Drugs of abuse dynamically regulate adult neurogenesis, which appears important for some types of learning and memory. Interestingly, a major site of adult neurogenesis, the hippocampus, is important in the formation of drug-context associations and in the mediation of drug-taking and drug-seeking behaviors in animal models of addiction. Correlative evidence suggests an inverse relationship between hippocampal neurogenesis and drug-taking or drug-seeking behaviors, but the lack of a causative link has made the relationship between adult-generated neurons and addiction unclear. We used rat intravenous cocaine self-administration in rodents, a clinically relevant animal model of addiction, to test the hypothesis that suppression of adult hippocampal neurogenesis enhances vulnerability to addiction and relapse. Suppression of adult hippocampal neurogenesis via cranial irradiation before drug-taking significantly increased cocaine self-administration on both fixed-ratio and progressive-ratio schedules, as well as induced a vertical shift in the dose-response curve. This was not a general enhancement of learning, motivation, or locomotion, because sucrose self-administration and locomotor activity were unchanged in irradiated rats. Suppression of adult hippocampal neurogenesis after drug-taking significantly enhanced resistance to extinction of drug-seeking behavior. These studies identify reduced adult hippocampal neurogenesis as a novel risk factor for addiction-related behaviors in an animal model of cocaine addiction. Furthermore, they suggest that therapeutics to specifically increase or stabilize adult hippocampal neurogenesis could aid in preventing initial addiction as well as future relapse.

The cocaine-addicted phenotype can be modeled in rats based on individual differences in preferred levels of cocaine intake and a propensity for relapse in withdrawal. These cocaine-taking and -seeking behaviors are strongly but differentially regulated by postsynaptic D 1 and D 2 receptors in the mesolimbic dopamine system. Thus, we determined whether addiction-related differences in cocaine selfadministration would be related to differential sensitivity in functional D 1 and D 2 receptor responses. Using a population of 40 outbred Sprague-Dawley rats trained to self-administer cocaine for 3 weeks, we found that animals with higher preferred levels of cocaine intake exhibited a vertical and rightward shift in the self-administration dose-response function, and were more resistant to extinction from cocaine self-administration, similar to phenotypic changes reported in other models of cocaine addiction. After 3 weeks of withdrawal from cocaine self-administration, high intake rats were subsensitive to the ability of the D 1 agonist SKF 81297 to inhibit cocaine-seeking behavior elicited by cocaine priming, but supersensitive to cocaine seeking triggered by the D 2 agonist quinpirole, when compared to low intake rats. Additionally, high intake rats developed profound increases in locomotor responses to D 2 receptor challenge from early to late withdrawal times, whereas low intake rats developed increased responsiveness to D 1 receptor challenge. In a second experiment, responses to the mixed D 1 /D 2 agonist apomorphine and the NMDA glutamate receptor antagonist MK-801 failed to differ between low and high intake rats. These findings suggest that cocaine addiction is related specifically to differential alterations in functional D 1 and D 2 receptors and their ability to modulate cocaine-seeking behavior.

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False positive acetaminophen tests may result when enzymatic-colorimetric assays are used, most commonly with bilirubin concentrations >10 mg/dl, leading to potential clinical errors in this setting. Bilirubin (or possibly other substances in acute liver failure sera) appears to affect the reliable measurement of acetaminophen, particularly with enzymatic-colorimetric assays.

A procedure for detection and quantification of free codeine, free morphine, and 6-acetylmorphine in urine is presented. The analytes were extracted at neutral pH by solid-phase extraction prior to derivatization to their trifluoroacetyl derivatives. The derivatized extracts were analyzed by gas chromatography/mass spectrometry in the electron impact mode. Confirmation of the analytes was accomplished by comparing the ion abundance ratios of the analytes to those of a previously analyzed standard. The qualitative ion abundance ratios were required to be within 20% of those of the standard for acceptance. Quantification was based on the tri-deuterated analogs of the analytes. Linearity was obtained in the range of 10 to 1000 ng/mL, with correlation coefficients of all analytes exceeding 0.999. Percent recoveries were 90% for codeine, 88% for morphine, and 85% for 6-acetylmorphine. No hydrolysis of 6-acetylmorphine occurs during the extraction procedure. The authors also studied the stability of 6-acetylmorphine at various storage conditions of pH, temperature, and chemical preservation. 6-Acetylmorphine was found to be stable for 12 weeks when stored at -17 degrees C.