In voles, growth of testes and the onset and maintenance of their spermatogenic and endocrine activity are influenced by light. From experiments employing several different photoperiods recurring every 12, 24, 36 or 48 hr, it seems that the effect of a photoperiod depends on the time of its occurrence during the day. Voles appear to have an endogenous circadian rhythm of photosensitivity. It is suggested that testes mature more rapidly or are maintained in a more active state if the external light stimulus coincides with the postulated endogenous photosensitive period.

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.

Hypogonadal (hpg) mice have a congenital deficiency of hypothalamic gonadotrophin-releasing hormone (GnRH) and the gonads consequently lack exposure to gonadotrophins during development. We injected male hpg mice with LH for 10 days to investigate whether LH alone can stimulate normal steroidogenesis in these animals. Control animals had an inactive interstitium and very few germ cells. Testicular content of androgens was undetectable by radioimmunoassay in control animals unless a single injection of LH was given 1 h before death, when androgens were just detectable. Control testes incubated in vitro with [3H]pregnenolone demonstrated that without gonadotrophin stimulation pregnenolone was metabolized only to progesterone in significant amounts. Assay for cholesterol side-chain cleavage cytochrome P450 (P450scc) mRNA showed basal expression in saline-treated hpg mouse testis. LH treatment induced hypertrophy and hyperplasia of Leydig cells and division of germ cells. Testicular androgen content increased significantly, with testosterone and androstenedione as the major androgens. LH-treated testes incubated with [3H]pregnenolone in vitro had a greater synthetic capacity for testosterone, suggesting an increase in 17 alpha-hydroxylase/C17-20-lyase activity. Basal and human chorionic gonadotrophin-stimulated androgen production in vitro increased markedly following LH treatment to levels previously described in the normal adult animal. LH treatment caused a rapid and transient increase in the hybridization of P450scc mRNA which was sevenfold greater than that of saline-treated controls when the animals were killed 1 h after the last injection but fell to control levels within 24 h of cessation of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

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The duration of the cycle of the seminiferous epithelium is a fundamental parameter of spermatogenesis in mammals (Heller & Clermont, 1964). Its measurement in the field vole (Microtus agrestis) could clarify the way in which seasonal changes in spermatogenesis in this species (Clarke & Forsyth, 1964) are brought about. Furthermore, in our laboratory colonies puberty in M. agrestis occurs at about 6 weeks of age, whereas in the bank vole (Clethrionomys glareolus) it is 5-6 weeks later (Greig, 1968). The duration of the seminiferous epithelial cycle has therefore also been estimated in C. glareolus to determine whether this dissimilarity is associated with a difference in the duration of the cycle of the seminiferous epithelium.As in other species (Roosen-Runge, 1962), spermatogenesis in M. agrestis (Grocock, 1972;Grocock & Clarke, 1975) and C. glareolus (Grocock, 1972) can be divided into 8 stages whose frequencies may be determined. The duration of a cycle of the seminiferous epithelium can be established by combining these data with observations on the progression through the epithelium of germ cells labelled with [3H]thymidine (Clermont & Trott, 1969). The complete process of spermatogenesis, from the first division of spermatogonia in stage 5 to the final release of spermatozoa in stage 8, comprises approximately 4\m=.\6 cycles (Grocock, 1972). MicrotusSexually mature males were used and, except where otherwise stated, were kept in a photoperiod of 16 hr light/day. Each was injected s.c. with 25 pCi [3H]thymidine (sp. act. 2 Ci/mmol; Radiochemical Centre, Amersham) in 0-1 ml distilled water. Wild M. agrestis were trapped in Wytham Wood, Oxford, in July 1971, brought into the laboratory and injected on the next day. They were killed in pairs at 4 hr, 4 days or 7 days after injection. The remaining animals, from the Department of Agricultural Science colony, were killed in groups of 6 at 4 hr, 6 days 20 hr, 8 days 22 hr or 18 days after injection. Twenty-four M. agrestis were matched in pairs for body weight, age and sexual development. Each animal of a pair was allocated at random to one of two treatments, 'summer' light (16L:8D) and 'winter' light (6L :18D) (Clarke & Kennedy, 1967). After 7 weeks in these light regimens all animals were injected with [3H]thymidine and killed 7 days later. Testes were fixed in absolute alcohol : glacial acetic acid (3 :1 v/v) for 24 hr and embedded in paraffin wax. Sections (5 pm) were mounted on subbed slides and dipped in Uford L4 nuclear research emulsion (Rogers, 1967). Slides were placed in black, light-proof, boxes for 3-5 weeks at 5°C, and then developed. They were finally stained with Harris's haematoxylin. Within each testis 50 tubules were classified into the 8 stages of spermatogenesis at each of two (or with wild animals, three) locations at least 300 pm apart. This gave totals of 200 or 300 tubules per animal. The most advanced cells labelled with [3H]thymidine were recorded for these tubules, so that by collating data for the different groups, the progression in ...