Summary
Rats were exposed to either a drug-induced state (1.0 mg/kg scopolamine) or an undrugged state (saline) at each stage of a three-stage procedure. They were first trained to lick a tube, then were exposed to classical fear conditioning in the absence of the tube, and finally were tested for conditioned suppression of licking. Animals tested at the midst of the dark period of the daily light/dark cycle displayed a failure of conditioned suppression if conditioning had occurred under the novel state; suppression was less consistently impaired in animals tested at the midst of the photoperiod. All animals exposed to a consistent drugged (or undrugged) state displayed conditioned suppression. Results suggest that experimental procedures frequently employed in studying drug manipulations of learning and memory may be biased against the transfer of training to the test situation. Scopolamine effects, often attributed to changes in learning or memory, may often represent a weakening in stimulus control of behavior resulting from transitions between drugged and undrugged states. Several factors are suggested as contributing to the diurnal difference in drug effects.
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Supported in part by N. I. H. Grant MH-0722705 to R. A. P. and N. S. F. Grant G11309 to the University of Pittsburgh Computer Center.
We thank Dr. Herbert Barry, III, for his comments on this research.
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Evans, H.L., Patton, R.A. Scopolamine effects on conditioned suppression: Influence of diurnal cycle and transitions between normal and drugged states. Psychopharmacologia 17, 1–13 (1970). https://doi.org/10.1007/BF00402087
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DOI: https://doi.org/10.1007/BF00402087