Effects of oxytocin on methamphetamine-induced conditioned place preference and the possible role of glutamatergic neurotransmission in the medial prefrontal cortex of mice in reinstatement

Neuropharmacology 56 (2009) 856–865

Contents lists available at ScienceDirect

Neuropharmacology journal homepage: www.elsevier.com/locate/neuropharm

Effects of oxytocin on methamphetamine-induced conditioned place preference and the possible role of glutamatergic neurotransmission in the medial prefrontal cortex of mice in reinstatement Jia Qi a, Jing-Yu Yang a, Fang Wang a, Ya-Nan Zhao a, Ming Song b, Chun-Fu Wu a, * a b

Department of Pharmacology, Life Science and Biopharmaceutics School, Shenyang Pharmaceutical University, Shenyang 110016, China Liaoning Institute of Crime Detectives, Shenyang 110032, China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 16 January 2008 Received in revised form 11 January 2009 Accepted 12 January 2009

Accumulating evidence has shown the neuroactive properties of oxytocin (OT), a neurohypophyseal neuropeptide, and its ability to reduce the abuse potential of drugs. The present study investigated the effects of OT on the conditioned place preference (CPP) induced by methamphetamine (MAP, 2.0 mg/kg, i.p.) in mice and the possible role of glutamatergic neurotransmission in the reinstatement of CPP. The results showed that OT (0.1, 0.5, 2.5 mg, i.c.v.) significantly inhibited the acquisition and facilitated the extinction of MAP-induced CPP and abolished the reinstatement of CPP induced by restraint stress. This effect of OT could be attenuated by atosiban (Ato, 2.0 mg, i.c.v.), a selective OT-receptor antagonist. OT failed to block the expression and the reinstatement of CPP induced by MAP challenge. Extracellular glutamate (Glu) levels in the medial prefrontal cortex (mPFC) were determined using microdialysis coupled to a high-performance liquid chromatography (HPLC) with a fluorescence detection system. The results indicated that OT markedly inhibited extracellular Glu levels induced by restraint stress in CPP mice, but not those induced by MAP priming. Ato also attenuated the effects of OT on the changes in Glu levels. Therefore, these findings suggest that OT inhibits drug reward-related behaviors induced by MAP via the OT receptor, and OT blocks the reinstatement of CPP, at least partially, by interfering with the glutamatergic system in the mPFC. Ó 2009 Elsevier Ltd. All rights reserved.

Keywords: Methamphetamine Oxytocin Conditioned place preference Microdialysis Glutamate Medial prefrontal cortex

1. Introduction Oxytocin (OT), a neurohypophyseal neuropeptide synthesized and released from the hypothalamo-neurohypophyseal system, has a wide range of behavioral effects beside its classic peripheral endocrine function. Parvocellular OT efferents of the paraventricular nucleus project to extra-hypothalamic brain areas and release OT into the brain (Sofroniew, 1983). It has been shown that OT is able to reduce the abuse potential of opiates and cocaine (Kovacs et al., 1987, 1990). We previously reported that OT inhibited methamphetamine (MAP)-induced hyperactivity by altering the dopamine (DA) turnover in the mesolimbic region of mice (Qi et al., 2008). These observations suggest that OT has the potential to interact with the reward system in the brain. While earlier studies have shown effects of OT on behavioral changes induced by drugs of abuse, especially psychostimulants (Sarnyai and Kovacs, 1994), no

* Corresponding author. Tel./fax: þ86 24 2384 3567. E-mail addresses: [email protected], [email protected] (C.-F. Wu). 0028-3908/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropharm.2009.01.010

evidence for OT impacting MAP-induced reward-related behavior has been obtained until now. MAP is a psychostimulant and one of the major drugs of abuse in many parts of the world, with approximately 10 million people aged 12 and upwards having abused methamphetamine during their lifetime in USA (Sheridan et al., 2006; NIDA report, 2007). Although the precise neurobiological mechanisms underlying its addictive behavior remain unknown, the rewarding effect of the drug plays a critical role (Sulzer et al., 2005). The conditioned place preference (CPP) paradigm, which contains different phases including acquisition, expression, extinction and reinstatement, is considered as a reliable measure of the reward properties of drugs including MAP in animals (Bardo and Bevins, 2000). Furthermore, it has been demonstrated that preference for the drug-paired environment can be reinstated by drug priming injections or stress (Parker and McDonald, 2000; Wang et al., 2002). Some investigations have indicated that OT can attenuate cocaine-induced stereotype sniffing behavior in rats (Sarnyai et al., 1991), exploratory hyperactivity in mice (Sarnyai et al., 1990), and OT-modulated behavioral adaptation to repeated treatment with cocaine in rats (Sarnyai et al., 1992). Although numerous studies have explored the

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

effect of OT on the reward of drugs of abuse employing different behavioral paradigms (Sarnyai et al., 1991, 1992; Sarnyai and Kovacs, 1994), no studies have been performed to investigate the effect of OT on MAP-induced CPP. Therefore, the present study was designed to evaluate the role of OT on MAP-induced reward response using the CPP paradigm. Glutamate (Glu), an excitatory amino acid, is involved in the long-lasting adaptative changes that occur in response to drug exposure (Pulvirenti, 2003). The relationship between the neurochemical function of MAP and Glu neurotransmission has been clearly established (Raudensky and Yamamoto, 2007; Ohmori et al., 1996). One of the major glutamatergic innervations of the ventral tegmental area (VTA) originates in the prefrontal cortex (PFC) (Taber et al., 1995), meanwhile the PFC receives dopaminergic projection from the VTA (Wolf, 2002). The synaptic plasticity of dopaminergic and glutamatergic neurotransmission has been reported to play key roles in psychostimulant abuse and relapse (Pierce and Kumaresan, 2006). The medial prefrontal cortex (mPFC), as a part of the PFC, contains a high density of glutamatergic neurons and projections, and has received considerable attention because of its involvement in drug reward behaviors, such as self-administration (Goeders et al., 1986), CPP (Zavala et al., 2003) and behavioral sensitization (Hao et al., 2007). Our previous study demonstrated that the glutamatergic system in the mPFC was involved in morphine dependence and withdrawal (Hao et al., 2005). Accumulated data show that OT inhibits Glu activation by binding to its receptors in the spinal cord, and prior OT application blocks increased neuronal firing rate produced by Glu in antinociceptive progress (Condes-Lara et al., 2005, 2006; Jo et al., 1998; Robinson et al., 2002). Furthermore, OT projections target multiple areas of the brain, including the brain stem, limbic system, especially the projection to the central amygdala (CeA) (Sofroniew, 1983), which can regulate the stress-related behavior (Neumann, 2008). Other investigations showed that under forced swimming conditions OT is released within the CeA of male rats where it inhibits the local release of excitatory amino acids, such as Glu, and thereby modulates the stress response (Bosch et al., 2007; Ebner et al., 2005). In consideration of the importance of the mPFC in drug reinstatement, the present study also investigated the effects of the extracellular Glu levels on the action of OT during the subsequent reinstatement of MAP-induced CPP. 2. Materials and methods 2.1. Animals Male Swiss mice, initially weighing 28–32 g, were obtained from the Department of Laboratory Animal Science, Shenyang Pharmaceutical University. The animals were housed in groups of six in clear plastic cages with free access to water and food in a room kept at a controlled ambient temperature (22  1  C), humidity (50  10%), and a 12-h light/dark cycle (lights on at 08:00). The mice were acclimatized to the housing conditions and handled for 7 days before starting the experimentation. New groups of animals were used in each experiment. Experiments were run between 09:00 and 16:00 under standard conditions with controlled temperature, dim lighting, and low noise. Every effort was made to minimize animal suffering and the number of animals used. All experiments were conducted according to the National Institutes of Health (NIH) Guide for the Care and Use of Laboratory Animals (NIH Publications No. 8023, revised 1996). The experimental procedures were approved by the University Committee on Animal Care and Use. 2.2. Chemicals MAP (purity > 98%, gift from Liaoning Institute of Crime Detectives) was dissolved in physiological saline. OT and atosiban (Ato) were purchased from Sigma Chemicals (St. Louis, MO, USA) and Sinopep Pharmaceutical Inc. (Hangzhou, China), respectively, and were dissolved in artificial cerebrospinal fluid (aCSF) (124 mM NaCl, 5 mM KCl, 1.25 mM NaH2PO4, 2 mM MgSO4, 10 mM glucose, pH ¼ 7.4). OT (0.1, 0.5, 2.5 mg/ml/mouse) and Ato (2.0 mg/ml/mouse) were administered intracerebroventricularly (i.c.v.) in a volume of 1 ml/mouse. MAP was administered

857

intraperitoneally (i.p.) in a volume of 0.1 ml/10 g, and a dose of 2.0 mg/kg was used based on the previous reports which showed that this induces strong locomotor sensitization, but never produces stereotypical behaviors, such as sniffing, circling, etc. (Shimosato and Ohkuma, 2000; Ginawi et al., 2005). The compounds ophthalaldehyde (OPA), a derivatization reagent and Glu were purchased from Sigma Chemicals. Glu can be detected by a fluorescence detector following precolumn derivatization with OPA. Ringer’s solution contained 147 mM NaCl, 4 mM KCl, and 2.3 mM CaCl2. All the other chemicals used were from commercial sources and of the highest available purity. 2.3. Apparatus The CPP apparatus was made of opaque Plexiglass and consisted of two rectangular-based chambers (20  15  15 cm each) separated by a guillotine door (5  5 cm) (Shenyang Pharmaceutical University, Shenyang, China). A battery of eight place-preference devices suitable for the application of an ‘‘unbiased’’ placeconditioning design was employed (Hao et al., 2008). Two chambers featured chambers with distinct visual and tactile cues. One of the chambers was colored with alternating black and white horizontal stripes (width 1 cm), and the other was colored with black dots (diameter 2.5 cm) on a white background. The floor in the left chamber (striped walls) had a relatively thinly embossed texture obtained with 2 mm2 punches, whereas that placed in the right chamber (black dots walls) had larger 4 mm2 punches. Entrance into and movements within the chambers were automatically recorded by computer, which recorded the time spent in each chamber, the locomotor activity and the location of the mouse in the apparatus during the session. A computer simultaneously operated the eight devices that were enclosed in sound-attenuating cubicles (Brabant et al., 2005). Animals were recorded on video camera and place preference behavior was analyzed using a tracking program (Computer Technology Center of Shenyang Pharmaceutical University, Shenyang, China) (Hao et al., 2008). Locomotor activity was measured by an ambulometer with four activity chambers (Model ZIL-2, Institute of Materia Medica, Chinese Academy of Medical Sciences, China). Activity chambers of 25  15 cm (diameter  height) consisted of opaque perspex walls and floors, and transparent perspex lids. Each chamber was equipped with infrared photobeams, which were connected to a computer to quantify locomotor activity. 2.4. Behavioral analysis The experimental procedures were followed as described in the references (Maldonado et al., 2007; Shoblock et al., 2005) and are shown in Fig. 1. 2.4.1. Cannulation surgery Surgical procedures for implantation of intracerebroventricular cannula were performed under anesthesia with chloral hydrate (400 mg/kg, i.p.). A 26-gauge stainless-steel guide cannula was directed into the lateral cerebral ventricle (A/P 0.2 mm, M/L þ1.0 mm, D/V 2.5 mm) unilaterally according to the atlas of Paxinos (Paxinos and Franklin, 2001) and was fixed to the skull by dental cement. Cannula was sealed to prevent obstruction and secured to the skull surface with dental cement. When the dental cement had hardened, a dummy cannula, cut to the same dimensions as the guide cannula, was inserted to seal the top of the guide cannula to prevent clogging and minimize possible infection. Antibiotics such as penicillin were given prophylactically. Intracerebroventricular injection was performed by inserting a 33-gauge stainless-steel injector tube into the guide cannula. The injector tube was attached to PE-10 tubing fitted to a 10-ml Hamilton syringe. One microliter of solution was then infused into the lateral cerebral ventricle over 2 min (Hao et al., 2007). At the end of the experiments, the mice were anaesthetized and sacrificed, then the brain was removed, and the trace of the undercutting was examined histologically. 2.4.2. Locomotor experiment Before beginning the experiments, mice were handled for 10 min and habituated to the apparatus without any injection for 60 min for 2 days. On the day of the test, five groups of mice were given aCSF, OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) and Ato (2.0 mg/ml/mouse, i.c.v.), respectively, and placed in the test chambers where counts of motor activity were recorded for 60 min. 2.4.3. Acquisition of MAP-induced CPP The experiment included three phases: three daily habituation sessions, six daily conditioning sessions and a final test session. At the beginning of the first session, all mice underwent surgery for implantation of an intracerebroventricular cannula and were then allowed 24 h to recover. During the first phase or preconditioning, animals were habituated to the apparatus by being placed in a particular chamber designated as the start chamber and allowed to freely explore both chambers for 15 min (900 s) each day for 2 days. The start chamber was counterbalanced with half the mice starting on the left side, and the other half starting on the right side of the conditioning chamber. On the third day, the preCPP test was carried out, which meant that the time each mouse spent in the two chambers was recorded automatically for a 900-s period. Animals showing a strong

858

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

Fig. 1. Experimental schedule for the acquisition, expression, extinction, and reinstatement of MAP-induced CPP in mice and the administration of OT. Each experiment utilized a new group of animals. Animals underwent six daily conditioning sessions after habituating to the apparatus. Following the establishment of CPP, mice were exposed to the apparatus with free access to both chambers for 1 h, which was the extinguishing session. Once the extinction criterion was met, the animals were tested for the presence of CPP the following day by being placed in the apparatus with free access to both chambers for 15 min after being given a saline-priming injection. When the extinction was determined, the reinstatement of CPP was performed by MAP (1.0 mg/kg) priming or restraint stress. The effects of OT (0.1, 0.5, 2.5 mg/ml/mouse) on the different sessions of CPP were assessed during the procedure.

unconditioned aversion or preference (less than 33% or more than 66% of the session time, i.e. 300 and 600 s, respectively) for any chamber were discarded (Maldonado et al., 2007). During the second phase, beginning the day after the habituation sessions, animals underwent an experiment with an unbiased counterbalanced CPP design including six daily conditioning sessions. On even days (days 4, 6 and 8), mice received either MAP (2.0 mg/kg, i.p.) or saline 30 min after OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) or aCSF was administered and then the animals were confined for 1 h in the drug-paired chamber. Ato (2.0 mg/ml/mouse, i.c.v.) was administered 10 min before OT administration. Within each group, the drug-paired chamber was counterbalanced, such that half the mice were confined to the striped chamber, while the other half were confined to the black dots chamber. This is an important step in the experimental procedure that avoids any preference bias before conditioning. On odd days (days 5, 7 and 9), mice were given OT or aCSF 30 min before saline was injected and confined for 1 h in the opposite compartment (saline-paired chamber). In the third phase, which took place 24 h after the last pairing session, mice were placed in the apparatus and given free access to the two chambers for 15 min and the amount of time spent in each chamber was recorded. This period of time was shown in a previous study to be adequate for the expression of MAP-induced CPP in mice (Kim et al., 1998). Doses were chosen based on previously published research in other behavioral paradigms (Wu and Yu, 2004; Kovacs et al., 1998). Furthermore, in the present study, the CPP paradigm was employed to determine whether OT had intrinsic reinforcing or aversive properties when used alone. 2.4.4. Expression of MAP-induced CPP The day after the pre-CPP test was completed, mice underwent conditioning during which they were exposed to each of the following three conditioning sessions: (1) on days 4, 6 and 8, mice received either MAP (2.0 mg/kg) or saline and were then confined for 1 h in the drug-paired chamber; (2) on days 5, 7 and 9, animals were injected with saline and confined in the opposite chamber for 1 h. The designation of drug-paired chamber was random and resulted in approximately equal representation of the two conditioning chambers as the drug-paired chamber across groups. On the following day, animals were given OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) or aCSF 30 min before being placed in the apparatus, with free access to both chambers, to determine the effect of OT on the expression of MAP-induced CPP. Ato (2.0 mg/ml/mouse, i.c.v.) was administered 10 min before OT administration. The time spent in each chamber was automatically recorded for 15 min. The difference, in seconds, between the times spent in the drug-paired chamber in the post-CPP test and that spent in the pre-CPP test is a measure of the degree of reward induced by MAP. If there is no difference, then OT has blocked MAP-induced CPP, while if there is a difference this indicates the drug cannot block this reward.

2.4.5. Extinction of MAP-induced CPP Following the establishment of CPP (on day 10), all mice underwent surgery for implantation of an intracerebroventricular cannula and were allowed 24 h to recover. The animals were exposed to the apparatus with free access to both chambers for 1 h, 30 min after injection of OT (0.1, 0.5, 2.5 mg/ ml/mouse, i.c.v.) or aCSF for five consecutive days (days 12–16) as extinction days 3–7. Ato (2.0 mg/ml/mouse, i.c.v.) was administered 10 min before OT administration. MAP was not administered in this session. A test for extinction of CPP was conducted every day for 15 min immediately after mice were placed in the apparatus. The criterion to consider the preference extinguished was the lack of statistical significance between the time spent by the animals of each group in the drug-paired chamber and that of the pre-CPP session but with the post-CPP. 2.4.6. Drug-primed reinstatement of MAP-induced CPP Mice, which met with the criterion for extinguishing, were given a priming injection of saline and immediately tested for reinstatement of CPP on the following day. Because saline priming could be thought as a mild stress or a cue to arouse CPP, mice were regarded as having stable extinction from CPP in this way (Zavala et al., 2003). Mice that failed to maintain extinction of CPP after received the saline priming underwent additional extinction training, and the other mice that remained extinguished after the saline priming were then tested for reinstatement of CPP. Animals that did not meet this criterion by day 21 were removed from the study. On the test day, the animals were given Ato (2.0 mg/ml/mouse, i.c.v.) 10 min before OT administration, and then OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) or aCSF was injected 30 min prior to a priming injection of MAP (1.0 mg/kg, i.p.). All the priming injections were given 15 min before the reinstatement tests in the colony room, noncontingent to the place where the previous conditioning injection was given. 2.4.7. Restraint stress-induced reinstatement of MAP-induced CPP After the extinction was determined, animals were submitted to immobilization-induced stress for 15 min. Restraint is a powerful stressor which is widely used in many studies (Lu et al., 2003). To induce restraint, when mice spontaneously passed into a cylindrical glass tube (4 cm in diameter and 10 cm in length, with holes 0.5 cm in diameter to permit respiration), two test tubes 0.5 cm in diameter were carefully introduced underneath the animal thus reducing the size of the tube to 3 cm so that it was impossible for the animal to turn. On the test day, mice were given OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) or aCSF was injected 30 min prior to the restraint stress. Ato (2.0 mg/ml/mouse, i.c.v.) was given 10 min before OT administration. Immediately after restraint, the reinstatement test was performed on the animals for 15 min.

J. Qi et al. / Neuropharmacology 56 (2009) 856–865 2.5. Microdialysis 2.5.1. Surgery A U-shaped dialysis probe (Fisone et al., 1987) was implanted vertically into the mPFC (Dalley et al., 2004) when analyzing the changes of Glu levels during the reinstatement process. The internal diameter of the probe was 200 mm and the external diameter was 310 mm. The coordinates for the dialysis probe were: A/P þ2.3 mm, M/L 0.5 mm, D/V 3.0 mm from the bregma and dural surface according to the atlas of Paxinos (Paxinos and Franklin, 2001). The active region of the dialysis probe was 3.0 mm in length. Mice were housed right after the operation and allowed 5 days to recover before the microdialysis experiment. Antibiotics such as penicillin were given prophylactically. At the end of the experiments, the mice were anaesthetized and sacrificed, then the brain was removed, and the trace of the undercutting was examined histologically. 2.5.2. Brain microdialysis procedure Brain microdialysis was performed to detect the levels of Glu in the mPFC of mice undergoing behavioral observation (Experiment 2.4.6 and 2.4.7). On the day of the experiment, Ringer’s solution was perfused through the dialysis probe at a rate of 2.0 ml/min using a microinfusion pump. The dialysate obtained over the first 30 min was discarded, and the perfusate was collected every 20 min. After Glu levels had stabilized, three consecutive samples were collected to determine basal levels (Yan et al., 2003; Hao et al., 2007). Mice, which were withdrawn from MAP, were injected with OT (2.5 mg/ml/mouse, i.c.v.) or aCSF 30 min prior to restraint for 15 min or were provoked by MAP (1.0 mg/kg). Ato (2.0 mg/ml/mouse, i.c.v.) was given 10 min before OT administration. The dialysis samples were collected for 200 min. 2.5.3. Determination of Glu Glu was measured by reverse-phase high-performance liquid chromatography (HPLC, 150  4.6 mm, C18, 5 mm particle size column, Agilent Technologies, USA) coupled to a fluorescence detector (excitation wavelength: 340 nm, emission wavelength: 450 nm, RF-10AxL, Shimadzu, Japan), following precolumn derivatization with OPA (Hao et al., 2005). The OPA solution was prepared as follows: 9 mg OPA was dissolved in 167 ml methanol, then 1.5 ml 0.4 M sodium borate and 7 ml 2mercaptoethanol were added and mixed well. The solution was stored at 4  C for one week and protected from light. Gradient elution was used to separate the mixture of amino acids. Mobile phase A consisted of 0.1 M sodium acetate buffer, pH 6.7 while mobile phase B consisted of 98% methanol and 2% tetrahydrofuran. The flow rate of the pump was set at 1.0 ml/ min. Both mobile phases were passed through a 0.22 mm filter and the column temperature was maintained at 37  C. 2.5.4. Histological verification In pilot studies, the anatomical accuracy of the needle placements was verified by injecting 5 ml trypan blue and dissecting the brains. Ninety percent of the animals showed dye filling all ventricles. At the end of the experiments, the mice were deeply anesthetized with pentobarbital (50 mg/kg, i.p.) and killed by decapitation, and then histological verification of probe placement was made from frozen coronal sections (20 mm in thickness) using a freezing microtome (AS-620, Shandon, USA). Mice with the correct cannula and probe placements were included in the final analysis (Fig. 2).

2.6. Statistical analysis The time spent in the MAP-paired chamber was expressed as mean  S.E.M. and was analyzed using a two-way analysis of variance (ANOVA) with repeated measures with groups as between-subjects factors and days as within-subjects factors. Data were analyzed for significant differences with a post hoc Fisher’s least significant difference (LSD) test when appropriate. One-way ANOVA followed by a post hoc Fisher’s LSD test was only run if there was an interaction between day and group. The levels of Glu were expressed as the percentage change compared with the respective basal value that was the mean of three consecutive samples before drug administration within a variance of 10%. Each point was expressed as mean  S.E.M. To assess the significance of differences between groups, the summed effects of drugs over the course of an experiment were used to compare the area under the curve (AUC) of the treatment by multifactor ANOVA or general linear models (GLM) followed by a post hoc Fisher’s LSD test. Two-way ANOVA was used to evaluate the interaction between every two groups. All statistical procedures were performed using the SPSS 13.0 software for windows (SPSS Inc., Chicago, IL, USA). The level of significance was taken as P < 0.05.

3. Results 3.1. Effect of OT on locomotor activity of mice As shown in Fig. 3 (n ¼ 12), OT (0.1, 0.5, 2.5 mg/ml/mouse, i.c.v.) or Ato (2.0 mg/ml/mouse, i.c.v.) administration per se did not affect the

859

locomotor activity in mice during the test period (F(4,55) ¼ 0.313, P > 0.05). 3.2. Effects of OT on the acquisition of MAP-induced CPP As shown in Fig. 4 (n ¼ 10–14), repeated measures ANOVA revealed significant effects of day (F(1,84) ¼ 22.99, P < 0.001), group (F(6,84) ¼ 3.40, P < 0.01) and day  group (F(6,84) ¼ 3.41, P < 0.01). Fisher’s LSD tests revealed that MAP (2.0 mg/kg) produced a significant place preference (P < 0.01), while no preference for either chamber was seen in mice in the saline group. OT (2.5 mg/ml/ mouse, i.c.v.) reduced the time spent in the MAP-paired chamber as compared with MAP group on the post-CPP test day significantly (P < 0.01), although no statistical difference was found after OT (0.1, 0.5 mg/ml/mouse, i.c.v.) administered. However, Ato (2.0 mg/ml/ mouse, i.c.v.) attenuated the inhibition by OT (2.5 mg/ml/mouse, i.c.v.) markedly (P < 0.05). OT (2.5 mg/ml/mouse, i.c.v.) and Ato (2.0 mg/ml/mouse, i.c.v.) per se did not produce any significant CPP or conditioned place aversion (CPA) as compared with saline group when administered alone (P ¼ 0.63 and P ¼ 0.77, respectively). 3.3. Effects of OT on the expression of MAP-induced CPP As shown in Fig. 5 (n ¼ 10), repeated measures ANOVA revealed a significant effect of day (F(1,57) ¼ 26.45, P < 0.001), but no effects of day  group (F(5,57) ¼ 1.11, P > 0.05) and group (F(5,57) ¼ 1.42, P > 0.05). The MAP administration resulted in a significant preference for the drug-paired chamber (P < 0.05). OT (0.1, 0.5, 2.5 mg/ml/ mouse, i.c.v.) had no statistically significant effects on the expression of CPP compared with the MAP group, suggesting that OT failed to inhibit the expression of CPP induced by MAP. No significant difference in the time spent in the drug-paired chamber was found after Ato was co-administered to the mice. 3.4. Effects of OT on the extinction of MAP-induced CPP As shown in Fig. 6 (n ¼ 10–14), repeated measures ANOVA performed on all the groups revealed significant effects of day (F(6,396) ¼ 25.21, P < 0.001), group (F(5,66) ¼ 41.09, P < 0.001) and day  group (F(30,396) ¼ 3.78, P < 0.001). Fig. 6B shows the time– response curve for extinction of CPP induced by MAP in mice. Separate one-way ANOVA revealed a significant group difference on extinction day 1 (Ext 1), Ext 3, Ext 4, Ext 5, Ext 6 and Ext 7 between the saline and the MAP groups (P < 0.01). Mice in the MAP group showed a marked preference for the drug-paired chamber on Ext 1, Ext 2 and Ext 3 after the post-condition phase (P < 0.001). Then, the place preference became weaker at Ext 4, however, it failed to return to the same level as the respective saline groups until Ext 7 (P < 0.05). Thus, the MAP-induced CPP had not disappeared seven days after the last drug-pairing session according to the present experimental protocol (Fig. 1). On the other hand, OT showed an accelerating effect on the extinction of MAP-induced CPP for Ext 3 (OT 0.1 mg, P ¼ 0.040, data not shown), Ext 4 (OT 0.5 mg, P ¼ 0.023, data not shown), and Ext 6 (OT 2.5 mg, P ¼ 0.041), respectively, compared with the MAP group. Furthermore, the effects of OT were observed on Ext 4 (OT 0.1 mg, P ¼ 0.095; OT 0.5 mg, P ¼ 0.109, data not shown) and Ext 5 (OT 2.5 mg, P ¼ 0.089) as compared with the respective saline groups, and the extinction was identified on Ext 6 and Ext 7, which suggests that the animals failed to show a preference for the MAP-paired chamber and OT (0.1, 0.5, 2.5 mg/ml/mouse) showed the accelerated effects on CPP extinction compared with MAP group. Moreover, based on the results of Ext 6 and Ext 7 (P ¼ 0.043, P ¼ 0.039, respectively), it is found that Ato attenuated the effect of OT (2.5 mg/ml/mouse) significantly.

860

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

Fig. 2. Location of the i.c.v. injection cannula and microdialysis probe in the mPFC. Silhouettes of the cannula and probe tracks were drawn onto representative sections of the mouse brain redrawn from the atlas of Paxinos and Franklin (Paxinos and Franklin, 2001).

3.5. Effects of OT on the MAP-primed reinstatement of MAP-induced CPP The results obtained for the reinstatement of MAP-induced CPP by priming injections of MAP (1.0 mg/kg) plus OT can be seen in Fig. 7. Mice that failed to maintain extinction of MAP-CPP after receiving the saline prime (0–4 out of 14 per group) underwent additional extinction training. Mice that remained extinguished (n ¼ 10–14) after the saline prime were tested on day 22. Repeated measures ANOVA revealed significant effects of day (F(4,264) ¼ 9.27, P < 0.001), but no effects of day  group (F(20,264) ¼ 1.25, P > 0.05) and group (F(5,66) ¼ 1.79, P > 0.05). A Fisher’s LSD test showed that the time spent in the drug-paired chamber was higher in the post-CPP test with respective saline groups in all mice undergoing MAP administration (P < 0.01). The post hoc LSD test indicated no significant differences in the time

Fig. 3. Time course of the effects of OT (0.1, 0.5, 2.5 mg/ml/mouse) or Ato (2.0 mg/ml/ mouse) on locomotor activity in mice. Mice were given i.c.v. injections of aCSF, OT or Ato 30 min before being tested for locomotor activity. The data are expressed as means  S.E.M. (n ¼ 12). Locomotor activity was analyzed using a two-way ANOVA with post hoc LSD tests.

spent in the drug-paired chamber among the groups after the saline-primed condition on day 20 (P > 0.05), which indicates that the extinction was stable. The priming injection of MAP (1.0 mg/kg, i.p.) completely reinstated the extinguished MAP-CPP (P < 0.001). Pretreatment with OT had no effect on abstinence and failed to inhibit the provoking effect of MAP in MAP-treated mice (P > 0.05). No significant difference was found between the OT (2.5 mg/ml/ mouse, i.c.v.) þ MAP group and the Ato þ OT þ MAP group.

Fig. 4. Effects of different doses of OT on the acquisition of CPP induced by MAP (2.0 mg/kg) in mice and the effect of OT (2.5 mg/ml/mouse) on the acquisition of CPP when used alone. On the test day, mice were placed into the apparatus and given free access to the two chambers for 15 min and the amount of time spent in each chamber was recorded. Results are presented as the mean  S.E.M. (n ¼ 10–14) time spent in the drug-paired chamber. Statistical analysis was performed by two-way ANOVA repeated measure with post hoc Fisher’s LSD tests. One-way ANOVA followed by a post hoc LSD test was used to determine the difference between groups on test day. **P < 0.01 compared with the saline group; ##P < 0.01 compared with the MAP group.

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

861

3.7. Interaction of OT and MAP priming on the extracellular Glu contents in the mPFC As shown in Fig. 9A, no statistical difference was found in the changes in Glu levels after OT administration per se. MAP challenge induced a significant increase in Glu levels in the saline þ MAP group and the MAP þ MAP group compared with the corresponding saline and MAP groups (F(1,18) ¼ 5.051, P < 0.05; F(1,17) ¼ 4.634, P < 0.05) (Fig. 9A and B). OT markedly attenuated the increased Glu levels in the OT þ saline þ MAP group challenged by MAP (F(1,18) ¼ 4.853, P < 0.05) (Fig. 9A). However, OT only showed a tendency to inhibit the MAP-challenged Glu level increase in mice after CPP was established, but no statistical difference was found (F(1,18) ¼ 3.051, P > 0.05) (Fig. 9B). Two-way ANOVA analysis showed no interaction between the MAP þ MAP group and the OT þ MAP þ MAP group in terms of the action on Glu release in the mPFC (F(1,18) ¼ 1.08, P > 0.05) (Fig. 9B). Fig. 5. Effects of different doses of OT on the expression of CPP induced by MAP (2.0 mg/kg) in mice. The time spent in each chamber was automatically recorded over 15 min. Results are presented as the mean  S.E.M. (n ¼ 10) time spent in the drugpaired chamber. Statistical analysis was performed by two-way ANOVA repeated measure with post hoc Fisher’s LSD tests. *P < 0.05 compared with the saline group.

3.6. Effects of OT on the restraint stress-induced reinstatement of MAP-induced CPP Mice that remained extinguished (n ¼ 10–14) after the saline prime were tested on day 22. As shown in Fig. 8, repeated measures ANOVA revealed significant effects of day (F(4,264) ¼ 52.24, P < 0.001), day  group (F(20,264) ¼ 1.86, P < 0.05) and group (F(5,66) ¼ 4.57, P < 0.01). A Fisher’s LSD test showed that all the groups spent significantly less time in the drug-paired chamber, and saline priming failed to reinstate CPP (P > 0.05) after the extinction session. Restraint stress for 15 min completely reinstated the extinguished MAP-CPP (P < 0.01). Pretreatment with OT (0.1, 0.5, 2.5 mg) inhibited the stress-induced CPP in MAP-treated mice significantly (P < 0.05). Furthermore, Ato (2.0 mg/ml/mouse, i.c.v.) attenuated the effect of OT (2.5 mg/ml/ mouse, i.c.v.) markedly (P < 0.05).

3.8. Interaction of OT and restraint stress on the extracellular Glu contents in the mPFC As shown in Fig. 10A, extracellular Glu levels in the mPFC were increased significantly by restraint stress in the saline þ stress group compared with that in the saline group (F(1,18) ¼ 9.37, P < 0.05). As demonstrated by the results in Fig. 10B, a similar phenomenon was found between the MAP þ stress group and the MAP group (F(1,17) ¼ 4.443, P < 0.05), i.e. restraint stress induced a significant increase in Glu levels in the mPFC. The maximal increase was 197% above the baseline and this was achieved about 20 min after stress. OT significantly inhibited the elevated levels of Glu in the saline þ stress group and the MAP þ stress group (P ¼ 0.019 and P ¼ 0.012, respectively). Furthermore, Ato attenuated the effect of OT markedly in the Ato þ OT þ saline þ stress group and the Ato þ OT þ MAP þ stress group (P ¼ 0.036 and P ¼ 0.038, respectively). Two-way ANOVA analysis showed a significant interaction between the MAP þ stress group and the OT þ MAP þ stress group in terms of the action on Glu release in the mPFC (F(1,18) ¼ 5.413, P < 0.05) (Fig. 10B).

Fig. 6. Effects of different doses of OT on the extinction of CPP induced by MAP (2.0 mg/kg) in mice. (A) Results are presented as the mean  S.E.M. time spent in the drug-paired chamber (n ¼ 10–14). The MAP injections resulted in a significant preference for the drug-paired chamber compared with the saline group (***P < 0.001). Data in (B) are expressed as mean  S.E.M. of 10–14 animals per group. Statistical analysis was performed by two-way ANOVA with repeated measure. Separate one-way ANOVA followed by a post hoc Fisher’s LSD test was used to revealed a significant group difference on extinction day (Ext 1, 3, 4, 5, 6 and 7) between the saline and MAP groups. *P < 0.05, **P < 0.01, ***P < 0.001 compared with the respective saline groups; #P < 0.05, ##P < 0.01 compared with the respective MAP groups; þP < 0.05 compared with the OT (2.5 mg) þ MAP group.

862

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

Fig. 7. Effects of different doses of OT on the CPP reinstatement induced by MAP priming injection in mice. Data are expressed as mean  S.E.M. of 10–14 animals per group. Statistical analysis was performed by two-way ANOVA repeated measure with post hoc Fisher’s LSD tests. **P < 0.01 compared with the saline group; ***P < 0.001 compared with the saline group receiving a saline injection on the reinstatement day.

4. Discussion The present study systematically investigated the effects of OT on MAP-induced CPP and the possible role of glutamatergic neurotransmission in the mPFC in reinstatement induced by MAP priming or stress. As expected, the administration of 2.0 mg/kg MAP to mice produced CPP (Kim et al., 1998). The present results are the first to show that OT inhibits the acquisition of MAPinduced CPP. There are several possible explanations for this novel observation. Firstly, the decreased acquisition of MAP-induced CPP might be due to OT blocking the reinforcing effects induced by MAP. It is well known that the reinforcing effect is related to mesolimbic

Fig. 8. Effects of different doses of OT on restraint stress-induced CPP reinstatement in mice. Data are expressed as mean  S.E.M. of 10–14 animals per group. ***P < 0.001 compared with the saline group; **P < 0.01 compared with the saline group receiving restraint stress on the reinstatement day; ##P < 0.01 compared with the MAP group, þ P < 0.05 compared with the OT (2.5 mg) þ MAP group.

dopaminergic neurotransmission. Studies have demonstrated that OT attenuates the change in DA levels induced by many reinforcing drugs, such as apomorphine (Succu et al., 2007), cocaine (Kovacs et al., 1990), morphine (Kovacs et al., 1998) and MAP (Qi et al., 2008). Earlier studies indicated that OT administration does not act on DA release or postsynaptic DA receptors, but modulated the presynaptic processes (Kovacs et al., 1990; Sarnyai et al., 1990). Secondly, the decreased acquisition of MAP-induced CPP could be due to the fact that OT reduced the ability to learn the association between reward and special location. OT attenuated learning and memory processes in animals and human volunteers (Ferrier et al., 1980; Kovacs and Telegdy, 1982) and it can, therefore, be considered as an amnestic neuropeptide (Bielsky and Young, 2004; Heinrichs et al., 2004). A third possible explanation is that OT could in itself cause an aversion to the conditioned place. However, the present results show that OT does not exhibit significant motivational properties in the CPP, i.e. there were no variations in the time spent by the mice in the OT-paired chamber after conditioning. Therefore, this possibility can be excluded. Contrary to the third supposition, Liberzon et al. have reported that OT produces a preference for the repeatedly associated environment (Liberzon et al., 1997). Since we did not observe a preference or an aversion it is likely that differences in the species of animals, the route of drug administration, the doses of OT, and the experimental design may have contributed to the differences between our results and those of Liberzon et al. The present results showed that when OT was administered prior to the expression of the CPP, on the post-CPP day, it failed to block expression of MAP-induced CPP, which suggests that memory retrieval is not compromised (Shoblock et al., 2005; Kotlinska and Biala, 1999; Graham et al., 2007). Expression of CPP would be predicted to be unaffected by OT, since the associations are already learned, and OT is incapable of restoring the preference for the MAP-paired chamber. Extinction of conditioned responses based on aversive or appetitive unconditioned stimuli (US) is used as a therapeutic measure to reduce cravings (Davis and Myers, 2002). Fig. 6 shows that OT significantly facilitates the extinction of CPP compared with the MAP group, although no dose-dependence was clear. It is reported that OT is differentially involved in behavioral regulations, and the literature suggests that it impairs memory when given by the i.c.v. route (Kovacs and Telegdy, 1982; Engelmann et al., 1996). OT treatment increases the extinction of pole-jumping avoidance behavior (Bohus et al., 1978) in a manner similar to direct application of OT and its fragment into the ventral hippocampus (Ibragimov, 1990). OT antiserum given i.c.v. causes the opposite effect, which was interpreted as an amnestic action of the endogenous neuropeptide (Bohus et al., 1978). It has been demonstrated that OT is able to influence the development of tolerance to, dependence on and reinstatement for abused drugs (Sarnyai and Kovacs, 1994). Drug-associated stimuli, stress, and drugs of abuse are hypothesized to trigger reinstatement to drug reward-related behaviors (Lu et al., 2003; Itzhak and Martin, 2002). Studies have shown that stressors, such as restraint (Pacchioni et al., 2002), footshock (Wang et al., 2002), tail pinching (Katz and Roth, 1979), and defeat (Covington and Miczek, 2001), induce drug reward and reinstatement efficiently. In the present study, restraint stress and MAP priming were employed to determine the effects of OT on reinstatement of CPP, and the results show that OT abolishes the reinstatement of CPP induced by restraint stress significantly but no that induced by MAP. The primary neural pathways through which drug priming and stress can trigger CPP reinstatement are different. Psychostimulants can produce rewarding effects by activating the mesolimbic dopamine system (Wise and Bozarth, 1987; Di Chiara and Imperato, 1988), consisting of dopaminergic neurons in the VTA and their

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

863

Fig. 9. Effects of OT on the Glu release in the mPFC induced by MAP priming of CPP mice. The data are expressed as mean  S.E.M. percent baseline Glu and each point represents a 20 min dialysate sampling period. MAPC represents the MAP-CPP group, and MAPP represents the MAP priming treatment. n ¼ 9–10, aP < 0.05 two-way ANOVA with post hoc Fisher’s LSD tests compared with the saline group; bP < 0.05 compared with the saline þ MAPP group; cP < 0.05 compared with the MAPC group.

target neurons in the nucleus accumbens (NAc). Considerable evidence suggests that the ability of psychostimulants to trigger reinstatement of drug reward-related behavior involves their direct ability to activate the mesolimbic dopamine system. The enhanced dopaminergic neurotransmission leads to the release of Glu in the PFC. Therefore, the elevated Glu level here is the result of the reinstatement induced by MAP. On the other hand, stress can activate VTA dopamine neurons through activation of an excitatory glutamatergic projection from the PFC to the VTA (Moghaddam, 1993). The elevated Glu level here is the reason for the reinstatement induced by stress. This projection forms monosynaptic inputs to VTA dopaminergic neurons (Sesack and Pickel, 1992), and can trigger dopamine release in the NAc (Murase et al., 1993). The mPFC, a part of the mesocorticolimibic system, provides a major glutamatergic projection to the VTA and the NAc to regulate DA release and simultaneously receives dopaminergic inputs from the VTA and NAc (Montaron et al., 1996; Conde et al., 1995), which is crucial for the rewarding effect of MAP. Other studies have shown that lesions in the mPFC, or its subregions, affect cocaine priminginduced reinstatement, suggesting that the PFC may serve as a possible common pathway for reinstatement of drug reward by stressors, priming injections of drugs, and drug-related cues (Sanchez et al., 2003). It is likely that the mPFC also plays a role in reinstatement of MAP-CPP because several lines of evidence suggest that this region is involved in the reinforcing and incentive motivational effects of psychostimulants (Isaac et al., 1989; Zavala et al., 2003). Therefore, in view of the Glu neurotransmission in the

mPFC, brain microdialysis was employed to further investigate the role of Glu in restraint stress-induced reinstatement of CPP. Forced swimming stress caused a significant increase in the release of OT and Glu within the CeA, and such locally released OT modulates the behavioral stress response by its inhibitory effects on the local release of excitatory amino acids (Glu and aspartate) (Ebner et al., 2005; Bosch et al., 2007). Moreover, oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission (Robinson et al., 2002; Condes-Lara et al., 2005, 2006). According to the present results, we hypothesize that OT partially inhibits extracellular Glu levels in the mPFC, which are aroused by restraint stress, and indicates that glutamatergic neurotransmission in the mesocorticolimibic system plays a key role in OT regulated CPP reinstatement induced by stress. Stress-induced reinstatement may utilize corticotropin releasing factor (CRF) and the hypothalamo-pituitary–adrenal (HPA) axis (Self and Nestler, 1998), which constitutes the main neuroendocrine stress system. Further, intracerebral OT is significantly involved in the regulation of the HPA axis (Neumann et al., 2000). Therefore, the involvement of OT on the HPA axis during the process of reinstatement cannot be excluded. Furthermore, as a ‘social neuropeptide’, oxytocin regulates social affiliation, anxiety, mood and aggression, and the raised brain oxytocin levels may ameliorate acute drug withdrawal symptoms (McGregor et al., 2008). Windle et al. showed that oxytocin may mediate its antistress effects through forebrain target sites, and the administration

Fig. 10. Effects of OT on the Glu release in the mPFC induced by restrain stress on CPP mice. The data are expressed as mean  S.E.M. percent baseline Glu and each point represents a 20 min dialysate sampling period. n ¼ 9–10, aP < 0.05 two-way ANOVA with post hoc Fisher’s LSD tests compared with the saline group; bP < 0.05 compared with the saline þ stress group; cP < 0.05 compared with the OT þ saline þ stress group; dP < 0.05 compared with the MAP group; eP < 0.05 compared with the MAP þ stress group; fP < 0.05 compared with the OT þ MAP þ stress group.

864

J. Qi et al. / Neuropharmacology 56 (2009) 856–865

of oxytocin significantly attenuated the release of ACTH and corticosterone and the increase in CRF mRNA expression in the hypothalamic paraventricular nucleus in response to restraint stress (Windle et al., 2004). No significant effects of OT on the Glu levels in the mPFC were observed during the reinstatement of CPP induced by MAP, which is in consistent with the results of behavioral investigations. Numerous studies have shown that drug priming can induce reinstatement of CPP (Parker and McDonald, 2000). The direct pharmacological effects of repeated drug exposure can produce adjuvant processes, such as sensitization of cellular responses to the neurotransmitters DA and Glu (White et al., 1995), which can increase sensitivity to the rewarding effects of drugs (Carlezon et al., 1997). It is possible that the enhanced output of Glu during the reinstatement process is too intense to be suppressed by OT in the present study. Since reinstatement could be triggered by different mechanisms, it is hypothesized from these studies that OT is not directly involved in the mechanism of reinstatement induced by MAP priming. The results of microdialysis indicate that OT has no effect on the elevated Glu level induced by MAP priming, which suggests that OT does not produce enough inhibition of DA transmission from VTA to PFC. It may be that adaptive regulation and sensitization of dopaminergic and glutamatergic neurotransmission occurred during the CPP acquisition process, while OT had no influence on these phenomena. However, OT showed an inhibitory effect on the stress-induced reinstatement because it blocked the release of Glu in the PFC. Moreover, the present study indicates that the action of OT on the MAP-induced CPP appears to be a receptormediated event, because Ato, the selective OT-receptor antagonist (Melin, 1993), significantly inhibits the effects of OT. In conclusion, the present study is the first to show that OT effectively blocked acquisition, facilitated extinction and suppressed restraint stress-induced reinstatement of CPP induced by MAP, although it has no effects on expression and MAP priminginduced reinstatement. The results indicated that OT, mainly via its receptor, partially attenuated the reward property of MAP and Glu neurotransmission was related to the inhibitory effect of OT on restraint stress-induced CPP reinstatement. Acknowledgements This study was partially supported by the Outstanding Youth Fund of Liaoning province, China. The authors thank Associate Professor Jie Jin of Shenyang Pharmaceutical University for her technical assistance in the design of the CPP apparatus. We appreciate Dr. Zack O.M. Howard (NIH/NCI-Frederick, MD, USA) on language editing of this paper. References Bardo, M.T., Bevins, R.A., 2000. Conditioned place preference: what does it add to our preclinical understanding of drug reward? Psychopharmacology (Berl.) 153, 31–43. Bielsky, I.F., Young, L.J., 2004. Oxytocin, vasopressin, and social recognition in mammals. Peptides 25, 1565–1574. Bohus, B., Urban, I., van Wimersma Greidanus, T.B., de Wied, D., 1978. Opposite effects of oxytocin and vasopressin on avoidance behaviour and hippocampal theta rhythm in the rat. Neuropharmacology 17, 239–247. Bosch, O.J., Sartori, S.B., Singewald, N., Neumann, I.D., 2007. Extracellular amino acid levels in the paraventricular nucleus and the central amygdala in high- and low-anxiety dams rats during maternal aggression: regulation by oxytocin. Stress 10, 261–270. Brabant, C., Quertemont, E., Tirelli, E., 2005. Evidence that the relations between novelty-induced activity, locomotor stimulation and place preference induced by cocaine qualitatively depend upon the dose: a multiple regression analysis in inbred C57BL/6J mice. Behav. Brain Res. 158, 201–210. Carlezon Jr., W.A., Boundy, V.A., Haile, C.N., Kalb, R.G., Neve, R.L., Nestler, E.J., 1997. Sensitization to morphine induced by viral-mediated gene transfer. Science 277, 812–814.

Conde, F., Maire-Lepoivre, E., Audinat, E., Crepel, F., 1995. Afferent connections of the medial frontal cortex of the rat. II. Cortical and subcortical afferents. J. Comp. Neurol. 352, 567–593. Condes-Lara, M., Maie, I.A., Dickenson, A.H., 2005. Oxytocin actions on afferent evoked spinal cord neuronal activities in neuropathic but not in normal rats. Brain Res. 1045, 124–133. Condes-Lara, M., Rojas-Piloni, G., Martinez-Lorenzana, G., Rodriguez-Jimenez, J., Lopez-Hidalgo, M., Freund-Mercier, M.J., 2006. Paraventricular hypothalamic influences on spinal nociceptive processing. Brain Res. 1081, 126–137. Covington, H.E., Miczek, K.A., 2001. Repeated social-defeat stress, cocaine or morphine. Effects on behavioral sensitization and intravenous cocaine selfadministration ‘‘binges’’. Psychopharmacology (Berl.) 158, 388–398. Dalley, J.W., Cardinal, R.N., Robbins, T.W., 2004. Prefrontal executive and cognitive functions in rodents: neural and neurochemical substrates. Neurosci. Biobehav. Rev. 28, 771–784. Davis, M., Myers, K.M., 2002. The role of glutamate and gamma-aminobutyric acid in fear extinction: clinical implications for exposure therapy. Biol. Psychiatr. 52, 998–1007. Di Chiara, G., Imperato, A., 1988. Drugs abused by humans preferentially increase synaptic dopamine concentrations in the mesolimbic system of freely moving rats. Proc. Natl. Acad. Sci. U. S. A. 85, 5274–5278. Ebner, K., Bosch, O.J., Kromer, S.A., Singewald, N., Neumann, I.D., 2005. Release of oxytocin in the rat central amygdala modulates stress-coping behavior and the release of excitatory amino acids. Neuropsychopharmacology 30, 223–230. Engelmann, M., Wotjak, C.T., Neumann, I., Ludwig, M., Landgraf, R., 1996. Behavioral consequences of intracerebral vasopressin and oxytocin: focus on learning and memory. Neurosci. Biobehav. Rev. 20, 341–358. Ferrier, B.M., Kennett, D.J., Devlin, M.C., 1980. Influence of oxytocin on human memory processes. Life Sci. 27, 2311–2317. Fisone, G., Wu, C.F., Consolo, S., Nordstrom, O., Brynne, N., Bartfai, T., Melander, T., Hokfelt, T., 1987. Galanin inhibits acetylcholine release in the ventral hippocampus of the rat: histochemical, autoradiographic, in vivo, and in vitro studies. Proc. Natl. Acad. Sci. U. S. A. 84, 7339–7343. Ginawi, O.T., Al-Majed, A.A., Al-Suwailem, A.K., 2005. NAN-190, a possible specific antagonist for methamphetamine. Regul. Toxicol. Pharmacol. 41, 122–127. Goeders, N.E., Dworkin, S.I., Smith, J.E., 1986. Neuropharmacological assessment of cocaine self-administration into the medial prefrontal cortex. Pharmacol. Biochem. Behav. 24, 1429–1440. Graham, D.L., Hoppenot, R., Hendryx, A., Self, D.W., 2007. Differential ability of D1 and D2 dopamine receptor agonists to induce and modulate expression and reinstatement of cocaine place preference in rats. Psychopharmacology (Berl.) 191, 719–730. Hao, Y., Yang, J.Y., Guo, M., Wu, C.F., Wu, M.F., 2005. Morphine decreases extracellular levels of glutamate in the anterior cingulate cortex: an in vivo microdialysis study in freely moving rats. Brain Res. 1040, 191–196. Hao, Y., Yang, J.Y., Sun, J.Y., Qi, J., Dong, Y.X., Wu, C.F., 2008. Lesions of the medial prefrontal cortex prevent the acquisition but not reinstatement of morphineinduced conditioned place preference in mice. Neurosci. Lett. 433, 48–53. Hao, Y., Yang, J.Y., Wu, C.F., Wu, M.F., 2007. Pseudoginsenoside-F11 decreases morphine-induced behavioral sensitization and extracellular glutamate levels in the medial prefrontal cortex in mice. Pharmacol. Biochem. Behav. 86, 660–666. Heinrichs, M., Meinlschmidt, G., Wippich, W., Ehlert, U., Hellhammer, D.H., 2004. Selective amnesic effects of oxytocin on human memory. Physiol. Behav. 83, 31–38. Ibragimov, R.Sh., 1990. Influence of neurohypophyseal peptides on the formation of active avoidance conditioned reflex behavior. Neurosci. Behav. Physiol. 20, 189–193. Isaac, W.L., Nonneman, A.J., Neisewander, J., Landers, T., Bardo, M.T., 1989. Prefrontal cortex lesions differentially disrupt cocaine-reinforced conditioned place preference but not conditioned taste aversion. Behav. Neurosci. 103, 345–355. Itzhak, Y., Martin, J.L., 2002. Cocaine-induced conditioned place preference in mice: induction, extinction and reinstatement by related psychostimulants. Neuropsychopharmacology 26, 130–134. Jo, Y.H., Stoeckel, M.E., Freund-Mercier, M.J., Schlichter, R., 1998. Oxytocin modulates glutamatergic synaptic transmission between cultured neonatal spinal cord dorsal horn neurons. J. Neurosci. 18, 2377–2386. Katz, R.J., Roth, K., 1979. Tail pinch induced stress-arousal facilitates brain stimulation reward. Physiol. Behav. 22, 193–194. Kim, H.S., Hong, Y.T., Oh, K.W., Seong, Y.H., Rheu, H.M., Cho, D.H., Oh, S., Park, W.K., Jang, C.G., 1998. Inhibition by ginsenosides Rb1 and Rg1 of methamphetamineinduced hyperactivity, conditioned place preference and postsynaptic dopamine receptor supersensitivity in mice. Gen. Pharmacol. 30, 783–789. Kotlinska, J., Biala, G., 1999. Effects of the NMDA/glycine receptor antagonist, L701,324, on morphine- and cocaine-induced place preference. Pol. J. Pharmacol. 51, 323–330. Kovacs, G.L., Sarnyai, Z., Barbarczi, E., Szabo, G., Telegdy, G., 1990. The role of oxytocin–dopamine interactions in cocaine-induced locomotor hyperactivity. Neuropharmacology 29, 365–368. Kovacs, G.L., Sarnyai, Z., Szabo, G., 1998. Oxytocin and addiction: a review. Psychoneuroendocrinology 23, 945–962. Kovacs, G.L., Szabo, G., Sarnyai, Z., Telegdy, G., 1987. Neurohypophyseal hormones and behavior. Prog. Brain Res. 72, 109–118. Kovacs, G.L., Telegdy, G., 1982. Role of oxytocin in memory and amnesia. Pharmacol. Ther. 18, 375–395. Liberzon, I., Trujillo, K.A., Akil, H., Young, E.A., 1997. Motivational properties of oxytocin in the conditioned place preference paradigm. Neuropsychopharmacology 17, 353–359.

J. Qi et al. / Neuropharmacology 56 (2009) 856–865 Lu, L., Shepard, J.D., Hall, F.S., Shaham, Y., 2003. Effect of environmental stressors on opiate and psychostimulant reinforcement, reinstatement and discrimination in rats: a review. Neurosci. Biobehav. Rev. 27, 457–491. Maldonado, C., Rodrı´guez-Arias, M., Castillo, A., Aguilar, M.A., Minarro, J., 2007. Effect of memantine and CNQX in the acquisition, expression and reinstatement of cocaine-induced conditioned place preference. Prog. Neuropsychopharmacol. Biol. Psychiatr. 31, 932–939. McGregor, I.S., Callaghan, P.D., Hunt, G.E., 2008. From ultrasocial to antisocial: a role for oxytocin in the acute reinforcing effects and long-term adverse consequences of drug use? Br. J. Pharmacol. 154, 358–368. Melin, P., 1993. Oxytocin antagonists in preterm labour and delivery. Baillieres Clin. Obstet. Gynaecol. 7, 577–600. Moghaddam, B., 1993. Stress preferentially increases extraneuronal levels of excitatory amino acids in the prefrontal cortex: comparison to hippocampus and basal ganglia. J. Neurochem. 60, 1650–1657. Montaron, M.F., Deniau, J.M., Menetrey, A., Glowinski, J., Thierry, A.M., 1996. Prefrontal cortex inputs of the nucleus accumbens–nigro-thalamic circuit. Neuroscience 71, 371–382. Murase, S., Grenhoff, J., Chouvet, G., Gonon, F.G., Svensson, T.H., 1993. Prefrontal cortex regulates burst firing and transmitter release in rat mesolimbic dopamine neurons studied in vivo. Neurosci. Lett. 157, 53–56. Neumann, I.D., 2008. Brain oxytocin: a key regulator of emotional and social behaviours in both females and males. J. Neuroendocrinol. 20, 858–865. Neumann, I.D., Wigger, A., Torner, L., Holsboer, F., Landgraf, R., 2000. Brain oxytocin inhibits basal and stress-induced activity of the hypothalamo-pituitary–adrenal axis in male and female rats: partial action within the paraventricular nucleus. J. Neuroendocrinol. 12, 235–243. NIDA report, 2007. Methamphetamine Addiction: Cause for Concern – Hope for the Future. Ohmori, T., Abekawa, T., Koyama, T., 1996. The role of glutamate in behavioral and neurotoxic effects of methamphetamine. Neurochem. Int. 29, 301–307. Pacchioni, A.M., Gioino, G., Assis, A., Cancela, L.M., 2002. A single exposure to restraint stress induces behavioral and neurochemical sensitization to stimulating effects of amphetamine: involvement of NMDA receptors. Ann. N. Y. Acad. Sci. 965, 233–246. Parker, L.A., McDonald, R.V., 2000. Reinstatement of both a conditioned place preference and a conditioned place aversion with drug primes. Pharmacol. Biochem. Behav. 66, 559–561. Paxinos, G., Franklin, K.B., 2001. The Mouse Brain in Stereotaxic Coordinates, second ed. Academic Press, San Diego. Pierce, R.C., Kumaresan, V., 2006. The mesolimbic dopamine system: the final common pathway for the reinforcing effect of drugs of abuse? Neurosci. Biobehav. Rev. 30, 215–238. Pulvirenti, L., 2003. Glutamate neurotransmission in the course of cocaine addiction. In: Herman, B.H. (Ed.), Glutamate and Addiction. Humana Press, New Jersey, pp. 171–181. Qi, J., Yang, J.Y., Song, M., Li, Y., Wang, F., Wu, C.F., 2008. Inhibition by oxytocin of methamphetamine-induced hyperactivity related to dopamine turnover in the mesolimbic region in mice. Naunyn Schmiedebergs Arch. Pharmacol. 376, 441–448. Raudensky, J., Yamamoto, B.K., 2007. Effects of chronic unpredictable stress and methamphetamine on hippocampal glutamate function. Brain Res. 1135, 129–135. Robinson, D.A., Wei, F., Wang, G.D., Li, P., Kim, S.J., Vogt, S.K., Muglia, L.J., Zhuo, M., 2002. Oxytocin mediates stress-induced analgesia in adult mice. J. Physiol. 540, 593–606. Sanchez, C.J., Bailie, T.M., Wu, W.R., Li, N., Sorg, B.A., 2003. Manipulation of dopamine d1-like receptor activation in the rat medial prefrontal cortex alters stress- and cocaine-induced reinstatement of conditioned place preference behavior. Neuroscience 119, 497–505.

865

Sarnyai, Z., Babarczy, E., Krivan, M., Szabo, G., Kovacs, G.L., Barth, T., Telegdy, G., 1991. Selective attenuation of cocaine-induced stereotyped behaviour by oxytocin: putative role of basal forebrain target sites. Neuropeptides 19, 51–56. Sarnyai, Z., Biro, E., Babarczy, E., Vecsernyes, M., Laczi, F., Szabo, G., Krivan, M., Kovacs, G.L., Telegdy, G., 1992. Oxytocin modulates behavioural adaptation to repeated treatment with cocaine in rats. Neuropharmacology 31, 593–598. Sarnyai, Z., Kovacs, G.L., 1994. Role of oxytocin in the neuroadaptation to drugs of abuse. Psychoneuroendocrinology 19, 85–117. Sarnyai, Z., Szabo, G., Kovacs, G.L., Telegdy, G., 1990. Oxytocin attenuates the cocaine-induced exploratory hyperactivity in mice. Neuroreport 1, 200–202. Self, D.W., Nestler, E.J., 1998. Relapse to drug-seeking: neural and molecular mechanisms. Drug Alcohol. Depend. 51, 49–60. Sesack, S.R., Pickel, V.M., 1992. Prefrontal cortical efferents in the rat synapse on unlabeled neuronal targets of catecholamine terminals in the nucleus accumbens septi and on dopamine neurons in the ventral tegmental area. J. Comp. Neurol. 320, 145–160. Sheridan, J., Bennett, S., Coggan, C., Wheeler, A., McMillan, K., 2006. Injury associated with methamphetamine use: a review of the literature. Harm Reduct. J. 3, 14. Shimosato, K., Ohkuma, S., 2000. Simultaneous monitoring of conditioned place preference and locomotor sensitization following repeated administration of cocaine and methamphetamine. Pharmacol. Biochem. Behav. 66, 285–292. Shoblock, J.R., Wichmann, J., Maidment, N.T., 2005. The effect of a systemically active ORL-1 agonist, Ro 64-6198, on the acquisition, expression, extinction, and reinstatement of morphine conditioned place preference. Neuropharmacology 49, 439–446. Sofroniew, M.V., 1983. Morphology of vasopressin and oxytocin neurones and their central and vascular projections. Prog. Brain Res. 60, 101–114. Succu, S., Sanna, F., Melis, T., Boi, A., Argiolas, A., Melis, M.R., 2007. Stimulation of dopamine receptors in the paraventricular nucleus of the hypothalamus of male rats induces penile erection and increases extra-cellular dopamine in the nucleus accumbens: involvement of central oxytocin. Neuropharmacology 52, 1034–1043. Sulzer, D., Sonders, M.S., Poulsen, N.W., Galli, A., 2005. Mechanisms of neurotransmitter release by amphetamines: a review. Prog. Neurobiol. 75, 406–433. Taber, M.T., Das, S., Fibiger, H.C., 1995. Cortical regulation of subcortical dopamine release: mediation via the ventral tegmental area. J. Neurochem. 65, 1407–1410. Wang, B., Luo, F., Ge, X.C., Fu, A.H., Han, J.S., 2002. Effects of lesions of various brain areas on drug priming or footshock-induced reactivation of extinguished conditioned place preference. Brain Res. 950, 1–9. White, F.J., Hu, X.T., Zhang, X.F., Wolf, M.E., 1995. Repeated administration of cocaine or amphetamine alters neuronal responses to glutamate in the mesoaccumbens dopamine system. J. Pharmacol. Exp. Ther. 273, 445–454. Windle, R.J., Kershaw, Y.M., Shanks, N., Wood, S.A., Lightman, S.L., Ingram, C.D., 2004. Oxytocin attenuates stress-induced c-fos mRNA expression in specific forebrain regions associated with modulation of hypothalamo-pituitary– adrenal activity. J. Neurosci. 24, 2974–2982. Wise, R.A., Bozarth, M.A., 1987. A psychomotor stimulant theory of addiction. Psychol. Rev. 94, 469–492. Wolf, M.E., 2002. Addiction: making the connection between behavioral changes and neuronal plasticity in specific pathways. Mol. Interv. 2, 146–157. Wu, W., Yu, L.C., 2004. Roles of oxytocin in spatial learning and memory in the nucleus basalis of Meynert in rats. Regul. Pept. 120, 119–125. Yan, P.G., Wu, C.F., Huang, M., Liu, W., 2003. Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice. Toxicol. Lett. 145, 69–78. Zavala, A.R., Weber, S.M., Rice, H.J., Alleweireldt, A.T., Neisewander, J.L., 2003. Role of the prelimbic subregion of the medial prefrontal cortex in acquisition, extinction, and reinstatement of cocaine-conditioned place preference. Brain Res. 990, 157–164.