Effects of apomorphine on novelty-induced place preference behavior in rats

Evaluation of the relationship between the gene expression level of orexin-1 receptor in the rat blood and prefrontal cortex, novelty-seeking, and proneness to methamphetamine dependence: A candidate biomarker

BACKGROUND

previous studies have suggested that methamphetamine (METH) abuse may affect orexin regulation. However, the data regarding the relationship between the current level of orexin and the vulnerability to METH abuse are minimal. Here, we have investigated the correlation between the gene expression level of the orexin-1 receptor (OX1R) in the rat prefrontal cortex (PFC) and blood lymphocytes and susceptibility to METH dependence and its impact on novelty-seeking behavior.

METHODS

male Wistar rats were first examined for novelty-seeking behavior by the novel object recognition test, and the expression level of OX1R in their blood lymphocytes was evaluated by real-time PCR. Then, the susceptibility to METH abuse was investigated by voluntary METH oral consumption test. According to the amounts of METH consumption, the animals were divided into two groups of METH preferring and non-preferring. Half of the rats in each group were sacrificed, and the level of OX1R in their blood lymphocytes and PFC tissue was measured. The other half were sacrificed for the same reason after two weeks of drug abstinence.

RESULTS

The indexes of novelty-seeking behavior were significantly higher in the METH- preferring group compared to the non-preferring animals. Furthermore, the expression level of OX1R in the blood lymphocytes and PFC in the preferring group was considerably higher than the non-preferring group.

CONCLUSION

Up-regulation of the mRNA expression level of OX1R in the lymphocytes and PFC may predict vulnerability to the METH consumption and novelty-seeking, which may serve as a potential biomarker for METH abuse.

Ibogaine Acute Administration in Rats Promotes Wakefulness, Long-Lasting REM Sleep Suppression, and a Distinctive Motor Profile

Ibogaine is a potent psychedelic alkaloid that has been the focus of intense research because of its intriguing anti-addictive properties. According to anecdotic reports, ibogaine has been originally classified as an oneirogenic psychedelic; i.e., induces a dream-like cognitive activity while awake. However, the effects of ibogaine administration on wakefulness (W) and sleep have not been thoroughly assessed. The main aim of our study was to characterize the acute effects of ibogaine administration on W and sleep. For this purpose, polysomnographic recordings on chronically prepared rats were performed in the light phase during 6 h. Animals were treated with ibogaine (20 and 40 mg/kg) or vehicle, immediately before the beginning of the recordings. Furthermore, in order to evaluate associated motor behaviors during the W period, a different group of animals was tested for 2 h after ibogaine treatment on an open field with video-tracking software. Compared to control, animals treated with ibogaine showed an increase in time spent in W. This effect was accompanied by a decrease in slow wave sleep (SWS) and rapid-eye movements (REM) sleep time. REM sleep latency was significantly increased in animals treated with the higher ibogaine dose. While the effects on W and SWS were observed during the first 2 h of recordings, the decrement in REM sleep time was observed throughout the recording time. Accordingly, ibogaine treatment with the lower dose promoted an increase on locomotion, while tremor and flat body posture were observed only with the higher dose in a time-dependent manner. In contrast, head shake response, a behavior which has been associated in rats with the 5HT_2A receptor activation by hallucinogens, was not modified. We conclude that ibogaine promotes a waking state that is accompanied by a robust and long-lasting REM sleep suppression. In addition, it produces a dose-dependent unusual motor profile along with other serotonin-related behaviors. Since ibogaine is metabolized to produce noribogaine, further experiments are needed to elucidate if the metabolite and/or the parent drug produced these effects.

Low startle magnitude may be a behavioral marker of vulnerability to cocaine addiction

Cocaine addicted men have low startle magnitude persisting during prolonged abstinence. Low startle rats show greater cocaine self-administration than high startle rats. Low startle may be a marker of a vulnerability to heightened cocaine-related behaviors in rats and similarly may be a marker of vulnerability to cocaine addiction in humans.

High impulsivity predicting vulnerability to cocaine addiction in rats: some relationship with novelty preference but not novelty reactivity, anxiety or stress

RATIONALE

Impulsivity is a vulnerability marker for drug addiction in which other behavioural traits such as anxiety and novelty seeking ('sensation seeking') are also widely present. However, inter-relationships between impulsivity, novelty seeking and anxiety traits are poorly understood.

OBJECTIVE

The objective of this paper was to investigate the contribution of novelty seeking and anxiety traits to the expression of behavioural impulsivity in rats.

METHODS

Rats were screened on the five-choice serial reaction time task (5-CSRTT) for spontaneously high impulsivity (SHI) and low impulsivity (SLI) and subsequently tested for novelty reactivity and preference, assessed by open-field locomotor activity (OF), novelty place preference (NPP), and novel object recognition (OR). Anxiety was assessed on the elevated plus maze (EPM) both prior to and following the administration of the anxiolytic drug diazepam, and by blood corticosterone levels following forced novelty exposure. Finally, the effects of diazepam on impulsivity and visual attention were assessed in SHI and SLI rats.

RESULTS

SHI rats were significantly faster to enter an open arm on the EPM and exhibited preference for novelty in the OR and NPP tests, unlike SLI rats. However, there was no dimensional relationship between impulsivity and either novelty-seeking behaviour, anxiety levels, OF activity or novelty-induced changes in blood corticosterone levels. By contrast, diazepam (0.3-3 mg/kg), whilst not significantly increasing or decreasing impulsivity in SHI and SLI rats, did reduce the contrast in impulsivity between these two groups of animals.

CONCLUSIONS

This investigation indicates that behavioural impulsivity in rats on the 5-CSRTT, which predicts vulnerability for cocaine addiction, is distinct from anxiety, novelty reactivity and novelty-induced stress responses, and thus has relevance for the aetiology of drug addiction.

High-novelty-preference rats are predisposed to compulsive cocaine self-administration

Sensation/novelty-seeking is amongst the best markers of cocaine addiction in humans. However, its implication in the vulnerability to cocaine addiction is still a matter of debate, as it is unclear whether this trait precedes or follows the development of addiction. Sensation/novelty-seeking trait has been identified in rats on the basis of either novelty-induced locomotor activity (high-responder (HR) trait) or novelty-induced place preference (high-novelty-preference trait (HNP)). HR and HNP traits have been associated with differential sensitivity to psychostimulants. However, it has recently been demonstrated that HR rats do not develop compulsive cocaine self-administration (SA) after protracted exposure to the drug, thereby suggesting that at least one dimension of sensation/novelty seeking in the rat is dissociable from the vulnerability to switch from controlled to compulsive cocaine SA. We therefore investigated whether HNP, as measured as the propensity to choose a new environment in a free choice procedure, as opposed to novelty-induced locomotor activity, predicts the vulnerability to, and the severity of, addiction-like behavior for cocaine. For this, we identified HR/LR rats and HNP/LNP rats before any exposure to cocaine. After 60 days of cocaine SA, each rat was given an addiction score based on three addiction-like behaviors (persistence of responding when the drug is signaled as not available, high breakpoint under progressive ratio schedule and resistance to punishment) that resemble the clinical features of drug addiction, namely inability to refrain from drug seeking, high motivation for the drug and compulsive drug use despite adverse consequences. We show that, as opposed to HR rats, HNP rats represent a sub-population predisposed to compulsive cocaine intake, displaying higher addiction scores than LNP rats. This study thereby provides new insights into the factors predisposing to cocaine addiction, supporting the hypothesis that addiction is sustained by two vulnerable phenotypes: a 'drug use prone' phenotype such as HR which brings an individual to develop drug use and an 'addiction prone' phenotype, such as HNP, which facilitates the shift from sustained to compulsive drug intake and addiction.

Prefrontal cortex lesions cause only minor effects on the hyperlocomotion induced by MK-801 and its reversal by clozapine

The non-competitive NMDA receptor antagonist MK-801 elicits a behavioural syndrome in rodents characterized by hyperlocomotion and stereotypies, which is antagonized by antipsychotic drugs. NMDA receptor antagonists increase prefrontal cortex (PFC) activity in rodents, as assessed by electrophysiological and neurochemical measures. The increase in glutamate outflow induced by systemic MK-801 administration in the medial PFC (mPFC) is prevented by the local administration of clozapine (Clz). In the present study, we examine whether a PFC lesion alters the behavioural syndrome induced by MK-801 in rats and the Clz-induced antagonism of MK-801 actions. We evaluated the hyperlocomotion, stereotypies and other behavioural changes induced by MK-801 in the open field and the effect of electrolytic lesions of the mPFC, and of cortical transection on the behavioural syndrome induced by MK-801 and its reversal by Clz. MK-801 (0.1-0.2 mg/kg i.p.) reduced rearings but only the higher dose induced hyperlocomotion. At this dose, MK-801 also increased disorganized movements, head weavings, and induced ataxia signs. An electrolytic lesion of the mPFC markedly reduced the number of rearings pre-treatment but caused a very slight attenuation of MK-801-induced hyperlocomotion. Cortical transection did not significantly alter MK-801 effects. Clz administration (1 mg/kg s.c.) significantly attenuated hyperlocomotion, head weavings and ataxia signs induced by MK-801 but did not prevent the decrease in rearings. The effect of Clz was essentially unaffected by electrolytic lesions of the mPFC. These results show that MK-801-induced motor syndrome and its reversal by Clz are mostly independent on PFC integrity.

The effects of inhaled acetone on place conditioning in adolescent rats

INTRODUCTION

Acetone is an ubiquitous ingredient in many household products (e.g., glue solvents, air fresheners, adhesives, nail polish, and paint) that is putatively abused; however, there is little empirical evidence to suggest that acetone alone has any abuse liability. Therefore, we systematically investigated the conditioned response to inhaled acetone in a place conditioning apparatus.

METHOD

Three groups of male, Sprague-Dawley rats were exposed to acetone concentrations of 5000, 10,000 or 20,000 ppm for 1 h in a conditioned place preference apparatus alternating with air for 6 pairing sessions. A place preference test ensued in an acetone-free environment. To test the preference of acetone as a function of pairings sessions, the 10,000 ppm group received an additional 6 pairings and an additional group received 3 pairings. The control group received air in both compartments. Locomotor activity was recorded by infrared photocells during each pairing session.

RESULTS

We noted a dose response relationship to acetone at levels 5000-20,000 ppm. However, there was no correlation of place preference as a function of pairing sessions at the 10,000 ppm level. Locomotor activity was markedly decreased in animals on acetone-paired days as compared to air-paired days.

CONCLUSION

The acetone concentrations we tested for these experiments produced a markedly decreased locomotor activity profile that resemble CNS depressants. Furthermore, a dose response relationship was observed at these pharmacologically active concentrations, however, animals did not exhibit a positive place preference.

Peer networks and sensation seeking: some implications for primary socialization theory

This article draws on recent work in sensation seeking and peer influences in drug use prevention and considers some possible implications for primary socialization theory. A particular point of focus is a postulate of the theory that an individual's personal characteristics and personality traits do not directly relate to drug use and deviance but ordinarily influence those outcomes only when they affect interactions between the individual and the primary socialization sources. The article suggests a more broadly encompassing perspective which holds that socialization learning through the primary socialization sources gives people's lives direction; it may be the tugs of activation needs which provide impetus for the actions. The authors cite a recent study in which they developed a structural equation model of influence of individual and peer variables on later alcohol and marijuana use. The model indicates an indirect route from individual sensation seeking through peers to drug and alcohol use, with adolescents picking persons of similar sensation-seeking levels, and the sensation-seeking level of these peers tending to influence alcohol and marijuana use. Although previous studies have suggested causal relationships between sensation seeking and drug use and between peer influence and drug use, the findings in this study suggest that the actual process involves both. [Translations are provided in the International Abstracts Section of this issue.]

The effects of anxiolytic drugs on novelty-induced place preference

Previous evidence has shown that rats exposed to a place preference apparatus prefer the novel compartment over the familiar. While this suggests that novelty is rewarding, an alternative interpretation is that rats avoid the familiar compartment because it is associated with some stress-related aversive event induced during the inescapable exposure sessions. To test this latter possibility, the benzodiazepine anxiolytic diazepam (0.1, 0.3, 1.0, 3.0 mg/kg) and the nonbenzodiazepine anxiolytic gepirone (0.1, 0.3, 1.0 mg/kg) were examined for their ability to alter novelty-induced place preference in rats. As expected, control animals showed a novelty-induced place preference. On the test day, this preference was disrupted by diazepam, but only at a dose (3 mg/kg) that also decreased locomotor activity. Gepirone failed to alter the preference behavior, even at a dose (1 mg/kg) that decreased locomotor behavior. In another experiment, rats spent more time in a familiar compartment that contained a novel object than in a familiar compartment with no object. These experiments indicate that preference for the novel compartment may reflect the rewarding effect of novelty rather than aversion to the familiar.

The effects of d-amphetamine on intake of food and a sweet fluid containing cocaine

Using a laboratory animal procedure designed to measure two aspects of reinforcement (self-administration and location preference), five adult rhesus monkeys each lived in three chambers: oral cocaine self-administration (0.26 mg/kg/delivery cocaine hydrochloride in a sweet fluid) was specific to one end chamber, food self-administration was specific to the other end chamber, and no food cues or fluid cues were available in the middle chamber. Throughout the 10-h experimental day monkeys experienced multiple food, cocaine, and choice (food vs. sweet cocaine fluid), sessions. Oral d-amphetamine (AMPH; 0.5-1.5 mg/kg) or placebo was administered before the sessions to determine if this anorectic drug would differentially alter food and sweet cocaine fluid self-administration. Further, the effects of AMPH on the length of time a monkey spent in each chamber, when the stimulus cues indicating commodity availability were not present (location preference) were determined. AMPH produced dose-dependent decreases in both food and cocaine self-administration without affecting choice behavior. AMPH also increased the length of time monkeys spent in the food chamber, even when no stimuli indicating food availability were present. These results indicate that the relationship between self-administration and location preference measures of reinforcement is not completely concordant. The current procedure may prove useful in studying these two measures of reinforcement.

Measuring reward with the conditioned place preference paradigm: a comprehensive review of drug effects, recent progress and new issues

This review gives an overview of recent findings and developments in research on brain mechanisms of reward and reinforcement from studies using the place preference conditioning paradigm, with emphasis on those studies that have been published within the last decade. Methodological issues of the paradigm (such as design of the conditioning apparatus, biased vs unbiased conditioning, state dependency effects) are discussed. Results from studies using systemic and local (intracranial) drug administration, natural reinforcers, and non-drug treatments and from studies examining the effects of lesions are presented. Papers reporting on conditioned place aversion (CPA) experiments are also included. A special emphasis is put on the issue of tolerance and sensitization to the rewarding properties of drugs. Transmitter systems that have been investigated with respect to their involvement in brain reward mechanisms include dopamine, opioids, acetylcholine, GABA, serotonin, glutamate, substance P, and cholecystokinin, the motivational significance of which has been examined either directly, by using respective agonist or antagonist drugs, or indirectly, by studying the effects of these drugs on the reward induced by other drugs. For a number of these transmitters, detailed studies have been conducted to delineate the receptor subtype(s) responsible for the mediation of the observed drug effects, particularly in the case of dopamine, the opioids, serotonin and glutamate. Brain sites that have been implicated in the mediation of drug-induced place conditioning include the 'traditional' brain reward sites, ventral tegmental area and nucleus accumbens, but the medial prefrontal cortex, ventral pallidum, amygdala and the pedunculopontine tegmental nucleus have also been shown to play important roles in the mediation of place conditioning induced by drugs or natural reinforcers. Thus, although the paradigm has also been criticized because of some inherent methodological problems, it is clear that during the past decade place preference conditioning has become a valuable and firmly established and very widely used tool in behavioural pharmacology and addiction research.

Psychobiology of novelty seeking and drug seeking behavior

There is considerable evidence that high novelty seekers are at increased risk for using drugs of abuse relative to low novelty seekers. This review examines the potential biological mechanism that may help explain the relationship between novelty seeking and drug seeking behavior. Evidence is summarized to suggest that exposure to novelty activates, at least in part, the same neural substrate that mediates the rewarding effects of drugs of abuse. It is argued that individual differences in response to novelty and drugs may relate to individual differences in the mesolimbic dopamine (DA) system of the brain. Individual differences in both novelty seeking and drug seeking behavior, while under some degree of genetic control, appear to be modifiable by early development experiences and this modification may relate to alterations in activity of the mesolimbic DA system. Within the context of this biological formulation, implications for the prevention and treatment of drug abuse are discussed.

Conditioned place preference paradigm: a novel approach for analgesic drug assessment against chronic pain

In response to concerns over the clinical relevance of analgesic testing paradigms which involve acute nociceptive stimuli, the present research examined the utility of the conditioned place preference (CPP) paradigm as a novel approach for determination of analgesic drug efficacy against chronic nociception. Rats display preferences for environments that have been previously paired with positively reinforcing drugs; whether place preference to the negatively reinforcing effects of analgesic drugs in an animal model of chronic pain occurs is yet unknown. The present research sought to determine whether animals experiencing chronic pain would display a place preference for an environment paired with analgesic drug treatment. Persistent inflammatory nociception was induced by unilateral injections of complete Freund's adjuvant (0.1 ml) into the rat hind paw. Place preference to the opiate agonist morphine, the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the non-steroidal anti-inflammatory drug (NSAID) indomethacin was examined in 3 separate experiments. Rats received 8 counter-balanced conditioning trials (4 drug, 4 no-drug) of 60 min each with various drug doses (morphine: 3.0 and 10.0 mg/kg; indomethacin: 2.5 and 5.0 mg/kg; MK-801: 0.03, 0.1 and 0.3 mg/kg, i.p.) or vehicle serving as the reinforcing stimuli in a 3 compartment (2 stimuli, 1 neutral) place preference apparatus. In general, morphine place preference was observed in both inflamed and non-inflamed groups; inflamed groups exhibited enhanced morphine place preference than non-inflamed groups. MK-801 produced a low-dose place preference in inflamed animals; higher doses of MK-801 produced a place aversion in both inflamed and non-inflamed groups. Indomethacin failed to produced place preference in either inflamed or non-inflamed groups. These data demonstrate that the negatively reinforcing properties of analgesic drugs can be assessed via the CPP paradigm. In addition, this paradigm offers greater clinical relevance as animals determine drug efficacy without the involvement of high-intensity, phasic nociceptive stimulation.

Trends in place preference conditioning with a cross-indexed bibliography; 1957-1991

The purpose of this work is to present a perspective of the conditioned place preference (CPP) test by offering an overview of the empirical research from 1957-1991. The intent is not to extensively analyze the controversies inherent to any behavioral technique but rather to present a survey of research using a descriptive statistics approach to explore topical issues. The objectives of this work are three-fold: (a) to provide an exhaustive bibliography of the CPP literature including articles, journal abstracts, book chapters and critical reviews; (b) to provide a cross-index of identified key words/drugs tested; and (c) to give an overview of selected procedural issues underlying CPP testing.