Journal ~)/"Neuroscience Methods, 39 ( 1991 ) 153-161
153
:~ 1991 Elsevier Science Publishers B.V. All rights reserved 0165-0270/91/$03.50
NSM 0128(I
A new motor test sensitive to aging and dopaminergic function Rend Drucker-Colfn and F e r n a n d o Garcla-Hernfindez Depto. de Neurociencias, Instituto de Fisiolog[a Celular, Unicersidad Nacional Autdnoma de M~xico, Apdo. Postal 70-600. Mexico 04510 D.F. (Mexico) (Received 4 March 199l) (Revised version received 3 May 1991 (Accepted 31 May 1991)
Key words: Motor test; Aging; Dopamine; Haloperidol; Amphetamine; L-Dopa Neurodegenerative disorders which involve motor impairment is characteristic of old age. Although there are a few tests which attempt to assess motor incapacities, many have utilized scales which have either a great deal of subjective evaluations or are subject to learning-performance complexities. This study describes a method able to measure motor impairment of aging rats which is subject to dopaminergic influences and has negligible practice effects. The test is designed so that rats have to traverse 2 meter beams of 15 ° inclination whose widths 3, 6, 12, 18 and 24 m m are changed on each test session using a table of random numbers. The time ceiling allowed for traversing the 2 m b e a m s was established at 120 sec. 3-month-old rats (n = 20) and aged rats (n = 20) with a m e a n age of 26.5 + 3.8 m o n t h s ranging from 23 to 34 m o n t h s were utilized in this study. All young rats traversed the beams, independently of beam width, while virtually none of the old rats traversed the 3 and 6 m m beams. However, as the beam width increased more and more aged rats ascended the beam. Nevertheless, there were always a few old rats who were unable to cross even on the widest beam. W h e n young rats were fitted with a lead belt which increased their body weight by approximately 40%, they still traversed all b e a m widths. On the other hand, haloperidol (0.1 and 0.2 m g / k g ) severly impaired the performance of young rats. Conversely, administration of a m p h e t a m i n e (1.0 m g / k g ) or L-dopa (50 m g / k g ) to old rats substantially improved their performance. The results suggest that beam taxis appears to be an effective and efficient test for screening motor dysfunction in aged rats and can be amenable to studies on changes of motor capabilities as a result of drugs a n d / o r brain damage.
Introduction
A deterioration in a variety of central nervous system functions is a widespread characteristic of the aging process. Underlying this deterioration a number of neurochemical and morphological changes have been documented (Bugiani et al., 1978; Finch et al., 1981; Severson et al., 1982; Strong et al., 1980). Probably the brain system most widely studied in relation to aging has been the nigro-striatal system, because a variety of neurological disorders with motor disturbances
Correspondence: Dr. Ren~ Drucker-Col~n, Instituto de Fisiologla Celular, Universidad Nacional A u t 6 n o m a de Mdxico, Apdo. Postal 70-600, 04510 M6xico, D.F., Mexico.
involve pathological changes in the basal ganglia. The best understood neurodegenerative disorder is probably Parkinson's disease, for which in addition there is a rodent model (Ungerstedt, 1971a,b) widely used in pharmacological and transplant studies (Ungerstedt, 1971a,b; Perlow et al., 1980; Bjorklund et al., 1980; Dunnett and Richards, 1990). Unfortunately, the rodent model of Parkinson's disease involves the unilateral application of the neurotoxin 6-hydroxydopamine (6OHDA) which can completely destroy the substantia nigra (SN) pars compacta. However, the Parkinson disease process is age related and involves a gradual bilateral degeneration of the SN. Therefore, it would be more appropriate to study aged rats and test their motor capabilities, assuming that motor behavior may be related to pro-
154
gressive nigrostriatal degeneration. Several tests have been developed previously (Marshall and Berrios, 1979; Campbell et al., 1980; Dean et at., 1981; Joseph et al., 1983) but these tests are either dependent on subjective criteria which make their reliability across observers from different laboratories difficult or else the tests rely on reflexive or memory aspects of behavior rather than on pure motor capabilities. There are a few tests which seem to specifically test motor capabilities, but these appear to be subject to performance improvements with practice (Campbell et al., 1980). This is a major problem for many applications because it precludes repeated testing. In this paper we report a new test which is not subject to practice effects and is capable of
3ram
6 mm
jJ~
Fig. 1. Illustrates the set up of the test. The inclination of 15 ° is obtained by the heights of the pedestals which support the wood strips and which are 42.5 and 100 cm.
12ram
18ram
Fig. 2. Top view photographs illustrating the relation between b e a m widths and size of rats.
155 d e t e c t i n g m o t o r deficits in a g e d rats as well as rats with a l t e r e d d o p a m i n e r g i c function.
Materials and methods
Subjects F o r t y m a l e W i s t a r rats w e r e u s e d in this study. O f t h e s e rats 20 w e r e 3 m o n t h s o f age a n d w e i g h e d 245 +_ 48 g at t h e b e g i n n i n g of the study a n d 230 +_ 42 g at the end. T h e r e m a i n i n g 20 rats w e r e t h e a g e d rats w h o s e m e a n age was 26.5 +_ 3.9 m o n t h s a n d m e a n w e i g h t 543 + 72 g at t h e beginning of the study a n d 509 _+ 74 g at the end. A l l rats were h e a l t h y from the b e g i n n i n g till the e n d of the testing p e r i o d which l a s t e d a p p r o x i m a t e l y 2 months.
Apparatus Fig. 1 illustrates the testing a p p a r a t u s . It consists of 2 m e t e r w o o d e n strips s u p p o r t e d by two
p e d e s t a l s at e a c h end. T h e p e d e s t a l s were of d i f f e r e n t heights (42.5 cm a n d 100 cm) in o r d e r to allow for an inclination of 15 °. This inclination was e n o u g h to stop a n i m a l s from crawling over the b e a m . T h e width of the strips v a r i e d and were 3, 6, 12, 18 a n d 24 ram. W i d t h s were v a r i e d by m e r e l y c l a m p i n g strips t o g e t h e r in o r d e r to o b t a i n d e s i r e d widths. A t the e n d of the inclined strip a cage was p l a c e d so that the a n i m a l s could step into t h e h o m e cage. Figs. 2 a n d 3 show actual p h o t o g r a p h s of rats t r a v e r s i n g all the b e a m widths used.
Testing All rats w e r e t r a i n e d to walk over a b e a m fl)r five days b e f o r e testing. T h e test p r o c e d u r e was identical for y o u n g a n d a g e d rats a n d p e r f o r m e d in the s a m e e n v i r o n m e n t b e t w e e n 10:00 a.m. and 12:00 a.m. T h e rat was p l a c e d on the lower end of the b e a m and the time n e e d e d to reach the h o m e cage was r e c o r d e d . A ceiling of 120 sec was
Y O U N G ÷
1 0 0 g
A G E D 3mm
6mm
12mm
18 m m
24mm
Fig. 3. Side"view photographs of a variety of positions rats adopt while traversing the various beam widths. In addition it illustrates a young rat wearing the 100 g lead belt around his body, middle pannel.
156
employed at the end of which the rat was removed and placed in the cage by hand and received a score of 120 sec. The beam width sequence used in each testing session was determined with a table of random numbers. Pilot studies showed that this manipulation almost completely eliminated practice effects. The measure utilized for each rat was 'total time' to reach the cage. However, during testing rats frequently had episodes of immobility. Accordingly, a second measure was taken designated as 'no movement time'. This measure reflected the amount of time that animals merely stood immobile with what appeared as olfactory and visual exploration of surroundings.
120 . . . . . . . . . . o,
i,t
co
TOTAL TIME
NUMBER OF RATS THAT CROSSEO
"\.T , o.
7
e*
80
i ~e
+1
r----I YOUNG I n=20
AGED n=30
i!
"\],
ivx r..)
Since young rats were usually about half the weight of old rats, a lead belt weighing 100 g (see Fig. 3) was placed around 10 young rats, in order to determine whether weight was an important factor in the capacity to traverse the beam. The 100 g weight represented an increase of about 40% of the total body weight of the young rats. One week after testing the young and aged rats, pharmacological tests were begun. All young rats were tested on the b e a m test after the i.p. injection of 0.1 and 0.2 m g / k g of haloperidol (Janssen) while all the aged rats were tested on thc beam test following i.p. injection of 1, 2 and 4 m g / k g of ( + )-amphetamine sulphate (Sigma) and by oral administration of 50, 100, 200 m g / k g of
40
AGED
T
o
1
_
©~o 3
6
°-~-~-o
12
18
i
YOUNG
15 J
24
NO MOVEMENT TIME
120
10 r~
T~
±
~f,
~E 80 (,,3 ,,t
+1
5
tX
,\
(--) 40 L~ oo
] ~°-~-o~o----~o 5
6
t2
18
AGED
YOUNG
24 BEAM WIDTH (mr'n)
0
,I | I
3
6
L
12
18
p
24
BEAM WIDYH ( r a n " '
Fig. 4. I l l u s t r a t e s the d i f f e r e n c e s b e t w e e n y o u n g and a g e d rats in total time to traverse the b e a m s and the n o - m o v e m e n t time, The bar g r a p h simply c o m p a r e s the n u m b e r of rats which successfully c r o s s e d the various b e a m s . N o t e t h a t even in the widest b e a m a few a g e d rats did not a c c o m p l i s h the crossing w i t h i n the t i m e limit of 120 sec. * P < 0.001 as c o m p a r e d to young rats.
157
L - D o p a (Sigma). A 1-week interval was a l l o w e d b e t w e e n each d r u g a d m i n i s t r a t i o n .
Statistics A F r i e d m a n test b e t w e e n groups, followed by a M a n n - W h i t n e y test to identify d i f f e r e n c e s bet w e e n g r o u p s on each b e a m width was u s e d to test significances.
Results Since a c o m p a r i s o n b e t w e e n 2 3 - 2 5 - m o n t h - o l d vs. 2 9 - 3 4 - m o n t h - o l d rats i n d i c a t e d that t h e r e were no significant differences, a g e d rats were a n a l y z e d t o g e t h e r as a group. C o m p a r i s o n of
p e r f o r m a n c e on the b e a m test b e t w e e n y o u n g a n d a g e d rats is i l l u s t r a t e d in Fig. 4. W h i l e y o u n g rats easily c r o s s e d the b e a m quickly, even on the n a r r o w e s t w o o d strip, a g e d rats w e r e u n a b l e to cross on the 3 a n d 6 m m strips a n d a g r a d u a l l y g r e a t e r n u m b e r of a n i m a l s w e r e able to cross as w i d t h i n c r e a s e d . It is also e v i d e n t that the a m o u n t of no m o v e m e n t time d e c r e a s e d as b e a m width i n c r e a s e d . F r i e d m a n test was significant P < 0.001 ( x = 87.36) and the M a n n - W h i t n e y s h o w e d significant d i f f e r e n c e s P < 0.001 on all r a m p widths b e t w e e n y o u n g a n d old rats. W h e n the 20 y o u n g rats were d i v i d e d into 2 g r o u p s of 10 and o n e g r o u p was fitted with the l e a d belt as d e s c r i b e d in M e t h o d s , they still r e a d ily crossed the b e a m s even on the n a r r o w e s t strip.
TOTAL TIME
120[
NUMBER OF RATS THAT CROSSED
___] Y O U N G
i ] Ld b9
+ Ix (j, i,i C,O
8o!
YOUNG + 100 g
I
i, []
YOUNG + 100g n=10
n=10 10 YOUNG
4oi
ot
S
[]
5
6
12
18
24
NO MOVEMENT TIME 120
uJ 8 0 (/3
+P JX (D hJ tn
40
YOUNG + 100g
i
[] \. \\
YOUNG
0-~_ \ ,
5
6
12
~ 1 ~
18 24 BEAM WIDTH ( r a m )
ot 3
6
12
18
24
BEAM WIDTH (ram)
Fig. 5. I l l u s t r a t e s the d i f f e r e n c e s b e t w e e n young rats with and w i t h o u t 100 g lead belts. A l t h o u g h the i n c r e a s e d w e i g h t slowed the y o u n g rats all were all able to cross. * P < 0.02 as c o m p a r e d to control.
158
However, there was a significant total time difference on the 3, 6 and 12 mm width strips ( P < 0.01), but only on the 3 mm width was no movement time significant ( P < 0.02) (see Fig. 5). Following the administration of Haloperidol young rats had great difficulties crossing the beams (Fig. 6). There was a significant difference both with the 0.1 m g / k g dose ( P < 0.001) (x = 38.82) and the 0.2 m g / k g ( P < 0.001) (x = 78.22), for total and no movement time. Also crossing at all beam widths were significantly different in comparisons between young rats with and without
HA F
haloperidol ( P < 0 . 0 1 ) , for both total and no movement time. When testing aged rats with amphetamine, the lowest dose of 1 m g / k g was the most effective ( P < 0 . 0 0 1 ) ( x = 17.81) for improving pcrformance in both total and no movement time. The doses of 2 and 4 m g / k g produced a large variability in the aged rats, mostly because stereotyped movements were elicited which interfcrred with their capacity to reach the cage. The same overall effect occurred with L-Dopa administration. Again the lowest dose of 50 m g / k g was most
LRIDOL NUMBER OF RATS THAT CROSSED
TOTAL TIME
120
..................... +
T* ,,,
80
T*
!*Ji'---+
....
+ T*
[, ~,, 0.2 m g / K g
T
(..P .4-0 i,1
!
i
0.1 ~ g / K g
_ 0,2 --g Kg
n=2C
'[-
)3
20
T*
;
? 0.1 rng/Kg
-~ 0 - - - 0 - ~ - ~ ' 0
YOUNG
\. 0
3
n=20
;U
+
b9
YOUNG ~
"
) ....
(/3
+ Ix
" [.
6
12
18
15
24
i
-
I
NO MOVEMENT TIME
10
12o
i*
[*
i* / _ _ ~
0.2 m g / K g
i.,J 80 U3
+
l ot.d
$.
40
!
CO
i
"O~o____o.~o 3
6
12
O. 1 m g / K g
YOUNG .... 18
24 BEAM WIDTH ( m m )
0 .3
6
12
18
24
B E A M WIDTH ( t u r n )
Fig. 6. Illustrates the effects of 2 doses of Haloperidol (0.1 and 0.2 mg/kg). It is evident from this figure that this dopaminc receptor antagonist not only slowed the rats significantly in all beam widths, but also rendered many rats incapable of crossing particularly at doses of 0.2 m g / k g . * P < 0.01 vs control, + P < 0.05 vs. 0.1 m g / k g .
159
D
-
Ak4 PH ET Ai\,i ] N E
TOTAL TIME 120 T
O
N U M B E R OF RATS THAT C R O S S E D
•
, ,,,
,,
L
l,
+1
\
1 rng/Kg n:20
20-
\ T
"\
•
AGED
40
.\
6O
I mg/Kg
t ~
o~
t
~°--°~-~-~o 3
6
12
18
YOUNG 24
NO MOVEMENT TIME
lol
120 T
0--0 uJ
1
\
"'\
Ix i,i
-AGED n=20
80 q
U3
0
~
80
(/3
I
i
T
1' r
T, ?\
+I ~ ! ,
~A CO
6~
•
+~---~
AGED I mg/Kg
I
" ° ~ - o ~ O ~ o 3
6
12
18
YOUNG 24
BEAM WIDTH ( m m )
5
6
12
18
24
BEAM WIDTH ( r a m )
Fig. 7. Illustrates the effects of 1 m g / k g of amphetamine on the performance of aged rats. Total time was improved in all beam widths and significant on the 12 and 18 mm beams (* P < 0.05 vs aged) and no-movement time was reduced on all beam widths (* P < 0.001 vs aged). Moreover, amphetamine increased considerably the number of aged rats able to cross at all widths.
effective in improving performance ( P
153
:~ 1991 Elsevier Science Publishers B.V. All rights reserved 0165-0270/91/$03.50
NSM 0128(I
A new motor test sensitive to aging and dopaminergic function Rend Drucker-Colfn and F e r n a n d o Garcla-Hernfindez Depto. de Neurociencias, Instituto de Fisiolog[a Celular, Unicersidad Nacional Autdnoma de M~xico, Apdo. Postal 70-600. Mexico 04510 D.F. (Mexico) (Received 4 March 199l) (Revised version received 3 May 1991 (Accepted 31 May 1991)
Key words: Motor test; Aging; Dopamine; Haloperidol; Amphetamine; L-Dopa Neurodegenerative disorders which involve motor impairment is characteristic of old age. Although there are a few tests which attempt to assess motor incapacities, many have utilized scales which have either a great deal of subjective evaluations or are subject to learning-performance complexities. This study describes a method able to measure motor impairment of aging rats which is subject to dopaminergic influences and has negligible practice effects. The test is designed so that rats have to traverse 2 meter beams of 15 ° inclination whose widths 3, 6, 12, 18 and 24 m m are changed on each test session using a table of random numbers. The time ceiling allowed for traversing the 2 m b e a m s was established at 120 sec. 3-month-old rats (n = 20) and aged rats (n = 20) with a m e a n age of 26.5 + 3.8 m o n t h s ranging from 23 to 34 m o n t h s were utilized in this study. All young rats traversed the beams, independently of beam width, while virtually none of the old rats traversed the 3 and 6 m m beams. However, as the beam width increased more and more aged rats ascended the beam. Nevertheless, there were always a few old rats who were unable to cross even on the widest beam. W h e n young rats were fitted with a lead belt which increased their body weight by approximately 40%, they still traversed all b e a m widths. On the other hand, haloperidol (0.1 and 0.2 m g / k g ) severly impaired the performance of young rats. Conversely, administration of a m p h e t a m i n e (1.0 m g / k g ) or L-dopa (50 m g / k g ) to old rats substantially improved their performance. The results suggest that beam taxis appears to be an effective and efficient test for screening motor dysfunction in aged rats and can be amenable to studies on changes of motor capabilities as a result of drugs a n d / o r brain damage.
Introduction
A deterioration in a variety of central nervous system functions is a widespread characteristic of the aging process. Underlying this deterioration a number of neurochemical and morphological changes have been documented (Bugiani et al., 1978; Finch et al., 1981; Severson et al., 1982; Strong et al., 1980). Probably the brain system most widely studied in relation to aging has been the nigro-striatal system, because a variety of neurological disorders with motor disturbances
Correspondence: Dr. Ren~ Drucker-Col~n, Instituto de Fisiologla Celular, Universidad Nacional A u t 6 n o m a de Mdxico, Apdo. Postal 70-600, 04510 M6xico, D.F., Mexico.
involve pathological changes in the basal ganglia. The best understood neurodegenerative disorder is probably Parkinson's disease, for which in addition there is a rodent model (Ungerstedt, 1971a,b) widely used in pharmacological and transplant studies (Ungerstedt, 1971a,b; Perlow et al., 1980; Bjorklund et al., 1980; Dunnett and Richards, 1990). Unfortunately, the rodent model of Parkinson's disease involves the unilateral application of the neurotoxin 6-hydroxydopamine (6OHDA) which can completely destroy the substantia nigra (SN) pars compacta. However, the Parkinson disease process is age related and involves a gradual bilateral degeneration of the SN. Therefore, it would be more appropriate to study aged rats and test their motor capabilities, assuming that motor behavior may be related to pro-
154
gressive nigrostriatal degeneration. Several tests have been developed previously (Marshall and Berrios, 1979; Campbell et al., 1980; Dean et at., 1981; Joseph et al., 1983) but these tests are either dependent on subjective criteria which make their reliability across observers from different laboratories difficult or else the tests rely on reflexive or memory aspects of behavior rather than on pure motor capabilities. There are a few tests which seem to specifically test motor capabilities, but these appear to be subject to performance improvements with practice (Campbell et al., 1980). This is a major problem for many applications because it precludes repeated testing. In this paper we report a new test which is not subject to practice effects and is capable of
3ram
6 mm
jJ~
Fig. 1. Illustrates the set up of the test. The inclination of 15 ° is obtained by the heights of the pedestals which support the wood strips and which are 42.5 and 100 cm.
12ram
18ram
Fig. 2. Top view photographs illustrating the relation between b e a m widths and size of rats.
155 d e t e c t i n g m o t o r deficits in a g e d rats as well as rats with a l t e r e d d o p a m i n e r g i c function.
Materials and methods
Subjects F o r t y m a l e W i s t a r rats w e r e u s e d in this study. O f t h e s e rats 20 w e r e 3 m o n t h s o f age a n d w e i g h e d 245 +_ 48 g at t h e b e g i n n i n g of the study a n d 230 +_ 42 g at the end. T h e r e m a i n i n g 20 rats w e r e t h e a g e d rats w h o s e m e a n age was 26.5 +_ 3.9 m o n t h s a n d m e a n w e i g h t 543 + 72 g at t h e beginning of the study a n d 509 _+ 74 g at the end. A l l rats were h e a l t h y from the b e g i n n i n g till the e n d of the testing p e r i o d which l a s t e d a p p r o x i m a t e l y 2 months.
Apparatus Fig. 1 illustrates the testing a p p a r a t u s . It consists of 2 m e t e r w o o d e n strips s u p p o r t e d by two
p e d e s t a l s at e a c h end. T h e p e d e s t a l s were of d i f f e r e n t heights (42.5 cm a n d 100 cm) in o r d e r to allow for an inclination of 15 °. This inclination was e n o u g h to stop a n i m a l s from crawling over the b e a m . T h e width of the strips v a r i e d and were 3, 6, 12, 18 a n d 24 ram. W i d t h s were v a r i e d by m e r e l y c l a m p i n g strips t o g e t h e r in o r d e r to o b t a i n d e s i r e d widths. A t the e n d of the inclined strip a cage was p l a c e d so that the a n i m a l s could step into t h e h o m e cage. Figs. 2 a n d 3 show actual p h o t o g r a p h s of rats t r a v e r s i n g all the b e a m widths used.
Testing All rats w e r e t r a i n e d to walk over a b e a m fl)r five days b e f o r e testing. T h e test p r o c e d u r e was identical for y o u n g a n d a g e d rats a n d p e r f o r m e d in the s a m e e n v i r o n m e n t b e t w e e n 10:00 a.m. and 12:00 a.m. T h e rat was p l a c e d on the lower end of the b e a m and the time n e e d e d to reach the h o m e cage was r e c o r d e d . A ceiling of 120 sec was
Y O U N G ÷
1 0 0 g
A G E D 3mm
6mm
12mm
18 m m
24mm
Fig. 3. Side"view photographs of a variety of positions rats adopt while traversing the various beam widths. In addition it illustrates a young rat wearing the 100 g lead belt around his body, middle pannel.
156
employed at the end of which the rat was removed and placed in the cage by hand and received a score of 120 sec. The beam width sequence used in each testing session was determined with a table of random numbers. Pilot studies showed that this manipulation almost completely eliminated practice effects. The measure utilized for each rat was 'total time' to reach the cage. However, during testing rats frequently had episodes of immobility. Accordingly, a second measure was taken designated as 'no movement time'. This measure reflected the amount of time that animals merely stood immobile with what appeared as olfactory and visual exploration of surroundings.
120 . . . . . . . . . . o,
i,t
co
TOTAL TIME
NUMBER OF RATS THAT CROSSEO
"\.T , o.
7
e*
80
i ~e
+1
r----I YOUNG I n=20
AGED n=30
i!
"\],
ivx r..)
Since young rats were usually about half the weight of old rats, a lead belt weighing 100 g (see Fig. 3) was placed around 10 young rats, in order to determine whether weight was an important factor in the capacity to traverse the beam. The 100 g weight represented an increase of about 40% of the total body weight of the young rats. One week after testing the young and aged rats, pharmacological tests were begun. All young rats were tested on the b e a m test after the i.p. injection of 0.1 and 0.2 m g / k g of haloperidol (Janssen) while all the aged rats were tested on thc beam test following i.p. injection of 1, 2 and 4 m g / k g of ( + )-amphetamine sulphate (Sigma) and by oral administration of 50, 100, 200 m g / k g of
40
AGED
T
o
1
_
©~o 3
6
°-~-~-o
12
18
i
YOUNG
15 J
24
NO MOVEMENT TIME
120
10 r~
T~
±
~f,
~E 80 (,,3 ,,t
+1
5
tX
,\
(--) 40 L~ oo
] ~°-~-o~o----~o 5
6
t2
18
AGED
YOUNG
24 BEAM WIDTH (mr'n)
0
,I | I
3
6
L
12
18
p
24
BEAM WIDYH ( r a n " '
Fig. 4. I l l u s t r a t e s the d i f f e r e n c e s b e t w e e n y o u n g and a g e d rats in total time to traverse the b e a m s and the n o - m o v e m e n t time, The bar g r a p h simply c o m p a r e s the n u m b e r of rats which successfully c r o s s e d the various b e a m s . N o t e t h a t even in the widest b e a m a few a g e d rats did not a c c o m p l i s h the crossing w i t h i n the t i m e limit of 120 sec. * P < 0.001 as c o m p a r e d to young rats.
157
L - D o p a (Sigma). A 1-week interval was a l l o w e d b e t w e e n each d r u g a d m i n i s t r a t i o n .
Statistics A F r i e d m a n test b e t w e e n groups, followed by a M a n n - W h i t n e y test to identify d i f f e r e n c e s bet w e e n g r o u p s on each b e a m width was u s e d to test significances.
Results Since a c o m p a r i s o n b e t w e e n 2 3 - 2 5 - m o n t h - o l d vs. 2 9 - 3 4 - m o n t h - o l d rats i n d i c a t e d that t h e r e were no significant differences, a g e d rats were a n a l y z e d t o g e t h e r as a group. C o m p a r i s o n of
p e r f o r m a n c e on the b e a m test b e t w e e n y o u n g a n d a g e d rats is i l l u s t r a t e d in Fig. 4. W h i l e y o u n g rats easily c r o s s e d the b e a m quickly, even on the n a r r o w e s t w o o d strip, a g e d rats w e r e u n a b l e to cross on the 3 a n d 6 m m strips a n d a g r a d u a l l y g r e a t e r n u m b e r of a n i m a l s w e r e able to cross as w i d t h i n c r e a s e d . It is also e v i d e n t that the a m o u n t of no m o v e m e n t time d e c r e a s e d as b e a m width i n c r e a s e d . F r i e d m a n test was significant P < 0.001 ( x = 87.36) and the M a n n - W h i t n e y s h o w e d significant d i f f e r e n c e s P < 0.001 on all r a m p widths b e t w e e n y o u n g a n d old rats. W h e n the 20 y o u n g rats were d i v i d e d into 2 g r o u p s of 10 and o n e g r o u p was fitted with the l e a d belt as d e s c r i b e d in M e t h o d s , they still r e a d ily crossed the b e a m s even on the n a r r o w e s t strip.
TOTAL TIME
120[
NUMBER OF RATS THAT CROSSED
___] Y O U N G
i ] Ld b9
+ Ix (j, i,i C,O
8o!
YOUNG + 100 g
I
i, []
YOUNG + 100g n=10
n=10 10 YOUNG
4oi
ot
S
[]
5
6
12
18
24
NO MOVEMENT TIME 120
uJ 8 0 (/3
+P JX (D hJ tn
40
YOUNG + 100g
i
[] \. \\
YOUNG
0-~_ \ ,
5
6
12
~ 1 ~
18 24 BEAM WIDTH ( r a m )
ot 3
6
12
18
24
BEAM WIDTH (ram)
Fig. 5. I l l u s t r a t e s the d i f f e r e n c e s b e t w e e n young rats with and w i t h o u t 100 g lead belts. A l t h o u g h the i n c r e a s e d w e i g h t slowed the y o u n g rats all were all able to cross. * P < 0.02 as c o m p a r e d to control.
158
However, there was a significant total time difference on the 3, 6 and 12 mm width strips ( P < 0.01), but only on the 3 mm width was no movement time significant ( P < 0.02) (see Fig. 5). Following the administration of Haloperidol young rats had great difficulties crossing the beams (Fig. 6). There was a significant difference both with the 0.1 m g / k g dose ( P < 0.001) (x = 38.82) and the 0.2 m g / k g ( P < 0.001) (x = 78.22), for total and no movement time. Also crossing at all beam widths were significantly different in comparisons between young rats with and without
HA F
haloperidol ( P < 0 . 0 1 ) , for both total and no movement time. When testing aged rats with amphetamine, the lowest dose of 1 m g / k g was the most effective ( P < 0 . 0 0 1 ) ( x = 17.81) for improving pcrformance in both total and no movement time. The doses of 2 and 4 m g / k g produced a large variability in the aged rats, mostly because stereotyped movements were elicited which interfcrred with their capacity to reach the cage. The same overall effect occurred with L-Dopa administration. Again the lowest dose of 50 m g / k g was most
LRIDOL NUMBER OF RATS THAT CROSSED
TOTAL TIME
120
..................... +
T* ,,,
80
T*
!*Ji'---+
....
+ T*
[, ~,, 0.2 m g / K g
T
(..P .4-0 i,1
!
i
0.1 ~ g / K g
_ 0,2 --g Kg
n=2C
'[-
)3
20
T*
;
? 0.1 rng/Kg
-~ 0 - - - 0 - ~ - ~ ' 0
YOUNG
\. 0
3
n=20
;U
+
b9
YOUNG ~
"
) ....
(/3
+ Ix
" [.
6
12
18
15
24
i
-
I
NO MOVEMENT TIME
10
12o
i*
[*
i* / _ _ ~
0.2 m g / K g
i.,J 80 U3
+
l ot.d
$.
40
!
CO
i
"O~o____o.~o 3
6
12
O. 1 m g / K g
YOUNG .... 18
24 BEAM WIDTH ( m m )
0 .3
6
12
18
24
B E A M WIDTH ( t u r n )
Fig. 6. Illustrates the effects of 2 doses of Haloperidol (0.1 and 0.2 mg/kg). It is evident from this figure that this dopaminc receptor antagonist not only slowed the rats significantly in all beam widths, but also rendered many rats incapable of crossing particularly at doses of 0.2 m g / k g . * P < 0.01 vs control, + P < 0.05 vs. 0.1 m g / k g .
159
D
-
Ak4 PH ET Ai\,i ] N E
TOTAL TIME 120 T
O
N U M B E R OF RATS THAT C R O S S E D
•
, ,,,
,,
L
l,
+1
\
1 rng/Kg n:20
20-
\ T
"\
•
AGED
40
.\
6O
I mg/Kg
t ~
o~
t
~°--°~-~-~o 3
6
12
18
YOUNG 24
NO MOVEMENT TIME
lol
120 T
0--0 uJ
1
\
"'\
Ix i,i
-AGED n=20
80 q
U3
0
~
80
(/3
I
i
T
1' r
T, ?\
+I ~ ! ,
~A CO
6~
•
+~---~
AGED I mg/Kg
I
" ° ~ - o ~ O ~ o 3
6
12
18
YOUNG 24
BEAM WIDTH ( m m )
5
6
12
18
24
BEAM WIDTH ( r a m )
Fig. 7. Illustrates the effects of 1 m g / k g of amphetamine on the performance of aged rats. Total time was improved in all beam widths and significant on the 12 and 18 mm beams (* P < 0.05 vs aged) and no-movement time was reduced on all beam widths (* P < 0.001 vs aged). Moreover, amphetamine increased considerably the number of aged rats able to cross at all widths.
effective in improving performance ( P
