title: Central cholinergic involvement in sequential behavior: impairments of performance by atropine in a serial multiple choice task for rats.
abstract: Two experiments examined whether muscarinic cholinergic systems play a role in rats' ability to perform well-learned highly-structured serial response patterns, particularly focusing on rats' performance on pattern elements learned by encoding rules versus by acquisition of stimulus-response (S-R) associations. Rats performed serial patterns of responses in a serial multiple choice task in an 8-lever circular array for hypothalamic brain-stimulation reward. Two experiments examined the effects of atropine, a centrally-acting muscarinic cholinergic receptor antagonist, on rats' ability to perform pattern elements where responses were controlled by rules versus elements, such as rule-inconsistent "violation elements" and elements following "phrasing cues," where responses were controlled by associative cues. In Experiment 1, 3-element chunks of both patterns were signaled by pauses that served as phrasing cues before chunk-boundary elements, but one pattern also included a violation element that was inconsistent with pattern structure. Once rats reached a high criterion of performance, the drug challenge was intraperitoneal injection of a single dose of 50 mg/kg atropine sulfate. Atropine impaired performance on elements learned by S-R learning, namely, chunk-boundary elements and the violation element, but had no effect on performance of rule-based within-chunk elements. In Experiment 2, patterns were phrased and unphrased perfect patterns (i.e., without violation elements). To control for peripheral effects of atropine, rats were treated with a series of doses of either centrally-acting atropine or peripherally-acting atropine methyl nitrate (AMN), which does not cross the blood-brain barrier. Once rats reached a high criterion, the drug challenges were on alternate days in the order 50, 25, and 100 mg/kg of either atropine sulfate or AMN. Atropine, but not AMN, impaired performance in the phrased perfect pattern for pattern elements where S-R associations were important for performance, namely, chunk-boundary elements. However, in the structurally more ambiguous unphrased perfect pattern where rats had fewer cues and presumably relied more on S-R associations throughout, atropine impaired performance on all pattern elements. Thus, intact muscarinic cholinergic systems were shown to be necessary for discriminative control previously established by S-R learning, but were not necessary for rule-based serial pattern performance.
authors.affiliation: Department of Psychology, Kent State University, Kent, OH 44242-0001, USA. Electronic address: sfountai@kent.edu.
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Fountain
authors.forename: James D
authors.initials: JD
authors.lastname: Rowan
authors.forename: Michael O
authors.initials: MO
authors.lastname: Wollan
mesh_terms: D000818:Animals; D001245:Association Learning / Q000187:drug effects*; D001285:Atropine / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects*; D002755:Choice Behavior / Q000187:drug effects*; D003463:Cues; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D051381:Rats; D012201:Reward; D012691:Serial Learning / Q000187:drug effects*
chemical_list: D018727:Muscarinic Antagonists; D001285:Atropine
keywords: Discriminative control; Muscarinic cholinergic systems; Rule learning; Serial multiple choice task; Serial pattern performance; S–R learning