title: Effects of chronic mild stress on rats selectively bred for behavior related to bipolar disorder and depression.
abstract: To test the possibility that chronic mild stress (CMS) might be unreliable in producing its often-intended outcome (i.e., decreased preference for sucrose, hypothesized to represent depression-relevant anhedonia) because it is typically applied to "normal" rats, a CMS procedure was applied to rats that may possess genetic susceptibility to affective disorders, having had been selectively-bred to show behavior indicative of such disorders. These rat lines were: Hyperactive (HYPER) rats, which show characteristics of bipolar disorder, Swim-test Susceptible (SUS) and Swim-test Resistant (RES) rats, being susceptible or resistant to effects of stress in the swim test, Swim High-active (SwHi) and Swim Low-active (SwLo) rats, which innately show high or low activity in the swim test. These selectively-bred lines were compared to normal, non-selectively bred (NS) rats. During CMS, HYPER rats, both females and males, as well as RES and SwHi rats, showed reduced consumption of a palatable 2% sucrose solution, and reduced preference for sucrose (vs. water) in comparison to non-stressed rats (no CMS) of the same lines. In contrast, CMS produced no decrease in sucrose consumption or in preference for sucrose in normal NS rats, and actually a caused a slight increase in sucrose consumption and preference in male NS rats. Other measures that indicate depression - food intake and motor activity in the home cage - were also assessed. SwLo and SwHi showed greater sensitivity to having their home-cage ambulatory activity reduced by CMS than did NS rats, but no other such differences relative to NS rats were seen for these other measures; thus, changes in sucrose intake or preference could not be explained by a change in caloric intake. These results suggest that the genetic attributes of animals can influence the outcome of CMS, and that the application of CMS to normal, non-selected rats may account, at least in part, for the unreliability of CMS in decreasing consumption of palatable substances and decreasing preference for such substances.
authors.affiliation: Department of Psychiatry, Emory University School of Medicine, Atlanta, GA 30306, United States.
authors.forename: Ryan
authors.initials: R
authors.lastname: Murray
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Boss-Williams
authors.forename: Jay M
authors.initials: JM
authors.lastname: Weiss
mesh_terms: D000818:Animals; D001714:Bipolar Disorder / Q000150:complications / Q000235:genetics / Q000523:psychology*; D001947:Breeding; D003863:Depression / Q000150:complications / Q000235:genetics / Q000523:psychology*; D004195:Disease Models, Animal; D004435:Eating / Q000235:genetics; D005518:Food Preferences; D009043:Motor Activity / Q000235:genetics; D012727:Sex Characteristics; D013315:Stress, Psychological / Q000150:complications / Q000235:genetics / Q000523:psychology*
keywords: Affective disorder; Bipolar disorder; Depression; Genetic predisposition; Rat model; Stress