Learning deficiencies in Borna disease virus-infected but clinically healthy rats.

Borna disease (BD) virus, a still unclassified neurotropic agent, causes either fatal encephalomyelitis or persistent asymptomatic infection in a variety of animal species. We monitored the neuronal functions of intracerebrally infected but healthy rats with three types of learning experiments. Spatial discrimination learning, using the y maze and the hole board, was significantly less successful in BD virus-infected (I) compared with mock-infected (M) rats. Similarly, I rats tended to show a certain emotional disturbance (reduced resting behavior and less anxiety) as evaluated by open-field and neophobia tests. Furthermore, in two aversive learning experiments (taste aversion and reaction suppression via Skinner box), it appeared that the I rats expressed a significantly diminished ability to learn pain avoidance compared with M rats. In conclusion, we found specific learning deficiencies together with subtle behavioral alterations suggesting that BD virus causes certain modulations of high integrative brain functions which are only detectable under experimental conditions.