Knob Density Research Articles

Effects of dietary Lactobacillus rhamnosus GG supplementation on the production performance, egg quality, eggshell ultrastructure, and lipid metabolism of late-phase laying hens

BackgroundToward the late phase of laying, the production performance of laying hens decreases, egg quality deteriorates, lipid metabolism weakens, and hepatic lipid accumulation is exacerbated. Probiotics as an alternative to antimicrobials have been employed in poultry-related industries. Lactobacillus rhamnosus GG (LGG) is currently the most researched and clinically validated probiotic, showing promising effects in multiple application areas. However, few studies have been conducted on livestock (including poultry) production.ResultsCompared with the CON group, the feed conversion ratio (P < 0.01) declined significantly in the LGG group. Eggshell strength (P < 0.001) and eggshell thickness (P < 0.001) were significantly increased by supplementation with LGG in the diet. The height (P < 0.001) and proportion (P < 0.05) of the effective layer and the mammillary knob density (P < 0.01) in the eggshell ultrastructure of the LGG group increased significantly, while the mammillary layer (P < 0.05) and knob width (P < 0.01) decreased significantly. The LGG-treated hens had significantly lower serum concentrations of low-density lipoprotein (P < 0.05), free fatty acids (P < 0.01), and liver triglyceride (P < 0.05) levels than those in the CON group.ConclusionsLGG supplementation significantly decreases the feed conversion ratio, improves eggshell quality by altering the ultrastructure, and improves lipid metabolism in the late laying period.

A Comparison between Vitamin D3 and 25-Hydroxyvitamin D3 on Laying Performance, Eggshell Quality and Ultrastructure, and Plasma Calcium Levels in Late Period Laying Hens.

Simple SummaryThe sharp decline of laying performance and eggshell quality is a common problem in late period laying hens. Vitamin D3 (VD3) is a necessary micronutrient which plays an important role in mineral and skeletal homeostasis. With the rapid development of genetic selection, commercial laying hens have increased requirements for performance and nutrients. The commercial supplementary dose of VD3 (62.5 µg/kg) for late period laying hens may be not enough to satisfy the production. In addition, 25-hydroxyvitamin D3 (25-OHD3) as an active metabolite of VD3, is a viable alternative to replace VD3. Therefore, the objective of this study was to compare the effects of different supplementary doses and sources between VD3 and 25-OHD3 on the laying performance and eggshell quality in late period laying hens. The results showed that supplementary 125 µg/kg doses of VD3 or 25-OHD3 had better effects in late period laying hens compared with 62.5 µg/kg doses of VD3. Additionally, there were no different effects on laying performance or eggshell quality in the hens fed dietary 125 µg/kg doses of VD3 or 25-OHD3.The objective of this study was to compare high supplementary doses (125 µg/kg) of vitamin D3 (VD3) or 25-hydroxyvitamin D3 (25-OHD3) with commercial supplementary doses (62.5 µg/kg) of VD3 on laying performance, eggshell quality and ultrastructure, and plasma calcium levels in late period laying hens. A total of 1512 Roman Gray (60-week-old) laying hens were allotted into three treatments with 12 replicates and 42 birds in each replicate. During the 12-week trial period, the layers were fed a basal diet supplemented with different doses of VD3 or 25-OHD3 (62.5 µg/kg VD3 in control group, CON; 125 µg/kg VD3 in high level VD3 group, VD3; 125 µg/kg 25-OHD3 in high level 25-OHD3 group, 25-OHD3). The results showed that high supplementary doses of VD3 or 25-OHD3 increased laying rate (p < 0.05). Moreover, the layers fed high doses of VD3 or 25-OHD3 diets had decreased unqualified egg rate and mortality (p < 0.05). High supplementary doses of VD3 or 25-OHD3 increased eggshell strength and eggshell thickness (p < 0.05). From observation in eggshell ultrastructure, high doses of VD3 or 25-OHD3 diets increased the palisade layer thickness and mammillary knob density (p < 0.05). Furthermore, high doses of VD3 or 25-OHD3 diets increased the calcium levels in plasma (p < 0.05). In summary, compared with 62.5 µg/kg doses of VD3, supplementary 125 µg/kg doses of VD3 or 25-OHD3 improved the laying performance, eggshell quality, and plasma calcium levels in late period laying hens. Additionally, there was an equal effect on laying performance and eggshell quality in the hens fed dietary 125 µg/kg doses of VD3 or 25-OHD3.

Hemoglobin S and C affect biomechanical membrane properties of P. falciparum-infected erythrocytes

During intraerythrocytic development, the human malaria parasite Plasmodium falciparum alters the mechanical deformability of its host cell. The underpinning biological processes involve gain in parasite mass, changes in the membrane protein compositions, reorganization of the cytoskeletons and its coupling to the plasma membrane, and formation of membrane protrusions, termed knobs. The hemoglobinopathies S and C are known to partially protect carriers from severe malaria, possibly through additional changes in the erythrocyte biomechanics, but a detailed quantification of cell mechanics is still missing. Here, we combined flicker spectroscopy and a mathematical model and demonstrated that knob formation strongly suppresses membrane fluctuations by increasing membrane-cytoskeleton coupling. We found that the confinement increased with hemoglobin S but decreases with hemoglobin C in spite of comparable knob densities and diameters. We further found that the membrane bending modulus strongly depends on the hemoglobinopathetic variant, suggesting increased amounts of irreversibly oxidized hemichromes bound to membranes.

The sickle cell trait affects contact dynamics and endothelial cell activation in Plasmodium falciparum-infected erythrocytes

Sickle cell trait, a common hereditary blood disorder, protects carriers from severe disease in infections with the human malaria parasite Plasmodium falciparum. Protection is associated with a reduced capacity of parasitized erythrocytes to cytoadhere to the microvascular endothelium and cause vaso-occlusive events. However, the underpinning cellular and biomechanical processes are only partly understood and the impact on endothelial cell activation is unclear. Here, we show, by combining quantitative flow chamber experiments with multiscale computer simulations of deformable cells in hydrodynamic flow, that parasitized erythrocytes containing the sickle cell haemoglobin displayed altered adhesion dynamics, resulting in restricted contact footprints on the endothelium. Main determinants were cell shape, knob density and membrane bending. As a consequence, the extent of endothelial cell activation was decreased. Our findings provide a quantitative understanding of how the sickle cell trait affects the dynamic cytoadhesion behavior of parasitized erythrocytes and, in turn, endothelial cell activation.

The Influence of Hen Aging on Eggshell Ultrastructure and Shell Mineral Components.

The eggshell, which is a complex and highly ordered structure, is very important factor for food safety and egg marketing. This study investigated the changes in eggshell structure and shell components in relationship to hen age. For this study, we examined the histological change of the endometrium of the 30-, 60-, and 72-wk-old commercial layers, and analyzed the ultrastructure and ionic composition of their eggshells. The results showed that histological deformation, fibrosis, atrophy and elimination of micro-villi in the uterus endometrium were found through microscopic observation that was associated with increasing hen age. Concentration of blood-ion components such as Ca2+, Na+, K+, and Cl– ions did not change with age. Along with the results from the ultrastructure analysis of the eggshell, the palisade layer ratio and the density of mammillary knobs were significantly decreased in older hens. In addition, the type B mammillary knobs were frequently observed with increasing hen age. In the mineral element assay from the eggshell, Ca2+, S2–, and Co2+ significantly decreased with increasing hen age, whereas Na+, K+, and V2+ significantly increased. Therefore, the damages of endometrial tissue inhibit the processes of ion transmission and the crystallization of eggshell formation, resulting in a large and non-uniform mammillary knob formation. This means the conditions of endometrial cells affect the formation of the eggshell structure. In conclusion, hen aging causes the weakness of the eggshell and degrades the eggshell quality.

Electron cryotomography of Mycoplasma pneumoniae mutants correlates terminal organelle architectural features and function.

The Mycoplasma pneumoniae terminal organelle functions in adherence and gliding motility and is comprised of at least eleven substructures. We used electron cryotomography to correlate impaired gliding and adherence function with changes in architecture in diverse terminal organelle mutants. All eleven substructures were accounted for in the prkC, prpC and P200 mutants, and variably so for the HMW3 mutant. Conversely, no terminal organelle substructures were evident in HMW1 and HMW2 mutants. The P41 mutant exhibits a terminal organelle detachment phenotype and lacked the bowl element normally present at the terminal organelle base. Complementation restored this substructure, establishing P41 as either a component of the bowl element or required for its assembly or stability, and that this bowl element is essential to anchor the terminal organelle but not for leverage in gliding. Mutants II-3, III-4 and topJ exhibited a visibly lower density of protein knobs on the terminal organelle surface. Mutants II-3 and III-4 lack accessory proteins required for a functional adhesin complex, while the topJ mutant lacks a DnaJ-like co-chaperone essential for its assembly. Taken together, these observations expand our understanding of the roles of certain terminal organelle proteins in the architecture and function of this complex structure.

Dietary manganese supplementation modulated mechanical and ultrastructural changes during eggshell formation in laying hens

This study evaluated the mechanical and ultrastructural changes during eggshell formation in laying hens by using the optimal levels of organic and inorganic manganese (Mn). A total of 270 62-wk-old Hy-Line Brown laying hens were fed a basal diet containing 25.1 mg Mn per kg feed for 2 wks, after which they were randomly allocated into 3 groups and fed the basal diet (control) or the basal diet supplemented with 120 mg Mn per kg feed from monohydrate Mn sulfate (an inorganic source of Mn), or 80 mg Mn per kg feed from an amino acid-Mn complex (an organic source of Mn) for 12 wks. For each group, 6 replicates of 15 hens were used with one hen per cage. Dietary Mn supplementation significantly increased eggshell-breaking strength and thickness in laying hens (P < 0.05). In neither was the elasticity of their eggshell membranes, measured during the nucleation and mammillary knob formation stages, affected by dietary Mn compared with the control (P > 0.05), whereas the breaking strength of the eggshells was greater at the linear and terminate deposition stages compared with the control (P < 0.05). Dietary Mn supplementation decreased the width of the mammillary knobs and the proportion of mammillary thickness, and increased the proportion of effective thickness of the whole eggshells (P < 0.05). Ultrastructural changes during the eggshell formation indicated that dietary Mn supplementation increased the nucleation site and mammillary knob densities, decreased the mammillary thickness, and increased the proportion of effective thickness and total thickness of the eggshells compared with the control (P < 0.05). Therefore, dietary Mn supplementation can improve the breaking strength and ultrastructure of the eggshells during their formation, and the mammillary and palisade layers are both crucial structures affected by Mn.

Cryo scanning electron microscopy of Plasmodium falciparum-infected erythrocytes.

Plasmodium falciparum invades erythrocytes as an essential part of their life cycle. While living inside erythrocytes, the parasite remodels the cell's intracellular organization as well as its outer surface. Late trophozoite-stage parasites and schizonts introduce numerous small protrusions on the erythrocyte surface, called knobs. Current methods for studying these knobs include atomic force microscopy and electron microscopy. Standard electron microscopy methods rely on chemical fixation and dehydration modifying cell size. Here, a novel method is presented using rapid freezing and scanning electron microscopy under cryogenic conditions allowing for high resolution and magnification of erythrocytes. This novel technique can be used for precise estimates of knob density and for studies on cytoadhesion.

Rolling Adhesion of Schizont Stage Malaria-Infected Red Blood Cells in Shear Flow

To avoid clearance by the spleen, red blood cells infected with the human malaria parasite Plasmodium falciparum (iRBCs) adhere to the vascular endothelium through adhesive protrusions called “knobs” that the parasite induces on the surface of the host cell. However, the detailed relation between the developing knob structure and the resulting movement in shear flow is not known. Using flow chamber experiments on endothelial monolayers and tracking of the parasite inside the infected host cell, we find that trophozoites (intermediate-stage iRBCs) tend to flip due to their biconcave shape, whereas schizonts (late-stage iRBCs) tend to roll due to their almost spherical shape. We then use adhesive dynamics simulations for spherical cells to predict the effects of knob density and receptor multiplicity per knob on rolling adhesion of schizonts. We find that rolling adhesion requires a homogeneous coverage of the cell surface by knobs and that rolling adhesion becomes more stable and slower for higher knob density. Our experimental data suggest that schizonts are at the border between transient and stable rolling adhesion. They also allow us to establish an estimate for the molecular parameters for schizont adhesion to the vascular endothelium and to predict bond dynamics in the contact region.

A spiral scaffold underlies cytoadherent knobs in Plasmodium falciparum–infected erythrocytes

AbstractMuch of the virulence of Plasmodium falciparum malaria is caused by cytoadherence of infected erythrocytes, which promotes parasite survival by preventing clearance in the spleen. Adherence is mediated by membrane protrusions known as knobs, whose formation depends on the parasite-derived, knob-associated histidine-rich protein (KAHRP). Knobs are required for cytoadherence under flow conditions, and they contain both KAHRP and the parasite-derived erythrocyte membrane protein PfEMP1. Using electron tomography, we have examined the 3-dimensional structure of knobs in detergent-insoluble skeletons of P falciparum 3D7 schizonts. We describe a highly organized knob skeleton composed of a spiral structure coated by an electron-dense layer underlying the knob membrane. This knob skeleton is connected by multiple links to the erythrocyte cytoskeleton. We used immuno-electron microscopy (EM) to locate KAHRP in these structures. The arrangement of membrane proteins in the knobs, visualized by high-resolution freeze-fracture scanning EM, is distinct from that in the surrounding erythrocyte membrane, with a structure at the apex that likely represents the adhesion site. Thus, erythrocyte knobs in P falciparum infection contain a highly organized skeleton structure underlying a specialized region of membrane. We propose that the spiral and dense coat organize the cytoadherence structures in the knob, and anchor them into the erythrocyte cytoskeleton. The high density of knobs and their extensive mechanical linkage suggest an explanation for the rigidification of the cytoskeleton in infected cells, and for the transmission to the cytoskeleton of shear forces experienced by adhering cells.

Plasmodium falciparum-infected erythrocyte knob density is linked to the PfEMP1 variant expressed.

ABSTRACTMembers of the clonally variant Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family mediate adhesion of infected erythrocytes (IEs) to vascular receptors. PfEMP1 expression is normally confined to nanoscale knob protrusions on the IE surface membrane. To investigate the relationship between the densities of these IE surface knobs and the PfEMP1 variant expressed, we used specific antibody panning to generate three sublines of the P. falciparum clone IT4, which expresses the PfEMP1 variants IT4VAR04, IT4VAR32b, and IT4VAR60. The knob density in each subline was then determined by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and compared to PfEMP1 and knob-associated histidine-rich protein (KAHRP) expression. Selection for uniform expression of IT4VAR04 produced little change in knob density, compared to unselected IEs. In contrast, selection for IT4VAR32b expression increased knob density approximately 3-fold, whereas IEs selected for IT4VAR60 expression were essentially knobless. When IT4VAR60+ IEs were subsequently selected to express IT4VAR04 or IT4VAR32b, they again displayed low and high knob densities, respectively. All sublines expressed KAHRP regardless of the PfEMP1 expressed. Our study documents for the first time that knob density is related to the PfEMP1 variant expressed. This may reflect topological requirements to ensure optimal adhesive properties of the IEs.

The Density of Knobs on Plasmodium falciparum-Infected Erythrocytes Depends on Developmental Age and Varies among Isolates

BackgroundThe virulence of Plasmodium falciparum malaria is related to the parasite’s ability to evade host immunity through clonal antigenic variation and tissue-specific adhesion of infected erythrocytes (IEs). The P. falciparum erythrocyte membrane protein 1 (PfEMP1) family expressed on dome-shaped protrusions called knobs on the IE surface is central to both. Differences in receptor specificity and affinity of expressed PfEMP1 are important for IE adhesiveness, but it is not known whether differences in the number and size of the knobs on which the PfEMP1 proteins are expressed also play a role. Therefore, the aim of this study was to provide detailed information on isolate- and time-dependent differences in knob size and density.Methodology/Principal FindingsWe used atomic force microscopy to characterize knobs on the surface of P. falciparum-infected erythrocytes. Fourteen ex vivo isolates from Ghanaian children with malaria and 10 P. falciparum isolates selected in vitro for expression of a particular PfEMP1 protein (VAR2CSA) were examined. Knob density increased from ∼20 h to ∼35 h post-invasion, with significant variation among isolates. The knob density ex vivo, which was about five-fold higher than following long-term in vitro culture, started to decline within a few months of culture. Although knob diameter and height varied among isolates, we did not observe significant time-dependent variation in these dimensions.Conclusions/SignificanceThe density of knobs on the P. falciparum-IE surface depends on time since invasion, but is also determined by the infecting isolate in a time-independent manner. This is the first study to quantitatively evaluate knob densities and dimensions on different P. falciparum isolates, to examine ex vivo isolates from humans, and to compare ex vivo and long-term in vitro-cultured isolates. Our findings contribute to the understanding of the interaction between P. falciparum parasites and the infected host.

Horizontal cell morphology in nocturnal and diurnal primates: A comparison between owl-monkey (Aotus) and capuchin monkey (Cebus)

Horizontal cell morphology was studied in the retina of the nocturnal owl-monkey, Aotus, and compared with that of its diurnal, close relative, the capuchin monkey, Cebus . Cells were initially labeled with DiI and the staining was later photoconverted in a stable precipitated using DAB as chromogen. The sizes of cell bodies, dendritic fields, and axon terminals, number of dendritic clusters, intercluster spacing, and intercone spacing were measured at increasing eccentricities. Two distinct morphological classes of horizontal cells were identified, which resembled those of H1 and H3 cells described in diurnal monkeys. A few examples of a third class, possibly corresponding to the H2 cells of diurnal monkeys, were labeled. Both H1 and H3 cells increased in size and had increasing numbers of dendritic clusters with eccentricity. H3 cells were larger and had a larger number of dendritic clusters than H1 cells. Owl-monkey H1 cells had larger dendritic fields than capuchin monkey H1 cells at all quadrants in the central and midperipheral retinal regions, but the difference disappeared in the far periphery. Owl-monkey and capuchin monkey H1 cells had about the same number of dendritic clusters across eccentricity. As owl-monkey H1 cells were larger than capuchin monkey H1 cells, the equal number of clusters in these two primates was due to the fact that they were more spaced in the owl-monkey cells. H1 intercluster distance closely matched intercone spacing for both the owl-monkey and capuchin monkey retinas. On the other hand, H3 intercluster distance was larger than intercone spacing in the retina of both primates. Owl-monkey H1 axon terminals had 2-3 times more knobs than capuchin monkey H1 axon terminals in spite of having about the same size and, consequently, knob density was 2-3 times higher for owl-monkey than capuchin monkey H1 axon terminals across all eccentricities. The differences observed between owl-monkey and capuchin monkey horizontal cells, regarding the morphology of their dendritic trees and axon terminals, may be related to the differences found in the cone-to-rod ratio in the retina of these two primates. They seem to represent retinal specializations to the nocturnal and diurnal life styles of the owl-monkey and capuchin monkey, respectively.

A banded topography in the developing rat's olfactory epithelial surface

In situ hybridization studies from various laboratories have shown that the rat's olfactory epithelium has four distinct regions in which most putative odor receptors are located. To determine whether morphological features accompany this biochemical patterning, olfactory epithelial surfaces of rat nasal endoturbinates and septa were examined with scanning electron microscopy, placing particular emphasis on endoturbinate IIb. There was some morphological patterning at embryonic day 15 (E15), but distinct regions were not yet discernible. Regionalization became distinct at E16 and E18. Posterior regions (Regions 1 and 2) had much higher receptor cell knob densities than more anterior regions closer to the respiratory epithelium (Regions 3 and 4). Supporting cell microvilli were longer in Region 1 than in Region 2. Apices of cells surrounding the receptor cells were flatter in Regions 1 and 2 than in Regions 3 and, especially, Region 4. In Regions 1-3, these surrounding cells were made up mainly of supporting cells; in Region 4 they included respiratory cells. Regions 3 and 4 also had glandular openings and scattered microvillous cells that resemble hair cells of the ear. Older fetuses and adults showed similar evidence of patterning, but detailed examination was precluded by the increased length and entanglement of receptor cell cilia and supporting cell microvilli. In conclusion, a distinct topographic pattern, involving both receptor and surrounding cells, emerges during development of the rat olfactory epithelial surface. Location of the bands roughly matches the zones seen by in situ hybridization.

A banded topography in the developing rat's olfactory epithelial surface

In situ hybridization studies from various laboratories have shown that the rat's olfactory epithelium has four distinct regions in which most putative odor receptors are located. To determine whether morphological features accompany this biochemical patterning, olfactory epithelial surfaces of rat nasal endoturbinates and septa were examined with scanning electron microscopy, placing particular emphasis on endoturbinate IIb. There was some morphological patterning at embryonic day 15 (E15), but distinct regions were not yet discernible. Regionalization became distinct at E16 and E18. Posterior regions (Regions 1 and 2) had much higher receptor cell knob densities than more anterior regions closer to the respiratory epithelium (Regions 3 and 4). Supporting cell microvilli were longer in Region 1 than in Region 2. Apices of cells surrounding the receptor cells were flatter in Regions 1 and 2 than in Regions 3 and, especially, Region 4. In Regions 1–3, these surrounding cells were made up mainly of supporting cells; in Region 4 they included respiratory cells. Regions 3 and 4 also had glandular openings and scattered microvillous cells that resemble hair cells of the ear. Older fetuses and adults showed similar evidence of patterning, but detailed examination was precluded by the increased length and entanglement of receptor cell cilia and supporting cell microvilli. In conclusion, a distinct topographic pattern, involving both receptor and surrounding cells, emerges during development of the rat olfactory epithelial surface. Location of the bands roughly matches the zones seen by in situ hybridization. J. Comp. Neurol. 388:293–306, 1997. © 1997 Wiley-Liss, Inc.

Marked restoration of density and total number of mature (knob-bearing) olfactory receptor neurons in rats recovering from early hypothyroid-induced growth retardation

Our recent studies have shown that restoration of thyroid function in developing hypothyroid rats results in upregulation of olfactory neurogenesis and compensatory proliferation of olfactory receptor neurons (ORN) in the olfactory epithelium (OE) (Paternostro and Meisami, Dev. Brain Res., 76 (1993) 151–161; ibid., 83 (1994) 151–162). It was not clear, however, whether the newly forming ORNs undergo complete maturational stages. To determine the effects of restoration of thyroid function on maturation of ORNs, the density and total number of mature ORNs were estimated in the OE of euthyroid and hypothyroid rats at postnatal days 1, 12, 25 and 90 and the results were compared with those in rats allowed to recover from early thyroid deficiency at weaning (day 25). As a marker for mature ORNs, and on the basis of one olfactory dendritic knob per ORN, the density and total number of the olfactory knobs were determined in the entire extent of the OE covering the nasal septum. Hypothyroidism was induced by adding propylthioracil (PTU) to the drinking water (1 g/1) from birth until days 12, 25 or 90 of age. Recovery from hypothyroidism was induced by withdrawal of PTU at day 25, leading to restoration of thyroid function and somatic growth recovery. The density of olfactory knobs was determined in 1 μm semi-thin sections stained with toluidine blue. In the normal rats, the number of olfactory knobs ( = mature ORNs) increase 8.5- and 3-fold during postnatal days 1–25 and 25–90 respectively, reaching a mean value of 4×106/septal OE, compared to 2.8- and 1.4-fold, respectively, for the hypothyroid rats. This led to deficits of 51% and 76% in the number of mature ORNs in the 25- and 90-day-old hypothyroid rats. In rats allowed to recover, the number of mature ORNs increased 4.5-fold during postnatal days 25–90 (3 × > hypothyroid rats and 1.5 × > controls). The results indicate marked upregulation of the maturational process of the ORNs and their compensatory accretion within the OE of the recovery group. The recovery process was not complete however, as indicated by a remaining deficint of about 25% in the total number of mature ORN, compared to normal 90-day controls. Thus thyroid hormones are essential for accretion of new mature ORNs in both the suckling and postweaning rats. Also, the ORNs show a remarkable ability to recover from severe early hypothyroid-induced growth retardation and attain normal mature state.

Marked restoration of density and total number of mature (knob-bearing) olfactory receptor neurons in rats recovering from early hypothyroid-induced growth retardation

Our recent studies have shown that restoration of thyroid function in developing hypothyroid rats results in upregulation of olfactory neurogenesis and compensatory proliferation of olfactory receptor neurons (ORN) in the olfactory epithelium (OE) (Paternostro and Meisami, Dev. Brain Res., 76 (1993) 151–161; ibid., 83 (1994) 151–162). It was not clear, however, whether the newly forming ORNs undergo complete maturational stages. To determine the effects of restoration of thyroid function on maturation of ORNs, the density and total number of mature ORNs were estimated in the OE of euthyroid and hypothyroid rats at postnatal days 1, 12, 25 and 90 and the results were compared with those in rats allowed to recover from early thyroid deficiency at weaning (day 25). As a marker for mature ORNs, and on the basis of one olfactory dendritic knob per ORN, the density and total number of the olfactory knobs were determined in the entire extent of the OE covering the nasal septum. Hypothyroidism was induced by adding propylthioracil (PTU) to the drinking water (1 g/1) from birth until days 12, 25 or 90 of age. Recovery from hypothyroidism was induced by withdrawal of PTU at day 25, leading to restoration of thyroid function and somatic growth recovery. The density of olfactory knobs was determined in 1 μm semi-thin sections stained with toluidine blue. In the normal rats, the number of olfactory knobs ( = mature ORNs) increase 8.5- and 3-fold during postnatal days 1–25 and 25–90 respectively, reaching a mean value of 4×10 6/septal OE, compared to 2.8- and 1.4-fold, respectively, for the hypothyroid rats. This led to deficits of 51% and 76% in the number of mature ORNs in the 25- and 90-day-old hypothyroid rats. In rats allowed to recover, the number of mature ORNs increased 4.5-fold during postnatal days 25–90 (3 × > hypothyroid rats and 1.5 × > controls). The results indicate marked upregulation of the maturational process of the ORNs and their compensatory accretion within the OE of the recovery group. The recovery process was not complete however, as indicated by a remaining deficint of about 25% in the total number of mature ORN, compared to normal 90-day controls. Thus thyroid hormones are essential for accretion of new mature ORNs in both the suckling and postweaning rats. Also, the ORNs show a remarkable ability to recover from severe early hypothyroid-induced growth retardation and attain normal mature state.

Influence of olfactory bulb on dendritic knob density of rat olfactory receptor neurons in vitro

The maturation of olfactory receptor cells is facilitated by the presence of their target tissue, the olfactory bulb. Organ cultures of embryonic rat olfactory mucosa (OM) maintained in the presence of the presumptive olfactory bulb (POB) had a significantly higher (1.6 ×) density of ciliated dendritic knobs than those without the POB. No significant difference was found in the density of non-ciliated dendritic knobs and total knob density in these two groups of cultures. A control group of explants in which OM and POB had been separated and recombined also showed an increased ciliated dendritic knob density. The area of the olfactory epithelium was the same whether or not the POB was present. In addition, scanning electron microscopy observations revealed a high degree of heterogeneity in the surface morphology of the olfactory epithelium.

Scanning electron microscope-analysis of the protrusions (knobs) present on the surface of Plasmodium falciparum-infected erythrocytes.

The nature of the surface deformations of erythrocytes infected with the human malaria parasite Plasmodium falciparum was analyzed using scanning electron microscopy at two stages of the 48-h parasite maturation cycle. Infected cells bearing trophozoite-stage parasites (24-36 h) had small protrusions (knobs), with diameters varying from 160 to 110 nm, and a density ranging from 10 to 35 knobs X micron-2. When parasites were fully mature (schizont stage, 40-44 h), knob size decreased (100-70 nm), whereas density increased (45-70 knobs X micron-2). Size and density of the knobs varied inversely, suggesting that knob production (a) occurred throughout intraerythrocytic parasite development from trophozoite to schizont and (b) was related to dynamic changes of the erythrocyte membrane. Variation in the distribution of the knobs over the red cell surface was observed during parasite maturation. At the early trophozoite stage of parasite development, knobs appeared to be formed in particular domains of the cell surface. As the density of knobs increased and they covered the entire cell surface, their lateral distribution was dispersive (more-than-random); this was particularly evident at the schizont stage. Regional surface patterns of knobs (rows, circles) were seen throughout parasite development. The nature of the dynamic changes that occurred at the red cell surface during knob formation, as well as the nonrandom distribution of knobs, suggested that the red cell cytoskeleton may have played a key role in knob formation and patterning.

Role of Ultrastructure in Determining Eggshell Strength

The relationship of eggshell mammillary structure to eggshell strength was studied. Eggshells produced from Single Comb White Leghorn hens of the Cornell high eggshell strength (HES) or low eggshell strength (LES) strains with similar shell thickness (HES: .356 ± .056 mm; LES: .307 ± .006 mm, P>.05) but with significantly different shell breaking strength as determined by quasi-static loading to failure (HES: 3.46 ± .12 kg; LES; 2.09 ± .11 kg, P<.05) were selected for measurement of mammillary knob distribution. Casts of mammillary knobs were made using a low viscosity epoxy resin and were gold-coated and viewed by scanning electron microscopy (SEM); mammillary knob density was measured from SEM photographs. Results showed that LES shells had smaller mammillary knob formations more densely situated than did HES shells (HES; 115.4 ± 7.8 knobs/cm2; LES 143.9 ± 10.8 knobs/cm2, P<.05). It is proposed that the greater interstitial area of the mammillary region of LES shells contributes significantly to their relative weakness.