Chronic access to a sucrose solution enhances the development of conditioned place preferences for fentanyl and amphetamine in male Long-Evans rats

Consumption of palatable food and fluids alters the behavioral consequences of psychoactive drugs. To further investigate the effects of intake of palatable nutrients on the rewarding properties of these drugs, the effects of chronic intake of a sweet sucrose solution on the development of conditioned place preferences (CPP) to a mu-opioid agonist, fentanyl, and to a stimulant drug, amphetamine, were examined. Male Long-Evans rats consumed laboratory chow and water or chow, water, and a 32% sucrose solution. CPP testing was conducted in a three-chamber apparatus. In Experiment 1 (over four conditioning days), rats received saline, 0.004, or 0.016 mg/kg sc fentanyl citrate before being placed on the nonpreferred side of the apparatus and saline (subcutaneously) before being placed on the preferred side during a separate session on the same day. When given access to all three chambers, rats injected with 0.016 mg/kg fentanyl spent significantly more time on the drug-paired side than rats injected with saline. Furthermore, sucrose-fed rats displayed a significantly greater CPP than chow-fed rats. After conditioning, rats were tested for fentanyl-induced antinociception using the tail-flick test. Using a cumulative dose procedure, fentanyl (0.003, 0.010, 0.030, and 0.100 mg/kg sc) led to dose-dependent increases in tail-flick latencies. Rats fed with sucrose displayed significantly greater responses to fentanyl than those in the chow group. In Experiment 2, rats spent significantly more time on the drug-paired side of the CPP apparatus following injections of 0.33 or 1.0 mg/kg amphetamine than after saline injections. Additionally, following injection of 0.33 mg/kg amphetamine, sucrose-fed rats spent significantly more time on the drug-paired side of the chamber than chow-fed rats.     

睾酮诱导小鼠形成条件性位置偏爱和雌激素受体相关

目的:研究雌激素受体与睾酮诱导小鼠条件性位置偏爱的关系。方法:通过皮下注射睾酮训练小鼠形成条件性位置偏爱;在注射睾酮前注射雌激素受体拮抗剂ICI182780和他莫西芬,通过观察睾酮条件性位置偏爱的变化来判断雌激素受体是否在其中起作用。结果:0.5、1、2 mg.kg-1睾酮训练12 d,可以诱导小鼠产生条件性位置偏爱。雌激素受体拮抗剂ICI182780(2 mg.kg-1)或他莫西芬(1 mg.kg-1)可以抑制睾酮诱导的小鼠条件性位置偏爱。结论:睾酮具有奖赏效应,雌激素受体可能参与睾酮的奖赏效应。     

孕酮对吗啡条件性位置偏爱大鼠相关脑区中枢多巴胺D2受体水平的影响

目的观察孕酮对于吗啡所致奖赏效应及相关脑区中D2受体水平的影响。方法 32只SD大鼠随机分为空白对照组、吗啡组、孕酮组和孕酮加吗啡组,建立吗啡条件性位置偏爱(CPP)模型,采用免疫组化法测定大鼠伏隔核、腹侧被盖区和纹状体D2受体的水平。结果与空白对照组比较,5mg·kg-1吗啡可诱导大鼠产生稳定的CPP效应(P<0.01),15mg·kg-1孕酮虽自身不能产生CPP效应,但与吗啡合用时能抑制吗啡CPP效应的获得。与空白对照组比较,吗啡组大鼠伏隔核、腹侧被盖区和纹状体中D2受体的平均光密度值降低(均为P<0.01)。与吗啡组比较,合用15mg·kg-1孕酮可使伏隔核和纹状体中D2受体的平均光密度值升高(P<0.01和P<0.05),而在腹侧被盖区中未见变化。结论孕酮可以有效抑制吗啡CPP效应,其机制可能与其逆转吗啡诱导的伏隔核和纹状体中D2受体水平的变化有关。     

Forebrain PENK and PDYN gene expression levels in three inbred strains of mice and their relationship to genotype-dependent morphine reward sensitivity

Rationale

Vulnerability to drug abuse disorders is determined not only by environmental but also by genetic factors. A body of evidence suggests that endogenous opioid peptide systems may influence rewarding effects of addictive substances, and thus, their individual expression levels may contribute to drug abuse liability.

Objectives

The aim of our study was to assess whether basal genotype-dependent brain expression of opioid propeptides genes can influence sensitivity to morphine reward.

Methods

Experiments were performed on inbred mouse strains C57BL/6J, DBA/2J, and SWR/J, which differ markedly in responses to morphine administration: DBA/2J and SWR/J show low and C57BL/6J high sensitivity to opioid reward. Proenkephalin (PENK) and prodynorphin (PDYN) gene expression was measured by in situ hybridization in brain regions implicated in addiction. The influence of the κ opioid receptor antagonist nor-binaltorphimine (nor-BNI), which attenuates effects of endogenous PDYN-derived peptides, on rewarding actions of morphine was studied using the conditioned place preference (CPP) paradigm.

Results

DBA/2J and SWR/J mice showed higher levels of PDYN and lower levels of PENK messenger RNA in the nucleus accumbens than the C57BL/6J strain. Pretreatment with nor-BNI enhanced morphine-induced CPP in the opioid-insensitive DBA/2J and SWR/J strains.

Conclusions

Our results demonstrate that inter-strain differences in PENK and PDYN genes expression in the nucleus accumbens parallel sensitivity of the selected mouse strains to rewarding effects of morphine. They suggest that high expression of PDYN may protect against drug abuse by limiting drug-produced reward, which may be due to dynorphin-mediated modulation of dopamine release in the nucleus accumbens.     

Neuropsychotoxicity of abused drugs: involvement of matrix metalloproteinase-2 and -9 and tissue inhibitor of matrix metalloproteinase-2 in methamphetamine-induced behavioral sensitization and reward in rodents

Matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) function to remodel the pericellular environment. We have investigated the role of the MMP/TIMP system in methamphetamine (METH) dependence in rodents, in which the remodeling of neural circuits may be crucial. Repeated METH treatment induced behavioral sensitization, which was accompanied by an increase in MMP-2/-9/TIMP-2 activity in the brain. An antisense TIMP-2 oligonucleotide enhanced the sensitization, which was associated with a potentiation of the METH-induced release of dopamine in the nucleus accumbens (NAc). MMP-2/-9 inhibitors blocked the METH-induced behavioral sensitization and conditioned place preference (CPP), a measure of the rewarding effect of a drug, and reduced the METH-increased dopamine release in the NAc. In MMP-2- and MMP-9-deficient mice, METH-induced behavioral sensitization and CPP as well as dopamine release were attenuated. The MMP/TIMP system may be involved in METH-induced sensitization and reward by regulating extracellular dopamine levels.     

Mid- to late gestational morphine exposure does not alter the rewarding properties of morphine in adult male rats

Prenatal exposure to drugs of abuse often leads to physiological and neurobiological abnormalities including decreased brain and body weight, cognitive deficits and behavioral alterations. A handful of studies showed increased vulnerability to drug abuse in prenatally drug-exposed offspring. Our work also demonstrated that prenatal exposure to analgesic doses of morphine during gestation days 11-18 increases mu-opioid receptor density in the nucleus accumbens and central amygdala of adult male rats. Both the nucleus accumbens and central amygdala play important roles in modulating drug-induced reward via the mesolimbic dopaminergic system. Therefore, two types of behavioral paradigms were used to test the hypothesis that the same prenatal morphine exposure would enhance the rewarding effects of morphine, making drug-exposed offspring more vulnerable to abuse this drug in adulthood. All experiments were performed with adult male offspring of saline-injected, morphine-injected or non-injected (control) dams. (1) The unbiased conditioned place preference (CPP) paradigm was used to investigate whether prenatal morphine exposure sensitizes adult male rats to non-contingent morphine reward. These adult animals were conditioned with 0.1, 0.3, 1, 3 or 5 mg/kg morphine. All control, prenatally saline- and morphine-exposed male rats preferred the morphine-paired compartment relative to the saline-paired compartment. However, the magnitude of morphine CPP in adult male rats was not dependent on the conditioning dose of morphine or prenatal morphine exposure. (2) Intravenous morphine self-administration was used to assess the behavioral response to contingent morphine reward. Each rat self-administered one of four doses of morphine (0.3, 1, 2 or 3 mg/kg/infusion). Morphine self-administration was not altered in prenatally morphine-exposed adult male offspring. Control males self-administered significantly less morphine at the lowest dose of morphine than both prenatally saline- and morphine-exposed males. Although our data show that prenatal exposure to an analgesic dose of morphine during the time of opioid receptor appearance does not enhance morphine CPP or self-administration, they do not exclude the possibility that this prenatal morphine exposure enhances the rewarding properties of other drugs of abuse.     

Anatomical disassociation of amphetamine's rewarding and aversive effects: An intracranial microinjection study

Amphetamine has rewarding properties in some behavioral paradigms, such as self-administration and conditioned place preference (CPP), but an aversive component is also apparent when the drug is tested with the conditioned taste aversion (CTA) paradigm. The persent study was an attempt to determine the neuroanatomical substrates of the drug's rewarding and aversive effects. Previous evidence suggested that amphetamine's stimulation of activity in dopaminergic synapses is critical for both effects. Amphetamine was therefore micro-injected bilaterally (10 g/0.5 l per side) into six different dopaminergic sites, each in a different group of animals: the medial prefrontal cortex, nucleus accumbens, anteromedial caudate nucleus, lateroventral caudate nucleus, amygdala, and the region subjacent to the area postrema (AP region). The effects of these injections in both the taste and place conditioning paradigms were examined in separate experiments. Of the six sites, a significant CPP was observed only with accumbens injections and a significant CTA was observed only with AP region injections. It was concluded that the accumbens plays a primary role in mediating the rewarding effects of amphetamine and that the AP region plays a primary role in mediating the CTA. This constitutes an anatomical disassociation of amphetamine's rewarding and aversive effects. The differential associative bias of place-reward and taste-aversion learning apparent in the results is discussed. Offprint requests to: N.M. White     

Cholecystokinin is necessary for the expression of morphine conditioned place preference

There is evidence that the neuropeptide cholecystokinin (CCK) is important for the rewarding effects of drugs of abuse. However, less is known regarding the role of CCK in drug seeking and craving. The present study investigated whether the CCK(B) antagonist L-365, 260 could block morphine-induced drug seeking using the conditioned place preference paradigm and whether the dopaminergic reward pathway contributes to the effect of L-365, 260 on expression of morphine place preference. We found that systemic administration of the CCK(B) antagonist L-365, 260 attenuates the expression of morphine-induced drug seeking as assessed using conditioned place preference (CPP) and shows that this effect is mediated by CCK(B) receptors in the anterior nucleus accumbens (NAcc). Additionally, we demonstrate that this effect is dependent on D(2) receptor activation in the anterior nucleus accumbens (NAcc). These results indicate that endogenous CCK modulates the incentive-salience of morphine-associated cues and suggest that CCK antagonists may be useful in the treatment of drug craving.     

17Beta-estradiol increases intracellular calcium concentration through a short-term and nongenomic mechanism in rat vascular endothelium in culture

17Beta-estradiol (E2) plays an important role in Ca2+ fluxes in several cell types. It has been proposed that some of its effects are of nongenomic origin E2 at vascular smooth muscle level can block calcium entry through L-type calcium channels, this mechanism cannot include vascular endothelial cells (VECs), in which increases in the intracellular calcium concentration ([Ca2+]i) are necessary to NO synthesis. We used male rat aorta ECs in culture loaded with fura-2 and a fluorescence imaging system to evaluate the short-term effects of E2 on [Ca2+]i kinetics. We explored the participation of the intracellular steroid receptor on the effects induced by E2, using tamoxifen (1 microM) and ICI 182,780 (10 microM). Our results showed that E2 (like bradykinin) induced an increase in [Ca2+]i. Such agonist-like effects showed a biphasic curve behavior. The 17beta-estradiol effects were not modified by the presence of the intracellular estradiol-receptor antagonist tamoxifen, but it is blocked in the presence of the ICI 182,780. The 17beta-estradiol effects were obtained even with restriction of steroid-free diffusion into cells (17beta-estradiol-bovine serum albumin). Phospholipase Cbeta activity is involved in these effects, because U-73122, a PLCbeta inhibitor, blocked E2 effects. All E2 effects were of rapid onset (milliseconds), exerted at the membrane level, and of rapid offset. We conclude that estradiol can influence the endothelium physiologic responses through effects of nongenomic origin.     

Conditioned locomotor activity but not conditioned place preference following intra-accumbens infusions of cocaine

In the first experiment, the conditioned place preference (CPP) paradigm was used to examine the rewarding properties of bilateral microinfusions of cocaine HCl into the nucleus accumbens (0, 12.5, 25, 50, or 100 µg). No dose of intra-accumbens cocaine induced a significant CPP. However, bilateral intra-accumbens infusions ofd-amphetamine sulfate (10 µg) or intraperitoneal administration of cocaine HCl (5 or 10 mg/kg) both produced a significant preference for the drug-paired compartment. In the second experiment, the ability of bilateral intra-accumbens infusions of cocaine HCl (50 µg) to elicit conditioned locomotor activity (CLA) was examined. During the conditioning trials, intra-accumbens cocaine significantly increased locomotor activity. On the test day, when no drug was administered, the group that had previously received cocaine in the activity chamber showed significantly greater locomotor activity than the vehicle control group. This demonstration of CLA indicates that rats are able to associate the effects of intra-accumbens infusions of cocaine with environmental stimuli; however, these infusions are not rewarding as measured by the CPP paradigm. In addition, these results may indicate important differences between the neural substrates for cocaine and amphetamine reward and reveal a dissociation between CPP and CLA.     

The nucleus accumbens as a site of action for rewarding properties of testosterone and its 5alpha-reduced metabolites

Testosterone (T)'s positive hedonic effects may be mediated by actions of its metabolites, dihydrotestosterone (DHT) or 3alpha-androstanediol (3alpha-diol), in the nucleus accumbens (NA). In Experiment 1, adult, intact, male rats were systemically administered 1 mg of T, DHT, 3alpha-diol or vehicle, at different time points to examine concentrations of androgens in the NA. Rats administered 3alpha-diol had significantly increased concentrations of 3alpha-diol in the region of the brain encompassing the NA. These data are consistent with previous data from our laboratory demonstrating that 3alpha-diol elicits a conditioned place preference (CPP) more effectively than either T or DHT, when administered systemically. In Experiment 2, rats received implants of T, DHT or 3alpha-diol to the NA immediately prior to placement in the CPP apparatus on conditioning days. Implants of T, DHT or 3alpha-diol, but not vehicle, significantly increased time spent on the non-preferred side of the chamber on the test day. This effect was only produced by androgenic stimulation of the shell of the NA and not the core of the NA. Thus, androgen regimens we have previously found to enhance CPP produced the greatest increases in 3alpha-diol concentrations in the NA region and direct implants of T, DHT or 3alpha-diol to the shell, but not the core, of the NA enhanced CPP. These data are consistent with the hypothesis that the hedonic effects of T may be due to actions of its metabolites in the NA.     

Conditioned taste aversion and place preference with buspirone and gepirone

The effects of the nonbenzodiazepine anxiolytics buspirone and gepirone were compared to diazepam at 1, 3, and 10 mg/kg using the conditioned taste aversion (CTA) paradigm. Buspirone and gepirone produced stronger CTA than diazepam (3 and 10 mg/kg) across repeated conditioning trials, indicating that these nonbenzodiazepine anxiolytics may have stronger aversive properties than diazepam. The effects of buspirone and gepirone (1 and 3 mg/kg) were also assessed using the conditioned place preference (CPP) paradigm. Both buspirone (1 and 3 mg/kg) and gepirone (3 mg/kg only) produced CPP, indicating that these drugs may have rewarding properties, and that buspirone is more potent than gepirone in producing CPP. These findings demonstrate that buspirone and gepirone have affective properties similar to abused drugs, and may therefore have abuse potential. It was also demonstrated that buspirone (3 mg/kg), but not gepirone (3 mg/kg), increased dopamine (DA) synthesis in the nucleus accumbens, a mesolimbic brain area thought to be involved in drug reward.     

Mice lacking the galanin gene show decreased sensitivity to nicotine conditioned place preference

Previous work has indicated that the neuropeptide galanin decreases sensitivity to the rewarding effects of morphine and cocaine, but increases alcohol drinking. The aim of the current study was to examine the role of galanin signaling in nicotine reward by testing the effects of nicotine in mice lacking galanin peptide (GAL −/−) as compared to wild-type (GAL +/+) controls. Using an unbiased, three-chamber conditioned place preference (CPP) paradigm the dose-response function for nicotine CPP was tested in GAL −/− and GAL +/+ mice. Since activation of extracellular signal-related kinase (ERK2) is involved in the rewarding effects of several classes of drugs of abuse, we then measured the level of ERK2 phosphorylation in the nucleus accumbens shell (NACsh) and core (NACco) of GAL −/− and GAL +/+ mice following re-exposure to the CPP chamber previously paired with nicotine as a marker of mesolimbic system activation. Finally, we examined whether acute nicotine administration affects ERK2 activity in GAL −/− and GAL +/+ mice. GAL −/− mice required a higher dose of nicotine to induce a significant CPP compared to GAL +/+ mice. In the conditioning groups showing significant expression of nicotine CPP, only GAL +/+ mice showed ERK2 activation in the NACsh. This suggests that the nicotine CPP observed in GAL +/+ mice resulted in differential recruitment of ERK signaling in the NACsh compared to GAL −/− mice. In addition, no activation of ERK2 was observed following acute nicotine administration in either genotype. These data, along with prior results, suggest that galanin alters sensitivity to drugs of abuse differentially, with morphine, cocaine and amphetamine place preference suppressed, and nicotine and alcohol preference increased, by galanin signaling.     

Tamoxifen dilates porcine coronary arteries: roles for nitric oxide and ouabain-sensitive mechanisms

BACKGROUND AND PURPOSE: Experiments were designed to determine the mechanism of the relaxation induced by tamoxifen in porcine coronary arteries at the tissue, cellular and molecular levels. EXPERIMENTAL APPROACH: Porcine left circumflex coronary arteries were isolated and isometric tension was measured. [Ca2+]i in native endothelial cells of intact arteries was determined by a calcium fluorescence imaging technique and eNOS ser1177 phosphorylation was assayed by Western blotting. KEY RESULTS: Tamoxifen induced an endothelium-dependent relaxation that was antagonized by ICI 182,780 and abolished by NG-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). L-Arginine reversed the effect of L-NAME while indomethacin was without effect. Tamoxifen-induced relaxation was attenuated by charybdotoxin (CTX) plus apamin, ouabain or by incubation in a K+ -free solution. Moreover, tamoxifen triggered extracellular Ca2+ -dependent increases in endothelial [Ca2+]i and this effect was abolished by ICI 182,780. Endothelium-independent relaxation to sodium nitroprusside was also inhibited by ouabain or in a K+ -free solution. Furthermore, tamoxifen increased endothelial nitric oxide synthase (eNOS) phosphorylation at Ser-1177 and ICI 182,780 prevented this effect. CONCLUSIONS AND IMPLICATIONS: The present results suggest that tamoxifen mainly induces endothelium-dependent relaxation and that endothelial nitric oxide (NO) is the primary mediator of this effect. NO-dependent responses may result from elevated [Ca2+]i in endothelial cells; an effect abolished by ICI 182,780. NO activates Na+/K+ -ATPase in vascular smooth muscle, leading to relaxation. These results suggest that tamoxifen is able to modulate eNOS phosphorylation directly.     

Essential role of protein kinase C in morphine-induced rewarding memory

Protein kinase C (PKC) is involved in intra-cellular signal transduction in various physiological and pathological processes including substance abuse. In the present study, the role of PKC in morphine-induced rewarding memory was investigated using the conditioned place preference (CPP) model. We found a significant translocation of PKCs from cytosol to membrane component in nucleus accumbens (NAc) of morphine-conditioned rats in a dose-dependent manner. The translocation was reduced gradually with the maintenance of morphine-induced CPP. Specifically, the protein level of PKCγ in membrane of the NAc was increased in morphine CPP rats, and decreased during the attenuation of morphine-induced CPP, while the protein level of PKCγ in cytosol of the NAc showed an opposite change. Furthermore, the PKC translocation inhibitor γV5-3 impaired the morphine-induced CPP when microinjected into the NAc. These findings indicated that PKC, especially the γ isoform, is essential for the acquisition and maintenance of morphine-associated reward memory. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.     

Role of nucleus accumbens dopamine D1 and D2 receptors in instrumental and Pavlovian paradigms of conditioned reward

RATIONALE: This study investigated the role of nucleus accumbens dopamine D1 and D2 receptors in two different paradigms of conditioned reward. OBJECTIVE: We addressed the question whether accumbal dopamine is important for the motor or for the motivational components of reward. METHODS: We compared the effects of intra-accumbal infusion of the dopamine D1 receptor antagonist SCH23390 (0.3, 1.0, 3.0 microg) and the D2 receptor antagonist sulpiride (0.3, 1.0, 3.0 microg) on conditioned lever pressing for food, with the effects on the inhibition of the startle response by a conditioned reward signal. RESULTS: Both the D1 and the D2 antagonist dose-dependently attenuated conditioned lever pressing for reward under a fixed-ratio of responding and increased the consumption of freely available lab chow. However, the preference for freely available pellets, and the attenuation of the startle response in the presence of a conditioned stimulus predicting reward were not impaired by blockade of accumbal dopamine receptors. CONCLUSIONS: Our data support the idea that dopamine in the nucleus accumbens is necessary for instrumental response selection in the context of reward rather than for the mere motor performance of behavior or for the evaluation of the hedonic properties of rewarding stimuli.     

Chronic effects of cannabis use on the human reward system: An fMRI study

Cannabis is one of the most used drugs of abuse. It affects the brain reward system in animals, and has proven rewarding and addictive potential in humans. We used functional MRI to measure brain activity during reward anticipation in a monetary reward task. Long-term cannabis users were compared to healthy controls. An additional control group consisting of nicotine users was included. Cannabis users showed attenuated brain activity during reward anticipation in the nucleus accumbens compared to non-smoking controls, but not compared to smoking controls. Cannabis users showed decreased reward anticipation activity in the caudate nucleus, compared to both non-smoking and smoking controls. These data suggest that nicotine may be responsible for attenuated reward anticipation activity in the accumbens, but that differences in the caudate are associated with the use of cannabis. Our findings imply that chronic cannabis use as well as nicotine, may cause an altered brain response to rewarding stimuli.     

Rewarding effects and reinstatement of MDMA-induced CPP in adolescent mice.

Although the rewarding effects of 3,4-methylenedioxy-metamphetamine (MDMA) have been demonstrated in self-administration and conditioned place preference (CPP) procedures, its addictive potential (ie, the vulnerability to relapse, measured by its ability to induce reinstatement of an extinguished response), remains poorly understood. In this study, the effects of MDMA (5, 10, and 20 mg/kg) on the acquisition, extinction and reinstatement of CPP were evaluated in mice, using two different protocols during acquisition of CPP. In the first experiment, animals were trained using a two-session/day schedule (MDMA and saline for 4 consecutive days), whereas in the second experiment, they were trained using an alternating day schedule (MDMA and saline each 48 h). After extinction, the ability of drug priming to reinstate CPP was evaluated. In Experiment 1, MDMA did not significantly increase the time spent in the drug-paired compartment during the post-conditioning (Post-C) test, although the preference was evident a week afterwards, lasting between 2 and 21 weeks. No reinstatement was observed after MDMA priming. In Experiment 2, all doses produced CPP in Post-C, which lasted between 1 and 4 weeks. MDMA induces reinstatement at doses up to 4 times lower than those used in conditioning. The analyses of brain monoamines revealed that the daily schedule of treatment induces a non-dose-dependent decrease in dopamine and serotonin (5-HT) in the striatum, whereas the alternating schedule produces a dose-dependent decrease of 5-HT in the cortex. These results demonstrate that MDMA produces long-lasting rewarding effects and reinstatement after extinction, suggesting the susceptibility of this drug to induce addiction.     

Rewarding properties of testosterone in intact male mice: a pilot study

The present study examined the rewarding properties of 4-androsten-17beta-ol-3-one testosterone in intact male mice using the conditioned place preference (CPP) technique. In Experiment 1, the pharmacokinetics of 0.8 and 1.2 mg/kg of testosterone were studied to determine the most appropriate temporal interval to test behavior. Additionally, the locomotor activity was recorded to control a possible interfering effect on CPP. The maximum testosterone concentration was registered at 45 min of administration, and no effects on activity were found. In Experiment 2, three groups of male OF-1 mice received four pairings of the least-preferred compartment with testosterone (0.8, 1, or 1.2 mg/kg, SC) for 30 min. On alternate days the preferred compartment was paired with vehicle for 30 min. The control group received vehicle in both compartments. No significant differences between groups were found in the time spent in the drug-paired compartment. However, when separate analyses were performed in conjunction with the color of the drug-paired compartment. CPP was observed only in animals pairing testosterone/black compartment. These results suggest that rewarding properties of testosterone treatment can be observed in male mice; these effects probably being dependent on the environmental cues used as conditioned stimuli.