Shunya Oka

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.

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.

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.

Serotonin-immunoreactive structures in the central nervous system of the garfish Lepisosteus productus (Semionotiformes, Osteichthyes)

Serotonin-immunoreactive (5HT-IR) neurons were investigated in the brain and rostral (cervical) spinal cord of the garfish, a non-teleost actinopterygian. The diencephalon contained a prominent 5HT-IR cell group consisting mainly of liquor-contacting neurons in the hypothalamic periventricular wall. Their ependymofugal processes formed thick bundles or patches within the hypothalamus and then arborized profusely. Other groups of 5HT-IR cells were found in the dorsal thalamus and in the caudal cortex of the hypothalamic inferior lobe. In the caudal brainstem, 5HT-IR cells were predominant in the raphe region. The spinal 5HT-IR cells were scattered rostrocaudally in the ventromedial zone. The structure corresponding to the submeningeal serotonergic system in the ventral spinal cord of the lamprey and stingray was demonstrated also in the garfish.

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.

Ontogenetic changes in neuropeptide Y-immunoreactive cerebrospinal fluid-contacting neurons in the hypothalamus of the cloudy dogfish, Scyliorhinus torazame (Elasmobranchii).

Ontogenetic changes in neuropeptide Y-immunoreactive (NPY-ir) cerebrospinal fluid (CSF)-contacting neurons in the dogfish hypothalamus were studied immunohistochemically. NPY-ir CSF-contacting neurons first appeared in the median infundibular floor of the embryo at the 34 mm stage. At the 40 mm stage, similar neurons were found also in the saccus vasculosus (SV). The number of these neurons increased during the 54-80 mm stages, and the cells in the infundibular floor extended their basal processes to the neuropil of the median eminence, whereas the cells in the SV sent their axonal fibers to the tractus sacci vasculosi. After hatching, NPY immunoreactivity in the ventral hypothalamus became less dense, and the labeled CSF-contacting neurons tended to be confined to the nucleus lateralis tuberis, similarly as in the adults. The occurrence of NPY-ir CSF-contacting neurons in the SV was transient during the embryonic periods.

Development of the caudal neurosecretory system of the chum salmon, Oncorhynchus keta, as revealed by immunohistochemistry for urotensins I and II

In order to make an immunohistochemical analysis of the development of the caudal neurosecretory system of the chum salmon, Oncorhynchus keta, we employed the peroxidase-anti-peroxidase technique using antisera specific for urotensins (U) I and II on artificially reared embryos, larvae, and juveniles of this species. Immunoreactivities for UI and UII were first demonstrated in the embryo immediately before hatching, showing labeled perikarya and fibers in the most caudal region of the spinal cord where the presumptive caudal neurosecretory system is located. However, distinct differentiation of the histological neurohemal organ had not yet begun in the embryo. Immunoreactive perikarya and fibers gradually increased in number, and an elaborate urophysis comparable to that of adults was demonstrated in the larvae about 5 months after hatching. At this stage, weak immunoreactivity against UI was detected in the neurohypophysis.

Immunohistochemical demonstration of urotensins I and II in the caudal neurosecretory system of the Japanese charr,Salvelinus leucomaenis, retained in sea water

This paper is concerned with part of the role and function of the caudal neurosecretory system of the charr,Salvelinus leucomaenis, studied by immunohistochemistry. In order to elucidate the different histologic changes, we examined the immunoreactivities of urotenisn I (UI) and urotensin II (UII) in 3 experimental groups: the feral (river) fish, the fresh-water aquarium-, and sea water aquarium-retained fish. Coexistence of UI and UII was demonstrated in most of the smaller and larger neurons distributed in and near the urophyseal system of all 3 groups. However, some of the larger neurons were immunoreactive only to a single hormone, UI or UII. Merely a few neurons indicated no reactivity for either UI or UII. No such clearcut differences were encountered immunohistochemically in the 3 groups. Neuronal and urophysial immuno-reactivity to UI of feral and fresh-water-retained fish was slightly stronger than that of sea water-retained fish. Moreover, in sea water-retained fish, the intensity of immunoreactivity for UI was variable, and the number of neurons positive for UII only was somewhat larger than that in feral and fresh-water-retained fish. A series of UII-positive cerebrospinal fluid (CSF)-contacting neurons were seen in the ependymal and subependymal layers ventral to the central canal of the spinal cord in every group. These CSF-contacting neurons might constitute another neurosecretory system aside from the ordinary caudal neurosecretory system equipped with urophysis. In contrast to the hypothalamohypophysial neurosecretory system, the caudal neurosecretory system did not show any significant changes among the 3 groups. This suggests that urotensins I and II have no essential role in osmoregulation of the charr.

Ontogenetic Development of the Caudal Neurosecretory System in the Chum Salmon, Oncorhynchus keta, with Regard to Its Ultrastructural Changes and with Relation to Neuropeptide Y-immunoreactive Fibers

Abstract The ontogeny of the caudal neurosecretory cells (Dahlgren cells) in the caudal spinal cord of the chum salmon, Oncorhynchus keta, was examined by conventional electron microscopy and with immunohistochemistry for urotensins (U) and neuropeptide Y (NPY). The precursors of the Dahlgren cells first appeared as agranular ovoid cells in the caudal region of the neural tube of 40-day-old embryos about one week before hatching. The occurrence of cytoplasmic granules in the immature Dahlgren cells became evident by the 14th day after hatching. At this moment, the U-positive reaction was merely demonstrated in some of the granules. Close association of NPY-positive fibers with the caudal neurosecretory structures was recognizable in 1-month-old larvae. Thus, it is apparent that the salmon Dahlgren cells start their secretory activity (production of the secretory granules) in early larval stages and that, thereafter, NPYergic afferent innervation of the caudal neurosecretory system becomes evident.