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D. M. G. Halpin and H. M. Charlton

Summary. Twice daily injections of purified ovine and human FSH were used to investigate the control of ovarian follicle development in hypogonadotrophic hypogonadal (hpg) mice. Treatment for 5 days with doses greater than 3 pg resulted in a significant increase in the total number of growing follicles and the development of antral follicles. This was associated with increases in uterine weights and vaginal opening, indicating that steroidogenesis had also been stimulated. Further studies of the effects of combined injections of FSH and LH, linked with morphological analysis of ovarian interstitial cells, suggested that any contribution of background or contaminating LH to the effects of the FSH injections was minimal. It therefore appears that, in mice, FSH alone is capable of stimulating an increase in the initiation of follicle growth, of triggering the development of antral follicles, and supporting ovarian steroidogenesis.

Keywords: ovary; ovarian follicle; FSH; steroidogenesis; hypogonadism

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Electrical stimulation of the anterior hypothalamus of the vole, Microtus agrestis, usually results in ovulation, whereas stimulation of areas in the posterior hypothalamus do not. Ovulation can also be elicited by injections of sheep median-eminence extracts, and by preparations of sheep luteinizing hormone. Observations on the number of corpora lutea formed, and ripe Graafian follicles remaining after treatment, suggest that mating is the most potent stimulus for ovulation, followed by electrical stimulation and hormone injection.

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D. M. G. Halpin, H. M. Charlton and M. J. Faddy

Summary. The rates of follicle growth and death in GnRH-deficient hypogonadal (hpg) mice and in normal mice were studied using the stochastic compartmental model of follicle dynamics. The rate estimates derived from this model suggest that in normal mice gonadotrophins act at several stages in the development of ovarian follicles. Gonadotrophins appear to regulate the number of follicles beginning to grow by controlling both the rate at which non-growing follicles enter the growing pool and the loss of non-growing follicles to atresia. They also appear to promote the growth of medium-sized follicles by reducing the rate of loss to atresia of these follicles rather than by stimulating growth per se. Furthermore, these data suggest that an intra-ovarian autoregulatory mechanism may exist to control the number of large follicles that are formed.

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C. A. Grocock, H. M. Charlton and M. C. Pike

Summary. A single subcutaneous injection of 5 or 1 mg oestradiol given to pregnant female mice on Day 14 of pregnancy resulted in all male offspring being cryptorchid. Pituitary LH content, testicular weights and structure, seminal vesicle weights and the structure of the reproductive tract as a whole were monitored on the day of birth and at 2, 4, 8 and 14 weeks of age. Apart from an initial significant reduction in pituitary LH at the time of birth, no other marked differences were seen between control and treated animals except that all oestrogen-treated males lacked a gubernaculum and the testes were freely mobile within the abdomen. Hypogonadal (hpg) male mice lacking GnRH are cryptorchid but have a normal gubernaculum and their testes develop and descend normally if treated with gonadotrophins. When the mothers of hpg mice were treated with oestradiol the male offspring lacked a gubernaculum. These results indicate that perturbations of the fetal hypothalamic/pituitary axis play no significant part in oestrogen-induced cryptorchidism in mice.

Keywords: cryptorchidism; gubernaculum; maternal; oestrogen; LH; mouse

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H. M. Charlton, S. R. Milligan and E. Versi

Summary. The lifespan of corpora lutea resulting from hormonally induced ovulations was prolonged by exogenous prolactin, concurrent lactation, or pregnancy. Treatment of mated females with bromocriptine resulted in failure of luteal function only when the drug was given before Day 6 of pregnancy. Pregnancy was dependent on the presence of the ovaries in its later stages. The results suggest that prolactin is luteotrophic in early pregnancy but that a placental luteotrophin may become effective by Day 6 of pregnancy.

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E. Versi, Sharon A. Chiappa, G. Fink and H. M. Charlton

Summary. Male voles reared in a stimulatory (long) photoperiod have significantly greater contents of hypothalamic Gn-RH and pituitary LH and greater testicular and seminal vesicle weights than do voles reared in inhibitory (short) photoperiods. The inhibitory effects of short photoperiod were reversed by pinealectomy.

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E. Versi, Sharon A. Chiappa, G. Fink and H. M. Charlton

Summary. There was a drop of 56% in the hypothalamic content of Gn-RH in female voles 5 min after mating compared with that in unmated but receptive animals. This suggests that the surge of LH in vole plasma associated with reflex ovulation is evoked by a massive release of Gn-RH.

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H. M. Charlton, C. Anne Grocock and Anna Ostberg

The pineal gland has been implicated as a part of the controlling mechanism for the hypothalamohypophysial-gonadal axis in several species. Removal of the pineal in ferrets (Herbert, 1971), hamsters (Hoffman & Reiter, 1965; Reiter, 1973) and bramblings (Haase & Follett, 1974) prevents the inhibitory effects of short photoperiods on the testes. Similar results have been obtained in the hamster by removing the superior cervical ganglia (Reiter & Hester, 1966) which innervate the pineal by postganglionic sympathetic fibres (Kappers, 1965). Clarke & Farrar (1975) have shown that chemical sympathectomy, using 6-hydroxy-dopamine, affects gonadal activity in voles.

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S. R. Milligan, H. M. Charlton and E. Versi

Summary. The development of luteal function in the vole is dependent on a neuroendocrine reflex which is initially activated by mating. Bromocriptine was used to destroy the CL initially induced by mating and fresh CL were induced by hormone treatment. The fate of such newly formed CL suggested that the luteotrophic effect of mating continued for about 10 days after mating, despite the destruction of the original mating-induced CL. The luteotrophic effect of mating therefore seems to be 'remembered'. A study of the fate of hormonally induced CL in females in which pregnancy had been blocked by exposure to a strange male suggested that the strange male may cause pregnancy failure by inhibiting or suppressing the luteotrophic 'mnemonic' activated by the stud mating.

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Department of Human Anatomy, South Parks Road, Oxford

(Received 13th July 1974)

Those areas of the hypothalamus that control LH release in the rat, a spontaneously ovulating species, have been well mapped out (Cross, 1973). The general consensus of opinion is that the ventromedial/arcuate nuclear complex is supposed to release LH in a tonic fashion, and the preoptic or suprachiasmatic area is thought of as a cyclic centre responsible for the rhythmic ovulatory surge of LH.

The position with regard to mammals that ovulate in response to copulation, e.g. the vole, Microtus agrestis (Breed, 1967), is less clear. Breed & Charlton (1971) identified the anterior hypothalamus and median eminence as sites that elicited ovulation or luteinization of ovarian follicles when electrically stimulated with a current in the form of a 50-cycle sine wave by means of a unipolar platinum electrode.

In the present series of experiments, the hypothalamus has been