Rats self-administer sufentanil in aerosol form.

An ultrasonic nebulizer was used to create a drug vapor to develop an animal model for the self-administration of inhaled nonvolatile psychoactive drugs. An aerosol mist of a sufentanil citrate solution (10, 25, 50, or 75 micrograms/ml) was delivered to rats in response to lever presses on an FR 5 schedule of reinforcement. The speed of acquisition of the operant response and the selectivity of the drug effect were examined. Rats given access to sufentanil vapor (50 or 75 micrograms/ml) in 13-15 h overnight training sessions reached an average of one reinforcement per hour on an FR 5 schedule of reinforcement significantly sooner than did rats given access to water vapor. Responding maintained by sufentanil during 2-h daily testing sessions was dose dependent at 25, 50, and 75 micrograms/ml. Substituting water vapor for each of the four sufentanil concentrations significantly reduced responding within 5-20 sessions. Naloxone (1 mg/kg, IP) decreased responding for sufentanil to the level attained under water vapor. Presentation of drugs in aerosol form thus provides reasonable means of demonstrating in animals the reinforcing properties of non-volatile drugs by the pulmonary or intranasal route.