Null mutation of the arginine-vasopressin gene in rats slows attentional engagement and facilitates response accuracy in a lateralized reaction time task

The neurophysin vasopressin is thought to play an important role in emotional behavior and aspects of cognition in the rat, and the pathophysiology of this system has been implicated in two neurodevelopmental disorders, namely autism and schizophrenia. Genetic deficiency of vasopressin in rats, resulting from a null mutation of the vasopressin gene, causes alterations of brain development with resulting behavioral and neurochemical phenotypes in adulthood. We previously demonstrated that partial vasopressin deficiency (rats heterozygous for the null mutation) produces enhanced visuospatial attention and motor speeding. Here, the results of studies of homozygous Brattleboro rats that are fully vasopressin deficient are reported. We trained subjects to perform a lateralized reaction time task that measures visuospatial divided attention; in task conditions in which the duration of target stimuli was varied from trial to trial, homozygous Brattleboro rats showed a performance phenotype that consisted of more accurate responding for longer duration, and less accurate responding for briefer duration, target stimuli. No differences in response times were measured. Further experiments revealed that two separate processes produced this complex phenotype: a relatively slowed period of attentional engagement (resulting in compromised detection of fast onset-fast offset stimuli) that only partially masks a generally more accurate pattern of responding. These results, taken with earlier data, indicate that vasopressin plays a critical role in regulating visual attention and cognition, either directly, or via early alterations in neurodevelopment.