Yoshiharu Honma

Ontogenetic development of gonadotropin-releasing hormone-like immunoreactive neurons in the brain of the chum salmon, Oncorhynchus keta

In the chum salmon, gonadotropin-releasing hormone-immunoreactive (GnRH-ir) cells were first detected in the olfactory placode of embryos at 16 days after fertilization, and then appeared sequentially in the olfactory nerve and the distal part of the forebrain by hatching. Four months after hatching, the terminal nerve was differentiated along the olfactory nerve, and GnRH-ir fibers extended to the hypothalamus and hypophysis. GnRH-ir cells occurred later in the preoptic area in about 1-year-old juveniles. These data suggest that GnRH neurons originate in the olfactory placode and then migrate into the brain along the olfactory nerve.

Engrailed Expression during Development of a Lamprey, Lampetra japonica: A Possible Clue to Homologies between Agnathan and Gnathostome Muscles of the Mandibular Arch

Developing lampreys were fixed at frequent intervals between the gastrula stage (6 days) and the earliest ammocoete larva (31 days). Expression of lamprey engrailed (en) gene was studied by labeling with a polyclonal antiserum (αEnhb‐1) raised against mouse en protein. Western blotting of proteins from developing lampreys reveals a major band (40±103Mr), which is probably lamprey en protein. Expression domains of en were demonstrated in developing lampreys by immunohistochemistry of whole mounts and histological sections. Expression of en first becomes detectable at the head protrusion stage (11/12 days) in neural tube cells at the mid/hindbrain boundary and soon thereafter in some mesodermal cells of the mandibular arch. These en‐expressing cells of the mandibular arch are located in the walls of vesicles of paraxial mesoderm that originate by enterocoely on either side of the pharynx. At the tailbud stage (15 days), en expression is also detectable in mesodermal cells of the anterior lip and in some mesodermal and epidermal cells in the region of the tailbud. By the eye spot stage (18 days), detectable en expression in the mandibular arch becomes limited to cells of the velothyroideus muscles, which drive the power stroke of the recently formed velum. At later stages, while the preceding expression domains fade, en expression begins in some epidermal cells associated with the lip papillae, gill slits, and nostril. We suggest that the velothyroideus muscles of lampreys may be homologous to certain jaw muscles of teleosts–namely, the levator arcus palatini and the dilator operculi, which express en continuously while differentiating from the myogenic mesoderm into identifiable muscle types.

Distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame

SummaryUsing a specific antiserum raised against synthetic neuropeptide Y, we examined the localization of immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame, by the peroxidase-antiperoxidase method. Immunoreactive perikarya were demonstrated in the ganglion of the nervus terminalis, the dorsocaudal portions of the pallium dorsale, the basal telencephalon, and the nucleus lateralis tuberis and the nucleus lobi lateralis in the hypothalamus. Labeled perikarya were also found in the tegmentum mesencephali, the corpus cerebelli, and the medulla oblongata. Some of the immunoreactive neurons in the hypothalamus were of the CSF-contacting type. The bulk of the labeled fibers in the nervus terminalis ran toward the basal telencephalon, showing radial projections and ramifications. Large numbers of these fibers coursed into the nucleus septi caudoventralis and the nucleus interstitialis commissurae anterioris, where they became varicose and occasionally formed fine networks or invested immunonegative perikarya. In the diencephalon, immunoreactive fibers were observed throughout the hypothalamus, e.g., in the pars neurointermedia of the hypophysis, the subependymal layer of the lobus inferior hypothalami, and in the neuropil of the posterior (mammillary) recess organ. Labeled fibers were scattered throughout the rest of the brain stem and were also seen in the granular layer of the cerebellum. These results suggest that, in the dogfish brain, neuropeptide Y or a related substance is involved in a variety of physiological processes in the brain, including the neuroendocrine control of the hypophysis.

Immunocytochemical distribution of FMRFamide-like substance in the brain of the cloudy dogfish, Scyliorhinus torazame

SummaryThe distribution of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH2) in the brain of the cloudy dogfish, Scyliorhinus torazame, was examined by immunocytochemistry. FMRFamide-like immunoreactivity was demonstrated to occur extensively in various regions of the dogfish brain, except for the corpus cerebelli. Immunoreactive neuronal perikarya were located in the ganglion of the nervus terminalis, the preoptic area, and the hypothalamic periventricular gray matter consisting of the nucleus medius hypothalamicus, the nucleus lateralis tuberis, and the nucleus lobi lateralis. some of the immunoreactive cells in the hypothalamus were identified as cerebrospinal fluid-contacting neurons. The bulk of the immunostained fibers in the nervus terminalis penetrated into the midventral portion of the telencephalon and ran dorsocaudally toward the basal telencephalon and hypothalamus, showing radial projections or ramifications. The labeled fibers were abundant in the midbasal part of the telencephalon and in the hypothalamus, where some fibers were found in loose networks around the cell bodies of the nucleus septi and hypothalamic periventricular nuclei. The fibers demonstrated in the hypothalamus terminated around the vascular wall of the primary capillary plexus of the median eminence or penetrated deeply into the pars intermedia of the hypophysis. These results suggest that, in the dogfish, an FMRFamide-like substance participates in the regulation of adenohypophysial function. This molecule may have a role as a neurotransmitter and/or neuromodulator in the central nervous system.

Immunohistochemical localization of neuropeptide Y-like substance in the brain and hypophysis of the brown hagfish, Paramyxine atami

The distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the brown hagfish, Paramyxine atami, was examined by use of the peroxidase-antiperoxidase method. Immunoreactive cells were found in two areas of the brain, the nucleus hypothalamicus of the diencephalon and the ventrolateral area of the caudal tegmentum, at the level of the nucleus motorius V–VII. The labeled cells of the nucleus hypothalamicus were loosely grouped and recognized as bipolar neurons. Immunolabeled fibers were widely distributed in the brain, showing the highest density in the diencephalon. They were sparse, or absent, in the olfactory bulb, habenula, primordium hippocampi, neurohypophysis, corpus interpedunculare, and dorsolateral area of the medulla oblongata. The fibers appeared to project exclusively from the ventral hypothalamus to various other portions of the brain: the anterolateral areas of the telencephalon via the basal hypothalamus, the pars dorsalis thalami, the dorsocaudal region of the mesencephalon, and the ventromedial portions of the tegmentum and anterior medulla oblongata. These findings suggest that, in the brown hagfish, NPY-like substance is involved in neuroregulation of various cerebral areas, but it may be of little significance in the control of pituitary function.

Immunohistochemical and ultrastructural characterization of the terminal nerve ganglion cells of the ayu, Plecoglossus altivelis (Salmoniformes, Teleostei)

Little is known on the cytological properties of the terminal nerve ganglion (TNG) cells in teleosts (Demski, 1993. Acta Anat., 148:81–95).

Ontogenetic changes in neuropeptide Y-like-immunoreactivity in the terminal nerve of the chum salmon and the cloudy dogfish, with special reference to colocalization with gonadotropin-releasing hormone-immunoreactivity

We observed ontogenetic changes of neuropeptide Y (NPY)-like-immunoreactivity in the terminal nerve (TN) of the chum salmon, a teleost, and the cloudy dogfish, an elasmobranch. In the chum salmon, NPY-like-immunoreactive (NPY-IR) cells first appeared in the olfactory placode of embryos at 16 days after fertilization, and then extended sequentially and centrally in the olfactory system. Colocalization of NPY- and gonadotropin-releasing hormone (GnRH)-like-immunoreactivities was also observed in TN ganglion cells. In the cloudy dogfish, NPY-IR cells first appeared in the rudimental TN ganglion of the embryo at the 40 mm stage. Then, the NPY-IR cells and fibers in the TN system increased in density during late embryonic periods. Colocalization of NPY- and GnRH-like-immunoreactivities in TN ganglion cells was not found in the developing or the adult dogfish.

Studies on Japanese chars of the genus Salvelinus. IV. The caudal neurosecretory system of the Nikkô-iwana, Salvelinus leucomaenis pluvius (Hilgendorf).

During a one-year period, seasonal changes in histology of the caudal neurosecretory system in a Japanese char, the Nikko-iwana, Salvelinus leucomaenis pluvius, from mountain tributaries were examined to possibly elucidate its function. The vascular supply to this system was also traced after injection of Chinese ink. The urophysis (neurophysis spinalis caudalis=neurohemal organ) of the Nikko-iwana is elongated and poorly differentiated. The neurosecretory material is stained principally by acidic dyes, but not by Gomoris chromalum hematoxylin or paraldehyde fuchsin. There are no clearcut seasonal changes in the apparent activity of the secretory cells or in the amount of secretory material stored in the neurohemal areas in adult fish. In larval fish, immediately after hatching the caudal neurosecretory system is not developed (there is neither a differentiated neurosecretory cell or a vascular plexus in the presumptive area of the urophysis). On the contrary, fuchsinophilic material is already visible in the hypothalamo-hypophysial neurosecretory system of the same specimens. An early indication of formation of the caudal neurosecretory system is found in parr-stage fish, which begin active swimming about 6 months after insemination. A possible role of the urophysial system, which is peculiar to the actinopterygian fishes with a homocercal tail, is discussed from phylogenetic, ontogenetic, and ecological aspects.

Ontogenetic development of neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system of the dogfish

This immunocytochemical study was carried out to elucidate the ontogenetic development of neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system of the cloudy dogfish, Scyliorhinus torazame. Immunostained cells first appeared in the pancreas of the embryo at the 15-mm stage, and were also detected in the vitellointestinal duct of the yolk stalk at the 20-mm stage. These cells were polymorphic, with occasional processes that were sometimes directed toward the vascular wall or into the cavity of the vitellointestinal duct. At the 34-mm stage, immunostained cells could also be found in the proximal part of the spiral intestine and, by the 74-mm stage, immunopositive cells were present in the gastric mucosa. In the gut and pancreas, the cells gradually increased in number with development, whereas in the vitellointestinal duct and internal yolk sac, they decreased and seemed to disappear following hatching. Thus, in juveniles, the distribution of the neuropeptide Y-like-immunoreactive cells in the gastroenteropancreatic endocrine system had attained that of adults. Electron-microscopic immunocytochemistry demonstrated that, in the labeled cells of the vitellointestinal duct, the neuropeptide Y-like antigen was located in cytoplasmic granules, as in the cells of the gut and pancreas.

Fine Structure of the Sterile Testis of Hybrid Threespine Stickleback between Marine and Landlocked Forms

The process and cause of male sterility of a hybrid between female marine (M) and male landlocked (L) forms (M ⧫ × L ♂) of the threespine stickleback were studied by examining the testes of this hybrid and backcross offspring between M ⧫ and F1 (L ⧫ × M ♂) (MOLM ♂). In the M form numerous spermatids were elaborated and contained in the apical processes of the Sertoli cells, whereas in the ML and MOLM forms there were a number of macrophages in the lobular cavity with numerous projected pseudopodia engulfing voraciously the spermatids. As a result of this heavy phagocytosis the seminiferous lobules were quite vacant. Curiously, the Sertoli cells also actively project its processes and pseudopodia to catch the spermatids. In addition to morphometrical, behavioral and biochemical-genetic differences, these findings of sterility seem to suggest that the M form and L form represent independent species.