Glick S D, Cox R D
Eur J Pharmacol. 1977 Apr 7;42(3):303-6. doi: 10.1016/0014-2999(77)90298-9.
Rats trained to bar-press on either a FI 15 sec or FR 30 schedule for water reinforcement were administered various doses of appomorphine, haloperidol, pilocarpine and scopolamine both before and 1--4 months after a 3-day period of continuous morphine administration. All drugs monotonically depressed response rates on both schedules with increasing dose. Chronic morphrine administration produced a persistent increase in sensitivity to apomorphine and pilocarpine and a persistent decrease in sensitivity to haloperidol and scopolamine. The results suggest that both dopaminergic and cholinergic supersensitivity are likely to be involved in protracted abstinence phenomena.