Effects of the dopamine/norepinephrine releaser phenmetrazine on cocaine self-administration and cocaine-primed reinstatement in rats

Rationale
Like other monoamine releasers such as D-amphetamine, chronic treatment with phenmetrazine can attenuate cocaine self-administration in monkeys.

Objectives
The present studies extended this finding to rodents and to cocaine-primed reinstatement, a putative laboratory animal model of relapse.

Methods
In experiment 1, rats self-administered food pellets or injections of 0.19 mg/kg cocaine (i.v.) under a progressive-ratio schedule. When responding was stable, subcutaneous osmotic pumps were implanted containing saline or (+)-phenmetrazine (25 or 50 mg/kg per day). In experiment 2, rats self-administered injections of 0.75 mg/kg cocaine under a fixed-ratio 1 schedule in daily 6-h sessions. When responding was stable, rats were removed from the self-administration environment for 7 days and treated continuously with saline, 5 mg/kg per day D-amphetamine or phenmetrazine (25 or 50 mg/kg per day) via osmotic pumps. Rats were then returned to the self-administration context while treatment continued, and responding was extinguished by removing response-contingent stimulus changes and cocaine injections. Once responding was extinguished, reinstatement tests were conducted using cocaine injections (10 mg/kg i.p.).

Results
Phenmetrazine decreased self-administration of cocaine, but not food pellets, during the 14-day treatment period; effects persisted for several days after treatment was discontinued. Moreover, cocaine-induced increases in responding during the reinstatement test were attenuated by D-amphetamine and both phenmetrazine doses.

Conclusions
These results extend the study of the effects of phenmetrazine on cocaine self-administration to a rodent model, and provide further support for the use of monoamine releasers as agonist medications for cocaine abuse.