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The effect of group vs. individual housing on behaviour and physiological responses to stress in the albino rat
J Psychosomatic Res , 1960, Vol
4, pp 185 to 190
Per&anon Press Ltd
Prmted m Northern Ireland
THE EFFECT OF GROUP VS. INDIVIDUAL HOUSING ON BEHAVIOUR AND PHYSIOLOGICAL RESPONSES TO STRESS IN THE ALBINO RAT J A
STERN,* G WINOKUR,” A EISENSTEIN,~ R TAYLOR and M SLY
THE effects of gentlmg and stressing animals on both behavlour and ablhty of adults to tolerate stress have received considerable emphasis in the recent experimental hterature (BERNSTEIN, 1957; BOVARD, 1954; RUEGAMERand SILVERMAN,1956, WEININGER, 1954, 1956) Both procedures, if introduced m early life, are reported to influence the ability to tolerate stress m later hfe WEININGER (1956) found that gentled animals are heavier and the skeletal length IS greater than that of non-gentled animals He also showed that when non-gentled animals were stressed by lmmoblhzatlon, adrenal weight was increased and an increased number of bleeding points was found m the stomach and duodenum Animals used by WEININGER m his experiments were housed mdlvldually In a previous mvestlgatlon (WINOKUR et al, 1959) we attempted to confirm WEININGER’S results, but our animals were housed m groups rather than mdlvldually Our study showed that group housmg prevented most of the differences between gentled and non-gentled ammals described by WEININGER Our results showed that handlmg rats for 5 or 10 mm dally from age 23 to 44 days had no effect on body weight or water Intake Differences m body length, tall length and heart size between handled and non-handled ammals lIkewIse were not observed followmg lmmoblhzatlon stress m group housed animals The only difference consistent with WEININCER’S report was, that non-handled ammals developed gastromtestmal lesions more frequently after 48 hr lmmoblhzatlon than did handled rats
A study by RUEGAMER and SILVERMAN (1956) presents data on physlologlcal differences between mdlvldually and group housed animals (2 per cage) This study suggests, although the authors did not discuss this point, that group housing decreases the level as well as the number of slgmficant differences observed on such variables as thyroid uptake, carcass length, food utlhzatlon and weight gam when gentled and non-gentled groups of animals are compared The results of our study and that of RUEGAMER and SILVERMANsuggest that group housing has a protective effect on adult ability to tolerate stressful sltuatlons The present experiment was undertaken to study the effect of dlfferentlal housing (without the variable of handling) on the stress response METHODS
AND
MATERIALS
Fifty-eight male albino rats were purchased from Sprague-Dawley, Ma&son, Wlsconsm and were 23 days old when received m our laboratory Ammals were randomly asslgned to two experlmental groups Twenty-eight were housed mchv~dually and 30 were group housed as described below Animals were handled only durmg experlmental procedures and then welghed at approxlmately 10 day intervals At ages 58 and 65 days they were exposed to the enclosed field test * From the Washmgton t From the Department
Umverslty School of Medlcme, of Preventwe Medlclne 185
Department
of Psychiatry
and Neurology
186
J A STERN,G WINOKUR,A EISENSTEIN,R TAYLORand M SLY
On days 82 and 83,20 of the group housed and 21 mdlvldually housed ammals were lmmoblhzed Animals were immobilized by taping the forepaws to the body The animal was then wrapped m gauze, a layer of tape was then applied and covered with plaster of parls bandage This produced a rlgld cast from which ammals were unable to escape No water or food was available during this period After 48 hr of lmmoblhzatlon, 12 animals from each group were randomly selected, decapltated, and the adrenal glands dlssected free Steroid secretlon by the Isolated adrenals of each animal was determmed (EISENSTEIN,1956) All evaluations except steroid secretion were carried out on the remammg animals from both groups which had been lmmoblhzed These were weight loss durmg lmmobd~zatlon, adrenal weights, evaluations of stomach lessons and mucosal colour A control group consistmg of 8 mdlvldually and 9 group housed ammals were fasted, deprlred of water for 48 hr and decapitated, and all evaluations, other than steroid output were carried out Cages Indlvldually housed animals were mamtarned m cages 10 m x 12 m x 12 m high with galvamzed steel side and rear walls The floor, top and front of cages were constructed of 4 m galvamzed hardware cloth A Richter-type graduated bottle supplied water, and a liberal amount of Purina lab chow pellets was present m cages at all times Faeces and urine dropped mto a tray below the cage Group housed ammals were kept m 10 m x 36 m x 12m cages otherwise identical with the mdlvidual cages Richter-type water bottles (four) were affixed to the front of the cages with supplementary bottles on each of the cage sides Again Purma lab chow pellets were present at all times Group housed animals were mamtamed m groups of 15 per cage Enclosedfield A 3 x 5 ft piece of plywood painted black and ruled mto 12 m squares constltuted the field which was enclosed by a 2 ft high galvanized sheet metal barrier A 200 watt shielded electric bulb was suspended 4 ft over the centre of the field Anlmdls were mdlvldually Introduced mto the same corner of the field and their behavlour observed for 2 mm Observations were tabulated each 15 set and the followmg aspects of behavlour recorded (a) (b) (c) (d)
Amount of movement m the field (total number of squares traversed) Number of different squares entered Number of times animal reared-either against a wall or free rearing Number of times during each 15 set period that ammal spent more than 7 set crouching in dn rmmoblle positron, or extending Itself-keepmg hmd legs m place (e) Number of boluses defaecated (f) Response to being removed from field Both adrenals were removed, dlssected free of surrounding tissue, Adrenal steroid secretion werghed, bisected and placed m 2 ml Krebs-Ringer phosphate-glucose solution, pH 7 4 One umt of ACTH was added and the mixture Incubated aeroblcally for 2 hr at 37’C m a Dubnoff metabolic Incubator Steroid hormones secreted mto the medmm were recovered and quantitatively determined utlhzmg a spectrophotometrlc technique (EISENSTEIN,1956) Stomach evaluatrons The stomach and a 3 m sectlon of mtestme was removed from each animal The stomach was then gently rinsed m tap water and and cut open along the greater curvature examined for areas of erosion, increased vascularlzatlon, and for the colour of the mocosal lmmg RESULTS
In Table 1 are presented the mean weights, t tests showed no significant differences between the groups Evaluation of enclosed field behavlour is summarized in Table 2 and indicates that slgmficant and consistent (over the two trials) differences in behavTndlvldually lour were observed between group and mdlvidually housed animals. housed animals exhIbited much less exploration of the field both as measured by the number of different squares entered during the 2 mm period as well as by the total number of squares traversed The mdlvldually housed animals showed significantly more crouching and extensor behavlour than was true of the other group These two categories of behavlour were combined because they appeared to be related (the extensor movements generally followed periods of crouching) and because of the Slgmficantly more animals m the relative infrequency of the latter measure.
187
Behaviour and phystologtcal responses to stress m the albino rat
mdrvldually housed group vocalized (squealed) when they were removed from the field. Slgmficantly more group housed animals defaecated in the field than did those housed mdrvrdually. Evaluation of response to stress of rmmobthzatlon IS depicted m Tables 3 and 4 which summarrze the results of body weight changes, adrenal weights, adrenal sterotd secretion, evaluation for stomach lesions, and colour of stomach lmmg TABLE
1 -COMPARISOV
OF BODY WEIGHTS
Weght at age (m days)
*
411 wetghts
’
No 30 28
Group housed Indtv housed
23 50 5* 49 3
33 107 2 108 6
43 163 0 164 6
53 235 3 229 5
64 288 1 292 6
74 331 1 329 4
82 357 3 352 2
III grammes TABLE
2
-ENCLOSED
FIELD EVALUATIONS
Median for
Medtan for , Medtan ( mdtv spht group housed , housed
Medtan for ’
Medtan for
Medtan 1
1~hg,‘z,“,pa’ ~~~~~, i
‘P1lt
’
15
0 05
Day 58 Test No dtfferent squares entered 1st mm activity 2nd min. activity Total activity Rearmg behaviour Crouch and extensor behavtour
, 2
3
’
25
005
0
3
~
Number of ammals exhtbttmg behavtour
I
Indtv
Group
~
I
P
1
Group
Indlv
43
82
60
25
1
P
Ii Ammals squealed when removed (%) Ammals defaecated m field (76) All
~ 27 40
I
79
I I 001
7
0 01
I,
001
i
001
p’s based on x2-tests
A comparrson of weight loss and adrenal weight between animals which were depraved of food and water compared to those whxh were also lmmobthzed mdtcates that rmmobrhzation produces a significantly greater weight loss than food and water deprlvatron alone and that It results m adrenal hypertrophy The comparison depicted m Table 3 IS for grouped data, 1.e group and indrvidually housed rmmoblhzed vs
188
J A
STERN, G
WINOKUR, A
EISENSTEIN,R TAYLOR and M
SLY
group and mdlvldually housed fasted Comparisons m which the data were not pooled also showed slgmficant differences The only other determmatlon which dlfferentlated between group and mdlvldually housed stressed ammals was the evaluation of stomach lesions Slgmficantly more animals with gastric lesions were found among those which had been group housed. TABLE 3 -PERCENTAGE WEIGHT LOSS, ADRENAL WEIGHT, AND STEROIDOUTPUT EVALUATIONS
) lmmob
Food and water
Immoblllzed
deprw
I
Inchv
Group
P”
(48 hr)
vs
depw
p*
) lndlv
,
P
I
18 1 194 521
18 6 189 521
Weight loss (“/,) Relative adrenal weight Adrenal steroid outputt * All p’s based on f-tests 7 Mnograms/lOO mg adrenal
ns ns
14 0 15 6
OF STOMACH LESIONSAND COLOUR
Immoblhzed
animals with
of forestomach
* Number
of animals
0001 0001
ns
48 hr deprw
x2 Criterion
Colour
, 1
I
I
stomach lesions
ns ns
weight
TABLE 4 -EVALUATIONS
No
130 150
p
I 18/21 9*/21
5120 17120
Pres
\s
abs
White vs yellow
0001
0 01
Group
,
In&v
x2
219
l/8
ns
919
S/S
ns
wth white forestomxh
Stomach lesions were also rated on a 5-point scale which considered size as well as Of five mdlvldually housed animals with stomach lesions none number of lesions was rated 4, two were rated 3, one was rated 2, and two received a rating of 1 Of 18 group housed animals with stomach lesions, eight were rated 4; three rated 3, one rated 2; and SIX received ratings of 1 Thus, the latter group not only had slgmficantly more animals which developed lesions but more severe lesions were found In this group DISCUSSION Our results indicate that group housing and mdlvldual housing of rats produces significant differences m response to a behavloural task as well as differences m response to lmmoblhzatlon stress as measured by occurrence of stomach lesions
The differences m enclosed field behavlour are Interpreted by us to indicate that the or “frightened” manner mdlvldually housed animals behaved m a more “emotional” The followmg two tenable explanattons for than was true for group housed animals the differences m emotional behavlour observed m the enclosed field are proposed.
Behawour and physlologlcal responses to stress m the albmo rat
189
One IS based on the restricted “Lebensraum” of mdividually housed animals, 1 e they restricted their exploratory behaviour on the enclosed field because of prior restrictions of such behaviour m their home cages The second explanation is based on the hypothesis that alteration of sensory-motor experrences produces changes m response to stressful situations. The differences m sensory-motor experiences in the present experiment mvolve the stimulation afforded by animals living m a group rather than m mdividual cages and the potential locomotor mhibitory effect of bemg housed m a small rather than a large cage If group housing of animals IS considered the “normal” habitat then the mdividually It is hypothesized (postfacto) housed animals were subjected to sensory deprivation that the deprived animals respond m a more “stressful” manner to exposure to a lighted enclosed field than do non-deprived or group housed animals Within the framework of the first hypothesis one might explain the lower incidence of stomach lesions m the mdlvidually housed animals on the basis that it was a less stressful experience for them m that they had been exposed to at least partial immobihzation for most of their hfe while the group housed animals had not experienced such deprivation prior to being immobilized. The hypothesis cast within the sensory-motor experience framework would have to state that mhibition of activity m stressful situations (as the mdlvidually housed animals apparently did m the enclosed field) is not detrimental to orgamsmic eqmhbrmm m all situations, but that it may actually enhance viabihty m some stressful situations Adrenal weight and steroid hormone secretion which are considered good mdtcaters of a stress response do not at first appear to be consonant with an interpretation of immoblhzation being more stressful for the group housed animals, as the greater Animals which were mcidence of stomach lesions m this group might suggest deprived of food and water but not immobilized had significantly smaller adrenals than the immoblhzed animals Thus immobillzatlon was a stressful procedure, but the housmg variable neither added to nor detracted from this effect as measured by adrenal weight. Unfortunately steroid secretion was not determined m food and water deprived-only animals so that a comparison of steroid output between immobilized Another mdlcation that immobilization and deprived-only animals was not possible was stressful is shown by the sigmficantly greater weight loss of these ammals as compared to deprived animals Individually housed animals could be differentiated not only on the basis of behaviour m the field but also m terms of behaviour variables which apparently had nothing to do with the differential effect of restricted vs non-restricted housmg experiences. When animals had to be handled one could observe more resistance to They would retreat being handled on the part of the mdividually housed animals from a hand put into their cage and would squeal while they were being removed from Group their cage, group housed animals were much less resistant to being handled housing may thus be assumed to have a “gentlmg” effect, possibly because the greater amount and variety of sensory experrences these animals are exposed to reduce then responsiveness to sensory stimuli incident to handling. The results of the present experiment thus mdicate that handling may be only one of a number of variables that sigmficantly affect the development of stomach lesions WEININCER (1956) showed that handlmg of mdtvidually housed ammals sigmficantly
190
J A STERN,G WINOKUR,A EISENSTEIN,R TAYLORand M SLY
reduced the incidence of stomach lesions when ammals were stressed by 48 hr of lmmoblhzatlon WINOKUR et al. (1959) showed that WEININGER’S results could also be obtained with group housed and gentled ammals (although they were unable to rephcate any of the remammg findings of WEININGER). The present experiment showed that group vs mdlvldual housmg in the absence of handling produced similar effects SUMMARY
AND
CONCLUSIONS
(1) Group vs mdlvldual housing produces differential effects on behavlour m an enclosed field, the group housed animals showing more exploratory and less “fearful” behavlour m this situation (2) In response to the stress of lmmob~hzatlon (plus fasting) slgmficantly more of the group as compared to mdlvldually housed animals develop stomach lesions (3) There IS no difference m adrenal weight, steroid output of the adrenal or body weight loss between the lmmoblhzed animals regardless of whether they had previously been group or mdlvldually housed (4) Immobkzatlon plus fasting IS a more stressful procedure than fasting alone 1s attested to by the greater weight loss and greater adrenal weights of the lmmoblllzed ammals REFERENCES BERNSTEINL (1957) The effects of varlatlons
m handlmg upon learmng and retention
J ranlp
Physlol Psycho1 50,162
BOVARDE W The effects of early and present experience on the response to stress Unpubhshed manuscript BOVARDE W (1954) A theory to account for the effects of early handlmg on vlablhty of the albmo rat Sczencc 120, 187 EISENSTHNA B (1956) Steroid secretron by the Isolated rat adrenal Proc Sot Exp Bzol Med. 91, 657. RUEGAMERW R and SILVERMAN F R (1956) Influence of gentling on physiology of the rat Proc Sot Exp Blol A4ed 92, 170 WEININGER0 (1954) Physlologtcal damage under emotional stress as a function of early experience Scrence 119,285 WEININGER0 (1956) The effects of early experience on behavlour and growth characterlstlcs J camp Phystol Psycho1 49, 1 WINOKURG , STERNJ A and TAYLORR (1959) Early handlmg and group housing effect on development and pathological processes m the rat J Psychosom Res 4, 1.
4, pp 185 to 190
Per&anon Press Ltd
Prmted m Northern Ireland
THE EFFECT OF GROUP VS. INDIVIDUAL HOUSING ON BEHAVIOUR AND PHYSIOLOGICAL RESPONSES TO STRESS IN THE ALBINO RAT J A
STERN,* G WINOKUR,” A EISENSTEIN,~ R TAYLOR and M SLY
THE effects of gentlmg and stressing animals on both behavlour and ablhty of adults to tolerate stress have received considerable emphasis in the recent experimental hterature (BERNSTEIN, 1957; BOVARD, 1954; RUEGAMERand SILVERMAN,1956, WEININGER, 1954, 1956) Both procedures, if introduced m early life, are reported to influence the ability to tolerate stress m later hfe WEININGER (1956) found that gentled animals are heavier and the skeletal length IS greater than that of non-gentled animals He also showed that when non-gentled animals were stressed by lmmoblhzatlon, adrenal weight was increased and an increased number of bleeding points was found m the stomach and duodenum Animals used by WEININGER m his experiments were housed mdlvldually In a previous mvestlgatlon (WINOKUR et al, 1959) we attempted to confirm WEININGER’S results, but our animals were housed m groups rather than mdlvldually Our study showed that group housmg prevented most of the differences between gentled and non-gentled ammals described by WEININGER Our results showed that handlmg rats for 5 or 10 mm dally from age 23 to 44 days had no effect on body weight or water Intake Differences m body length, tall length and heart size between handled and non-handled ammals lIkewIse were not observed followmg lmmoblhzatlon stress m group housed animals The only difference consistent with WEININCER’S report was, that non-handled ammals developed gastromtestmal lesions more frequently after 48 hr lmmoblhzatlon than did handled rats
A study by RUEGAMER and SILVERMAN (1956) presents data on physlologlcal differences between mdlvldually and group housed animals (2 per cage) This study suggests, although the authors did not discuss this point, that group housing decreases the level as well as the number of slgmficant differences observed on such variables as thyroid uptake, carcass length, food utlhzatlon and weight gam when gentled and non-gentled groups of animals are compared The results of our study and that of RUEGAMER and SILVERMANsuggest that group housing has a protective effect on adult ability to tolerate stressful sltuatlons The present experiment was undertaken to study the effect of dlfferentlal housing (without the variable of handling) on the stress response METHODS
AND
MATERIALS
Fifty-eight male albino rats were purchased from Sprague-Dawley, Ma&son, Wlsconsm and were 23 days old when received m our laboratory Ammals were randomly asslgned to two experlmental groups Twenty-eight were housed mchv~dually and 30 were group housed as described below Animals were handled only durmg experlmental procedures and then welghed at approxlmately 10 day intervals At ages 58 and 65 days they were exposed to the enclosed field test * From the Washmgton t From the Department
Umverslty School of Medlcme, of Preventwe Medlclne 185
Department
of Psychiatry
and Neurology
186
J A STERN,G WINOKUR,A EISENSTEIN,R TAYLORand M SLY
On days 82 and 83,20 of the group housed and 21 mdlvldually housed ammals were lmmoblhzed Animals were immobilized by taping the forepaws to the body The animal was then wrapped m gauze, a layer of tape was then applied and covered with plaster of parls bandage This produced a rlgld cast from which ammals were unable to escape No water or food was available during this period After 48 hr of lmmoblhzatlon, 12 animals from each group were randomly selected, decapltated, and the adrenal glands dlssected free Steroid secretlon by the Isolated adrenals of each animal was determmed (EISENSTEIN,1956) All evaluations except steroid secretion were carried out on the remammg animals from both groups which had been lmmoblhzed These were weight loss durmg lmmobd~zatlon, adrenal weights, evaluations of stomach lessons and mucosal colour A control group consistmg of 8 mdlvldually and 9 group housed ammals were fasted, deprlred of water for 48 hr and decapitated, and all evaluations, other than steroid output were carried out Cages Indlvldually housed animals were mamtarned m cages 10 m x 12 m x 12 m high with galvamzed steel side and rear walls The floor, top and front of cages were constructed of 4 m galvamzed hardware cloth A Richter-type graduated bottle supplied water, and a liberal amount of Purina lab chow pellets was present m cages at all times Faeces and urine dropped mto a tray below the cage Group housed ammals were kept m 10 m x 36 m x 12m cages otherwise identical with the mdlvidual cages Richter-type water bottles (four) were affixed to the front of the cages with supplementary bottles on each of the cage sides Again Purma lab chow pellets were present at all times Group housed animals were mamtamed m groups of 15 per cage Enclosedfield A 3 x 5 ft piece of plywood painted black and ruled mto 12 m squares constltuted the field which was enclosed by a 2 ft high galvanized sheet metal barrier A 200 watt shielded electric bulb was suspended 4 ft over the centre of the field Anlmdls were mdlvldually Introduced mto the same corner of the field and their behavlour observed for 2 mm Observations were tabulated each 15 set and the followmg aspects of behavlour recorded (a) (b) (c) (d)
Amount of movement m the field (total number of squares traversed) Number of different squares entered Number of times animal reared-either against a wall or free rearing Number of times during each 15 set period that ammal spent more than 7 set crouching in dn rmmoblle positron, or extending Itself-keepmg hmd legs m place (e) Number of boluses defaecated (f) Response to being removed from field Both adrenals were removed, dlssected free of surrounding tissue, Adrenal steroid secretion werghed, bisected and placed m 2 ml Krebs-Ringer phosphate-glucose solution, pH 7 4 One umt of ACTH was added and the mixture Incubated aeroblcally for 2 hr at 37’C m a Dubnoff metabolic Incubator Steroid hormones secreted mto the medmm were recovered and quantitatively determined utlhzmg a spectrophotometrlc technique (EISENSTEIN,1956) Stomach evaluatrons The stomach and a 3 m sectlon of mtestme was removed from each animal The stomach was then gently rinsed m tap water and and cut open along the greater curvature examined for areas of erosion, increased vascularlzatlon, and for the colour of the mocosal lmmg RESULTS
In Table 1 are presented the mean weights, t tests showed no significant differences between the groups Evaluation of enclosed field behavlour is summarized in Table 2 and indicates that slgmficant and consistent (over the two trials) differences in behavTndlvldually lour were observed between group and mdlvidually housed animals. housed animals exhIbited much less exploration of the field both as measured by the number of different squares entered during the 2 mm period as well as by the total number of squares traversed The mdlvldually housed animals showed significantly more crouching and extensor behavlour than was true of the other group These two categories of behavlour were combined because they appeared to be related (the extensor movements generally followed periods of crouching) and because of the Slgmficantly more animals m the relative infrequency of the latter measure.
187
Behaviour and phystologtcal responses to stress m the albino rat
mdrvldually housed group vocalized (squealed) when they were removed from the field. Slgmficantly more group housed animals defaecated in the field than did those housed mdrvrdually. Evaluation of response to stress of rmmobthzatlon IS depicted m Tables 3 and 4 which summarrze the results of body weight changes, adrenal weights, adrenal sterotd secretion, evaluation for stomach lesions, and colour of stomach lmmg TABLE
1 -COMPARISOV
OF BODY WEIGHTS
Weght at age (m days)
*
411 wetghts
’
No 30 28
Group housed Indtv housed
23 50 5* 49 3
33 107 2 108 6
43 163 0 164 6
53 235 3 229 5
64 288 1 292 6
74 331 1 329 4
82 357 3 352 2
III grammes TABLE
2
-ENCLOSED
FIELD EVALUATIONS
Median for
Medtan for , Medtan ( mdtv spht group housed , housed
Medtan for ’
Medtan for
Medtan 1
1~hg,‘z,“,pa’ ~~~~~, i
‘P1lt
’
15
0 05
Day 58 Test No dtfferent squares entered 1st mm activity 2nd min. activity Total activity Rearmg behaviour Crouch and extensor behavtour
, 2
3
’
25
005
0
3
~
Number of ammals exhtbttmg behavtour
I
Indtv
Group
~
I
P
1
Group
Indlv
43
82
60
25
1
P
Ii Ammals squealed when removed (%) Ammals defaecated m field (76) All
~ 27 40
I
79
I I 001
7
0 01
I,
001
i
001
p’s based on x2-tests
A comparrson of weight loss and adrenal weight between animals which were depraved of food and water compared to those whxh were also lmmobthzed mdtcates that rmmobrhzation produces a significantly greater weight loss than food and water deprlvatron alone and that It results m adrenal hypertrophy The comparison depicted m Table 3 IS for grouped data, 1.e group and indrvidually housed rmmoblhzed vs
188
J A
STERN, G
WINOKUR, A
EISENSTEIN,R TAYLOR and M
SLY
group and mdlvldually housed fasted Comparisons m which the data were not pooled also showed slgmficant differences The only other determmatlon which dlfferentlated between group and mdlvldually housed stressed ammals was the evaluation of stomach lesions Slgmficantly more animals with gastric lesions were found among those which had been group housed. TABLE 3 -PERCENTAGE WEIGHT LOSS, ADRENAL WEIGHT, AND STEROIDOUTPUT EVALUATIONS
) lmmob
Food and water
Immoblllzed
deprw
I
Inchv
Group
P”
(48 hr)
vs
depw
p*
) lndlv
,
P
I
18 1 194 521
18 6 189 521
Weight loss (“/,) Relative adrenal weight Adrenal steroid outputt * All p’s based on f-tests 7 Mnograms/lOO mg adrenal
ns ns
14 0 15 6
OF STOMACH LESIONSAND COLOUR
Immoblhzed
animals with
of forestomach
* Number
of animals
0001 0001
ns
48 hr deprw
x2 Criterion
Colour
, 1
I
I
stomach lesions
ns ns
weight
TABLE 4 -EVALUATIONS
No
130 150
p
I 18/21 9*/21
5120 17120
Pres
\s
abs
White vs yellow
0001
0 01
Group
,
In&v
x2
219
l/8
ns
919
S/S
ns
wth white forestomxh
Stomach lesions were also rated on a 5-point scale which considered size as well as Of five mdlvldually housed animals with stomach lesions none number of lesions was rated 4, two were rated 3, one was rated 2, and two received a rating of 1 Of 18 group housed animals with stomach lesions, eight were rated 4; three rated 3, one rated 2; and SIX received ratings of 1 Thus, the latter group not only had slgmficantly more animals which developed lesions but more severe lesions were found In this group DISCUSSION Our results indicate that group housing and mdlvldual housing of rats produces significant differences m response to a behavloural task as well as differences m response to lmmoblhzatlon stress as measured by occurrence of stomach lesions
The differences m enclosed field behavlour are Interpreted by us to indicate that the or “frightened” manner mdlvldually housed animals behaved m a more “emotional” The followmg two tenable explanattons for than was true for group housed animals the differences m emotional behavlour observed m the enclosed field are proposed.
Behawour and physlologlcal responses to stress m the albmo rat
189
One IS based on the restricted “Lebensraum” of mdividually housed animals, 1 e they restricted their exploratory behaviour on the enclosed field because of prior restrictions of such behaviour m their home cages The second explanation is based on the hypothesis that alteration of sensory-motor experrences produces changes m response to stressful situations. The differences m sensory-motor experiences in the present experiment mvolve the stimulation afforded by animals living m a group rather than m mdividual cages and the potential locomotor mhibitory effect of bemg housed m a small rather than a large cage If group housing of animals IS considered the “normal” habitat then the mdividually It is hypothesized (postfacto) housed animals were subjected to sensory deprivation that the deprived animals respond m a more “stressful” manner to exposure to a lighted enclosed field than do non-deprived or group housed animals Within the framework of the first hypothesis one might explain the lower incidence of stomach lesions m the mdlvidually housed animals on the basis that it was a less stressful experience for them m that they had been exposed to at least partial immobihzation for most of their hfe while the group housed animals had not experienced such deprivation prior to being immobilized. The hypothesis cast within the sensory-motor experience framework would have to state that mhibition of activity m stressful situations (as the mdlvidually housed animals apparently did m the enclosed field) is not detrimental to orgamsmic eqmhbrmm m all situations, but that it may actually enhance viabihty m some stressful situations Adrenal weight and steroid hormone secretion which are considered good mdtcaters of a stress response do not at first appear to be consonant with an interpretation of immoblhzation being more stressful for the group housed animals, as the greater Animals which were mcidence of stomach lesions m this group might suggest deprived of food and water but not immobilized had significantly smaller adrenals than the immoblhzed animals Thus immobillzatlon was a stressful procedure, but the housmg variable neither added to nor detracted from this effect as measured by adrenal weight. Unfortunately steroid secretion was not determined m food and water deprived-only animals so that a comparison of steroid output between immobilized Another mdlcation that immobilization and deprived-only animals was not possible was stressful is shown by the sigmficantly greater weight loss of these ammals as compared to deprived animals Individually housed animals could be differentiated not only on the basis of behaviour m the field but also m terms of behaviour variables which apparently had nothing to do with the differential effect of restricted vs non-restricted housmg experiences. When animals had to be handled one could observe more resistance to They would retreat being handled on the part of the mdividually housed animals from a hand put into their cage and would squeal while they were being removed from Group their cage, group housed animals were much less resistant to being handled housing may thus be assumed to have a “gentlmg” effect, possibly because the greater amount and variety of sensory experrences these animals are exposed to reduce then responsiveness to sensory stimuli incident to handling. The results of the present experiment thus mdicate that handling may be only one of a number of variables that sigmficantly affect the development of stomach lesions WEININCER (1956) showed that handlmg of mdtvidually housed ammals sigmficantly
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J A STERN,G WINOKUR,A EISENSTEIN,R TAYLORand M SLY
reduced the incidence of stomach lesions when ammals were stressed by 48 hr of lmmoblhzatlon WINOKUR et al. (1959) showed that WEININGER’S results could also be obtained with group housed and gentled ammals (although they were unable to rephcate any of the remammg findings of WEININGER). The present experiment showed that group vs mdlvldual housmg in the absence of handling produced similar effects SUMMARY
AND
CONCLUSIONS
(1) Group vs mdlvldual housing produces differential effects on behavlour m an enclosed field, the group housed animals showing more exploratory and less “fearful” behavlour m this situation (2) In response to the stress of lmmob~hzatlon (plus fasting) slgmficantly more of the group as compared to mdlvldually housed animals develop stomach lesions (3) There IS no difference m adrenal weight, steroid output of the adrenal or body weight loss between the lmmoblhzed animals regardless of whether they had previously been group or mdlvldually housed (4) Immobkzatlon plus fasting IS a more stressful procedure than fasting alone 1s attested to by the greater weight loss and greater adrenal weights of the lmmoblllzed ammals REFERENCES BERNSTEINL (1957) The effects of varlatlons
m handlmg upon learmng and retention
J ranlp
Physlol Psycho1 50,162
BOVARDE W The effects of early and present experience on the response to stress Unpubhshed manuscript BOVARDE W (1954) A theory to account for the effects of early handlmg on vlablhty of the albmo rat Sczencc 120, 187 EISENSTHNA B (1956) Steroid secretron by the Isolated rat adrenal Proc Sot Exp Bzol Med. 91, 657. RUEGAMERW R and SILVERMAN F R (1956) Influence of gentling on physiology of the rat Proc Sot Exp Blol A4ed 92, 170 WEININGER0 (1954) Physlologtcal damage under emotional stress as a function of early experience Scrence 119,285 WEININGER0 (1956) The effects of early experience on behavlour and growth characterlstlcs J camp Phystol Psycho1 49, 1 WINOKURG , STERNJ A and TAYLORR (1959) Early handlmg and group housing effect on development and pathological processes m the rat J Psychosom Res 4, 1.