Intramuscular Route of Administration Increases Potency in Eliciting Cocaine-Induced Behavioral Sensitization.

Abstract

Background: Cocaine is the number one abused psychostimulant drug that reaches addiction criterion in the US. In animals, repeated administration of cocaine results in behavioral sensitization which is thought to represent adaptations in the mesolimbic dopamine neural circuitry, the reward pathway. Cocaine-induced behavioral sensitization is evident in rodents and quail when cocaine is administered intraperitoneally (IP).

Objectives: The purpose of the current study was to investigate dose-dependent and temporal effects of acute and chronic intramuscular (IM) administration of cocaine in male quail.

Methods: After habituation to the test chambers, male quail received an IM injection of saline, 3 or 10 mg/kg cocaine and were immediately placed in the chambers. Distance traveled (in meters) was recorded in 5 min time bins for 30 min. Testing was conducted once per day for ten days with each subject receiving the same treatment throughout the experiment. Other behaviors including pecking, preening, and feather fluffing were measured.

Results: Cocaine-induced behavioral sensitization and tolerance were evident at relatively low doses of IM cocaine. Dose-dependent effects were evident. IM cocaine also reduced feather fluffing, a behavior that typically occurs during hypothermia.

Conclusions: The findings replicated and extended previous research with pigeons and suggested that IM administration of cocaine may be a relatively potent route of administration. Potency of drugs of abuse may be related to the bioavailability of a drug and its addictive properties. Thus, studying drugs of abuse using an IM route of administration may be useful in drug addiction research.