Effects of intraventricular injections of norepinephrine on brain-pituitary-ovarian function in the rabbit

In estrous estrogen-primed female rabbits with electrodes chronically implanted in various subcortical regions of the brain, the intraventricular injection of an ovulation-inducing dose of norepinephrine (NE) stimulated a prolonged episode of high amplitude 40–60 cps electroencephalographic (EEG) activity in the olfactory bulb (OB) and its projections. This activity, which started usually between 30 and 60 min after NE injection and was maintained continously for periods up to an hour there-after, was regularly absent in the same rabbits when they were pseudopregnant and non-ovulatory to NE. Similar OB-EEG activity and ovulation had been observed earlier in response to intraventricular histamine under ligh pentobarbital anesthesia. The ovulatory response to histamine was eliminated by massive midbrain lesions or removal of the olfactory bulb, but intraventricular NE still induced ovulation after such losses. The ovulatory effectiveness of NE was blocked, however, by low doses of pentobarbital or high doses of atropine, neither of which inhibitied the obulatory response to intraventricular epinephine. Atropine and α-adrenergic blocking agents also prevented the ovulatory response to intraventricular histamine. It is suggested that histamine activates pituitary-ovarian function by stimulating central noradrenergic elements and that NE has more of the physiological-pharmacological characteristics of a natural central nervous activator of luteinizing hormone-releasing hormone than has epinephrine.