Early coping experience and later aversive conditioning in cats

97

PSP 00050

EARLY COPING

THOMAS

W. NICHOLAS

(Accepted Kq

June

words:

Kittens

15th.

were given

experience.

allowing

one member served

reached early

treatment;

early

differential Separate

heart

to early

treatment

early

groups

of a weight

asymptote

gave evidence

be related

S. STEFAN

control.

shock.

experience

in order

behavior

the first

Heart

pair

measures.

rate did not differentiate an increased

escaping tendency

Effects on development from early environmenmanipulation have been recorded from body

weight, brain chemistry and behavior (Bennett et al.. 1964; Bennett et al., 1970). While some research has clearly demonstrated the effects of deficient stimulation on later sensory (Hubel Wiesel, 1965; Wiesel and Hubel. 1965) and ceptual studies

(Held and Hein, have suggested that

and per-

1963) function, other anatomical differences

obtained in subjects reared in restricted or enriched environments might also reflect differences in learning or other cognitive functions (Krech et al., 1962: Greenough et al., 1972: Melzak. 1962). In addition to early manipulation in rearing condi-

Corrapondencr: wood

Plaza,

S. Soltysik, University

MRRC.

of California,

NPI

58-258,

Los Angeles.

760

West-

CA 90024.

U.S.A.

0167-8760/84/$03.00

;I 1984 Elsevier

Science

Publishers

B.V.

coping while

task

from

with

during

heart

confined

a passive

were

member tested

ones.

Rather,

of age.

by

was confined:

a third

since

kittens

the older

for effects

classical

rate

of an inescapable

4 or 12 weeks

of differential

conditioning.

rate response

defensive

heart

the result

at either

the other

were measured

with

conditioning

12 week old subJects.

a potentiated

kittens to react

behavior

runw’ay

for 4 and

classical

of age. the suhJects

activity only

aversive

behavior.

different

At 6 months

and somatic

response

-

motivated

an escape

was significantly trials.

learning

an obJective

in a shock

to acquire

rate and amplitude.

reflecting

escape

to compare

treated

few shock

in one or more

perhaps

behavior

were

sibling

Escape

within

rate. respiration

experience.

- coping

INTRODUCTION

tal

IN CATS

SOLTYSIK

of kittens

matched

of acquisition

with

CONDITIONING

1984)

as a handled

a running

groups

and

AND LATER AVERSIVE

development early experience defensive responses - kitten

aversive subject

EXPERIENCE

in 4 week heart

While kittens

all

could

rate was related

to

response.

tions, some studies have investigated the effects of specific behavioral treatments in early development. Wilson et al. (1965) varied environmental complexity and also handling in kittens. They found that handling did not interact with complexity; however, handling increased ior to humans and unfamiliar creased the acquisition which might reasonably fear.

The

manipulations

of shock avoidance, effects result from a decrease in

implication early

approach behavobjects and de-

is clear in

that

development

experimental may

affect

emotionality. and thereby modify the behavioral response normally expressed in a fear-provoking situation. It has also been shown that, in adult subjects, behavior to a fear-provoking situation can be modified through a coping response. A coping response is generally taken to be a learned behavior which allows a subject to overcome the aversive consequences of stressful situations. For example,

rats which acquired control shocks were protected from

over aversive electric the physiological con-

sequences of stress, when compared with control subjects that were subjected to the identical shock stimuli (Weiss, 1968). Also, within the paradigm described as learned helplessness (Maier and Selig-

discrete categories of simple heart rate acceleration or deceleration. In addition. a small amount of data suggests that once developed, the aversive conditiomng heart rate pattern is stable: Soltysik et al. (1982) present the heart rate pattern of one cat

several

months

after

initial

conditioning,

and

man. 1976; Seligman et al.. 1971) subjects immobilized by inescapable shock could overcome

the pattern is substantially Thus, much evidence

the immobility if they were forced to perform an avoidance response. Thus, active coping has been

structured and standardized environment of classical conditioning, some cats react with acceleration as the predominant heart rate response, while

shown to alleviate the deleterious effects of stressful shock. However, the term, coping, is also used by Obrist (1981, 1982) to refer to both active and passive strategy. Active coping is linked with the heart rate acceleration which results from action or the anticipation of action. Passive coping is linked with heart rate deceleration, resulting from tasks characterized by inaction or little effort. While the concept of passive coping is intuitively acceptable, there is often uncertainty about the specific behaviors involved. With somewhat less uncertainty. another view of coping behavior would relate coping to the active and passive defensive reactions shown by animals to aversive stimulation. In that framework the heart rate acceleration or deceleration to a fear-provoking stimulus is taken as evidence that an animal has responded with an active or passive defensive reaction (Konorski. 1967). The heart rate response of adult cats has been extensively studied (Santibanez-H et al., 1963; Hein, 1969; Howard et al.. 1974) with the result that a deceleration of heart rate is the typical response attributed to cats within the aversive classical conditioning paradigmn. However, depending on the particular methodology, a leg flexion response may be acquired, and in that case cats with conditioned flexion tend to show an anticipatory heart rate acceleration in the C-US interval (Brunner. 1969; Soltysik et al., 1982). More recently, Nicholas et al. (1983) have presented an ontogeny of aversive conditioning heart rate patterns for kittens. That work suggests that the heart rate component of the response to aversive stimulation develops before the expression of an overt skeletal response. They reported that kittens at about 8 weeks of age show no evidence of acquired somatic response, but do divide themselves into

unchanged. shows that in the highly

others react with deceleration. What causes the difference in response? One approach to that question could assume an effect of early environment. In that case, the tendency to react to the aversive classical conditioning paradigm with active or passive coping (Obrist, 1981) or active or passive defensive response (Soltysik et al.. 1982) and the concomitant acceleration or deceleration of heart rate. might depend on the results of an early experience with aversive stimulation. If so. then the acquisition early in life of a particular coping response to aversive stimulation might result in some characteristic behavior later in life. Apparently the kitten heart rate pattern does not begin to show individual differentiation before 4 weeks after birth (Soltysik et al., 1982). For that reason it was decided to provide one group of subjects with an environmental manipulation at 4 weeks of age and, for contrast, another group at 12 weeks of age, the point at which kitten heart rate pattern seems to acquire adult characteristics (Nicholas et al., 1983). The environmental manipulation was subdivided into 3 conditions, and the conditions were filled with littermates. In one condition the subject was assigned to function as the handled control. In a second condition another subject received a series of aversive electric shocks over which it had no control. In the third condition another subject received the same aversive shock experience, but it was able to exert some degree of control over the experience. In particular, the subject in the third condition was required to objectively manifest an active coping strategy to early aversive stimulation by the acquisition over trials of a running response. At 6 months of age. each subject was tested by its performance in a learning situation, the acquisition of aversive

YY

classical

conditioning

in Nicholas

by the procedure

training.

described

Su&ects The subjects were kittens raised from birth the Mental Retardation Research Colony

litters

The kittens were reared with their sizes no larger than 5. For kittens larger

than

5. the

lightest

kittens

in at

siblings born to were

re-

moved within the first week after birth. The litters were separated from their mothers at 8 weeks of age. Food and water were continuously available in each litter cage. The subjects were handled several times each week, since routine colony care involved weighing, feeding, inspection and vaccination. Apparutus and surgery Early training. Kittens were exposed to an early training experience at either 4 or 12 weeks of age. A straight runway was used to provide a standardized

early

experience.

The straight

runway

(90

X

22 cm) was constructed with a goal box at one end and a start box and shock box at the other end, all of the same dimensions (30 X 22 cm). A shock grid composed of 0.64 cm diameter brass rods formed a floor for the runway, start box, and shock box: the goal box had a solid wood floor. A constant alternating current (AC) shock of 0.4 mA was supplied to the grid floor by a model 2903 shocker-scrambler (BRS/LVE, Beltsville. MD). Opaque, cloth-covered plexiglass lids formed a roof for the entire apparatus, and wooden guillo-

tine doors separated the start box and the goal box from the runway. Raising the start box door automatically triggered a timer which continued until the goal box door trapped the subject in the goal box; closing the goal box door also terminated the AC grid shock. Before

size

ranged

from

subject. In litters with 4 kittens sometimes form only one R and assign the two remaining kittens

METHOD

UCLA. in litter

Litter

runway

3 to 5 kittens.

With a litter size of 5 it was possible to form two R and S subject pairs, while also having one H

et al. (1983).

training,

the

members

of each

litter were assigned as handled control subjects (H), running subjects (R), or confined shock subjects (S). Within each litter, the R and S siblings were matched as closely as possible by weight in an attempt to obtain equivalent subjects for early

it was useful to S pair, and then as handled con-

trols in order to increase the group size for the H condition. During runway training, an R subject was placed in the start box, and the matching S littermate

was

placed

in the

The grid shock was turned start box door was opened;

adjoining

shock

box.

on for 3 s before the this procedure insured

that every R and S subject received at least 3 seconds of grid shock on every trial. The grid shock was terminated for both the R subject and the S subject when the goal box door trapped the R subject in the goal box. Since the weight-matched R and S subjects stood on the same shock grid floor, and since the shock duration was controlled by the running time of the R subject. a rough equivalence of the physical parameters of shock duration and intensity was assumed for this yoked-subject training procedure. After each training trial, the R subject and the S subject were returned to a carrying box, where the rest of the litter remained. Between training trials the H subject was handled and placed in the goal box for 1 min before being returned to the

carrying box. Runway training consisted of a 10 trial training session in the morning and afternoon each day for 5 consecutive days. was

Lute training. At 6 months of age each given classical conditioning training.

subject While

giving all kittens late training at the same age did result in a slightly longer intertask interval for the 4 week subjects, it was important that the maturing kittens undergo classical conditioning at an objective and equivalent point in development. As a prerequisite to classical conditioning training in the second apparatus, a restraint stand, each animal was anesthetized with pentobarbital and prepared with an embedded ECG electrode and an acrylic cranial cap. Surgery took place for all subjects two weeks before training in the restraint stand. The details of the surgery and a complete description of the restraint stand has been published (Wolfe and Soltysik. 1981). Briefly, the acrylic cranial cap

can

be bolted

to the

restraint

stand.

thus

rigidly

fixing the subject’s head during training. A cloth harness serves to secure the subject’s body while freeing the legs to walk on a treadmill. Taken together, the surgery. restraint apparatus. and associated electronic equipment permit the recording of heart rate and skeletal responses (see Nicholas et al., 1983). as well as respiration (see Soltysik et al.. 1983) and vocalization during classical conditioning training. The classical conditioning procedure consisted of the pairing electric shock; were controlled

of a tactile stimulus stimulus presentation electromechanically.

tioned

(CS)

stimulus

of 1 g force directed kitten’s sacral region.

was

with brief and timing The condi-

a 5.2 second

air stream

at a shaved portion of the The unconditioned stimulus

(US) was a 4.0 mA, 200 ms. 60 Hz shock delivered through surface electrodes at the tail and the left plantar surface. In previous work (Nicholas et al.. 1983) it was found that in the initial trials of classical conditioning training. cats are very reactive to the 4.0 mA US; however, an increasing ahock procedure allows the 4.0 mA US to be tolerated. Therefore training was always begun with a US Intensity of 2.25 mA and increased by 0.25 mA at each session. until in later sessions the intensity reached 4.0 mA. The lower used in early sessions was an effective

shock level US. since a

prompt leg flexion was always observed. The classical conditioning training consisted 12 sessions.

The

first

session

was

of

a habituation

session during which the air CS was presented alone on 5 trials in order to provide data on the subjects’ pretraining responses to the CS. In the next 10 sessions the air CS and the shock US were paired in 10 trials per session by presenting the

Each subject’s leg flexion, tion patterns were formed

heart rate, and respiraas an average of several

trials. The performance for each response measure prior to conditioning was computed as an average of the 5 pretraining trials of the habituation session. Acquisition performance for each response measure was computed as an average of the last 20 trials of CS-US pairing (sessions 9 and 10). Average extinction performance was taken from the last 5 trials of the 20 trial extinction session. since little decrease in responding was noticed until late in the extinction period. Leg fkuion. The vertical deflection of a potentiometer defined leg flexion. as well as walking or running in the restraint stand. for all subjects. The potentiometer was attached by an insulated metal rod to the left rear (shocked) leg. The output of the potentiometer was then amplified and displayed by a chart recorder as a continuous line graph for the duration of every trial. A digitizing tablet (Houston Instruments. Austin, TX) was used to enter the flexion graphs into a computer. Ileurt rutr. The procedures for recording and analysis of heart rate have been described in Nicholas et al. (1983). Briefly, heart rate (R wave to R wave) is recorded from an embedded abdominal electrode during the 10 s pre-CS period and the 5 s CS presentation of every trial. A computer analysis allows the interbeat intervals to be sampled every 250 ms, thus defining a heart rate function of 40 pre-CS and 20 CS heart points on any single trial. To equate for ferences

in heart

rate

level

between

subjects,

rate difthe

mean pre-CS trial heart rate is always subtracted. thus allowing heart rate to be expressed as a deviation from the pre-CS level. Respirution. Detailed procedures for recording

air CS was presented alone for 20 trials. Every trial in all sessions consisted of a 10 s pre-CS period and a 5 s CS presentation. The

and analysis of respiration data have been described in Wolfe and Soltysik (1981) and Soltysik et al. (1983). The respiration rate and amplitude data are derived from a thermister suspended next to the subject’s naris. The transducer accurately follows inhalation and exhalation and supplies a continuous sine function which is recorded on chart paper; the sine function describes both a relative measure of the amount of respiration directed upon it and the respiration rate. The respi-

intertrial

ration

shock 5000 ms after air onset, thus defining a 5 s interstimulus interval (ISI). Acquisition sessions were run twice daily. The increasing shock procedure was used. from the first to the eighth acquisition session; however, the US of the last 3 acquisition sessions (30 trials) was always 4.0 mA. The twelfth session was an extinction procedure: the

interval

varied

between

2 and

4 min.

data

were

recorded

during

the

10 s pre-CS

101

_ ACC!UISITION

period and the 5 s CS presentation of every trial. After using a digitizing tablet to enter the respiration

data

ration every

rate is similar to that for heart rate. On trial the interpeak interval of each positive

into

a computer,

the analysis

IIF

ESC’QPE

RESPONSE

of respi-

on the respiration sine wave is measured, and then a respiration rate function, consisting of 20 pre-CS and 10 CS respiration points, is derived by sampling the interpeak intervals every 500 ms. The respiration amplitude is computed by constructing a continous envelope on the respiration sine wave from the vertical distance between positive and negative peaks. The peak to peak amplitude envelope is then sampled every 500 ms and displayed as a percentage of the pre-CS amplitude.

peak

!i @1 0

AND

DISCUSSION

the

1. Average runway

allowed

Early

times

training

Runway manipulation

training. The in the runway

running

apparatus

to escape

grid

is expressed

TRAItlING

performance for

4

3

2

RUNWriY Fig.

RESULTS

1

4 and

shock.

Group

as one standard

UkYS

during

the

5

early

12 week

training

groups

variability

in

(Run)

in running

deviation.

early environmental apparatus was desig-

ned to produce two subjects, each with a different response to substantially the same shock stimulus. For the R subjects, entering the goal box prevented further grid shock and allowed the acquisition of an organized running response. The yoked S subjects, however, had no control over the grid shock. It can be noted that the prevalent reaction to grid shock among confined S kittens was vocali-

period.

zation and immobility. On a descriptive level. that observation seems consistent with the notion that experience with inescapable shock may result in inactivity, either a transient and biochemical one

the time of early training. Four week R kittens were consistently slow to leave the start box and less organized in running, since they often turned around and had to retrace their paths. In contrast. 12 week R subjects generally acquired a distinct start box exit and uninterrupted passage to the goal box within the first training session. The graph of kitten running performance (Fig. 1) clearly suggests that the escape task was quite easy for the older kittens to learn.

(Weiss et long-lasting Black,

al., 1975; learned

1974; Glazer

Glazer et inactivity and Weiss,

al., 1975) (Bracewell

or a and

1976).

Runwa_y escape. Daily escape performance is shown in Fig. 1 for the R subjects in the 4 week and 12 week groups. A large heterogeneity of variance in the raw data was improved (F = 4.10; df = 5,7; 0.05 < P < 0.10) by a reciprocal transformation, and escape performance over the 5 day training period for the 4 and 12 week R was tested with a trend analysis (Dixon and 1979). A significant main effect for Days (F df = 4,48; P < 0.001) gave evidence of a change in escape performance over the

subjects Brown, = 6.64; general training

tion

However, (F = 6.19;

a significant df = 4,48;

Age

X

Days

P -C 0.001)

interac-

confirmed

that the form of the performance curve for each age is not the same, suggesting that escape acquisition was different weeks of age. The trend fact confirms

Lute

for

early

training

at 4 or

12

analysis for runway performance the behavioral observations made

in at

truining

Analysis. The design of the classical conditioning phase of the experiment called for the recording of all response measures in each subject during an initial habituation session, in which the CS was presented habituation

without the measurement

shock was

US. Since the obtained for all

groups before any presentation of paired CS and US. it was reasonable to form a comparison group by averaging the response during habituation from the handled, running, and confined shock groups. The comparison group was then used as the standard from which to assess possible changes in response during acyuisition and extinction. The use of a numerically larger habituation control group allowed a better estimate of the subjects’ naive.

tered into Table I as a group mean for each early training category: the pre-CS respiration rate (respiration rate points 1 to 20) was entered into Table II. Among the habituation data; two-tailed f-tests of the 10 s pre-CS habituation heart rate and respiration rate (Tables I and II) did not reach statistical significance, thus failing to give evidence of any difference in baseline response between 4 and 12 week kittens at six months of age.

pretraining Also, the

However, an inspection of both the pre-CS heart rate and respiration rate means (Tables I and

with

response arrangement

several

smaller

by

using all available of a large control

treatment

groups

met

data. group the re-

II) suggests

that the baseline

response

for both

age

quirements for Dunnett’s test (Edwards, 1972). a multiple comparisons test based in part on the

groups tended to decrease throughout ing. The Dunnett’s test gave evidence

error mean square from a preliminary one-way analysis of variance. Separate habituation comparison groups were formed for the 4 and 12 week kittens, and a separate Dunnett’s analysis was

4 week kittens, both the heart rate and respiration rate pre-CS response during habituation is significantly different from the pre-CS response in both the acquisition and extinction stages of training. The change in pre-CS heart rate is less complete among 12 week kittens, but two out of 3 groups do show a statistically significant change at the extinction period. A uniform decrease in the baseline level of heart rate and respiration rate would not necessarily be completely unexpected, since some

computed

age group. The 10 s pre-CS response represents a measurement of the steady state or resting response of the kittens immediately before the CS presentation of each trial. Since both heart rate and respiration rate were continuously recorded for the duration of every trial. two different meaPrr-CS

for each haselinr.

sures of the 10 s pre-CS baseline level were available to use in assessing differences between 4 and

adaptation to the restraint stand, chamber, and shock current might the course of classical conditioning

12 week

extinction

kittens

at 6 months

of age. Pre-CS

respi-

ration amplitude was not assessed. because respiration amplitude was a relative measurement. dependent on amplifier gain settings which can differ over training rate for each habituation,

sessions. The averaged pre-CS heart subject (heart rate points l-40) from acquisition. and extinction was en-

late trainthat for the

experimental continue over training and

sessions.

CS huhituution response. In a second set of measurements differences were found between the 4 and 12 week kittens at 6 months of age. The response of the 4 and 12 week kittens to an unpaired CS was tested by f-tests of the heart rate and

respiration

response

measures,

and

the results

-FABLE 1

t1 04 R 04 s 04 H 12 R 12

180 1X6 170 176 168

24 22 I6 2x 40

7 x 6 4 4

169 1x1 1x0 170 150

12 IX 19 22 27

7 8 6 4 4

s 12

196

36

5

188

30

5

* = two-t&d Huhituurmi

P > 0.05.

P 4 0.05. 4 ueek:

drrtu:

mean = 197. SD. = 15. n = 21: 12 wek,

* * * *

* * * * *

mean = 193. SD. = 15. n = 13; two-tatled

I = 0.74. df=

32,

103

Group ugr

Extinction

Acqursitron

(wreks) H 04

Dunnert

k t

MWfl

S. D.

n

MtWl

S. D.

n

Ac'q.

EUI.

66

14

7

61

22

8

*

*

R 04

52

12

8

49

14

8

*

*

s 04

50

10

4

43

16

7

*

*

H 12

68

18

4

61

22

4

*

*

R 12

57

15

4

48

25

4

*

*

s 12

68

22

5

61

21

5

*

*

* = two-tailed Hahrtuarmn

P i 0.05. da/a:

4 week;

mean =74,

SD.

= 18.

n = 21;

12 week,

mean = 86.

S.D. = 22,

n = 13:

two-tailed

I = 1.60.

df = 32.

P > 0.05

listed in Tables III-V. It was found that the respiration rate during habituation exceeded the critical value (t = 2.03; df = 32; P = 0.05) for a two-tailed r-test (Table IV). The difference in the level of the respiration rate during the 5 s CS presentation in the habituation period can be seen in Fig. 4, where the 12 week subjects’ respiration rate to an unpaired CS appears somewhat faster than that of the 4 week subjects’ response. CS leg flexion. The individual flexion patterns during CS presentation were averaged into group patterns and classified by early training condition. There was no leg activity during the CS for the habituation period or the extinction period. During acquisition, while there was little or no evidence of a discrete leg flexion, walking, or running response among individual did express a small amount

subjects, all subjects of leg activity shortly

before the onset of the shock US which, it can be noted, in no way imitated the topography of the unconditioned flexion. However, since leg activity was observed during acquisition but not during habituation or extinction, some somatic conditioning can be suspected. A case has been presented (Soltysik et al., 1982; Nicholas et al., 1983) that rather than acquire a discrete leg flexion, learned anticipation

many cats appear to express of a shock US by tensing or

crouching, somatic responses which would account for the leg activity seen exclusively during CS-US pairing in all subjects. CS heart rate. Individual heart rate patterns

during

CS presentation

(heart

rate points

41-60)

were averaged into group patterns and classified by the early training categories. The group heart rate patterns obtained from the 5 CS habituation trials, the last 20 acquisition trials, and the last 5 extinction trials are shown in Fig. 2, along with an estimate of the variability within each group. The statistical analysis of the beat-by-beat CS heart rate pattern involves special difficulties often seen in physiological data notably, serial correlation and variability (Richards, 1980). Within the present

methodology,

an individual

subject’s

heart

rate pattern is quite reliable, since it is derived from an average of several trials in a highly standardized

situation.

However,

within the group pat-

terns there is a small variability around CS onset, which increases up to the time of the UCS (Fig. 2). The normal solution to heterogeneity, transformation, is not always effective, thus compromising the use of an analysis of variance. However, quantification and analysis of heart rate is possible by examining a small portion of the heart rate pattern. What appears to be the important differentiating characteristic of the heart rate pattern during CS presentation is a change in the deceleration amplitude. Among the heart rate patterns described in Fig. 2, a small deceleration is evident during the CS for both the 4 and 12 week groups in the habituation period; the deceleration appears to show an increase during acquisition for the 4 week groups, but not for the 12 week groups. Moreover, the decrease in pre-CS, or baseline,

104

GROUP FOUR

_

10-m

HABITUQTION

IO--

QCBUISITION

HEART

RATE

WEEK

TWELVE

CS DURATION Fig. 2. The heat-by-heat

patternof

PATTERNS

heart rate during C‘S presenta

Run and Shocked) in the habituation,

acquisition.

and extinction

heart rate over classical conditioning sessions (Table I) could in no way be responsible for an increase in CS heart rate deceleration (Fig. 2). The 5 s heart rate patterns during CS presentation which are described in Fig. 2 are each graphed as 20 points (heart rate points 41-60); the heart rate deceleration appears to be maximum at slightly less than midway in the CS interval. To allow a detailed examination of any effect in heart rate deceleration response, a mean was computed from heart rate points 48, 49 and 50 to define the peak deceleration near the middle of the CS presentation. The peak heart rate deceleration was computed for each subject in each of the habituation, acquisition, and extinction stages of training. The change in peak heart rate deceleration across

WEEK

IN SECONDS (heart rate p~inl.\ 41-60)

for wch earl? training group (Handled.

stages of classica I conditwning

classical

tralnlng. Group

conditioning

sessions

variability

is shown

IS plotted

in Fig. 3

for each early training group. The data described in Fig. 3 suggest that classical conditioning training resulted in little or no reliable change in the heart rate of 12 week kittens; however, among the 4 week kittens. a strong effect during classical conditioning is evident in the heart rate among both the R and the S groups. The results of Dunnett’s test, comparing the peak heart rate deceleration in acquisition and extinction with the deceleration in habituation, are shown in Table III. A significant change in the level of heart rate deceleration during acyuisition is a?parent only among the R and S 4 week subjects, a result consistent with the relationship described in Fig.

3. Little

change

resulted

in the heart

rate

105 0

CHANGE

IN CS

HEART

deceleration

RATE

DECELERATION

as a result

dure, suggesting

of the extinction

that the deceleration

proce-

in acquisi-

tion was a very reliable response. CS respiration rate. Individual respiration rate patterns during CS presentation (respiration rate points 21-30) were averaged into group patterns by early training categories. An initial inspection

8.

- 8

-17

of the acquisition data revealed considerable uniformity, since among the group patterns respiration rate in the CS-US IS1 steadily increased,

-25

beginning within the first onset. Because respiration

half second after CS rate pattern did not

0

differ among the groups, the data within each age category were averaged into summary patterns for

_ 8

of training. In Fig. 4 the summary respiration rate pattern for habituation shows little change during

-17

the CS, while the pattern for acquisition shows a steady increase until about midway in the 5 s ISI. The respiration rate pattern for extinction appears to show a recovery to habituation levels, especially after the midpoint of the CS presentation. Like

the habituation,

-25

.I...

,

HUB.

Fig. 3. across training tics for

TABLE

and extinction

stages

heart rate, the changes in CS respiration rate were not reliably related to the steadily decreasing preCS baseline (Table II).

t

CICQ.

EXPERIMENTAL

acquisition

EXT.

PEPIOOS

The change in average peak heart rate deceleration classical conditioning training stages for each early group (Handled, Run and Shocked). Descriptive statisthe heart rate deceleration are listed in Table III.

To determine if the maximum respiration rate among the stages of classical conditioning training was statistically different, summary respiration rate means were computed from the respiration rate (points 24, 25 and 26) at the middle of the CS

III

Heart rate deceleratmn during CS presentation

expressed (IS (I derriurion from the pre-CS

mean

Extrncrion

Dunnerr’s I

Group Age (weeks)

Acquisition Mean

S. D.

n

Mean

SD.

n

Acq.

EXZ.

H 04 R 04 s 04 H 12

-8 -20 -19 -8

9 15 10 15

7 8 6 4

-12 -21 -23 -17

8 16 9 16

1 8 6 4

* * -

_ * * *

R12 s 12

-5 -11

20 21

4 5

-12

11 4

4 5

-

_ _

* = two-tailed P < 0.05. Hahrtuntion data: 4 week, mean = -5.5, P > 0.05

1

SD. = 4.3. n = 21; 12 week. mean = -5.4,

S.D. = 7.6. n = 13; two-tailed

I = 0.03, df = 32,

125

RESPIRQTION

J_

RFlTE

IV. The Dunnett’s test revealed that classical conditioning was much more effective for the 4 week groups because among the three 12 week groups,

HAS . . .. . .. WQ

FOUR

1oc

only one demonstrated a significant change in respiration rate during acquisition. As a result of the extinction procedure, respiration rate was effectively modified in only one of the 4 week groups (Table IV). CS respirution unqditude. Individual respiration amplitude patterns during CS presentation (respiration amplitude points 21-30) were averaged into

WEEK

7: j--

,_..,+.,, .._,,..,..,....+. 5c3 ....................~. ,....,,I, ,,,..(,,,,,,.,, groups

by early training respiration rate.

”

.

case

-

1013

TWELUE

plitude crease

WEEK

5 01

..,,..,..,..,,,,,,.,, I.......,,,,,,,........

I..,...................I......,...............)

2

1

3

CS OURFlTION Fig. 4. Average

Group

respiration

for both and

early

extinction

variability

stages

CS presentation

ages in the habituation. of classical

ia plotted

5

IN SECONDS

rate during

training

4

. .. ..... . . t.

conditioning

as one standard

(points acquisitraining.

deviation.

decreased

during

spective of the age group experience; a significant amplitude trials.

also

acquisition.

characterized

the

irre-

late

extinction

.$ t

MNIII

S. D.

n

MeWI

S D.

n

Acy.

E.z f.

H 04

110

25

7

86

31

7

*

*

R 04

x5

I8

8

81

10

8

*

s 04

99

3s

6

62

28

6

*

*

H 12

141

56

4

73

31

4

*

R I2 S 12

105 111

68 31

4 5

63 83

40 32

4 5

_ *

_

_

* = two-tailed

proam-

or type of early training reduction in respiration

l!lunnrtt

EHlIKfWfl

Acyu~rwn

Group Age (weX.s)

the of

pattern in acquisition appeared as a dein amplitude which reached a minimum

significantly

presentation for each subject in each of the habituation. acquisition and extinction phases; the summary respiration rate data is shown in Table

ffahiruutron

As was inspection

slightly less than midway through the CS-US ISI. In order to quantify the decrease in respiration amplitude, summary means were computed from respiration amplitude (points 23 and 24) near the midpoint of the CS presentation for each subject in each of the habituation, acquisition. and extinction phases. The summary values were then averaged by early training condition and entered into Table V. The Dunnett’s tests for the respiration amplitude data (Table V) are consistent with the relationship shown in Fig. 5; respiration amplitude

7’5

tion,

categories. an initial

the data suggested that most of the groups duced the same basic pattern. The respiration

1215

21-30)

for

P c 0.05. d&o:

4 week.

mean

= 7b, S.D. = 20. n = 21: 12 week.

mean

= 93. S.D. = 21. n = 13: two-tailed

t = 2.27.

df = 32. P < 0.05.

107

RESPIRfiTION

GENERAL

AMPLITITUOE

An unexpected result in the experiment was the finding that escape performance was severely retarded (Fig. 1) in 4 week kittens, but not in older kittens. It is certainly true that small kittens can-

96.

82.

EXT . . ...a....

not run as quickly as larger subjects, and thus kitten performance in a large apparatus may need to be specially considered (Feigly and Spear, 1970). Nevertheless, a real qua/itatiue difference in runway escape behavior, which did not seem related

68.

54.

40 / 110

82

68

54

40 0

5

2.5 CS DURATION

5. Average

acquisition. training.

respiration

21-30)

for both and

Group

variability

IN SECONDS

amplitude early

extinctlon

the

apparent.

kitten

or the

apparatus,

during

training stages

of

is plotted

CS presentation

ages in the habituation, classical

conditioning

as one standard

deviation.

have reported that the acquisition of active avoidance is the same for young or old kittens. If escape and active avoidance are viewed as examples of aversive instrumental avoidance, then the two behaviors ought to be correlated. The discrepancy might be reconciled if a maturational change in active behavior occurs at 8 weeks of age. Some reports of kitten development do indicate changes in motor activity (Levine et al., 1980) and heart rate pattern (Nicholas et al., 1983) at about 8 weeks of life. If maturation is important in avoidance choice

behavior, then Davis and Jensen’s (1976) of 7 weeks for their older group may have

precluded

any

avoidance.

The maturational

correct,

TABLE

size of the

,p...,,. ,,, .,..,,,.,.,.~"""~.~~..~.~~‘ differential t

96

Fig.

to either was quite

It is not clear why escape behavior should show expression as a function of age, while active avoidance does not; Davis and Jensen (1976)

TWEL','E WEEK

(points

DISCUSSION

would

observation support

of the

differential

hypothesis, notion

that

active if proven aversive

V

Maxrmum

respiration

Group Age (weeks)

amplitude

during

CS presentation Dunnett’s

Extinction

Acquisition

t

Mean

S. D.

n

Mean

S. D.

n

Acq.

Ext.

56

32

I

78

27

7

*

*

R 04

51

29

8

50

31

8

*

*

s 04

39

18

6

64

22

6

*

* *

H 04

H 12

38

19

4

73

22

4

*

R 12

63

40

4

73

24

4

*

*

s 12

36

11

5

63

15

5

*

*

* = two-tailed Huhituution

P < 0.05. duta: 4 week.

mean

= 95, SD.

= 20,n = 21: 12 week. mean

= 87. SD.

= 15. n = 13: two-tailed

t=

1.61, df = 32, P > 0.05.

10x

instrumental

learning

tasks

are suitable

for relat-

ing development to behavior. Early training in the runway apparatus was an attempt to present an equivalent grid shock stimulus and yet, to establish an objective coping response in one littermate while another underwent an inescapable aversive experience. Detection of any lasting effects of the early acquisition of coping or non-coping behavior was designed to be at 6 months of age during classical conditioning training. The pm-CS data (Tables I and II) provided no evidence that the 4 and 12 week kittens were different in baseline response, but a significant

difference

was found

in the respiration

rate to

an unpaired CS (Table IV). While the data during CSUS pairing (Tables IIILV) showed little relation to the escaping or non-escaping dimension of

Such a sensitization

effect

was suggested

earlier

by

Flynn (1960) and Wilson (1969) and recently described for the aversive conditioning heart rate pattern of 4 week kittens by Soltysik et al. (1982). However, the complete uniformity of deceleratory heart rate pattern in the present sample of kittens (Fig. 2) can be contrasted with earlier data presented by Nicholas et al. (1983); that report involved no early experience treatment. and it described both acceleratory and deceleratory heart rate trends during classical conditioning. If sensitization is an appropriate model only for the heart rate of very young kittens (Soltysik et al.. 1982). then the similarity in heart rate pattern over classical conditioning sessions in the present data strongly handling.

suggests or both

that had

early experience. extensive a long-lasting effect on the

early training. the heart rate pattern was an important response for differentiating among early training conditions. With respect to the heart rate during classical conditioning. there was considerable uniformity of pattern among the various early training groups (Fig. 2). The uniformity in the heart rate pattern of habituation and acquisition may have resulted from the extensive handling required for early training

expression of heart rate. Even though the heart rate pattern did show considerable similarity before and after aversive

and kitten maintenance during the lengthy experiment. Denenberg (1972) has argued that infant animal handling is not a neutral event: handling.

ration amplitude could be related to training experiences. However, during

particularly sults. among ity. Changes dling

have,

before weaning, may have many rethem alterations in emotional reactivin emotional reactivity due to hanin fact. been

reported

in kittens

(Meier

and Stuart. 1959; Wilson et al., 1965). Interestingly, the uniformity of the deceleratory pattern (Fig. 2) during habituation seems to indicate that whether shocked or not in early training. the kittens came to the test at 6 months of age with a heart rate response which is characteristic of the passive defensive reaction (Konorski, 1967). As training proceeded from habituation to acquisition, response changes in heart rate were not due to a change in pattern, but to a change in amplitude. A similar pattern in the heart rate of both the habituation and acquisition training periods might tion effect, an already

argue for the operation of a sensitizathat is. a UCS-induced exaggeration of present response (Mackintosh. 1974).

classical conditioning, it nevertheless response related to differential early the runway apparatus, a fact which

was the only experience in suggests that

heart rate and respiration measures did not covary (Grossman. 1983). In spite of large changes during CSUS pairing, neither respiration rate nor respi-

conditioning, the heart rate deceleration two 4 week groups which had experienced early training was significantly different heart

rate response

in the handled-only

the early classical from the shock in from the group

(Fig.

3). In this regard, heart rate responses have previously been reported as a measure of behavioral plasticity at early postnatal periods. when other systems are immature and limited as response measures of acquisition (Bloch and Martinova. 1981: Martin and Alberts, 1982). It can also be noted that persistent effects resulting from early experience with shock are not necessarily restricted to physiological measures like heart rate. Chen and Amsel (1982) have shown that rat pups given inescapable shock have increased resistance to the extinction of an appetitive runway task. acquired 35 days after the shock experience. However, in the present data heart rate indexed an early experience with shock after a training to test interval of

109

5 months, suggesting that heart rate may be especially valuable in detecting changes in emotional or autonomic

reactivity

resulting

from

early

aver-

with

shock

did

not

affect

the

heart rate response to a neutral stimulus, since the habituation heart rate patterns to CS alone (Fig. 2) were the same for subjects which were either shocked or handled ever, early experience

during early training. Howwith shock must be an im-

portant factor for the heart rate seen during later CS-US pairing, since an exaggerated heart rate deceleration (Fig. 3) did not appear among control subjects which were not shocked, but which were equally handled with equivalent time in the runway apparatus. If it can be assumed that the early shock experience was important in the later heart rate expression to a conditioned aversive then the lack of heart rate effects among may

have

been

due

to their

stimulus. the older

reduced

of the running

responded

with

a

response shock

conditioning. manipulations

result

in response

difference

was

at 4 weeks

potentiated

heart rate in later classical differential early coping in any

which

of

deceleratory However. did not to

CS- US

pairing. That fact may argue (as does Obrist. 1982) that the coping or non-coping dichotomy is not easily established on the basis of an objective response. Alternatively. the data do not obviate the possibility that may be established

differential in infancy.

coping responses but with limited

utility in determining long-term behavioral characteristics. Either hypothesis would be reasonable for further research.

ACKNOWLEDGEMENTS

ex-

posure to early shock, since they acquired an escape response much faster than the 4 week kittens. A connection between the exaggerated heart rate deceleration seen in 4 week kittens and the early experience with shock may be supplied by the known dependence of heart rate on ongoing or intended somatic activity. In one account (Obrist, 1981; 1982) inactivity and heart rate deceleration are, themselves. assumed to be characteristic behaviors in the aversive classical conditioning paradigm. If so, then rather than ferential coping behavior, the result

in spite

trained in the R subjects. In summary, kittens given age

sive experience. Early experience

kittens

kittens,

acquiring difof early train-

The research was supported the National Institute of Child

by HD 05958 from Health and Human

Development. Several people contributed to the effort required for this project. David Weber and Tony Valdez constructed and repaired equipment. Jay Kruze assisted with computer hardware and software. Susan Nickel and Richard Gayek, D.V.M. helped to insure that surgeries and kitten care followed current standards. Finally, those who volunteered their time in kitten handling and data transcription were Majella Pleta. Alan Oda and Steve

Berg.

ing with shock at 4 weeks of age may have been to produce relatively inactive subjects. The difficulty which young kittens acquired an escape response would then mean that the early experience with shock was substantially the same for escaping and confined subjects, and that experience resulted in a long-lasting reduction of motor activity. Such an interpretation is generally consistent with the notion that inescapable shock may produce a learned helplessness (Maier and Seligman, 1976; Maier and Jackson, 1977; Seligman et al., 1971) or that one result of exposure to shock over trials may be the acquisition of a tendency to be inactive (Glazer and Weiss, 1976). The interpretation also allows that a similar coping strategy may have been acquired in the shocked 4 week R and S with

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