Cocaine Is Low on the Value Ladder of Rats: Possible Evidence for Resilience to Addiction

International audienceBACKGROUND:Assessing the relative value of cocaine and how it changes with chronic drug use represents a long-standing goal in addiction research. Surprisingly, recent experiments in rats--by far the most frequently used animal model in this field--suggest that the value of cocaine is lower than previously thought.METHODOLOGY/PRINCIPAL FINDINGS:Here we report a series of choice experiments that better define the relative position of cocaine on the value ladder of rats (i.e., preference rank-ordering of different rewards). Rats were allowed to choose either taking cocaine or drinking water sweetened with saccharin--a nondrug alternative that is not biologically essential. By systematically varying the cost and concentration of sweet water, we found that cocaine is low on the value ladder of the large majority of rats, near the lowest concentrations of sweet water. In addition, a retrospective analysis of all experiments over the past 5 years revealed that no matter how heavy was past cocaine use most rats readily give up cocaine use in favor of the nondrug alternative. Only a minority, fewer than 15% at the heaviest level of past cocaine use, continued to take cocaine, even when hungry and offered a natural sugar that could relieve their need of calories.CONCLUSIONS/SIGNIFICANCE:This pattern of results (cocaine abstinence in most rats; cocaine preference in few rats) maps well onto the epidemiology of human cocaine addiction and suggests that only a minority of rats would be vulnerable to cocaine addiction while the large majority would be resilient despite extensive drug use. Resilience to drug addiction has long been suspected in humans but could not be firmly established, mostly because it is difficult to control retrospectively for differences in drug self-exposure and/or availability in human drug users. This conclusion has important implications for preclinical research on the neurobiology of cocaine addiction and for future medication development

Se souvenir qu'il faut oublier: Marc Antoine et l'art de l'oubli augustéen

This article provides a viewpoint on historical, epigraphic and literary proofs that testify of a complex form of damnatio memoriae against Mark Antony, Octavian’s enemy, the Augustus to be. The very notion of damnatio memoriae, which consists of a condemnation of the memory of a given individual, raises issues regarding Mark Antony. The first part of this article discusses various elements to attempt to explore whether or not Mark Antony has actually been victim of this type of memory condemnation, orchestrated by the princeps. The second part examines poetical references to the character of Mark Antony in Vergil’s, Propertius’ and Horace’s works, which confirm the application of a political strategy of forgetting targeting the defeated enemy. Between said and unsaid, Mark Antony’s character is subject to a poetical stigmatization, sometimes focusing on its name itself, sometimes applied under allusive form, like a kind of infamia that reinforces and confirms the analysis performed in the first part of the article. One must remember that one must forget: this could be the most applicable saying when it comes to the study of the treatment of Mark Antony’s memory during the Augustan period

Relationship between response rate and reinforcement frequency in variable-interval schedules: II. Effect of the volume of sucrose reinforcement

Three rats were exposed to variable-interval schedules specifying a range of different reinforcement frequencies, using three different volumes of .32 molar sucrose (.10, .05, and .02 milliliters) as the reinforcer. With each of the three volumes, the rates of responding of all three rats were increasing, negatively accelerated functions of reinforcement frequency, the data conforming closely to Herrnstein's equation. In each rat the value of the constant K(H), which expresses the reinforcement frequency needed to obtain the half-maximal response rate, increased with decreasing reinforcer volume, the values obtained with .02 milliliters being significantly greater than the values obtained with .10 milliliters. The values of the constant R(max), which expresses the theoretical maximum response rate, were not systematically related to reinforcer volume. The effect of reinforcer volume upon the relationship between response rate and reinforcement frequency is thus different from the effect of the concentration of sucrose reinforcement: In a previous experiment (Bradshaw, Szabadi, & Bevan, 1978) it was found that sucrose concentration influenced the values of both constants, R(max) increasing and K(H) decreasing with increasing sucrose concentration