Kazuhiko Tsuneki

Ultrastructure of pars nervosa and pars intermedia of the lamprey, Lampetra tridentata

SummaryThe pars intermedia of the adult lamprey is separated by perivascular spaces and a capillary plexus from the pars nervosa. No penetration of nerve fibers into the pars intermedia was found. The pars nervosa, which constitutes the posterior wall of the infundibulum, consists of an ependymal layer and a fuchsinophilic fiber layer; the latter contains at least four different types of axonal endings. The pars intermedia is avascular and is composed of a small proportion of non-secretory cells and a large proportion of secretory cells. The secretory granules in the cells of the pars intermedia seem to be discharged toward the capillaries that separate the pars intermedia from the pars nervosa. Although no direct nervous or vascular connections were found between the pars nervosa and pars intermedia, a mechanism of control of secretory activity in the pars intermedia cells by the central nervous system appears likely.

Seasonal Development of Gonads of the Hagfish, Eptatretus burgeri, Correlated with Their Seasonal Migration

Abstract Seasonal development of gonads was studied in the hagfish, Eptatretus burgeri, caught near the Misaki Marine Biological Station facing the Sagami Bay of the Pacific coast of Japan, during periods from October 1971 to March 1973 and from November 1977 to December 1978. The hagfish were collected at water depths of 6 to 10 m (shallow water) in Koajiro Bay close to the Station or water depths of 50 and 100 m (deep water), about 1,600 and 4.800 m west to the Station. They were collected monthly from both shallow and deep waters, but they could not be collected from shallow water during warmer summer months (July-September) due to seasonal migration. The mean total lengths of the females collected in both shallow and deep waters during January to April were 40.7± 0.4 cm (± SEM; n=317) and 34.5± 0.3 cm (± SEM; n=556), respectively. In both locations, developing eggs longer than 5 mm were found in females larger than 39 cm in total length. There was no difference in the annual growth curves of developing eggs between shallow and deep water: the sizes of the developing eggs were the smallest in October, and was the largest in September. There was no apparent difference in testicular development between two locations, so these data were combined. Testicular development occurs in males larger than 38 cm in total length. The testis weight was the heaviest in July, and was the lightest in September. In autumn and winter, most testicular follicles contained only spermatogonia. In spring, follicles containing spermatocytes increased. Follicles with spermatids or maturing sperms were relatively abundant in summer. Although egg deposition is supposed to occur in September and/or early October somewhere in deep water, both testis weight and spermatogenesis were minimal at this time. Why testis development is lowest at the time when females presumably deposit eggs is discussed in relation to the question of the location of the spawning ground.

Parenchymal fine structure of the subfornical organ in the Japanese quail, Coturnix coturnix japonica

SummaryThe surface ultrastructure of the subfornical organ (SFO) was investigated in the Japanese quail. The SFO consists of a body and a stalk. The body of the SFO can be divided into rostral and caudal parts. On the rostral part, each ependymal cell possesses a short central solitary cilium; clustered cilia are also occasionally seen. Microvilli are abundant. On the caudal part, cells with a solitary cilium are fewer in number, and clustered cilia are rarely found. Microvilli are not as abundant as on the rostral part. In addition, large bulbous protrusions, tufts of small protrusions, deep funnel-shaped hollows, small pinocytotic invaginations and possible cerebrospinal fluid-contacting axons are sporadically observed on the surface of various regions of the body. Each ependymal cell of the stalk has a wide apical surface. A central solitary cilium, microvilli and other structures are observed more rarely on the stalk than on the body, while clustered cilia are not seen on the stalk. These structures are compared with those of the mammalian SFO and further discussed in relation to the possible dipsogenic receptor function for angiotensin II.

Distribution of monoamine oxidase and acetylcholinesterase in the hypothalamo-hypophysial system of the lamprey, Lampetra japonica

SummaryHistochemical distributions of monoamine oxidase (MAO) and acetylcholinesterase (AChE) were studied in the hypothalamo-hypophysial system of the lamprey. The anterior part of the neurohypophysis which lies parallel to the pars distalis was strongly MAO positive. The posterior part of the neurohypophysis which is contiguous to the pars intermedia showed relatively weak activity of MAO. Considering differences in enzyme concentrations together with other anatomical characteristics, the possibility that the anterior neurohyp physis of the lamprey could be comparable to the tetrapod median eminence and the posterior neurohypophysis comparable to the pars nervosa is discussed. The activity of AChE was not detected in the hypothalamo-hypophysial neurosecretory system.

Histochemical distribution of monoamines in the hypothalamo-hypophysial region of the lamprey, Lampetra japonica

SummaryThe distribution of monoamine fluorescence was studied in the hypothalamo-hypophysial region of the lamprey. Groups of intensely fluorescent cells were observed in the lateral walls of the caudal part of the third ventricle. The anterior part of the neurohypophysis which is situated over the pars distalis showed weak fluorescence. The posterior part of the neurohypophysis which is contiguous to the pars intermedia contained highly fluorescent material in its rostral part. The distribution of monoamines in the lamprey neurohypophysis is compared with that in the higher vertebrates and their functional significance is discussed.

Monoamine oxidase and acetylcholinesterase in the neurohypophysis of the hagfish, Eptatretus burgeri

Abstract The peripheral region of both dorsal and ventral walls of the neurohypophyseal sac of the hagfish, Eptatretus burgeri , showed strong monoamine oxidase (MAO) activity. Acetylcholinesterase (AChE) activity was detected only in the dorsal wall anterior to the infundibular stalk and in the ventral wall, except for the ependymal cells. AChE was not detected in the dorsal wall posterior to the stalk, where aldehyde-fuchsin-positive material is deposited. From these distribution patterns of MAO and AChE the identity of the structural specializations of the neurohypophysis are discussed as compared with distributions of MAO and AChE in the median eminence and the pars nervosa of higher vertebrates.

Morphometric classification of neurosecretory granules in the neurohypophysis of the hagfish, Eptatretus burgeri

SummaryNeurosecretory axons in the neurohypophysis of the hagfish, Eptatretus burgeri, were statistically classified into six types according to the size of secretory granules. These types are comparable with those in higher vertebrates. The concentration of each axon type is different in three regions: anterior dorsal wall, posterior dorsal wall, and ventral wall. The regional differences of the hagfish neurohypophysis are discussed in relation to the regional differentiation of the tetrapod neurohypophysis into the median eminence and the pars nervosa.

Ultrastructure of the Neuro‐and Adenohypophysis of the Teleost, Chasmichthys dolichognathus*

Ultrastructure of the Neuro‐and Adenohypophysis of the Teleost, Chasmichithys dolichognathus

Ultrastructure of the neurohemal hypothalamic floor of the frog, Rana catesbeiana

SummaryThe fine structure of the hypothalamic floor was studied in the frog, Rana catesbeiana. The regions slightly anterior and posterior to the swollen hypothalamic floor part, which has been classically designated as the median eminence, contained neurosecretory axon terminals abutting on the capillary walls. The region relatively far anterior to the swollen part did not show neurosecretory axons terminating on capillary walls. The neural stalk contiguous to the rostral border of the pars intermedia had few neurosecretory axon terminals which end on the terminal portions of the ependymal processes covering the capillary wall. The functional significance of the regional differentiation of the frog neurohypophysis is discussed in connection with the regional differentiation of various secretory cells in the adenohypophysis.