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J. R. Clarke and S. Hellwing

Investigation of bank voles (Clethrionomys glareolus) from the field led Brambell & Rowlands (1936) to conclude that in this species ovulation occurs spontaneously during an oestrous cycle similar to that of the mouse. However, under laboratory conditions it has been shown that in several microtine rodents (e.g. Microtus spp. and Clethrionomys glareolus) ovulation is induced by copulation (Breed, 1967; Richmond & Conaway, 1969; Clarke, Clulow & Greig, 1970; Clulow & Mallory, 1970; Cross, 1972; Gray, Davis, Zerylnick & Dewsbury, 1974). The aim of the present work was to investigate whether ovulation in the bank vole can be induced by stimuli from males other than those provided by coitus.

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J. R. Clarke and S. Hellwing

Summary. Analysis of records of a bank vole breeding colony suggests that fertility is high immediately post partum, declines during established lactation and rises after weaning of young. Mating tests with lactating females and females whose young had been removed at birth showed that receptivity is reduced during lactation, although amongst the females which did mate there was no difference between lactating and non-lactating animals in the proportion which produced litters. However, average size of litters at birth was significantly larger for the lactating than for the non-lactating females. There is some evidence suggesting that this difference may arise after ovulation has occurred. Virgin females were no more receptive or fertile than lactating females.

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Norah Spears and J. R. Clarke

Summary. Weanling male and female field voles from laboratory stock and from the Fl generation of wild-caught animals were placed in a long (16L:8D) or short (6L:18D) photoperiod for 28 or 56 days. Both types of field vole showed the well-established effect of photoperiod upon sexual maturation, with animals in the long photoperiod having larger and more active gonads than animals in the short photoperiod. After 28 and 56 days laboratory stock females were more mature, sexually, and had a higher growth rate than did Wild F1 females. There was no difference between the two types of males at 28 days, but by 56 days laboratory stock males were more sexually mature and had a higher growth rate than did Wild F1 males. These differences between the two types occurred in the long and short photoperiods. There was no interaction between photoperiod and type of vole. The use of laboratory stock animals in experiments could lead to an incorrect assessment of the effect of photoperiod in the control of seasonal breeding in wild populations.

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J. R. CLARKE and SUSANNE FREARSON

Sexually mature male voles, Microtus agrestis, in our colony develop oily fur on the hindquarters at the age of about 3 months. In the following 1 to 2 months, hair is lost from these regions revealing raised patches of bright pink skin. Each patch is about 20 mm long and 15 mm wide, has a coarse texture, one or two characteristic folds (Pl. 1, Fig. 1) and a musty odour. Histologically, the skin contains very greatly enlarged holocrine sebaceous glands (Pl. 1, Fig. 2). These specialized sebaceous patches persist for as long as 14 months. They do not occur in females.

In view of the significance of androgens in the control of the growth and activity of sebaceous glands (Ebling, 1963), the rôle of the testes and of androgen in the maintenance and development

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Norah Spears and J. R. Clarke

Summary. Weanling male and female field voles were placed in long or short photoperiods, kept at 18°C or 4°C, and fed (ad libitum) diets containing 24%, 16%, 8% and 4% protein, for 6 weeks. Animals in the long photoperiod were more sexually mature than were animals in the short photoperiod. Temperatures had no effect on females, but did affect males: those kept at 4°C had heavier testes and wider seminiferous tubules than those kept at 18°C. There was little difference between the animals on 24%, 16% and 8% protein diets. Animals on 4% protein diets had retarded growth rates and were significantly less sexually mature than those on the other 3 diets, males having smaller testes and seminal vesicles and narrower seminiferous tubules and females having smaller ovaries and uteri.

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Norah Spears and J. R. Clarke

Summary. The effect of mature males on the sexual development of young female and male field voles, reared in either long (stimulating) or short (inhibiting) photoperiods, was examined. Females reared in the presence of a mature male had a more advanced state of sexual maturation (as indicated by uterine weight) than did females reared in isolation from males, in long and short photoperiods (P < 0·01). No interaction between photoperiod and male presence was found. Augmented uterine growth occurred not only when young females were separated from mature males by a wire mesh or solid metal screen but also when they were merely exposed to bedding previously used by mature males. Castrated males had no effect on the sexual development of females. The effect of mature males on the sexual development of young males was less clear, although there was some indication that the presence of adult males inhibited their sexual development in long and short photoperiods. For males and females, growth rate was stimulated by long photoperiod, but no effect of male presence on growth rate was found.

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R. P. Craven and J. R. Clarke

Summary. Male voles were reared from birth to the age of 56 days in photoperiods of 16L:8D or 6L:18D. In 16L:8D testes increased 10-fold in size between the age of 14 and 56 days, and there were concomitant increases in diameter of seminiferous tubules and seminal vesicle weight. Spermatozoa were present in tubules by 35 days. In 6L:18D no significant changes with age occurred in testis size, diameter of seminiferous tubules or seminal vesicle weight. LH secretion increased with age in 16L:8D, but not in 6L:18D, and pituitary and plasma levels were higher in the former than in the latter by 35 days. Pituitary levels of FSH were high up to 21 days in 16L:8D, and up to 35 days in 6L:18D. At 35 days the mean pituitary level was significantly higher in the 6L:18D than in 16L:8D. Plasma levels of FSH were significantly higher in 16L:8D at 14 and 21 days, and then gradually declined. In 6L:18D plasma FSH rose to a maximum at 35 days, but did not reach the levels occurring at an earlier age in voles in 16L:8D. The relationship between pituitary and plasma levels of FSH in the two photoperiods is compatible with the idea of a storage and a readily releasable pool of the hormone within the pituitary gland. In 16L:8D changing levels of LH and FSH seem to be due to the onset of testicular activity with consequent feedback effects of testicular hormones upon the anterior pituitary gland.

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R. P. Craven and J. R. Clarke

Summary. Male voles were reared from birth to age 28 days in 6L:18D. Pairs of animals showing similar sexual development were assigned at random to 16L:8D or 6L:18D. Treatments continued for a further 56 days. Increase in the activity of the hypothalamo—hypophysial system occurred within 4 days of exposure to 16L:8D, as shown by significant elevation of plasma LH and FSH. Pituitary LH did not increase until Day 7, and pituitary FSH did not increase until Day 21. After exposure to 16L:8D for 4 days, pituitary FSH was lower than in corresponding animals in 6L:18D. These discrepancies between pituitary and plasma values of gonadotrophins indicate that increase in hormone release occurs before synthesis is fully stimulated. Enhanced output of testicular hormones probably began between Day 7 and Day 14, as indicated by an increase in seminal vesicle weight, yet plasma and pituitary concentrations of LH and FSH remained elevated. This suggests that long photoperiods may cause direct stimulation of the hypothalamo—hypophysial system which increasing values of testicular hormones are initially unable to inhibit. The response of this system in voles to an abrupt change from a non-stimulating to a stimulating photoperiod has a time course resembling that for the Soay ram but appreciably slower than for the Japanese quail.

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J. O. Nerquaye-Tetteh and J. R. Clarke

Summary. Laboratory bred bank voles of different age and reproductive status were bilaterally ovariectomized, treated with exogenous oestrogen or progesterone or both, and given an artificial decidual stimulus (crushing with artery forceps). An hormonal regimen of oestrogen (100 ng) followed by progesterone (1 mg) and small amounts of oestrogen (10 ng) was necessary for maximal development of the decidual cell reaction (DCR). A DCR did not develop if the animals were treated with only oestrogen or progesterone. Middle-aged virgin females 5–7 months old had larger responses than did young virgin females 2–3 months old, and parous females, 15–19 months old and having had at least 10 litters, had a response similar to that of virgin females of about the same age. The size of the DCR in old parous females was inversely related to the time elapsing since the last litter. It is concluded that in its hormonal requirements for a successful DCR the bank vole is similar to the mouse. The results also suggest that the increase in fertility of bank voles up to the age of about 100 days may in part be explained by increased response of the endometrium to blastocysts. The reduction in size of the DCR in old animals is a consequence of ageing rather than of repeated pregnancies.

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J. O. Nerquaye-Tetteh and J. R. Clarke

Summary. In bank voles blastocysts arising from mating immediately after parturition do not implant in used zones of the preceding pregnancy but in the regions between them. However, if mating is postponed until 12 or more days after parturition blastocysts do implant in used zones of the previous pregnancy. Implantations also occur at zones used two pregnancies previously. It seems likely that the absence of implantations at recently used zones of the uterus is determined by the uterus rather than blastocysts.

Keywords: used endometrial sites; blastocysts; post-partum mating; bank vole