e m e n t of tile limbic system in social behavior and the c o r r e s p o n d i n g physiological r e s p o n s e patterns.

REFERENCES 1. Anand, B. K. and S. Dua. Circulatory and respiratory changes induced by electrical stimulation of limbic system (visceral brain). Neurophysiology 19: 393-400, 1956. 2. Anton, A. H. Effect of group size, sex, and time on organ weights, catecholamines, and behavior in mice. Physiol. Behav. 4: 483, 1969. 3. Bronson, F. H. Establishment of social rank among grouped male mice: Relative effects on circulating FSH, LH and corticosterone. Physiol. Behav. 1 0 : 9 4 7 - 9 5 1 , 1973. 4. Christian, J. J. Social subordination, population density, and mammalian evolution. Science 168: 84, 1970. 5. Coover, G. D., L. Goldman and S. Levine. Plasma corticosterone levels during extinction of a lever-press response in hippocampectomized rats. Physiol. Behav. 7: 727-732, 1971. 6. Cragg, B. G. Autonomic functions of the hippocampus. Nature 182: 675-676, 1958. 7. Cragg, B. G. and L. H. Hamlyn. Histologic connections and electrical and autonomic responses evoked by stimulation of the dorsal fornix in the rabbit. Expl Neurol. 1 : 1 8 7 213, 1959. 8. Ely, D. L. and J. P. Henry. Effects of prolonged social deprivation on murine behavior patterns, blood pressure and adrenal weight. J. comp. physiol. Psychol. 87:733 740, 1974. 9. Ely, D. L., E. G. Greene and J. P. Henry. Minicomputer monitored social behavior of mice with hippocampus lesions. Behav. Biol. 16: 1-29, 1976. 10. Ely, D. L., J. P. Henry and R. D. Ciaranello. Long-term behavioral and biochemical differentiation of dominant and subordinate mice in population ages. Psychosom. Med. 36: 463, 1974. 11. Ely, D. L., J. P. Henry and C. J. Jarosz. Effects of marihuana (~9 -THC) on behavior patterns and social roles in colonies of CBA mice. Behav. Biol. 13: 263-276, 1975. 12. Ely, D. L., J. A. Henry, J. P. Henry and R. D. Rader. A monitoring technique providing quantitative rodent behavior analysis. Physiol. Behav. 9: 675-679, 1972. 13. Glick, D., D. V. Redlich and S. Levine. Fluorometric determination of corticosterone and cortisol in 0.02-0.05 milliliters of plasma or submilligram samples of adrenal tissue. Endocrinology 74: 653-655, 1964. 14. Henry, J. P., J. P. Meehan and P. M. Stephens. The use of psychosocial stimuli to induce prolonged systolic hypertension in mice. Psychosom. Med. 29: 408-432, 1967. 15. Henry, J. P., D. L. Ely, F. M. C. Watson and P. M. Stephens. Ethological methods as applied to the measurement of emotion. In: Emotions, Their Parameters and Measurement, edited by L. Levi. New York: Raven Press, 1975, pp. 469-497.

16. Hess, W. R. Das Zwischenhirn. Schwabe: Basel, 1949. 17. Holdstock, T. L. Plasticity of autonomic functions in rats with septal lesions. Neurop,sTchologia 8:147 160, 1970. 18. tsaacson, R. L. Neural systems of the limbic brain and behavioral inhibition. In: Inhibition and Learning, edited by R. Boakes and J. Halliday. New York: Academic Press, 1972, pp. 497 525. 19. Kaada, B. R. Somatamotor, autonomic and electrocorticographic responses to electrical stimulation of rhinencephalic and other structures in primates, cat and dog. Acta physiol. scan& (Suppl.)24: 83, 1951. 20. Kaada, B. R., R. S. Eeldman and T. Langfetdt. Failure to modulate autonomic reflex discharge by hippocampal stimulation in rabbits. Physiol. Behav. 7:225 231, 1971. 21. Kawakami, M., K. Seto, E. Turosawa, K. Yoshida, T. Miyamoto, M. Sekiguchi and Y. Hattori. Influence of electrical stimulation of lesion in limbic structure upon biosynthesis of adrenocorticoid in the rabbit. Neuroendocrinology 3: 337-348, 1968. 22. Koikegami, H., T. Dodo, Y. Mochida and H. Takahashi. Stimulation experiments on the amygdaloid nuclear complex and related structures. Effects upon the renal volume, urinary secretion, movements of the urinary bladder, blood pressure and respiratory movements. Folia physchiat, neurol, lap. 11: 157-206, 1957. 23. Kolb, B. and A. J. Nonneman. l-rontolimbic lesions and social behavior in the rat. Physiol. Behav. 13:637 643, 1974. 24. Leshner, A. L. and D. K. Candland. Endocrine effects of grouping and dominance rank in squirrel monkeys. Physiol. Behav. 8:441 .-445, 1972. 25. Moberg, G. P., V. Scapagnini, J. deGroot and W. 1:. Ganong. Effect of sectioning the fornix on diurnal fluctuation in plasma corticosterone levels in the rat. Neuroendocrinology 7:11 15, 197l. 26. Nakadate, G. M. and J. deGrool. Fornix transection and adrenocortical function in rats. Anat. Rec. 145: 338, 1963. 27. Nauta, W. J. H. An experimental study of the fornix system in the rat. J. comp. Neurol. 104:247 272, 1956. 28. Nonneman, A. J. and B. E. Kolb. Lesions of hippocampus or prefrontal cortex alter species-typical behaviors in the cat, Behav. Biol. 12:41 54, 1974. 29. Pampiglione, G. and M. A. Falconer. Some observations upon stimulation of the hippocampus in man. Electroenceph. clin. Neurophysiol. 8: 718, 1956. 30. Pfaff, D. W., M. T. A. Silva and J. M. Weiss. Telemetered recording of hormone effects on hippocampal neurons. Science 172:394 -395, 1971.

HIPPOCAMPUS AND AUTONOMIC NERVOUS SYSTEM 31. Powell, D. A., S. R. Goldberg, G. W. Dauth, E. Schneiderman and N. Schneiderman. Adrenergic and cholinergic blockade of cardiovascular responses to subcortical electrical stimulation in unanesthesized rabbits. Physiol. Behav. 8: 9 2 7 - 9 3 6 , 1972. 32. Torii, S. and H. Kawamura. Effects of amygdaloid stimulation on blood pressure and electrical activity of hippocampus. Jap. J. Physiol. 19: 3 7 4 - 3 8 4 , 1960.

1083 33. Ursin, H. and B. R. Kaada. Functional localization within the amygdaloid complex in the cat. Electroenceph. clin. Neurophysiol. 12: 1-20, 1960. 34. Votaw, C. L. and E. W. Lauer. Blood pressure, pulse, and respiratory changes produced by stimulation of the hippocampus of the monkey. Expl Neurol. 7 : 5 0 2 - 5 1 7 , 1963.