Hiroya Takahashi

Human chorionic gonadotropin induces all stages of spermatogenesis in vitro in the male Japanese eel (Anguilla japonica)

In the cultivated male Japanese eel, spermatogonia are the only germ cells present in the testis. Using a newly developed organ culture system, we obtained evidence that human chorionic gonadotropin (HCG) can induce the entire process of spermatogenesis, in vitro, from spermatogonia to spermatozoa within 24 days. The HCG-induced spermatogenesis in vitro was accompanied by a marked activation of Sertoli cells and Leydig cells, occurring prior to the beginning of spermatogonial proliferation. These results indicate that gonadotropin triggers spermatogenesis in the Japanese eel and further suggest that this effect of gonadotropin is mediated through the actions of testicular somatic cells.

Increased calcitonin levels during ovarian development in the eel, Anguilla japonica

Abstract Female silver eels ( Anguilla japonica ) were matured with repeated injections of chum salmon pituitary homogenate. Blood samples and ovaries were taken at various stages of ovarian development for the analysis of serum immunoreactive calcitonin (CT), Ca content, and gonadosomatic index. Serum CT levels gradually increased in accordance with an increase in gonadosomatic index and the highest level was observed at the time of ovulation. An increase in serum Ca level was also observed during ovarian development. These results suggest an involvement of CT in sexual maturation in the eel.

Effects of extracellular environments on the motility of spermatozoa in several marine sculpins with internal gametic association

Abstract 1. 1. The motility of spermatozoa in several marine sculpins, which exhibit a special reproductive manner of the internal gametic association, was measured in various artificial solutions, ovarian fluid and seminal plasma. 2. 2. In the elkhorn sculpin, Alcichthys alcicornis, spermatozoa showed high motility in solutions of 300 to 400 mOsm/kg, containing sodium ion, with pH higher than 7.5, which coincided with the nature of ovarian fluid of the fish. 3. 3. Spermatozoa of sunrise sculpin, Pseudoblennius cottoides, and elegant sculpin, Bero elegans, were motile at osmolalities isotonic to the ovarian fluid but not at osmolalities higher than 500 and 800 mOsm/kg, respectively, indicating that the gametic association in these fish is carried out exclusively in their ovaries. 4. 4. Spermatozoa of littledragon sculpin, Blepsias cirrhosus, were motile at osmolalities higher than 300 mOsm/kg, but not in sea water, suggesting an internal gametic association to occur in this species of sculpins. 5. 5. The results indicate that spermatozoa of the marine sculpins with the internal gametic association show their motility in environmental conditions appropriate to respective reproductive modes.

Reproductive cycles ofSebastes taczanowskii, compared with those of other rockfishes of the genusSebastes

SynopsisSeasonal reproductive cycles were examined in both sexes ofSebastes taczanowskii, captured in southern Hokkaido, Japan. The reproductive cycle in females was divided into four periods: recovery (July–August), vitellogenesis (September–March), gestation (April–May) and parturition (June). Spermatozoa were first observed in November in the ovarian cavity, where no structural specialization was present for sperm storage. Fertilization of oocytes appeared to occur in April, when the oocytes underwent a rapid process of final maturation. Embryos developed in the ovary quite synchronously and were released in June; empty ovaries indicated the rockfish has a single parturition. The reproductive cycle in males comprised five periods: resting (December–July), early maturation (February–May), mid-maturation (June–August), late maturation (September–October) and functional maturation (November). In November when active spermatogenesis had been completed, a large amount of spermatozoa was preserved in the sperm duct, and the males were therefore ready for mating. A comparison was made of the reproductive cycles of four species of the genusSebastes inhabiting southern and northern waters of Japan. It suggests that the northern species tend to prolong gametogenesis in both sexes while the southern species have the opposite tendency. Sperm storage in the ovary also tends to be longer in the northern than in the southern species.

THE OCCURRENCE OF HISTOCHEMICAL ACTIVITY OF 3β‐HYDROXYSTEROID DEHYDROGENASE IN THE DEVELOPING TESTES OF POECILIA RETICULATA

In the mature testes of the guppy, Poecilia reticulata, some groups of cells, distributed sparsely in the interspace between the peripheral germ cell layer and the hilar duct system, show evident histochemical response for Δ5‐3β‐hydroxysteroid dehydrogenase (3β‐HSD). In the testis of newly delivered guppies, somatic cells are present in the testicular hilus as a compact mass without revealing any structural differentiation. In the testis of juvenile fish of the 8mm stage about 7 days after birth, interstitial cells resembling histologically those of adult testes become differentiated from the somatic cell mass and, though only in some specimens, coincidentally begin to display weak but obvious histochemical response for 3β‐HSD. Thereafter the occurrence of enzyme activity becomes increasingly regular in the developing testes, and attains the adult pattern of distribution in testes of all specimens after the 11 13mm stage or 17 ∽ 20 days of age.

Spermiogenesis in the Nile tilapia Oreochromis niloticus with notes on a unique pattern of nuclear chromatin condensation

Spermiogenesis in the Nile tilapia, Oreochromis niloticus, was observed ultrastructurally. The process of spermatid differentiation can be divided into six distinct stages based mainly on changes in the nucleus of spermatids. During the latter half of the process, nuclear chromatin condenses progressively to form many dense globules, which ultimately adhere tightly to pack the head of mature spermatozoa. During chromatin condensation the nucleus diminishes in size, and part of the nuclear envelope and nucleoplasm forms a vesicular structure that is finally discarded from the cells together with an associated thin layer of cytoplasm. The spermatozoon comprises a roundish head, a relatively small midpiece, and a relatively short flagellum consisting of the usual 9+2 axoneme. No acrosomal structure is developed during spermiogenesis.

Annual changes in fine structure of inner epithelial lining of the ovary of a marine sculpin, Alcichthys alcicornis (Teleostei: Scorpaeniformes), with internal gametic association

Alcichthys alciocornis has a viscous ovarian fluid in the ovarian cavity, which plays an important role in its unique mode of reproduction called internal gametic association (i.e., internal insemination and sperm‐egg association but a delay in the physiological fertilization until spawning). Seasonal changes in fine structure of the inner epithelial lining and capillary endothelium of the ovary revealed that ovarian fluid originated as a result of the secretory activity of the tissues. The ovarian cavity of A. alcicornis is lined with an ovigerous lamella epithelium and an ovarian wall epithelium. During the spawning period, both epithelia actively secreted proteinaceous substances which seemed to constitute the ovarian fluid. The substances appear to be synthesized in the rough‐surfaced endoplasmic reticulum from the material which was transported from the blood capillary, taken into the epithelial cells by endocytosis, accumulated in secretory vesicles via Golgi apparatus in the cells, and finally released into the ovarian cavity by exocytosis. Microapocrine secretion was also observed to occur in both epithelia. Secretory activity of both epithelia by exocytosis and microapocrine secretion showed distinct seasonal changes. Active exocytosis and microapocrine secretion were observed during the spawning period (April–May). These activities slightly declined during the degeneration period (May–June) and were lost during the early recovery period (July). During the mid to late recovery period (October–March), there was some exocytosis but no microapocrine secretion.

PROCESS OF FUNCTIONAL SEX REVERSAL OF THE GONAD IN THE FEMALE GUPPY, POECILIA RETICULATA, TREATED WITH ANDROGEN BEFORE BIRTH

In the guppy, Poecilia reticulata, ovarian differentiation occurs during the embryonal life by 14 days after the preceding parturition. Testicular differentiation begins with the appearance of prominent aggregations of stroma cells in the gonadal hilus occurring by 18 days following the last parturition.

Beobachtungen ueber die Gynandromorphen Honigbienen, mit besonderer Beruecksichtigung ihrer Handlungen innerhalb des Volkes

Zusammenfassung1.Bei ungefähr 40 gynandromorphen Honigbienen (Apis mellifera ligustica) wurden ihre Struktur und ihre Handlungen beobachtet.2.Sie zeigten äußerlich verschiedene Mosaiktypen. Meistenteils überwogen die männlichen Elemente am Kopf, die weiblichen dagegen am Hinterleib.3.Das innere Mosaik im Gehirne und in den Keimdrüsen entsprach ziemlich dem der äußeren Charaktere. Aber bei einigen am Kopf äußerlich vollkommen männlichen Individuen wurde eine schwach weibliche Tendenz im Gehirn beobachtet.4.Die in Kleinvölker eingeleiteten Gynandromorphen könnten, ohne durch die Volksgenossen hinausgezerrt zu werden, innerhalb der Völker ihr Leben behalten. Verschiedene Arbeiterin-Handlungen wurden sogar an äußerlich ♂-köpfigen Individuen beobachtet.5.Korrelation zw. Kopftyp (-♂) und Handlung könnte, vielleicht aus Materialmangel, nicht festgestellt werden.6.In Bezug auf die Ausführung der-Handlungen durch ♂-köpfige Individuen wurden einige Annahmen gegeben.Summary1.Structure and behaviour of gynandromorphic honeybees were observed on about 40 individuals ofApis mellifera ligustica.2.They showed externally various types of mosaics. In the majority, the male elements were predominant in the head, but the females in the abdomen.3.The internal mosaics corresponded fairly well with the external ones in brain and gonads. A slight female tendency was, however, observed in the brains of certain individuals whose heads completely male-type externally.4.When successfully introduced into other nucleus colonies, the gynandromorphic bees could maintain their normal life in that colony, with no sign of any aggressions from other workers. Various worker-behaviours were observed even in the individuals with externally completely male head.5.Correlation between head-type and behaviour could not be determined, perhaps due mainly to the lack of a sufficient material.6.Some assumptions were proposed concerning performance of worker-behaviours by individuals with completely male head.

Responses of two different types of pituitary gonadotrophs of the loach, Misgurnus anguillicaudatus, to gonadectomy and to exogenous sex steroids

Abstract In the proximal pars distalis of the pituitary gland of the loach, Misgurnus anguillicaudatus , two basophilic cell types with different localities, staining properties, and cytological characteristics are discernible other than thyrotrophs and somatotrophs. Ultrastructural changes of these two types of basophils, termed the globular and the vesicular cells according to their ultrastructural features, were examined in loaches of both sexes which had been subjected to bilateral gonadectomy and to treatment with sex hormones during the late prespawning period. Complete gonadectomy stimulated the globular cells to show dilation of the rough endoplasmic reticulum and a decrease in the amount of cytoplasmic granules. The changes were less intense in males than in females 60 days after gonadectomy. The vesicular cells did not show evident alterations following ovariectomy in females but did respond to castration in males with an enlargement of the cytoplasmic vesicles characteristic of the cell type. After six injections of estradiol (50 μg/fish) to females during a month, the globular cells became atrophic with accumulation of cytoplasmic granules, while the vesicular cells exhibited rather slight changes of their activity including an activation of the Golgi apparatus. Similar administrations of testosterone (100 μ/fish) to males elicited regressive changes of both the globular and the vesicular cells, and shrinkage to a lamellar form of cytoplasmic vesicles in the latter cells is particularly notable. The results were discussed in terms of the possible existence of two distinct types of pituitary gonadotrophs in the loach, each of which may play a role at different stages of the sexual cycle of the fish of each sex.