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Open Access Research

Insulin-like growth factor-I peptides act centrally to decrease depression-like behavior of mice treated intraperitoneally with lipopolysaccharide

Sook-Eun Park124, Marcus Lawson123, Robert Dantzer1234, Keith W Kelley1234 and Robert H McCusker1234*

Author Affiliations

1 Integrated Immunology and Behavior Program, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3873, USA

2 Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3873, USA

3 Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3873, USA

4 Department of Pathology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3873, USA

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Journal of Neuroinflammation 2011, 8:179  doi:10.1186/1742-2094-8-179

Published: 21 December 2011

Abstract

Centrally administered insulin-like growth factor (IGF)-I has anti-depressant activity in several rodent models, including lipopolysaccharide (LPS)-induced depression. In this study we tested the ability of IGF-I and GPE (the N-terminal tri-peptide derived from IGF-I) to alter depression-like behavior induced by intraperitoneal (i.p.) administration of LPS in a preventive and curative manner. In the first case, IGF-I (1 μg) or GPE (5 μg) was administered i.c.v. to CD-1 mice followed 30 min later by 330 μg/kg body weight i.p. LPS. In the second case, 830 μg/kg body weight LPS was given 24 h prior to either IGF-I or GPE. When administered i.p., LPS induced full-blown sickness assessed as a loss of body weight, decrease in food intake and sickness behavior. None of these indices were affected by IGF-I or GPE. LPS also induced depression-like behavior; assessed as an increased duration of immobility in the tail suspension and forced swim tests. When administered before or after LPS, IGF-I and GPE abrogated the LPS response; attenuating induction of depression-like behaviors and blocking preexistent depression-like behaviors. Similar to previous work with IGF-I, GPE decreased brain expression of cytokines in response to LPS although unlike IGF-I, GPE did not induce the expression of brain-derived neurotrophic factor (BDNF). LPS induced expression of tryptophan dioxygenases, IDO1, IDO2 and TDO2, but expression of these enzymes was not altered by GPE. Thus, both IGF-I and GPE elicit specific improvement in depression-like behavior independent of sickness, an action that could be due to their anti-inflammatory properties.

Keywords:
IGF-I; depression-like behavior; sickness; lipopolysaccharide