Hypophysectomy-induced striatal hypersensitivity and mesolimbic hyposensitivity to apomorphine.

Seven days post-hypophysectomy female rats display a hyposensitivity to the locomotor effects of apomorphine and a hypersensitivity to the stereotypy effects of apomorphine, while at 28 days post-hypophysectomy they are hypersensitive to both the locomotor and stereotypy effects of apomorphine. The hyposensitivity to the locomotor effects, at 7 days post-hypophysectomy, was associated with a decrease in 3H-spiroperidol binding and an increase in tyrosine hydroxylase activity in the nucleus accumbens septi, whereas the hypersensitivity, at 28 days post-hypophysectomy, was associated with an increase in 3H-spiroperidol and a decrease in tyrosine hydroxylase activity in the n. accumbens septi. The increased apomorphine-induced stereotypy in both the 7 and 28 days post-hypophysectomized animals was related to an increased 3H-spiroperidol binding and a decreased tyrosine hydroxylase activity in the striatum. These behavioral and neurochemical data demonstrate that following hypophysectomy female rats will develop a transient decrease in dopamine receptor sensitivity in the n. accumbens septi, while the dopamine sensitivity in the striatum is increased. Thus the hypophysectomized female rat may prove to be a valuable model to study these two separate dopamine systems and their possible modulatory roles in the display of various behaviors.