Enhanced habituation and decreased anxiety by environmental enrichment and possible attenuation of these effects by chronic α-tocopherol (vitamin E) in aging male and female rats

Middle-aged 330-day-old male and female hooded rats were group-housed for nearly 5 months in either standard cages, or in cages containing objects. Each cage also provided either pure water, or a solution of vitamin E (DL-α-tocopherol acetate) for drinking. Records were kept of averages for each cage of the rats' body weights and the volume of fluid/100 g average body weight drunk. The average daily dose of tocopherol was approximately 162 and 173 mg/kg for males and females respectively. Males (but not females) kept in enriched cages weighed less than those from standard cages. They also drank less fluid than females who also drank more tocopherol solution than males. When 490+ days old, for rats provided with water, enrichment led to decreased open-field ambulation and increased within-session decrements in the response (habituation). Enrichment also led to decreased occupancy of the center of the apparatus for males only and, for all rats combined, increased grooming behavior. It was concluded that the effects of enrichment on aged rats were due to increased within-session habituation to novelty and decreased anxiety similar to what has been suggested for younger animals. Tocopherol appeared to interfere with effects of enrichment possibly because of pro-oxidant-related increased anxiety.