Partial kindling and emotional bias in the cat: lasting aftereffects of partial kindling of the ventral hippocampus

BEHAVIORAL AND NEURALBIOLOGY38, 205-222 (1983)

Partial Kindling and Emotional Bias in the Cat: Lasting Aftereffects of Partial Kindling of the Ventral Hippocampus I. Behavioral Changes R . E . ADAMEC AND C. STARK-ADAMEC1

Scott Laboratory, Wellesley Hospital and Department of Psychiatry, University of Toronto, Toronto, Ontario M4Y 1J3, Canada Repeated electrical evocation of afterdischarges in the perforant-path ventral hippocampal system of the cat produces lasting changes in species characteristic behavioral responses to environmental threat. After 7 to 12 afterdischarges, cats showed greatly enhanced defensive (withdrawal) responses to rats, and mildly enhanced defensive responses toward mice. Measures of predatory attack which negatively correlate with withdrawal from rats were also changed in a direction consistent with the increase in withdrawal tendency. There was little effect of afterdischarges on the same parameters of attack on mice. Thus the stimulation seemed to attenuate predatory aggression by increasing defensive sensitivity to the threat posed by prey self-defense, and not by reducing predatory motivation per se. The change in defensiveness was not restricted to the predatory test situation, however. Tests of defensive response to conspecific threat vocalizations revealed an increased defensive responding to this stimulus as well. On the other hand, there was no change in social responsiveness shown toward a highly familiar human. Given the sudden onset (1 hr to 24 hr after the last afterdischarge), the long-lasting nature of the change (30-60 days) which persisted in the absence of seizures, and the generality of expression of the behavioral change, it was concluded that the afterdischarges produced an interictally maintained alteration in a defensive personality characteristic of the cats.

Delgado and his colleagues (Delgado & Anand, 1953; Alonso de Florida & Delgado, 1958) were the first to report lasting aftereffects on behavior of high frequency trains of subconvulsive electrical stimulation of limbic system areas in cats. Similarly, lasting alteration of mood and cognition has been reported as a consequence of human limbic stimulation (Ervin, Mark, & Stevens, 1969; Monroe, 1970; Stevens, Mark, Ervin, Pacheco, The research reported in this paper was supported by a grant to R. Adamec from the Medical Research Council of Canada (MRC Grant MA 7022). R. Adamec was supported by an Ontario Mental Health Foundation Scholarship, and C. Stark-Adamec was supported by a National Health Research Scholar Award (NHRDP 6606-1912-48). The technical assistance of R. Riar, B. Vari, and M. Graham is gratefully acknowledged. Send requests for reprints to Dr. Robert Adamec. 205 0163-1047/83 $3.00 Copyright© 1983by AcademicPress, Inc. All rightsof reproductionin any form reserved.

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ADAMEC AND STARK-ADAMEC

& Suematsu, 1969). More recently, lasting behavioral changes have been associated with limbic stimulation that results in kindling. Kindling is a permanent increase in epileptogenicity produced by subconvulsive electrical brain stimulation (Goddard, McIntyre, & Leech, 1969; Racine, 1978). The lasting interictally maintained neural and behavioral changes associated with kindling have been used to suggest that kindling may be a neural-animal model for several forms of lasting behavioral alterations including learning (Douglas & Goddard, 1975; Goddard, McNaughton, Douglas, & Barnes, 1978), development of human psychoses (Post, Ballenger, Uhde, Putnam, & Bunney, 1981), human psychopathology accompanying alcohol abuse (Post & Ballenger, 1981), and psychopathology associated with complex partial seizures (Livingston, 1978; Adamec, Stark-Adamec, Perrin, & Livingston, 1981; Stark-Adamec & Adamec, 1980). In a recent theoretical review of the literature (Adamec & Stark-Adamec, 1983) several hypotheses have been proposed linking lasting behavioral changes with lasting changes in brain function as a consequence of experimentally induced seizures. These hypotheses were proposed in the context of an attempt to understand how limbic epilepsy might induce interictally maintained changes in emotional behavior. These hypotheses state that following repeated limbic seizures: (A) Behavioral changes likely depend on some form of lasting posttetanic potentiation of synaptic transmission. (B) Behavioral changes require enhancement of many synapses distal to the stimulated focus. (C) A variety of neurotransmitters may be lastingly potentiable. Both the variety and pattern of changes in neurotransmitters are relevant to the nature of the behavioral changes observed following potentiation induced by kindling stimulation. (D) The nature of the behavioral changes produced by kindling may be critically dependent upon which brain circuits are potentiated, and in what order. The locus and timing of brain stimulation is thus important in behavioral outcome. (E) Brain circuit changes mediating behavioral changes may not only involve enhancement of excitatory processes, but also suppression of transsynaptically conducted neural activity. Thus, pattern and distribution of transsynaptic excitability changes may be crucial in determining the nature of behavioral changes induced by kindling. This series of studies was done to directly test hypotheses A and E. Hypotheses B, C, and D will be considered in the context of the results of these studies and prior findings. The behavioral model chosen for these investigations was the conflict between predatory aggression and defense in the domestic cat. This behavioral system was chosen for two reasons. First, there has been a

PARTIAL KINDLING, EMOTIONAL BIAS, I

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great deal of descriptive and quantitative behavioral work in adult cats (Adamec, 1975, 1978; Leyhausen, 1956) and in kittens (Leyhausen, 1965; Adamec, Stark-Adamec & Livingston, 1980a, 1980b, 1980c) which suggests that a stable predisposition to respond defensively to a variety of environmental threats, arising early in life, opposes aggressive behavior displayed toward formidable prey species (adult male rats). Secondly, the role of the limbic system in this conflict has been thoroughly investigated by John Flynn and his colleagues (Flynn, Foote, & Edwards, 1970). Their work revealed a system of tonic inhibitory modulators of predatory attack, one of which involves the basomedial amygdala, and tonic facilitators of attack, one of which involves the ventral hippocampus. Other literature (Kaada, 1972; Stokman & Glusman, 1970) suggests that the basomedial amygdala functions as an excitatory modulator of defensive behavior as well. These circuits involving the amygdala and ventral hippocampus can be described as a set of opponent tonic modulators of attack and defense (Adamec, 1978). "Tonic" here means lasting exertion of some behaviorally detectable action; "modulation" means not behaviorally provocative but affecting some parameter of the behavior (e.g., latency to perform it). Moreover, Adamec (1975, 1978) has shown that the modulating action of these circuits may be lastingly enhanced by "partial kindling," which involves repeated electrical evocation of afterdischarges without full kindling to the point of overt motor convulsions. The purpose of these studies, then, is to extend the initial findings of enhancement of limbic modulation of the conflict between aggression and defense. Among the parameters of limbic function examined are measures of interictal conduction of neural activity between limbic structures. Of particular interest are the questions of how repeated afterdischarges (ADs) alter this conduction, how long these alterations are maintained interictally, and how these brain changes correlate with behavioral changes. For the sake of clarity, this study is divided into two reports. The first will detail methods and results of the behavioral analysis. The second report will describe the results of the physiological changes accompanying repeated brain stimulation. METHODS

Subjects Subjects were seven adult cats weighing between 2.0 and 4.5 kg and ranging in age from 4-5 years. Six female and one male were used. All cats were reared in the laboratory as part of a developmental study (Adamec et al., 1980a, 1980b, 1980c). The behavioral profiles of these cats, therefore, were thoroughly studied over a number of years and found to be stable (Adamec et al., 1980a; Adamec, Stark-Adamec, & Livingston, 1983).

208

ADAMEC AND STARK-ADAMEC

Behavioral Testing The sequence of experimental events over the course of this study is outlined in Table 1. As indicated in Table 1, aggressive and defensive behavioral tendencies were repeatedly tested during the study. The testing environment and testing methods have been described in detail elsewhere (Adamec, 1978; Adamec et al., 1980a, 1983) so they will be only briefly reviewed here. Cats were examined in three different situations to test: (1) their social responses to a human (Person Test): (2) their aggressive TABLE 1 Sequencing of Behavioral and Electrophysiological Tests Test 1 2 3 4 5 6

9 10

11

12 13 14 15 16 17 18 19 20

21

Description Aggressive-defensive behavior testing Surgery Postsurgical recovery Postsurgical behavioral retesting Evoked potential threshold determination Evoked potential intensity series A. Amygdala-VMH B. Perforant path-dentate Double pulse stimulation series A. Amygdala B. Perforant path Afterdischarge threshold determination A. Amygdala B. Perforant path-dentate Behavioral retesting (RMP) Double pulse stimulation series A. Amygdala B. Perforant path Repeated evocation of afterdischarges by perforant or VHPC stimulation 1 hr Post-AD behavioral testing Double pulse series stimulation (1 hr after last behavioral test) 1 Day post-AD behavioral testing Double pulse series stimulation (1 hr after last behavioral test) 1 week post-AD behavioral testing Double pulse series stimulation (1 hr after last behavioral test) 20 Days post-AD behavioral tests Double pulse series stimulation (1 hr after last behavioral test) 1 or 2 Month post-AD behavioral tests double pulse series stimulation (1 hr after last behavioral test) Afterdischarge threshold determination (ADT)

Days 1-5 7 8-28 29-34 35-39 40-41 42-43 44

45-47 48-50 51 51 52-54 or 52-57 55 or 58 55 or 58 55 or 58 55 or 58 55 or 58 62 or 65 62 or 65 92 or 95 92 or 95 102 or 132 102 or 132 103 or 133

PARTIAL KINDLING, EMOTIONAL BIAS, I

209

and defensive responses to 140-g male hooded rats and 30-g male albino mice; and (3) their defensive responses to recorded feline threat vocalizations of an aggressive male cat (Howl Test). All testing was done between 10 AM and 3 PM, after their initial daily feeding at 9 AM. (Cats were kept on a normal day-night light cycle of 14 hr light, 10 hr darkness). Testing involved one 3-day block of rat (R), mouse (M), and person (P) testing (all in RMP order). Previous research varying order of testing revealed no order effects (Adamec, 1974). Following RMP testing, two tests of response to threat vocalizations on successive days were then carried out. On the day following the second threat vocalization test, a single series of RMP testing was done. RMP testing alone was done for tests 1,9,12,14,16, and 20 in Table 1. RMP plus howl testing was done for tests 4 and 18 in Table 1. We avoided excessive howl testing because of the severity of the threat posed and because of evidence of lasting (at least 24 hr) effects on social behavior toward humans (Adamec et al., 1983). Howl tests conducted on these cats up to a year prior to the initiation of the current study indicated that response to howls were stable (Adamec et al., 1983).

Behavioral Measures All behavior was videotaped and later analyzed in slow motion by a trained rater. A variety of measures were taken which correlational analysis revealed may be considered to measure opposing tendencies of approachattack and withdrawal (Adamec et al., 1983). These measures have also been described in detail elsewhere (Adamec et al., 1980a).

Predatory Attack Behaviors The measures used are summarized in Table 3. The most efficient form of predatory attack is a single paw pin followed by a bite to the nape of the neck (Leyhausen, 1965, and personal observations). Single paw pinning refers to a rapid placing of a paw on the prey in sustained contact, resulting in stabilizing of the prey for a bite. Biting is self-evident. Hard and gentle paw strikes were scored following the description of Leyhausen (1956). Hard striking (HPS) was defined as rapid (clearly visible only in slow motion) striking and withdrawal of forepaws making sufficiently forceful contact with prey to displace the target in space. Gentle striking (GPS) involved either aborted or foreshortened strikes with insufficient force to move the target. In addition to latency, duration, and frequency of occurrence, attention was paid to the targetting of biting and of pawing. Thus attacks to front (head-neck), middle (body), and rear (rump-tail) were scored separately. This was done since it has been reported that when cautious, defensive cats attack rats, they attack the rear parts of the body in apparent avoidance of head-neck regions (Adamec, 1975; Adamec et al., 1980a; Leyhausen, 1965).

210

ADAMEC AND STARK-ADAMEC

Defensive Behaviors in the Predatory Situation The approach-withdrawal (AW) score (Table 3) was measured by timing the duration between a withdrawal of head or body from prey to the time of reapproach (to within 1 foot) of the prey. Successive withdrawal durations were summed and expressed as an average AW score, measuring "willingness" to reapproach prey after a threatening defensive prey response to approach. Indeed, over 90% of cat withdrawals from prey are in response to some form of prey self-defense (Adamec et al., 1980a). Given this dependence of AW on prey defense, three measures of rodent self-defense were also employed, following a postural analysis suggested by Grant and Macintosh (1963). These were measures of frequency of: (1) active defense (e.g., upright boxing posture); (2) passive defense (e.g., crouching and freezing); and (3) escape (fleeing) (Adamec et al., 1980a).

Person Test Measures These measures appear in Table 2 and are self explanatory.

Howl Test Measures The Howl Test was divided into four consecutive testing periods: a control period of 60 sec (Pre-Howl Control); a howl period of 255 sec in which recorded threat howls were played through loudspeakers mounted on the walls of the testing enclosure (Howl Period); a 30-sec period of playing recorded violent cat fight sounds (Fight Period); and a 60-sec postvocalization control period of silence (Post-Fight Control). All measures (latency and duration) were taken separately in each test period and then expressed as a percentage of the total time of a given test period. These measures are outlined in Table 2. Measures of time spent under the canopy assessed the tendency of the cats to seek shelter within a dark enclosure in one corner of the room. The crouch-tail-wrap measure assessed defensive Posturing described by Andrew (1972) as a self-warming response to threat in a variety of mammalian species. This test was administered twice, in 2 days, to assess habituation to the threat.

Surgery and Electrode Implantation After the first set of behavioral tests, four electrodes were stereotaxically implanted using sterile surgical technique under combined xylazine (2.2 mg/kg) and Nembutal (15 mg/kg) anaesthesia. All electrodes were implanted in the left hemisphere in the basomedial amygdala (AMY), the ventromedial hypothalamus (VMH), the dentate area of the ventral hippocampus (VHPC), and the perforant path input pathway (PP) from the entorhinal cortex to the VHPC. Combination stimulating and recording electrodes were implanted in the PP and AMY. Bipolar stimulating leads were 0.007 in diameter Teflon

211

P A R T I A L K I N D L I N G , E M O T I O N A L BIAS, I TABLE 2 Measures UsedinthePersonand

HowlTests Units of m e a s u r e in each test

Timed measures Measure

Latency

Duration

Person Test

Howl Test

Time u n d e r the canopy

X

X

sec/180

sec/P a

Time s p e n t in a crouched-tailwrapped posture

X

X

sec/180

sec/P

Time freezing

X

X

Nb

sec/P

Time n e a r test p e r s o n

X

X

sec/180

N

Time to follow test person: from shelf from floor

X X

X X

sec/10 sec/10

N N

Time rubbing b o d y against test p e r s o n

X

X

sec/180

N

Untimed measures Measure

M e t h o d o f scoring

Entry u n d e r the c a n o p y

Slinking Walking

R e s p o n s e to petting

P u s h head to stroke Push body to stroke

Activity

1 pt./slink 1 pt./walk

U s e d in test: Final score

Person

Howl

X

X

Slinks/ (slinks + walk)

1 pt./stroke 1 pt./stroke

1 p t . / 1 foot square c r o s s e d in testing r o o m

S u m pts./10

X

N u m b e r of squares crossed/min X

Purring

Purr = 1 pt. N o purr = 0 pt.

N u m b e r of points X

" In the Howl T e s t all timed m e a s u r e s were e x p r e s s e d as a ratio of time in seconds divided by the duration o f the test period (P) in which the m e a s u r e was scored. Duration of t h e s e test periods were: Pre-Howl Control, P = 60 sec; Howl, P = 255 sec; Fight, P = 30 sec; Post-Fight Control, P = 60 sec. b N m e a n s that the m e a s u r e w a s not u s e d in a particular test.

212

ADAMEC AND STARK-ADAMEC

coated platinum-10% irridium wires separated by 0.5-mm vertically. Recording electrodes were teflon coated stainless steel (0.003 in diameter). Electrodes were mounted in 23-gauge stainless-steel tubes. In combined stimulation and recording electrodes, a single recording lead was placed midway between the stimulating leads. The entire electrode assembly was held in place by dental acrylic cement bound to stainless-steel screws bolted to the skull. One stainless-steel skull screw imbedded in the skull over the occipital cortex served as a reference. A second skull screw over the right frontal cortex served as a ground. All electrode leads were terminated in gold amphenol pins fixed in two multiple lead plastic screw caps mated to stimulating and recording microdot cable leads to the equipment. Postoperative care included sterile housing for 3 days combined with subcutaneous chloramphenicol (50 mg x 2) and 100/xg of vitamin B12 (cyanocobalamin), with hand feeding of Nutravit supplement. Cats were maintained in cages sterilized daily with daily changes of sterilized cat litter (dust-free shavings). Cats were allowed at least 3 weeks postoperative recovery prior to testing.

Physiological Testing The rationale and details of the evoked potential physiological testing described in Table 1 will be covered in the second report. Afterdischarge threshold (ADT) was determined as the minimal intensity (to within 50/xA peak current) required to evoke an electrographic seizure (AD) which outlasted a stimulus train of 3 sec of 62.5 pulses/sec. Pulses in the train were 1-msec biphasic square waves. Repeated evocation of ADs in the PP or VHPC was done using threshold intensities. ADs were repeatedly evoked by direct electrical stimulation of the VHPC in three cats, and by PP stimulation in the remaining four cats. Stimulations were applied twice per day at 10 AM and 4 PM for 2 days, and at 10 h i on the third day. One hour after the fifth AD and after being in the home cage, cats were tested behaviorally. Six of the seven cats received five such stimulations and one required a total of 10. As indicated in Table 1, no seizures were triggered thereafter until the final redetermination of perforant path afterdischarge threshold.

Histology At the end of the experiments, cats were deeply anaesthetized with an overdose of Nembutal. Small anodal lesions were made through the recording electrodes (5 mA for 5 sec). Cats were then perfused intracardially with saline and then 10% formal saline mixed with a 1% solution of potassium ferrocyanide to mark the lesion locations. Brains were blocked in the stereotaxic and stored in Formalin (10%) for at least 2 weeks. Sectioning at 30 ~z with a cryostat was done and every fifth section

PARTIAL KINDLING, EMOTIONAL BIAS, I

213

through the electrode tract was saved. Sections were counterstained with luxol fast blue and cresyl violet, and electrode locations verified. All electrodes were found to be in the desired locations.

Statistical Analyses o f Behavioral Data All data were examined using analysis of variance for repeated measures designs (Winer, 1962). All designs included two independent groups (G), a VHPC group of cats stimulated repeatedly in the VHPC and a PP group of cats stimulated repeatedly in the PP. There was a repeated measure independent variable examined for brain stimulation effects which included three levels: postsurgical control (C), behavior observed 1 day following the last repeated AD (S1), and final tests 30 to 60 days following the last AD ($2). When attack measures involving target of the attack were analyzed, a third repeated measure variable was included examining attack to the front, middle, and rear of the prey. Data for each of these levels were derived from averages of measures taken over all RMP tests done at each of these time points. No differences were found on any measure when pre-, postsurgical, and poststimulation prior to repeated AD tests were compared. Nor were there any differences noted within any series of three RMP tests. These general statements also apply to body weight, which was measured (to the nearest 0.2 kg) before every test. Moreover, all behavioral measures were found to be stable in these cats over a retest period of one year prior to this study. These findings are reported elsewhere (Adamec et al., 1980a; Adamec et al., 1983). Analysis of Howl test data involved four-way analyses of variance with the group condition described above. The stimulation condition had two levels, prestimulation control and postrepeated AD. The remaining two repeated measure variables examined were: test Days 1 and 2 and test periods 1-4; Pre-Howl Control, Howl, Fight, and Post-Fight Control. Data were routinely tested for homogeneity of variance (F MAX test, Wirier, 1962). Where appropriate, data were transformed to satisfy ANOVA test assumptions. A priori mean contrasts involving stimulation effects were done using t tests under the hypothesis that repeated AD should alter limbic modulation function in aggressive-defensive behavior.

RESULTS AND DISCUSSION Given the complexity of the results, they will be discussed as they are presented. An overview will be addressed in the general discussion.

Response to Rats and Mice Mice have been found to pose less of a threat to defensive cats than do rats (Adamec, 1975, 1978; Adamec et al., 1980a). The mouse test thus provides a useful contrast in which to assess both the degree of

214

ADAMEC AND STARK-ADAMEC

change in defensiveness and effects on predatory attack which may be independent of defensiveness. In general, repeated stimulation of PP and VHPC had the same effects on behavior. Effects of repeated stimulation on responses to rats and mice appear in Tables 3 and 4. Defensive response. Repeated stimulation resulted in a lasting and stable increase in withdrawal from rats and mice. The effect appeared one day after the last AD (S1) and persisted unchanged for 30-60 days ($2). With one exception, these effects were also apparent within 1 hr of the last AD. The change in response to rats was more dramatic, involving a three- to fourfold increase over control (Tables 3 and 4). This change in response to prey cannot be accounted for by a change in prey self-defense. All measures of rat defense decreased to a stable low level at S1 and persisted unchanged at $2. Mouse defense was unchanged. Prior research has indicated that naturally more defensive cats respond with longer withdrawals to the same prey threat than do less defensive cats (Adamec et al., 1980a), suggesting a greater defensive sensitivity to the threat posed by prey. Apparently, repeated AD induces a similar increased sensitivity to prey threat. Moreover, the decrease in rat self-defense, but lack of change in mouse self-defense are consistent with the decrease in predatory attack intensity toward rats and the relatively small change in attack intensity toward mice about to be described. Attack response. Previous research has shown that most measures of attack against rats are strongly negatively correlated with withdrawal tendency from rats (Adamec et al., 1980a). In view of the increase in defensive response to rats, it is not surprising, then, that latency to bite, HPS, and GPS of rats (in sec) all increased to higher levels at S 1 and $2 (Table 3). Similarly frequency of HPS of rats decreased at S1 and $2. On the other hand, there is only a trend for cats to spend less time biting rats (Table 3). It should be noted, however, that these cats were not very aggressive at the outset, displaying little initial tendency to bite rats. Thus, their biting behavior may have been initially nearly asymptotically low, with little possibility of further decrease. Taken together with the cat withdrawal and prey response data, these results suggest that repeated AD attenuated attack by enhancing the cats' defensive responsiveness to the threat posed by rats. The effects of repeated AD on mouse biting present a different pattern. While latency to bite mice did not change, there was a decrease in time spent biting frontal targets after repeated AD. This finding is consistent with the mild increase in withdrawal from mice, since frontal targets on prey are avoided by naturally defensive cats (Adamec, 1975; Adamec et al., 1980a). In addition, other factors interacting with withdrawal tendency could

Stimulation Stimulation Stimulation Stimulation Stimulation b None' Stimulation Stimulation' Stimulation None Stimulation

AW (Approach-withdrawal) Active prey defense Passive prey defense Prey escape Latency to bite Time biting Latency to hard paw strike Frequency of hard paw strike Latency to gentle paw strike Frequency of gentle paw strike Frequency of sniffing prey

<.01 <.01 <.01 <.01 <.09 <.01 <.05 <.05 <.01

5.49 4.84 5.75 7.55

p

21.07 9.96 7.89 14.96 3.07

F

19.7

39.3 10.8 69.0 13.8 343.8 8.5 466.2 2.7 499.2

C

> 11.0

< 175.0 >6.0 >27.6 >5.4 <451.2 2.6 <573.6 >.6 <600.0

S1

Means ~

= 14.7

= 103.6 =3.0 = 35.4 = 5.4 =499.2 1.4 = 571.8 =0.0 = 600.0

$2

a Stimulation effects F values have 2 and 10 degrees of freedom associated with them. F o r all mean contrasts all t(10) > 3.10, p < .02. b Latency in seconds out o f a m a x i m u m of 600 sec. In the case of Latency to Bite, mean contrasts significant with all t(10) > 2.35, p < .05. c Means are expressed as a percentage of time near prey. In the case of Time Biting, there is a trend t o w a r d a d e c r e a s e at S1, $2, vs C (all t(10) > 1.30, p < .17).

Effects

Measure

Analysis of variance effects

TABLE 3 Effects on Predatory Aggressive and Defensive Behavior of Repeated Afterdischarges in the Perforant P a t h - V e n t r a l H i p p o c a m p a l System: Response to Rat Prey

©

r~

~Z

Z

7~

Stimulation None None None None Stimulation by target on prey

None None None None Stimulation

AW (Approach-withdrawal) Active prey defense Passive prey d e f e n s e Prey escape L a t e n c y to bite Time biting

L a t e n c y to Frequency Latency to Frequency Frequency

<.05

4.20

<.01

<.01

4.57

9.43

p

F

12.3

Fb3.8 M 1.7 R 0.8

5.1

C

<18.9

> 1.6 = 1.7 =0.5

<7.5

S1

Means"

=23.9

= 0.7 =0.4 =2.3

=7.3

$2

Stimulation effects F values have 2 and 10 degrees of f r e e d o m and Stimulation x Target F v a l u e s h a v e 4 a n d 20 d e g r e e s o f f r e e d o m a s s o c i a t e d with them. F o r all m e a n c o n t r a s t s all t(10) and t(20) > 3.00, p < .02. b M e a n s are e x p r e s s e d as a percentage of time near prey. M e a n s associated with targets are d e s i g n a t e d by F for frontal targets, M for middle, and R for rear targets.

hard paw strike of hard p a w strike gentle p a w strike of gentle paw strike of sniffing prey

Effects

Measure

Analysis of variance effects

TABLE 4 Effects on Predatory A g g r e s s i v e and Defensive Behavior of Repeated Afterdischarges in the Perforant P a t h - V e n t r a l H i p p o c a m p a l S y s t e m : R e s p o n s e to M o u s e Prey

>

>

>

>

>

t~

PARTIAL KINDLING, EMOTIONAL BIAS, I

217

have contributed to the decrease in biting the front of mice. Two of these are: the tendency of mice to flee in response to biting attacks, and the difficulty of biting the small frontal part of the mouse. There was no change in biting middle and rear targets of mice. This finding may be due to the initially, and perhaps asymptotically, low level of biting. Indeed, biting frontal targets exceeded biting other targets only in the control tests [t(20) = 2.89, p < .05]. The relative lack of effects on other measures of attack on mice raises two points. First, attack measures on mice are not strongly negatively correlated with withdrawal tendency. Given the mild increase in withdrawal from mice, it is not surprising that most attack measures against mice did not change. Second, the fact that some measures of attack against mice did not change, whereas they did change when rats were the prey, suggests that brain stimulation did not suppress attack tendency per se. Rather diminution of attack against rats on these measures reflects more the conflicting effects of greatly enhanced withdrawal from rat prey. The differences in enhancement of sensitivity to the threat posed by rats and mice also appear in the frequency of sniffing measure. Naturally defensive cats display decreased tendencies to commit sensitive facial areas to potential threats, even as mild as those encountered in a novel environment (Adamec et al., 1983). It is consistent with this finding that cats in this study decreased their sniffing of the rat coincident with increases in withdrawal (Table 3). On the other hand, the cats increased their sniffing of mice (Table 4). These opposite patterns of change likely are due to the less threatening nature of the mouse, and the possibility that the cats shifted from biting mice to intention bites followed by sniffing. The increased response to mice also indicates that the decrease in sniffing rats is not due to some stimulation induced olfactory deficit. Social Responses to Humans

There were no stimulation-related changes in response to humans in the Person Test, though it has been reported that naturally more defensive cats differ in their social response to humans (Adamec et al., 1983). It should be noted that for practical reasons the test person in this study was an individual who has known and fed the cats all of their lives, i.e., a minimum of 4 years (R. Adamec). This high degree of familiarity may have mitigated against any changes in response that might be expected to be associated with enhanced defensiveness. Response to Threat Howls

Repeated AD resulted in evidence of enhanced defensive response on two measures of response to threat howls; time spent freezing [Stimulation x Test Day x Test Period F(3, 12) = 9.55, p < .01] and time spent in a defensive crouched-tail-wrapped posture [Stimulation x Test Period

218

ADAMEC AND STARK-ADAMEC

F(3, 20) = 3.66, p < .05]. Prior to repeated AD, (Fig. 1) cats showed evidence of increased freezing to threat vocalizations which persisted into the Post-Fight Control on Test Day 1 [all t(12) > 3.67, p < .05]. On Test Day 2, freezing only increased in response to threat howls, returning to control levels in the fight and post-fight control periods [all t(12) > 4.09, p < .01]. Thus, there was an apparent habituation of freezing in response to threat vocalization on second exposure. Following repeated AD, the Test Day 1 response pattern resembled the prestimulation Test Day 1 response quite closely [all t(12) > 2.18, p < .05]. On Test Day 2 following repeated AD, however, the cats did not show the prestimulation habituation of freezing to threat vocalizations. Instead there was enhanced freezing to vocalization which persisted into the Post-Fight Control period [all t(12) > 2.99, p < .02, Fig. 1]. Time spent in a crouched-tail-wrapped posture also showed a poststimulation enhancement, but in a pattern which differed from freezing (Fig. 2). Unlike freezing, there was no habituation over repeated exposure (no Test Day effects) in either pre- or poststimulation conditions. The effect of repeated AD was to greatly increase crouching in the Howl, Fight, and Post-Fight Control periods on both Test Days [all t(12) > 2.77, p < .05]. PRE S T I M

POST

STIM

80

m

,,,,,o'

,j/111 DAY 1

ff

DAY 2

/'/

=""".

60

.

EZ

R

! ~

i,," It

40

20

•

Pre

Howl

Fight

!

Post

Pre

Howl

Fight

Post

F1G. 1. Mean time spent freezing is plotted versus Howl Test period. The mean times are expressed as a percentage of the total time of the given test period in which measurement of time freezing was taken. Day 1 and Day 2 refer to the first and second consecutive daily Howl Tests. Pre- and poststim refer to tests done before and after repeated evocation of afterdiseharges in the perforant path-ventral hippocampal system.

PARTIAL KINDLING, EMOTIONAL BIAS, I

219

50 Post

Z

Stim.

¢

40

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FIG. 2. Mean time spent in a crouched-tail-wrapped posture is plotted versus Test period. The mean times are expressed as a percentage of the total time of the test period in which measurements were taken. Data are collapsed over the two daily Tests. Pre- and poststim refer to tests done before and after repeated evocation of discharges in the perforant path-ventral hippocampal system.

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These data indicate that the enhanced response to threat seen in predatory tests is not specific to stimuli from prey, but is generalized to other sources of species-characteristic threat. These results are consistent with the high correlations found between withdrawal responses from prey and these responses to vocal threat (Adamec et al., 1983; Adamec & StarkAdamec, 1983). It is also apparent that the cats adopted an immobility " s t r a t e g y " in response to threat, rather than seeking shelter under the canopy, since measures involving entry under the canopy did not change. It is unlikely that the stimulation effects are merely due to repeated exposure to the test, for two reasons. First, freezing initially habituated to vocal threat, leading one to predict further habituation should have occurred on repeated exposure. Just the opposite was observed. Second, these cats have been tested in this situation repeatedly in the past with no apparent change in response patterns (Adamec et al., 1983).

Body Weight Cats were weighed prior to every test (to the nearest 0.2 kg). Analysis of these data revealed a Group × Stimulation interaction [F(2~ 8) = 5.92, p < .05]. Cats stimulated repeatedly in the VHPC showed no change in weight over the stimulation conditions C, S1, and $2 (2.31, 2.30, 2.27, mean body weight in kilograms, respectively). Cats receiving stimulation in the PP showed a stable increase in body weight after repeated stimulation (2.80, 3.27, 3.33 kg, mean body weight observed at C, S1, and $2 re-

220

ADAMEC AND STARK-ADAMEC

spectively, all t(8) > 4.55, p < .01). Given the similarity in behavioral changes in both groups, it is unlikely that the weight change in the PP group accounts for the change in defensiveness. More likely, PP stimulation, in addition to altering defensiveness, may have produced a parallel, but independent, alteration in body weight regulation. GENERAL DISCUSSION Taken together, the data indicate that repeated activation of 7-12 AD's in the perforant path-ventral hippocampal system results in a lasting increase in sensitivity to a variety of species-characteristic threats. The impact of this change on aggressive behavior appears to be an attenuation of attack as a result of a conflict between enhanced defensive mechanisms and largely unchanged attack mechanisms, as revealed by the persistence of most aggressive responses toward mice. The only attack response toward mice altered in any way was biting tendency, with a decrease in frontal biting. This result is consistent with the mild threat posed by mice, the mild enhancement of withdrawal from mice produced by brain stimulation, and the greater threat to sensitive facial areas of the cat posed by a biting attack to the front of prey. It is of interest that response to a highly familiar and socially rewarding stimulus (the test person) did not change. These results suggest that the effects of repeated AD on defensive response are influenced by prior positive experiences with a given stimulus. Given the generality of behavioral response change, and the modulation of degree of that change by the severity of threat, the results suggest that the brain stimulation altered a defensive personality characteristic of these cats. These results are somewhat surprising in view of prior evidence that electrical excitation of the VHPC facilitates predatory aggression in cats (Siegal & Flynn, 1972). To understand this apparent contradiction, the results of the physiological studies must be considered. These results are the topic of the second report. REFERENCES Adamec, R. (1974). Neural correlates of long-term changes in predatory behaviour in the cat. Ph.D. thesis, McGill University. Adamec, R. (1975). Behavioural and epileptic determinants of predatory attack behaviour in the cat. Canadian Journal of Neurological Science, November, 457-467. Adamec, R. (1978). Normal and abnormal limbic system mechanisms of emotive biasing. In K. E. Livingston and O. Hornykiewicz (Eds.), Limbic Mechanisms, pp. 405-455. New York: Plenum. Adamec, R. E., Stark-Adamec, C., & Livingston, K. E. (1980). The development of predatory aggression and defense in the domestic cat (Felis catus) I. Effects of early experience on adult patterns of aggression and defense. Behavioral and Neural Biology, 30, 389-409. (a) Adamec, R. E., Stark-Adamec, C., & Livingston, K. E. (1980). The development of predatory aggression and defense in the domestic cat (Felis catus). II. Development

PARTIAL KINDLING, EMOTIONAL BIAS, I

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of aggression and defense in the first 164 days of life. Behavioral and Neural Biology, 30, 410-434. (b) Adamec, R. E., Stark-Adamec, C., & Livingston, K. E. (1980c). The development of predatory aggression and defense in the domestic cat (Felis catus). III. Effects on development of hunger between 180 and 365 days of age. Behavioral and Neural Biology, 30, 435-447. (c) Adamec, R., Stark-Adamec, C., & Livingston, K. E. (1983). The expression of an early developmentally emergent defensive bias in the adult domestic cat (Felis catus) in non-predatory situations. Applied Animal Ethology, 10, 89-108. Adamec, R., & Stark-Adamec, C. (1983). Limbic kindling and animal behavior Implications for human psychopathology. Biological Psychiatry, 18(2), 269-293. Alonso de Florida, F., & Delgado, J. M. R. (1958). Lasting behavioral and EEG changes in cat induced by prolonged stimulation of the amygdala. American Journal of Physiology, 193, 223-229. Andrew, R. J. (1972). The information potentially available in mammal displays. In R. A. Hinde (Ed.), Non-verbal Communication, pp. 179-206. London: Cambridge Univ. Press. Delgado, J. M. R., & Anand, B. K. (1953). Increase of food intake induced by electrical stimulation of the lateral hypothalamus. American Journal of Physiology, 172, 162168. Douglas, R. M., & Goddard, G. V. (1975). Long-term potentiation of the perforant pathgranule cell synapse in the rat hippocampus. Brain Research, 86, 205-215. Ervin, F. R., Mark, V. H., & Stevens, J. (1969). Behavioral and affective responses to brain stimulation in man. In J. Zubin & C. Shagass (Eds.), Neurobiological Aspects of Psychopathology, pp. 54-65. New York: Grune & Stratton. Flynn, J. P., Foote, W., & Edwards, S. (1970). Neural mechanisms involved in a cat's attack on a rat. In R. E. Whalen, R. F. Thompson, M. Verzeano, & N. M. Weinberger (Eds.), The Neural Control of Behavior, pp. 210-240. New York: Academic Press. Grant, E. C., & Macintosh, J. H. (1963). A comparison of the social postures of some common laboratory rodents. Behaviour, 21, 246-259. Goddard, G. V., McIntyre, D. C., & Leech, C. K. (1969). A permanent change in brain function resulting from daily electrical stimulation. Experimental Neurology, 25, 295330. Goddard, G. V., & Douglas, R. M. (1976). Does the engram of kindling model the engram of normal long-term memory? In J. A. Wada (Ed.), Kindling, pp. 1-18. New York: Raven Press. Goddard, G. V., McNaughton, B. L., Douglas, R. M., & Barnes, C. A. (1978). Synaptic change in the limbic system: Evidence from studies using electrical stimulation with and without seizure activity. In K. E. Livingston, & O. Hornykiewicz (Eds.), Limbic Mechanisms, pp. 355-368. New York: Plenum. Kaada, B. R. (1972). Stimulation and regional ablation of the amygdaloid complex with reference to functional representations. In B. E. Eleftheriou (Ed.), The Neurobiology of the Amygdala, pp. 205-282. New York: Plenum. Leyhausen, P. (1956). Verhaltensstudien an Katzen. Zeitschrift~r Tierpsychologie Beiheft, 2, 1-120. Leyhausen, P. (1965). Uber die funktion der relativen stimmungeshierarchie. Zeitschrift fur Tierpsychologie, 22, 412-494. Livingston, K. E. (1978). The experimental clinical interface: Kindling as a dynamic model of induced limbic system dysfunction. In K. E. Livingston & O. Hornykiewicz (Eds.), Limbic Mechanisms, pp. 521-534. New York: Plenum. Monroe, R. R. (1970). Episodic Behavioural Disorders: A Psychodynamic and Neurophysiologic Analysis. Cambridge, Mass.: Harvard Univ. Press.

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Post, R. M., & Ballenger, J. C. (1981). Kindling models for the progressive development of behavioral psychopathology: Sensitization to electrical, pharmacological, and psychological stimuli. In H. M. van Praag, M. H. Lader, O. J. Rafaelsen, & E. J. Sachar (Eds.), Handbook of Biological Psychiatry, Part IV, pp. 609-651. New York: Dekker. Post, R. M., Ballenger, J. C., Uhde, T. W., Putnam, F. W., & Bunney, W. E., Jr. (1981). Kindling and drug sensitization: Implications for the progressive development of psychopathology and treatment with carbamazepine. The Psychopharmacology of Anticonvulsants (The British Association for Pharmacology Monograph series). Oxford: Oxford Univ. Press. Racine, R. (1978). Kindling: The first decade. Neurosurgery, 3(2), 234-252. Siegal, A., & Flynn, J. P. (1968). Differential effects of electrical stimulation and lesions of the hippocampus and adjacent regions upon attack behavior in cats. Brain Research, 1, 252-262. Stark-Adamec, C., & Adamec, R. (1980). Summary of the integration of applied and experimental psychology. Applied Psychology Newsletter, Vol. 6, Issue 1, 9-12. Stevens, J. R., Mark, V. H., Ervin, F. R., Pacheco, P., & Suematsu, K. (1969). Deep temporal stimulation in man. Archives of Neurology, 21, 157-169. Stokman, C. J., & Glusman, M. (1970). Amygdaloid modulation of hypothalamic flight in cats. Journal of Comparative and Physiological Psychology, 71, 365-375. Winer, B. J. (1962). Statistical Principles in Experimental Design. New York: McGrawHill.