Age at group formation alters behavior and physiology in male but not female CD-1 mice

Alessandro Bartolomucci, Alessio Chirieleison, Laura Gioiosa, Graziano Ceresini, Stefano Parmigiani, Paola Palanza

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30 Scopus citations


In the laboratory environment, rodents are usually housed in unisexual groups, which are assembled after weaning. Housing of unfamiliar subjects has been described, however, as a stressful social setting for rodents and other mammals. Aim of the present study was to evaluate whether the age at which house mice are grouped might affect their behavior and physiology. Male or female unisexual groups were formed at different ages: at weaning, i.e., before puberty (JUV); at adolescence, i.e., after puberty (AD); and controls were raised with siblings since birth (CON). Results show that age at group formation induced several behavioral and physiological alterations in males but not in females. Specifically, when compared to controls, JUV males showed higher aggression, smaller preputial gland, and a marked reduction of neophobia in the free exploratory paradigm. Fewer changes occurred in the AD males, which showed reduced neophobia in the free exploratory paradigm and, when adults, a reduction in body weight. Females were not affected by the experimental treatment. Surprisingly, the basal corticosterone assessed at the nadir was lower for both males and females JUV and AD respect to CON. In conclusion, it is clear that mixing groups at different ages has profound effects on mouse behavior and physiology.

Original languageEnglish (US)
Pages (from-to)425-434
Number of pages10
JournalPhysiology and Behavior
Issue number2-3
StatePublished - Sep 15 2004

Bibliographical note

Funding Information:
Financially supported by Italian MURST (COFIN 2000) and University of Parma (FIL 2000). Authors wish to thank Anna Moles for statistical advice, Valeria Vascelli and Romano Romani for technical assistance, and Sara Campi for help in collecting the data.


  • Aggressive behavior
  • Corticosterone
  • Elevated plus maze
  • Free exploratory paradigm
  • Housing
  • Sex differences
  • Stress
  • Welfare


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