Addiction-related alterations in D1 and D2 dopamine receptor behavioral responses following chronic cocaine self-administration.

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 D1 and D2 receptors in the mesolimbic dopamine system. Thus, we determined whether addiction-related differences in cocaine self-administration would be related to differential sensitivity in functional D1 and D2 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 D1 agonist SKF 81297 to inhibit cocaine-seeking behavior elicited by cocaine priming, but supersensitive to cocaine seeking triggered by the D2 agonist quinpirole, when compared to low intake rats. Additionally, high intake rats developed profound increases in locomotor responses to D2 receptor challenge from early to late withdrawal times, whereas low intake rats developed increased responsiveness to D1 receptor challenge. In a second experiment, responses to the mixed D1/D2 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 D1 and D2 receptors and their ability to modulate cocaine-seeking behavior.

Lamotrigine in patients with bipolar disorder and cocaine dependence.

BACKGROUND: Bipolar disorder is associated with the highest substance abuse rates of any psychiatric illness. Therefore, treatments that stabilize mood and decrease drug use or cravings are of great interest. Open-label lamotrigine was examined in 30 outpatients with DSM-IV bipolar disorder and cocaine dependence. Lamotrigine was either added to existing medication regimens or used as monotherapy. METHOD: Lamotrigine was started at a dose of 25 mg/day (12.5 mg/day in those taking valproic acid) and titrated to a maximum dose of 300 mg/day. Subjects received a baseline evaluation including a structured clinical interview and weekly assessments for 12 weeks with the Hamilton Rating Scale for Depression (HAM-D), Young Mania Rating Scale (YMRS), Brief Psychiatric Rating Scale (BPRS), and Cocaine Craving Questionnaire (CCQ). At each appointment, a urine sample was obtained, and participants reported drug use during the previous week. The subjects consisted of 13 men and 17 women with cocaine dependence and bipolar I disorder (N = 22), bipolar II disorder (N = 7), or bipolar disorder not otherwise specified (N = 1), with a mean +/- SD age of 35.4 +/- 7.2 years. Data were analyzed using the last observation carried forward on all subjects who completed the baseline evaluation and at least 1 postbaseline assessment. RESULTS: Significant improvement was observed in HAM-D, YMRS, and BPRS scores (p < or =.02). Cravings also significantly decreased as measured by the CCQ (p <.001). Dollar amount spent on drugs decreased nonsignificantly. Lamotrigine was well tolerated, with no subjects discontinuing due to side effects. CONCLUSION: Lamotrigine treatment was well tolerated in this sample and associated with statistically significant improvement in mood and drug cravings but not drug use. The findings suggest that larger controlled trials of lamotrigine are needed in this population.