title: The relationship between adjunctive drinking, blood ethanol concentration and plasma corticosterone across fixed-time intervals of food delivery in two inbred mouse strains.
abstract: Schedules of intermittent food delivery induce excessive fluid intake, termed schedule-induced polydipsia (SIP), and hypothalamic-pituitary-adrenal (HPA) axis activation is important for the expression and maintenance of this adjunctive behavior. Previous work has focused on examining the relationship between water intake and plasma corticosterone (CORT) in rats at a single or a limited range of fixed time (FT) intervals. However, little remains known regarding SIP and the corresponding stress response (1) across the bitonic function that epitomizes adjunctive behavior, (2) when ethanol is the available fluid, and (3) when a species other than rat or multiple strains are studied. Here we report the findings from ethanol-preferring C57BL/6J (B6) and non-preferring DBA/2J (D2) mice serially exposed to progressively larger FT intervals (0 → 60 min) and given access to either water or a 5% (v/v) ethanol solution. Following 2 weeks of experience with each schedule, blood samples were collected at the conclusion of the last 60-min session to evaluate CORT and the blood ethanol concentration (BEC) achieved. While both strains exhibited a bitonic function of ethanol intake and BEC that peaked at or near a 5-min interval, only D2 mice showed a similar response with water. In contrast, CORT levels rose monotonically with incremental increases in the FT interval regardless of the strain examined or fluid type offered, indicating that glucocorticoid release likely reflects the aversive aspects of increasing intervals between reinforcement rather than engagement in adjunctive behavior. These findings also caution against the use of a single intensity stressor to evaluate the relationship between stress and ethanol intake, as the magnitude of stress appears to affect ethanol consumption in a non-linear fashion.
authors.affiliation: Department of Behavioral Neuroscience, Oregon Health and Science University, Portland, OR, USA; Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science University, Beaverton, OR, USA. Electronic address: fordma@ohsu.edu.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Ford
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Steele
authors.forename: Aubrey D
authors.initials: AD
authors.lastname: McCracken
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Finn
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Grant
mesh_terms: D000428:Alcohol Drinking / Q000097:blood*; D000818:Animals; D003216:Conditioning, Operant; D003345:Corticosterone / Q000097:blood*; D004327:Drinking Behavior; D000431:Ethanol / Q000097:blood*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D012055:Reinforcement Schedule; D013045:Species Specificity
chemical_list: D000431:Ethanol; D003345:Corticosterone
keywords: Adjunctive behavior; Blood ethanol concentration; C57BL/6 mice; Corticosteroid; DBA/2 mice; Drinking patterns; Excessive alcohol consumption; HPA axis; Schedule-induced polydipsia; Stress