Lateral Hypothalamic Mediation of Midbrain Catecholaminergic Influences on Preovulatory Surges of Serum Gonadotropin and Prolactin in Female Rats*

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Abstract
To investigate the involvement of the midbrain ascending pathways in the control of ovulation, bilateral coronal transections were produced at three rostro-caudal levels in the lateral hypothalamus as well as in the lateral forebrain on the day of proestrus. Although lateral forebrain transections failed to block spontaneous ovulation, transections in both the anterolateral hypothalamus (ALH) and the midlateral hypothalamus blocked ovulation and the proestrous surges of serum LH, FSH,and PRL. When electrochemical stimulation was applied to the diagonal band of Broca, ovulation could be induced in animals with ALH transections. Moreover, the effects of intraventricular saline, norepinephrine (NE; 40 μg), or dopamine (40μg) on the induction of preovulatory surges of serum gonadotropin and PRL were examined in proestrous rats with ALH transections. Ovulation was restored by the intraventricular injection of NE, but not of dopamine. In ALH-transected animals which ovulated in response to intraventricular NE, serum concentrations of LH, FSH, and PRL were higher than those of ALH-transected animals injected with saline. These results suggest that the lateral hypothalamus plays an important role in the control of preovulatory surges of serum gonadotropin and PRL by mediating the midbrain catecholaminergic innervation of the preoptic-hypothalamic area.

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