Subchronic memantine effects revealed by multimodal MRI
Sekar S et al.
Effect of antipsychotic drugs on LMA in sub-chronic memantine treated rats:
Habituation phase
3-way ANOVA on total distance travelled during the habituation phase revealed a main effect for anti-psychotic drug treatments
(haloperidol: F(3,108) = 115, p<0.001; olanzapine: F(3,108) = 33, p<0.001; risperidone: F(3,108) = 27, p<0.001). Trends were
observed for sub-chronic x drug treatment interaction (haloperidol experiment, Table 4) and for interactions sub-chronic x drug
treatment and sub-chronic x drug treatment x assigned challenge (olanzapine experiment). One-way ANOVA detected a main effect
for anti-psychotic drug treatments in both sub-chronic vehicle treated rats (haloperidol: F(3,56) = 62, p<0.001; olanzapine: F(3,56) =
18, p<0.001; risperidone: F(3,56) = 17, p<0.001), as well as in sub-chronic memantine treated ones (haloperidol: F(3,56) = 61,
p<0.001; olanzapine: F(3,56) = 17, p<0.001; risperidone: F(3,56) = 12, p<0.001). In sub-chronic vehicle treated rats, haloperidol
treatment resulted in dose-dependent statistically significant reductions in total distance travelled at all doses tested, but only at the
highest dose in sub-chronic menantine treated rats. Olanzapine and risperidone also showed statistically significant reductions in total
distance travelled at the two highest doses tested in the sub-chronic vehicle treated rats, and again only at the highest dose tested in the
sub-chronic menantine treated rats.
Acute memantine challenge phase
Three-way ANOVA revealed main effects for sub-chronic (haloperidol: F(1,108) = 135, p<0.001); olanzapine: F(1,108) = 57,
p<0.001; but not for risperidone: F(1,108) = 0, p = ns), drug treatment (haloperidol: F(3,108) = 33, p<0.001; olanzapine: F(3,108) =
40, p<0.001; risperidone: F(3,108) = 27, p<0.001), acute memantine challenge (haloperidol: F(1,108) = 189, p<0.001; ); olanzapine:
F(1,108) = 133, p<0.001; but not for risperidone: F(1,108) = 0, p = ns) and several interactions (Table 4).
Post hoc comparisons showed highly significant effects of acute memantine administration on total distance travelled
(hyperlocomotion response) in each of the three drug trials in both sub-chronic memantine (haloperidol experiment: t(18) = -8.4,
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Subchronic memantine effects revealed by multimodal MRI
Sekar S et al.
p<0.001; olanzapine experiment: t(18) = -15.8, p<0.001; risperidone experiment: t(18) = -6.2, p<0.001) and sub-chronic vehicle
treated rats (haloperidol experiment: t(18) = -4.9, p<0.001; olanzapine experiment: t(18) = -2.3, p=0.038; but not in the risperidone
experiment),
Consistent with the observations reported in Table 3, this was associated with a significantly higher total distance travelled induced by
acute memantine administration in sub-chronic memantine treated rats compared to the sub-chronic vehicle treated ones (haloperidol
experiment: t(18) = -6.9, p<0.001; olanzapine experiment: t(18) = -9.0, p<0.001; risperidone experiment: t(18) = -5.5, p<0.001). This
is indicative of a sensitisation of sub-chronic memantine treated rats to an acute memantine induced hyperlocomotion response.
Haloperidol dose-dependently inhibited memantine-induced hyperlocomotion in both sub-chronic vehicle treated rats (F(3,36) = 24,
p<0.001) and in sub-chronic memantine treated ones (F(3,36) = 9, p<0.001) (Table 4). Lowest active dose (LAD) in sub-chronic
vehicle treated animals was 0.04 mg/kg whereas in sub-chronic memantine animals a LAD of 0.02 mg/kg was observed. However,
haloperidol does not completely reverse acute memantine-induced hyperlocomotion in the sub-chronic memantine group in contrast to
the sub-chronic vehicle group.
Similar observations were made in olanzapine and risperidone treated rats (Table 4).
Olanzapine dose-dependently inhibited
memantine-induced hyperlocomotion in both sub-chronic vehicle treated rats (F(3,36) = 4, p=0.014) and in sub-chronic memantine
treated ones (F(3,36) = 43, p<0.001). In sub-chronic vehicle treated animals a trend effect against acute memantine induced
hyperlocomotion was observed at 0.63 mg/kg whereas the LAD in sub-chronic memantine animals was 0.16 mg/kg. Risperidone dosedependently inhibited memantine-induced hyperlocomotion in sub-chronic memantine treated ones (F(3,36) = 7, p=0.001: LAD =
0.08 mg/kg), but not in sub-chronic vehicle treated rats. Haloperidol (0.08 mg/kg), olanzapine (0.63 mg/kg) and risperidone (0.16
mg/kg) each significantly reduced total distance travelled vs. vehicle controls in non-challenged animals of both sub-chronic groups,
indicating reduced spontaneous locomotor activity at these doses.
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Subchronic memantine effects revealed by multimodal MRI
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Table 1: Experimental design of the behavioural experiments
Cohort
Acute doseresponse
(7 groups)
Sub-chronic
testing
(6 groups)
Antipsychotic
testing
(36 groupsl;
n=12rats per
antipsychotic drug)
Sub-chronic
etreatment
-
Drug pre-treatment
Acute challenge
-
VEH
VEH
-
PCP (3 doses)
MEM (3 doses)
VEH
VEH
MEM
MEM
PCP
PCP
-
VEH
MEM
VEH
MEM
MEM
PCP
VEH
-
VEH
Low-dose: HAL, OLAN or RIS
MEM
MEM
MEM
MEM
MEM
MEM
MEM
MEM
Medium-dose: HAL, OLAN or RIS
High-dose: HAL, OLAN or RIS
High-dose: HAL, OLAN or RIS
VEH
VEH
Low-dose: HAL, OLAN or RIS
Medium-dose: HAL, OLAN or RIS
High-dose: HAL, OLAN or RIS
High-dose: HAL, OLAN or RIS
MEM
MEM
VEH
VEH
MEM
MEM
MEM
MEM
VEH
Abbreviation and doses: VEH: vehicle for respective treatment, PCP: phencyclidine [acute doses: 0.63, 1.25 or 2.5 mg/kg, SC], MEM: memantine
[acute doses: 10, 20, 40 mg/kg, IP], Sub-chronic VEH (saline IP, 5 consecutive days), Sub-chronic MEM (20 mg/kg, IP/day, 5 consecutive days),
Sub-chronic PCP (1.25 mg/kg, SC/day, 5 consecutive days), HAL: haloperidol (doses: 0.02, 0.04, 0.08 mg/kg, SC), OLAN: olanzapine (doses:
0.16, 0.31, 0.63 mg/kg, SC), RIS: risperidone (doses: 0.04, 0.08, 0.16 mg/kg, SC). Based on the outcome from acute dose-response study,
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Subchronic memantine effects revealed by multimodal MRI
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challenge dose of MEM and PCP was (20 mg/kg, IP) and (2.5 mg/kg, SC) respectively for all subsequent testing in the sub-chronic and
antipsychotic testing cohorts.
Table 2: Effect of acute PCP or memantine (MEM) on total distance travelled (TDT) in rats: dose response study in nonpretreated rats; total distance travelled during 30 min in the habituation phase prior to administration of PCP or memantine
and during 60 min after administration. Data are mean±SEM, n=10/group.
Challenge
(mg/kg)
PCP
MEM
TDT (cm)
Habituation
Challenge
0
0.63
1.25
2.5
4416
4672
4086
4178
±
±
±
±
167
216
143
163
3802
3365
3214
5801
±
±
±
±
323
277
283
636
0
10
20
40
4416
4488
4372
4599
±
±
±
±
167
232
123
191
3802
2764
6289
4597
±
±
±
±
323
267
463
643
* vs dose 0, ** p ≤ 0.01
4
**
**
Subchronic memantine effects revealed by multimodal MRI
Sekar S et al.
Table 3: Effect of acute PCP or memantine (MEM) total distance travelled (TDT) in sub-chronic PCP or memantine treated
rats: total distance travelled during 30 min in the habituation phase prior to administration of PCP or memantine and during
60 min after administration of PCP (2.5 mg/kg) or MEM (20 mg/kg) or vehicle. Data are mean±SEM, n=10/group (n=20/group
in habituation) because similar treatment groups were pooled for analysis); ** p<0.01, *** p<0.001 vs. vehicle; +++ p<0.001 vs.
corresponding treatment group in sub-chronic vehicle treated rats.
TDT (cm)
Subchronic
(mg/kg)
Habituation
Challenge
Vehicle
MEM 20
Vehicle
3981 ± 109
3737 ± 279
7681 ± 496
MEM 20
3888 ± 132
3455 ± 528
11745 ± 894
PCP 1.25
3841 ± 86
Vehicle1
4178 ± 163
PCP 2.5
***
***/###
###
13165 ± 857
16093 ± 1613
5801 ± 636
* vs vehicle challenge in respective sub-chronic group, *** p ≤ 0.001
+ vs sub-chronic PCP-MEM challenge, +++ p ≤ 0.001
# vs sub-chronic vehicle-MEM challenge, ### p ≤ 0.001
1
data form separate study
5
+++
Subchronic memantine effects revealed by multimodal MRI
Sekar S et al.
Table 4: Effect of treatment with haloperidol (HAL), olanzapine (OLAN) or risperidone (RIS) on memantine (MEM, 20
mg/kg)-induced hyperlocomotion in sub-chronic vehicle or MEM (20 mg/kg) treated rats. Total distance traveled (TDT)
during 30 min in the habituation phase prior to administration of acute MEM and TDT during 60 min after administration of
MEM (20 mg/kg) or vehicle. Data are mean±SEM, n=10/group, except in habituation data where n=20/group when similar
treatment groups were pooled for analysis; * p<0.05, ** p<0.01, *** p<0.001 vs. vehicle treatment; + p<0.05, ++ p<0.01, +++
p<0.001 vs. vehicle treatment in acute MEM challenged treatment groups; ### p<0.001 vs. corresponding treatment group in
sub-chronic vehicle treated rats.
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Subchronic memantine effects revealed by multimodal MRI
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TDT (cm)
Habituation
Challenge
Sub-chronic
Sub-chronic
Vehicle
MEM
Vehicle
Treatment
(mg/kg)
HAL
0
3887 ± 139
0.02
0.04
3301 ± 173
2974 ± 114
0.08
1713 ± 99
OLAN 0
RIS
Vehicle
3441 ± 86
*
**
***
##
***
3323 ± 118
0.16
3582 ± 239
3056 ± 102
0.31
2069 ± 242
***
2591 ± 141
***
0.63
2151 ± 148
***
2230 ± 126
***
0
3687 ± 193
3432 ± 152
0.04
0.08
3419 ± 293
2974 ± 225
3398 ± 174
3022 ± 242
0.16
2071 ± 122
***
3676 ± 265
5614 ± 293
4875 ± 457
3960 ± 288
3537 ± 182
*
MEM 20
3378 ± 159
3111 ± 158
1774 ± 87
2306 ± 136
MEM
796 ± 130
***
3197 ± 380
1812 ± 217
**
3423 ± 512
Acute Challenge
Vehicle
***
MEM 20
3532 ± 274
++
1854 ± 238
+++
4968 ± 676
*
927 ± 105
***
1740 ± 237
7
11857 ± 779
10517 ± 569
+
8611 ± 748
++
+++
***/###
5963 ± 819
10320 ± 638
+
4445 ± 323
7253 ± 368
+++
4858 ± 521
+++
3148 ± 358
4285 ± 478
*
***/###
12543 ± 501
(+)
3584 ± 265
1377 ± 173
***
3808 ± 363
10344 ± 991
4264 ± 518
3156 ± 385
***
15088 ± 1351
3292 ± 304
8909 ± 880
6653 ± 945
2185 ± 190
***
5381 ± 410
***/###
++
+++
Subchronic memantine effects revealed by multimodal MRI
Sekar S et al.
Habituation data
* vs dose 0, * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001
# vs dose 0 in sub-chronic vehicle ## p ≤ 0.01
Challenge data
* vs dose 0 + vehicle challenge, * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001
+ vs dose 0 + MEM challenge, (+) trend, + p ≤ 0.05, ++ p ≤ 0.01, +++ p ≤ 0.001
# vs dose 0 in sub-chronic vehicle-MEM chall, ### p ≤ 0.001
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Subchronic memantine effects revealed by multimodal MRI
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9