A review of atropinic drug effects on exploratory choice behavior in laboratory rodents

Modification of one or more of several mechanisms such as habituation, memory, attention, and sensory acuity, as well as drug aversions, may be relevant when accounting for the effects of atropinics on various exploratory-motivated behaviors.

Abstract

Effects of atropinic drugs on various forms of exploratory-motivated behavior are reviewed. Whereas spontaneous alternation and preferences for novelty are reduced by such compounds, there are no clear-cut effects on reactions to complexity as in head-poke tests. However, novelty-reinforced learned behavior is consistently increased. In view of examples of drug-induced familiarity preferences, significant effects of peripherally acting atropinics, and a number of inconsistent findings, no single explanation based on interference with central cholinergic activity accounts for all findings. In addition to their highly suspect validity as measures of exploratory-motivated behavior, the effects of atropinic drugs on various motor activities are largely dependent upon other factors such as type of activity sampled, apparatus, dose, previous experiences, and strain of the subjects. However, in general, atropinics increase nonspecific motor activity and (in high doses) ambulation. Contrary to controls, animals exposed to novel stimuli under the influence of scopolamine or atropine remain highly responsive to the same stimuli when observed subsequently in an undrugged state. Similarities between the behavioral effects of brain lesions and atropinics support the septohippocampal axis as an important site of atropinic drug action for all of the choice and activity responses discussed. In view of the similar effects of a number of drugs with different central actions, the diversity of findings must be considered in the light of interactions between several neurotransmitters and behavioral mechanisms. Modification of one or more of several mechanisms such as habituation, memory, attention, and sensory acuity, as well as drug aversions, may be relevant when accounting for the effects of atropinics on various exploratory-motivated behaviors.