The role of subtypes of the opioid receptor in the anxiolytic action of chlordiazepoxide
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Neuropharmacology 37 (1998) 223 – 232
The role of subtypes of the opioid receptor in the anxiolytic action
of chlordiazepoxide
Anders Ågmo *, Catherine Belzung
Laboratoire de Psychophysiologie, Faculté des Sciences, Uni6ersité de Tours, Parc de Grandmont, 37200 Tours, France
Accepted 4 December 1997
Abstract
Previous studies have shown that the opiate antagonist naloxone blocks the anxiolytic-like effects of benzodiazepines in several
models of anxiety, including the elevated plus-maze. Although naloxone preferentially binds to the m opioid receptor, its selectivity
is rather low. The opioid receptor subtype important for anxiolytic-like actions of benzodiazepines in the plus-maze remains,
therefore, unknown. In the present experiments, the ability of antagonists selective for subtypes of the opioid receptor to block
the anxiolytic-like effects of chlordiazepoxide in the elevated plus-maze was evaluated in Swiss mice. Chlordiazepoxide, 5 mg/kg,
increased the proportion as well as the number of open arms entries without modifying closed arms entries. Lower doses of the
benzodiazepine were ineffective. The m receptor antagonist b-funaltrexamine, 10 and 20 mg/kg, the d antagonist naltrindole, 10
mg/kg, and the k antagonist nor-binaltorphimine, 2.5 and 5 mg/kg, were then combined with chlordiazepoxide, 5 mg/kg.
b-funaltrexamine, 10 mg/kg, reduced the effects of the benzodiazepine while the dose of 20 mg/kg completely blocked the effects.
Nor-binaltorphimine was ineffective at a dose of 2.5 mg/kg, but completely inhibited the actions of chlordiazepoxide when the
dose was 5 mg/kg. Naltrindole was ineffective. None of the antagonists affected plus-maze behavior when administered alone. It
was concluded that the m and k receptors are important for the anxiolytic-like actions of chlordiazepoxide in the elevated plus
maze. © 1998 Elsevier Science Ltd. All rights reserved.
Keywords: Benzodiazepines; Opioids; Anxiety; Elevated plus-maze; Mouse; Opioid receptors
1. Introduction Tsuda et al., 1996) while they are readily eliminated by
GABAA receptor antagonists (File, 1982; Ågmo and
The opiate antagonist naloxone has been reported to Fernández, 1991). Therefore, it is unlikely that the
block the anxiolytic effects of benzodiazepines, barbitu- naloxone-induced blockade of anxiolysis is a conse-
rates and meprobamate in several behavioral quence of putative GABA antagonistic properties of
paradigms, one of which is the elevated plus-maze this compound (Dingledine et al., 1978). In fact, the
(Ågmo et al., 1995 and unpublished observations; opiate antagonist does not bind to any significant de-
Billingsley and Kubena, 1978; Koob et al., 1980; Sou- gree to receptors that may be important for anxiolytic
brié et al., 1980; Duka et al., 1981; Belzung and Ågmo, activity such as GABAA, 5-HT1A or dopamine recep-
1997). Naloxone has also been found to have similar tors (Goldinger et al., 1981; Carlsson and Seeger, 1982;
effects in humans (Duka et al., 1982). The antagonism
Martin et al., 1991). It is likely, then, that naloxone
is specific to anxiolytic-like actions, because motor in-
blocks anxiolytic activity through an action at opiate
coordination, hypothermia or anticonvulsive effects of
receptors. As a tentative explanation for this, we have
benzodiazepines and pentobarbital are not blocked by
proposed that anxiolytic-like effects of benzodiazepines
the opiate antagonist (File 1982; Ågmo et al. 1995;
and pentobarbital are possible only if endogenous opi-
oid systems are activated (Ågmo et al., 1995).
* Current address: SSV, Box 2024, 60009 Norrköping, Sweden. There is, in fact, evidence showing that benzodi-
E-mail: anders.aagmo@nystromska.soderkoping.se azepine receptor agonists activate endorphins and
0028-3908/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0028-3908(98)00003-3224 A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232
enkephalins at some brain sites (Duka et al., 1979; 2. Methods
Wüster et al., 1980; Harsing et al., 1982), and that this
activation is blocked by naloxone (Duka et al., 1980). 2.1. Subjects
Furthermore, central and peripheral opioid systems are
stimulated by several kinds of stressors in rats and Male Swiss mice, 7 weeks of age, were obtained from
humans (Blake et al., 1987; Boone and McMillen, 1994; Janvier (Le Genest Saint Isle, France). The subjects
Hennig et al., 1994; Larsen and Mau, 1994; Sched- were housed five per cage under a reversed light/dark
lowski et al., 1995; Yamada and Nabeshima, 1995). In cycle (12/12 h, lights on 2000) at a constant tempera-
the human, an inverse relationship between the con- ture (2291°C). Commercial rodent pellets and water
centration of b-endorphin in cerebrospinal fluid and were freely available. Experiments started about 3
subjective experience of stress has been reported (Brady weeks after the animals had arrived in the laboratory.
et al., 1991). It has also been proposed that plasma The work reported in this paper was conducted in
b-endorphin concentration is related to the decrease accordance with the Guide for Care and use of Labora-
in anxiety, as evaluated through a questionnaire, ob- tory Animals established by the National Institutes of
served after long-distance running (Appenzeller et al., Health of the United States of America and with
1980; Dienstbier et al., 1981). In this context it must applicable local laws.
be noted that procedures used to study anxiety are
almost always stressful to the subject, be it rat or 2.2. Apparatus and procedure
human, as evidenced by increased corticosteroid secre-
tion (e.g. Pellow et al., 1985). Thus, stress seems to be The experimental situation should be sufficiently
an important component of experimental anxiety. The stressful to activate opioid systems (see Section 1), be
above-mentioned observations suggest that opioids sensitive to benzodiazepines, and be ethologically rele-
vant. This latter means that the behavior displayed in
indeed may be implicated in anxiety mechanisms.
the situation should be present in the animals’ normal
Moreover, intracerebroventricular infusion of b-endor-
behavioral repertoire. The elevated plus-maze seems to
phin enhances flunitrazepam binding in the cortex (Go-
fulfil these criteria. The procedure is based on rodents’
mar et al., 1993a,b). This fact suggests that opioid
natural tendency to avoid open spaces (Treit et al.,
systems interact with at least some anxiolytic drugs
1993) and it does not contain any experimenter-con-
at a cellular level. However, opiate agonists them-
trolled aversive element. Nevertheless, exposure to it is
selves do not reliably produce anxiolytic-like effects
stressful for the subjects. In fact, a test on the plus-
in animal models of anxiety (McMillan and Leander,
maze enhances plasma corticosteroids as much as mod-
1975; Pollard and Howard, 1990), although there is
erate electric shock (Friedman et al., 1967; Pellow et al.,
one report showing anxiolytic effects of the k opioid
1985).
agonist U50488H in the elevated plus-maze (Privette The plus-mazes were made of polyvinylchloride and
and Terrian, 1995). However, another purported k elevated to a height of 38.5 cm. The opposing closed
agonist, ethylketocyclazocine, has been found to sup- arms (27× 5 cm) had 15 cm high walls and were
press punished responding in an operant task, suggest- covered by dark paper during tests. The open arms
ing an anxiogenic effect (DeRossett and Holzman, (27× 5 cm) were brightly lit by a 60 W transparent
1985). bulb hanging 50 cm above each arm. Light intensity on
To further our understanding of the interactions the open arms’ surface was about 550 lux. The arms
between opioid systems and benzodiazepines it extended from a central platform (5 × 5 cm). At the
would be useful to determine at which opioid receptor beginning of the test, the mouse was placed on the
naloxone acts when blocking anxiolytic-like actions central platform with its head facing an open arm. The
of benzodiazepines. This was the purpose of the pre- number of entries onto each arm was registered on a
sent experiments. The selective opioid receptor antago- hand-held computer (Psion Organiser) over 5 min. The
nists b-funaltrexamine (m), naltrindole (d) and mouse was considered to be on the central platform
nor-binaltorphimine (k) were administered together whenever two paws were posed on it, and on any of the
with chlordiazepoxide to Swiss mice and anxiolytic- arms when the four paws were on it. All tests were
like effects evaluated with the elevated plus-maze. performed between the 6th and 9th hour of the dark
When the present studies were completed, a report phase of the light/dark cycle. The test room was lit by
appeared (Tsuda et al., 1996) showing that the anti- the lamps installed over the plus-mazes only.
conflict effect of diazepam in the Vogel procedure was
blocked by b-funaltrexamine and nor-binaltorphimine 2.3. Design
but not by naltrindole. Here we extend these observa-
tions to another benzodiazepine and to another anxiety A parallel groups design was used, in such a way that
test. all doses of a drug or all combinations of drugs in eachA. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232 225
particular experiment were run in a single session. The The effects of the opiate antagonists alone were then
order of drug treatments within each session was ran- evaluated. As can be seen in Fig. 2, there was no
domized. There were 7 – 10 mice per dose. Only experi- statistically significant effect on the proportion of open
mentally naive animals were used. arms entries (F(3, 33)= 1.18, NS), number of open
arms entries, (F(3, 33)= 0.33, NS) or on the number of
2.4. Drugs
Chlordiazepoxide HCl (Sigma, St. Louis, MO), b-
funaltrexamine HCl, naltrindole HCl and nor-binaltor-
phimine 2HCl (all three from Research Biochemicals,
Natick, MA in the first two antagonist experiments and
from Tocris Cookson, Bristol, UK, in the others) were
dissolved in physiological saline and injected i.p. in a
volume of 1 ml/100 g body weight. The intervals be-
tween drug injection and behavioral observation were
the following: naltrindole, 15 min; chlordiazepoxide, 30
min; nor-binaltorphimine, 3 h; b-funaltrexamine, 20 h.
Controls were injected with saline vehicle at the corre-
sponding interval. The pretreatment times were those
used in previous studies where the antagonists have
been shown to effectively antagonize opiate effects and
have maximal receptor specificity (Endoh et al., 1992;
Negus et al., 1993; Porthogese et al., 1980; Suzuki et al.,
1994)
2.5. Statistics
The proportion of entries on the open arms (number
of open entries/total number of entries) was used as
indicator of anxiolytic-like effects as originally sug-
gested by Pellow et al. (1985). The number of entries on
the closed arms has been reported to mainly represent
motor activity (Lister, 1987; Belzung and Le Pape,
1994; Cruz et al., 1994; Dawson et al., 1995) and was
used here as a control for motor effects of the drugs. In
addition, we report the number of open arms entries.
These parameters were subjected to one factor
ANOVAs. Homogeneity of error variances was deter-
mined by Hartley’s Fmax test before using results of any
ANOVA. In case of non-homogeneous error variances
data were analyzed with Kruskal – Wallis ANOVA. A
posteriori comparisons were made with Tukey’s HSD
test or the Mann–Whitney U-test.
3. Results
Chlordiazepoxide increased the proportion of entries
on the open arms (F(3, 28) = 7.66, P =0.001). A poste-
riori comparisons showed that the minimum effective
dose was 5 mg/kg (Fig. 1A). The number of open arms
Fig. 1. Effects of several doses of chlordiazepoxide on the proportion
entries was also increased by the drug (F(3, 28) = 5.00,
of open arms entries (A) and on the number of entries onto the open
PB 0.01), and again the minimum effective dose was 5 (B) and closed (C) arms in the elevated plus-maze. Data are means 9
mg/kg (Fig. 1B). No effect was found on the number of S.E.M. !, different from saline, PB0.05; !!, P B0.01. There were
closed arms entries (F(3, 28) = 1.73, NS) (Fig. 1C). eight animals per dose.226 A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232
closed arms entries (F(3, 33)=2.84, NS). It appeared,
however, that b-funaltrexamine, 20 mg/kg, reduced the
number of closed arms entries. This effect was not
statistically reliable. Naltrindole showed a slight ten-
dency to increase the proportion of open arms entries,
but this effect was far from significant.
Because the proportion of open arms entries was very
low in this experiment, we made a replication with a
slightly modified procedure. Instead of illuminating the
open arms with 60 W transparent bulbs, we used similar
red bulbs here. Additional doses of the antagonists were
also used. As can be seen in Fig. 3, no effect was
obtained (proportion of open arms entries, H=6.30,
NS; number of open arms entries, H= 5.01, NS; num-
ber of closed arms entries, H=8.26, NS). It seems safe
to conclude that none of the antagonists has any reliable
intrinsic effect in the plus-maze.
When chlordiazepoxide, 5 mg/kg, was combined with
the selective m antagonist b-funaltrexamine, 10 mg/kg,
the d antagonist naltrindole, 10 mg/kg, or the k antag-
onist nor-binaltorphimine, 2.5 mg/kg, a treatment effect
was found with regard to the proportion of open arms
entries (F(4, 42)= 5.53, P= 0.001). A posteriori com-
parisons showed that chlordiazepoxide+ saline in-
creased this proportion while the combination
chlordiazepoxide+ b-funaltrexamine differed neither
from saline + saline nor from chlordiazepoxide +saline.
Thus, the effects of chlordiazepoxide were partially
antagonized by this drug. Naltrindole and nor-binaltor-
phimine did not reduce the effects of chlordiazepoxide
on the proportion of open arms entries. Data are shown
in Fig. 4A.
Analysis of the number of open arms entries showed
a difference between groups, F(4, 42)= 5.93, PB0.001.
The Tukey test revealed that the groups treated with
chlordiazepoxide+ saline, chlordiazepoxide+nal-
trindole and chlordiazepoxide+nor-binaltorphimine
made more entries on the open arms than control. This
was not the case for the group given chlordiazepoxide +
b-funaltrexamine. Data are summarized in Fig. 4B.
No effect of any drug or combination of drugs was
observed on the number of closed arms entries
(F(4, 42)=0.76, NS) (Fig. 4C). To summarize, neither
naltrindole nor nor-binaltorphimine reduced the effects
of chlordiazepoxide in the elevated plus-maze. However,
b-funaltrexamine, 10 mg/kg, partially antagonized the
effects of chlordiazepoxide. In an additional experiment
we determined if a larger dose of b-funaltrexamine
could completely suppress the effects of chlordiazepox-
Fig. 2. Effect of b-funaltrexamine (b-FTA), 20 mg/kg, naltrindole ide. Furthermore, Tsuda et al. (1996) reported that
(NALT), 10 mg/kg and of nor-binaltorphimine (NBI), 2.5 mg/kg on nor-binaltorphimine, 3 mg/kg, blocked the effects of
the proportion of open arms entries (A), on the number of open arms
entries (B) and on the number of closed arms entries (C) in the
diazepam in the Vogel test. Therefore, it was surprising
elevated plus-maze test in male mice. Data are means 9 S.E.M. Doses that the drug was ineffective here at a very similar dose.
are expressed as mg/kg. There were ten animals per drug except for This prompted us to perform an experiment where
b-funaltrexamine where there were seven. nor-binaltorphimine was given in a larger dose.A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232 227
In these additional experiments, chlordiazepoxide, 5
mg/kg, was combined either with 20 mg/kg of b-funal-
trexamine or with 5 mg/kg of nor-binaltorphimine.
There was an effect of treatment on the proportion of
entries on the open arms (F(2, 25)=10.68, PB0.001)
in the experiment with b-funaltrexamine. The group
given chlordiazepoxide+saline differed from control
and from b-funaltrexamine+ chlordiazepoxide. Data
are shown in Fig. 5A. There was also an effect on the
number of open arms entries, F(2, 25)= 11.87, PB
0.001. Chlordiazepoxide +saline increased this number.
This increase was completely blocked by b-funaltrex-
amine (Fig. 5B). No effect was found on the number of
closed arms entries (F(2, 25)=0.70, NS) (Fig. 5C).
These results showed that b-funaltrexamine, at a dose
of 20 mg/kg, completely blocked the effect of
chlordiazepoxide.
In the experiment with nor-binaltorphimine there was
also an effect of treatment (F(2, 26)= 7.67, PB 0.01)
on the proportion of open arms entries. Chlordiazepox-
ide increased this proportion (Fig. 5A), an effect that
was completely blocked by nor-binaltorphimine. In
fact, the group given chlordiazepoxide+ nor-binaltor-
phimine differed from chlordiazepoxide+ saline but
not from control. There was also a treatment effect on
the number of open arms entries (Fig. 5B). Again, the
effect of chlordiazepoxide was completely blocked by
nor-binaltorphimine. No effect was found on the num-
ber of closed arms entries (H= 3.63, NS) (Fig. 5C).
4. Discussion
Chlordiazepoxide, 5 mg/kg, was the lowest effective
dose in our version of the elevated plus-maze. The drug
enhanced the proportion of open arms entries without
affecting closed arms entries. This is indicative of an
anxiolytic-like effect independent of any possible ac-
tions on locomotor activity. The opiate antagonists
were ineffective when administered alone. This was
observed in two separate experiments with different
baselines. It seems, therefore, that the blockade of the
actions of chlordiazepoxide observed after antagonist
treatment cannot be a consequence of summation of
opposite effects.
The selective d antagonist naltrindole was unable to
block the anxiolytic-like response to chlordiazepoxide.
A crucial question is whether this lack of effect is due
to an inadequate dose. It has been reported that doses
as low as 0.5 and 0.3 mg/kg i.p. or s.c. completely block
morphine-induced conditioned place preference and
sensitization to cocaine, respectively (Heidbreder et al.,
1993; Suzuki et al., 1994). The dose used in the present
Fig. 3. Parameters of plus-maze behavior in male mice tested under
study, 10 mg/kg, can therefore be considered as very
red light and treated with different doses of the opiate antagonists
b-funaltrexamine (b-FTA), naltrindole (NALT) and nor-binaltor- high, and should have produced a considerable block-
phimine (NBI). Data are means 9 S.E.M. Doses are expressed as ade of d receptors. It seems, therefore, that the d
mg/kg. There were eight animals per dose. receptor is not important for the anxiolytic-like actions228 A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232
of chlordiazepoxide in the elevated plus maze test. The
same holds for the actions of diazepam in the Vogel test
(Tsuda et al., 1996).
The m antagonist b-funaltrexamine reduced the anxi-
olytic-like actions of chlordiazepoxide when adminis-
tered at a dose of 10 mg/kg and completely blocked
these effects at a dose of 20 mg/kg. The k antagonist
nor-binaltorphimine also blocked the anxiolytic-like ac-
tions of chlordiazepoxide. These results coincide with
an earlier study (Tsuda et al., 1996). b-Funaltrexamine
is known to be a highly selective, irreversible inhibitor
of the m receptor (Porthogese et al., 1980; Ward et al.,
1982). It produces a 3- to 6-fold rightward shift in the
dose effect curve for the analgesic actions of morphine
and the selective m agonist alfentanil when administered
at a dose of 20 mg/kg (Hayes et al., 1986; Negus et al.,
1993). Nor-binaltorphimine binds with high affinity and
selectivity to the k receptor in vitro (Takemori et al.,
1988). However, in vivo this compound has a weak m
antagonistic effect during the first 2 h after s.c. adminis-
tration, but thereafter it is a highly specific and long-
lasting k antagonist (Endoh et al., 1992). Thus, present
data suggest that simultaneous activity at m and k
receptors is essential for the manifestation of the anxi-
olytic-like action of chlordiazepoxide. It is most un-
likely that any of the antagonists interacts with
non-opioid receptors to an extent sufficient to explain
their inhibition of anxiolysis.
The mechanism by which b-funaltrexamine and nor-
binaltorphimine inhibits chlordiazepoxide-induced anx-
iolysis is unknown. It does not seem to be related to
inhibition of stress-induced analgesia, because both m, d
and k antagonists reduce such analgesia (see Yamada
and Nabeshima, 1995, for a review), frequently at doses
lower than those used in the present studies. It is also
unlikely that opioid actions on GABAergic neurons is
involved. Benzodiazepines are supposed to facilitate
GABAergic neurotransmission (e.g. Lüddens and Ko-
rpi, 1995) whereas opioids are known to inhibit
GABAergic interneurons in the hippocampus (Pang
and Rose, 1989; Cohen et al., 1992), a structure be-
lieved to be important for anxiety and anxiolysis (Gray,
1982). Opposing effects of benzodiazepines and opioids
are incompatible with the results of present and earlier
studies where opiate antagonists block anxiolysis. An-
other possibility is that opioid and benzodiazepine ac-
tions on serotonergic systems is the critical factor. A 5
min plus-maze test produces enhanced release of sero-
Fig. 4. The proportion (A) and number of open arms entries (B), and tonin in the hippocampus, and this may be related to
the number of entries into the closed arms (C) in male mice treated
the fear or ‘anxiety’ produced by this situation (Mars-
with chlordiazepoxide (CDO), 5 mg/kg, in combination with the
selective m antagonist b-funaltrexamine (b-FTA), 10 mg/kg, the d den et al., 1992; File et al., 1993). It has also been
antagonist naltrindole (NALT), 10 mg/kg, or the k antagonist nor- reported that treatment with diazepam blocks the in-
binaltorphimine (NBI), 2.5 mg/kg. Data are means9 S.E.M. S, sa- crease in serotonin release observed upon exposure to a
line. !, different from control, P B0.05; !!, PB 0.01. There were plus-maze (Wright et al., 1992) or to conditioned fear-
ten animals each in the groups treated with saline+ saline, saline+
chlordiazepoxide and b-funaltrexamine + chlordiazepoxide. Nine ani-
stress (Yoshioka et al., 1995), confirming earlier data
mals were treated with naltrindole + chlordiazepoxide and eight with showing that benzodiazepines inhibit serotonergic sys-
nor-binaltorphimine+chlordiazepoxide. tems (Wise et al., 1972; Stein et al., 1975). This effectA. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232 229 Fig. 5. Parameters of plus-maze behavior in male mice treated with chlordiazepoxide in combination either with b-funaltrexamine, 20 mg/kg (b-FTA; left side), or nor-binaltorphimine, 5 mg/kg (NBI; right side). Data are means9S.E.M. SAL, saline. !, different from control, PB 0.05; !!, P B 0.01. 2 , different from chlordiazepoxide + saline, P B 0.05; 22, P B0.01. N= 10 (saline + saline and saline +chlordiazepoxide) or 8 (b-funaltrexamine + chlordiazepoxide) in the b-funaltrexamine experiment. There were eight animals per group in the nor-binaltorphimine experiment.
230 A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232
may be related to benzodiazepines’ anxiolytic action. In (Ågmo et al., 1989; Rodrı̀guez et al., 1993). Again, the
fact, reduced serotonergic activity has anxiolytic effects mechanisms are not known, but it is an additional
(e.g. Schreiber and de Vry, 1993; Westenberg and den example of opioid–serotonin interactions. Such interac-
Boer, 1994). Stimulation of m receptors reduces sero- tions do not seem to be exclusive for anxiety.
tonin release (Passarelli and Costa, 1989), whereas ago-
nists selective for the d or k receptors are ineffective
(Yoshioka et al., 1993). Stress enhances proopiome- Acknowledgements
lanocortin mRNA in the arcuate nucleus (Larsen and
Mau, 1994), suggesting increased release of endorphins. Part of the b-funaltrexamine HCl employed in the
b-endorphin is active at presynaptic, transmitter release present studies was provided by Research Biochemicals
inhibiting, m receptors (Schoffelmeer et al., 1991). It International as part of the Chemical Synthesis Pro-
could be supposed, then, that stress-induced opioid gram of the National Institute of Mental Health, Con-
release reduces stress-induced serotonin release. Such tract N0IMH30003. Anne Marie Le Guisquet provided
an effect of opioids may explain their purported capac- excellent animal care. The figures were produced by
ity (see Section 1 McCubbin, 1993) to attenuate the Serge Barreau.
impact of stressors. If m receptors were blocked, stress-
induced opioid release would be unable to reduce sero-
tonergic activity and this could reduce the effectiveness References
of benzodiazepines. Stimulation of k receptors has also
been reported to inhibit neurotransmitter release, par- Abercombie, E.D., Keefe, K.A., DiFrischia, D.S., Zigmond, M.J.,
ticularly the release of dopamine (Manzanares et al., 1989. Differential effects of stress on in vivo dopamine release in
1991; Donzanti and Althaus, 1992). Interestingly, do- striatum, nucleus accumbens, and medial prefrontal cortex. J.
pamine is also released in response to stress (Abercom- Neurochem. 52, 1655 – 1658.
Ågmo, A., Fernández, H., Picker, Z., 1989. Naloxone inhibits the
bie et al., 1989; Finlay et al., 1995). Maybe opioid facilitatory effects of 8-OH-DPAT on male rat sexual behaviour.
actions on dopamine release inhibiting k receptors, Eur. J. Pharmacol. 166, 115 – 116.
which contributes to anxiolysis. However, neither m Ågmo, A., Fernández, H., 1991. Benzodiazepine receptor ligands and
receptor-mediated reduced serotonin release nor k re- sexual behavior in the male rat: The role of GABAergic mecha-
ceptor-mediated reduced dopamine release is by itself nisms. Pharmacol. Biochem. Behav. 38, 781 – 781.
Ågmo, A., Galván, A., Heredia, A., Morales, M., 1995. Naloxone
sufficient for anxiolysis. Both effects seem to be neces- blocks the antianxiety but not the motor effects of benzodi-
sary at the same time if benzodiazepines are to exert azepines and pentobarbital: experimental studies and literature
their anxiolytic actions. Data showing that mice lacking review. Psychopharmacology 120, 186 – 194.
a functional proopiomelanocortin gene show an abnor- Appenzeller, O., Standefer, J., Appenzeller, J., Atkinson, R., 1980.
Neurology of endurance training: V. Endorphins. Neurology 30,
mal response to stress (Rubinstein et al., 1996) and that
418 – 419.
BALB/c mice are insensitive to the antagonistic effects Belzung, C., Ågmo, A., 1997. Naloxone blocks anxiolytic-like effects
of naloxone in several anxiety tests (Belzung and of benzodiazepines in Swiss but not in BALB/c mice. Psychophar-
Ågmo, 1997) provide some support for this notion. The macology 132, 195 – 201.
BALB/c mice are known to have a deficient opioid Belzung, C., Le Pape, G., 1994. Comparison of different behavioral
test situations used in psychopharmacology for measurement of
release in response to stress (Miczek and Thompson,
anxiety. Physiol. Behav. 56, 623 – 628.
1984; Carmody et al., 1986). The fact that systemically Billingsley, M.L., Kubena, R.K., 1978. The effects of naloxone and
administered opiates are generally poor anxiolytics (see picrotoxin on the sedative and anticonflict effects of benzodi-
above) and present and earlier data showing that opioid azepines. Life Sci. 22, 897 – 906.
antagonism blocks the anxiolytic-like actions of benzo- Blake, M.J., Stein, E.A., Czech, D.A., 1987. Drinking-induced alter-
ations in reward pathways: an in vivo autoradiographic analysis.
diazepines indicates that opioid m and k as well as
Brain Res. 413, 111 – 119.
benzodiazepine receptors need to be activated simulta- Boone, J.B. Jr., McMillen, D., 1994. Differential effects of prolonged
neously in order for anxiolysis to occur. restraint stress on proenkephalin gene expression in the brainstem.
In this context it may be interesting to note that Mol. Brain Res. 27, 290 – 298.
benzodiazepines, opiates and some serotonin agonists, Brady, K.T., Lydiard, R.B., Ballenger, J.C., Shook, J., Laraia, M.,
Fossey, M., 1991. CSF opioids in panic disorder. Biol. Psychiatry
among these 5-HT1A agonists, increase food intake
30, 512 – 514.
(Levin et al., 1985; Dourish et al., 1986; Cooper, 1989). Carlsson, K.R., Seeger, T.F., 1982. Interaction of opiates with do-
This effect is blocked by naloxone, suggesting that pamine receptors: receptor binding and behavioral essays. Phar-
opioids are involved in the action of all three classes of macol. Biochem. Behav. 16, 119 – 124.
drugs (Cooper, 1983; Fletcher, 1991). Here is another Carmody, J., Jamieson, D., de Porteere, R., 1986. Opioid-indepen-
dent hyperalgesia induced in mice by pentobarbitone at low
example of benzodiazepine – opioid – serotonin interac-
dosage. Naunyn-Schmiedeberg’s Arch. Pharmacol. 334, 193–195.
tions. We have also shown that the facilitatory actions Cohen, G.A., Doze, V.A., Madison, D.V., 1992. Opioid inhibition of
of the serotonin1A agonists 8-OH-DPAT and lisuride GABA release from presynaptic terminals of rat hippocampal
on male rat sexual behavior are abolished by naloxone interneurons. Neuron 9, 325 – 335.A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232 231
Cooper, S.J., 1983. Benzodiazepine-opiate antagonist interactions in Gomar, M.D., Castillo, J.L., del Aguila, C.M., Fernández, B.,
relation to feeding and drinking behavior. Life Sci. 32, 1043 – Acuña-Castroviejo, D., 1993a. Intracerebroventricular injection of
1051. naloxone blocks melatonin-dependent brain [3H]-flunitrazepam
Cooper, S.J., 1989. Benzodiazepines and appetite: recent pre-clinical binding. Neuroreport 4, 987 – 990.
advances and their clinical implications. Hum. Psychopharmacol. Gomar, M.D., Fernández, B., Castillo, J.L., del Aguila, C.M.,
4, 81 – 89. Acuña-Castroviejo, D., 1993b. Suppressive effect of simultaneous
Cruz, A.P.M., Frei, F., Graeff, F.G., 1994. Ethopharmaological injection of ACTH1 – 10 and b-endorphin on brain
analysis of rat behavior on the elevated plus-maze. Pharmacol. [3H]flunitrazepam binding. Neuroreport 5, 252 – 254.
Biochem. Behav. 49, 171–176. Gray, J.A., 1982. The Neuropsychology of Anxiety: An Inquiry into
Dawson, G.R., Crawford, S.P., Collinson, N., Iversen, S.D., Trickle- the Function of the Septo-Hippocampal System. Oxford Univer-
bank, M.D., 1995. Evidence that the anxiolytic-like effects of sity Press, Oxford.
chlordiazepoxide on the elevated plus maze are confounded by Harsing, L.G., Yang, H.Y., Costa, E., 1982. Evidence for g-aminobu-
increases in locomotor activity. Psychopharmacology 118, 316 – tyric acid (GABA) mediation in the benzodiazepine inhibition of
met5-enkephalin elicited by depolarization. J. Pharmacol. Exp.
323.
Ther. 220, 616 – 620.
DeRossett, S.E., Holzman, S.G., 1985. Effects of opiate antagonists
Hayes, A.G., Skingle, M., Tyers, M.B., 1986. Reversal by b-funal-
and putative k agonists on unpunished and punished operant
trexamine of the antinociceptive effect of opioid agonists in the
behavior in the rat. Psychopharmacology 86, 386–391.
rat. Br. J. Pharmacol. 88, 867 – 872.
Dienstbier, R.A., Crabbe, J., Johnson, G.O., Thorland, W., Jor-
Heidbreder, C., Goldberg, S.R., Shippenberg, T.S., 1993. Inhibition
gensen, J.A., Sadar, M.M., LaVelle, D.C., 1981. Exercise and
of cocaine-induced sensitization by the d-opioid receptor antago-
stress tolerance. In: Sacks, M.H., Sachs, M.L. (Eds.), Psychology nist naltrindole. Eur. J. Pharmacol. 243, 123 – 127.
of Running. Human Kinetics Publishers, Campaign, IL, pp. 192 – Hennig, J., Laschefski, U., Opper, C., 1994. Biopsychological changes
210. after bungee-jumping: b-endorphin immunoreactivity as a media-
Dingledine, R., Iversen, L.L., Breuker, E., 1978. Naloxone as a tor of euphoria? Neuropsychobiology 29, 28 – 32.
GABA antagonist: evidence from iontophoretic, receptor binding Koob, G.F., Strecker, R.E., Bloom, F.E., 1980. Effects of naloxone
and convulsant studies. Eur. J. Pharmacol. 47, 19–27. on the anticonflict properties of alcohol and chlordiazepoxide.
Donzanti, B.A., Althaus, J.S., 1992. Kappa agonist-induced reduc- Subst. Alcohol Actions/Misuse 1, 447 – 457.
tion in dopamine release: site of action and tolerance. Res. Larsen, P.J., Mau, S.E., 1994. Effect of acute stress on the expression
Comm. Chem. Pathol. Pharmacol. 78, 193–210. of hypothalamic messenger ribonucleic acids encoding the endoge-
Dourish, C.T., Hutson, P.H., Kennett, G.A., Curzon, G., 1986. nous opioid precursors preproenkephalin A and proopiome-
8-OH-DPAT-induced hyperphagia: Its neural basis and possible lanocortin. Peptides 15, 783 – 790.
therapeutic relevance. Appetite 7, 127–140. Levin, A.S., Morley, J.E., Gosnell, B.A., Billington, C.J., Bartness,
Duka, T., Cumin, R., Haefely, W., Herz, A., 1981. Naloxone blocks T.J., 1985. Opioids and consummatory behavior. Brain Res. Bull.
the effect of diazepam and meprobamate on conflict behaviour in 14, 663 – 672.
rats. Pharmacol. Biochem. Behav. 15, 115–117. Lister, R.G., 1987. The use of a plus-maze to measure anxiety in the
Duka, T., Wüster, M., Herz, A., 1980. Benzodiazepines modulate mouse. Psychopharmacology 92, 180 – 185.
striatal enkephalin levels via a GABAergic mechanism. Life Sci. Lüddens, H., Korpi, E.R., 1995. Biological function of GABAA/ben-
26, 771 – 776. zodiazepine receptor heterogeneity. J. Psychiat. Res. 29, 77–94.
Duka, T., Wüster, M., Herz, A., 1979. Rapid changes in enkephalin Manzanares, J., Kookingland, K.J., Moore, K.E., 1991. Kappa opi-
levels in rat striatum and hypothalamus induced by diazepam. oid receptor-mediated regulation of dopaminergic neurons in the
Naunyn-Schmiedeberg’s Arch. Pharmacol. 309, 1–5. rat brain. J. Pharmacol. Exp. Ther. 256, 500 – 505.
Duka, T., Millan, M.J., Ulsamer, B., Doenicke, A., 1982. Naloxone Marsden, C.A., Wright, I.K., Beckett, S.G., Fulford, A., Rex, A.,
attenuates the anxiolytic action of diazepam in man. Life Sci. 31, 1992. Animal models of anxiety: involvement of serotonin. J.
1833 – 1836. Psychopharmacol. Abstr. Book A2.
Endoh, T., Matsuura, H., Tanaka, C., Nagase, H., 1992. Nor-binal- Martin, D.C., Introna, R.P., Aronstam, R.S., 1991. Fentanyl and
torphimine: A potent and selective k-opioid receptor antagonist sufentanyl inhibit agonist binding to 5-HT1A receptors in mem-
with long-lasting activity in vivo. Arch. Int. Pharmacodyn. Ther. branes from rat brain. Neuropharmacology 30, 323 – 327.
McCubbin, J.A., 1993. Stress and endogenous opioids: behavioral
316, 30 – 42.
and circulatory interactions. Biol. Psychol. 35, 91 – 122.
File, S.E., 1982. Chlordiazepoxide-induced ataxia, muscle relaxation
McMillan, D.E., Leander, J.D., 1975. Drugs and punished respond-
and sedation in the rat: effects of muscimol, picrotoxin and
ing. V. Effects of drugs on responding suppressed by response-de-
naloxone. Pharmacol. Biochem. Behav. 17, 1165–1170.
pendent and response-independent electric shock. Arch. Int.
File, S.E., Zangrossi, H. Jr., Andrews, N., 1993. Social interaction
Pharmacol. 213, 22 – 27.
and elevated plus-maze tests: changes in release and uptake of
Miczek, K.A., Thompson, M.L., 1984. Analgesia resulting from
5-HT and GABA. Neuropharmacology 32, 217–221. defeat in social confrontation: the role of endogenous opioids in
Finlay, J.M., Zigmond, M.J., Abercombie, E.D., 1995. Increased the brain. In: Bandler, R. (Ed.), Modulation of Sensorimotor
dopamine and norepinephrine release in medial prefrontal cortex Activity During Alterations in Behavioral States. Alan R. Liss,
induced by acute and chronic stress: effects of diazepam. Neuro- New York, pp. 431 – 456.
science 64, 619 – 628. Negus, S.S., Pasternak, G.W., Koob, G.F., Weinger, M.B., 1993.
Fletcher, P.J., 1991. Opiate antagonists inhibit feeding induced by Antagonist effects of b-funaltrexamine and naloxonazine on
8-OH-DPAT: possible mediation in the nucleus accumbens. Brain alfentanil-induced anti-nociception and muscle rigidity in the rat.
Res. 560, 260 – 267. J. Pharmacol. Exp. Ther. 264, 739 – 745.
Friedman, S.B., Ader, R., Grota, L.J., 1967. Plasma corticosterone Pang, K., Rose, G.M., 1989. Differential effects of methionine5-
response to parameters of electric shock in the rat. Psychosom. enkephalin on hippocampal pyramidal cells and interneurons.
Med. 29, 323 – 328. Neuropharmacology 28, 1175 – 1181.
Goldinger, A., Müller, W.E., Wollert, U., 1981. Inhibition if glycine Passarelli, F., Costa, T., 1989. Mu and delta opioid receptors inhibit
and GABA receptor binding by several opiate agonists and serotonin release in rat hippocampus. J. Pharmacol. Exp. Ther.
antagonists. Gen. Pharmacol. 12, 477–479. 248, 299 – 305.232 A. Ågmo, C. Belzung / Neuropharmacology 37 (1998) 223–232
Pellow, S., Chopin, P., File, S.E., Briley, M., 1985. Validation of Suzuki, T., Yoshiike, M., Mizoguchi, J., Kamei, J., Misawa, M.,
open: closed arm entries in an elevated plus maze as a measure of Nagase, H., 1994. Blockade of d-opioid receptors prevents mor-
anxiety in the rat. J. Neurosci. Methods 14, 149–167. phine-induced place preference in mice. Jpn. J. Pharmacol. 66,
Pollard, G.T., Howard, J.L., 1990. Effects of drugs on punished 131 – 137.
behavior: pre-clinical tests for anxiolytics. Pharmacol. Ther. 45, Takemori, A.E., Ho, B.Y., Naeseth, J.S., Porthogese, P.S., 1988.
401 – 424. Nor-binaltorphimine, a highly selective kappa-opioid antagonist
Porthogese, P.S., Larson, D.L., Sayre, L.M., Fries, D.S., Takemori, in analgesic and receptor binding assays. J. Pharmacol. Exp. Ther.
A.E., 1980. A novel opioid receptor site directed alkylating agent 246, 255 – 258.
Treit, D., Menard, J., Royan, C., 1993. Anxiogenic stimuli in the
with irreversible narcotic antagonist and reversible agonistic activ-
elevated plus-maze. Pharmacol. Biochem. Behav. 44, 463–469.
ities. J. Med. Chem. 23, 233–234.
Tsuda, M., Suzuki, T., Misawa, M., Nagase, H., 1996. Involvement
Privette, T.H., Terrian, D.M., 1995. Kappa opioid agonists produce
of the opioid system in the anxiolytic effect of diazepam in mice.
anxiolytic-like behaviors on the elevated plus-maze. Psychophar- Eur. J. Pharmacol. 307, 7 – 14.
macology 118, 444 – 450. Ward, S.J., Porthogese, P.S., Takemori, A.E., 1982. Pharmacological
Rodrı̀guez, C., Rojas, J., Ågmo, A., 1993. The facilitatory effects of characterization in vivo of the novel opiate, b-funaltrexamine. J.
lisuride on male rat sexual behavior are blocked by naloxone. Pharmacol. Exp. Ther. 220, 494 – 498.
25th Annu. Conf. Reprod. Behav., East Lansing, MI. Westenberg, H.G.M., den Boer, J.A., 1994. The neuropharmacology
Rubinstein, M., Mogil, J.F., Japón, M., Chan, E.C., Allen, R.G., of anxiety: A review on the role of serotonin. In: den Boer, J.A.,
Low, M.J., 1996. Absence of opioid stress-induced analgesia in Sitsen, J.M.A. (Eds.), Handbook of Depression and Anxiety: A
mice lacking b-endorphin by site-directed mutagenesis. Proc. Biological Approach. Marcel Dekker, New York, pp. 405–446.
Natl. Acad. Sci. USA 93, 3995–4000. Wise, C.D., Berger, B., Stein, L., 1972. Benzodiazepines: anxiety-re-
Schedlowski, M., Flüge, T., Richter, S., Tewes, U., Schmidt, R.E., ducing activity by reduction of serotonin turnover in the brain.
Wagner, T.O.F., 1995. b-endorphin, but not substance P, is Science 177, 180 – 183.
increased by acute stress in humans. Psychoneuroendocrinology Wright, I.K., Upton, N., Marsden, C.A., 1992. Effect of established
20, 103 – 110. and putative anxiolytics on extracellular 5-HT and 5-HIAA in the
Schoffelmeer, A.N.M., Wardeh, G., Hogenboom, F., Mulder, A.H., ventral hippocampus of rats during behaviour on the elevated
1991. b-endorphin: A highly selective endogenous opioid agonist X-maze. Psychopharmacology 109, 338 – 346.
for presynaptic mu opioid receptors. J. Pharmacol. Exp. Ther. Wüster, M., Duka, T., Herz, A., 1980. Diazepam effects on striatal
met-enkephalin levels following long-term pharmacological ma-
258, 237 – 242.
nipulations. Neuropharmacology 19, 501 – 505.
Schreiber, R., De Vry, J., 1993. Neuronal circuits involved in the
Yamada, K., Nabeshima, T., 1995. Stress-induced behavioral re-
anxiolytic effects of the 5-HT1A receptor agonists 8-OH-DPAT,
sponses and multiple opioid systems in the brain. Behav. Brain
ipsapirone and buspirone in the rat. Eur. J. Pharmacol. 249, Res. 67, 133 – 145.
341 – 351. Yoshioka, M., Matsumoto, M., Togashi, H., Smith, C.B., Saito, H.,
Soubrié, P., Jobert, A., Thiebot, M.H., 1980. Differential effects of 1993. Opioid receptor regulation of 5-hydroxytryptamine release
naloxone against the diazepam-induced release of behavior in rats from the hippocampus measured by in vivo microdialysis. Brain
in three aversive situations. Psychopharmacology 69, 101– 105. Res. 613, 74 – 79.
Stein, L., Wise, C.D., Belluzzi, J.D., 1975. Effects of benzodiazepines Yoshioka, M., Matsumoto, M., Togashi, H., Saito, H., 1995. Effects
on central serotonergic mechanisms. Adv. Biochem. Psychophar- of conditioned fear stress on 5-HT release in the rat prefrontal
macol. 14, 29 – 44. cortex. Pharmacol. Biochem. Behav. 51, 515 – 519.
.You can also read
