Conditioned Place Preference Scores Research Articles

Sexually dimorphic intracellular responses after cocaine-induced conditioned place preference expression

Sex differences in cocaine’s mechanisms of action and behavioral effects have been widely reported. However, little is known about how sex influences intracellular signaling cascades involved with drug–environment associations. We investigated whether ERK/CREB intracellular responses in the mesocorticolimbic circuitry underlying cocaine environmental associations are sexually dimorphic. We used a standard 4 day conditioned place preference (CPP) paradigm using 20mg/kg cocaine—a dose that induced CPP in male and female Fischer rats. In the nucleus accumbens (NAc) following CPP expression, cocaine treated animals showed increased phosphorylated ERK (pERK), phosphorylated CREB (pCREB) and ΔFosB protein levels. In the hippocampus (HIP) and caudate putamen (CPu), pERK and FosB/ΔFosB levels were also increased, respectively. Cocaine females had a larger change in HIP pERK and CPu ΔFosB levels than cocaine males; partly due to lower protein levels in saline female rats when compared to saline males. Prefrontal cortex (PfC) pCREB levels increased in cocaine males, but not females, whereas PfC pERK levels were increased in cocaine females, but not males. CPP scores were positively correlated to NAc pERK, HIP pERK and CPu FosB protein levels, suggesting that similar to males, the ERK/CREB intracellular pathway in mesocorticolimbic regions undergoes cocaine induced neuroplasticity in female rats. However, there seem to be intrinsic (basal) sexual dimorphisms in this pathway that may contribute to responses expressed after cocaine-CPP. Taken together, our results suggest that cellular responses associated with the expression of learned drug–environment associations may play an important role in sex differences in cocaine addiction and relapse.

Inhibitory effects of processed Aconiti tuber on morphine-induced conditioned place preference in rats

Our previous studies indicated that processed Aconiti tuber (PAT), a traditional Chinese herbal medicine, had antinociceptive effects and inhibitory effects on morphine tolerance by activation of kappa-opioid receptor (KOR). Preclinical studies also demonstrated that KOR agonists functionally attenuate addictive behaviors of morphine, such as conditioned place preference (CPP). Therefore, we hypothesize that PAT may inhibit morphine-induced CPP in rats. (1) Five groups of rats (n=8 for each group) were alternately subcutaneous (s.c.) injected with morphine 10mg/kg (one group receive normal saline as a control) and normal saline for 8 days and oral co-administrated with distilled water or PAT 0.3, 1.0, or 3.0 g/kg daily on days 2-9 during CPP training, respectively. (2) Other four groups of rats were randomly s.c. injected with nor-binaltorphimine (nor-BNI; 5mg/kg) or normal saline (as a control) 120 min before alternately s.c. with morphine and normal saline and oral co-administrated with distilled water or PAT 3.0 g/kg daily. Each rat was acquired pre-conditioning and post-conditioning CPP data and assayed dynorphin concentrations by radioimmunoassay in rat's nucleus accumbens (NAc) after CPP training. (1) PAT 1.0 or 3.0 g/kg dose-dependently decreased the morphine-induced increase of CPP scores. (2) Nor-BNI completely antagonized the inhibition of PAT on morphine-induced CPP. (3) PAT dose-dependently increased dynorphin content in rats' NAc after CPP training. (1) PAT dose-dependently inhibited morphine-induced CPP. (2) The inhibition of PAT on morphine-induced CPP was probably due to activation of KOR by increasing dynorphin release in rats' NAc.

Differential effects of morphine on conditioned place preference and locomotor activity in adult and adolescent rats

Objective To test whether adolescent rats are more sensitive than adult rats to morphine' s rewarding actions and locomotor activating effects. Methods Conditioned place preference(CPP) procedure was used to examine drug-induced reward and locomotor activity. Adolescent ( Postnatal day 35 ) and adult ( P67 ) male rats received either saline or morphine (3 mg/kg) for 6 days and the locomotor response in the drug paired chamber was recorded during conditioned training. CPP effects were tested 24h after the last training. Results In adolescent rats, morphine CPP effect was not present [ saline group (20. 89 ±31. 14) s, morphine group (90. 75 ± 27.91)s, P = 0. 15], however, morphine CPP effect occurred in adult rats[saline group (31.5 ± 41. 24) s, morphine group(266. 13 ± 32. 26) s, P < 0. 001 ]. Adult rats presented higher CPP score than adolescent rats(P < 0.001). The locomotor response was significantly higher in day 3 ～ 6 than day 1 in the adolescent treated with morphine (P<0.05 or <0. 01). The locomotor response was significantly higher in day 2-6 than day 1 in the adolescent treated with morphine(P<0. 05 or < 0. 01 ) .which suggested that both adolescent and adult rats exhibited similar behavioral sensitization to morphine administration. Two-way ANOVA indicated that the main effect of age was not significant(F_(1,14) =0. 33, P = 0. 57) ,the interaction effect of age x treat was not significant(F_(5,70) = 0.85, P = 0.52) .there was no age difference between adolescent and adult rats in behavioral sensitization effects. Conclusion Compared with adult rats, adolescent rats don' t present morphine CPP, but show the similar morphine behavioral sensitization. Key words: Drug addiction; Morphine; Conditioned place preference; Locomotor sensitization

The Nucleus Accumbens Core has a More Important Role in Resisting Reactivation of Extinguished Conditioned Place Preference in Morphine-addicted Rats

We investigated the roles of the core and shell subfields of the nucleus accumbens (NAc) in drug- or foot-shock-induced reactivation of extinguished conditioned place preference (CPP) in morphine-addicted rats. Rats were given electrolytic lesions to either the core or shell after CPP was established. After surgery, a reduction of CPP scores to morphine was observed in all groups. During the reacquisition of morphine-seeking behaviour, rats in the shell and sham lesion groups regained their CPP, while the CPP in core lesion rats remained severely impaired. Similarly, foot-shock-induced reactivation of CPP in the core lesion group was significantly lower than that of the shell and sham lesion groups, and there was no significant difference between these latter groups. Our results demonstrate that NAc core and shell lesions elicited dissociable effects on reactivation of extinguished CPP in rats, suggesting that the NAc core might play a more important role in resisting reactivation of extinguished CPP in morphine-addicted rats.

Gene Expression Profiling of Rewarding Effect in Methamphetamine Treated Bax-deficient Mouse

Methamphetamine is an illicit drug that is often abused and can cause neuropsychiatric and neurotoxic damage. Repeated administration of psychostimulants such as methamphetamine induces a behavioral sensitization. According to a previous study, Bax was involved in neurotoxicity by methamphetamine, but the function of Bax in rewarding effect has not yet been elucidated. Therefore, we have studied the function of Bax in a rewarding effect model. In the present study, we treated chronic methamphetamine exposure in a Bax-deficient mouse model and examined behavioral change using a conditioned place preference (CPP) test. The CPP score in Bax knockout mice was decreased compared to that of wild-type mice. Therefore, we screened for Bax-related genes that are involved in rewarding effect using microarray technology. In order to confirm microarray data, we applied the RT-PCR method to observe relative changes of Bcl2, a pro-apoptotic family gene. As a result, using our experiment microarray, we selected genes that were associated with Bax in microarray data, and eventually selected the Tgfbr2 gene. Expression of the Tgfbr2 gene was decreased by methamphetamine in Bax knockout mice, and the gene was overexpressed in Bax wild-type mice. Additionally, we confirmed that Creb, FosB, and c-Fos were related to rewarding effect and Bax using immunohistochemistry.

Perseverance of exploration in novel environments predicts morphine place conditioning in rats

Reactivity to novelty has been related to operant drug self-administration but does not seem involved in the conditioned place preference (CPP). To further assess this issue our aims were to investigate: (1) the importance of the initial versus delayed activity in the novel environment to predict the CPP induced by morphine; (2) the separate contribution of trait anxiety in morphine CPP. Male Sprague–Dawley rats were exposed to a circular corridor for 30 min to assess reactivity to novelty and to the elevated plus-maze and the light–dark tests as measures of anxiety and morphine CPP was then studied (three pairings with 5 mg/kg s.c. morphine and three with saline). Delayed activity in the corridor (16–30 min) correlated positively with CPP score, whereas the initial activity (0–15 min) did not. High-responders (HR), those more active during the second half of the corridor, developed morphine CPP in contrast to low-responders (LR). Also, HR and LR did not differ in anxiety nor any plus-maze or light–dark test measure correlated with CPP behaviour. Enhanced vulnerability to develop morphine CPP is predicted by a higher delayed activity in a novel environment, regardless of anxiety.

Neurokinin-1 Receptor-Expressing Neurons in the Amygdala Modulate Morphine Reward and Anxiety Behaviors in the Mouse

Mice lacking the neurokinin-1 (NK1) receptor, the preferred receptor for the neuropeptide substance P (SP), do not show many of the behaviors associated with morphine reward. To identify the areas of the brain that might contribute to this effect, we assessed the behavioral effects of ablation of neurons expressing the NK1 receptor in specific regions of the mouse brain using the neurotoxin substance P-saporin. In a preliminary investigation, bilateral ablation of these neurons from the amygdala, but not the nucleus accumbens and dorsomedial caudate putamen, brought about reductions in morphine reward behavior. Subsequently, the effect of ablation of these neurons in the amygdala on anxiety behavior was assessed using the elevated plus maze (EPM), before conditioned place preference (CPP), and locomotor responses to morphine were measured. Loss of NK1 receptor-expressing neurons in the amygdala caused an increase in anxiety-like behavior on the EPM. It also brought about a reduction in morphine CPP scores and the stimulant effect of acute morphine administration relative to saline controls, without affecting CPP to cocaine. NK1 receptor-expressing neurons in the mouse amygdala therefore modulate morphine reward behaviors. These observations mirror those observed in NK1 receptor knock-out (NK1-/-) mice and suggest that the amygdala is an important area for the effects of SP and the NK1 receptor in the motivational properties of opiates, as well as the control of behaviors related to anxiety.

Concurrent evaluation of locomotor response to novelty and propensity toward cocaine conditioned place preference in mice

Neural and physiological factors underlying individual differences in the vulnerability to drug abuse are the major questions remained to be determined. The present study described new methods that concurrently assess the relationship between locomotor response to novelty and conditioned place preference (CPP) for cocaine in mice using a novel activity monitor, SCANET. The activity monitor simultaneously measured the distance traveled and the amount of time spent in each side of a two-compartment CPP chamber, and the latency to the first entry into the other side of the CPP chamber. Mice were divided into two groups according to their locomotor response to the first exposure to the CPP chamber during a preconditioning session; high-responder (HR) and low-responder (LR) mice. Following conditioning sessions, the CPP score was shown to be higher in LR mice than in HR mice, especially at low doses of cocaine. In a separate experiment with SCANET, we measured the latency to the first entry into the white-floored compartment from the black-floored compartment of the CPP chamber as an index of anxiety-like behavior. The latency was significantly prolonged in the LR group as compared with the HR group. Thus, the new methods described here are considered to be useful for examining animal models of drug addiction with respect to anxiety-like behavior.

Differential effects of trihexyphenidyl on place preference conditioning and locomotor stimulant activity of cocaine and methamphetamine.

Cocaine produces rewarding and locomotor stimulant effects by increasing extracellular dopamine (DA) levels in the terminal areas of the mesolimbic DA system. Our recent in vitro studies have shown that a muscarinic receptor antagonist, trihexyphenidyl (THP) inhibits the binding of a cocaine analogue to the DA transporter at concentrations that are ineffective in inhibiting 3H-DA uptake, suggesting that THP may attenuate the actions of cocaine selectively. The present study examined whether THP could affect conditioned place preference (CPP) for and locomotor stimulant activity of cocaine and methamphetamine (MAP) in mice. Mice were injected with cocaine (10 mg/kg) or MAP (1 mg/kg) in one compartment of the CPP chamber 4 times every second day. On alternate days the animals received saline in the other compartment of the CPP chamber. Pretreatment with THP was made 10 min before cocaine or MAP injection. The CPP score and locomotor activity were assessed using a novel activity monitor, SCANET. Cocaine and MAP produced CPP for the drug-paired compartment. Pretreatment with THP (0.05-5 mg/kg) had no influence on cocaine-induced CPP at any dose tested. In contrast, MAP-induced CPP was completely antagonized by THP at 5 mg/kg, which produced no CPP by itself. Another muscarinic receptor antagonist, scopolamine (SCP, 3 mg/kg) neither caused CPP by itself nor affected the development of cocaine- or MAP-induced CPP. Both THP and SCP enhanced spontaneous, cocaine- or MAP-induced locomotor activity. Though the present conditioning treatments failed to develop locomotor sensitization to cocaine, THP, but not SCP, acted cooperatively with cocaine to develop locomotor sensitization. The development of locomotor sensitization to MAP was retarded by SCP but was not affected by THP. These results suggest that, contrary to our anticipation, THP has a unique characteristic of specifically counter-acting the rewarding properties of MAP via a non-cholinergic (muscarinic) mechanism.

Conditioned locomotion and place preference elicited by tactile cues paired exclusively with morphine in an open field.

A novel version of the conditioned place preference (CPP) technique was used in an attempt to determine whether tactile stimuli previously associated with morphine elicit approach and sustained contact. Empirical support for this view has been equivocal, prompting some to question the validity of the CPP technique. In the present study, rats received, during conditioning, morphine (10 mg/kg, IP) paired exclusively with an open field floor made of four quadrants of one texture (CS+) and saline with another floor made of four quadrants of a different texture (CS-). On the test for CPP, rats were given saline and placed in an open field containing either 1, 2, or 4 quadrants of the CS+ (with 3, 2, 0 quadrants of the CS-, respectively). These animals showed high absolute CPP scores on the test, spending, on average, as much as 83% and 75% of their time on the CS+ when two and one CS+ quadrants, respectively, were present. Concurrent measures of activity indicated that animals were most active when all four quadrants were CS+ and least active when zero or one CS+ quadrant was present. Thus, once an animal approached and made contact with the CS+ it tended to maintain contact with this stimulus and to reduce its approach to and contact with other stimuli. The differentiating features of this version of the CPP technique, as well as the relationship between morphine-induced conditioned locomotion and CPP, are discussed.

Thoracic Injuries

The orexinergic system is found to cooperate in mediating stress-induced drug relapse. The orexinergic terminals innervate neurons of the hippocampal dentate gyrus (DG) which is a key structure in the maintenance and reinstatement of drug addiction. However, the specific contribution of intra-DG orexin receptors to stress-induced reinstatement has not been completely known. In the current study, the effects of intra-DG administration of SB334867, an orexin-1 receptor (OX1R) antagonist, and TCS OX2 29, an orexin-2 receptor (OX2R) antagonist, were investigated on the reinstatement induced by a sub-threshold dose of morphine and food deprivation (FD) stress. Adult male rats received different doses of SB334867 or TCS OX2 29 (3, 10, and 30 nM/0.5 μl DMSO 12%) bilaterally into the DG in separate groups, following the acquisition and extinction of morphine-induced conditioned place preference (CPP). Then, the reinstatement was evaluated by the 24 h FD stress and/or a sub-threshold dose of morphine (0.5 mg/kg, s.c.). CPP scores and locomotor activities were recorded during the test. The findings indicated that pre-treatment with the highest dose of SB334867 (30 nM) and two higher doses of TCS OX2 29 (10 and 30 nM) blocked the sub-threshold dose and FD stress-induced reinstatement of morphine. The effect of TCS OX2 29 on reduction of reinstatement was more pronounced than that of SB334867. It suggests a role for the orexin receptors, especially OX2R within the DG region in the stress-induced reinstatement of morphine-seeking behaviours in extinguished rats.