Behavioral and neurochemical differences between Fischer 344 and Harlan-Wistar rats raised identically.

Inbred Fisher 344 and outbred Harlan-Wistar rats were compared in the elevated plus maze, the black-and-white box, the social interaction test, and a modified open-field test, to assess the contribution of genetic factors to aversion-motivated behavior. All animals used were born and raised under identical conditions. Compared to the Wistar rats, the Fischer rats displayed a more pronounced fearful behavior in all tests. In a separate microdialysis study, the relationship between behavioral variations to biochemical differences was assessed, with serotonin (5-HT) release in the ventral hippocampus being measured during the elevated plus-maze test. Exposure to the elevated plus-maze induced an increase in hippocampal 5-HT in the (more anxious) Fischer rats but not in the (less anxious) Wistar rats. The results confirm the influence of genetic factors on emotionality in rats and demonstrate a close, although not simple, relationship between the serotonergic system and "anxiety-related" behavior.