Single Lamina Research Articles

Distribution and origin of bombesin, substance P and somatostatin in cat spinal cord

Bombesin (BN), substance P-(SP) and somatostatin (SRIF) were measured in individual laminae of the cervical, thoracic and lumbar (L) spinal cord of control cats, and in the L6 segment of cats receiving a spinal hemisection (L2) or deafferentation via dorsal rhizotomy at L6, 7, S1. The interlaminar distribution of BN, SP, and SRIF was remarkably similar. Highest concentrations were found in the superficial dorsal horn, and progressively less was found proceeding ventrally. Some intersegmental variations in peptide concentration within a single lamina were found. Dorsal rhizotomy caused a significant decline in BN, SP and SRIF in lamina I-III, therefore all three peptides appear to be contained in dorsal root ganglion cells. Evidence is presented for the existence of ascending BN and SP projections originating in lamina I-III and VII, for a descending SRIF pathway terminating in lamina VIII, and for an ascending BN path in lamina VIII. Dorsal root afferents to lamina VIII influence levels of BN, SP and SRIF.

Does laminar position determine the receptive field properties of cortical neurons? A study of corticotectal cells in area 17 of the normal mouse and the reeler mutant

The neocortex of the reeler (rl) mutant mouse develops abnormally; as a result, the orderly arrangement of cells in laminae containing neurons of similar size and configuration is severely disrupted. The reeler mutant thus offers an opportunity to study the role played by laminar position in establishing the interneuronal connections of the cortex. Since the receptive field properties of neurons in the primary visual cortex (area 17) are determined by these complex interconnections, a study of receptive field properties provides a useful way to test whether functionally important connections are altered by abnormal cell position. We chose the corticotectal (CT) cells of area 17 for this analysis because they have distinctive receptive field properties and can be identified positively by antidromic stimulation with electrodes in the superior colliculus. In addition, CT cells are located in a single lamina (layer V) in the visual cortex of normal mice, but are distributed from surface to white matter in the reeler visual cortex. We characterized the receptive fields of identified CT cells in area 17 of normal mice and reeler mutants and studied several properties of these cells quantitatively. Corticotectal cells in the visual cortex of the normal mouse have high rates of spontaneous activity and large receptive fields that are neither oriented nor directional; they respond to moving stimuli over a wide range of stimulus velocities, have high peak velocity sensitivities, and show very little spatial summation. Corticotectal cells in the visual cortex of the reeler mutant do not differ significantly in these characteristics, although CT cells with extremely large receptive fields are encountered somewhat more frequently in reeler cortex. These findings indicate that the detailed connections which determine the receptive field properties of CT cells are properly established in the reeler mutant mouse despite the markedly abnormal positions of CT cells in reeler visual cortex.

Structural chemistry of outer dense fibers of rat sperm.

Structural chemistry of outer dense fibers of rat sperm.

The retina-lamina projection in the crab Leptograpsus variegatus.

In the crab, Leptograpsus variegatus, the projection of retinula cell axons to the lamina was investigated by tracing them through a series of semi-thin sections. Forty-four such axons were traced from a single group of ommatidia as far as the distal layers of the lamina. The eight receptor axons of one ommatidium project to a single lamina cartridge. Therefore, because the crab has a fused rhabdom, angular information is conserved in vision, and the outside world is projected literally onto the lamina, just as it is in the standard non-dipteran pattern of insects. The belief of previous workers that other decapod eyes show neural superposition was an inference based primarily on the patterns of penetration of the basement membrane by receptor axons, and on degeneration experiments. This evidence is reviewed, shown to be inadequate and discussed in the light of the projection now demonstrated for Leptograpsus.

Ultrastructural analysis of the apical ectodermal ridge during vertebrate limb morphogenesis: I. The human forelimb with special reference to gap junctions

The fine structure of the human forelimb apical ectodermal ridge of stages 12–19 was examined using techniques of transmission electron microscopy, freeze fracture, and scanning electron microscopy. This paper reports the presence of subcellular structures that distinguish the inductively active apical ectoderm from adjacent dorsal and ventral ectoderms. The apex of the human forelimb begins development with an epithelium of two cell layers (stage 12) which thickens at the distal tip during stages 13 and 14 into a multilayered apical ectodermal ridge. During this transition we have observed that the basal lamina differentiates from a bilayered structure to the definitive single lamina. Some cells in the ectoderm become detached from the basal lamina as stratification begins. At the same time these cells show increased mitotic activity and the developing ridge cells acquire gap junctions. Annular gap junctions are also observed. Gap junctions are not observed in adjacent, presumably noninductive, epithelia. Finally, the ridge cells next to the basal lamina acquire bundles of microfilaments that are oriented in the dorsal-ventral plane in the basal cytoplasm of the cells. The apical ridge reaches its greatest dimensions during stage 15. The number and peripheral extent of gap junctions also appear to be greatest at this same time. At stage 17, cells within the ridge begin to die, and other ridge cells engulf them. By stage 19, gap junctions in the apical epithelium are sparse and are of lesser diameter than in the definitive ridge. In addition, the oriented bundles of microfilaments present at stages 14–17 are absent. Thus, at stage 19 a morphologically distinct apical ectodermal ridge is no longer present. The apex of the limb is covered by two cell layers typical of human embryonic epidermis.

Retinogeniculate projections in albino and ocularly hypopigmented rats.

The retinogeniculate fiber projections were studied by degeneration methods in several strains of rats with pigmentation in their eyes and pelts ranging from the intensely pigmented self phenotype to the albino. The ipsilateral retinogeniculate input in the self, Irish, and hooded rats, and rats with "bicolor fundus" is located medially within the dorsal alteral geniculate nucleus (LGd) and is seen as a single lamina of moderately dense degeneration.

The Organization of the Lamina ganglionaris of the Bee

Abstract Bee, Vision, First Optic Ganglion The lamina ganglionaris of the bee contains the first synaptic region in the optic tract. The nine retinula cells of one visual unit (ommatidium) either end in the lamina as short visual fibres or end as long visual fibres in the second optic ganglion (medulla). Each axon bundle of nine fibres from one ommatidium is associated with four different second order neurons (L-fibres) to form a single lamina cartridge. Processes of additional fibres invade single groups of cartridges.

The ultrastructure of the cat olfactory bulb.

AbstractThe fine structure of the olfactory bulb was investigated in the cat. Five types of bulbar neurons were identified on the basis of size, location, cytoplasmic organelles and synaptic complexes with the neuron perikaryon. The smallest diameter neurons were predominatly located in the glomerular and granule cell layers. Ultrastructural characteristics for these two neuron populations, viz., periglomerular and internal granule cells, were identical. Tufted cells, smaller in diameter than mitral cells, were located in the external plexiform and glomerular layers and possessed all the morphological characteristics of the mitral cells. Mitral cells were the largest bulbar neurons and were located in a single lamina. Stellate (short‐axon) neurons were found in the glomerular, external plexiform and granule cell layers.Reciprocal synapses were observed in all laminae of the bulb except the primary olfactory nerve and deeper granule cell layers. Such synapses were found in the glomeruli, on tufted and mitral cells, in the neuropil of the external plexiform layer, and on the axon hillock and initial segments of the mitral cells. The morphology in the cat olfactory bulb corroborated bulbar ultrastructure described for other mammals.

Microfolding in the Castile and Todilto Evaporites, Texas and New Mexico

The Castile laminated calcite-anhydrite of Eddy County, New Mexico, and Culberson County, Texas, and the Todilto laminated calcite of Valencia County, New Mexico, contain small-scale fold chains characterized by varying degrees of buckle shortening in successive laminae. These microfolds are associated with larger folds and have apparently resulted from compression generated by tectonism. In the Castile formation, anhydrite laminae, with an average thickness of about 1.1 mm, alternate with thinner calcite laminae (usually about 0.4 mm) which have thickened and thinned in the deformed zones to accommodate folding of the anhydrite laminae. Castile micro-folds generally have a wavelength of less than 1 cm and occur in hinge areas of “megafolds” with wave-lengths of about 0.5 to 2.5 m. The microfolds are cylindrical and have uniform axial trends. Particular zones in the Castile sequence were predisposed to microfolding, a tendency which apparently existed for tens of kilometers. In these zones, relatively thin anhydrite laminae commonly have been deformed by buckling, whereas thicker anhydrite laminae commonly have reacted to stress by increasing in thickness normal to bedding; laminae of intermediate thickness have been deformed by a combination of these processes. Thicker anhydrite laminae in some places have acted as struts which have prevented or reduced the degree of buckling of adjacent thinner laminae. The over-all style of microfolding has been determined usually by variability in the thickness of successive calcite and anhydrite laminae. In the Todilto limestone member, white laminae of finely crystalline calcite with thicknesses up to about 0.5 mm are intermittently present. These laminae commonly are micro-folded. Usually only a single lamina is involved in the microfolding, and adjacent dark colored, coarser crystalline limestone layers are unfolded. The folds, in profile, are of irregular pattern and usually have wavelengths between about 0.5 to 1.0 cm. In plan, the folds are composed of a complex array of miniature highs and depressions; no trend is apparent. The Todilto limestone at the locality studied apparently reacted to compressive stress by increasing in thickness normal to bedding as well as by buckling. The white, lithologically distinct laminae were subjected to buckle shortening, took up slack, and were microfolded in open spaces generated along bedding surfaces as layer-parallel shortening of adjacent dark limestone beds took place. Many microfolds in other laminated and thin-bedded sequences probably had origins analogous to those of the Castile and Todilto formations.

The electrical responses of the retinal receptors and the lamina in the visual system of the fly Musca.

Slow electrical responses were recorded from receptors and from the lamina of the visual pathway of the fly Musca. (a) Receptors 1 to 6 in the retinal ommatidia are identified by their response dichroic sensitivity planes. The half-width of their angular sensitivity distributions is estimated 2.5° in dark adaptation, and found not to vary with ambient illumination. The retinula cells are only excited by light that enters the eye through their overlying corneal facets. (b) The responses of the lamina show no detectable dichroic sensitivity, though in favourable cases their angular sensitivity distributions may be as narrow as those of the receptors. It is shown that these responses are excited by light that enters the six facets of the corneal projection of the single lamina cartridge synapse. The retinula fibres of passage through the lamina, originating from ommatidial cells 7 and 8, evidently do not contribute excitation to the responses. (c) It is shown that the separate responses contributed by the individual receptors of the projection are added linearly at the lamina response compartment over a wide range of light intensities.

THE MORPHOLOGICAL EFFECTS OF PROTEIN SYNTHESIS INHIBITION IN MARSILEA

Marsilea vestita and M. drummondii were grown in sterile cultures to which concentrations of the protein synthesis inhibitors, 2‐thiouracil (10 mg/liter) and 5‐fluorouracil (1 mg/liter) had been added. When young sporelings are grown in a solution of thiouracil at optimum concentration, there is an inhibition of the rate of leaf formation, a retardation of the leaf heteroblastic series, and all leaves develop as land forms. When thiouracil is added to plants which are already producing typical adult, quadrifid leaves, the effects depend on whether the treated plants are water or land forms. Plants which are typically water forms convert to land forms. After treatment successive leaves develop typical sunken stomata on both leaf surfaces. The tissues of the rhizome, root and petiole are more compact and, in general, the cells of the plant have thicker walls. Vascular patterns are not changed, though the size of the rhizome, root and petiole may be reduced. Plants which are typically land forms are less affected than the water forms, but they show a small reduction in apex volume and an apparent reversion of the leaflet number from the typical quadrifid leaf to a trifid, bifid, or single lamina condition. In both land and water forms apical dominance may be broken by treatment with 10 mg/liter thiouracil or 1 mg/liter fluorouracil and numerous lateral branches develop. Higher concentrations (15–25 mg/liter of thiouracil) may result in abnormal development of lateral axillary buds, petiole bases and leaflets. The meristems of the plant are differentially sensitive to thiouracil; leaflet meristems are most sensitive, the root meristems are the least sensitive. It appears that a true reversion to juvenile leaf development need not occur even though protein synthesis and the volume of the apex are reduced. The development of the land or water form in Marsilea appears to depend on rate of growth. Hence inhibition of the growth of typical water forms, through inhibition of protein synthesis, causes a shift in development toward the morphology typical of land forms.

Interpreting the Concept of the Sedimentation Unit

ABSTRACT Consideration is given here to the interpretation of Otto's concept of the sedimentation unit and to Apfel's definition of a phase. Otto's definition tacitly assumes that the stratified internal structure of the sedimentation unit is causally related to small erratic fluctuations or perturbations within the transport system. These are referred to as nonassignable causes. Both Otto and Apfel selected velocity as the critical and diagnostic parameter, and they related the bedded structure of the unit to chance variations in velocity, or to fluctuations in the competency of the transporting current. Laboratory experiments involving the deposition of artificial sedimentation units demonstrate that: (a) a well-defined bedded structure can develop under steady-state con itions of flow (velocity) and sediment transport, (b) velocity fluctuations represent but one of a number of important processes responsible for the sorting and segregation of grain sizes into a bedded structure. Furthermore, the experimental evidence suggests that a microchange in regimen may trigger the deposition of a group of laminae rather than a single lamina. A genetic interpretation of the laminated internal structure is not particularly meaningful until such time as further information becomes available on the mechanics of depositional processes. Therefore the connotation essentially constant used by Otto in his definition of the sedimentation unit must be interpreted rather liberally in the light of present knowledge, because well-defined lamination can be formed under an a parently wide range of flow conditions, including the special case of uniform flow conditions. It is claimed, therefore, that these considerations tarnish the conceptive framework of the sedimentation unit.

An electron microscopic study of Hashimoto thyroiditis.

An electron microscopic study has been made of thyroid tissue obtained from four patients with Hashimoto thyroiditis. Contrary to what has been inferred from earlier light microscopy studies, the basement membrane in Hashimoto thyroiditis is remarkably continuous, taking the form of a single lamina some 50 mµ thick. It differs from that of the normal adult human thyroid in that there is no re‐duplication of the membrane. In Hashimoto thyroiditis, temporary gaps in the basement membrane occur which are just sufficient to allow the passage of leucocytes in and out of the thyroid follicles. Small breaks in the basement membrane may occur in necrotic thyroid follicles, and cytoplasmic debris of the epithelial cells then escapes into the stroma.A mutual activity between invading lymphocytes and the epithelial cells of the thyroid follicles is inferred from the observation that tenuous processes of the epithelial cells embrace the invading lymphocytes and that bulbous lymphocytic processes abut against or invaginate the epithelial cells. It is conceivable that this intimate contact allows antibody bound to the lymphocyte to be directly transferred to the cells of the thyroid epithelium.

Wachstum von Einkristall-Lamellen in dem engen Raum zwischen parallelen Glasfl�chen

Single crystal lamina of potassium chlorate and potassium chloride are grown from the solution in the narrow space between two parallel glass surfaces. Electron micrographs are taken at 60 and 80 keV. The monocrystalline structure is demonstrated by the diffraction of a parallel electron beam. The exact thickness of the crystals can be determined from the subsidiary maxima within the Bragg reflections in a convergent beam pattern. Other crystals are under investigation.

Single Quartz Crystal Point Focusing X-Ray Monochromator

A point focusing x-ray monochromator which uses Bragg reflection from a single lamina of quartz bent in such a way that its atomic planes are given two principal radii of curvature has been constructed for use in low-angle diffraction studies. It was found that the crystal reflects 2.78% of the incident Cu Kα1 radiation into a converging beam one meter long, with a resolution of better than half a millimeter except for a very faint halo. The instrument has been used to obtain diffraction patterns from normal and sickle-cell human hemoglobin and also from southern bean mosaic virus. The speed of the present instrument is roughly two hundred times that of an equivalent pinhole collimating system. A similar but still faster instrument is being constructed.