Neuropsychopharmacology (2006) 31, 1869–1879
& 2006 Nature Publishing Group All rights reserved 0893-133X/06 $30.00
www.neuropsychopharmacology.org
Antipsychotic-Like vs Cataleptogenic Actions in Mice of Novel
Antipsychotics Having D2 Antagonist and 5-HT1A Agonist
Properties
Laurent Bardin*,1, Mark S Kleven2, Catherine Barret-Grévoz1, Ronan Depoortère1 and
Adrian Newman-Tancredi1
1
Division of Neurobiology 2, Centre de Recherche Pierre Fabre, Castres, France; 2Department of Psychology, University of Pennsylvania,
Philadelphia, PA, USA
A new generation of proven or potential antipsychotics, including aripiprazole, bifeprunox, SSR181507 and SLV313, exhibit agonist
actions at serotonin 5-HT1A receptors, but little comparative data are available on their pharmacological profiles. Here, we compared in
mice the in vivo antipsychotic-like vs cataleptogenic activities of these compounds with those of drugs that exhibit little interaction at
5-HT1A receptors, such as haloperidol, olanzapine and risperidone. All the drugs dose-dependently reduced apomorphine-induced
climbing or sniffing and, with the exception of ziprasidone, produced complete suppression of these responses. In the bar catalepsy test,
when administered alone, haloperidol, olanzapine and risperidone produced marked catalepsy, whereas, at doses up to 40 mg/kg,
aripiprazole, SLV313, SSR181507, and sarizotan produced little or no catalepsy. The latter compounds, therefore, displayed a large
separation between doses with ‘antipsychotic-like’ and those with cataleptogenic actions. When 5-HT1A receptors were blocked by
pretreatment with WAY100635 (2.5 mg/kg, s.c.), cataleptogenic properties of SSR181507 and sarizotan were unmasked, and the
catalepsy induced by bifeprunox was enhanced. In the case of aripiprazole and SLV313, although WAY100635 produced upward shifts in
their dose–response, the magnitude of catalepsy appeared to reach an asymptotic plateau, suggesting that other mechanisms may be
involved in their low cataleptogenic liability. The present data confirm that 5-HT1A receptor activation reduces or even completely
prevents the cataleptogenic potential of novel antipsychotic agents. Further, they indicate that the balance of affinity and/or efficacy
between D2 and 5-HT1A receptors profoundly influences their pharmacological activities, and will likely impact their therapeutic profiles.
Neuropsychopharmacology (2006) 31, 1869–1879. doi:10.1038/sj.npp.1300940; published online 19 October 2005
Keywords: 5-HT1A receptor; antipsychotic; apomorphine; catalepsy; dopamine D2 receptor; mice
INTRODUCTION
Although conventional neuroleptics control positive symptoms in schizophrenia, they also induce extrapyramidal side
effects (EPS) such as dystonia, parkinsonism, akathisia and
tardive dyskinesia. These effects are mediated by blockade
of dopamine D2 receptors, but their expression can
be modulated by other systems, most notably, serotonin
(5-HT) (for review, see: Meltzer et al, 2003). Hence, the
development of newer generation antipsychotics has been
focused on multiple receptorial mechanisms that could lead
*Correspondence: Dr L Bardin, Division of Neurobiology 2, Centre de
Recherche Pierre Fabre, 17 Avenue Jean Moulin, 81106 Castres,
France, Tel: + 33 56371 4216, Fax: + 33 56371 4363,
E-mail: laurent.bardin@pierre-fabre.com
Received 25 April 2005; revised 2 September 2005; accepted 8
September 2005
Online publication: 14 September 2005 at http://www.acnp.org/
citations/Npp091405050259/default.pdf
to improved clinical efficacy and reduced EPS liability. In
particular, focus on 5-HT2A and 5-HT2C receptor subtypes
led to the development of antipsychotics (eg risperidone
and olanzapine) that antagonize these receptors, in addition
to D2 receptors. Recently, particular attention has been
given to the 5-HT1A receptor as a promising additional
target for antipsychotic therapy (for review, see: Millan,
2000; Bantick et al, 2001). In fact, 5-HT1A receptor agonists
attenuate antipsychotic-induced EPS in humans (Yoshida
et al, 1998), non-human primates (Christoffersen and
Meltzer, 1998) and rats (Prinssen et al, 1999, 2002). In
addition, 5-HT1A receptor activation increases dopamine
release in a regionally-selective manner in the prefrontal
cortex (Ichikawa and Meltzer, 2000), suggesting alleviation
of the proposed deficiency in dopaminergic neurotransmission in this brain region of schizophrenics (Honey et al,
1999). Indeed, amelioration of this ‘hypofrontality’ is
associated with improvement in negative and cognitive
symptoms of schizophrenia (Honey et al, 1999). Consistent
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1870
with this idea, clinical studies have reported that buspirone
and tandospirone, two partial agonists at 5-HT1A receptors,
substantially ameliorate cognitive performance and reduce
the incidence of EPS in schizophrenic patients treated
with haloperidol (Sumiyoshi et al, 2001a, b). The atypical
antipsychotic clozapine, which displays improved capacity
to treat negative symptoms with minimal EPS liability,
exhibits agonist properties at 5-HT1A receptors (NewmanTancredi et al, 1998; Cussac et al, 2002) and both its absence
of cataleptogenic properties and its elevation of dopamine
release in frontal cortex are partially mediated by 5-HT1A
receptors (Millan et al, 1998; Rollema et al, 1997). The
ability of clozapine to occupy 5-HT1A receptors in nonhuman primates at clinically-relevant doses has been
demonstrated by PET scans with [3H]WAY100635 (Bantick
et al, 2000; Chou et al, 2003). In addition, the more recent
antipsychotic, ziprasidone, which also activates 5-HT1A
receptors, has a notably low incidence of EPS in humans
(Daniel et al, 1999). Lastly, 5-HT1A agonists exert antidepressant- and anxiolytic-like properties (Blier and Ward,
2003), of particular interest to schizophrenic patients of
whom an appreciable proportion suffer from comorbid
anxiety and/or depression (Buchanan et al, 2002). Thus,
combined 5-HT1A agonist and D2 antagonist properties
would be expected to have a wider spectrum of activity than
currently used antipsychotics, and in particular, exhibit
greater efficacy against negative/cognitive symptoms with
reduced EPS liability.
In this context, several laboratories have reported the
development of a new generation of potential antipsychotic
agents with varying levels of agonist/antagonist actions at
D2 and 5-HT1A receptors. These compounds, currently in
various phases of development, include SLV313 (Glennon
et al, 2002), SSR181507 (Claustre et al, 2003), bifeprunox
(DU127090; Wolf, 2003) as well as sarizotan (EMD128130;
Bartoszyk et al, 2004), that seems, however, to have been
lately reoriented towards an antidyskinetic indication.
Nonetheless, these compounds display marked diversity in
their actions at 5-HT1A receptors in vitro, with varying
potencies and efficacies for activation of cellular signal
transduction (Newman-Tancredi et al, 2005), likely to
profoundly influence their profile of action. Indeed, the
extent to which 5-HT1A agonists are able to reverse
neuroleptic-induced catalepsy is dependent on their efficacy: high-efficacy activation seems necessary to completely
abolish haloperidol-induced catalepsy (Prinssen et al,
1999, 2002). Further, the intrinsic activity of a series
of 5-HT1A receptor ligands correlates positively with
the magnitude of their antidepressant-like effects in the
forced swimming test (Koek et al, 2001). The issue,
therefore, arises as to what could be the desirable balance
of affinity and efficacy between D2 and 5-HT1A receptors
that would exhibit antipsychotic activity with reduced EPS
liability.
As no formal comparison between the pharmacological profiles of these new generation ligands is available,
we set out to compare the antipsychotic vs cataleptogenic activity of drugs varying in 5-HT1A agonist vs D2
antagonist properties, along with those of more typical
and atypical antipsychotics (see Table 1). First, we used
the apomorphine-induced climbing and stereotypies tests
(considered predictive of antipsychotic potential) and the
Neuropsychopharmacology
Table 1 Classification of Tested Compounds Based on an
Abbreviated Binding Profile
Family
Compound
Mode of action
Conventional
Haloperidol
Predominant D2 antagonism
Antipsychotics
Fluphenazine
Raclopride
Eticlopride
Atypical antipsychotics
Clozapine
Multiple actions: predominant
Risperidone
D2 and 5-HT2A antagonism
Olanzapine
Ziprasidone
Nemonapride
Aripiprazole*
New generation
SLV314
Mixed D2 partial agonism or
putative antipsychotics
SLV313
antagonism and 5-HT1A
Sarizotan
agonism
Bifeprunox
SSR181507
*Predominant D2 and 5-HT1A partial agonism.
catalepsy paradigm (thought to predict EPS liability).
Second, drug-interaction studies were conducted using
the 5-HT1A antagonist, WAY100635 (Forster et al, 1995),
with the aim of determining whether activation of
5-HT1A receptors is responsible for ‘masking’ the induction of catalepsy that would be expected following D2
receptor blockade. Such a pattern of pharmacological
interaction has been observed in rats for another antipsychotic exhibiting both D2 antagonist properties and,
less potently, 5-HT1A agonist properties, nemonapride
(Prinssen et al, 1998). This compound induces catalepsy
at low doses but, when doses are sufficient to activate
5-HT1A receptors, catalepsy is attenuated, and blockade of
5-HT1A receptors by WAY100635 pretreatment ‘unmasks’
this 5-HT1A receptor influence (Prinssen et al, 1998; Kleven
et al, 2005).
METHODS
Animals
Male NMRI mice (Iffa-Credo, Lyon, France) weighing 20–
24 g upon arrival were group-housed for a 5-day quarantine
period in polycarbonate Type III cages (internal dimensions
375 215 149 mm3, L l H; floor surface 806 cm2) in an
environmentally controlled room (ambient temperature,
21711C; relative humidity, 5575%; 12 : 12 light : dark cycle,
lights on at 0700). Standard laboratory food (A04; Animal
Food and Engineering, Epinay sur Orge, France) and
filtered water (0.22 mm pore diameter; in bottles) were
freely available. The mice were transferred to the experimental room on the day before experiments and housed
individually in polystyrene hanging cages (internal dimensions 220 185 80 mm3, L l H; floor surface 187 cm2),
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1871
where they were food-restricted but had free access to
water. All experiments were performed in a quiet room,
between 0900 and 1600, by a single experimenter and
in a blind fashion with respect to the treatment administered. Animals were handled and cared for in accordance with the Guide for the Care and Use of Laboratory
Animals (National Institutes of Health, USA), the European
Directive 86/609, and the internal protocoles (No 194
and 240) were carried out in compliance with local
ethical committee guidelines for animal research. Mice
were used only once and were killed immediately after the
experiment.
Apomorphine-Induced Climbing and Sniffing
Each animal was placed into cylindrical wire-mesh cages
(diameter, 14 cm; height, 13 cm; mesh size, 3 mm) and
allowed to adapt for 60 min. Thereafter, mice were injected
twice, first with test compound or saline (i.p. or s.c.),
followed 45 min later by s.c. injection of apomorphine
(2.5 mg/kg). The observational method used was an
adaptation of the method of Fray et al (1980), combined
with a time-sampling procedure (Waddington, 1986).
Behavioral observations were made from 55 to 65 min after
the first injection: animals were observed for 10 s every
minute for the presence or absence of climbing (ie all fours
paws on the cage, above the floor). Sniffing was scored when
the animal showed uninterrupted sniffing for at least 3 s
during this 10 s sampling period. Thus, the score for
climbing or sniffing could vary from 0 to 10 for the entire
observation period.
Catalepsy
Each animal was injected with the test compound or saline
(i.p. or s.c.) and the catalepsy procedure was measured
using the bar test 60 min after the injection: the forelimbs
were placed on a cylindrical metal bar (diameter, 0.4; 3.5 cm
above the table) and the time during which both forelimbs
remained on the bar was recorded up to a maximum of 30 s.
The test was repeated three times (inter-trial interval:
1 min). Animals were put back in their home cage after each
measurement of catalepsy.
In order to investigate the effects of 5-HT1A receptors on
catalepsy induced by some antipsychotics, WAY100635
(2.5 mg/kg) or saline were administered s.c., 15 min before
test compounds (s.c. or i.p.) that is, 75 min before recording
catalepsy.
Analysis of Data
Drug effects on apomorphine-induced behaviors were
expressed as the mean7SEM score and the dependent
variables used for catalepsy were the mean duration (s)
of three trials and the percentage of animals showing
a duration of 30 s in one or more trials. Data were analyzed with a one-way ANOVA followed by post hoc
comparisons using Dunnett’s test. Interactions between
WAY100635 and antipsychotics were analyzed with a twoway ANOVA, with pretreatment (WAY100635 or saline) and
the doses of antipsychotics as the factors, followed by
Dunnett’s post hoc tests. A P-value o0.05 was considered
statistically significant. To calculate ED50 values, the results
were expressed as the percentage of mice showing reduction of apomorphine-induced climbing and sniffing (ie
scores o9), and as the percentage of mice presenting at
least once a duration of catalepsy of 30 s. The climbing
and sniffing criterion for calculation of ED50 were based
upon the incidence of each particular behavior observed
in control animals treated with apomorphine 2.5 mg/kg
(Kleven et al, 1996). ED50 values and their associated
confidence limits were calculated with the Litchfield and
Wilcoxon probit analysis procedure (Tallarida and Murray,
1987) implemented using a procedure written using the
Research Programming Language (RPL) of RS/1 (Bolt,
Beranek and Newman, Cambridge, MA), that used all data
points between 0 and 100% effects to correct 0 and 100%
effects (Litchfield and Wilcoxon, 1949). When less than two
intermediate effects were observed, 0 and/or 100% effects
were transformed by means of Berkson’s adjustment
(Hubert, 1984) to permit the use of the Litchfield and
Wilcoxon procedure.
Drugs
Ziprasidone HCl, risperidone, olanzapine, aripiprazole,
bifeprunox mesylate (DU127090; N-[4-[(3-chloro-4-fluorophenyl)amino]-7-[3-(morpholin-4-yl)propoxy]quinazolin6-yl]prop-2-enamide mesylate), SSR181507 HCl ((3-exo)-8benzoyl-N-[[(2S)7-chloro-2,3-dihydro-1,4-benzodioxin-1-yl]
methyl]-8-azabicyclo[3.2.1]octane-3-methanamine monohydrochloride), sarizotan HCl (EMD-128130; (-)-3-[[[(R)-2-chromanylmethyl]amino]methyl]-5-(p-fluorophenyl)pyridine
monohydrochloride), nemonapride and WAY100635 (N-[2[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)
cyclohexanecarboxamide dihydrochloride) were synthesized by JL Maurel, Chemistry Department, Centre de
Recherche Pierre Fabre (Castres, France). SLV313 (piperazine, 1-(2,3-dihydro-1,4-benzodioxin-5-yl)-4-[[5-(4-fluorophenyl)-3-pyridinyl]methyl) and SLV314 ((2R)-2H-1,4-Benzoxazin-3(4H)-one, 8-[4-[3-(5-fluoro-1H-indol-3-yl)propyl]-1piperazinyl]-2-methyl) was obtained from Solvay Duphar
B.V. (Weesp, The Netherlands). Haloperidol, fluphenazine,
eticlopride HCl, raclopride and apomorphine hydrobromide were purchased from Sigma RBI (St Quentin Fallavier,
France) and clozapine from Tocris (Illkirch, France).
Raclopride, fluphenazine, eticlopride, WAY100635 and
apomorphine were prepared and administered s.c. in
distilled water, whereas aripiprazole, bifeprunox, sarizotan,
and ziprasidone were prepared as a suspension in aqueous
Tween 80 (1% v/v in distilled water) and administered i.p.
SSR181507, SLV313, SLV314, nemonapride, haloperidol,
clozapine, olanzapine, and risperidone were prepared in
distilled water with a drop of lactic acid, after which the
pH was adjusted to 5–7 with a 1 N solution of sodium
hydroxide and injected s.c. An injection volume of
1 ml/100 g was used throughout and doses refer to the
weight of the free base. Taking into consideration that
at doses of 40 mg/kg and above several compounds (eg
clozapine, olanzapiney) begin to exert major interfering
effects (eg ataxia, sedationy) that would greatly complicate
interpretation of data, absolute upper limits of 40 mg/kg
were retained.
Neuropsychopharmacology
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1872
RESULTS
substantially less effective or potent than haloperidol and
risperidone, they too produced dose-dependent increases
in catalepsy. Nemonapride induced catalepsy in a biphasic
manner: that is, less catalepsy at higher doses. In contrast,
SSR181507 and sarizotan did not induce catalepsy when
tested at doses up to 40 mg/kg. As shown in Table 2, the
ED50 values of drugs that activate 5-HT1A receptors, that is,
SSR181507, sarizotan, aripiprazole, clozapine, and SLV313
were greater than 40 mg/kg. In contrast, the ED50 values of
haloperidol, eticlopride, fluphenazine, and risperidone,
none of which interact with 5-HT1A receptors, were 100fold lower (0.4, 0.4, 0.29, and 0.65 mg/kg, respectively).
The percentage of mice fulfilling the criteria for reduction
of apomorphine-induced climbing and presence of catalepsy (for calculations of ED50 values) is illustrated in
Figure 3. Bifeprunox, aripiprazole, nemonapride, SLV313,
sarizotan, and SSR181507 were characterized by potent
reversal of apomorphine-induced climbing with a broad
separation with respect to cataleptogenic activity. The
catalepsy vs climbing dose ratio was calculated by dividing
ED50 values for inhibiting apomorphine-induced climbing
with those for eliciting catalepsy: bifeprunox, nemonapride
and SLV313 showed wider separation in this dose ratio
(173.3–1000) than did haloperidol and risperidone (4.4–5.4:
Table 2).
Antagonism of Apomorphine-Induced Climbing
and Sniffing
All drugs dose-dependently reduced apomorphine-induced
climbing and, with the exception of ziprasidone, produced
complete suppression of this response at higher doses
(Figure 1, filled circles). Apomorphine-induced sniffing
(open circles) was also decreased in a dose-dependent
manner over a similar dose-range, except for bifeprunox,
SSR181507 and SLV313 that reduced or blocked sniffing only
at the higher doses. In contrast, ziprasidone and sarizotan
exhibited little effect on apomorphine-induced sniffing, even
at the highest dose tested (40 mg/kg).
Table 2 shows a summary of ED50 estimates, 95%
confidence limits and the maximal effects observed. The
majority of compounds were somewhat more potent for
antagonism of climbing than sniffing behavior. Nevertheless,
the confidence limits of their ED50’s overlapped. Ziprasidone
was the only compound that yielded markedly different
ED50’s for climbing (2.2 mg/kg) vs sniffing (440 mg/kg). The
ability of the antipsychotics to inhibit apomorphine-induced
climbing and sniffing correlated positively (r ¼ 0.75 and
0.78, Po0.001, respectively) with their affinity at rat D2
receptors but not with their affinity at rat 5-HT1A receptors
(r ¼ 0.17 and 0.28, P40.05, respectively) (based on
affinity values published by Newman-Tancredi et al, 2005).
Catalepsy in Combination with WAY100635
When administered in combination with saline,
WAY100635 (2.5 mg/kg) did not induce catalepsy (data
not shown). Pretreatment with WAY100635 produced a
shift to the left of the haloperidol and ziprasidone dose–
response curve (F(1,48) ¼ 5.1 and F(1,36) ¼ 5.3, Po0.05,
Catalepsy
Haloperidol and risperidone dose-dependently induced
catalepsy at low doses in the bar test (Figure 2). Although
bifeprunox, aripiprazole, clozapine, and SLV313 were
Olanzapine
Haloperidol
Ziprasidone
Clozapine
Bifeprunox
SSR181507
Behavior Score
10.0
Climbing
Sniffing
7.5
*
*
*
0.0
1
*
100
0.01 0.1
1
10
100
SLV314
0.01 0.1
1
10
*
* *
*
Risperidone
10.0
*
*
10
100
Nemonapride
0.01 0.1
1
10
100
0.001 0.01 0.1
1
10
SLV313
Aripiprazole
0.01 0.1
1
10
100
Sarizotan
*
*
*
*
5.0
*
2.5
0.01 0.1
*
* * *
7.5
0.0
*
*
*
* *
0.01 0.1
Behavior Score
*
*
5.0
2.5
*
*
*
*
*
*
*
1
*
*
10
* *
100
0.01 0.1
1
*
*
10
100
*
* *
* * * *
0.001 0.01 0.1
1
*
* * *
10
0.01 0.1
1
10
100
*
0.01 0.1
*
* *
1
10
100
0.01 0.1
1
10
100
Dose (mg/kg)
Figure 1 Effects of antipsychotics on apomorphine-induced climbing (filled circles) and sniffing (open circles) in mice. Values represent the mean7SEM
behavioral score of seven animals during observation periods (10 s every min, from 55 to 65 min after drug administration). Apomorphine (2.5 mg/kg, s.c.)
was administered 45 min after different doses of antipsychotics. *Po0.05 compared with apomorphine control groups using Dunnett’s test, following
significant ANOVA. Note the different x-axis scale for nemonapride and bifeprunox. N ¼ 7/dose.
Neuropsychopharmacology
Table 2 Antagonism of Apomorphine-Induced Climbing and Sniffing Compared with Induction of Catalepsy in Mice
Apomorphine-induced climbing
Drug
Route
Dose range (mg/kg)
ED50
95% CL
Apomorphine-induced sniffing
Catalepsy
Maximum effectsa
ED50
95% CL
Maximum effectsa
ED50
95% CL
Maximum effectsa
Dose-Ratiob
s.c.
0.04–10
0.09
0.05–0.17
070 (2.5)
0.32
0.19–0.53
0.370.2 (2.5)
0.4
0.07–2.2
21.573.2 (10)
4.4
Risperidone
s.c.
0.04–40
0.12
0.04–0.35
070 (2.5)
0.79
0.26–2.4
070 (2.5)
0.65
0.15–2.7
27.472.4 (40)
5.4
Fluphenazine
s.c.
0.01–2.5
0.05
0.02–0.13
070 (0.16)
0.08
0.04–0.18
070 (0.63)
0.29
0.13–0.64
28.271.1 (2.5)
5.8
Olanzapine
i.p.
0.16–40
1.5
0.18–12
070 (10)
4.3
1.2–16
0.4370.3 (10)
13
4.6–38
22.273.9 (40)
8.7
Raclopride
s.c.
0.63–40
1.2
0.55–2.5
070 (2.5)
1.9
0.91–4.2
0.770.1 (10)
11
2.8–42
21.574.2 (40)
9.2
SLV314
s.c.
0.04–2.5
0.06
0.03–0.14
070 (2.5)
0.34
0.16–0.72
1.470.6 (2.5)
0.5
0.19–1.3
1773.3 (2.5)
8.3
Clozapine
i.p.
0.63–40
8.7
3.1–25
171 (40)
24
9.1–65
2.971.8 (40)
440
F
11.875.1 (40)
44.6
Eticlopride
s.c.
0.0025–40
0.02
0.008–0.05
070 (0.04)
0.03
0.01–0.07
0.370.2 (0.16)
0.4
19.673.5 (40)
20
Nemona pride
s.c.
0.0025–40
0.001
0.0002–0.006
070 (0.16)
0.03
0.01–0.06
0.170.1 (0.63)
0.76
0.27–2.1
17.174(0.63)
760
Ziprasidone
i.p.
0.63–40
2.2
0.76–6.2
2.171.5 (40)
440
F
8.470.8 (40)
36
13–96
17.874.4 (40)
16.4
Aripiprazole
i.p.
0.16–40
2.2
0.39–12
070 (2.5)
4.1
2.1–8.1
0.370.2 (40)
440
F
8.773.6 (2.5)
418.2
Bifeprunox
i.p.
0.01–40
0.03
0.01–0.07
070 (10)
0.11
0.038–0.35
3.471.3 (2.5)
5.2
1.5–18
23.871.8 (40)
173.3
SLV313
s.c.
0.04–40
0.04
0.01–0.16
070 (2.5)
0.34
0.16–0.72
2.770.8 (2.5)
440
F
8.873.7 (40)
41000
SSR181507
s.c.
0.63–40
3.6
1.5–8.7
070 (10)
20
Sarizotan
i.p.
2.5–40
5.2–37
070 (40)
440
14
0.004–39
9.4–41
270.7 (40)
440
F
2.572.4 (40)
411.1
F
6.371.6 (40)
440
F
270.9 (40)
42.9
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
Haloperidol
a
The maximal scores that could be obtained for climbing/sniffing and catalepsy were 10 and 30, respectively. Between parentheses: dose at which the maximal effect was observed.
Dose-ratio was calculated by dividing the ED50 values for inhibition of apomorphine-induced climbing with that for induction of catalepsy.
b
Neuropsychopharmacology
1873
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
Duration of Catalepsy (sec)
1874
30
Olanzapine
Haloperidol
* *
*
Ziprasidone
Bifeprunox
SSR181507
*
*
*
20
*
*
*
10
* *
*
0
0.01 0.1
1
10
100
0.01 0.1
Risperidone
Duration of Catalepsy (sec)
Clozapine
*
1
10
100
SLV314
0.01 0.1
1
10
Nemonapride
0.01 0.1
1
10
100
0.01 0.1
Aripiprazole
1
10
100
SLV313
0.01 0.1
1
10
100
Sarizotan
*
30
* *
*
*
20
*
*
*
10
100
*
* *
*
* *
*
0
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
Dose (mg/kg)
Figure 2 Effects of antipsychotics in the catalepsy bar test in mice. Values represent the duration of catalepsy in s and are expressed as mean7SEM,
N ¼ 7/dose. The antipsychotics were administered s.c. or i.p. at 60 min before testing. *Po0.05 compared with saline control using Dunnett’s test, following
significant ANOVA.
Haloperidol
Olanzapine
Clozapine
Ziprasidone
Bifeprunox
SSR181507
% Animals affected
100
75
50
25
Climbing
Catalepsy
0
0.01 0.1
1
10
100
Risperidone
0.01 0.1
1
10
100
SLV314
0.01 0.1
1
10
100
0.01 0.1
Nemonapride
1
10
100
Aripiprazole
0.001 0.01 0.1
1
10
SLV313
100
0.01 0.1
1
10
100
Sarizotan
% Animals affected
100
75
50
25
0
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.001 0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
0.01 0.1
1
10
100
Dose (mg/kg)
Figure 3 Effects of antipsychotics on apomorphine-induced climbing (filled circles) and in the catalepsy bar test (open squares) in mice. Values represent
the percentage of animals showing climbing scores o9 and one or more catalepsy duration of 30s (see Materials and Methods section for details). Drugs on
the left-hand side of the graph have little or no interaction at 5-HT1A receptors whereas drugs on the right-hand side of the graph have 5-HT1A agonist
properties. This order was retained based on the data of affinity at 5-HT1A receptors for these compounds (Newman-Tancredi et al, 2005). Note the
different x-axis scale for nemonapride and bifeprunox. N ¼ 7/dose.
respectively; Figure 4). After pretreatment with WAY100635,
significant levels of catalepsy were observed for aripiprazole
(F(1,72) ¼ 12.4, Po0.001), SLV313 (F(1,60) ¼ 25.6, Po0.001),
bifeprunox (F(1,96) ¼ 33.6, Po0.001) and nemonapride
(F(1,60) ¼ 14.1, Po0.001). In the case of nemonapride,
Neuropsychopharmacology
pretreatment with WAY100635 enhanced significantly the
effects of low doses and prevented the decrease in catalepsy
at higher doses. For aripiprazole and SLV313, the magnitude of catalepsy appeared to reach an asymptotic plateau
(Figure 4). In contrast, pretreatment with WAY100635
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1875
Duration of Catalepsy (sec)
Haloperidol
Bifeprunox
SSR181507
30
*
20
*
*
* *
*
*
10
+ SAL
+ WAY (2.5)
0
0.01 0.1
1
10 100
Nemonapride
Duration of Catalepsy (sec)
Ziprasidone
0.01 0.1
1
10 100
0.0010.01 0.1
1
10 100
SLV313
Aripiprazole
0.01 0.1
1
10 100
Sarizotan
*
30
*
*
* *
*
*
20
*
*
*
10
0
0.01 0.1
1
10 100
0.01 0.1
1
10 100
0.01 0.1
1
10 100
0.01 0.1
1
10 100
Dose (mg/kg)
Figure 4 Effects of haloperidol, nemonapride, ziprasidone, aripiprazole, bifeprunox, SSR181507, SLV313 or sarizotan alone or in combination with
WAY100635 in the catalepsy bar test. Values are means7SEM of the duration of catalepsy in s, N ¼ 7/group. WAY100635 (2.5 mg/kg, s.c.; filled squares) or
saline (open squares) was administered 15 min before antipsychotics, which were administered 60 min before testing. *Po0.05 compared with animals
treated with saline using Dunnett’s test, following significant ANOVA.
produced a marked incidence of catalepsy in SSR181507and sarizotan- treated rats (F(1,36) ¼ 51.2, Po0.001 and
F(1,48) ¼ 31.8, Po0.001, respectively).
DISCUSSION
Several laboratories have reported the development of a new
generation of potential antipsychotic agents with varying
levels of agonist/antagonist actions at D2 and agonist
activity at 5-HT1A receptors. These compounds, currently
undergoing various stages of clinical development, include
SLV313, SSR181507, and bifeprunox, along with another
compound with potent 5-HT1A agonist properties, sarizotan, originally developed as an antipsychotic but more
recently redirected towards an antidyskinetic indication.
However, these compounds display marked diversity in
their actions at 5-HT1A receptors in vitro, with varying
potencies and efficacies for activation of cellular signal
transduction (Newman-Tancredi et al, 2005). The present
data confirm that 5-HT1A receptor activation reduces the
cataleptogenic potential of novel antipsychotic agents but
show also that their profile of action is highly diverse and
is likely to be related to their affinity/efficacy at both D2
and 5-HT1A receptors.
Antipsychotic Activity of the New Generation of
Antipsychotics: Influence of 5-HT1A Receptor
Agonist Properties
In accordance with previous studies, conventional (haloperidol, fluphenazine), atypical (olanzapine, clozapine,
risperidone, and ziprasidone) as well as new generation
potential antipsychotic agents (eg SSR181507, bifeprunox,
SLV313) dose-dependently antagonized apomorphine-induced climbing in mice. Apomorphine-induced sniffing was
also blocked in a dose-dependent manner over a similar
dose range by all these drugs, with the exception of
ziprasidone and sarizotan, which did not block sniffing at
the highest dose tested, 40 mg/kg. Activity in this model is
predictive of efficacy against the positive symptoms of
psychosis (Protais et al, 1976) and demonstrates in vivo
antagonist activity at dopamine D2 receptors of these
compounds. A correlation analysis based on affinities at
rat striatal D2 sites (Newman-Tancredi et al, 2005) shows
that the ability of antipsychotics to inhibit apomorphineinduced climbing and sniffing correlated positively with
their affinity at rat D2 receptors. Indeed, reflecting its potent
blockade of D2 receptors in limbic/striatal structures, haloperidol was highly active in this model (ED50 ¼ 0.09 mg/kg)
whereas clozapine was active only at higher doses
Neuropsychopharmacology
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1876
(ED50 ¼ 8.7 mg/kg), which corresponds to its lower affinity
at D2 receptors (Brunello et al, 1995). The activity of
haloperidol and clozapine in this preclinical test is
consistent with their clinical potency requiring low- and
high-dose ranges, respectively, to control the positive
symptoms of schizophrenia (Meltzer, 1995). Nemonapride
potently blocked apomorphine-induced stereotyped behavior: this compound interacts with both D2 and 5-HT1A
receptors but D2 receptor antagonism is seen at doses
approximately 16–64 times lower than those having 5-HT1A
agonist properties (Assié et al, 1997). In clinical studies,
nemonapride was reported to have therapeutic efficacy in
schizophrenia and to produce relatively mild EPS (Kudo
et al, 1989). SLV313, SSR181507 and bifeprunox, compounds that have balanced affinity at D2 and 5-HT1A
receptors, dose-dependently and potently reduced climbing
and stereotyped behaviors produced by apomorphine. In
contrast, ziprasidone and sarizotan have little effect at the
highest doses tested in this model. It might have been the
case that antagonist effects could have been observed at
higher doses (or alternatively at other postinjection
observation times). However, as mentioned in the Methods
section, the use of doses above 40 mg/kg was precluded
because of interfering side-effects that could be observed
with some compounds at this ceiling dose. Ziprasidone has
similar affinity at 5-HT1A and D2 receptors but also multiple
interactions at numerous other receptor subtypes (Seeger
et al, 1995; Newman-Tancredi et al, 2005) whereas sarizotan
has high efficacy at 5-HT1A receptors and partial agonist
properties at D2 receptors (Kuzhikandathil et al, 2004;
Bartoszyk et al, 2004, Newman-Tancredi et al, 2005). The
results with sarizotan are in agreement with earlier studies
showing its weak antagonism of methylphenidate-induced
behaviors in rats, another measure predictive of antipsychotic activity (Kleven et al, 2004). Taken together, these
data indicate that 5-HT1A activation does not alter the
antipsychotic-like effects of D2 antagonists in this model of
positive symptoms of schizophrenia. Accordingly, for active
avoidance behavior in mice, another animal model of
antipsychotic potential, the coadministration of the 5-HT1A
antagonist SL88.0338 did not modify the activity of
SSR181507 (Depoortere et al, 2003). In addition, data
obtained in rats suggest that the potency of D2 antagonists
(such as raclopride) in the same test is even enhanced by
addition of a compound with 5-HT1A agonist properties
(such as 8-OH-DPAT: Prinssen et al, 1996).
In clinical studies, buspirone and tandospirone, two
partial agonists at 5-HT1A receptors, substantially improved
negative symptoms scores and reduced the incidence of
EPS in schizophrenic patients treated with haloperidol
(Sumiyoshi et al, 2001a, b). In a single case study, Pantelis
and Barnes (1993) have found that, when given together
with neuroleptics, low doses of buspirone had beneficial
effects on anxiety and psychosis whereas higher doses
exacerbated psychosis. Thus, whereas preclinical studies
generally find that 5-HT1A agonists attenuate neurolepticinduced EPS (see Introduction), the therapeutic effects of
combined 5-HT1A agonist/D2-like antagonist compounds
remain largely uncharacterized and await further clinical
studies. Indeed, sarizotan, which exhibits very high efficacy
at 5-HT1A receptors and partial agonist properties at D2
receptors (Bartoszyk et al, 2004; Newman-Tancredi et al,
Neuropsychopharmacology
2005) is now in development as an antidyskinetic agent in
L-DOPA-treated Parkinson’s disease patients (Bartoszyk
et al, 2004) likely because of insufficient antipsychotic
activity (present data and Kleven et al, 2004). In contrast,
interestingly, an older neuroleptic, tiospirone, with very
low efficacy at 5-HT1A receptors (Newman-Tancredi et al,
1998, 2005), exhibited antipsychotic properties in humans
comparable with those of haloperidol, but with a lower
incidence of EPS (Moore et al, 1987).
Non-Catalepogenic Properties of the New Generation of
Antipsychotics: Role of 5-HT1A Receptors
The atypical antipsychotics, clozapine, ziprazidone as well
as the new generation of potential antipsychotic agents (eg
SSR181507, aripiprazole, SLV313) induced little or no
catalepsy compared with the typical antipsychotics, haloperidol, or fluphenazine in the bar test. ED50 values for
SSR181507, sarizotan, aripiprazole, clozapine, and SLV313
were greater than 40 mg/kg, which is 100-fold higher than
for haloperidol. However, we cannot exclude that pharmacokinetic peculiarities of some of these drugs (such as slow
brain penetration or else: see below) may explain the fact
that little or no catalepsy was observed under our experimental conditions (ie observation 1 h after drug administration). In fact, it has been reported that the maximum
catalepsy response to aripiprazole occurred at 8 h postadministration (Hirose et al, 2004). This is an interesting
observation, considering that in both rats and humans, a
major metabolite of aripiprazole is a pure dopamine D2
antagonist (Lawler et al, 1999), which may mitigate the D2
receptor partial agonist properties of aripiprazole. Nevertheless, these results are generally consistent with previous
literature for these ligands concerning their low cataleptogenic liability in rats (Glennon et al, 2002; Depoortere
et al, 2003; Wolf, 2003; Bartoszyk et al, 2004; Kleven et al,
2005). Additionally, pretreatment with the 5-HT1A receptor
antagonist, WAY100635, enhanced or reinstated catalepsy
induced by antipsychotics, consistent with results reported
by Kleven et al (2005). For example, WAY100635 pretreatment induced near maximal catalepsy in the bar test for
SSR181507 and sarizotan, which alone, even at doses up to
40 mg/kg, induced no catalepsy. Depoortere et al (2003)
have also reported that in coadministration with SL88.0338,
another 5-HT1A antagonist, SSR181507 produced catalepsy
in rats. Nemonapride induced catalepsy in a biphasic
manner: that is, catalepsy at low but not at high doses,
and pretreatment with WAY100635 reinstated nemonapride-induced catalepsy at higher doses. These findings
extend previous data reported by Prinssen et al (1998),
indicating that the 5-HT1A receptor agonist properties of
nemonapride at high doses are responsible for its lowered
propensity to produce catalepsy in rats. These observations
demonstrate that activation of 5-HT1A receptors plays an
important role in the relatively low or noncataleptogenic
liability seen with compounds reported to have dual
D2/5-HT1A actions (for review, see: Millan, 2000; Bantick
et al, 2001). Another important finding of the present study
was that pretreatment with WAY100635 enhanced catalepsy
induced by the dopamine D2-like receptor antagonist
haloperidol in mice. This confirms previous data reported
by Prinssen et al (1998), showing that cotreatment with
Novel antipsychotics and 5-HT1A agonist properties
L Bardin et al
1877
WAY100635 slightly, but significantly, enhanced haloperidol-induced catalepsy in rats. While having no effect
on catalepsy itself, WAY100635 likely increases neurolepticinduced catalepsy by blockade of 5-HT1A auto-receptors
controlling tonic 5-HT release. Thus depletion of 5-HT
by repeated treatment with the 5-HT synthesis inhibitor
p-chlorophenylalanine methyl ester, abolished the enhancement by WAY100635 of catalepsy induced by raclopride
(Prinssen et al, 2000). In addition, tonic 5-HT1A receptor
activity has been demonstrated in animals during
periods of active arousal (for review, see Routledge, 1996)
and antipsychotic-induced catalepsy is very sensitive to
5-HT1A receptor stimulation (for review, see Wadenberg,
1996).
In the case of aripiprazole and SLV313, although
WAY100635 produced upward shifts in their dose–response
curves, the magnitude of catalepsy appeared to reach an
asymptotic plateau, suggesting that other mechanisms may
be involved in their low cataleptogenic liability. Indeed,
although a partial agonist at 5-HT1A receptors, aripiprazole
exhibits efficacy lower than that of other antipsychotics in
assays of G-protein activation and adenylyl cyclase activity
in cloned human and native rat hippocampal membranes
(Newman-Tancredi et al, 2005). Moreover, as well as
activating 5-HT1A receptors, aripiprazole is also a D2
receptor partial agonist (Bartoszyk et al, 2004) and has
interactions at numerous other receptor subtypes (Shapiro
et al, 2003) including 5-HT2A and 5-HT2C, targets that are
known to profoundly influence antipsychotic drug action
(Meltzer et al, 2003). In this context, it is likely that
aripiprazole’s partial D2 agonist properties or multireceptor profile contribute to both its weak cataleptogenic
profile and the limited catalepsy obtained in the presence of
WAY100635. It has been recently suggested that aripiprazole is capable of directing D2 receptor signalling to specific
intracellular responses (Urban et al, 2004) and it may be
speculated that such signalling pathways are specifically
involved in motor control, for example in brain regions
such as striatum that display high densities of D2 receptor
expression. In contrast, SLV313 exhibits balanced 5-HT1A/
D2 affinity and intermediate efficacy at 5-HT1A receptors,
but little interaction with D1, 5-HT2A or a1/2 adrenergic
receptors (Newman-Tancredi et al, 2005; Assié MB,
unpublished observations). SLV313 blocks psychostimulant-induced behaviors in rodents in the absence of
catalepsy; of the compounds tested here SLV313 had the
highest antipsychotic-like vs catalepsy separation (present
data; Glennon et al, 2002; Kleven et al, 2005) suggesting that
its balance of 5-HT1A/D2 properties produces a favorable
antipsychotic profile. In contrast, SLV314, another ‘selectively nonselective’ 5-HT1A agonist/D2 antagonist (Roth
et al, 2004), exhibits affinity at 5-HT1A receptors that is two
orders of magnitude lower than that of D2 receptors and its
cataleptogenic liability is higher than that of SLV313
(ED50 ¼ 0.5 vs 440 mg/kg). In addition to exerting classical
antipsychotic-like effects, SLV314 has also been reported to
induce antidepressant and anxiolytic-like effects (McCreary
et al, 2002) probably due to its potent serotonin reuptake
inhibition properties rather than to its direct 5-HT1A
activation (Tuinstra et al, 2002). Taken together, these data
suggest that the lack of catalepsy of these novel antipsychotics (eg SSR181507, aripiprazole, SLV313) depend on
both the affinity and efficacy of these ligands at 5-HT1A and
D2 receptors.
Conclusions
A new generation of potential antipsychotics is being
developed, including bifeprunox, SSR181507 and SLV313,
which selectively targets 5-HT1A receptors as well as
dopamine D2 receptors. The present data confirm that
antipsychotics that activate 5-HT1A receptors exhibit low
EPS liability and support the concept that combined D2
receptor blockade and 5-HT1A activation is a promising
strategy to reduce the EPS liability of antipsychotics, while
retaining desired antipsychotic properties (Bantick et al,
2001; Millan 2000). Nevertheless, the present data indicate
also that the balance of affinity and efficacy at both D2 and
5-HT1A receptors profoundly influences the pharmacological profile of these new generation antipsychotics, and will
likely impact their therapeutic profiles.
ACKNOWLEDGEMENTS
The present study was funded by Pierre Fabre Médicament.
All authors are employees of the Pierre Fabre Research
Centre. The authors thanks, N Consul-Denjean, E Senaux
and L Hejoaka for technical expertise and J Besnard for
assistance with data management and analysis. We thank
Solvay-Duphar, for the kind donation of SLV313 and
SLV314.
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