Evidence for octopaminergic modulation of an insect visceral muscle

Two dorsal unpaired median neurons (DUMOV1 and DUMOV2) lying in the posterior region of the VIIth abdominal ganglion of Locusta migratoria have axons which project to the muscles of the oviducts. This study reports the presence of octopamine within isolated DUMOV cell bodies, as well as in the oviducal nerve and innervated oviducal muscle. Individual cell bodies were pooled and found to contain about 0.34 pmol of octopamine per cell body giving an approximate value of 1.27 mM octopamine. Octopamine is concentrated within the area of oviducal muscle which receives DUMOV axons. Pharmacological studies reveal that the amplitude of neurally-evoked contractions of the oviducal muscle is reduced in a dose-dependent manner by octopamine, with threshold lying between 5 X 10(-10) M and 7 X 10(-9) M. The receptors for this response show a specificity for octopamine and synephrine, with an order of potency being octopamine = synephrine greater than metanephrine greater than tyramine greater than dopamine. The presence of octopamine throughout this neural pathway, coupled with the demonstration of octopaminergic modulation of muscular contraction, supports the hypothesis that octopamine serves a physiological role in this visceral system.     

Fine structure of camel erythrocytes in relation to its functions

The fine structure of the red cells in Arabian camels was investigated and certain characteristic features were noted. The plasmalemma of camel erythrocytes are tri-laminar, the inner and outer membranes are of high electron density between which is a zone of lesser electron density. No intracellular organelles were observed with the occasional exception of a small number of mitochondria. In the camel erythrocyte, a marginal band consisting of 30-45 microtubules was observed in many cells. Some of the possible functions of the marginal band in camel erythrocytes are discussed.     

Fine structure of the down feather during its early development

The down feather of the chick embryo has been examined by electron microscopy during three distinct stages of its early development; the presumptive stage, represented by dorsal skin of an area from which the feather organ will arise; the thickening stage, during which areas of the basal epidermis form spurs projecting into the mesenchyme, and the latter condenses under a thickened area of the epidermis; the elevation stage, at which time the basal epidermis flattens, the entire epidermis increases in thickness, and the underlying mesenchyme becomes more compact. As development proceeds the rough endoplasmic reticulum of the epidermal cells dilates, but during the elevation stage begins to flatten, and Golgi is observed with increasing frequency. The mitochondria do not appear to differ except for those in the periderm during the presumptive stage, in which case they reveal a vacant matrix and irregular cristae. Evidence is presented for actual contact between basal epidermal spurs and filopodia of cells within the mesenchyme, some of which contain numerous vesicles. The basal epidermal spurs are also seen in intimate association with collagen and anchor filaments and a network of reticulin. Evidence is also presented for the presence of neuronal elements within the mesenchyme during the thickening stage. Cross sections of cell processes within the condensations of the mesenchyme resemble unmyelinated nerve fibers, and cross sections of filopodia similar to arborizing axons abound at and within the basal lamina of both the thickening and elevation stages. Further support for the presence of nerve fibers within the mesenchyme comes from positive staining results with Bodian's and Ungewitter's methods. This comparative study of three stages of early development of the feather organ serves as a basis for more detailed investigations of each stage.     

Fine structure of a lepidopteran nervous system and its accessibility to peroxidase and lanthanum

Summary The avascular ventral nerve cord of the moth, Manduca sexta, possesses an extensive dorsal mass of connective tissue in which lie fibroblasts that produce a collagen-like protein. The lateral and ventral surfaces of the nerve cord are ensheathed by an acellular neural lamella. Beneath this lies a layer of microtubule-laden perineurial cells which are separated from one another at their peripheral borders by lacunae containing electron-opaque material to which the cells are attached by hemi-desmosomes. Beyond these spaces, narrow intercellular clefts occur between the interdigitating perineurial plasma membranes; these are then connected by both gap and tight junctions. The axons beneath are surrounded by glia which also contain many microtubules and which are linked to one another by desmosomes and tight junctions.When intact nerve cords are incubated in horseradish peroxidase, reaction product is subsequently found within the neural lamella as well as in the lacunae and clefts between perineurial cells, but not beyond this level. Desheathed preparations, however, contain peroxidase within the cytoplasm of the exposed glial cells. Lanthanum penetrates the neural lamella and the lacunae, clefts and gap junctions between adjacent perineurial cells, but no further. It therefore appears that the tight junctions in the perineurium may be the site of restriction to the entry of ions and molecules, the existence of which has been suggested previously by electrophysiological investigations.I am grateful to Miss Yvonne R. Carter for her invaluable technical assistance and to Dr. J.E. Treherne and Dr. D.B. Sattelle for helpful discussions.     

Roles of octopaminergic and dopaminergic neurons in appetitive and aversive memory recall in an insect

Background  

In insect classical conditioning, octopamine (the invertebrate counterpart of noradrenaline) or dopamine has been suggested to mediate reinforcing properties of appetitive or aversive unconditioned stimulus, respectively. However, the roles of octopaminergic and dopaminergic neurons in memory recall have remained unclear.     

Fine structure and innervation of an annelid muscle with the longest recorded sarcomere

The fine structure of myoepithelial cells of the proventriculus of a marine annelid (Syllis spongiphila) is described. The contractile system of these muscle fibers includes a single medial Z band. The thick filaments possess a ~140 Å paramyosin-like periodicity, but the filament disposition in these cells corresponds to that of other striated muscles, and actin orbitals in the A band number up to 20. The distance between the centers of the two H bands in the largest cells is ca. 40 µ Dyads involving T-system invaginations and isolated vesicles of the sarcoplasmic reticulum are situated at all sarcomere levels. Insertions of the contractile material onto invaginations of the inner and outer cell surfaces are described. Presumed polyaxonal neuromuscular junctions are established across wide synaptic clefts and include terminals with spherical and non-spherical synaptic vesicles. Inclusions occupying the core of each muscle cell appear to be rich in magnesium.     

Fine structure and optical properties of an ostracode (Crustacea) nauplius eye

Summary InNotodromas monachus, the three cups of the nauplius eye are formed by four pigment cells. The insides of the cups are lined with tapetal cells, which produce several layers of reflecting crystals. The reflecting crystals form a concave mirror in each cup upon which the retinular cells rest. The two-celled rhabdoms are few and perpendicular to the tapetal layer. The axons from the tripartite eye leave the retinular cells distally in three separate groups. The eye is thus of the inverse type. Large lens cells, with a low refractive index, are present in the open part of each cup. Distal to the lens cells, highly refractive lenses are formed in the cuticle. These lenses serve to decrease the effective curvature of the mirrors, thus enabling the reflectors to produce a focused image on the retina. The ventral cup differs by the lack of a cuticular lens and has degenerated-appearing cellular elements. The investigated nauplius eye is the only one known with both a mirror and a highly refractive lens in the dioptric apparatus.This investigation has been supported by grants from the Swedish Natural Science Research Council (grant no. 2760-009) and the Royal Physiographic Society of Lund.     

Fine structure of aphid stylet pathways and its use in host plant resistance studies

Conclusion Although there have been reports, based on light microscope observations, of damage to mesophyll tissue as a result of stylet penetration, we saw no evidence of this in our wax sections. However, the use of the electron microscope revealed that such damage does occur, and has also shown that both inter- and intracellular penetration routes exist, often within the same track, whereas we had formerly believed the stylet pathways of these aphids to be almost entirely intercellular. The intramural-extracellular route of penetration, characterised by the presence of stylets and or saliva between the cell wall and plasmalemma, requires the greater resolution of electron microscopy and cannot be distinguished in light microscope preparations.Our results suggest that an accurate indication of the stylet pathway cannot be obtained from the use of light microscopy alone, and raise serious doubts about the value of previous studies describing the route of stylet penetration. Light microscopy shows the track only at the tissue level and not at the cellular level. We advocate that all future studies of aphid stylet penetration should utilise both light and electron microscope studies because only the higher resolution of the latter technique will indicate the true stylet pathway and the end points of the tracks. Only then can the feeding site be determined with any precision.     

Fine structure of interphase nuclei

The initiation and replication sites of DNA synthesis in the plasmodial nuclei of Physarum polycephalum were studied with electron microscopic autoradiography. By using both thin sectioning and whole mount techniques, it was shown that the dense chromatin masses in the nucleus consisted of predominantly elementary chromatin-like fibrils, approximately 300 Å in diameter while the electron transparent region in the nucleus consisted of predominantly finer fibrils, less than 100 Å in diameter. With electron microscopic autoradiography it was found that (1) the initiation sites of DNA synthesis were definitely in the boundary regions between the dense chromatin masses and the electron transparent region, (2) the initiation and replication sites of DNA synthesis were definitely not on the nuclear membrane, (3) within a few minutes, replication sites migrated from the initiation sites to the electron transparent region and (4) in this electron transparent region, almost all of the nuclear DNA was synthesized.     

Fine structure of Methanomonas methanooxidans

Résumé Chez 5 bactéries anaérobies facultatives: Providencia alcalifaciens, Edwardsiella tarda, Aeromonas hydrophila, mutants catégorie 1 de Providencia stuartii et Hafnia, la nitrate-réductase B a un caractère inductible et sa biosynthèse est réprimée par O₂. Chez Micrococcus denitrificans, elle est constitutive et non répressible par NH₄ ⁺ ou par O₂. Dans le cas d'une bactérie aérobie stricte qui assimile le nitrate: Pseudomonas putida, elle est constitutive (ou faiblement inductible), non répressible par NH₄ ⁺, atteint un niveau plus élevé dans les cultures sur milieu complexe que dans les cultures sur milieu synthétique.O₂ exerce une action sur le fonctionnement de la nitrate-réductase B: l'aération inhibe réversiblement et de façon presque complète la réduction de NO₃ ^- en NO₂ ^-, aux dépens du glucose comme donneur d'électrons, par des suspensions cellulaires d'E. tarda, M. denitrificans, P. putida, et du mutant de Hafnia.

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Bacterial nitrate reductasesIV. Regulation of the biosynthesis and activity of enzyme B

Summary 5 facultative anaerobic bacteria (Providencia alcalifaciens, Edwardsiella tarda, Aeromonas hydrophila, and category 1 mutants of Providencia stuartii and Hafnia) form nitrate reductase B inducibly; the biosynthesis of the enzyme is repressed by O₂. In Micrococcus denitrificans, the enzyme is constitutive and its intracellular level is unaffected by the presence either of NH₄ ⁺ or O₂. A strict aerobe that assimilates nitrate, Pseudomonas putida, similarly forms nitrate reductase B constitutively, although the level of the enzyme is higher in cultures grown on complex than on synthetic media.O₂ affects the activity of nitrate reductase B: the reduction of NO₃ ^- to NO₂ ^-, with glucose as electron donor, by suspensions of E. tarda, M. denitrificans, P. putida and the mutant of Hafnia, is almost totally but reversibly inhibited by aeration.

     

Fine structure of Sporocytophaga myxococcoides

Summary Electron microscopic examination of thin sections of vegetative cells and microcysts of S. myxococcoides indicates that the vegetative cells have a fine structure basically identical to that of other gram-negative bacteria. Microcysts, on the other hand, possess not only an extensive internal membrane system, an additional intermediate layer interposed between the plasma membrane and cell wall, but also a thick fibrillar outer coat or capsule.