Cytodifferentiation and immunocharacteristics of adenohypophysial cells in the toad, Bufo melanostictus

Ontogenetic profile of FSH and LH in Rana esculenta

Circulating levels and pituitary content of FSH and LH were determined by specific radioimmunoassays in Rana esculenta starting a few days after hatching until the completion of metamorphosis. Both gonadotropins were found in the pituitary as well as in the blood plasma at all stages of development examined here. The plasma concentrations of FSH and LH were more or less uniform during pre- and prometamorphosis, but increased significantly at the onset of metamorphic climax. The plasma levels of FSH and LH remained high at the completion of metamorphosis. The pituitary content of FSH and LH was low in early premetamorphosis. It increased slightly through prometamorphosis and metamorphic climax, following which a highly significant increase occurred. Whereas plasma concentrations of FSH and LH were essentially similar within a single stage of development, the pituitary FSH content was severalfold higher than pituitary LH. The significance of these results is discussed in relation to the functional maturation of the brain-pituitary-gonadal axis in the frog.

Immunochemical identification of thyrotropes and gonadotropes in the pars distalis and pars tuberalis of the toad (Bufo boreas) with reference to ontogenic changes

Morphologically distinct secretory cells in the pituitary pars distalis and pars tuberalis of larval and adult toads (Bufo boreas) immunoreactive cells in the pars distalis. Thyrotropin immunoactivity appears in pars tuberalis and pars distalis before gonadotropin immunoreactivity during early development. Antisera which distinguish gonadotropes (stained with human and sea turtle LH beta) and thyrotropes (stained with human TSH beta) as separate cell types in the pars distalis of the adult toad immunoreact with the same single type of cell in the pars distalis of the tadpole up through metamorphosis, suggesting the existence of a single pluripotent, glycoprotein-producing precursor cell early in development. Gonadotropin antisera do not react with the pars tuberalis in tadpoles or adults.

A novel and simple technique for ectopic transplantation of the pituitary gland

Sites for ectopic transplantation of the pituitary include the kidney capsule of mammals, the anterior eye chamber, the so-called hypophysiotropic area of the brain, the third cerebral ventricle, and the tail of the amphibian tadpole. Transplantation of pituitary in the kidney capsule of mammals is a simple technical procedure but most nonmammalian species do not offer such a convenient site. Transplantation of pituitaries at other ectopic sites involves technical sophistication and cannot be undertaken by all investigators, and retrieving the transplant is often difficult. A new technique is described to overcome these difficulties. Silastic tube pieces (7-10 mm) were ligated at both ends and cut longitudinally, and pituitaries taken from sister animals (homologous donors) were inserted through the incision. The Silastic tubes were then implanted either in the abdominal cavity or in the liver of rat, Japanese quail, and toad. They were retrieved after 7 or 14 days (in the case of rat and Japanese quail) or after 10 or 20 days (in the case of toad), and the pituitary was sectioned and stained immunocytochemically using rat and human prolactin (PRL) antisera. Taking the preponderance of PRL cells in the pars distalis as a parameter for determining the viability and functional status of the transplants (because ectopically transplanted pituitaries secrete abundant PRL), it was found that 13 of 16 pituitary homografts had been well established and there was no visible host-graft incompatibility. The technique reported is novel and simple, and it ensures quick delivery of the grafts and their easy retrieval without any loss whatsoever. It is expected that the technique would be very useful and would find wider application because it can also be employed for transplanting other organs/tissues into a wide range of animals, including invertebrates.

Immunohistochemistry and tinctorial affinity of adenohypophysial cells of the rat snake Ptyas mucosus (Colubridae)

Immunocharacteristics of the adenohypophysial cells of the rat snake Ptyas mucosus (Colubridae) were studied with an unlabeled antibody enzyme technique (PAP method) using rabbit antisera against mammalian/synthetic hypophysial hormones. Adenohypophysial cells were identified on the basis of their specific immunoreactivity with various heterologous antisera. As in other reptiles, there was regional localization of pars distalis (PD) cell types in this snake. The gonadotropic (GTH) cells were identified by their specific immunoreactivity with anti-porcine (p)LH beta serum and were distributed uniformly throughout the PD. The thyrotropic (TSH) cells, recognized by their specific immunoreactivity with anti-human (h)TSH beta serum, were found in the medial PD. The prolactin (PRL) and growth hormone (GH) cells were revealed by their specific immunoreactivity with anti-ovine (o)PRL and anti-hGH sera, respectively; the former were confined to the anterior two-thirds of the PD, and the latter were restricted to the posterior third of the PD. The corticotropic (ACTH) cells, identified by their specific immunoreactivity with the anti-ACTH1-24 serum, were localized in the anterior two-thirds of the PD. Though both ACTH and PRL cells were confined to the same area of the PD, they could be distinguished by their distinctive morphology and distribution pattern. Cells of the pars intermedia were revealed by their immunoreactivity to anti-alpha MSH (melanophore-stimulating hormone) and anti-ACTH1-24 sera. Among each adenohypophysial cell type, there was variation in the intensity of immunoreactivity and morphological features, which may be due to their heterogeneity, reflecting various stages of cellular activity. Unlike most other snake species, the occurrence of a rudimentary pars tuberalis in P. mucosus containing a few immunoreactive GTH and TSH cells appeared to be a novel finding. The occurrence of the PRL-like and TSH-like immunoreactivity seen in certain neuronal perikarya and fibers of the hypothalamus and median eminence conforms with earlier observations in other tetrapods. To resolve certain discrepancies in the literature, the tinctorial affinities of immunohistochemically identified adenohypophysial cell types of P. mucosus were studied using various conventional staining methods and were compared with those of other reptilian species studied earlier, including snakes of the family Colubridae.

Vascular permeability in the peripheral autonomic and somatic nervous systems: controversial aspects and comparisons with the blood-brain barrier

Endothelium, choroidal epithelium, and arachnoid exclude plasma proteins from most parts of the mammalian central nervous system (CNS). Nerve roots, in contrast, have permeable capillaries and permeable pia-arachnoid sheaths. Diffusion of plasma proteins into the cerebrospinal fluid is probably prevented by slow bulk flow along a pressure gradient from the subarachnoid space into the veins of the roots. In nerves, the perineurium prevents diffusion of proteins from the epineurium into the endoneurium. Capillaries within fascicles are permeable to macromolecules, though less so than the microvessels of roots and ganglia. Endoneurial vascular permeability is lowest in rats and mice, but even in these species albumin is normally present in the extracellular spaces around the nerve fibers. The so-called blood-nerve barrier is not equivalent to the blood-brain barrier. Capillaries in sensory and sympathetic ganglia are fully permeable to macromolecules, and extravasated protein is in contact with neuronal cell bodies and neurites. An impenetrable perineurium surrounds each ganglion, but serves no obvious purpose when the vessels inside are as permeable as those outside. The enteric nervous system lacks a perineurium, and the neurons in its avascular ganglia and tracts are exposed to extracellular fluid formed by permeable vessels in adjacent tissues of the gut. The reasons for excluding macromolecules from some parts of the nervous system are obscure. Carrier-mediated transport, which maintains a constant supply of ions, glucose, and other metabolites to cells in the CNS, would be impossible if larger molecules could diffuse freely. Presumably the metabolic needs of ganglia are adequately met by exchange vessels similar to those of nonnervous tissues. Most of the CNS is protected from exogenous toxic substances that bind to plasma proteins. Peripheral neurons and glial cells are damaged by some such substances because of the lack of blood-tissue barriers.

Node distribution and packing density in the rat CNS-PNS transitional zone

The density of nodes of Ranvier was examined at CNS, PNS, and transitional zone (TZ) levels of rat lumbar ventral motoneurone fibres. It was found to be significantly greater in the TZ than at the other levels: The difference was sevenfold for the ventral root and at least fourfold for central fibre levels. Node distribution and spacing was examined within the two main types of TZ found in rat ventral rootlets: the first, in which the TZ is short and is approximately on a level with the surface of the cord; and the second, in which it is much longer and extends into the proximal part of the rootlet. Node spacing was estimated as nearest neighbour distance, the true distance between adjacent node centres. This is a better estimate of node spacing than simple density since it measures the actual linear distance between nodes over which any interaction between them would be likely to take place. Despite marked differences in the dimensions of the two types of TZ, nearest neighbour distance distribution was very similar in each, suggesting that similar mechanisms may influence their spacing during development. The TZ contains especially large amounts of interstitial tissue, mainly composed of astrocyte processes, separating the fibres traversing it. The proportion of the TZ composed of interstitium was over three times that in the ventral root and nearly twice that at the CNS level studied. The large amounts of astrocytic tissue in the TZ may be related to the high packing density of nodes. It may function to regulate extracellular ionic concentrations in the TZ and to maintain a stable ionic environment for the transitional nodes.

Immunohistochemical studies on the development of the hypothalamo-hypophysial system in Xenopus laevis

BACKGROUND

Few attempts have been made to clarify the relational development of the hypothalamo-adenohypophysial and -neurohypophysial systems in species higher than amphibians.

METHODS

The appearance and topographical distribution of endocrine and neuroendocrine cells and fibers in these systems were immunohistochemically examined in the larvae of Xenopus laevis from immediately before hatching (stage 32, Nieuwkoop and Faber's classification) to the end of metamorphosis (stage 66).

RESULTS

(1) Each endocrine cell differentiated until the middle premetamorphic period. MSH cells initially appeared in the posterior half of the pituitary anlage at stage 35/36, followed by the differentiation of GH cells at stage 39 in the middle part, PRL cells at stage 46 in the anterior half of the pituitary anlage, and LH cells at stage 50 in the posterior two thirds of the pars distalis. With the progression of development, the cells which differentiated at early stages shifted from their initial positions; MSH cells, to the pars intermedia; and GH cells, to the posterior half of the pars distalis. 2) Oxytocin and vasopressin fibers were observed at stage 47/48 in the median eminence, and converged to the pars nervosa at later stages. 3) Neuroendocrine fibers innervated the median eminence during the middle premetamorphic to prometamorphic period: SOM fibers, at stage 45; CRH, 47/48; GRH, 48; dopamine, 58; and LHRH, 60. The cells containing these hormones were observed in the (presumptive) preoptic and/or infundibular nuclei.

CONCLUSION

These results suggest the following three chronological steps in the development of hypothalamo-hypophysial systems and their target organs: independent development of target organs at early developmental stages; appearance of hypophysial hormones to control the development of target organs at middle developmental stages; appearance of hypothalamic hormones to control the function or maturation of the hypophysis at late developmental stages.

Differential appearance of the subunits of glycoprotein hormones (LH, FSH, and TSH) in the pituitary of bullfrog (Rana catesbeiana) larvae during metamorphosis

The ontogeny of gonadotrophs and thyrotrophs in the bullfrog pituitary was examined immunohistochemically using monoclonal antibodies against bullfrog lutropin beta-subunit (LH beta), follitropin beta-subunit (FSH beta) and its alpha-subunit, and polyclonal anti-human thyrotropin beta-subunit (TSH beta) serum. Immunoreactive alpha-subunit- and TSH beta-, but not FSH beta- and LH beta-containing cells were observed at embryonic stage 24 (Shumway's classification). Immunoreactive FSH beta cells first appeared at Taylor-Korllos stage V, and immunoreactive LH beta cells at stage X. Throughout metamorphosis, several gonadotrophs containing both FSH and LH were found in the ventrocaudal region, but most gonadotrophs contained only FSH. Immunoreactive alpha-subunit cells were always more frequent than the sum of immunoreactive beta-subunit cells, which was confirmed by quantitative studies using immunohistochemical and RIA techniques.

Ontogeny of the hypothalamo-neurohypophysial system in the toad, Bufo melanostictus: an immunohistochemical study

Employing unlabeled antibody enzyme technique, the development of the hypothalamo-neurohypophysial system of the common Indian toad, Bufo melanostictus, has been studied by using antiserum raised in rabbit against bovine neurophysin. Immunoreactivity to the antiserum is first observed at stage 22 (Gosner, 1960) in the presumptive preoptic nucleus and at stage 23 in the presumptive median eminence and pars nervosa. As development proceeds, progressive increase in the immunoreactivity in all the components of the hypothalamo-neurohypophysial system is observed. The detection of neurohypophysial hormones (stages 22-23) much before the appearance of limb buds (stages 25-26) may be due to the greater sensitivity of the immunohistochemical technique.