Effect of parasympathetic blockade on ventilatory and cardiac depression induced by opioids

Non-pharmacological factors that determine drug use and addiction

Based on their pharmacological properties, psychoactive drugs are supposed to take control of the natural reward system to finally drive compulsory drug seeking and consumption. However, psychoactive drugs are not used in an arbitrary way as pure pharmacological reinforcement would suggest, but rather in a highly specific manner depending on non-pharmacological factors. While pharmacological effects of psychoactive drugs are well studied, neurobiological mechanisms of non-pharmacological factors are less well understood. Here we review the emerging neurobiological mechanisms beyond pharmacological reinforcement which determine drug effects and use frequency. Important progress was made on the understanding of how the character of an environment and social stress determine drug self-administration. This is expanded by new evidence on how behavioral alternatives and opportunities for drug instrumentalization generate different patterns of drug choice. Emerging evidence suggests that the neurobiology of non-pharmacological factors strongly determines pharmacological and behavioral drug action and may, thus, give rise for an expanded system's approach of psychoactive drug use and addiction.

Opposite environmental gating of the experienced utility ('liking') and decision utility ('wanting') of heroin versus cocaine in animals and humans: implications for computational neuroscience

BACKGROUND

In this paper, we reviewed translational studies concerned with environmental influences on the rewarding effects of heroin versus cocaine in rats and humans with substance use disorder. These studies show that both experienced utility ('liking') and decision utility ('wanting') of heroin and cocaine shift in opposite directions as a function of the setting in which these drugs were used. Briefly, rats and humans prefer using heroin at home but cocaine outside the home. These findings appear to challenge prevailing theories of drug reward, which focus on the notion of shared substrate of action for drug of abuse, and in particular on their shared ability to facilitate dopaminergic transmission.

AIMS

Thus, in the second part of the paper, we verified whether our findings could be accounted for by available computational models of reward. To account for our findings, a model must include a component that could mediate the substance-specific influence of setting on drug reward RESULTS: It appears of the extant models that none is fully compatible with the results of our studies.

CONCLUSIONS

We hope that this paper will serve as stimulus to design computational models more attuned to the complex mechanisms responsible for the rewarding effects of drugs in real-world contexts.

Heroin versus cocaine: opposite choice as a function of context but not of drug history in the rat

RATIONALE

Previous studies have shown that rats trained to self-administer heroin and cocaine exhibit opposite preferences, as a function of setting, when tested in a choice paradigm. Rats tested at home prefer heroin to cocaine, whereas rats tested outside the home prefer cocaine to heroin. Here, we investigated whether drug history would influence subsequent drug preference in distinct settings. Based on a theoretical model of drug-setting interaction, we predicted that regardless of drug history rats would prefer heroin at home and cocaine outside the home.

METHODS

Rats with double-lumen catheters were first trained to self-administer either heroin (25 μg/kg) or cocaine (400 μg/kg) for 12 consecutive sessions. Twenty-six rats were housed in the self-administration chambers (thus, they were tested at home), whereas 30 rats lived in distinct home cages and were transferred to self-administration chambers only for the self-administration session (thus, they were tested outside the home). The rats were then allowed to choose repeatedly between heroin and cocaine within the same session for seven sessions.

RESULTS

Regardless of the training drug, the rats tested outside the home preferred cocaine to heroin, whereas the rats tested at home preferred heroin to cocaine. There was no correlation between drug preference and drug intake during the training phase.

CONCLUSION

Drug preferences were powerfully influenced by the setting but, quite surprisingly, not by drug history. This suggests that, under certain conditions, associative learning processes and drug-induced neuroplastic adaptations play a minor role in shaping individual preferences for one drug or the other.

The Affective and Neural Correlates of Heroin versus Cocaine Use in Addiction Are Influenced by Environmental Setting But in Opposite Directions

Previous studies have shown that individuals with heroin and cocaine addiction prefer to use these drugs in distinct settings: mostly at home in the case of heroin and mostly outside the home in the case of cocaine. Here we investigated whether the context would modulate the affective and neural responses to these drugs in a similar way. First, we used a novel emotional task to assess the affective state produced by heroin or cocaine in different settings, based on the recollections of male and female drug users. Then we used fMRI to monitor neural activity during drug imagery (re-creating the setting of drug use) in male drug users. Consistent with our working hypothesis, the majority of participants reported a shift in the affective valence of heroin from mostly pleasant at home to mostly unpleasant outside the home (p < 0.0001). The opposite shift was observed for cocaine; that is, most participants who found cocaine pleasant outside the home found it unpleasant when taken at home (p < 0.0014). Furthermore, we found a double dissociation, as a function of drug and setting imagery, in BOLD signal changes in the left PFC and caudate, and bilaterally in the cerebellum (all p values <0.01), suggesting that the fronto-striatal-cerebellar network is implicated in the contextualization of drug-induced affect. In summary, we report that the same setting can influence in opposite directions the affective and neural response to psychostimulants versus opiates in humans, adding to growing evidence of distinct substrates for the rewarding effects of these two drug classes.SIGNIFICANCE STATEMENT The rewarding effects of addictive drugs are often thought to depend on shared substrates. Yet, environmental influences can unmask striking differences between psychostimulants and opiates. Here we used emotional tasks and fMRI to explore the influence of setting on the response to heroin versus cocaine in individuals with addiction. Simply moving from one setting to another significantly decreased heroin pleasure but increased cocaine pleasure, and vice versa. Similar double dissociation was observed in the activity of the fronto-striatal-cerebellar network. These findings suggest that the effects of opiates and psychostimulants depend on dissociable psychological and neural substrates and that therapeutic approaches to addiction should take into account the peculiarities of different drug classes and the settings of drug use.

Substance-specific environmental influences on drug use and drug preference in animals and humans

Epidemiological, clinical, and preclinical evidence indicate that the setting of drug use can exert a powerful modulatory influence on drug reward and that this influence is substance-specific. When heroin and cocaine co-abusers, for example, report on the circumstances of drug use, they indicate distinct settings for the two drugs: heroin being used preferentially at home and cocaine being used preferentially outside the home. Similar results were obtained in laboratory rats. These findings will be interpreted in the light of a novel model of drug reward, based on the emotional appraisal of central and peripheral drug effects as a function of environmental context. I argue here that drug addiction research has not paid sufficient attention to the substance-specific aspects of drug abuse and this may have contributed to the present dearth of effective treatments. Pharmacological and cognitive-behavioral therapy, for example, should be tailored so as to allow the addict to anticipate, and cope with, the risks associated, in a substance-specific manner, to the different settings of drug use.

Endogenous opiates: 1987

This paper is the tenth installment of our annual review of the research during the past year involving the endogenous opiate system. It covers the nonanalgesia and behavioral studies of the opiate peptides published in 1987. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal activity; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.