Behavioral responses of long-term hyperprolactinaemic rats.

Rats with long-term endogenous hyperprolactinaemia induced by pituitary homografts under the kidney capsule displayed an enhancement of amphetamine- and apomorphine-induced stereotypy, a facilitated acquisition of active avoidance behavior and a decreased responsiveness to electrical footshock. However, no difference between homografted and sham-operated rats was observed with respect to grooming behavior. It is concluded that at least two processes occur during prolonged hyperprolactinaemia, i.e. development of tolerance to prolactin with respect to enhanced grooming activity and of supersensitivity of postsynaptic dopaminergic receptor systems. These two processes may be dependent or independent from each other.