Environmental Enrichment Protects Tear Secretion from the Deleterious Effects of Acute Stress

Abstract

Purpose: Environmental Enrichment (EE) is defined as a living environment with a combination of complex inanimate and social stimulation. We investigated the tear secretion in mice by the effects of EE living conditions, and EE under acute stress.

Methods: Male C57BL/6JJcl mice were exposed to EE (n=12) and compared to mice living in a standard environment (ST) (n=12) for 4 weeks. After 4 weeks, mice were restrained once as an acute stress test for 4 hours. Tear secretion was measured by using cotton threads (Zone Quick) for 30 seconds once a week, and pre- and post-acute stress. The mice were sacrificed and the lacrimal glands (LG) were removed for gene expression analysis. Total RNA was extracted from the LGs of mice, then real time PCR was performed for Interleukin (IL)-1β, IL-6 and IL-12.

Results: Tear secretion in the EE group increased compared to the ST group at week 1, week 3 and week 4. Especially tear secretion in the EE group was significantly higher (2.8±1.1 mm) than in the ST group (1.7±0.6 mm, P<0.01) at week 1. After the acute stress test, the tear secretion decreased only in the ST group (pre-: 3.8±1.9 mm, post-: 2.3±1.1 mm, P=0.06). Tear secretion in the EE group didn’t change after the acute stress (pre-: 5.2±2.0 mm, post-: 5.1±2.5 mm). In the real time PCR, IL-1β and IL-6 expression significantly increased compared to pre- in only the ST group (P<0.01, P<0.05, respectively).<br />

Conclusions: The results of this study suggest that environmental enrichment may increase tear secretion and prevent a reduction of tear secretion from acute stress.