The acquisition, extinction and spontaneous recovery of Pavlovian drug conditioning induced by post-trial dopaminergic stimulation/inhibition

• Published in: Pharmacology, biochemistry and behavior Vol. 156; pp. 24 - 29
• Main Authors: Santos, Breno Garone, Carey, Robert J, Carrera, Marinete Pinheiro
• Format: Journal Article
• Language: English
• Published: United States 01.05.2017
• Subjects: Animals; Apomorphine - pharmacology; Conditioning, Classical - drug effects; Dopamine - pharmacology; Male; Rats; Rats, Wistar; Post-trial; Spontaneous recovery; Trace-conditioning; Extinction; Apomorphine; Novel environment
• ISSN: 0091-3057; 1873-5177
• DOI: 10.1016/j.pbb.2017.04.002

In contextual drug conditioning, the onset of the drug treatment is contiguous with the contextual cues. Evidence suggests that drug conditioning also can occur if there is a discontinuity between the onset of the drug effect and offset of the contextual cues. Here we examine whether post-trial contextual drug conditioning conforms to several Pavlovian conditioning tenets namely: acquisition, extinction and spontaneous recovery. Six groups of rats received apomorphine (0.05 or 2.0mg/kg) and vehicle immediately or after a 15min delay following a 5min non-drug exposure to an open-field during three successive days (conditioning phase). The extinction phase occurred on days 4-8, in which all post-trial treatments were vehicle injections. After 2days of non-testing, the final test was performed. The results showed that on the first test day, the activity levels of the 6 groups were statistically equivalent. On test day 2, there were marked differences in activity levels selectively between the two immediate post-trial apomorphine treatment groups. The immediate low dose apomorphine group displayed a reduction in activity and the immediate high dose group an increase in activity relative to their day 1 levels. The activity levels of both vehicle groups and both apomorphine delay groups remained equivalent to their day 1 activity levels. On test day 3, the differences in activity levels between the two immediate post-trial apomorphine groups increased but the activity levels of the vehicle groups and the 15min delay post-trial apomorphine groups remained unchanged. In the extinction phase, the conditioned activity differences between the two immediate post-trial apomorphine groups were gradually eliminated. During the final test, the activity differences between the immediate post-trial apomorphine groups were partially restored, indicative of spontaneous recovery. These findings are consistent with several basic elements of Pavlovian conditioning and are supportive of drug induced trace conditioning.