CLONIDINE BLOCKS ACQUISITION BUT NOT EXPRESSION OF CONDITIONED OPIATEWITHDRAWAL IN RATS

Previous studies in rodents have reported that clonidine, an alpha(2)- adrenergic receptor agonist, attenuated conditioned aversions to nalox one-precipitated opiate withdrawal when administered prior to each wit hdrawal conditioning episode. The current study was designed to determ ine whether clonidine could modify the expression of previously establ ished conditioned place aversions and conditioned suppression of opera nt responding. Dose- and time-dependent effects of clonidine on activi ty and suppression of operant responding for food identified appropria te treatment parameters for subsequent studies in which rats rendered dependent on opiates through implantation of morphine pellets were tes ted for: (1) conditioned place aversion; and (2) conditioned suppressi on of operant responding for food (fixed ratio-15 schedule), in a para digm wherein rats received four pairings of naloxone with a distinct t one and odor stimulus. Clonidine dose-dependently blocked the acquisit ion of both conditioned behaviors when administered prior to naloxone on each conditioning trial, but was ineffective in blocking the expres sion of these conditioned withdrawal signs when administered prior to the test session. [Neuropsychopharmacology 19:406-416, 1998] (C) 1998 American College of Neutropsychopharmacology. Published by Elsevier Sc ience Inc.