Discriminative stimulus properties of oxazepam in the pigeon

Five pigeons were trained to discriminate IM injections of oxazepam (4.0 mg/kg) from vehicle with responding maintained under a fixed-ratio 30 schedule of food delivery. Under test conditions, responding increased in a dose-dependent manner in all pigeons after the administration of other benzodiazepines including diazepam (0.01–1.0 mg/kg), temazepam (0.01–3.0 mg/kg), halazepam (0.1–56.0 mg/kg), and midazolam (0.1–1.0 mg/kg) as well as the barbiturate pentobarbital (2.0–8.0 mg/kg) and the non-benzodiazepine anxiolytic CL 218,872 (1.0–8.0 mg/kg). At the higher doses of each of these compounds, over 80% of responding occurred on the oxazepam-appropriate key. Cocaine (0.5–4.0 mg/kg), bupropion (3.0–56.0 mg/kg) and nortriptyline (3.0–56.0 mg/kg) failed to substitute for oxazepam even at doses that decreased rates of responding. The discriminative stimulus (DS) effects of the lowest doses of oxazepam and CL 218,872 that produced 100% drug-appropriate responding were blocked by the benzodiazepine antagonist Ro 15–1788. This antagonism was reversed by increasing the dose of the agonists. The DS effects of diazepam were antagonized partially by Ro 15–1788 (3 of 5 pigeons), and the antagonism was reversed by higher doses of diazepam in two of these pigeons. The DS effects of pentobarbital were antagonized by Ro 15–1788 in 2 of 5 pigeons, but the blockade was not reversed by higher pentobarbital doses.