Prolactin as a link between behavioral and immune differences between the Roman rat lines.

Roman high (RHA)- and low (RLA)-avoidance rats are two lines of Wistar rats genetically selected on the basis of their active avoidance behavior in a shuttle-box. They also differ in several other behavioral responses, such as their locomotor activity in novel environments (open-field, circular corridor), with the RHA rats being more active than the RLA animals, as well as in endocrine reactivity and immune functions. These experiments were designed to investigate further the neuroendocrine characteristics of these animals as a possible link between the brain and immune functions. Despite the marked behavioral and immune differences observed, no between-lines variation could be found in basal hypothalamo-pituitary-adrenocortical axis activity or in its responses to different protocols of novel environment stress, or after corticotropin-releasing factor (CRF) challenge. On the other hand, stimulated prolactin levels were higher in the low avoidance line. These results exclude the pituitary-adrenocortical axis and suggest prolactin as a link between behavioral and immune differences between the Roman lines. Moreover, these results indicate that these rats may be an excellent model for the study of the relationships between the brain and the immune system.