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A. W. BLACKSHAW and D. HAMILTON

Summary.

Immersion of the scrotal rat testis in water at 42° C for 30 min produces dye chromophilia within 1 hr (eosin or alcian blue) in pachytene and diplotene primary spermatocytes. Within 2 hr, changes in acid phosphatase and amino-peptidase reactions occur. Chromatin is lost and only cytoplasmic remnants remain after 30 hr. More severe damage (43° C for 1 hr) increases the amounts of free acid phosphatase and proteinase in the testis.

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M. A. McGuckin and A. W. Blackshaw

Summary. Plasma testosterone (T) concentrations, measured in wild bats of P. poliocephalus in Queensland in 1983–87, showed a peak during the mating season in March. Plasma androstenedione (A) concentrations changed less dramatically with season. Mean testicular concentration and total content of T and A was substantially greater in March than in regressed testes in July–October. Paired adrenal glands were heavier during February to April than during September to November. In the same wild population, throughout a single breeding season (1987), plasma T concentrations were significantly higher in mid-March than 3 weeks previously or 3 weeks later. Testicular T content rose as the breeding season progressed, being greatest during March, coinciding with the large rise in plasma T concentrations. Testicular T concentration and content were correlated significantly with plasma T concentrations. Adrenal glands contained T, but the absolute concentrations were much lower than in the testis. No significant changes in plasma, testicular or adrenal A concentrations were found as the breeding season progressed. The large increase in plasma T during the mating season appears to be due to increased testicular production.

Keywords: testosterone; androstenedione; testis; flying fox; mating

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A. G. Wheeler and A. W. Blackshaw

Summary. Twenty ewes in which maintained corpora lutea had been established were subject to 1 of 3 treatments: denervation of the ovaries by freezing, denervation of the ovaries using the chemical 6-hydroxydopamine, or control. The animals were exposed sequentially to normal (24·5°C), cold (10·7°C), normal (23·8°C), hot (39·4°C) and normal (24·6°C) temperatures, each for 1 week. On the final 3 days of exposure rectal temperatures and heart rates were measured, and on the final day the body weights, respiratory rates, and blood glucose concentrations were measured and a series of 5 blood samples was collected from each ewe for determination of the progesterone concentrations. The progesterone concentration was greatest during the hot period in 8 of the 12 animals, particularly in the ewes with denervated ovaries (6 of the 7 animals). This suggests that high ambient temperatures increase progesterone concentrations non-specifically, and that denervated ovaries are more sensitive to the circulating catecholamines that presumably mediate this effect. The progesterone concentrations were lower (P < 0·001) in the groups with freezing or chemically denervated ovaries (2·86 and 2·73 ng/ml respectively) than in the control group (3·38 ng/ml), suggesting that the ovarian innervation plays a physiological role in regulating progesterone secretion.

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M. A. McGuckin and A. W. Blackshaw

Summary. Adult male flying foxes Pteropus poliocephalus and P. scapulatus were captured in south-east Queensland and kept in outdoor enclosures. Testicular size (TS), plasma testosterone concentrations (PTC) and body weight (BW) were measured over 1-year periods. Testicular recrudescence in P. poliocephalus began before the summer solstice and TS was greatest during mid-March (autumn) and lowest from July to September. Large increases in PTC were observed in all indiviuals ∼ 1 month after the peak in TS. BW also increased around the time of the mating season, changes being correlated significantly with changes in TS. Mating occurred between April and June, and births from late October to late November. In P. scapulatus, TS was greatest in the spring (October) and least in the autumn (February to May); PTC fluctuated throughout the year in this species but, unlike P. poliocephalus, did not show a single large increase in the mating season. BW showed a similar seasonal pattern to that seen in P. poliocephalus, being greatest at the time of greatest TS. Mating occurred in October to November, and births in autumn. In captivity, in outdoor enclosures, these species maintained the seasonal reproductive patterns observed in the wild. The 2 species respond differently to the same environmental cues in terms of regulation of the timing of their breeding seasons.

Keywords: season; reproduction; flying fox; testis; testosterone

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R. D. A. Cameron and A. W. Blackshaw

Summary. Boars were heated for 6 h/day in a climate chamber (mean maximum temperatures, 33·4 ± 3·1–37·7 ± 2·0°C, and relative humidities 40–80%) for 4, 5 and 7 days respectively (4 boars/group). Significant increases in the proportion of morphologically abnormal spermatozoa were seen in all groups for the end of Week 2 and up to Week 5 after treatment. Boars exposed for 7 days were, in general, more severely affected.

Ejaculate volumes, gel volumes, sperm concentration and daily sperm outputs were not affected significantly in any of the groups, although changes were seen in individual animals. In some boars heat stress early in the treatment period produced an acute rise in body temperature which appeared to have a greater effect on semen quality than did the duration of exposure.

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S. E. Jolly and A. W. Blackshaw

Summary. The testes of the common sheath-tail bat of tropical Australia undergo a seasonal migration between the abdomen and the scrotal pouches, while each cauda epididymidis is permanently maintained in the scrotal pouch. Straps of smooth muscle attach to both the cranial and caudal poles of the testes, and these extend cranially to the diaphragm and caudally to the cauda epididymidis. The testicular arteries are not coiled. Among the environmental factors investigated, maximum temperature correlated most significantly with testicular descent, and the number of spermatogonia per bat also correlated most significantly with maximum temperature. Body temperature of a captive bat ranged from 25 to 38°C and this was closely related to body weight and ambient temperature. It seems likely that the scrotal pouch provides a temperature slightly below that of the body and so facilitates sperm storage in the permanently scrotal cauda epididymidis. Migration of the testes probably serves to ameliorate the seasonal temperature fluctuations to which they are exposed while the relatively high correlation between maximum environmental temperature and spermatogonial numbers suggests that temperature may be a proximate influence on reproduction in the sheath-tail bat.

Keywords: testicular migration; spermatogenesis; temperature regulation; sheath-tail bat

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J. S. H. ELKINGTON and A. W. BLACKSHAW

Summary.

A factorial experiment, using injections of oestradiol, testosterone and pregnant mare serum gonadotrophin (pmsg), has been used to show the main effects and the interactions of these hormones on the rat testis. Oestradiol caused a decrease in testis and seminal vesicle weight, seminiferous tubule diameter, lactate (LDH) and glucose-6-phosphate (G-6-PDH) dehydrogenase activity in the interstitial tissue, and cessation of spermatogenesis at the pachytene primary spermatocyte stage. Testosterone and pmsg antagonized most of these effects, but testosterone alone caused a decrease in activity of LDH and G-6-PDH in the interstitial tissue, and pmsg did not influence the effect of oestradiol on the seminal vesicle weight.

Oestradiol significantly decreased the activity of the unusual isoenzyme of LDH (LDH-X) in the rat testis, and it seems likely that the induction of LDH-X synthesis occurs during the pachytene primary spermatocyte stage of spermatogenesis. Testosterone and pmsg stimulated LDH-X synthesis when combined with oestradiol, while testosterone, but not pmsg, caused stimulation of LDH-X synthesis when injected alone.

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A. W. BLACKSHAW and J. S. H. ELKINGTON

Summary.

The body and testis weights increase linearly with time during growth of the immature rat. Between 20 and 30 days of age, there is an increase in lactate dehydrogenase (LDH) activity in the interstitial and tubular tissue of the testis and glucose-6-phosphate dehydrogenase (G-6-PDH) in the interstitial cells. LDH-X isoenzymes appear between 20 and 30 days of age and are associated with the seminiferous tubular epithelium. There is a linear increase in seminiferous tubule diameter with age until 60 days, after which time there is no further tubular growth.

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S. E. Jolly and A. W. Blackshaw

Summary. Peak spermatogenic activity of the common sheath-tail bat occurs in autumn, declines over winter and ceases in spring. Accessory glands enlarge in spring when mating occurs, but are regressed at other times of the year. Spermatozoa are stored in the cauda epididymidis throughout the year, and their numbers increase progressively from early summer to late autumn. Sperm storage permits asynchrony of male and female cycles and allows each to be optimally timed in relation to environmental conditions. The temporal separation of primary and secondary sexual functions in the male enables the insemination of females close to ovulation and is a consequence of the burden of sperm storage being placed upon the male.

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M. Lin, R. C. Jones and A. W. Blackshaw

Summary. A regular, well defined spermatogenic cycle was found in the Japanese quail by examining thin sections of isolated lengths of seminiferous tubules embedded in epoxy resin to resolve the structure of developing spermatids. The stages of the cycle initially were identified in studies using a preparatory method for fixation which separated adjacent cellular associations. The cycle was divided into 10 stages with relative frequencies (%) of Stages I to X respectively of: 11·9, 14·8, 24·1, 10·3, 8·2, 6·4, 9·4, 5·5, 3·8 and 5·4. The duration of one cycle was 2·69 ± 0·08 days (mean ± s.e.m.) as determined by intraventricular injection of [3H]thymidine and autoradiographic examination of the testes 1–4 days later. It was estimated that lifespans were 2·01 days for type B spermatogonia, 3·86 days for primary spermatocytes, 0·15 days for secondary spermatocytes, and 4·54 days for spermatids. The results suggest that the kinetics of spermatogenesis in the quail are fundamentally similar to the pattern in mammals.

Keywords: spermatogenesis; Japanese quail