THE EFFECT OF OVARIAN STEROIDS ON HYPOTHALAMIC NOREPINEPHRINE NEURONAL ACTIVITY

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Abstract
The concentration of norepinephrine [NE] and the apparent turnover of NE in the hypothalamus was studied in castrated rats and after the injection of ovarian steroids. Both parameters were found to vary not only with the hormone treatment, but also with the time of the day. NE concentration in the anterior hypothalamus of castrated male and female rats was significantly higher in the afternoon than in the morning, but no statistical difference was observed in the concentration of NE in the posterior hypothalamus. Three days after the injection of a single dose of 20 .mu.g estradiol benzoate, NE concentration and apparent turnover were found with decreased significant values in the anterior hypothalamus of castrated females, killed in the afternoon. Progesterone 2 mg injected 3 days after the priming dose of estradiol benzoate, produced 4 h later in the afternoon a significant rise in NE concentration and apparent turnover. The apparent turnover of hypothalamic NE in the afternoon may be reduced by estrogen and increased by estrogen plus progesterone.

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