Long-lasting behavioral effects and recognition memory deficit induced by chronic mild stress in mice: effect of antidepressant treatment.
BACKGROUND
Many studies support the validity of the chronic mild stress (CMS) model of depression in rodents. However, most of them focus on analysis of reactivity to rewards during the CMS and/or depressive-like behavior shortly after stress. In this study, we investigate acute and long-term effects of CMS and antidepressant treatment on depressive, anxiety-like behavior and learning.


METHODS
Mice (C57BL/6) were exposed to CMS for 6 weeks and anhedonia was evaluated by weekly monitoring of sucrose intake. Paroxetine (10 mg kg(-1)day(-1) i.p.) or saline were administered the last 3 weeks of CMS and continued for 2 weeks thereafter. Behavioral tests were performed over the last week of CMS (acute effects) and 1 month later (long-term effects).


RESULTS
Mice exposed to CMS displayed both acute and long-term decreased sucrose intake, increased immobility in the forced swimming test (FST) and impaired memory in the novel object recognition test. It is interesting to note that a correlation was found between the cognitive deficits and the helpless behavior in the FST induced by CMS. During the CMS procedure, paroxetine treatment reverted partially recognition memory impairment but failed to prevent the increased immobility in the FST. Moreover, it decreased on its own sucrose intake. Importantly, the long-term effects of CMS were partially prevented by chronic paroxetine.


CONCLUSIONS
CMS leads to a long-term altered behavioral profile that could be partially reverted by chronic antidepressant treatment. This study brings novel features regarding the long-term effects of CMS and on the predictive validity of this depression animal model.
Elizalde
N
N
Department of Pharmacology, University of Navarra, 31080, Pamplona, Spain.
Gil-Bea
F J
FJ
Ramírez
M J
MJ
Aisa
B
B
Lasheras
B
B
Del Rio
J
J
Tordera
R M
RM
D000818:Animals; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology*; D001007:Anxiety / Q000523:psychology*; D003863:Depression / Q000523:psychology*; D004326:Drinking / Q000187:drug effects; D004924:Escape Reaction / Q000187:drug effects; D005106:Exploratory Behavior / Q000187:drug effects; D005239:Fear / Q000187:drug effects; D006380:Helplessness, Learned; D007274:Injections, Intraperitoneal; D008134:Long-Term Care; D008297:Male; D011939:Mental Recall / Q000187:drug effects*; D051379:Mice; D009042:Motivation; D009043:Motor Activity; D017374:Paroxetine / Q000494:pharmacology*; D010364:Pattern Recognition, Visual / Q000187:drug effects; D021641:Recognition, Psychology / Q000187:drug effects*; D013315:Stress, Psychological / Q000150:complications*; D013395:Sucrose / Q000008:administration & dosage; D013649:Taste / Q000187:drug effects
D018687:Antidepressive Agents, Second-Generation; D017374:Paroxetine; D013395:Sucrose