Serge H. Ahmed

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Differential access to cocaine self-administration produced two patterns of drug intake in rats. With 1 hour of access per session, drug intake remained low and stable. In contrast, with 6 hours of access, drug intake gradually escalated over days. After escalation, drug consumption was characterized by an increased early drug loading and an upward shift in(More)
Rationale: When access time to a continuous schedule of drug self-administration is restricted, animals tend to limit intake to a certain level over time and across doses. This observation suggests an endogenous constraint or set point that determines the individual’s preferred level of pharmacological effects. Objectives: To assess whether the transition(More)
The transition from drug use to drug addiction is associated with a process of escalation, whereby drug use becomes excessive and difficult to control. Several mechanisms have been advanced to explain escalating patterns of drug use as opposed to nonescalating patterns. Although current evidence favors hedonic tolerance, there remains some dispute about the(More)
Reinstatement of drug-seeking behavior after extinction constitutes a potential animal model of relapse to drug abuse. In a typical reinstatement experiment, previously drug-trained rats undergo extinction during which responding is no longer followed by drug delivery. After significant extinction is observed, rats are then exposed to an event expected to(More)
In standard drug self-administration settings, animals have no choice than drug use. As a result, serious doubt exists about the interpretation of drug use in experimental animals. Is it symptomatic of an underlying addiction state or merely an expectable response to lack of choice? This incertitude in turn casts a shadow over many behavioral and(More)
A paradoxical aspect of the transition to drug addiction is that drug users spend progressively more time and effort to obtain drug hedonic effects that continually decrease with repeated experience. According to the hedonic allostasis hypothesis, increased craving for and tolerance to the hedonic effects of drugs result from the same chronic alteration in(More)
The transition from stable to escalated levels of cocaine self-administration has been shown to depend upon drug availability. The generality of this phenomenon is assessed here by studying the effects of availability on heroin self-administration. Two groups of rats were trained on a 1-h continuous schedule of self-administration, after which, access to(More)
Rats provided limited daily access to cocaine (1 h) maintain stable levels of drug self-administration over time while those switched to longer access (6 h or more) exhibit escalating patterns of drug intake. These results are reminiscent of human recreational and compulsive drug-taking behavior, respectively. We found that the brains of(More)
BACKGROUND 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(More)
BACKGROUND Refined sugars (e.g., sucrose, fructose) were absent in the diet of most people until very recently in human history. Today overconsumption of diets rich in sugars contributes together with other factors to drive the current obesity epidemic. Overconsumption of sugar-dense foods or beverages is initially motivated by the pleasure of sweet taste(More)