The effects of drug discrimination history on drug discrimination and on punished and unpunished responding.

Pigeons trained to discriminate methamphetamine from saline after a history of training to discriminate pentobarbital from saline responded on the drug key after both pentobarbital and methamphetamine, but the association of these drugs by reinforcing their discriminative stimulus responses on the same key did not influence their effects on either punished or unpunished responding. Similarly, pigeons trained to discriminate morphine from saline after a history of discrimination of buspirone from saline, responded on the drug key after both buspirone and morphine, but the association of their discriminative stimulus responses did not influence their effects on either punished or unpunished responding. Whether the effects of these drugs as discriminative stimuli, or their effects on punished and unpunished responding were studied first in the session did not influence the effects of these drugs. Low doses of methamphetamine or pentobarbital did not produce responding on the drug key in birds trained to discriminate higher doses of both drugs, but combinations of these doses did produce responding on the drug key. However, these combinations of low doses of methamphetamine with pentobarbital did not increase the rate-increasing effects of pentobarbital on punished responding.