Effects of auditory and thermal stimuli on 3,4- methylenedioxymethamphetamine (MDMA)-induced neurochemical and behavioral responses
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The amphetamine derivative, 3,4-methylenedioxymethamphetamine (MDMA), is a popular drug often taken by young adults at dance clubs or rave parties. Laser light shows, fast-paced electronic music, and hot crowded dance floors are characteristic of these events, and Ecstasy users report that the acute effects of the drug are potentiated by these stimulatory conditions. However, it remains largely unknown how environmental stimuli impact the neurochemical and physiological effects of MDMA. The aim of the first study presented in this dissertation was to investigate how auditory stimuli (music, white noise, and no additional sound) influence MDMA conditioned place preference (CPP), self-administration, and nucleus accumbens (NAcc) dopamine (DA) and serotonin (5-HT) responses. Findings revealed a significant CPP for animals exposed to white noise during MDMA conditioning trials. After self-administration of MDMA (1.5 mg/kg), NAcc DA and 5-HT were highest in rats exposed to music during the test session. The second study aimed to investigate the effects of ambient temperature (23°or 32°C) on long-term MDMA self-administration and neurochemical responses. Results indicated no difference in self-administration or locomotor activity rates for the high versus room temperature groups across sessions. However, MDMA (3.0 mg/kg) administered in high ambient temperature resulted in significantly greater NAcc serotonin release compared to when taken at room temperature, but no differences in dopamine response was determined between the two conditions. Overall, these results indicate that auditory and thermal stimuli can effect MDMA-induced behavioral and neurochemical responses. The last aim tested a novel apparatus and method for use in animal models of drug reinforcement. By combining traditional CPP and self-administration procedures, this approach provided more informative data and circumvented some inherent drawbacks of each method alone. In addition to confirming the ability to produce drug conditioned place preferences after short- and long-term experiments, the long-term version of the procedure revealed a significant positive relationship between lever response rate and CPP magnitude. Therefore, this experimental design can be used to identify subgroups of rats that may vary in sensitivity to drug motivational effects. Further study of these populations may be useful in the development of behavioral and pharmacological therapies for drug addiction.