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An observational analysis of the behavioural effects of β-Phenylethylamine in isolated and grouped mice
Prog, Neurr>Psychopharmocol & Biol. Psychlat. 1982. Vol, 6. pp. t43-158 Printed in Great Britain. All rights reserved.
0278-5846182/020143-16508.0010 Copyright © 1982 Pergamon Press Ltd.
AN OBSERVATIONAL ANALYSIS OF THE BEHAVIOURAL EFFECTS OF ~-PHENYLETHYLAMINE IN ISOLATED AND GROUPED MICE
COLIN T
DOURISH
Psychiatric Research Division, University Hospital Saskatoon, Saskatchewan, Canada
(Final form, February,
1982)
Abstract
Dourish, Colin T.: An observational analysis of the behavioural effects of ~-phenylethylamine in isolated and grouped Rice. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 6: I.
2.
3.
4.
Male Swiss mice were treated systemically with B-phenylethylamine (PEA, 25-150 mg/kg), and observed in isolation or in groups of five. The effects of PEA were scored on 13 separate components of behaviour which were produced or increased by the drug. PEA at a dose of 25 mg/kg depressed activity and caused sedation, but at 50 mg/kg produced a brief stimulation of activity. At higher dose levels (75-150 mg/kg) the compound induced a biphasic stimulation of activity which was associated with the development of two distinct groups of stereotyped activities. Group testing significantly antagonized early phase stereotypy (forepaw padding, headweaving, compulsive grooming) but had no effect on, or potentiated, late phase stereotypy (rearing, licking). In addition grouped mice were more active and hyperreactive than isolated mice. The results are briefly discussed in the light of the possibility of a cateqholamine/ indoleamine interaction in the control of the hyperactivity syndrome induced by PEA in the mouse.
K eywords: 8-phenylethylamine, catecholamines, components of behaviour, hyperactivity, indoleamines, interaction, isolated and grouped mice, stereotypy.
Abbreviations:
8-phenylethylamine
(PEA); 5-hydroxytryptamine
(5-HT).
Introduction
~-Phenylethylamine
(PEA) has been detected in the brain and peripheral tissues of man and
animals (Philips etal., 1964; Jackson and Temple,
1978; Durden etal.,
1973; Boulton etal.,
1975; Nakajima etal.,
1970) and has been proposed as a possible neurotransmitter or
"synaptic activator" (Boulton,
1976, 1979).
locomotor activity in mice (Schulte etal.,
PEA produces amphetamine-like stimulation of 1941; Nakajima etal.,
143
1964) which is
144
C.T. Dourish
potentiated by pretreatment with a monoamine oxidase inhibitor, (Mantegazza and Riva, 1963), since PEA is a specific substrate for monoamine oxidase and is, therefore, oxidized extremely rapidly (Philips and Boulton, 1979; Durden and Philips, 1980).
A comprehensive series of
studies by Jackson (see review by Jackson, 1978 and references therein), using grouped mice, indicated that PEA has a biphasic effect on locomotor activity. PEA
a
At a dose of 50 mg/kg of
short-lived locomotor stimulation was produced (peak 4-6 minutes post injection, dura-
tion 15 minutes), whereas at higher doses of 75-150 mg/kg the drug produced an "early" phase of stereotyped behaviour followed by a "late" increase in locomotor activity (20-60 minutes post injection).
Jackson (1978) has proposed that both dopamine and noradrenaline are
involved in the early phase locomotor stimulation whereas dopaminergic mechanisms may be dominant in the late phase.
These findings, and the majority of other reports on the
effects of PEA in mice, were based on data generated by photobeam interruptions, a method which has been subject to ~,ch criticism as the sole measure of behavioural responses (Krsiak et al., 1970; Fray et al., 1980).
An observational method, which was adopted in the
present study, can detect drug induced changes even at low doses, and, in addition, can identify different components of behaviour which may have separate neurochemical substrates.
The purpose of the present study was to perform a detailed observational analysis of the behavioural effects of a wide range of doses of PEA in the mouse, scoring 13 individual components of behaviour for each animal tested.
The study includes a comparison of the effects
of PEA in isolated and grouped (n ffi 5) mice since some previous reports have indicated that the drug either depresses (Fischer et al., 1967) or has no effct on activity (Jackson, 1978) in isolated mice, but paradoxically, stimulates activity in grouped mice (Jackson, 1978). Although it is well established that many of the behavioural effects of PEA in rodents involve an action on brain catecholamine systeu~ (Jackson, 1978; Braestrup and Randrup, 1978; Moja et al., 1978) recent evidence suggests that a behavioural syndrome produced by PEA in the rat may primarily involve brain 5-HT mechanisms (Sloviter et al., 1980; Dourish, 1981). Therefore a further aim of the observational analysis was to provide a basis for the examination o~ the neurochemical substrates of the PEA response in succeeding interaction studies.
Methods
Animals.
Male Swiss albino mice (18-25 g body weight) were used in the experiments.
The
animals were housed in hanging wire cages, in groups of 20, with food and water ad lib. Lighting operated on a 12 h dark-12 h light cycle (lights on 6 a.m.) and temperature was maintained at 20-23°C.
Dru~s.
B-Phenylethylamine hydrochloride (Sigma) was made up in distilled water and injected
intra-peritoneally in a volume of I0 ml/kg in all cases. in terms of the salt.
Doses of the drug were calculated
Behavioural effects of B-phenylethylamine in mice
A p p a r a t u s and P r o c e d u r e s . ing conditions
Mice were randomly a l l o c a t e d
and e a c h a n i m a l was u s e d once o n l y .
145
t o i n d i v i d u a l or group (n = 5) t e s t -
Within the individual
test
condition
a n i m a l s were a s s i g n e d t o one o f s i x d r u g t r e a t m e n t s which c o n s i s t e d o f PEA a t d o s e s o f 25, 50, 75, 100 and 150 mg/kg Within the group t e s t
and t h e d i s t i l l e d
condition,
t r e a t m e n t s which c o n s i s t e d ed i n c i r c u l a r
plastic
procedure.
or c o n t r o l
solution
solution
referred
to as 0 mg/kg.
g r o u p s of f i v e mice were a s s i g n e d t o one o f f o u r d r u g
o f PEA a t d o s e s o f 0, 50, 75 and 100 mg/kg.
c a g e s o f 22 cm d i a m e t e r and 25 cm h i g h .
g r o u p o f a n i m a l s was p l a c e d i n t h e t e s t injection
water control
Each i n d i v i d u a l
cage f o r a 30 m i n u t e h a b i t u a t i o n
Following habituation
T e s t i n g was c o n d u c t a n i m a l or
period p r i o r to any
a n i m a l s were weighed and i n j e c t e d w i t h t h e d r u g
and i m m e d i a t e l y r e t u r n e d t o t h e cage to b e g i n t h e t e s t .
The mice were
o b s e r v e d and r a t e d on 13 c o m p o n e n t s o f b e h a v i o u r which bad b e e n found i n p r e l i m i n a r y e x p e r i m e n t s to be i n d u c e d or i n c r e a s e d by PEA ( T a b l e 1). on a 0-4 s c a l e d e p e n d i n g on t h e i n t e n s i t y each t e s t
Each mouse or group of mice was s c o r e d
of the behaviour e x h i b i t e d
(Table 2).
a n i m a l or group o f a n i m a l s on e a c h i t e m were d e t e r m i n e d d u r i n g a l t e r n a t e
minute periods until
all
drug e f f e c t s
t i m e s , and each g r o u p t e s t
bad d i s s i p a t e d .
Each i n d i v i d u a l
test
Scores for five
was r u n e i g h t
a minim,-- of f i v e t i m e s .
Table 1
B e h a v i o u r a l Components u s e d in t h e O b s e r v a t i o n a l A n a l y s i s
Eehavioural Component
Explanatory Notes
Freezing
Inactive in one location
Forward Walking
Co-ordinated locomotor activity includin~ forward
Rearing
Both front paws off the ground
Grooming
Includes normal and abortive or compulsive cleaning
walkin~ o r r u n n i n ~
of the body Sniffing Backward W a l k i n g
Backward w a l k i n g or backward c i r c l i n g
Headweaving
Repetitive,
Padding
Repetitive
Hyperreactivity
Startle
Tremor
Head, paw or whole body s h a k e
fast,
s i d e t o s i d e head movements
t r e a d i n g of the forepaws
r e s p o n s e t o a p e n c i l t a p on c a g e
Jumping Licking Vocalization
Compulsive licking or biting of cage walls or floor
146
C.T. Dourish
Table 2
Behavioural
Rating Scale Used to Score Each Component
Score
Behavioural
in the Analysis
Frequency
Absent Mild intensity; Moderate
present
intensity;
I-2 times
present 3-4 times
High intensity;
present 5 or more times
Severe;
for prolonged
present
periods
Statistical Analysis
Due to the ordinal nature of the rating scale employed, describing
the scores obtained
rect median was calculated was carried out on both.
in addition
valid.
examine time course of drug effect).
Therefore
to the mean and where applicable
Mean and median scores were calculated
ponent at each dose level over the complete
graphically
the use of the mean as a method of
is not totally statistically
the more cor-
statistical
analysis
for each behavioural
com-
test and for each five minute sample period
However,
means were plotted
in depicting
as the points generated using the mean are more discrete
(to
the data
than those generated
using the median.
Results were analysed using two nonparametric Kruskal-Wallis
one-way analysis
of variance,
to locate specific group differences.
statistical
tests (Siegel,
1956),
the
followed by the Mann-Whitney U test (2-tailed)
The Spearman rank-order
correlation
tween items was calculated
for each dose of PEA, and for each time period,
and group test conditions,
using an Apple II microcomputer.
coefficient
be-
in both isolated
Interrater Reliability
The mice were rated by two observers Interrater reliability
one of whom was unaware of the drug treatment.
for the scores generated by the observational
by the weighted Kappa (Hall,
analysis was determined
1974).
A random sample of 400 pairs of ratings by the two observers was used in the determination.
The results using the 0-4 Scale were 82.6% no difference;
9.4% one point disagree-
Behavioural effects of 8-phenylethylamine in mice
147
ment~ 5.2% two points disagreement; 2.2% three points disagreement; 0.6% four points disagreement.
The value of the weighted Kappa was 0.82 (P<.01).
Results
Dose Response Effects
The effects of PEA on the 13 behavioural components rated in the analysis are shown in Tables 3 and 4.
In isolated mice PEA produced a dose dependent decrease in freezing when
administered at doses above 50 mg/kg.
A lower dose of 25 mg/kg, however, induced a sedative
effect and significantly increased freezing scores (p<.05, Table 3).
The decrease in freez-
ing observed in isolated mice at doses of 50 mg/kg of PEA, and above, did not appear to be directly related to an increase in coordinated locomotor activity since forward walking was significantly increased at only one dose level (50 mg/kg, p<.05; Table 3).
In contrast.
Table 3
Dose Response Effects of B-Phenylethylamine in Isolated Mice
Behavioural Category
Dose of 8-phenylethylamine (mg/kg) 0
25
50
75
4.00*
1.80
1.00
I00
150
0.40*
0.33*
Freezing
3.13
Forward Walking
1.96
1.50
4.00*
3.05
2.70
2.91
Rearing
1.50
0.50
0.80
0.41
0.I0
0.99
Grooming
1.55
0*
2.00
3.12"
3.70***
3.33***
Sniffing
1.91
3.75*
4.00*
4.00**
4.00*
4.00**
Backward Walking
0
0
0
0
0.70**
1.33"**
Headweaving
0
3.37***
3.30***
3.88***
Padding
0
2.37**
2.20***
2.55***
Hyper-reactivity
0
3.00***
2.10"*
1.40"*
Tremor
0
0
0
0
0
Jumping
0.5
0
0
0
0
Licking
0
0
Vocalization
0
0
1.50"* 0 2.25***
4.00*** 0 2.25***
0.25 0
2.12"** 0
0.80 0
1.30"** 0 0.99** 0
Each score represents a median value of 8 animals on a 0-4 scale. Statistical comparisons (Mann-Whitney U Test) a r e between drug and control values: * p<.05; ** p<.02; *** p<.01.
148
C.T. Dourish
when PEA was administered at the same dose levels to grouped mice a consistent increase in forward walking or running was observed (Table 4, Fig. la)
PEA, at doses above 50 mg/kg, induced a syndrome of repetitive or compulsive behaviours in both isolated and grouped mice.
The syndrome included headweaving,
padding, hyperreactiv-
ity, compulsive sniffing, rearing, grooming and licking (Tables 3 and 4).
There was a sig-
nificant interaction between drug dose and isolated or group testing with respect to a number of these behaviours (p < .05, Kruskal-Wallls test).
Headweaving and compulsive grooming
were significantly reduced in a group test at a dose of i00 mg/kg of PEA (Fig. Ib and Fig. 2a).
Similarly, forepaw padding was suppressed in a group test at doses of 75 and i00 mg/kg of PEA (Fig 2b). 4).
Sniffing, however, appeared to be unaffected by group testing (Tables 3 and
In contrast the hyperreactive responses of running, jumping and vocalization were
significantly increased in group tests at all dose levels of PEA which were employed (Table 3, Figs. la and 3).
Indeed, jumping and vocalization were virtually absent in isolated mice
(Table 3). b
Table 4
Dose Response Effects of ~-Phenylethylamine
Behavioural
in Grouped Mice
Dose of ~-phenylethylamine (mg/kg)
Category
0 (5)
50 (5)
75 (6)
ioo (5)
Freezing
2.68
1.16
0.51
0.36
Forward Walking
1.56
2.82*
3.08*
2.92*
Rearing
1.30
0.70
2.23
1.60
Grooming
1.96
0.92
2.30
2.56
Sniffing
1.70
3.86*
3.75*
Backward Walking
0
0
0
Headweaving
0
3.04*
2.40*
Padding
0
0
0
Hyperreactivity
0
2.63*
2.55*
Tremor
0
Jumping
0
0.56
0
0.26
1.27
2.04*
3.25*
3.50*
2.75*
Licking Vocalization
0.70
0
0 1.90"
3.76* 0.12 1.60" 0.66 1.24" 0 0.22
Each score represents a median value on a 0 - 4 Scale with number of experiments in parenthesis. Statistical comparisons (Mann-Whitney U Test) are between drug and control groups: *p<.Ol
Behavioural effects of B-phenylethylamine in mice
149
Similarly, rearing was significantly increased in group tests (p<.05, Mann Whitney U test) at doses of 75 and I00 mg/kg of PEA, whereas licking was potentiated by group testing at a dose of I00 mg/kg (Tables 3 and 4).
Backward walking and tremor were evident at the highest dose levels of PEA (I00 and 150 mg/kg) which were tested but only occurred to a very slight extent (Table 3). signs of peripheral stimulation such as piloerection,
In addition,
salivation and Straub tail were a con-
sistent observation in all drug treated animals.
Time Course Effects
There was a significant drug, time course interaction on forward walking in both isolated and grouped mice (p<.05, Kruskal-Wallis test).
A dose of 50mg/kg of PEA produced only a
brief stimulant effect but doses of 75-150 mg/kg of the drug induced a triphasic effect on walking which consisted of an initial stimulant effect (1-5 minutes post-injection), ceeded by a depression (5-20 minutes post-injection), (20-45 minutes post-injection, Fig. 4a).
suc-
followed by a late stimulant effect
The biphasic stimulant pattern was more pronounced
at the higher doses.
The time courses of the various drug-induced compulsive behaviours appeared to fall into two distinct groups which may have had a close parallel in the observed effects on forward walking.
Headweeving, grooming and padding appeared within five minutes, reached a peak
5-25 minutes post-injection,
and declined thereafter (Figs. 4a, 5a and 6).
In contrast
rearing and licking had a slow onset, tended to increase throughout the test period, and reached e peak 25-45 minutes post-injection (Fig. 6a and b). activity showed a gradual increase over time (Fig. 7).
Similarly jumping and hyperre-
Compulsive sniffing did not appear
to fall into either group and remained at a high level throughout the test period.
Correlations Between Behavioural Components
Significant correlations between behavioural components are summarized in Table 5.
Scores
from isolated and grouped animals were combined since consistent correlations were obtained across the two conditions.
Significant relationships generally varied with dose and time
although there was a consistent positive correlation between sniffing end headweaving, and sniffing and grooming in all cases.
At the lowest dose levels (25-50 mg/kg) freezing was negatively correlated with rearing and walking but positively correlated to sniffing, headweaving and hyperreactivity.
The
hyperreective responses of jumping and vocalization were positively correlated to hyperreactivity.
At intermediate dose levels (75-100 mg/kg) all of the behavioural components were
observed with the exception of tremor and there were a large number of positive correlations between the components.
Forward walking was positively correlated with the late phase
150
C.T. Dourish
Table
5
The Direction of the Significant Spearman Rank Order Correlations Behavioural Components in Isolated or Grouped Mice After Various
Between Scores on the Dose Levels of PEA. =
(a)
PEA 25-50 mg/kg
~J •H
~1 =
.~
.1~
}~
Freezing Forward Walking Rearing Grooming Sniffing Headweaving Ryperreactivity Jumping Licking Vocalization
~J
~)
I .r~
•
~.~
~
÷
+
--
+
+
+
+
+
+
+ +
.,-4
0
+ +
o~ (b)
+
Freezing Forward Walking Rearing Grooming Sniffing Backward Walking Headweaving Padding Hyperreactivity Jumping Licking Vocalization
(c)
o
PEA 75-i00 mg/kg
+
+
+
-
+
+ +
+ +
+
+
+ +
_ ± +
+ +
+ + +
+
+
÷
+ +
PEA 150 mg/kg
-+
+
--+
+
t~ ~J
~.-I
~I
O
.,-I
0,-4
Freezing + Forward Walking + Rearing 4÷ Grooming + ÷ + Sniffing ÷ + Backward Walking + Headweaving + Padding Hyperreactivity Tremor Lickin~ (+ indicates a significant positive correlation and - indicates a significant negative correlation during one or more time samples. ± indicates a change in direction of a correlation over time.)
Behavioural
effects
of ~-phenylethylamine
~ 3-
3-
2-
"i 2-
iZ
o
.9 1-
25
50
75
100
/ ;
150
in mice
i!
¢
¢
75
1;0
a
2;
5;
150
PEA(mglkg)
PEA ( m g l k g )
Fig. la: Effects of B-phenylethylamine (PEA) on forward walking in isolated (O----O) and grouped (O----e) mice. All values are mean ± SEM on a 0-4 Scale. Significant differences (Mann-Whitney U test) between drug and control animals are indicated by the following letters: a, p<.05; b, p<.02; c, p<.01. Fig Ib: Effects of PEA on headweaving in isolated (O O) and grouped (O------e) mice. All values are mean ± SEM on a 0-4 Scale. Significant differences (Mann Whitney U test) betwee drug and control animals are indicated by the following letters: a, p<.05; b, p<.02; c, < 01 Significant differences (Mann-Whitney V test) between isolated and grouped animals P " " ' ~ ~ care indicated by letters with superscrlpts: a , p<.05; b , p<.02; , p<.01.
¢
.E E o
.cm "o "u
1-
o. t-
(9
u
215 5~) 75 PEA(mglkg)
Fig. 2a: described Fig. 2b: described
2-
2-
o
1(~0
150
/ 0
25
75
50
100
1~;0
PEA(mglkg)
Effects of PEA on grooming in isolated and grouped mice. for Fig. I. Effects of PEA on padding in isolated and grouped mice. for Fig. I.
Conventions Conventions
are as are as
152
C.T. Dourish
4¢ c
m
¢
3-
.£ L
£ 2~
o
B
2'5
~
75
1(}0
150
PEA (mgJ k g )
A) and grouped (b---~) mice, and Fig. 3. Effects of PEA on vocalization in isolated (~ jumping in isolated (O O) and grouped (O---~) mice. Conventions are as described for Fig. I.
A 3"
m 3c
.v
>
|
D
-r "P
1-
1-
0
Minutes Post Injection
Minutes Post injection
Fig. 4a. Time course of forward walking in isolated and grouped mice treated with PEA. values are mean ± SEM on a 0-4 scale. (O O) isolated control; (~ A) PEA 75 mg/kg
i s o l a t e d ; ([~---O) PEA 100 mg/kg i s o l a t e d . (H) grouped; ( H ) PEA 100 mg/kg grouped. Fig. 4b. Time c o u r s e of headweaving i n i s o l a t e d C o n v e n t i o n s a r e as d e s c r i b e d f o r Fig. 4a.
grouped c o n t r o l ;
(A~----A) PEA 75 mg/kg
and grouped mice t r e a t e d w i t h PEA.
All
Behavioural effects of B-phenylethylamlne in mice
152
4-
3-
m
:E "D
.£ E
2-
o 0
1-
0
o
r
s
,~ Minutes
r
2s
3'5
4~
r---~--
o
s
Post Injection
I'5 Minutes
2'5
3'5
4'5
Post Injection
Fig. 5a. Time course of grooming in isolated and grouped mice treated with PEA Conventions are as described for Fig. 4a. Fig. 5b. Time course of padding in isolated and grouped mice treated with PEA. are as described for Fig. 4a.
Conventions
41 B
o n*
15
Minutes
25
35
Post Injection
45
;
,'5
~
3s
__.__~ 4s
Minutes Post injection
Fig. 6a. Time course of rearing in isolated and grouped mice treated with PEA. are as described for Fig. 4a. Fig. 6b. Time course of licking in isolated and grouped mice treated with PEA. are as described for Fig. 4a.
Conventions Conventions
C.T. Dourish
154
4"
m D cL -r
CL E
1
0
1~ Minutes
~5 Post
3~
4~
Injection
Fig. 7. Time course of hyperactivity (open symbols) and jumping (closed symbols) in grouped mice treated with PEA. (O O) Control; (~ A) PEA 75 mg/kg; (O O) PEA I00 mg/kg.
compulsive behaviour of licking, rearing, hyperreactivity and jumping
It is also of note
that walking showed an initial negative correlation with compulsive licking behaviour. Padding was positively correlated with sniffing,
headweaving and backward walking while
grooming was associated with sniffing and backward walking.
The highest dose level (150
mg/kg) marked the appearance of tremor which was positively correlated with compulsive behaviours including padding,
grooming and backward walking.
Forward walking was again
positively correlated to licking.
Discussion
The present data confirm and extend the findings of Jackson (1972) that PEA exerts a b iphasic stimulant effect on locomotor activity in mice, in this instance measured by observations of the forward walking component (Fig. 4a).
The observational analysis suggests
that the biphasic effect of PEA on activity may be closely related to the emergence of various compulsive or stereotyped behaviours which appear to fall into two distinct groups. Early phase activity is associated with compulsive grooming, forepaw padding, sniffing and headweaving while late phase activity appears to involve compulsive sniffing, ing and hyperreactivity.
rearing,
These observations are only partly in agreement with those of
lick-
Behavioural effects of ~-phenylethylamine in mice
155
Jackson (1972, 1974) who claims that late phase activity is devoid of any stereotypy and characterized by co-ordinated locomotor activity.
Notwithstanding this report the present
observations demonstrated a clear increase in rearing and licking stereotypies, which was particularly marked at a dose of I00 mg/kg, during the late phase of activity stimulation (i.e. 20-45 minutes post-injection,
Fig. 6).
Interestingly forward walking showed an initi-
al negative correlation with licking (PEA 75-100 mg/kg, Table 5) which changed to a significant positive correlation with rearing and licking towards the end of the test period.
In
the present experiment, the late phase of stimulation was generally characterized by animals walking or running around the cage and rearing to sniff and lick the cage walls.
The observation of compulsive licking behaviour in mice, reported in the present study, is an example of an important species difference in response to the systemic administration of PEA, since previous investigations have failed to demonstrate a similar response in the rat, even in combination with a monoamine oxidase inhibitor, unpublished observations).
(Braestrup et al., 1975; Dourish,
The failure of PEA to produce licking in the rat has been attri-
buted to the inhibitory effect of increased noradrenergic stimulation produced by the compound (Braestrup and Randrup, 1978).
Possibly this could indicate that the slow onset of
licking observed in the present study could be due to an initial strong release of noradrenaline which would inhibit the expression of this behavioural component.
This explanation
stands in general agreement with the hypothesis of Jackson (1978) that both dopamine and noradrenaline are involved in the early phase of locomotor stimulation whereas dopaminergic mechanisms are dominant in the late phase.
Although PEA-induced licking in mice has been previously noted (Jackson, study is the first report of PEA-induced compulsive or abortive grooming.
1972) the present This behaviour is
distinguished from normal grooming by its persistence, and failure to complete the cleaning act by touching the body (hence the term abortive), and is consistent with the observation of a similar behavioural pattern induced by d-amphetamine
(Thomas and Handley, 1978).
Grooming and other compulsive behaviours, such as padding and headweaving,
associated with
the early phase of PEA stimulation (0-20 minutes post-injection) were significantly supressed by group testing, whereas, rearing and licking associated with the late phase stimulation, were unaffected or increased in a group test.
The development of the early phase com-
pulsive behaviours may have been retarded by the hyperreactive responses of running,
jumping
and vocalization (sometimes referred to as "Popcorn behaviour," Sabelli et al., 1975) which were significantly increased in group test conditions.
These observations could explain
some of the discrepancies relating to the effects of PEA in isolated and grouped mice.
For
example a study by Fischer et al. (1967) measured activity of isolated mice for I0 minutes after administration of a 40 mg/kg dose of PEA and reported a depression of activity. sumably during this brief time period stereotyped behaviour such as grooming, headweaving would tend to depress activity counts.
Pre-
padding and
However, in a longer group test, as used
by Jackson (1972, 1974), hyperreactive responses could mask any depression of activity due
156
C.T. Dourish
to the induction of stereotyped behaviour.
This is exemplified by the present observational
analysis in which animals in group tests were observed to engage in bursts of stereotyped activity which was frequently interrupted by contact with another animal producing the "Popcorn behaviour" outlined above.
Hyperreactive responses did not interfere with rearing and licking and it appears possible that the behavioural components which are dominant in the late phase of PEA stimulation have a single neurochemical substrate, which may be dopamine.
Indeed it has previously been pro-
posed (Jackson, 1978) that dopaminergic mechanisms are dominant in the late phase activity stimulation.
It is well established that PEA is a specific substrate for monoamine oxidase and, as such, is oxidized very rapidly (Philips and Boulton,
1979; Durden and Philips, 1980).
Con-
sequently, it is possible that there might be a correlation between the biphasic stimulant effect of PEA on activity and an initial increase in brain PEA levels after injection followed by a rapid decline in levels due to deamination by monoamine oxidase.
Further experi-
ments are required to determine whether such a causal relationship exists.
One aim of the present study was to provide an observational basis for the future investigation of the neurochemical substrates of the various components of behaviour which are produced or increased by PEA in the mouse.
The observational data presented are consistent
with the proposed role of catecholaminergic systems which may be involved in sniffing, rearing, licking, hyperreactivity and forward walking.
The data also suggest the possiblity of
an indoleaminergic involvement in the expression of such behavioural components as padding and headweaving which are thought to be mediated by 5-HT in the rat (Sloviter et al., 1980; Dourish, 1981).
Although currently still under investigation,
the possibility of a catecholamine/indolea-
mine interaction in the control of the PEA hyperactivity syndrome in the mouse is supported by preliminary findings from antagonist interaction studies (Dourish, unpublished observations).
Conclusion
Observational analysis confirms that PEA has a biphasic stimulant effect on activity in the mouse.
It appears, however, that contrary to previous reports (Jackson, 1978), both
phases of the stimulant action are associated with the appearance of stereotyped activities; forepaw padding, headweaving and grooming are dominant in the early phase while rearing, licking and hyperreactivity are more important in the late phase.
The grouping of behavi ~
oural components observed suggests the possible involvement of an indoleamine system, in addition to catecholamines in the expression of PEA-induced hyperactivity in the mouse.
Behavioural effects of B-phenylethylamine in mice
157
Acknowledgements
The author thanks Dr. A.A. Boulton for suggesting this topic and for helpful discussions, and B. Dourish for excellent technical assistance and writing of computer programs. Financial support from Saskatchewan Health and the M.R.C. of Canada is acknowledged.
References
BOULTON, A.A. (1976) Cerebral aryl alkyl aminergic mechanisms. In: Trace Amines and the Brain, E. Usdin and M. Sandier (eds.) pp 21-40, Marcel Dekker, New York. BOULTON, A.A. (1979) Trace amines in the central nervous system. In: International Review of Biochemistry, Physiological and Pharmacological Biochemistry, 26, K.F. Tipton (ed.), 179-205, University Park Press, Baltimore. BOULTON, A.A., JUORIO, A.V., PHILIPS, S.R., and WU, P.H. (1975) Some arylalkylamines in rabbit brain. Brain Res., 96: 212-216. BRAESTRUP, C., ANDERSEN, H., and RANDRUP, A. (1975). The monoamine oxidase B inhibitor deprenyl potentiates phenylethylamine behaviour in rats without inhibition of catecholamine metabolite formation. Eur. J. Pharmacol., 34: 181-187. BRAESTRUP, C. and RANDRUP, A. (1978) Stereotyped behaviour in rats induced by phenylethylamine, dependence on dopamine and noradrenaline, and possible relation to psychoses? In, Noncatecholic Phenylethylamines, Part I, Phenylethylamine: Biological Mechanisms and Clinical Aspects, A.D. Mosnaim and M.E. Wolf (eds.) pp 245-269, Marcel Dekker, New York. DOURISH, C.T. (1981) Behavioural effects of acute and chronic 8-phenylethylamine administration in the rat: evidence for the involvement of 5-hydroxytryptamine. Neuropharmacology, 20: 1067-1072. DURDEN, D.A., PRILIPS, S.R., and BOULTON, A.A. (1973) Identification and distribtion of B-phenylethylamine in the rat. Can. J. Biochem., 51: 995-1002. DURDEN, D.A., and PHILIPS, S.R. (1980) Kinetic measurements of the turnover rates of phenylethylamine and tryptamine in vivo in the rat brain. J. Neurochem., 34: 1725-1732. FISCHER, E., LUDMER, R.J., and SABELLI, H.C. (1967) The antagonism of phenylethylamine to catecholamines on mouse motor activity. Acta Physiol. Lat. Am., 17: 15-21. FRAY, P.J., SAHAKIAN, B.J., ROBBINS, T.W., KOOB, G.F., and IVERSEN, S.D. (1980) An observational method for quantifying the behavioural effects of dopamine agonists: Contrasting effects of d-amphetamine and apomorphine, Psychopharmacology, 69: 253-259. HALL, J.N., (T974) Inter-rater reliability of ward rating Scales?-- Br. J. Psychiat., 125: 248-255. JACKSON, D.M., (1972) The effect of 8-phenylethylamine upon spontaenous motor activity in mice: a dual effect on locomotor activity. J. Pharm. Pharmacol., 24: 383-389. JACKSON, D.M. (1974) The involvement of noradrenergic systems in the locomotor activity stimulation in mice produced by B-phenylethylamine. J. Pharm. Pharmacol., 26: 651-654. JACKSON, D.M. (1978) 8-phenylethylamine: Studies on the mechanism of its stimulant effects. In: Noncatecholic phenylethylamines., Part i, Phenylethylamine: Biological Mechanisms and Clinical Aspects, A.D. Mosnaim and M.E. Wolf (eds) pp 289-313, Marcel Dekker, New York. JACKSON, D.M. and TEMPLE D.M. (1970) ~-phenylethylamine as a cardiotonic constituent of tissue extracts. Comp. Gen. Pharmacol., I: 155-159. KRSIAK, M.H., STEINBERG, H. and STOLERMAN, T.D. (1970) Uses and limitations of photocell activity cages for assessing effects of drugs. Psychopharmacologia, 17: 258-274. MANTEGAZZA, P. and RIVA, M. (1963) Amphetamine-like activity of ~-phenylethylamine after a monoamine oxidase inhibitor in vivo J. Pharm. Pharmacol., 15: 472-478. MOJA, E.A., STOFF, D.M., GILLIN, J.C. and WYATT, R.J. (1978) Neuroleptics attenuate stereotyped behaviour induced by 8-phenylethylamine in rats. Biol. Psychiat., 13: 291-295. NAKAJIMA, T., KAKIMOTO, Y., and SANO, I. (1964) Formation of 8-phenylethyla--mine in mammmlian tissue and its effects on motor activity in the mouse. J. Pharmacol. Exp. Ther., 143: 319-325. PHILIPS, S.R., ROZDILSKY, B. and BOULTON, A.A. (1978) Evidence for the presence of metatyramine, Rara-tyramine, tryptamine and phenylethylamine in rat brain and several areas of human brain. Biol. Psychiat. 13: 51-57. PHILIPS, S.R. and BOULTON, A.A. ~ 9 7 9 ) The effect of monoamine oxidase inhibitors on some arylalkylamines in rat striatum. J. Neuroehem. 33: 159-167. SABELLI, H.C., VAZQUEZ, A.J., and FLAVIN, D. (19755"- Behavioural and electrophysiologieal effects of phenylethanolamine and 2-phenylethylamine. Psychopharmacologia, 42: 117-125.
158
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SCHULTE, J.W., REIF, E.C., BADER, J.A., LAWRENCE, W.S. and TAINTER, M.L. (1941). Further study of central stimulation from sympathomimetic amines. J. Pharmaco[. Exp. Ther., 71: 62-72. SIEGEL, S. (1956) Non Parametric Statistics for the Behavioural Sciences, McGraw-Hill, New York. SLOVITER, R.S., CONNOR, J.D. and DRUST, E.G. (1980) Serotonergic properties of ~-phenylethylamine in rats. Neuropharmacology, 19: 1071-1074. THOMAS, K.V. and HANDLEY, S.L. (1978) On the mechanism of amphetamine-induced behavioural changes in the mouse. I. An observational analysis of dexamphetamine. Arzneim. Forsch., 28: 827-833.
Inquiries and reprint requests should be addressed to:
Dr. C.T. Dourish Psychiatric Research Division, University Hospital Saskatoon, Saskatchewan SIN OXO, Canada
0278-5846182/020143-16508.0010 Copyright © 1982 Pergamon Press Ltd.
AN OBSERVATIONAL ANALYSIS OF THE BEHAVIOURAL EFFECTS OF ~-PHENYLETHYLAMINE IN ISOLATED AND GROUPED MICE
COLIN T
DOURISH
Psychiatric Research Division, University Hospital Saskatoon, Saskatchewan, Canada
(Final form, February,
1982)
Abstract
Dourish, Colin T.: An observational analysis of the behavioural effects of ~-phenylethylamine in isolated and grouped Rice. Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 6: I.
2.
3.
4.
Male Swiss mice were treated systemically with B-phenylethylamine (PEA, 25-150 mg/kg), and observed in isolation or in groups of five. The effects of PEA were scored on 13 separate components of behaviour which were produced or increased by the drug. PEA at a dose of 25 mg/kg depressed activity and caused sedation, but at 50 mg/kg produced a brief stimulation of activity. At higher dose levels (75-150 mg/kg) the compound induced a biphasic stimulation of activity which was associated with the development of two distinct groups of stereotyped activities. Group testing significantly antagonized early phase stereotypy (forepaw padding, headweaving, compulsive grooming) but had no effect on, or potentiated, late phase stereotypy (rearing, licking). In addition grouped mice were more active and hyperreactive than isolated mice. The results are briefly discussed in the light of the possibility of a cateqholamine/ indoleamine interaction in the control of the hyperactivity syndrome induced by PEA in the mouse.
K eywords: 8-phenylethylamine, catecholamines, components of behaviour, hyperactivity, indoleamines, interaction, isolated and grouped mice, stereotypy.
Abbreviations:
8-phenylethylamine
(PEA); 5-hydroxytryptamine
(5-HT).
Introduction
~-Phenylethylamine
(PEA) has been detected in the brain and peripheral tissues of man and
animals (Philips etal., 1964; Jackson and Temple,
1978; Durden etal.,
1973; Boulton etal.,
1975; Nakajima etal.,
1970) and has been proposed as a possible neurotransmitter or
"synaptic activator" (Boulton,
1976, 1979).
locomotor activity in mice (Schulte etal.,
PEA produces amphetamine-like stimulation of 1941; Nakajima etal.,
143
1964) which is
144
C.T. Dourish
potentiated by pretreatment with a monoamine oxidase inhibitor, (Mantegazza and Riva, 1963), since PEA is a specific substrate for monoamine oxidase and is, therefore, oxidized extremely rapidly (Philips and Boulton, 1979; Durden and Philips, 1980).
A comprehensive series of
studies by Jackson (see review by Jackson, 1978 and references therein), using grouped mice, indicated that PEA has a biphasic effect on locomotor activity. PEA
a
At a dose of 50 mg/kg of
short-lived locomotor stimulation was produced (peak 4-6 minutes post injection, dura-
tion 15 minutes), whereas at higher doses of 75-150 mg/kg the drug produced an "early" phase of stereotyped behaviour followed by a "late" increase in locomotor activity (20-60 minutes post injection).
Jackson (1978) has proposed that both dopamine and noradrenaline are
involved in the early phase locomotor stimulation whereas dopaminergic mechanisms may be dominant in the late phase.
These findings, and the majority of other reports on the
effects of PEA in mice, were based on data generated by photobeam interruptions, a method which has been subject to ~,ch criticism as the sole measure of behavioural responses (Krsiak et al., 1970; Fray et al., 1980).
An observational method, which was adopted in the
present study, can detect drug induced changes even at low doses, and, in addition, can identify different components of behaviour which may have separate neurochemical substrates.
The purpose of the present study was to perform a detailed observational analysis of the behavioural effects of a wide range of doses of PEA in the mouse, scoring 13 individual components of behaviour for each animal tested.
The study includes a comparison of the effects
of PEA in isolated and grouped (n ffi 5) mice since some previous reports have indicated that the drug either depresses (Fischer et al., 1967) or has no effct on activity (Jackson, 1978) in isolated mice, but paradoxically, stimulates activity in grouped mice (Jackson, 1978). Although it is well established that many of the behavioural effects of PEA in rodents involve an action on brain catecholamine systeu~ (Jackson, 1978; Braestrup and Randrup, 1978; Moja et al., 1978) recent evidence suggests that a behavioural syndrome produced by PEA in the rat may primarily involve brain 5-HT mechanisms (Sloviter et al., 1980; Dourish, 1981). Therefore a further aim of the observational analysis was to provide a basis for the examination o~ the neurochemical substrates of the PEA response in succeeding interaction studies.
Methods
Animals.
Male Swiss albino mice (18-25 g body weight) were used in the experiments.
The
animals were housed in hanging wire cages, in groups of 20, with food and water ad lib. Lighting operated on a 12 h dark-12 h light cycle (lights on 6 a.m.) and temperature was maintained at 20-23°C.
Dru~s.
B-Phenylethylamine hydrochloride (Sigma) was made up in distilled water and injected
intra-peritoneally in a volume of I0 ml/kg in all cases. in terms of the salt.
Doses of the drug were calculated
Behavioural effects of B-phenylethylamine in mice
A p p a r a t u s and P r o c e d u r e s . ing conditions
Mice were randomly a l l o c a t e d
and e a c h a n i m a l was u s e d once o n l y .
145
t o i n d i v i d u a l or group (n = 5) t e s t -
Within the individual
test
condition
a n i m a l s were a s s i g n e d t o one o f s i x d r u g t r e a t m e n t s which c o n s i s t e d o f PEA a t d o s e s o f 25, 50, 75, 100 and 150 mg/kg Within the group t e s t
and t h e d i s t i l l e d
condition,
t r e a t m e n t s which c o n s i s t e d ed i n c i r c u l a r
plastic
procedure.
or c o n t r o l
solution
solution
referred
to as 0 mg/kg.
g r o u p s of f i v e mice were a s s i g n e d t o one o f f o u r d r u g
o f PEA a t d o s e s o f 0, 50, 75 and 100 mg/kg.
c a g e s o f 22 cm d i a m e t e r and 25 cm h i g h .
g r o u p o f a n i m a l s was p l a c e d i n t h e t e s t injection
water control
Each i n d i v i d u a l
cage f o r a 30 m i n u t e h a b i t u a t i o n
Following habituation
T e s t i n g was c o n d u c t a n i m a l or
period p r i o r to any
a n i m a l s were weighed and i n j e c t e d w i t h t h e d r u g
and i m m e d i a t e l y r e t u r n e d t o t h e cage to b e g i n t h e t e s t .
The mice were
o b s e r v e d and r a t e d on 13 c o m p o n e n t s o f b e h a v i o u r which bad b e e n found i n p r e l i m i n a r y e x p e r i m e n t s to be i n d u c e d or i n c r e a s e d by PEA ( T a b l e 1). on a 0-4 s c a l e d e p e n d i n g on t h e i n t e n s i t y each t e s t
Each mouse or group of mice was s c o r e d
of the behaviour e x h i b i t e d
(Table 2).
a n i m a l or group o f a n i m a l s on e a c h i t e m were d e t e r m i n e d d u r i n g a l t e r n a t e
minute periods until
all
drug e f f e c t s
t i m e s , and each g r o u p t e s t
bad d i s s i p a t e d .
Each i n d i v i d u a l
test
Scores for five
was r u n e i g h t
a minim,-- of f i v e t i m e s .
Table 1
B e h a v i o u r a l Components u s e d in t h e O b s e r v a t i o n a l A n a l y s i s
Eehavioural Component
Explanatory Notes
Freezing
Inactive in one location
Forward Walking
Co-ordinated locomotor activity includin~ forward
Rearing
Both front paws off the ground
Grooming
Includes normal and abortive or compulsive cleaning
walkin~ o r r u n n i n ~
of the body Sniffing Backward W a l k i n g
Backward w a l k i n g or backward c i r c l i n g
Headweaving
Repetitive,
Padding
Repetitive
Hyperreactivity
Startle
Tremor
Head, paw or whole body s h a k e
fast,
s i d e t o s i d e head movements
t r e a d i n g of the forepaws
r e s p o n s e t o a p e n c i l t a p on c a g e
Jumping Licking Vocalization
Compulsive licking or biting of cage walls or floor
146
C.T. Dourish
Table 2
Behavioural
Rating Scale Used to Score Each Component
Score
Behavioural
in the Analysis
Frequency
Absent Mild intensity; Moderate
present
intensity;
I-2 times
present 3-4 times
High intensity;
present 5 or more times
Severe;
for prolonged
present
periods
Statistical Analysis
Due to the ordinal nature of the rating scale employed, describing
the scores obtained
rect median was calculated was carried out on both.
in addition
valid.
examine time course of drug effect).
Therefore
to the mean and where applicable
Mean and median scores were calculated
ponent at each dose level over the complete
graphically
the use of the mean as a method of
is not totally statistically
the more cor-
statistical
analysis
for each behavioural
com-
test and for each five minute sample period
However,
means were plotted
in depicting
as the points generated using the mean are more discrete
(to
the data
than those generated
using the median.
Results were analysed using two nonparametric Kruskal-Wallis
one-way analysis
of variance,
to locate specific group differences.
statistical
tests (Siegel,
1956),
the
followed by the Mann-Whitney U test (2-tailed)
The Spearman rank-order
correlation
tween items was calculated
for each dose of PEA, and for each time period,
and group test conditions,
using an Apple II microcomputer.
coefficient
be-
in both isolated
Interrater Reliability
The mice were rated by two observers Interrater reliability
one of whom was unaware of the drug treatment.
for the scores generated by the observational
by the weighted Kappa (Hall,
analysis was determined
1974).
A random sample of 400 pairs of ratings by the two observers was used in the determination.
The results using the 0-4 Scale were 82.6% no difference;
9.4% one point disagree-
Behavioural effects of 8-phenylethylamine in mice
147
ment~ 5.2% two points disagreement; 2.2% three points disagreement; 0.6% four points disagreement.
The value of the weighted Kappa was 0.82 (P<.01).
Results
Dose Response Effects
The effects of PEA on the 13 behavioural components rated in the analysis are shown in Tables 3 and 4.
In isolated mice PEA produced a dose dependent decrease in freezing when
administered at doses above 50 mg/kg.
A lower dose of 25 mg/kg, however, induced a sedative
effect and significantly increased freezing scores (p<.05, Table 3).
The decrease in freez-
ing observed in isolated mice at doses of 50 mg/kg of PEA, and above, did not appear to be directly related to an increase in coordinated locomotor activity since forward walking was significantly increased at only one dose level (50 mg/kg, p<.05; Table 3).
In contrast.
Table 3
Dose Response Effects of B-Phenylethylamine in Isolated Mice
Behavioural Category
Dose of 8-phenylethylamine (mg/kg) 0
25
50
75
4.00*
1.80
1.00
I00
150
0.40*
0.33*
Freezing
3.13
Forward Walking
1.96
1.50
4.00*
3.05
2.70
2.91
Rearing
1.50
0.50
0.80
0.41
0.I0
0.99
Grooming
1.55
0*
2.00
3.12"
3.70***
3.33***
Sniffing
1.91
3.75*
4.00*
4.00**
4.00*
4.00**
Backward Walking
0
0
0
0
0.70**
1.33"**
Headweaving
0
3.37***
3.30***
3.88***
Padding
0
2.37**
2.20***
2.55***
Hyper-reactivity
0
3.00***
2.10"*
1.40"*
Tremor
0
0
0
0
0
Jumping
0.5
0
0
0
0
Licking
0
0
Vocalization
0
0
1.50"* 0 2.25***
4.00*** 0 2.25***
0.25 0
2.12"** 0
0.80 0
1.30"** 0 0.99** 0
Each score represents a median value of 8 animals on a 0-4 scale. Statistical comparisons (Mann-Whitney U Test) a r e between drug and control values: * p<.05; ** p<.02; *** p<.01.
148
C.T. Dourish
when PEA was administered at the same dose levels to grouped mice a consistent increase in forward walking or running was observed (Table 4, Fig. la)
PEA, at doses above 50 mg/kg, induced a syndrome of repetitive or compulsive behaviours in both isolated and grouped mice.
The syndrome included headweaving,
padding, hyperreactiv-
ity, compulsive sniffing, rearing, grooming and licking (Tables 3 and 4).
There was a sig-
nificant interaction between drug dose and isolated or group testing with respect to a number of these behaviours (p < .05, Kruskal-Wallls test).
Headweaving and compulsive grooming
were significantly reduced in a group test at a dose of i00 mg/kg of PEA (Fig. Ib and Fig. 2a).
Similarly, forepaw padding was suppressed in a group test at doses of 75 and i00 mg/kg of PEA (Fig 2b). 4).
Sniffing, however, appeared to be unaffected by group testing (Tables 3 and
In contrast the hyperreactive responses of running, jumping and vocalization were
significantly increased in group tests at all dose levels of PEA which were employed (Table 3, Figs. la and 3).
Indeed, jumping and vocalization were virtually absent in isolated mice
(Table 3). b
Table 4
Dose Response Effects of ~-Phenylethylamine
Behavioural
in Grouped Mice
Dose of ~-phenylethylamine (mg/kg)
Category
0 (5)
50 (5)
75 (6)
ioo (5)
Freezing
2.68
1.16
0.51
0.36
Forward Walking
1.56
2.82*
3.08*
2.92*
Rearing
1.30
0.70
2.23
1.60
Grooming
1.96
0.92
2.30
2.56
Sniffing
1.70
3.86*
3.75*
Backward Walking
0
0
0
Headweaving
0
3.04*
2.40*
Padding
0
0
0
Hyperreactivity
0
2.63*
2.55*
Tremor
0
Jumping
0
0.56
0
0.26
1.27
2.04*
3.25*
3.50*
2.75*
Licking Vocalization
0.70
0
0 1.90"
3.76* 0.12 1.60" 0.66 1.24" 0 0.22
Each score represents a median value on a 0 - 4 Scale with number of experiments in parenthesis. Statistical comparisons (Mann-Whitney U Test) are between drug and control groups: *p<.Ol
Behavioural effects of B-phenylethylamine in mice
149
Similarly, rearing was significantly increased in group tests (p<.05, Mann Whitney U test) at doses of 75 and I00 mg/kg of PEA, whereas licking was potentiated by group testing at a dose of I00 mg/kg (Tables 3 and 4).
Backward walking and tremor were evident at the highest dose levels of PEA (I00 and 150 mg/kg) which were tested but only occurred to a very slight extent (Table 3). signs of peripheral stimulation such as piloerection,
In addition,
salivation and Straub tail were a con-
sistent observation in all drug treated animals.
Time Course Effects
There was a significant drug, time course interaction on forward walking in both isolated and grouped mice (p<.05, Kruskal-Wallis test).
A dose of 50mg/kg of PEA produced only a
brief stimulant effect but doses of 75-150 mg/kg of the drug induced a triphasic effect on walking which consisted of an initial stimulant effect (1-5 minutes post-injection), ceeded by a depression (5-20 minutes post-injection), (20-45 minutes post-injection, Fig. 4a).
suc-
followed by a late stimulant effect
The biphasic stimulant pattern was more pronounced
at the higher doses.
The time courses of the various drug-induced compulsive behaviours appeared to fall into two distinct groups which may have had a close parallel in the observed effects on forward walking.
Headweeving, grooming and padding appeared within five minutes, reached a peak
5-25 minutes post-injection,
and declined thereafter (Figs. 4a, 5a and 6).
In contrast
rearing and licking had a slow onset, tended to increase throughout the test period, and reached e peak 25-45 minutes post-injection (Fig. 6a and b). activity showed a gradual increase over time (Fig. 7).
Similarly jumping and hyperre-
Compulsive sniffing did not appear
to fall into either group and remained at a high level throughout the test period.
Correlations Between Behavioural Components
Significant correlations between behavioural components are summarized in Table 5.
Scores
from isolated and grouped animals were combined since consistent correlations were obtained across the two conditions.
Significant relationships generally varied with dose and time
although there was a consistent positive correlation between sniffing end headweaving, and sniffing and grooming in all cases.
At the lowest dose levels (25-50 mg/kg) freezing was negatively correlated with rearing and walking but positively correlated to sniffing, headweaving and hyperreactivity.
The
hyperreective responses of jumping and vocalization were positively correlated to hyperreactivity.
At intermediate dose levels (75-100 mg/kg) all of the behavioural components were
observed with the exception of tremor and there were a large number of positive correlations between the components.
Forward walking was positively correlated with the late phase
150
C.T. Dourish
Table
5
The Direction of the Significant Spearman Rank Order Correlations Behavioural Components in Isolated or Grouped Mice After Various
Between Scores on the Dose Levels of PEA. =
(a)
PEA 25-50 mg/kg
~J •H
~1 =
.~
.1~
}~
Freezing Forward Walking Rearing Grooming Sniffing Headweaving Ryperreactivity Jumping Licking Vocalization
~J
~)
I .r~
•
~.~
~
÷
+
--
+
+
+
+
+
+
+ +
.,-4
0
+ +
o~ (b)
+
Freezing Forward Walking Rearing Grooming Sniffing Backward Walking Headweaving Padding Hyperreactivity Jumping Licking Vocalization
(c)
o
PEA 75-i00 mg/kg
+
+
+
-
+
+ +
+ +
+
+
+ +
_ ± +
+ +
+ + +
+
+
÷
+ +
PEA 150 mg/kg
-+
+
--+
+
t~ ~J
~.-I
~I
O
.,-I
0,-4
Freezing + Forward Walking + Rearing 4÷ Grooming + ÷ + Sniffing ÷ + Backward Walking + Headweaving + Padding Hyperreactivity Tremor Lickin~ (+ indicates a significant positive correlation and - indicates a significant negative correlation during one or more time samples. ± indicates a change in direction of a correlation over time.)
Behavioural
effects
of ~-phenylethylamine
~ 3-
3-
2-
"i 2-
iZ
o
.9 1-
25
50
75
100
/ ;
150
in mice
i!
¢
¢
75
1;0
a
2;
5;
150
PEA(mglkg)
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Fig. la: Effects of B-phenylethylamine (PEA) on forward walking in isolated (O----O) and grouped (O----e) mice. All values are mean ± SEM on a 0-4 Scale. Significant differences (Mann-Whitney U test) between drug and control animals are indicated by the following letters: a, p<.05; b, p<.02; c, p<.01. Fig Ib: Effects of PEA on headweaving in isolated (O O) and grouped (O------e) mice. All values are mean ± SEM on a 0-4 Scale. Significant differences (Mann Whitney U test) betwee drug and control animals are indicated by the following letters: a, p<.05; b, p<.02; c, < 01 Significant differences (Mann-Whitney V test) between isolated and grouped animals P " " ' ~ ~ care indicated by letters with superscrlpts: a , p<.05; b , p<.02; , p<.01.
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152
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i s o l a t e d ; ([~---O) PEA 100 mg/kg i s o l a t e d . (H) grouped; ( H ) PEA 100 mg/kg grouped. Fig. 4b. Time c o u r s e of headweaving i n i s o l a t e d C o n v e n t i o n s a r e as d e s c r i b e d f o r Fig. 4a.
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Behavioural effects of B-phenylethylamlne in mice
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Fig. 7. Time course of hyperactivity (open symbols) and jumping (closed symbols) in grouped mice treated with PEA. (O O) Control; (~ A) PEA 75 mg/kg; (O O) PEA I00 mg/kg.
compulsive behaviour of licking, rearing, hyperreactivity and jumping
It is also of note
that walking showed an initial negative correlation with compulsive licking behaviour. Padding was positively correlated with sniffing,
headweaving and backward walking while
grooming was associated with sniffing and backward walking.
The highest dose level (150
mg/kg) marked the appearance of tremor which was positively correlated with compulsive behaviours including padding,
grooming and backward walking.
Forward walking was again
positively correlated to licking.
Discussion
The present data confirm and extend the findings of Jackson (1972) that PEA exerts a b iphasic stimulant effect on locomotor activity in mice, in this instance measured by observations of the forward walking component (Fig. 4a).
The observational analysis suggests
that the biphasic effect of PEA on activity may be closely related to the emergence of various compulsive or stereotyped behaviours which appear to fall into two distinct groups. Early phase activity is associated with compulsive grooming, forepaw padding, sniffing and headweaving while late phase activity appears to involve compulsive sniffing, ing and hyperreactivity.
rearing,
These observations are only partly in agreement with those of
lick-
Behavioural effects of ~-phenylethylamine in mice
155
Jackson (1972, 1974) who claims that late phase activity is devoid of any stereotypy and characterized by co-ordinated locomotor activity.
Notwithstanding this report the present
observations demonstrated a clear increase in rearing and licking stereotypies, which was particularly marked at a dose of I00 mg/kg, during the late phase of activity stimulation (i.e. 20-45 minutes post-injection,
Fig. 6).
Interestingly forward walking showed an initi-
al negative correlation with licking (PEA 75-100 mg/kg, Table 5) which changed to a significant positive correlation with rearing and licking towards the end of the test period.
In
the present experiment, the late phase of stimulation was generally characterized by animals walking or running around the cage and rearing to sniff and lick the cage walls.
The observation of compulsive licking behaviour in mice, reported in the present study, is an example of an important species difference in response to the systemic administration of PEA, since previous investigations have failed to demonstrate a similar response in the rat, even in combination with a monoamine oxidase inhibitor, unpublished observations).
(Braestrup et al., 1975; Dourish,
The failure of PEA to produce licking in the rat has been attri-
buted to the inhibitory effect of increased noradrenergic stimulation produced by the compound (Braestrup and Randrup, 1978).
Possibly this could indicate that the slow onset of
licking observed in the present study could be due to an initial strong release of noradrenaline which would inhibit the expression of this behavioural component.
This explanation
stands in general agreement with the hypothesis of Jackson (1978) that both dopamine and noradrenaline are involved in the early phase of locomotor stimulation whereas dopaminergic mechanisms are dominant in the late phase.
Although PEA-induced licking in mice has been previously noted (Jackson, study is the first report of PEA-induced compulsive or abortive grooming.
1972) the present This behaviour is
distinguished from normal grooming by its persistence, and failure to complete the cleaning act by touching the body (hence the term abortive), and is consistent with the observation of a similar behavioural pattern induced by d-amphetamine
(Thomas and Handley, 1978).
Grooming and other compulsive behaviours, such as padding and headweaving,
associated with
the early phase of PEA stimulation (0-20 minutes post-injection) were significantly supressed by group testing, whereas, rearing and licking associated with the late phase stimulation, were unaffected or increased in a group test.
The development of the early phase com-
pulsive behaviours may have been retarded by the hyperreactive responses of running,
jumping
and vocalization (sometimes referred to as "Popcorn behaviour," Sabelli et al., 1975) which were significantly increased in group test conditions.
These observations could explain
some of the discrepancies relating to the effects of PEA in isolated and grouped mice.
For
example a study by Fischer et al. (1967) measured activity of isolated mice for I0 minutes after administration of a 40 mg/kg dose of PEA and reported a depression of activity. sumably during this brief time period stereotyped behaviour such as grooming, headweaving would tend to depress activity counts.
Pre-
padding and
However, in a longer group test, as used
by Jackson (1972, 1974), hyperreactive responses could mask any depression of activity due
156
C.T. Dourish
to the induction of stereotyped behaviour.
This is exemplified by the present observational
analysis in which animals in group tests were observed to engage in bursts of stereotyped activity which was frequently interrupted by contact with another animal producing the "Popcorn behaviour" outlined above.
Hyperreactive responses did not interfere with rearing and licking and it appears possible that the behavioural components which are dominant in the late phase of PEA stimulation have a single neurochemical substrate, which may be dopamine.
Indeed it has previously been pro-
posed (Jackson, 1978) that dopaminergic mechanisms are dominant in the late phase activity stimulation.
It is well established that PEA is a specific substrate for monoamine oxidase and, as such, is oxidized very rapidly (Philips and Boulton,
1979; Durden and Philips, 1980).
Con-
sequently, it is possible that there might be a correlation between the biphasic stimulant effect of PEA on activity and an initial increase in brain PEA levels after injection followed by a rapid decline in levels due to deamination by monoamine oxidase.
Further experi-
ments are required to determine whether such a causal relationship exists.
One aim of the present study was to provide an observational basis for the future investigation of the neurochemical substrates of the various components of behaviour which are produced or increased by PEA in the mouse.
The observational data presented are consistent
with the proposed role of catecholaminergic systems which may be involved in sniffing, rearing, licking, hyperreactivity and forward walking.
The data also suggest the possiblity of
an indoleaminergic involvement in the expression of such behavioural components as padding and headweaving which are thought to be mediated by 5-HT in the rat (Sloviter et al., 1980; Dourish, 1981).
Although currently still under investigation,
the possibility of a catecholamine/indolea-
mine interaction in the control of the PEA hyperactivity syndrome in the mouse is supported by preliminary findings from antagonist interaction studies (Dourish, unpublished observations).
Conclusion
Observational analysis confirms that PEA has a biphasic stimulant effect on activity in the mouse.
It appears, however, that contrary to previous reports (Jackson, 1978), both
phases of the stimulant action are associated with the appearance of stereotyped activities; forepaw padding, headweaving and grooming are dominant in the early phase while rearing, licking and hyperreactivity are more important in the late phase.
The grouping of behavi ~
oural components observed suggests the possible involvement of an indoleamine system, in addition to catecholamines in the expression of PEA-induced hyperactivity in the mouse.
Behavioural effects of B-phenylethylamine in mice
157
Acknowledgements
The author thanks Dr. A.A. Boulton for suggesting this topic and for helpful discussions, and B. Dourish for excellent technical assistance and writing of computer programs. Financial support from Saskatchewan Health and the M.R.C. of Canada is acknowledged.
References
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Inquiries and reprint requests should be addressed to:
Dr. C.T. Dourish Psychiatric Research Division, University Hospital Saskatoon, Saskatchewan SIN OXO, Canada