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Effects of centrally active drugs on four models of experimentally-induced agreession in rodents
Life Sciences Vol . 8, Part 1, pp . 705-718, 1989 . Printed in Great Britain
Pergamon Press
EFFECTS OF CENTRALLY ACTIVE DRUGS ON FOUR MODELS OF EXPERIMENTALLY-INDUCED AGGRESSION IN RODENTS R . Duane Sofia () Union Carbide Corporation, Sterling Forest Research Center, Department of Pharmacology, Tuxedo, N .Y . (Received 22 January 1989 ; in final form 1 April 1989) Aggression and fighting behavior are particularly common among animals living in a free social environment . Animals inbred under laboratory conditions, such as mice and rats, lose this fighting behavior . However, tàere are certain methods available for inducing aggression in laboratory rodents . Yen et al . (1) and Valzelli et al .(2) and others were able to induce fighting in standard albino mice after prolonged isolation . Several investigators have studied the effects of various drugs oa isolated mouse aggression and have reported that certain agents were able to reduce fighting behavior . However, only DaVanzo et al .(3) compared reversal of aggression with overt neurotoxicity . Tedeschi et al .(4) elicited fighting behavior in paired mice who were exposed to a mild but continuous electric footshock. Several drugs were tested for their ability to inhibit or abolish this behavior . The measure of selectivity for suppressing the number of fighting episodes was obtained by the ratio between an effective dose and a depressant dose on'spontaneous motor activity . An increased reactivity or hyper-irritability state ineluding an aggression reaction to inanimate stimuli was induced in rats by bilateral lesioning of the septal area of the brain ~l ~Present address : Pharmakon Laboratories, Scranton, Pa . 18510 705
706
DRUGS AND AGGRESSION
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("septal rats") as first described by Brady and Neuta (5) and later by Stark and Henderson (6) and others . In another study Stark and Henderson (~) reported on the effects of depressant drugs on 2~yper-reactivity in septal rats . Ataxia or neurotoxi city was determined by visual observation only . ?2esults revealed that some phenothiazines and chlordiazepoxide successfully blocked septal rat aggression . F~arli (8) observed that some laboratory rats will immedi~.tely attack and kill a mouse when introduced into its cage . `Phe term "killer rat" was used to describe this muricidal effect by Horovitz et al .(9) . In their studies on the effects of a variety of drugs in this mouse-killing test, Horovitz et al .(10) ascribed selective antimuricidal doses as those which were lower than neurotoxic doses, as measured by the rotarod method of Durham and Miya (11) . Usinr; this criterion, anti-depressants, stimulants, and antihistaminics were selectively active is these studies . Utilizing the four models of aggre:sive behavior desc~ibed, studies were undertaken to determine whether various psychoactive agents exhibited selectivity in inhibiting aggressive behavior . mhe author considers the rotarod method a re liable an9 accurKte measurement of drug-induced neurotoxicity or neurological deficit . Drug specificity in these studies were considered selective only when it occurred at doses which were significantly lower than those which impaired rotarod performance . èEaterials and Methods Isolation-Induced Aggre ssion .
L".ale albino mice, Swiss-
Webster strain (obtained fi!om Manor Farms, Staatsburg, N.Y .), weighing 16-26 grams at the start of this experiment, were iso-
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70 7
lated in cages (12 x 12 x 18 em) for a period of eight weeks at a constant temperature (24° C ±2) and humidity (N 5U%) and given food and water ad libitum . Fighting was obtained when one isolate was placed in the home cage of another isolate . Invariably 10076 of the mice studied showed consistent figkitinq behavior which persisted throughout a 3 minute testing period . Drugs or vehicle (0 .25`
methylcellulose) were injected intraperitoneally
into both mice 3J minutes prior to testing with complete inhibition of fighting considered as the end point . ED 50 s were determined as the dose necessary to abolish fighting in 50% of the pairs . Electric Shock-Induced Fighting .
Paired naive albino
mi^.e v~ere confined in a plastic box (4 .5 x 8 .5 x 12 cm), the floor of which consisted of a stainless steel grid . The mice were exposed for 3 minutes to a continuously scrambled shock of 3 milliamperes intensity . Fitz;htin? was considered when the 2 mice stood face to face on their hind legs and sparred and bit at one another. Drugs were injected intraperitoneally 3J minutes prior to testing . ^he number of fighting episodes in a 3 minute test period w"~s counted for a control group and a drug-treated group (5 pairs each) . Inhibition was considered when a pair of mice exhibited a 5096 reduction in fighting episodes from the average number observed in the corresponding; control group . Septal Rat Aggression .
rJ!ale hooded Lonq Evans rata (ob-
tained from Blue Spruce Farms, Altamont, N .Y .), weighing 250300 grams, were used in this study . Bilflteral electrolytic lesioning of the septal area of the brain was performed using a slight moc9ification of the method described by Stark and Nenderson (6) . The A-P and lateral stereotaxic coordinates were ~,8 and U .5 respectivel,y . The electrode tip was lowered to a depth
70 8
DRUGS AND AGGRF~3SION
Yol. 8, No . 13
of +1 .2 nm . Anodal DC current of ~ milliamperea intensity waa applied for 15 seconds . Septal lesioned animals were tested 3 to 6 days post-operatively . A scoring system was used which attempted to evaluate the "aggressiveness" observed in the septal rat syndrome . Two inanimate stimuli, a pencil ând a glove, were offered to the tail-restrained animal . Reactions were graded as follows :
0 = indifference to either object ; 1 = nib-
bling of one or both objects ; 2 = voracious attack of one object ; and 3 = voracious attack of both objects . Only those subjects which elicited a score of 3 were used~in the drug studies . Animals were tested prior to study, given drug intraperitoneally, and retested 60 minutes later . Animals which showed a 0 or 1 score at retest were considered blocked and ED~a were obtained on this all-or-none basis . Muricidal Rat Studies .
Aale hooded Long Evans rats were
also used in this phase of the study . Rats were housed individually for 6 to 8 weeks and kept on a constant food intake of approximately 15 grams per day of solid food and water ad libi tum . At the end of the isolation period, the subjects were tested for mouse-killing responses . Only those rats which killed mice within 2 minutes after presentation on 3 consecutive days were used (this method for obtaining killer rats yielded approximately 30% of the original colony) . Selected e.nimals were tested for muricidal behavior prior to drug treatment and at 30 and 60 minutes after intraperitoneal injection of the drug . Only those animals which exhibited antimuricidal effects at both testing intervals were considered inhibited and ED~s were determined as described above . Rotarod Test .
Mice and rata were trained to maintain
theMSelves on a slowly revolving wooden rod ( 5 rev ./min .) .
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DRUGS AND AGGRESSION
709
Mice were tested 15 and 30 minutes after intraperitoneal injection while rats were studied 15,30 and 60 minutes after drug injection . Neurotoxicity was considered when the animals fell from the rotarod more than once during a 1 minute testing period . Mean effective doses (ED50 ) and mean neurotoxic doses (NTD50 ) ~rith 95% confidence limits and potency ratios between them were calculated according to the method of Litchfield and Wilcoxon (12) . The drugs used in these experiments were : chlorpromazine HC1, methotrimeprazine, thioridazine HC1, thiothixene, clomacran P04 (supplied by Smith, Kline and French, chemically 9-[3 dimethylamiaopropyl] chloracridane), chlordiazepoxide HC1, diazepam, tetrabenazine methanesulfoaate, benzquinamide, meprobamate, trifluperidol, sodium pentobarbital, imipramiae HCl, desipramine, and thiazesim HC1 (supf~lied by E .R . Squibb and Sons, chemically 5-[2-dimethylaminoethyl] -2,3-dihydro-2-phenyl1,5-benzothiazepin-4(5H)-one) . Doses are expressed in terms of the salt (or base when a salt was not available) and drugs were either suspended or solubilize9 in 0 .25% methylcellulose . Results Table 1 compares the ED 50 s of the agents studied in the isolated mouse fighting and elect ic shock-induced fighting behavior in mice together with their respective NTD50 s . Several drugs displayed activity in these models but only after doses near neurotoxic ones . However, only thiazesim in the isolated mouse and thioridazine, clomacran, chlordiazepoxide and diazepam in the electic shock-induced fighting models of aggression yielded results which were significantly different from their NTD50 . No ED 50 value could be obtained for thiazesim in the
710
DRUGS AND AGGRESSION
Vol. 8, No . 13
TABLE 1 Effects of Various Drugs on Isolated Mouse Aggression and Electric Shock-Induced Fighting and Mouse Rotarod Performance Drug
Chlor " romazine
so a e ouse _ A _ression _
Rotarod NTD50 mg/kg N (95 C .L .) 0 .7 (0 .1r-l .l
ED50 mg /k C .L .
N
" " " "
Thioridazine
" "
: "
:"
Chlordia e " oxide
" " .
Desi~~ramine
ll i
~
4 .8 .$-6 0
~
33 "4 1$ 0-62 0
"
"
"
"
"
"
" "
it
"
" "
28 .0-110
" " Thiazesim N - Number of mice or pairs of mice used . * - Significantly Below thé NTD50 .
1 20
83 .6 ( 67 7-103_ .3) " ~I~
1_5
0 .37 ~(0 .17-0 .8 )
0
16 .4 ~ 1 . -1 .
" ~ 1 l~:â~~l~ " :
" _ 8 .1 2- 2 .
~
"
*
*
3 .0
_
Me "~robamate
Imi "gsmine
2 .6 2 1- ,
.!
Tetrabenazine
Pentobarbital
I1
~
Diaze "~am
Benz " uinamide
N
3 .4 _ 2. - ,
~
Clomacran
Triflu "~eridol
ED50 mg/k C .L .
1 .6 0 .8- .2
Methotrime "~razine l'
Thiothixene
ectr c oc Induced Fi htin
~
20~2 .2 45 .6 -62 -_-_-
20 1
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DRUGS AND AGGRESSION
711
TABLE 2 Effects of Various DruF~s on Septal Rat Aggression and ltat Iwluricidal Activity and Rat Rotarod Performance Drug
Ch orr~romazine
Rotarod NTD 0 mg kg (95~ C .L .) 1 .7 1 .0-2 .$
Septal Rat A ression ED50 mg k (95~ C .L .~
N $~
12 .1 $ .4-17 .4
' Muricidal Rat Behavior ED5 mg N (959~+ C .L .~ N ~ ~ "
9 .0 . .1-16 .0
20
44 .6 ~ 120 .6 (33 .5-59 .3) ~(63 .9-227 .6)
2$
4 .$ (2 .2-10 .3)
f 10 .9 ~~ 76 .1 241 (6 .1-19 .5) ~ (53 .0-109 .2)
20
Thiothixene
12 .5 (7 .9-19 .9)
100 .0 43 .4 18~ (22 .1-$5 .6)_l'~(56 .7-176 .2)
16
Clomacran
2 .1 (0 .7-6 .7)
24
9 .2 (5 .1-16 .5)
Chlordiaze "~oxide
$ .$ (5 .9-13 .1)
24
23 .8 ~~ (7 .2-79 .1) t
Diazepam
4 .0 (2 .4-6 .5)
1$
17 .2 ~ ziy .o (1C .~-27 .3) ~ (15u .$-305 .9)
22
Tetrabenazine
1 .4 (1 .G-2 .1)
1$
45 .3 57 .$ (33 " 5-61 .2) ~ (35 .3-94 .7)
17
Benzquinamide
6 .$ (4 .3-10 .7)
1$
z6 .4 57 .9 (14 .6-47.9) ~ (40 .6-$2 .4)
25
N!ethotrime "~razine
7 .3 ( . -10.1)
Thioridazine
~
v
I
~ 39 .6 :'k] (25 .3-62 .0) 20 .2 (14 .6-27 .9)
16 20
Meprobamate
$5 .0 I 156 .1 301 .8 (67 .1-107 .3)~2!~ (105 .1-231 .9)I~I,(194 .5-471 .6)
23
Trifluperidol
0 .2$ (0 .26-0 .31)
1$
1 .4 (0 .6-3 .5)
0 .55 (0 .49-0 .62)
30
Pentobarbital
10 .4 (7 .1-15 .2)
1$
17 .3 ~I 25 .3 (15 .0-19.9) i i (21 .3-30 .1)
15
Imi "~ramine
z3 .o (16 .F-31 .6)
~??,
52 .7 (30 .4-91 .5)
~
15
Desi "!ramine
36 .0 (27 .0-4$ .0)
1$
45 .4 (41 .1-50 .3)
11 .9 ~ ~ I (6 .3-22 .4)
I~I~I
$ .1 (5 .2-12 .4)
32 .2 I 24 .8 34 .6 Thiazesim ~ (23 .4-44 .2) I24I (16 .1-3$ .3) I15 (23 .1-51 .7) N - Number of rats used . * - Sipnific2ntly below the IJTD50 .
1$ I40
71 2
DRUGS AND AGGRESSION
Vol. 8, No . 13
electric shock-induced fighting procedure since only minimal activity appeared at a dose (5O mg/kg) which caused some deaths . Data presented in Table 2 illustrates the results obtained with the same drugs mentioned previously for abolishing septal-lesioned rat aggression and muricidal behavior in rats aloas~ with their effects on rat rotarod performance . None of the drugs used showed a selective effect in the septal-lesioned rat . Only the two antidepressants, imipramine and desipramine, had a selective inhibitory action in the muricidal rat . These results are in agreement with the work of Horovitz et al .(10) . Discussion For az~y therapeutic agent used it would be desirable to show minimal aide effects at effective pharmacologic doses . For antagonizing aggressive behavior it would be advantageous to demonstrate activity at doses which are not overtly depressing . In these studies it may be observed that all the depressant and antidepressant drugs were capable of blocking aggressive . behavior, but only after doses which caused neurotoxicity . bccept for a few isolated examples little consistency was obtained for selective antiaggressive activity . Thiazesim was active against isolated mouse aggression but not specifically effective in any of the other procedures outlined . The latter observation is not in agreement with Horovitz et al,(1U,13) who have reported that thia,esim was capable of selectively blocking the muricidal rat response and septal rat aggression . The discrepancy between the results of the muricidal rat assay in this study and those of Horovitz and co-workers may lie in the difference between the methods of testing, the strain of rat used, or the short duration of action of thiazesim . In their study using the septal rat procedure, Horovitz et al .(13) used several
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DRUGS AND AGGRESSION
713
parameters observed in the syndrome (6) including the aggressive behavioral portion to determine the effects of thiazesim . Essentially our evaluation of drug activity was based primarily on grading the latter response only . In the electric shock-induced fighting thioridazine, clomacran, chlordiazepoxide and diazepam showed selective antia~gressive activity . These findings are in aggreement with those reported by Tedéschi et al .(4) who have shown that most phenothiazines and reserpine are relatively nonselective in suppressing fighting behavior . No drug used was able to abolish septal lesioned-induced aggression using the experimental parameter described . A possible explanation for this may be that the sensitivity of the septal lesioned rat to a drug may be altered since Adler (14) has shown that lesioning may induce variations in the permeability of the blood-brain barrier . Thus, perhaps a more valià comparison of specificity for this test, as well as others, would have been the use of a more analogous animal in the neurotoxicity phase of the studies . Only the two antidepressants in the group of drugs tested, imipramine and desipramine, displayed a significant blockade of the muricidal response in rats . This is in agreement with other workers (10) who have shown that depressants are not selectively active in this model of aggression . On the basis of the results of this investigation, it has been shown that no one drug or class of drugs is capable of blocking all four types of ar~gression studied at doses below their respective neurotoxic dose . Therefore, the question may be raised as to whether or not these models are producing a similar type of ngTression . In recent reviews on the pharmaco-
71 4
DRUGS AND AGGRESSION
Vol. 8, No . 13
logical control and the physiological basis of aggression, Valaelli (15) and Moyer (16) pointed out that the basic mechaniam(s) of spontaneous or experimentally-induced aggression are not well understood . Attempts to elucidate this problem have been approached biochemicall .y (3,17,18,19), behaviorally (20, 21,22), and anatomically (23,24) . Thus far no consistent findings have been reported . bHith the current increase of interest in the: area of aggressive behavior and its control (25), emphasis on underatanding the underlying mechanisms involved in the four models of aggression discussed in this paper and others that can be induced in rodents and higher species should be of major concern, since this understandinp~ might aid in the design of new drugs to control aggression . Summary Four models of experir^ent~3'l,y-induced aggression in rodents were used to determine the effectiveness of various centrally active compounds . Comparison of effective doses to those cawing evidence of neurotoxicity revealed that no one drug or class of drugs was consistently effective in the four models presented . Only thiazesim in isolated mouse aggression, thioridazine, clomacr~n, chlor9iazepoxide and diazepam in the electric shock-induced fighting and imipramin~ and desipramine in the muricida~l rat assay exhibited selective activity . No drug significantly reduced aeptal-lesion ar~gression in rats . Acknowledgements The author expresses his appreci~~tion for thF: technical assistance of Miss Carole Ten Hoeve, A7rs . Aonnie '"c!:ormick, and tAra . Linda Stapleton ; to '.9r. .7effrey N!alick for preparation of septal -lesioned rats ; and to the following companies for drug
Vol . 8, No . 13
DRUGS AND AGGRESSION
71 5
supplies : Geigy Pharmaceuticals ; Hofiman LaRoche, Inc . ; Lederle Laboratories, Inc . ; McNeil Laboratories, Inc . ; Charles Pfizer and Co,,
Inc . ; S~.ndoz Pharmaceuticals ; Smith, K'.ine and French
L boratories ; E .R . Squibb and Sons, 7nc . ; and .Uallace Laboratories . References 1 . C.Y . Yen, R .L . Stanger and N . Mi'lman, Arch . Int . Pharmaco d~n ., 123, 179, 1959 . 2 . L . Valzelli, E . Giacalone and S . Garattini, Europ .~J . Pharnacol ., 2, 144, 1967 . 3 . J .P . DaVanzo, M. Daugherty, R . Ruckart and L . Kang, Psycho pharmacologia ( Berlin ), 9, 21U, 1966 . 4 . R .E . Tedeschi, D .H . Tedeschi, A . T~+ucha, L. Cook, P .A . Mattie and F,J . Fellows, J . Pharmacol . Exp . Ther ., 1~, 28, 1959 . 5 . J.V . Brady and W .J .H . Nauta, J. Com . Physiol . Ps9chol ., 46, 339, 1953 . -_ 6 . P . Stark and J .K . Henderson, Intl . J . Neuropharmacol ., ~, 7 . P . Stark and J .K . Henderson, Intl . J . Neuropharmacol ., 5, 3p~5, 1966 . 8 . P. Karli, Behavior (Leiden) , 10 ; 81, 1956 . 9 . Z,P. Horovitz, P,'~J. Ragozzino and R .C, Leaf, Life Sciences , 4, 199, 1965 . 10 . Z .P . Horovitz, J,J . Pula, J .P . High, J .C . Burke and R .^, . Leaf, Intl . J. ~europharmacol ., 5, 405, 1966 . 11 . N .W . Dunhan and T .S . Miya, J . Amer . Pharm . Assoc . (Sçi . Edn .), 46, 208, 1957 " 12 . J .T . Litchfield, Jr . and F . Wilcoxon, J . Pharmacol . ~. Ther ., 96, 99, 1949 . 13 . Z .P . Horovitz, A .F . Furgiuele, L.J . Brannick, J .C . Burke and B .N . Craver, Nature , 200, 369, 1963 . . 14, N .W, Adler, J. Phsrmacol . F~ . Ther . , 134, 214, 1961 . 15 . L . Valzelli, Advances in Pharmacolo and P .A . Shore , Aca etc-$r ess,
, (Dds . S . Garattini York, ~, 79, 1907 .
16, K .E . Mover, Communications in Pehavioral Biology , 2, 65, 1968 . _
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DRUGS AND AGGRESSION
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17 . E . Giacalone, M. Taasella, L . Valzelli and S . Garattini, Biochem . Pharmacol ., ~, 1315, 1968 . 18 . A .B . Rothballer, Brain Function, Volume 5, A ression and Defense, Neural Mec~anism~Social Patterns, F . s . C .~ . amen e a~-B . L~nds~ey~,ûn vers ty -moo Z°-a~ifornia Press, Los Angeles, 135, 1967 " 19 . M .E . Goldberg and A .I . Sehinn, Biochem . Pharmacol ., 18, 532, 1969 . _ 20 . R .E . Ulrich and W .H . Crame, Science , 143, 971, 1964 . 21 . H.C . Nieloon, A .H . McIver and R .S . Boswell, Exptl . Neuro ., 11, 147, 1965 . 22 . A .S . Kulkarni, Ps9chol . Record , 18, 385, 1968 . 23 . P. Ropartz, Anim . Behav ., 16, 97, 1968 . 24 . Z .P . Horovitz, Proceedin s on _the First International S p~osium_ on Aati- e ressent D ~ ru s_, (F~s.S . arat in an~ token , Excerp a ed~câFoundation, Amsterdam, 121, 1966 . 25 . Proceedin s on the International S osium on A ressive Bearmaco av or : ioc~mis~r , ~, , oc~; Mar o Negr , st u o c erc e Farmaco oq che, M an, Italy, in press .
Pergamon Press
EFFECTS OF CENTRALLY ACTIVE DRUGS ON FOUR MODELS OF EXPERIMENTALLY-INDUCED AGGRESSION IN RODENTS R . Duane Sofia () Union Carbide Corporation, Sterling Forest Research Center, Department of Pharmacology, Tuxedo, N .Y . (Received 22 January 1989 ; in final form 1 April 1989) Aggression and fighting behavior are particularly common among animals living in a free social environment . Animals inbred under laboratory conditions, such as mice and rats, lose this fighting behavior . However, tàere are certain methods available for inducing aggression in laboratory rodents . Yen et al . (1) and Valzelli et al .(2) and others were able to induce fighting in standard albino mice after prolonged isolation . Several investigators have studied the effects of various drugs oa isolated mouse aggression and have reported that certain agents were able to reduce fighting behavior . However, only DaVanzo et al .(3) compared reversal of aggression with overt neurotoxicity . Tedeschi et al .(4) elicited fighting behavior in paired mice who were exposed to a mild but continuous electric footshock. Several drugs were tested for their ability to inhibit or abolish this behavior . The measure of selectivity for suppressing the number of fighting episodes was obtained by the ratio between an effective dose and a depressant dose on'spontaneous motor activity . An increased reactivity or hyper-irritability state ineluding an aggression reaction to inanimate stimuli was induced in rats by bilateral lesioning of the septal area of the brain ~l ~Present address : Pharmakon Laboratories, Scranton, Pa . 18510 705
706
DRUGS AND AGGRESSION
Vol . 8, No . 13
("septal rats") as first described by Brady and Neuta (5) and later by Stark and Henderson (6) and others . In another study Stark and Henderson (~) reported on the effects of depressant drugs on 2~yper-reactivity in septal rats . Ataxia or neurotoxi city was determined by visual observation only . ?2esults revealed that some phenothiazines and chlordiazepoxide successfully blocked septal rat aggression . F~arli (8) observed that some laboratory rats will immedi~.tely attack and kill a mouse when introduced into its cage . `Phe term "killer rat" was used to describe this muricidal effect by Horovitz et al .(9) . In their studies on the effects of a variety of drugs in this mouse-killing test, Horovitz et al .(10) ascribed selective antimuricidal doses as those which were lower than neurotoxic doses, as measured by the rotarod method of Durham and Miya (11) . Usinr; this criterion, anti-depressants, stimulants, and antihistaminics were selectively active is these studies . Utilizing the four models of aggre:sive behavior desc~ibed, studies were undertaken to determine whether various psychoactive agents exhibited selectivity in inhibiting aggressive behavior . mhe author considers the rotarod method a re liable an9 accurKte measurement of drug-induced neurotoxicity or neurological deficit . Drug specificity in these studies were considered selective only when it occurred at doses which were significantly lower than those which impaired rotarod performance . èEaterials and Methods Isolation-Induced Aggre ssion .
L".ale albino mice, Swiss-
Webster strain (obtained fi!om Manor Farms, Staatsburg, N.Y .), weighing 16-26 grams at the start of this experiment, were iso-
Vol . 8, No . 13
DRUGS AND AGGRESSION
70 7
lated in cages (12 x 12 x 18 em) for a period of eight weeks at a constant temperature (24° C ±2) and humidity (N 5U%) and given food and water ad libitum . Fighting was obtained when one isolate was placed in the home cage of another isolate . Invariably 10076 of the mice studied showed consistent figkitinq behavior which persisted throughout a 3 minute testing period . Drugs or vehicle (0 .25`
methylcellulose) were injected intraperitoneally
into both mice 3J minutes prior to testing with complete inhibition of fighting considered as the end point . ED 50 s were determined as the dose necessary to abolish fighting in 50% of the pairs . Electric Shock-Induced Fighting .
Paired naive albino
mi^.e v~ere confined in a plastic box (4 .5 x 8 .5 x 12 cm), the floor of which consisted of a stainless steel grid . The mice were exposed for 3 minutes to a continuously scrambled shock of 3 milliamperes intensity . Fitz;htin? was considered when the 2 mice stood face to face on their hind legs and sparred and bit at one another. Drugs were injected intraperitoneally 3J minutes prior to testing . ^he number of fighting episodes in a 3 minute test period w"~s counted for a control group and a drug-treated group (5 pairs each) . Inhibition was considered when a pair of mice exhibited a 5096 reduction in fighting episodes from the average number observed in the corresponding; control group . Septal Rat Aggression .
rJ!ale hooded Lonq Evans rata (ob-
tained from Blue Spruce Farms, Altamont, N .Y .), weighing 250300 grams, were used in this study . Bilflteral electrolytic lesioning of the septal area of the brain was performed using a slight moc9ification of the method described by Stark and Nenderson (6) . The A-P and lateral stereotaxic coordinates were ~,8 and U .5 respectivel,y . The electrode tip was lowered to a depth
70 8
DRUGS AND AGGRF~3SION
Yol. 8, No . 13
of +1 .2 nm . Anodal DC current of ~ milliamperea intensity waa applied for 15 seconds . Septal lesioned animals were tested 3 to 6 days post-operatively . A scoring system was used which attempted to evaluate the "aggressiveness" observed in the septal rat syndrome . Two inanimate stimuli, a pencil ând a glove, were offered to the tail-restrained animal . Reactions were graded as follows :
0 = indifference to either object ; 1 = nib-
bling of one or both objects ; 2 = voracious attack of one object ; and 3 = voracious attack of both objects . Only those subjects which elicited a score of 3 were used~in the drug studies . Animals were tested prior to study, given drug intraperitoneally, and retested 60 minutes later . Animals which showed a 0 or 1 score at retest were considered blocked and ED~a were obtained on this all-or-none basis . Muricidal Rat Studies .
Aale hooded Long Evans rats were
also used in this phase of the study . Rats were housed individually for 6 to 8 weeks and kept on a constant food intake of approximately 15 grams per day of solid food and water ad libi tum . At the end of the isolation period, the subjects were tested for mouse-killing responses . Only those rats which killed mice within 2 minutes after presentation on 3 consecutive days were used (this method for obtaining killer rats yielded approximately 30% of the original colony) . Selected e.nimals were tested for muricidal behavior prior to drug treatment and at 30 and 60 minutes after intraperitoneal injection of the drug . Only those animals which exhibited antimuricidal effects at both testing intervals were considered inhibited and ED~s were determined as described above . Rotarod Test .
Mice and rata were trained to maintain
theMSelves on a slowly revolving wooden rod ( 5 rev ./min .) .
Vol. 8, No . 13
DRUGS AND AGGRESSION
709
Mice were tested 15 and 30 minutes after intraperitoneal injection while rats were studied 15,30 and 60 minutes after drug injection . Neurotoxicity was considered when the animals fell from the rotarod more than once during a 1 minute testing period . Mean effective doses (ED50 ) and mean neurotoxic doses (NTD50 ) ~rith 95% confidence limits and potency ratios between them were calculated according to the method of Litchfield and Wilcoxon (12) . The drugs used in these experiments were : chlorpromazine HC1, methotrimeprazine, thioridazine HC1, thiothixene, clomacran P04 (supplied by Smith, Kline and French, chemically 9-[3 dimethylamiaopropyl] chloracridane), chlordiazepoxide HC1, diazepam, tetrabenazine methanesulfoaate, benzquinamide, meprobamate, trifluperidol, sodium pentobarbital, imipramiae HCl, desipramine, and thiazesim HC1 (supf~lied by E .R . Squibb and Sons, chemically 5-[2-dimethylaminoethyl] -2,3-dihydro-2-phenyl1,5-benzothiazepin-4(5H)-one) . Doses are expressed in terms of the salt (or base when a salt was not available) and drugs were either suspended or solubilize9 in 0 .25% methylcellulose . Results Table 1 compares the ED 50 s of the agents studied in the isolated mouse fighting and elect ic shock-induced fighting behavior in mice together with their respective NTD50 s . Several drugs displayed activity in these models but only after doses near neurotoxic ones . However, only thiazesim in the isolated mouse and thioridazine, clomacran, chlordiazepoxide and diazepam in the electic shock-induced fighting models of aggression yielded results which were significantly different from their NTD50 . No ED 50 value could be obtained for thiazesim in the
710
DRUGS AND AGGRESSION
Vol. 8, No . 13
TABLE 1 Effects of Various Drugs on Isolated Mouse Aggression and Electric Shock-Induced Fighting and Mouse Rotarod Performance Drug
Chlor " romazine
so a e ouse _ A _ression _
Rotarod NTD50 mg/kg N (95 C .L .) 0 .7 (0 .1r-l .l
ED50 mg /k C .L .
N
" " " "
Thioridazine
" "
: "
:"
Chlordia e " oxide
" " .
Desi~~ramine
ll i
~
4 .8 .$-6 0
~
33 "4 1$ 0-62 0
"
"
"
"
"
"
" "
it
"
" "
28 .0-110
" " Thiazesim N - Number of mice or pairs of mice used . * - Significantly Below thé NTD50 .
1 20
83 .6 ( 67 7-103_ .3) " ~I~
1_5
0 .37 ~(0 .17-0 .8 )
0
16 .4 ~ 1 . -1 .
" ~ 1 l~:â~~l~ " :
" _ 8 .1 2- 2 .
~
"
*
*
3 .0
_
Me "~robamate
Imi "gsmine
2 .6 2 1- ,
.!
Tetrabenazine
Pentobarbital
I1
~
Diaze "~am
Benz " uinamide
N
3 .4 _ 2. - ,
~
Clomacran
Triflu "~eridol
ED50 mg/k C .L .
1 .6 0 .8- .2
Methotrime "~razine l'
Thiothixene
ectr c oc Induced Fi htin
~
20~2 .2 45 .6 -62 -_-_-
20 1
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DRUGS AND AGGRESSION
711
TABLE 2 Effects of Various DruF~s on Septal Rat Aggression and ltat Iwluricidal Activity and Rat Rotarod Performance Drug
Ch orr~romazine
Rotarod NTD 0 mg kg (95~ C .L .) 1 .7 1 .0-2 .$
Septal Rat A ression ED50 mg k (95~ C .L .~
N $~
12 .1 $ .4-17 .4
' Muricidal Rat Behavior ED5 mg N (959~+ C .L .~ N ~ ~ "
9 .0 . .1-16 .0
20
44 .6 ~ 120 .6 (33 .5-59 .3) ~(63 .9-227 .6)
2$
4 .$ (2 .2-10 .3)
f 10 .9 ~~ 76 .1 241 (6 .1-19 .5) ~ (53 .0-109 .2)
20
Thiothixene
12 .5 (7 .9-19 .9)
100 .0 43 .4 18~ (22 .1-$5 .6)_l'~(56 .7-176 .2)
16
Clomacran
2 .1 (0 .7-6 .7)
24
9 .2 (5 .1-16 .5)
Chlordiaze "~oxide
$ .$ (5 .9-13 .1)
24
23 .8 ~~ (7 .2-79 .1) t
Diazepam
4 .0 (2 .4-6 .5)
1$
17 .2 ~ ziy .o (1C .~-27 .3) ~ (15u .$-305 .9)
22
Tetrabenazine
1 .4 (1 .G-2 .1)
1$
45 .3 57 .$ (33 " 5-61 .2) ~ (35 .3-94 .7)
17
Benzquinamide
6 .$ (4 .3-10 .7)
1$
z6 .4 57 .9 (14 .6-47.9) ~ (40 .6-$2 .4)
25
N!ethotrime "~razine
7 .3 ( . -10.1)
Thioridazine
~
v
I
~ 39 .6 :'k] (25 .3-62 .0) 20 .2 (14 .6-27 .9)
16 20
Meprobamate
$5 .0 I 156 .1 301 .8 (67 .1-107 .3)~2!~ (105 .1-231 .9)I~I,(194 .5-471 .6)
23
Trifluperidol
0 .2$ (0 .26-0 .31)
1$
1 .4 (0 .6-3 .5)
0 .55 (0 .49-0 .62)
30
Pentobarbital
10 .4 (7 .1-15 .2)
1$
17 .3 ~I 25 .3 (15 .0-19.9) i i (21 .3-30 .1)
15
Imi "~ramine
z3 .o (16 .F-31 .6)
~??,
52 .7 (30 .4-91 .5)
~
15
Desi "!ramine
36 .0 (27 .0-4$ .0)
1$
45 .4 (41 .1-50 .3)
11 .9 ~ ~ I (6 .3-22 .4)
I~I~I
$ .1 (5 .2-12 .4)
32 .2 I 24 .8 34 .6 Thiazesim ~ (23 .4-44 .2) I24I (16 .1-3$ .3) I15 (23 .1-51 .7) N - Number of rats used . * - Sipnific2ntly below the IJTD50 .
1$ I40
71 2
DRUGS AND AGGRESSION
Vol. 8, No . 13
electric shock-induced fighting procedure since only minimal activity appeared at a dose (5O mg/kg) which caused some deaths . Data presented in Table 2 illustrates the results obtained with the same drugs mentioned previously for abolishing septal-lesioned rat aggression and muricidal behavior in rats aloas~ with their effects on rat rotarod performance . None of the drugs used showed a selective effect in the septal-lesioned rat . Only the two antidepressants, imipramine and desipramine, had a selective inhibitory action in the muricidal rat . These results are in agreement with the work of Horovitz et al .(10) . Discussion For az~y therapeutic agent used it would be desirable to show minimal aide effects at effective pharmacologic doses . For antagonizing aggressive behavior it would be advantageous to demonstrate activity at doses which are not overtly depressing . In these studies it may be observed that all the depressant and antidepressant drugs were capable of blocking aggressive . behavior, but only after doses which caused neurotoxicity . bccept for a few isolated examples little consistency was obtained for selective antiaggressive activity . Thiazesim was active against isolated mouse aggression but not specifically effective in any of the other procedures outlined . The latter observation is not in agreement with Horovitz et al,(1U,13) who have reported that thia,esim was capable of selectively blocking the muricidal rat response and septal rat aggression . The discrepancy between the results of the muricidal rat assay in this study and those of Horovitz and co-workers may lie in the difference between the methods of testing, the strain of rat used, or the short duration of action of thiazesim . In their study using the septal rat procedure, Horovitz et al .(13) used several
Vol. S, No . 13
DRUGS AND AGGRESSION
713
parameters observed in the syndrome (6) including the aggressive behavioral portion to determine the effects of thiazesim . Essentially our evaluation of drug activity was based primarily on grading the latter response only . In the electric shock-induced fighting thioridazine, clomacran, chlordiazepoxide and diazepam showed selective antia~gressive activity . These findings are in aggreement with those reported by Tedéschi et al .(4) who have shown that most phenothiazines and reserpine are relatively nonselective in suppressing fighting behavior . No drug used was able to abolish septal lesioned-induced aggression using the experimental parameter described . A possible explanation for this may be that the sensitivity of the septal lesioned rat to a drug may be altered since Adler (14) has shown that lesioning may induce variations in the permeability of the blood-brain barrier . Thus, perhaps a more valià comparison of specificity for this test, as well as others, would have been the use of a more analogous animal in the neurotoxicity phase of the studies . Only the two antidepressants in the group of drugs tested, imipramine and desipramine, displayed a significant blockade of the muricidal response in rats . This is in agreement with other workers (10) who have shown that depressants are not selectively active in this model of aggression . On the basis of the results of this investigation, it has been shown that no one drug or class of drugs is capable of blocking all four types of ar~gression studied at doses below their respective neurotoxic dose . Therefore, the question may be raised as to whether or not these models are producing a similar type of ngTression . In recent reviews on the pharmaco-
71 4
DRUGS AND AGGRESSION
Vol. 8, No . 13
logical control and the physiological basis of aggression, Valaelli (15) and Moyer (16) pointed out that the basic mechaniam(s) of spontaneous or experimentally-induced aggression are not well understood . Attempts to elucidate this problem have been approached biochemicall .y (3,17,18,19), behaviorally (20, 21,22), and anatomically (23,24) . Thus far no consistent findings have been reported . bHith the current increase of interest in the: area of aggressive behavior and its control (25), emphasis on underatanding the underlying mechanisms involved in the four models of aggression discussed in this paper and others that can be induced in rodents and higher species should be of major concern, since this understandinp~ might aid in the design of new drugs to control aggression . Summary Four models of experir^ent~3'l,y-induced aggression in rodents were used to determine the effectiveness of various centrally active compounds . Comparison of effective doses to those cawing evidence of neurotoxicity revealed that no one drug or class of drugs was consistently effective in the four models presented . Only thiazesim in isolated mouse aggression, thioridazine, clomacr~n, chlor9iazepoxide and diazepam in the electric shock-induced fighting and imipramin~ and desipramine in the muricida~l rat assay exhibited selective activity . No drug significantly reduced aeptal-lesion ar~gression in rats . Acknowledgements The author expresses his appreci~~tion for thF: technical assistance of Miss Carole Ten Hoeve, A7rs . Aonnie '"c!:ormick, and tAra . Linda Stapleton ; to '.9r. .7effrey N!alick for preparation of septal -lesioned rats ; and to the following companies for drug
Vol . 8, No . 13
DRUGS AND AGGRESSION
71 5
supplies : Geigy Pharmaceuticals ; Hofiman LaRoche, Inc . ; Lederle Laboratories, Inc . ; McNeil Laboratories, Inc . ; Charles Pfizer and Co,,
Inc . ; S~.ndoz Pharmaceuticals ; Smith, K'.ine and French
L boratories ; E .R . Squibb and Sons, 7nc . ; and .Uallace Laboratories . References 1 . C.Y . Yen, R .L . Stanger and N . Mi'lman, Arch . Int . Pharmaco d~n ., 123, 179, 1959 . 2 . L . Valzelli, E . Giacalone and S . Garattini, Europ .~J . Pharnacol ., 2, 144, 1967 . 3 . J .P . DaVanzo, M. Daugherty, R . Ruckart and L . Kang, Psycho pharmacologia ( Berlin ), 9, 21U, 1966 . 4 . R .E . Tedeschi, D .H . Tedeschi, A . T~+ucha, L. Cook, P .A . Mattie and F,J . Fellows, J . Pharmacol . Exp . Ther ., 1~, 28, 1959 . 5 . J.V . Brady and W .J .H . Nauta, J. Com . Physiol . Ps9chol ., 46, 339, 1953 . -_ 6 . P . Stark and J .K . Henderson, Intl . J . Neuropharmacol ., ~, 7 . P . Stark and J .K . Henderson, Intl . J . Neuropharmacol ., 5, 3p~5, 1966 . 8 . P. Karli, Behavior (Leiden) , 10 ; 81, 1956 . 9 . Z,P. Horovitz, P,'~J. Ragozzino and R .C, Leaf, Life Sciences , 4, 199, 1965 . 10 . Z .P . Horovitz, J,J . Pula, J .P . High, J .C . Burke and R .^, . Leaf, Intl . J. ~europharmacol ., 5, 405, 1966 . 11 . N .W . Dunhan and T .S . Miya, J . Amer . Pharm . Assoc . (Sçi . Edn .), 46, 208, 1957 " 12 . J .T . Litchfield, Jr . and F . Wilcoxon, J . Pharmacol . ~. Ther ., 96, 99, 1949 . 13 . Z .P . Horovitz, A .F . Furgiuele, L.J . Brannick, J .C . Burke and B .N . Craver, Nature , 200, 369, 1963 . . 14, N .W, Adler, J. Phsrmacol . F~ . Ther . , 134, 214, 1961 . 15 . L . Valzelli, Advances in Pharmacolo and P .A . Shore , Aca etc-$r ess,
, (Dds . S . Garattini York, ~, 79, 1907 .
16, K .E . Mover, Communications in Pehavioral Biology , 2, 65, 1968 . _
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17 . E . Giacalone, M. Taasella, L . Valzelli and S . Garattini, Biochem . Pharmacol ., ~, 1315, 1968 . 18 . A .B . Rothballer, Brain Function, Volume 5, A ression and Defense, Neural Mec~anism~Social Patterns, F . s . C .~ . amen e a~-B . L~nds~ey~,ûn vers ty -moo Z°-a~ifornia Press, Los Angeles, 135, 1967 " 19 . M .E . Goldberg and A .I . Sehinn, Biochem . Pharmacol ., 18, 532, 1969 . _ 20 . R .E . Ulrich and W .H . Crame, Science , 143, 971, 1964 . 21 . H.C . Nieloon, A .H . McIver and R .S . Boswell, Exptl . Neuro ., 11, 147, 1965 . 22 . A .S . Kulkarni, Ps9chol . Record , 18, 385, 1968 . 23 . P. Ropartz, Anim . Behav ., 16, 97, 1968 . 24 . Z .P . Horovitz, Proceedin s on _the First International S p~osium_ on Aati- e ressent D ~ ru s_, (F~s.S . arat in an~ token , Excerp a ed~câFoundation, Amsterdam, 121, 1966 . 25 . Proceedin s on the International S osium on A ressive Bearmaco av or : ioc~mis~r , ~, , oc~; Mar o Negr , st u o c erc e Farmaco oq che, M an, Italy, in press .