Marlene Schwanzel-Fukuda

Luteinizing hormone-releasing hormone (LHRH)-expressing cells do not migrate normally in an inherited hypogonadal (Kallmann) syndrome

Kallmann syndrome inherited hypogonadotropic hypogonadism with anosmia, is associated with an X-chromosome deletion at Xp 22.3. In a Kallmann fetus, we have found an absence of luteinizing hormone-releasing hormone (LHRH)-expressing cells in the brain despite dense clusters of LHRH cells and fibers in the nose. LHRH-containing cells and neurites end in a tangle beneath the forebrain, within the dural layers of the meninges, on the dorsal surface of the cribriform plate of the ethmoid bone. Normal fetal brains, matched for age and sex, had LHRH cells and fibers, as expected, in the hypothalamus and preoptic area. Since LHRH-expressing cells recently were discovered to migrate from the olfactory placode into the brain, it appears that the hypogonadotropism of the Kallmann syndrome can be accounted for by a failure of LHRH cells to migrate into the brain.

Migration of luteinizing hormone—releasing hormone (LHRH) neurons in early human embryos

Luteinizing hormone‐releasing hormone (LHRH) neurons originate in the epithelium of the medial olfactory pit and migrate from the nose into the forebrain along nerve fibers rich in neural cell adhesion molecule (N‐CAM). The present study examined the ontogenesis of LHRH neurons in early human embryos and found a similar pattern of development of these cells. Luteinizing hormone‐releasing hormone immunoreactivity was detected in the epithelium of the medial olfactory pit and in cells associated with the terminal‐vomeronasal nerves at 42 (but not 28–32) days of gestation. The migration route of these cells was examined with antibodies to N‐CAM and antibodies to polysialic acid (PSA‐N‐CAM), which is present on N‐CAM at certain stages of development. Neural cell adhesion molecule immunoreactivity was present in a population of cells in the olfactory placode of the earliest embryos examined (28–32 days) and later (42 and 46 days) throughout the migration route. The PSA‐N‐CAM immunoreactivity was not detected until 42 days and was present in a more limited distribution in nerve fibers streaming from the olfactory placode and along the caudal part of the migration route below the forebrain. Previous studies have indicated that the highly sialated form of N‐CAM is less adhesive. The PSA‐N‐CAM may therefore facilitate the migration of these cells by lessening the adhesion between the fascicles that make up the migration route, expediting the passage of cords of LHRH cells between the nerve fibers as these cells move toward the brain.

Gonadotropin-releasing hormone gene expression in teleosts

Expression of multiple molecular forms of gonadotropin-releasing hormone (GnRH) mRNAs and GnRH peptides were examined in the brains of tilapia (Oreochromis mossambicus) and sockeye salmon (Oncorhynchus nerka), using in situ hybridization histochemistry and immunohistochemical techniques. After otherwise identical conditions, lesser background and stronger GnRH hybridization signals were observed on cryostat vs. paraffin sections. In both fresh and Bouins-fixed paraffin-embedded tissues, there was a good correlation between the distribution of GnRH mRNA and GnRH peptide-containing cells. Although the brains of tilapia and the sockeye were immunoreactive to three forms of the GnRH molecule (salmon, mammal, chicken-II), GnRH mRNA expression was site-specific and species-specific. In the tilapia, ganglionic cells of the nucleus olfactoretinalis, basal telencephalon and the anteroventral preoptic area were immunoreactive to salmon-, and mammalian-GnRH peptide. Neurons of the nucleus olfactoretinalis expressed cichlid-GnRH I mRNA. The preoptic neurons, despite the immunoreactivity, expressed no hybridization signals. Midbrain neurons were immunoreactive to salmon-GnRH but expressed cichlid-GnRH II beta (= chicken-GnRH II) mRNA hybridization signals. In the sockeye, ganglionic cells along the extracerebral course of the nervus terminalis were immunoreactive to mammalian-, chicken-II and salmon-GnRH. These neurons expressed only salmon-GnRH mRNA hybridization signals. Intracerebral GnRH expression in the sockeye was delayed till smoltification. The basal telencephalon and midbrain neurons immunoreactive to salmon-GnRH, formed no hybridization signals with GnRH antisense probes. Oligonucleotide probes complementary to chicken-GnRH I and mammalian-GnRH revealed no hybridization signals in the tilapia and in the sockeye brain. Fibers, immunoreactive to salmon-, mammalian-, and chicken II-GnRH were seen in close association with growth hormone cells. Chicken-GnRH II-immunoreactive fibers were also seen in close proximity to somatolactin cells in the sockeye salmon.

Axonal projections and peptide content of steroid hormone concentrating neurons.

The axonal projections of cell groups containing the most dense collections of steroid hormone concentrating cells have been demonstrated with retrograde neuroanatomical tracing methods. Horseradish peroxidase revealed large numbers of neurons in ventrolateral ventromedial nucleus (VL-VM) which project to dorsal midbrain. Wheat germ agglutinin (immunocytochemical recognition method) revealed large numbers of neurons in medial basal hypothalamus (MBH) and particular subdivisions of paraventricular nucleus (PVN) that project to dorsal caudal medulla or spinal cord. Fluorescent dyes revealed that many preoptic area (POA), anterior hypothalamic (AHA), and bed nucleus of the stria terminalis (BNST) neurons project to ventral tegmental area of Tsai (VTA). Also many neurons in POA and BNST project to amygdala. A method which enabled simultaneous demonstration of the steroid binding capacity and axonal projections of neurons in the same tissue section revealed that 26-36% estradiol (E2) concentrating cells in VL-VM project to dorsal midbrain. E2 concentrating neurons in POA and BNST project to amygdala and E2 concentrating POA neurons project to VTA. These neurons, which send their axons to cell groups located in different brain regions, are probably under the genomic-regulatory influence of E2. Using a method which allows simultaneous demonstration of peptide content and steroid hormone concentrating capacity of cells, many oxytocin-neurophysin and vasopressin-neurophysin containing magnocellular neurons in the caudal PVN were found to concentrate E2. About 4% of the beta-endorphin and about 6% of the dynorphin containing neurons in the MBH concentrate E2. In contrast, virtually none (less than 0.2%) of the LHRH containing hypothalamic neurons concentrate E2.

GnRH Neurons and Other Cellular and Molecular Mechanisms for Simple Mammalian Reproductive Behaviors

Publisher Summary This chapter discusses the burgeoning evidence that gonadotropin-releasing hormone (GnRH)—also known as luteinizing hormone-releasing hormone (LHRH)—neurons originate in the epithelium of the olfactory pit and migrate across the nasal septum into the developing forebrain that has recently been reviewed. With immunocytochemistry, LHRH-expressing neurons were found migrating from the epithelium of the olfactory pit along branches of the terminalis and vomeronasal nerves into the mouse forebrain. When LHRH cells were visualized near the olfactory placode, the greatest amount of immunoreactivity was seen surrounding the nuclear envelope. LHRH immunoreactivity was not seen in the Golgi apparatus or in neurosecretory granules, suggesting through morphological evidence that it is not secreted during the nasal portion of the migration route. Quantitatively, not only fewer cells were seen on the migration route compared to various control conditions but also fewer LHRH cells were seen expressing, even in the olfactory placode itself. Notably, the anti- neural cell adhesion molecule (NCAM) manipulation did not destroy the scaffolding itself and is not claimed to be powerful enough that a single microinjection can destroy the passage of all LHRH cells.

Migration of LHRH-immunoreactive neurons from the olfactory placode rationalizes olfacto-hormonal relationships.

Nerve cells that express luteinizing hormone-releasing hormone (LHRH), essential for reproductive functions, originate in the epithelium of the medial olfactory placode. While the peripheral origin of this physiologically important brain peptide is surprising, associations between olfactory and reproductive systems are well documented in behavioral studies of pheromones and in clinical studies of disorders including hypogonadotropic hypogonadism with anosmia or olfactory-genital dysplasia. Mechanisms underlying this migration include a close association with neural cell adhesion molecules (NCAM), but are likely also to involve other physical and chemical factors.

The terminal nerve in odontocete cetaceans.

Cetaceans evolved from land mammals that entered the seas in the early Eocene’ some 5 5 to 60 million years ago. During the course of their evolution as completely aquatic mammals, the external respiratory opening shifted to the top of the head to allow the animal to take a breath while swimming rapidly. Two openings (blowholes) are present in baleen whales and one in toothed whales. In dolphins such as Tursiops truncatus a single blowhole with its muscular plug sits atop a system containing three pairs of asymmetrical sacs, below which are paired respiratory passages, two nasal cavities separated by a bony nasal septum. Although there are no olfactory nerve endings, and much of the anatomical arrangement is unique to cetaceans, the paired external air passages and their associated cartilage, sacs, plugs, ligaments, and muscles are referred to as the nasal system. In early fetal stages of both mysticetes (baleen whales) and odontocetes (toothed whales), the olfactory bulb, nerve, and tracts are present. As the fetus develops, these structures degenerate and are completely absent from mature odontocete brains. 01factory tracts, but not nerves or bulbs, are found in a t least some adult mysticete brains. Although the more peripheral olfactory components of the cetacean adult mysticete brains. Although the more peripheral olfactory components of the cetacean nervous system are absent or rudimentary, other brain structures traditionally thought to be involved in olfaction are present in all of the adult odontocetes so far studied. In the odontocete rhinic lobe, the olfactory lobes and septa1 areas are large and hippocampus and subiculum are small, the well-developed entorhinal cortex is more anteriorly located in the temporal lobe, and the presubiculum is more posterior than in other mammals, but, in general, the rhinencephalon displays the same basic structural arrangement as in primates or carnivores? The seemingly paradoxical presence

Electron microscopic identification of luteinizing hormone-releasing hormone-immunoreactive neurons in the medial olfactory placode and basal forebrain of embryonic mice

Luteinizing hormone-releasing hormone is a decapeptide found in the brain and nose of all vertebrates that have been examined by immunocytochemical procedures with antiserum to luteinizing hormone-releasing hormone. It regulates the release of both luteinizing hormone and follicle-stimulating hormone from the gonadotropes of the anterior pituitary gland and promotes mating behavior. After about 11 days of embryogenesis in mice, luteinizing hormone-releasing hormone-immunoreactive cells are detected by immunocytochemical procedures in the medial olfactory placode, in the primordium of the vomeronasal organ. As they leave the olfactory placode, they run under the epithelial layer of the nasal septum associated with vomeronasal and terminalis nerves. Clustered, they stream toward the primordium of the olfactory bulb, passing along its ventromedial surface. Eventually, the largest numbers reach the septal and preoptic areas of the brain. Electron microscopic immunocytochemistry showed that luteinizing hormone-releasing hormone-immunoreactive product is accumulated just outside the nuclear envelope and in the lumen of rough endoplasmic reticulum adjacent to the cell nucleus of cells in and adjacent to the olfactory placode. As luteinizing hormone-releasing hormone-immunoreactive neurons migrate, they assume a fusiform shape and the immunoreaction product extends from the area around the nucleus throughout the cytoplasm, notably in processes which extend toward the direction of migration. Before and during migration, luteinizing hormone-releasing hormone was not detected in the Golgi apparatus or neurosecretory granules. It is inferred that as far as ultrastructural evidence is concerned, these neurons do not have a secretory function before they attain their target organs.

Localization of choline acetyltransferase and vasoactive intestinal polypeptide-like immunoreactivity in the nervus terminalis of the fetal and neonatal rat

Ganglia of the nervus terminalis have been shown to contain luteinizing hormone-releasing hormone (LHRH) immunoreactive cells in several mammalian species. These cells are always accompanied by clusters of cells non-immunoreactive to antiserum to LHRH. Using immunocytochemical procedures, we found choline acetyltransferase (ChAT) and vasoactive intestinal polypeptide (VIP) present in cell bodies and in nerve processes throughout the peripheral, intracranial and central projections of the nervus terminalis. In addition, a dense plexus of substance P (SP) immunoreactive fibers was seen in the nasal mucosa surrounding the nasal glandular acini and blood vessels. A number of SP reactive fibers were traced with the olfactory nerves through the cribriform plate of the ethmoid bone and appeared to enter the brain in the area of the central roots of the nervus terminalis.

Anosmin-1 immunoreactivity during embryogenesis in a primitive eutherian mammal.

Kallmann syndrome is hypogonadotropic hypogonadism coupled with anosmia. A morphological study found that the endocrine disorder in X-linked Kallmann syndrome is due to failed migration of gonadotropin releasing-hormone (GnRH) neurons from the olfactory placode to the brain during development. Anosmia results from agenesis of the olfactory bulbs and tracts. The gene responsible for the X-linked form of Kallmann syndrome, KAL-1, has been characterized. The orthologues of KAL-1 have been isolated in the chick and the zebrafish, but still await identification in rodents. In the present study, we used polyclonal and monoclonal antibodies to the human KAL-1 encoded protein, anosmin-1, in a primitive mammal, the Asian musk shrew. Musk shrews are insectivores and are therefore evolutionarily closer to primates than rodents. By immunoblot analysis of musk shrew tissues, a band of the expected apparent molecular mass (95 kDa) was detected in several structures of the central nervous system, but not in liver or muscle, which is consistent with the gene expression pattern previously reported in the chick. By immunohistochemical analysis, anosmin-1 was detected in the developing olfactory epithelium, the olfactory, vomeronasal and terminalis nerves, the olfactory bulbs, the cerebellum and the cerebral cortex and in several other regions of the brain, during musk shrew embryogenesis. Furthermore, migrating gonadotropin releasing-hormone (GnRH)-immunoreactive neurons were seen in close association with anosmin-1-immunoreactive fibers. Assuming that the protein is present at the surface of these fibers, we suggest a possible direct role of anosmin-1 in the migration of GnRH neurons in this species.