Seasonal changes in testosterone levels and androgen-dependent organs in male moles (Talpa europaea)

Novelties of conception in insectivorous mammals (Lipotyphla), particularly shrews

In the order Lipotyphla (Insectivora), certain reproductive features differ quite distinctly from the eutherian norms, and are of interest with regard to the evolution of mammalian gamete function and perhaps for questions of lipotyphlan phylogeny. As seen in one or more members of five lipotyphlan families (shrews, moles, hedgehogs, golden moles, tenrecs), these features can involve the configuration of the male tract including the penis, the morphology of the sperm head, the anatomy of the oviduct and the patterns of sperm transport within it, the character of the cumulus oophorus, and the way in which fertilising spermatozoa interact with the eggs. However, the picture is by no means uniform within the order. Reproductive idiosyncrasies occur variously in the different lipotyphlan families, and appear consistently and strikingly in shrews--the group studied most extensively. Compared to the patterns in most Eutheria, the most interesting anomalies in soricids include (a) the regulation of sperm transport to the site of fertilisation by oviduct crypts, whose arrangement can vary even according to species, (b) a circumscribed matrix-free cumulus oophorus that appears essential for fertilisation as the inducer of the acrosome reaction, (c) barbs on the acrosome-reacted sperm head by which it may attach to the zona pellucida. With regard to the bearing such reproductive traits might have on lipotyphlan systematics, the African mouse shrew (Myosorex varius) displays a mix of traits that characterize either crocidurine or soricine shrews, consistent with the proposal that it belongs in a more primitive tribe, Myosoricinae, or subfamily, the Crocidosoricinae, from which the crocidurine and soricine lines probably evolved. Moreover, although elephant shrews are assigned now to a separate order (Macroscelidea), they display several of the unusual reproductive features seen in lipotyphlans, particularly in chrysochlorids and tenrecs. On the other hand, if used as a phylogenetic yardstick, none of the reproductive features described serves to define the Lipotyphla as classically constituted within one order, nor necessarily all the relationships suggested by recent sequencing studies of nuclear and mitochondrial genes.

Testis-like steroidogenesis in the ovotestis of the European mole, Talpa europaea

The female European mole (Talpa europaea) presents a vivid paradox in relation to our contemporary understanding of mammalian sexual differentiation. These animals are exceptional among female mammals in that they possess bilateral ovotestes. The ovotestis contains a morphologically normal ovarian component that develops during the spring breeding season and a histologically defined testicular region, the interstitial gland, which enlarges during autumn when the ovarian component decreases in size. In correlation with this unusual gonadal situation, the female mole displays a penile clitoris traversed by a urethral canal. Although the histology of the ovotestis is well documented and has recently been extended to an additional three species of the genus Talpa, there have been no clear indications of the physiological function, particularly androgen production, of the ovotestis in these female moles. This paper presents the first clear evidence of seasonal variation in plasma testosterone concentrations, which parallel the growth and regression of the "testicular" interstitial gland, in T. europaea. Plasma androstenedione did not show significant seasonal variation, but plasma testosterone (1.06 +/- 0.2 ng/ml) and gonadal testosterone concentration (1.57 +/- 0.65 microgram/mg protein) in females in autumn were significantly higher (p < 0.02) than plasma (0.4 +/- 0.2 ng/ml) and gonadal (0.24 +/- 0.21 microgram/mg) concentrations in pregnant or immediately postpartum females in spring. Our data also reveal selective metabolic production of testosterone from radiolabeled steroid precursors (progesterone and androstenedione) by these ovarian interstitial tissues and male testes; estradiol is produced by ovarian tissue but not interstitial gland or testis.

Quantitative microscopic changes in the mole rat's accessory sex organs during an annual cycle

BACKGROUND

The mole rat, Spalax ehrenbergi, is a solitary, aggressive subterranean rodent. The present study summarizes a year-round investigation of morphological changes in the mole rat's accessory sex organs.

METHODS

Mole rats maintained in the laboratory were killed after 3 months of acclimation; additional animals trapped in the wild were killed immediately. The accessory sex organs were processed for routine histological examination. Tissues were fixed in Bouin's solution, embedded in paraffin blocks, and stained by hematoxylin-eosin. A systemic sampling approach was used to photomicrograph the tissues for histomorphometric assessment.

RESULTS

The volume fraction (Vv, mean +/- SEM) of prostate connective tissue from animals kept in captivity increased significantly in January (0.49 +/- 0.05 mm3/mm3) and April (0.43 +/- 0.04 mm3/mm3) but only 0.26 +/- 0.03 mm3/mm3 in November. In the field group, the Vv of prostate connective tissue was significantly higher in January (0.58 +/- 0.08 mm3/mm3) and April (0.62 +/- 0.08 mm3/mm3) and lower in November (0.44 +/- 0.03 mm3/mm3) and February (0.43 +/- 0.03 mm3/mm3), with a concomitant decrease in prostate tubuli and lumen. The prostate tubuli star volume (v*) in laboratory animals increased in November (0.009 +/- 0.002 mm3) and May (0.09 +/- 0.02 mm3). The same pattern was shown in the field group, with a significant increase in December (0.012 +/- 0.002 mm3) and March (0.007 +/- 0.001 mm3). The Cowper tubuli Vv in the captive animals increased during February (0.24 +/- 0.02 mm3/mm3), with a concomitant reduction in the connective tissue (0.05 +/- 0.02 mm3/mm3). The Cowper tubuli v* in same animals increased in December, April, and July (1.37 +/- 0.18 x 10(-4) mm3, 0.94 +/- 0.10 x 10(-4) mm3, 1.52 +/- 0.20 x 10(-4) mm3, respectively). In field group, a slight decrease in star volume took place from November to May (1.25 +/- 0.16 mm3 to 0.39 +/- 0.05 mm3, respectively). Testosterone levels appeared to be higher in the field group than in the laboratory group. In December the values were 1.62 +/- 0.15 ng/ml in the field group and 0.55 +/- 0.12 ng/ml in the laboratory group, and in May the laboratory group values were 1.66 +/- 0.12 ng/ml.

CONCLUSIONS

In captivity and in the field, male mole rats probably undergo an annual cycle of accessory gland tissue structural changes that are correlated with testosterone secretion.

The testes of moles (Talpa europaea) retain a considerable microsomal capacity for androgen synthesis during seasonal regression

Seasonal changes in testicular histology and steroidogenesis were investigated in the mole (Talpa europaea). Androgen synthesis was examined by incubating [4-14C]pregnenolone (P) and [4-14C]dehydroepiandrosterone (DHA) with testicular minces in a static incubation system. The metabolites formed were characterized by thin-layer chromatography. Morphological changes were studied by routine histological methods. During sexual quiescence spermatogenesis was arrested. The regressive seminiferous tubules consisted predominantly of Sertoli cells and spermatogonia. On the other hand, histological quantification suggested that season has no significant effects on the number or the nuclear dimensions of Leydig cells in this species. The capacity of the regressive testes (per unit weight) to metabolize P and DHA to testosterone (T) was somewhat greater in regressive (48.5%, 49.4%) than in active (33.2%, 41.6%) testes. The results also suggest that the greater in vitro T production encountered during reproductive quiescence is due possibly to an increase in the activity of 17 beta-hydroxysteroid dehydrogenase (per unit weight). Our data on Leydig cell numbers indicate, however, that the capacity of the individual Leydig cells to produce T is decreased during sexual regression. T. europaea appears to be quite exceptional among seasonally breeding small mammals exhibiting pronounced annual changes in spermatogenesis in that the testes retain a considerable enzymatic capacity to produce testosterone from pregnanes during sexual quiescence. The results suggest that pituitary as well as paracrine regulation of the annual testicular cycle in this species differs from that generally encountered in seasonal breeders.

Effect of differential photoperiod treatment on Leydig cell ultrastructure in the bank vole (Clethrionomys glareolus, S.)

Juvenile bank voles (18-22 days of age) born and reared in a stimulatory long photoperiod (18L:6D, lights on 0600-2400 hr) were subjected either to a long photoperiod (18L:6D, Group L) or to a short photoperiod (6L:18D, lights on 0800-1400 hr, Group S) for 6 to 8 weeks whereafter the animals were killed by decapitation. Possible photoperiod-induced changes in Leydig cell ultrastructure were studied by conventional transmission electron microscopy and stereological methods. Striking differences in Leydig cell ultrastructure between the experimental groups were encountered. Light deprivation induced a marked decrease in the cytoplasmic and nuclear volume as well as in the amounts of smooth endoplasmic reticulum (SER), rough endoplasmic reticulum, mitochondria, and lipid inclusions in the Leydig cells. The number of myelin bodies and dense bodies seemed to be somewhat higher in the regressive Group S Leydig cells. These results are in good agreement with our previous histological and biochemical studies on the effects of photoperiod on Leydig cell function and suggest that in the bank vole the volume of mitochondria and SER in particular correlates positively with the steroidogenic capacity (the activity of C20 alpha 22-C27 desmolase, 17 alpha-hydroxylase, and C17-20 lyase in particular) in the Leydig cell.

Seasonal changes in the testes and accessory reproductive organs and seasonal and circadian changes in plasma testosterone concentrations in the male grey squirrel (Sciurus carolinensis)

A 27-month study of cycles of regression and recrudescence of testis function in adult, grey squirrels in a natural environment in southern England has shown concomitant variation in mean testes weights, mean plasma testosterone concentrations, and mean weights of accessory sex organs, this variation being closely associated with months of the year. Testis regression occurred in the period June to August, the exact timing differing among individuals. In 1979-1980 the testes of all squirrels then remained regressed for 7 months, whereas in the autumn of 1980 testes were regressed in most squirrels for 4 months. There was also evidence of testis regression in some individuals in March 1979 and March 1981. Males born and housed in a small woodland enclosure in 1979-1980 and well fed with grain did not experience the long period of regressed testes. Plasma testosterone concentrations measured hourly over 24 hr in squirrels with large, active testes varied from 0.4 to 20 nmol/l, both within and between individuals, the higher concentrations being observed between midday and midnight. The range in the age of males at puberty, based on fusion of the epiphyses of the wrist, was 1.0 to 1.25 year. Juvenile males housed in a woodland enclosure together with adult males and females remained prepubertal up to 2 years of age.

Leydig cell differentiation during the reproductive cycle of the seasonal breeder Camelus dromedarius: an ultrastructural analysis

Spermatogenesis and Leydig cell development in the dromedary were analyzed at the ultrastructural level and correlated with fluctuations of testosterone synthesis during the mating and nonmating seasons. It was found that (1) spermatogenesis and diameter of the seminiferous tubules are dissociated from seasonal fluctuations of testosterone synthesis as they remain similar throughout the year; (2) the volume of the interstitial tissue and the rate of testosterone synthesis are correlated since both increase during the mating season and both diminish during the nonmating season; (3) during the mating season, reduction of the tubular smooth endoplasmic reticulum (SER) and proliferation of condensed SER correspond to the relatively high rate of testosterone synthesis by the 4-ene pathway; (4) during the mating season there is a drastic reduction of the SER and proliferation of myelin figures within the Leydig cells which disrupt at the end of their differentiation. During the nonmating season, testosterone synthesis is probably impaired only at the final stage of differentiation of the Leydig cell.

The differentiation of Leydig cells, steroidogenesis, and the spermatogenetic wave in the testis of Necturus maculosus

The study of seminiferous tubule--Leydig cell interactions in relation to specific germ cell stages during the cycle of the seminiferous epithelium is extremely difficult in most mammalian species due to the continual presence of different spermatogenetic stages in the testis from the onset of puberty. The problem is also compounded by the uniform distribution of both seminiferous tubules and interstitial tissue throughout the entire testis. This difficulty can be circumvented, however, by studying certain species where there is a topographical distribution of germ cell stages within the testis. The urodele amphibian Necturus maculosus exhibits a breeding cycle during which a longitudinal wave of spermatogenesis occurs along the length of the testis, resulting in a spatial and temporal segregation of differentiating germ cells. Moreover, this topographical pattern of spermatogenesis is also reflected in the degree of development of adjacent Leydig cells. This anatomical arrangement allows distinct testicular regions to be obtained using a dissecting microscope. The isolated zones, containing germ cells and Leydig cells in various stages of development, were analyzed for 17 alpha-hydroxylase, C-17,20-lyase, and aromatase activities (key enzymes for the synthesis of androgens and estrogen), estrogen binding, and cytochrome P-450 content. Functional parameters were then correlated with the morphology of Leydig cells in the various zones observed by both light and electron microscopy. It was found that there existed a distinct correlation between the state of differentiation of the leydig cells, their steroidogenic potential, and the distribution of estrogen receptors. These results in Necturus indicate indicate in this species, at least, the steroidal microenvironment of different germ cell associations may be quite specific.

Correlative study of the ultrastructure and the physiology of the seasonal regression of the epididymal epithelium in the hedgehog Paraechinus micropus

The seasonal variations in the ultrastructure and physiology of the epididymis of hedgehog were studied in relation to the reproductive functions. Five adult male hedgehogs were sacrificed every alternate month for one calendar year and the epididymis was fixed in Bouin's, Zenker and formol-calcium for light microscopy and in cold buffered glutaraldehyde, post-fixed in osmium tetraoxide for electron microscopy. The epididymal epithelium consists of four types of cells, the principal, the apical, the dark and the basal cells. The principal cells like other steroid synthesizing cells, contain the extensive Golgi apparatus, the smooth and the rough endoplasmic reticulum (SER and RER), the secretory vesicles and the lipid granules during the breeding season, but they are practically devoid of these cell organelles during regression, except for the retarded Golgi and moderate RER. The basal cell, on the other hand, show lipids and well developed organelles during regression but poorly developed structure in the sexually active hedgehog and possibly function as the cells storing lipids during regression and which are subsequently used at the beginning of the recrudescence. The epididymal epithelium recrudesces along with the seminiferous epithelium prior to the spermatozoa reaching the epididymal lumen, whereas the accessory sex glands which are also the extratesticular androgen dependent organs, still show regressed structure. Thus, the ultrastructural and the physiological observations suggest that the principal cells are probably the site of androgen synthesis and they become fully developed along with the cells in the testis on stimulation from the pituitary at the beginning of the recrudescence.