Ultrastructural localization of the calcium-binding protein parvalbumin in neurons of the song system of the zebra finch,Poephila guttata

Summary The distribution of parvalbumin (PV) within neurons of the vocal motor nucleus hyperstriatum ventralepars caudalis (HVc) was investigated in the forebrain of adult male zebra finches by means of light and electron microscopy using the indirect immunoperoxidase technique. Parvalbumin-reaction product was located in the amorphous material of perikarya, dendrites and nuclei, and associated to microtubuli, postsynaptic densities and intracellular membranes; it was found in some axons and Gray type-2 boutons, but rarely in type-1 boutons and never in the Golgi apparatus. These observations suggest that parvalbumin may regulate calcium-dependent processes at the postsynaptic membrane and in the cytosol. Furthermore, the partial association of parvalbumin to microtubuli points to an involvement in calcium-dependent tubular functions. Calcium currents and microtubular assembly or transport may be relevant for the known functions of HVc in song learning.     

Functional aspects of the postovulatory follicle in the ovary of the African catfish,Clarias gariepinus,after induced ovulation

Summary In captive African catfish, Clarias gariepinus, ovulation was induced with human chorionic gonadotropin (HCG) 4 I.U./g body weight to study the function of postovulatory follicles (POFs). Ultrastructural and enzyme-histochemical data indicate that, apart from special theca cells, the granulosa of relative young POFs (i.e., from 16 h and 28 h after HCG-injection) is capable of producing steroids. Possible functions of the synthesized steroids are discussed. Histological comparison of POFs from stripped and from unstripped fish, as well as histochemical investigation of the contents of ovulated ova and granulosa of POFs at 48 h after HCG-injection, showed that the latter structure is involved in phagocytosis of the disintegrating ovulated eggs. The polysaccharide-lipid-protein material, initially taken up by heterophagolysosomes of the granulosa cells, subsequently undergoes fatty degeneration. The granulosa cells of the POFs showed strong acid phosphatase activity and abundant granular endoplasmic reticulum from 16 h after HCG-injection onward; heterophagolysosomes appeared at 32 h. These results indicate that after ovulation the phagocytotic function of the granulosa develops progressively. Autophagolysosomes, responsible for the final disintegration of POFs, become increasingly evident in the granulosa cells with increasing time after ovulation.     

Early appearance of catecholaminergic neurons in the central nervous system of precocial and altricial avian species

Summary The early appearance of catecholaminergic neurons, as revealed by fluorescence histochemistry, has been determined in the central nervous system of quail, pheasant, and pigeon embryos. The first neuronal assemblies displaying specific fluorescence are the locus coeruleus and the nucleus subcoeruleus ventralis. Taking into account the differences in the length of the prehatching period of these three avian species, the first catecholamine-containing neurons appear earlier in the precocial quail and pheasant than in the altricial pigeon.Investigation supported by grants from the Italian National Research Council (CNR) No 83.02058.04 (R.G.) and No 83.00492.04 (G.C.P.).     

Interneuronal and glial-neuronal gap junctions in the lamina ganglionaris of the compound eye of the housefly,Musca domestics

Summary The cell-body layer of the lamina ganglionaris of the housefly, Musca domestica, contains the perikarya of five types of monopolar interneuron (L1–L5) along with their enveloping neuroglia (Strausfeld 1971). We confirm previous reports (Trujillo-Cenóz 1965; Boschek 1971) that monopolar cell bodies in the lamina form three structural classes: Class I, Class II, and midget monopolar cells. Class-I cells (L1 and L2) have large (8–15 m) often crescentshaped cell bodies, much perinuclear cytoplasm and deep glial invaginations. Class-II cells (L3 and L4) have smaller perikarya (4–8 m) with little perinuclear cytoplasm and no glial invaginations. The midget monopolar cell (L5) resides at the base of the cell-body layer and has a cubshaped cell body. Though embedded within a reticulum of satellite glia, the L1–L4 monopolar perikarya and their immediately proximal neurites frequently appose each other directly. Typical arthropod (-type) gap junctions are routinely observed at these interfaces. These junctions can span up to 0.8 m with an intercellular space of 2–4 nm. The surrounding nonspecialized interspace is 12–20 nm. Freezefracture replicas of monopolar appositions confirm the presence of -type gap junctions, i.e., circular plaques (0.15–0.7 m diam.) of large (10–15 nm) E-face particles. Gap junctions are present between Class I somata and their proximal neurites, between Class I and Class II somata and proximal neurites, and between Class II somata. Intercartridge coupling may exist between such monopolar somata. The cell body and proximal neurite of L5 were not examined. We also find that Class I and Class II somata are extensively linked to their satellite glia via gap junctions. The gap width and nonjunctional interspace between neuron and glia are the same as those found between neurons. The particular arrangement and morphology of lamina monopolar neurons suggest that coupling or low resistance pathways between functionally distinct neurons and between neuron and glia are probably related to the metabolic requirements of the nuclear layer and may play a role in wide field signal averaging and light adaptation.     

Effect of clomiphene citrate on the rabbit ovary

Summary The effect of clomiphene citrate on the rabbit ovary was studied in mature nulliparous rabbits pretreated with three consecutive doses ranging from 0.01–10.0 mg/kg per day. With increasing doses a trend of decrease in mean ovarian weight (mg/kg body weight) is observed 2 days after termination of treatment. Five days later a significant increase occurs, which then subsides again to control values on day 12 after termination of treatment. During this period, no matings or injections of luteinizing hormone were performed to trigger ovulation; consequently no ovulations are observed. Folliculogenesis appears as normally; number and morphology of follicles are within normal ranges. No endogenous, spontaneous gonadotropin surges are detected in blood serum up to the 7th day after termination of treatment (2 and 10 mg doses). The surface epithelium of the ovary resembles normal germinal epithelium; however, after treatment with high doses a secretory-like activity is observed, accompanied with ultrastructural changes.Supported by the Deutsche Forschungsgemeinschaft, Special Program on Biology and Clinics of Reproduction. (Grant Be 524/7-7).Visiting Scientist from the Department of Obstetrics and Gynecology, Hadassah University Hospital, Jerusalem, Israel.     

Histochemistry and ultrastructure of adrenergic and acetylcholinesterase-containing nerves supplying follicles and endocrine cells in the guinea-pig ovary

Summary With the use of an anti-human S-100 protein antibody, it was possible to reveal a characteristic cell type in the anterior lobe of the normal human pituitary. These cells, so-called folliculo-stellate cells, were present in all pituitaries studied but their number varied from one gland to another. Immunoreactive cells, isolated or grouped, were arranged close to various secretory granulated cells. Especially by use of double immunoenzymatic labeling, it was evident that these cells are spatially related either to somatotropes, prolactin cells and corticotropes, or to glycoprotein-containing cells. Such immunoreactive cells were rare or absent in pseudo-follicular arrangements of secretory granulated cells. Since it is now possible to identify this cell type by light microscopy and since no reliable functional significance is known, it seems more advisable to term this cell type stellate cell instead of folliculostellate cell.     

Effect of initial developmental stage on morphology of transplanted embryonic chick pancreas

Summary It has been reported that only certain types of pancreatic parenchymal cells survive transplantation. This study examines whether the extent of differentiation of the pancreas at the time of transplantation affects the resulting morphology or viability of its components. Segments of chick pancreas or its primordia from stages preceding formation of dorsal bud (60 h) through hatching (day 21) were implanted in the abdominal region of three-day chick embryos. After various periods of growth, grafts were examined by light- and electron microscopy. In all transplants, individual endocrine cells (A, B, D, PP) and islet structure were identical to those of normal embryos of comparable age. The exocrine portion also appeared normal in implants from embryos younger than seven days. In grafts from older donors, however, normal acini and ducts were replaced by dilated, irregularly shaped tubules from which new islets appeared to develop. These results suggest that transplantation causes structural modification of exocrine tissue, which may reflect its initial functional capabilities. These observations are compared with similar structural alterations that occur following experimental obstruction of ducts and in human pancreatic pathology.     

Immunofluorescence staining of thin-filament sections not participating in actomyosin crossbridges: Studies by use of a monoclonal antibody specific to actin

Summary Monoclonal antibodies (mcab) were produced in vitro by fusing mouse X63-Ag8.653 plasmacytoma cells with spleen cells from a Balb/c mouse immunized with primary cultures of chick skeletal muscle (pmcc). After cloning on agar, stable clones were obtained, the antibodies of which stain specifically the I-band of myofibrils in the immunofluorescence (IF) procedure. For further characterization of these mcab their affinities to muscle proteins were tested by immunoblotting and by enzyme-linked immunosorbent assay (ELISA). Mcab specific for actin were revealed by these criteria. One of the anti-actin antibodies, mcab 647, reveals a variety of IF-staining patterns on myofibrils. On rest-length myofibrils the I-band is labeled only. However, at sarcomere lengths below 2 m, where the thin filaments meet in the middle of the A-band and form a region of double overlap, an additional fluorescent band appears in this position. The fluorescence intensity of this band is increased significantly in shorter sarcomeres. Finally, when the I-band has disappeared at a sarcomere length of 1.5 m, fluorescence is located exclusively in the middle of the A-band. These IF-staining patterns suggest that only those sections of the thin filament are stained that do not participate in actomyosin crossbridges.     

Mesenchymal control of branching pattern in the fetal mouse lung

The effect of mesenchyme on specialization of respiratory epithelium in the fetal mouse was tested in organ cultures. Heterologous combinations were made between respiratory and non-respiratory lung epithelia and the corresponding mesenchymes. Isolated terminal respiratory buds of fetal mouse lungs were recombined with mesenchyme from chick lung parabronchi, mouse trachea or from the avascular, non-respiratory air sacs of chick lungs. Isolated non-branching chick air sacs were combined with mouse terminal bud mesenchyme or mesenchyme from the respiratory branches of chick lungs. Air sac epithelia branched in a pattern characteristic of the chick lung when combined with chick respiratory mesenchyme and in a pattern characteristic of mouse lung when combined with mouse terminal bud mesenchyme. Mouse terminal bud epithelia did not branch with either mouse tracheal mesenchyme or chick air sac mesenchyme but branched in a chick pattern with chick parabronchial mesenchyme. Electron microscopic examination of the cultures showed that all chick air sac epithelial cultures failed to produce surfactant (lamellar bodies) even when they branched. Control cultures of mouse terminal buds contained large numbers of lamellar bodies; mesenchyme which suppressed branching reduced the number of lamellar bodies to only a few in a small proportion of the cells. Culture medium supplemented with growth factors and hormones increased the number of lamellar bodies in heterologous mouse combinations but did not bring the number to control levels. Supplemented medium had no effect on lamellar body production by chick air sac epithelium. The results indicate that branching pattern is determined by the mesenchyme surrounding the epithelial primordium. However, the capacity to synthesize surfactant is determined by the source of the epithelium; mesenchyme may control the degree of expression but not the absolute presence or absence of the differentiated condition.     

Auxin action: the search for the receptor

Abstract. The molecular specificity of the substances which have auxin activity implies the existence of specific receptors. There have been many efforts to identify and isolate these receptors on the assumption that they should bind auxins with affinities coordinate to their activities in bioassays. However, the known complexity of auxin uptake and metabolism make this assumption seriously deficient. Although several such binding sites have, in fact, been identified, proof of a connection between these sites and auxin action has been lacking. Definite proof would include a requirement that the site be reconstituted, together with the appropriate macro-molecular machinery, to construct a model of an auxin response. At the moment, our ignorance of the biochemistry and molecular biology of auxin growth responses makes such a proof difficult. However, two avenues of research promise to accelerate the rate of progress. The increasingly potent tools of molecular biology should soon allow the dissection of auxin-regulated gene expression, while improved knowledge of plasma membrane proton pumps and the mechanism of cell wall biosynthesis should produce, in parallel, an understanding of the auxin regulation of acid growth.