Prolonged ozone exposure effects behaviour, hormones and respiratory muscles in young female rats

This study evaluated behavioural and physiological (hormonal status, muscle structure) affects of prolonged ozone exposure in young females rats. Female Wistar rats were exposed at 0.12ppm of ozone during 6h per day for 15days. Prolonged ozone exposure, though not continuous, produced remarkable behavioural disturbances with an increase in drinking, grooming and resting, and a reduction of rearing, jumping-play and locomotor activities. Besides, ozone exposure was accompanied by increased plasma levels of corticosterone and free triiodothyronine (FT3). Expression of myosin heavy chain (MHC) was significantly affected in three of the five muscles studied. MHC 2B decreased significantly to the benefit of MHC 2A in diaphragm compared to control. MHC 2X increased in Anterior Digastric and decreased in Masseter Superficialis under ozone, to the benefit of MHC 2B in Masseter Superficialis. The plasma corticosterone level increase suggested that prolonged exposure to ozone was stressful. This increase could explain also the increased levels of FT3. Modified respiratory behaviour and hormonal changes both appear to be at the origin of the observed muscular adaptation.