Altered emotionality of the vasopressin-deficient Brattleboro rat.

Observation of open field behavior of vasopressin-deficient (DI) and normal Long-Evans rats indicated elevated levels of open field activity for the DI rats. Exposure to an acoustic stressor resulted in decreased activity in both groups of animals but with a lesser effect on the DI rat. Handling prior to experimentation diminished the differences between DI and normal rats. Although both groups displayed an equivalent rise in plasma corticosterone in response to the open field, the addition of the acoustic stressor resulted in greater elevation of corticosterone in the normal animals. The behavioral and hormonal data suggest that the DI rat exhibits decreased emotional reactivity. Measurement of brain neurotransmitter levels revealed higher concentrations of serotonin, norepinephrine and dopamine in the limbic regions of the DI rat. These alterations may underlie the behavior reflecting decreased emotionality of the DI rat. In turn, the altered emotional state may be the basis for alteration in performance on learning/memory tasks of these animals. Thus, vasopressin effects on the retrieval and/or consolidation of information may not be direct but rather through its ability to influence the emotional state of the animal.