Sensitivity changes to morphine and other drugs induced by cholinergic blockade.

Mice were given several atropine injections at a high dosage level. After 2 to 5 days of cessation of treatment the effects of morphine, arecoline, amphetamine, pentylenetetrazol, reserpine, and hexobarbital were determined and compared with those found in saline injected controls. The influence of atropine treatment on tolerance development to morphine was also studied. After withdrawal of atropine a reduction of the analgesic responses to morphine and arecoline was observed. A decrease in hexobarbital sleeping time was also found. There was no significant influence on the analgesic effect of amphetamine, on the depressant action of reserpine, and on the convulsant effect of pentylenetetrazol. The influence of the administration and further withdrawal of atropine on tolerance development to morphine was masked by the concomitant reduction of morphine analgesia. It was impossible to observe a supersensitivity to the pharmacological agents studied.