Ontogenesis of [3H]serotonin binding sites in the hypothalamus of the female rat: relation to serotonin-induced LH release in moxestrol-pretreated rats.

The release of luteinizing hormone (LH) evoked by exogenous serotonin (5 mg/kg, i.p.) was measured at different developmental ages in the female rat. Since LH response to serotonin is modulated by estrogen, moxestrol, a synthetic compound which does not bind to alpha-fetoprotein, was administered 48 h before serotonin or saline injections. Serotonin was ineffective in releasing LH in 5-day females pretreated with moxestrol; the response increased abruptly at 12 and 18 days and from then onwards decreased gradually. This is in clear contrast to the development of the serotonin-induced prolactin release, which is absent in the first postnatal week, becomes evident on day 12 and increases gradually as the rat approaches puberty. In a second group of experiments, the ontogenesis of hypothalamic-preoptic suprachiasmatic [3H]serotonin binding was studied in 5-, 16-, 27- and 37-day-old female rats. A specific serotonergic binding site could be quantified at 5 days (Bmax 4.31 : 1.89 fmol/micrograms DNA; Kd: 2.74: 1.17 nM). A gradual increase of both Bmax and Kd was observed as the animal matured: the number of binding sites almost doubled from day 16 to day 27, and increased even further by 37 days (Bmax 24.21 : 5.16 fmol/micrograms DNA). These data indicate: a specific [3H]serotonin binding site in hypothalamic-preoptic suprachiasmatic area is present in the first postnatal week of the female rat; Bmax and Kd values increase from 5 to 37 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)