Evaluation of a forage allocation model for Theodore Roosevelt National Park

We developed a forage allocation model using a deterministic, linear optimization module in a commercially available spreadsheet package to help resource managers in Theodore Roosevelt National Park (TRNP), North Dakota determine optimum numbers of four ungulate species, bison (Bison bison), elk (Cervus elaphus), mule deer (Odocoileus hemionus), and feral horses, in the Park. TRNP staff actively managed bison, elk, and feral horse numbers within bounds suggested by our model from 1983 to 1996. During this period, we measured vegetation at 8 grassland and 12 wooded sites at 1-3 year intervals to determine if model solutions were appropriate for maintaining stable conditions in important plant communities in the Park. The data we recorded at these sites indicated minimal change in plant communities from 1983 to 1996. Changes in most vegetation categories that we expected when animal numbers exceeded model optimums for short periods (decreases in coverage/stem numbers of palatable plant species, increases in bare ground or unpalatable plant species) did not occur consistently under high or low precipitation conditions. The lack of sensitivity of our model to decreases in overall production of palatable plant species that occurred due to drought, fire, expansion of black-tailed prairie dog (Cynomys ludovicianus) colonies, and the spread of leafy spurge (Euphorbia esula) in areas of the Park where we did not have monitoring sites suggested that the model under-estimated the total number of ungulates that the Park could support. Management for population levels of ungulates defined by the model probably led to over protection of common plant communities and insufficient protection of rare plant communities. Detecting changes in rare plant communities could have been accomplished by re-designing our vegetation monitoring program, but changing emphasis to protection of rare plants would have likely promoted under use of grazing-tolerant habitat types, dissatisfaction in tourists visiting the Park to see large mammals, and large increases in cost and intrusiveness of management activities such as fencing and control of ungulate populations. The model was a flawed representation of grazing dynamics in TRNP, but we believe it succeeded in making management personnel aware of the biological constraints they face when making management decisions.

Neuroglandular synapses in the pharynx of the sea anemone Aiptasia pallida (Cnidaria, Anthozoa)

Scanning and transmission electron microscopy of the pharynx of the sea anemone Aiptasia pallida revealed a heavily ciliated epidermis and two types of gland cells not known previously to be innervated. By tracing serial cross sections of the pharynx, we located and characterized two types of neuroglandular synapses (i.e., those having clear vesicles and those with dense-cored vesicles). The diameters of the vesicles at each synapse were averaged; clear vesicles ranged from 70 to 103 nm in diameter and were observed at synapses to both mucous and zymogenic gland cells. Dense-cored vesicles ranged from 53 to 85 nm in diameter and were observed at synapses to two mucous gland cells. One mucous gland cell had three neuroglandular synapses, one with clear vesicles and two with dense-cored vesicles. The occurrence of either clear or dense-cored vesicles at neuroglandular synapses suggests that at least two types of neurotransmitter substances control the secretion of mucus in the sea anemone pharynx. To date, only clear vesicles have been observed at a neurozymogenic gland cell synapse in the pharynx. No evidence of immunoreactivity to phenylethanolamine-N-methyl transferase was observed at neuroglandular synapses, suggesting that adrenaline is not a transmitter in the pharynx of A. pallida.

Comparative ultrastructure of Clara cells in neonatal and older cattle

Calf lungs were fixed with glutaraldehyde and examined by scanning (SEM) and transmission (TEM) electron microscopy to compare the ultrastructure of Clara cells in terminal bronchioles of neonatal calves and older cattle. In the neonatal calf, SEM revealed numerous smooth-surfaced Clara cells protruding above a similar number of ciliated cells, whereas in older animals the surface of Clara cells was lobulated. Thin sections examined by TEM revealed numerous cuboidal to columnar Clara cells with indented nuclei and a pale cytoplasm filled with faintly granular glycogen in the neonatal calf. Some cells were characterized by apical dense and/or pale membrane-bound granules or secretory droplets. Many cells had an apical tubular network of cisternae that were partly smooth and partly decorated with ribosomes. Ultrastructural comparison of Clara cells in a 2-day-old calf with those of 14- and 19-day-old, 4- and 5. 5-month-old, and 3.5-year-old cattle revealed a striking reduction in the amount of glycogen per cell after 14 days. The number of cells with apical granules was small at all ages, and the density of the secretory granules varied greatly in different cells. A variable amount of smooth endoplasmic reticulum (SER) was present but was less prominent than cisternae of ribosomal endoplasmic reticulum (RER). In older cattle, the limited amount of SER compared to the RER and secretory granules suggests that bovine Clara cells are more likely to be secretory than detoxifying.

Interalveolar septal changes with Pasteurella haemolytica-induced pneumonia in exertion-stressed calves

This study compared the effects of exertion stress and exertion stress combined with P. haemolytica infection on cells in the pulmonary capillaries and interalveolar septa adjacent to pneumonic lung. Two calves stood on an Anamill treadmill to serve as nonexercised controls and four calves were run to exhaustion (exertion-stressed) on the treadmill. Two of these four calves were inoculated endobronchially with 5 x 10(9) CFU of virulent Pasteurella haemolytica immediately following treadmill exercise. All calves were euthanized 24 h later and lung tissue was collected from the right mid-caudal lung lobe, next to the area of the gross lesion in inoculated calves. Ultrastructural evidence of increased metabolic activity of pulmonary intravascular macrophages (PIMs) and slight alveolar edema were present after exertion stress, but no changes in numbers of PIMs and platelets were observed between exertion-stressed and control calves. Lungs of calves that were subjected to stress and experimental infection had increases in size, number, and metabolic activity of PIMs, and numerous platelets that were interspersed among the PIMs. These findings suggest that exercise has minimal effect on the cellular changes in interalveolar septa after 24 h. However, exercise with P. haemolytica infection can stimulate PIM activity at short distances (<2.5 mm) from the gross pneumonic lesion. It is possible that the alterations in PIMs are stimulated by cytotoxic products arising from a nearby lesion in which bacteria and infiltrated cells are present.

Ultrastructure of Pasteurella haemolytica-induced changes in gnotobiotic calf lung

Gnotobiotic calves born and maintained in a germ-free environment until inoculated with a pathogen are model animals for studying the progression of a specific disease, such as pneumonic pasteurellosis. To investigate early progression of pneumonic pasteurellosis, we compared the ultrastructure of regions of gas-exchange in the lungs of three challenge-exposed and three uninoculated control gnotobiotic calves. Three calves were inoculated endobronchially with a bolus of 7.9 x 10(10) CFU of Pasteurella haemolytica A1 and studied in a specific pathogen-free environment until severe respiratory distress occurred, at which time they were euthanized. Slices of lung tissue from the midregion of the right dorsal caudal lobe (area of lesion) of infected and control calves were fixed in glutaraldehyde and prepared for scanning (SEM) and transmission (TEM) electron microscopy. SEM revealed bacteria among long tangled strands of fibrin in pulmonary alveoli that became obliterated with cellular debris. TEM revealed areas of encapsulated and/or nonencapsulated bacteria among the cellular debris and patches of fibrin. Many neutrophils and macrophages that infiltrated the alveoli had phagocytosed bacteria and undergone degradation. Less cellular damage was present when encapsulated bacteria bordered the interalveolar septa than when nonencapsulated lysed bacteria were present. Where lysed bacteria were present, the pulmonary capillaries were dilated because of swollen, degranulated neutrophils, fibrin clots, and cellular necrosis. Both encapsulated and nonencapsulated bacteria were present in the lung tissue of gnotobiotic calves within the first 24 h after endobronchial inoculation of early log phase P. haemolytica. Loss of capsular material around individual and divided pairs of bacteria led to their consequential aggregation, lysing, and severe damage to the adjacent pulmonary capillaries and interalveolar septa.

Ultrastructure of neuro-spirocyte synapses in the sea anemone Aiptasia pallida (Cnidaria, Anthozoa, Zoantharia)

Using transmission electron microscopy of serially sectioned tentacles from the sea anemone Aiptasia pallida, we located and characterized two types of neuro-spirocyte synapses. Clear vesicles were observed at 10 synapses and dense-cored vesicles at five synapses. The diameters of vesicles at each neuro-spirocyte synapse were averaged; clear vesicles ranged from 49-89 nm in diameter, whereas the dense-cored vesicles ranged from 97-120 nm in diameter. One sequential pair of synapses included a neuro-spirocyte synapse with clear vesicles (81 nm) and a neuro-neuronal synapse with dense-cored vesicles (168 nm). A second synapse on the same cell had dense-cored vesicles (103 nm). An Antho-RFamide-labeled ganglion cell and three different neurites were observed adjacent to spirocytes, but no neuro-spirocyte synapses were present. Many of the spirocytes also were immunoreactive to Antho-RFamide. The presence of sequential neuro-neuro-spirocyte synapses suggests that synaptic modulation may be involved in the neural control of spirocyst discharge. The occurrence of either dense-cored or clear vesicles at neuro-spirocyte synapses suggests that at least two types of neurotransmitter substances control the discharge of spirocysts in sea anemones.

Ultrastructure of neurons and synapses in the tentacle epidermis of the sea anemone Calliactis parasitica

The anatomical organization of neutrons and synaptic pathways in tentacles of sea anemones is poorly understood. Transmission electron microscopy of serial thin sections was carried out on various regions of tentacles of the sea anemone Calliactis parasitica in order to locate and characterize typical epidermal neutrons and synapses. Both surface-oriented sensory cells with ciliary cones and basally located ganglion cells lacking a cilium have Golgi-derived granular or faintly cored vesicles. Similar vesicles are present at synaptic loci on some ganglion and muscle cells. The synaptic contacts on the longitudinal muscle cells are generally en passant rather than terminal. They vary from single neuromuscular synapses to pairs of neurites innervating the same muscle cell or one neurite innervating two or more muscle cells. Both two-way and one-way interneuronal synapses with vesicles aligned at paired synaptic membranes with dense material in a 14-20-nm-wide cleft are present in the epidermal nerve plexus. The vesicles average from 50 to 80 nm in diameter and vary from electron lucent to faintly cored. The results of this study demonstrate the presence of a complex system of epidermal neuronal pathways with specific synaptic loci in this modern representative of a first-evolved nervous system.

Exercise-induced changes in the lung of Shetland ponies: ultrastructure and morphometry

The ultrastructural changes in pulmonary alveoli produced by running two ponies on a high speed treadmill at 7.6 m/sec, 3-degree incline, for 2 min support the hypothesis of pulmonary capillary stress failure as an explanation for exercise-induced pulmonary hemorrhage (EIPH). Light microscopy combined with scanning and transmission electron microscopy confirmed the presence of red blood cells and proteinaceous material in the alveolar lumina and interstitial swelling in approximately one third of the pulmonary alveoli examined. Morphometric analysis revealed that the blood-gas barrier was 30-77% thicker on the thin respiratory surface of the interalveolar septa in the cranial lobe of the two exercised ponies, i.e., 0.62 and 0.46 micron, compared to that of the unexercised control pony (0.35 micron). No change in blood-gas barrier thickness was observed in the caudal lobe, although that is where EIPH lesions have been observed in race-horses. Vascular pressures were low (20 mm Hg) in the pulmonary circulation of the Shetland pony at rest but increased more than three fold to 63 mm Hg during exercise. These preliminary morphological and physiological results indicate that a short burst of near-maximal exercise in a non-athletic equine can lead to structural changes in the blood-gas barrier and leakage of blood from pulmonary capillaries despite pulmonary vascular pressures being significantly lower than previously found in the racehorse.

Classification of Nerve Cells Dissociated From Tentacles of the Sea Anemone Calliactis parasitica

Nerve cells from tentacles of the sea anemone Calliactis parasitica were dissociated in 1000 units/ml of collagenase for scanning electron microscopic studies and in 0.125% elastase followed by 12 units/ml of ficin for cell counts using light microscopy. The studies revealed 33 distinguishable neuronal shapes, which were categorized as either sensory cells having an apical cilium or ganglion cells with or without a perikaryal cilium and further subdivided into unipolar, bipolar and multipolar neurons based on the number of processes that extended from the perikaryon. Unipolar sensory cells were characterized by an apical cilium adjacent to the perikaryon and a long, simple or terminally branched axon. Unipolar ganglion cells lacked an apical cilium. Bipolar sensory cells had a neck between the cilium and perikaryon and an oppositely directed axon. Bipolar ganglion cells had isopolar processes or asymmetrical processes, which were simple or complexly branched. One type of bipolar ganglion cell with isopolar processes had a perikaryal cilium. Multipolar sensory cells had a distinct neck between the perikaryon and the cilium and two or more simple or complexly branched processes extending from the triangularly shaped cell body. Multipolar ganglion cells had variously shaped perikarya from which extended three or more short or long processes that were simple or complexly branched. One type of tripolar ganglion cell had a perikaryal cilium. The different types of nerve cells were quantified, and statistical comparisons were made.

Ultrastructural Localization of Antho-RWamides I and II at Neuromuscular Synapses in the Gastrodermis and Oral Sphincter Muscle of the Sea Anemone Calliactis parasitica

Light microscopic studies have shown that the sea anemone neuropeptides Antho-RWamides I (<Glu-Ser-Leu-Arg-Trp-NH2) and II (<Glu-Gly-Leu-Arg-Trp-NH2) are located in neurons associated with the oral sphincter muscle of the sea anemone Calliactis parasitica. In the present ultrastructural study, using the immunogold technique, we found Antho-RWamide-like material in the granular vesicles of neurons that make synaptic contacts with the myonemes of both gastrodermal and oral sphincter muscle cells of Calliactis. Gastrodermal nerve cells contained immunoreactive granular vesicles averaging 149.3 +/- 4.1 nm in diameter; smaller granular vesicles (47.5 +/- 2.5 nm) were present at a labelled synapse. Neurites associated with the sphincter muscle had immunoreactive granular vesicles averaging 78.8 +/- 3.3 nm in diameter with smaller granular vesicles (63 +/- 4.4 nm) at three labelled neuromuscular synapses. All Antho-RWamide-immunoreactive vesicles were irregularly granular, unlike the typical dense-cored vesicles observed at some other synapses in sea anemones. No evidence was found of storage or release at nonsynaptic sites (paracrine secretion). The Antho-RWamide immunoreactive neurites innervate the sphincter muscle fibers directly rather than through intermediate neuronal pathways. This is the first ultrastructural evidence of a neuropeptide at a coelenterate neuromuscular synapse.

The nervous systems of cnidarians

Cnidarians have simple nervous systems and it was probably within this group or a closely-related ancestor that nervous systems first evolved. The basic plan of the cnidarian nervous system is that of a nerve net which, at some locations, has condensed to form nerve plexuses, or circular or longitudinal nerve tracts which may be syncytia. At the ultrastructural level, many cnidarian neurons have the combined characteristics of sensory, motor, inter- and neurosecretory neurons and thus appear to be multifunctional. We propose that these multifunctional neurons resemble the ancestors of the more specialized neurons that we find in higher animals today. The primitive nervous system of cnidarians is strongly peptidergic: from a single sea anemone species Anthopleura elegantissima, we have now isolated 16 different novel neuropeptides. These peptides are biologically active and cause inhibitions or contractions in muscle preparations or isolated muscle cells from sea anemones. The various peptides are located in at least six distinct sets of neurons showing that sea anemone neurons have already specialized with respect to their peptide content. Using immuno-electronmicroscopy, we have found that the peptides are located in neuronal dense-cored vesicles associated with both synaptic and non-synaptic release sites. All these data indicate that evolutionarily "old" nervous systems use peptides as transmitters. We have also investigated the biosynthesis of the cnidarian neuropeptides. These neuropeptides are made as large precursor proteins which contain multiple (up to 36) copies of immature neuropeptides. Thus, the biosynthesis of neuropeptides in cnidarians is very efficient and comparable to that of higher invertebrates, such as molluscs and insects, and vertebrates.

Actinobacillus pleuropneumoniae in gnotobiotic piglets: ultrastructural changes in the pulmonary alveoli with dose and time

The ultrastructural changes in pulmonary alveoli produced by transtracheal inoculation of 10(6) and 10(8) CFU of Actinobacillus pleuropneumoniae serotype 5 in gnotobiotic piglets were studied after 1 and 4 h. At 1 h postinoculation (p.i.) with 10(6) or 10(8) CFU, no gross change in lung and no evidence of infiltration of cells into alveoli was observed. At 4 h p.i., at a dose of 10(6) CFU, a generalized red mottling occurred in the dorsal half of the caudal lobe, which revealed ultrastructural evidence of neutrophil infiltration into alveoli along with fibrin and a few erythrocytes. At 4 h p.i., at a dose of 10(8) CFU, there was a bilateral lung lesion characterized by a generalized mottling and congestion, within which we observed ultrastructural evidence of bacteria and cellular debris in the alveoli and fibrin clots and cellular necrosis in the alveolar septum. By using gnotobiotic piglets and visualizing the effects of bacterial inoculum on cellular ultrastructure of the lung, we have demonstrated that both dose and time play roles in the early pathogenesis of experimental porcine pleuropneumonia. The developing lesion in lungs of gnotobiotic piglets infected with pure cultures of A. pleuropneumoniae can be controlled experimentally. This experimental procedure can provide a base of reproducible, sequential, ultrastructural changes with which to compare the role of inflammatory mediators in the lung and the effects of drugs on immunologic events in the lung.

Antho-RFamide Immunoreactivity in Neuronal Synaptic and Nonsynaptic Vesicles of Sea Anemones

Antho-RFamide is a neuropeptide isolated from the sea anemone Anthopleura elegantissima. Antho-RFamide immunoreactivity was localized in four different populations of neuronal vesicles in the tentacle nerve plexus of Anthopleura. Small, opaque, neuronal vesicles, averaging 49 nm in diameter, were gold-labeled at two-way synapses. Heterogranular vesicles, averaging 184 nm in diameter, were gold-labeled in a neuronal swelling adjacent to a muscle cell process. These vesicles were similar in size to a third class of gold-labeled dense-cored vesicles. A fourth class of immunogold-labeled vesicles observed in neuronal swellings had light cores and averaged 129 nm in diameter. Using 5-nm gold particles, we observed a heavy labeling of the granular cores of the dense-cored vesicles, suggesting that the immunoreactivity is specific to the vesicle core. The ultrastructural demonstration of Antho-RFamide immunoreactivity in interneuronal synaptic vesicles, together with the immunofluorescence and electrophysiological studies of other investigators, suggest that Antho-RFamide plays a role in neurotransmission in sea anemones.

Multifunctional features of a gastrodermal sensory cell in Hydra: three-dimensional study

Computer-assisted, three-dimensional reconstructions of two gastrodermal sensory cells from transmission electron micrographs of serial sections of Hydra revealed a unipolar morphology with the nucleus near an apical cilium and a simple unbranched axon with a widened terminal. The sensory cells were similar in size and shape to a unipolar sensory cell isolated from macerated gastrodermis and examined with scanning electron microscopy. In thin sections, the cells were characterized by the presence of numerous dense-cored vesicles in the axon and its terminal. A few dense-cored vesicles were aligned at electron-dense synaptic foci in the axon terminal of the sensory cell, which formed an axo-axonal synapse with a nearby centrally located ganglion cell and a neuromuscular synapse with the basal myoneme of a digestive cell. The ganglion cell possessed a perikaryal cilium and a slender axon that extended adjacent to the sensory cell terminal, where it formed an en passant axo-axonal synapse in reciprocal arrangement with that of the sensory cell. In addition, the ganglion cell axon formed a neuromuscular synapse in sequence with the sensory cell axo-axonal synapse. The presence of a large number of neurosecretory-like granules, apical cilium and reciprocal interneuronal and neuromuscular synaptic loci suggests that this gastrodermal sensory cell, characterized ultrastructurally for the first time, represents a third type of multifunctional neuron in Hydra. Thus, Hydra may contain primitive stem-like neurons, which are sensory-motor and also function in both neurosecretion and neurotransmission.

Preservation of tracheal mucus by nonaqueous fixative

Two nonaqueous fixatives, composed of fluorocarbon solvents with dissolved osmium tetroxide, were used to determine the feasibility of preserving the mucous coat in bovine and rat trachea for light and electron microscopy. Aqueous fixatives, while providing excellent cytological preservation, wash away the mucous lining, precluding ultrastructural analysis. Inclusion of ruthenium red or alcian blue within aqueous fixative improved retention of mucus, but provided incomplete, patchy results. Fixation with nonaqueous fluorocarbon solvent and dissolved osmium tetroxide preserved a continuous mucous epiphase layer above a clear hypophase layer. Subcomponents of the mucus included an electron dense surface layer, interrupted patches of mucus above the surface layer and electron dense membrane-like material within the mucus. This method of fixation will preserve mucus for light, scanning and transmission electron microscopy, using either intratracheal or immersion methods of fixation. The latter would enable use of materials from large animal models, autopsy or an abattoir.

Lysosomal interconnections and horseradish peroxidase compartmentalization in three-dimensionally reconstructed bovine alveolar macrophages

Following a 1-h incubation of bovine alveolar macrophages in 1 to 2 mg/ml exogenous horseradish peroxidase (HRP), ultrathin sections revealed vacuolar interconnections among both labeled and unlabeled vacuoles constituting the lysosomal compartment. Four entire cells and their vacuolar components were subsequently computer resconstructed from serial transmission electron micrographs and measured using a morphometric technique. HRP-labeled and unlabeled vacuoles ranged in size from 0.5 micron to greater than or equal to 4.0 microns in diameter and occupied up to 25% of the cytoplasmic volume. HRP-containing vacuoles were distributed throughout each cell in a clumped distribution (P less than 0.05) and occupied up to 75% of the total vacuole compartment. Up to 60% of all vacuoles were interconnected through a series of openings formed by membrane fusions (average pore diameter 0.42 micron), which resulted in a labyrinth of vacuoles comprising up to 55% of the total volume of the lysosomal compartment. The area of open interconnections resulting from vacuolar fusions represented less than 1% of the total surface area of the lysosomal membrane. Rotation of a three-dimensionally reconstructed macrophage about the Y-axis revealed an interconnected vacuolar network of 75 fused vacuoles in a chain up to 21 microns in length. We have demonstrated that HRP-labeled vacuoles interconnect with each other as well as with preexisting unlabeled vacuoles. As a result of such interconnections, individual vacuoles become contributing members of a large, continuous, lysosomal compartment in bovine alveolar macrophages.

A combined high-voltage and scanning electron microscopic study of two types of sensory cells dissociated from the gastrodermis of Hydra

Sensory cells dissociated from gastrodermis of Hydra were studied using high-voltage electron microscopy (HVEM) for visualization of internal features and scanning electron microscopy (SEM) to clarify surface details. HVEM revealed whole cell morphology, nuclear shape and location, apical ciliary-microvillar organization, length of microtubule bundles, and distribution of dense-cored vesicles in axonal processes and nerve terminals. SEM of the same cells revealed surface blebs and membrane perforations not easily recognized by HVEM alone. Hence, mapping of SEM surface structures can be used to determine what is surface versus interior structures in the HVEM image and thus aid in interpreting such images. The maceration procedure revealed a previously undescribed, pyriform-shaped sensory cell with oppositely-directed basal processes. This combined HVEM-SEM study of whole cells provided evidence of possible synaptic loci in an axon terminal and demonstrated a new morphological type of gastrodermal sensory cell in Hydra. These early-evolved sensory cells appear to be sensory-motor with neurosecretory granules.

Ultrastructural localization of RFamide-like peptides in neuronal dense-cored vesicles in the peduncle of Hydra

The presence of Arg-Phe-amide (RFamide)-like peptides in dense-cored vesicles in neurons of the peduncle of Hydra was demonstrated by immunogold electron microscopy. Thin sections of Lowicryl-embedded tissue labeled with antisera to RFamide and 5-nm gold-conjugated, secondary antibody and of Epon-Araldite-embedded tissue labeled with 15-nm gold particles revealed a concentration of RFamide-like immunoreactivity over the granular cores of vesicles in epidermal ganglion cells. Gold-labeled, dense-cored vesicles were present in the perikaryon, long thin neurites, and axon terminals of these neurons. The aggregation of labeled dense-cored vesicles in an axon terminal on the myoneme of an epitheliomuscular cell suggests a possible function of RFamide-like peptides in neuromuscular transmission. Gold staining of dense-cored vesicles completely disappeared when the RFamide antiserum was preabsorbed with 10 micrograms/ml RFamide. These results are the first demonstration that the dense-cored vesicles of Hydra neurons contain a neuropeptide.

Use of a monoclonal antibody to classify neurons isolated from the head region of Hydra

A mouse monoclonal antibody (JD1) to Hydra attenuata using the peroxidase-antiperoxidase (PAP) method revealed unipolar, bipolar, and multipolar sensory and ganglion cells in the head region of H. littoralis. Neurons isolated from macerated hypostomes and tentacles were classified according to the number of their cytoplasmic processes and the position of the cilium, when present, relative to the perikaryon. PAP-stained sensory cells had an apical ciliary cone, whereas ganglion cells did not. Neurons with cytoplasmic processes longer than 50 microns stained faintly, whereas those with processes shorter than 50 microns in length stained mainly dense brown. Unipolar neurons had an oval, crescent, round, or elliptic perikaryon with a single short axon. The perikaryal shape of bipolar neurons varied from round to tall triangular, short triangular, crescent, oval, or elliptic with two oppositely directed symmetric or asymmetric processes. Asymmetric processes were present in a bipolar sensory cell with a long apical cilium typical of gastrodermal sensory cells. One type of bipolar ganglion cell had a short perikaryal cilium. Another type had neurites longer than 50 microns. We found seven morphological variations of multipolar neurons, including one with an apical knob, two with a short perikaryal cilium, two with cytoplasmic loops near the perikaryon, one with perpendicular processes projecting from the major neurites, and one with a branched process longer than 50 microns opposite a tangled mass of neurites.

Ultrastructure of enterochromaffin cells and associated neural and vascular elements in the mouse duodenum

Enterochromaffin cells of adult mouse duodenum were studied with light- and electron-microscopical techniques. They were distinguished from other enteroendocrine cells by their pleomorphic, electron-dense secretory granules in the basal cytoplasm. At the apices of enterochromaffin cells, tufts of short microvilli bordered the gut lumen. At their bases, irregular cytoplasmic extensions were either in contact with or passed through the basal lamina. The presence of cytoplasmic extensions in close proximity to fenestrated capillaries and subepithelial nerves suggested an endocrine or paracrine function. Electron micrographs of serial thin sections were used to reconstruct an enterochromaffin cell from the crypt epithelium in three dimensions and to determine its relationship with the underlying neural plexus. Although extensions from the serially sectioned and reconstructed cell and other enterochromaffin cells studied in crypt epithelia protruded through the basal lamina, no synaptic contacts were seen. Evidence of a synaptic contact between a neurite and another type of enteroendocrine cell (possibly an intestinal A cell), suggested a neurocrine role for some of the basally-granulated cells. Possible functions of enterochromaffin cells are discussed in the light of recent literature on the system of enteroendocrine cells, also known as APUD (amine precursor uptake and decarboxylation) cells and/or paraneurons.

Ultrastructural alterations of motor cortex synaptic junctions in Brown Swiss cattle with weaver syndrome

An ultrastructural comparison was made between the motor cortex synapses of the brain of 4 adult Brown Swiss cattle with weaver syndrome and 2 healthy cattle (a Holstein steer and a Guernsey cow). Compared with the healthy cattle, the paramembranous densities at synaptic junctions of cattle with weaver syndrome had a decreased mean height of the presynaptic dense projections (P less than 0.001), had significantly smaller peak-to-peak distances (P less than 0.001), and had a significantly decreased mean thickness of the postsynaptic density (P less than 0.0001). These synaptic changes in cattle with weaver syndrome may be associated with clinical manifestations of the syndrome, such as impairment of transmitter release, instability of postsynaptic receptor sites, lesion-induced synaptic turnover from injury elsewhere in the CNS, or loss of a specific cell population of the motor cortex.

Light and electron microscopic localization of a monoclonal antibody in neurons in situ in the head region of Hydra

A mouse monoclonal antibody to Hydra attenuata was used to demonstrate immunoreactive product in neurons in situ, in both whole mount and sectioned hypostomes and tentacles of H. oligactis and H. littoralis. Immunoreactive cells were concentrated around the mouth and scattered along the length of the tentacles. In the hypostome, nerve cells sent one or more processes orally and the others aborally but the processes were more distinctly stained in H. oligactis. A thin strand of five to six perihypostomal neurons was present close to the hypostome-tentacle junction. In the tentacles, neurons with long processes contacted up to five different batteries of nematocysts. Neural processes were associated with nematocyst batteries in three ways: 1) forming a perikaryal loop to encircle a centrally located stenotele, 2) branching at a distance from the perikaryon to contact a variety of nematocysts, and 3) terminal branching by one or more neurons with contacts on one to several nematocysts within a battery. Immunocytochemical localization of neurons in Hydra by light microscopy was correlated for the first time with electron microscopy. Peroxidase-antiperoxidase (PAP)-positive sensory cells were concentrated around the mouth opening. PAP-positive ganglion cells were predominant in the tentacles. Sensory cells were elongate or spindle-shaped (unipolar), triangular with two oppositely directed processes (bipolar), and multipolar (tripolar or tetrapolar) with one of the processes extending to the epidermal surface. Ganglion cells were either unipolar or bipolar or multipolar, with neurites paralleling the mesoglea and occasionally having processes abut on it.

Scanning electron microscopy of neurons isolated from the pedal disk and body column of Hydra

Segments of pedal disk and body column were cut from specimens of Hydra littoralis and separated into epidermis and gastrodermis, then macerated to isolate neurons for scanning electron microscopy. Bipolar and multipolar ganglion cells were present in both tissue layers, whereas sensory cells were found only in the gastrodermis. A single cilium projected from the perikaryon of some bipolar and multipolar ganglion cells; the cilium was long in the pedal disk ganglion cells and short in those from the body column. Ganglion cells from the pedal disk had short, thick processes, whereas those from the body column had long, thin neurites. Gastrodermal sensory cells were characterized as unipolar by the presence of an apical cilium near the perikaryon or as asymmetrical bipolar by the presence of a narrow neck region between the perikaryon and cilium. The axon was short in pedal disk sensory cells and long in those from the body column.

Ultrastructure of cyclic changes in the murine uterus, cervix, and vagina

The regional and cyclic changes in the murine genital epithelium were studied by transmission and scanning electron microscopy to provide a morphological standard to serve as a basis for investigation of host-parasite relationships in genital infections. Thus, we examined not only mucosal epithelial cell changes, but also surface mucus, normal flora and inflammatory cells. Ultrastructurally, at proestrus/estrus, we found uterine and most cervical epithelial cells covered with microvilli overlaid with mucus-like secretions and evidence of internal secretory activity. There was little normal flora anywhere in the tract. At early metestrus, we found squamous cervicovaginal epithelial cells with low discontinuous microrugae, extensive normal flora and many neutrophils beginning to migrate through the epithelium. The flora and neutrophils could explain the relative lack of susceptibility to infection at that time. At diestrus the appearance of a newly regenerated epithelium and lack of normal flora suggested that initiation of infection could occur at this stage; however, the presence of large numbers of neutrophils ready to phagocytize invading bacteria indicated a deterrent to infection. This study of cyclic changes in flora, mucus, neutrophils and epithelial cells provided ultrastructural evidence to support an earlier hypothesis that the greatest susceptibility to gonococcal infection in mice occurred at proestrus/estrus.

High voltage electron stereomicroscopy of the cilium-stereociliary complex of perioral sensory cells in Hydra

The cilium-stereociliary complex in perioral neurons of Hydra was examined by electron microscopy, with emphasis on stereomicrographs of serial, 0.5 micron thick, longitudinal and transverse sections. Longitudinal sections revealed (1) flat-topped cones in which the cilium was bent and the ciliary chamber appeared heart-shaped, and (2) pointed cones in which the cilium was straight and the ciliary chamber appeared triangular. Transverse sections revealed 10-12 stereocilia forming a cone over a central cilium with nine peripheral doublets of microtubules but with often more than two central microtubules. The ciliary membrane was fluted; fine filaments connected the outfoldings of membrane with the center of the microtubule doublets. Thin sections revealed 7 nm microfilaments in the stereocilia cores which branched basally into thick and thin roots; the thick roots surrounded the base of the central cilium. The cilium-stereociliary complex was enveloped by an epitheliomuscular cell sheath with a free margin distally and a septate junction proximally. In flat-topped cones the free margin of the enveloping epitheliomuscular cell was closely applied to the top of the cilium-stereociliary complex, whereas in pointed cones the cilium-stereociliary complex projected above the free margin of the sheath. Thus, the 7 nm actin-like filaments in the stereocilia might function to contract and open the complex in response to favorable stimuli so that the cilium is in contact with the aqueous environment.

Perioral synaptic connections and their possible role in the feeding behavior of Hydra

Electron microscopic observations of serially sectioned perioral neurons revealed a complex synaptic organization in which reciprocal synapses were observed for the first time in Hydra. Sensory cells had reciprocal synapses with each other and with ganglion cells, which in turn had reciprocal synapses with each other. A two-way chemical synapse with vesicles on both sides of the paramembranous densities was observed between ganglion cells; none was found between sensory cells. Ganglion cell axons participated in serial axo-axo-epitheliomuscular synapses. Two-cell pathways formed by direct sensory cell-nematocyte or neuromuscular synapses and three-cell pathways forming indirect sensory cell-ganglion cell-nematocyte or neuromuscular synaptic interconnections were found. It is possible that either simple direct changes in or direct effects on threshold stimuli could trigger both nematocyst discharge and/or muscular contraction and effect more complex intermediate pathways modulating feeding behavior. Each large epitheliomuscular cell enveloped from one to four sensory cells in the perioral region. The concentration of sensory cells around the mouth and their complex synaptic connections with each other and with ganglion and effector cells support our hypothesis for neural control of feeding behavior in Hydra.

Numbers, distribution, and types of neurons in the pedal disk of Hydra based on a serial reconstruction from transmission electron micrographs

The numbers, distribution, and types of neurons in a pedal disk of Hydra littoralis were determined from electron micrographs of 567 serial sections approximately 0.12 micron thick. Of 248 neurons counted, we found 234 ganglion cells in the epidermis and 14 in the gastrodermis. No sensory cells with surface projecting cilia were observed in either epithelial layer of the foot region. We found ciliary structures in 196 (84%) of the epidermal neurons: 55 had a well defined cilium-stereociliary complex, 30 had a cilium lacking stereocilia, and 111 could not be classified. In contrast, 38 epidermal neurons lacked evidence of ciliary structures; 10 of the 14 gastrodermal neurons had one or more centrioles, some with an elaborate pericentriolar rootlet system, but no cilium or stereocilia. Neuronal perikarya could be classified into those with dense heterochromatic nuclei and those with light granular nuclei; often these two nuclear variations were observed in paired or triad arrangements of epidermal neurons. In addition, 68 (29%) of the epidermal neurons were characterized by the presence of small dense granules (115-178 nm in diameter) in the cytoplasm around the periciliary space. Although 32 pairs and 5 triads of contiguous neuronal perikarya were present in the epidermis, only two paired neuronal perikarya were present in the gastrodermis. The major concentration of neurons was approximately midway between the basal surface and the region of transition of epitheliomuscular cells into glandulomuscular cells. There was no evidence of large neuronal aggregations suggestive of ganglia in the pedal disk.

Ultrastructure of the dinoflagellate Polykrikos. II. The nucleus and its connections to the flagellar apparatus

Electron microscopy of the colonial dinoflagellate Polykrikos kofoidi revealed a nuclear cortex formed of two electron-dense cortical layers directly beneath the nuclear envelope. Nuclear pores were confined to vesicular outpocketings of the nuclear envelope over circular discontinuities in the cortical layers. A conspicuous fibrous ribbon extended from the nucleus to the flagellar apparatus of each zooid. The ribbons resembled in their structure and position the attractophores of termite flagellates. Each flagellar apparatus consisted of two flagella, two elongate axial kinetosomes, an oblique kinetosome, and two roots of markedly different periodicities.

Ultrastructure of the dinoflagellate Polykrikos. I. Development of the nematocyst-taeniocyst complex and morphology of the site for extrusion

Development of the nematocyst-taeniocyst complex in the four-zooid stage of a dinoflagellate, Polykrikos kofoidi, was studied by electron microscopy. We observed the following stages: formation of large spherical bodies in islets of cytoplasm containing extensive rough endoplasmic reticulum and Golgi complexes; differentiation of an anlage of first the nematocyst and then the taeniocyst into a tandem pair; and, maturation of the complex into a nematocyst with operculum and capsule, and a taeniocyst with head, neck and body. In the intermediate stages of dinoflagellate cnidogenesis the structurally elaborate pattern of development differed from that of coelenterate nematocysts but in certain features the mature organelles of both groups were similar. Nematocyst-taeniocyst complexes migrated into chutes on zooids and four near the junction of the annulus and sulcus at the flagellar bases. The specialized chute was partially lined by thimble-shaped organelles of unknown function. The taeniocyst protruded from the surface in association with a striated fibre whose structure and position were those of a trigger to discharge the two organelles. We found no cytostome in this holozoic colony; the structure of the chute suggested that it might also function as a cytostome.

Analysis of relationships between pericytes and gas exchange capillaries in neonatal and mature bovine lungs

Neonatal and mature bovine lungs were examined ultrastructurally to quantitatively assess pericyte envelopment of gas exchange capillaries and proximities of pericyte margins to endothelial cell junctions. Pericytes were observed on 91% of the cross-sectioned capillary profiles examined, with 18 and 26% coverage in neonatal and mature lungs, respectively. Chi-square analysis indicated a random occurrence of endothelial cell junctions under pericytes; however, pericyte processes tended to end near endothelial cell junctions. In the neonatal and mature lungs, 38 and 40%, respectively, of all endothelial junctions were within 0.5 microns of the margins of pericyte processes; such distances covered only 16 and 17% of the circumferences of the capillary profiles examined. Thus, endothelial cell junctions were located near pericyte margins over twice as often as would occur in a random distribution. If pericytes are contractile cells, as recent research indicates, they may function as regulators of lymph formation by influencing the permeability of endothelial cell junctions in the gas exchange capillaries.

Microfilament-associated adhering junctions (6 nm F-maculae adherentes) connect bovine pulmonary fibroblasts in vivo

Fibroblasts in the pulmonary alveolar septa of neonatal and mature cattle form spot-shaped intercellular junctions with each other where 6 nm microfilaments adhere to the plasma membranes. The junctions have variable cleft widths (10-20 nm) and a diffuse periodic intracleft substance. Impinging 6 nm microfilaments and plaque specializations were present in thin sections of junctions ranging from 0.4 to 0.6 micron in length. The microfilaments involved in junctions are parts of either cortical cytoplasmic webs or highly organized bundles. Two or more fibroblasts may form one complex of junctions and multiple junctions may occur between two fibroblasts. It is proposed that the in vivo fibroblast junction be named a 6 nm F-macula adherens, based on size of the associated microfilaments and type of junctional specialization.

Types of neurons and synaptic connections at hypostome-tentacle junctions in Hydra

Using transmission electron microscopy of thin sections we have examined neuronal concentrations at hypostome-tentacle junctions in Hydra littoralis. A total of 194 ganglion cells were counted in 587 serial thin sections of a single hypostome-tentacle junction. We found two distinct types of ganglion cells: those with and those lacking stereocilia. The majority of the neurons observed lacked stereocilia; in a single hypostome-tentacle junction only 37% of the ganglion cells possessed a kinocilium surrounded by rodlike stereocilia. Most of the ganglion cells (55%) were clustered together in the oral or upper epidermis of the hypostome-tentacle junction: Nineteen percent were in the lateral and 26% in the aboral or lower epidermis. The two types of ganglion cells did not differ significantly in their distribution. Both types of ganglion cell had synaptic contacts with other neurons and with epitheliomuscular cells. More than 85% of the neuroneuronal and 61% of the neuroepitheliomuscular cell synapses were located in the oral epidermis of a hypostome-tentacle junction. In addition, two-way chemical synapses and a gap junction between neurons were observed at hypostome-tentacle junctions. Our morphological evidence of synaptic connectivity in neuronal clusters at hypostome-tentacle junctions suggests that primitive ganglia are present in Hydra.

Neuro-epitheliomuscular cell and neuro-neuronal gap junctions in Hydra

Gap junctions have been described ultrastructurally between neurons and epitheliomuscular cells and between neurons and their processes in the hypostome, peduncle and basal disc of Hydra. All gap junctions examined in Hydra exhibit two apposed plasma membranes having a 2-4 nm gap continuous with the extracellular space. The gap junctions are variable in length from 0.1-1.6 micrometers and appear linear or V-shaped in section. Neuronal gap junctions in Hydra occur infrequently as compared to chemical synapses. Electron microscopy of serial sections has demonstrated the presence of adjacent electrical and chemical synapses (neuromuscular junctions) formed by the same neuron. In addition, multiple gap junctions were present between two neurons. This is the first ultrastructural demonstration of electrical synapses in the nervous system of Hydra. Such synapses occur in neurons previously characterized as sensory-motor-interneurons on the basis of their chemical synapses; these neurons appear to represent a type of stem cell characterized by having both electrical and chemical synapses.

A second sensory--motor--interneuron with neurosecretory granules in Hydra

Using serial-sectioning techniques for conventional transmission and high-voltage electron microscopy, we characterized the ultrastructural features and synaptic contacts of the sensory cell in tentacles of Hydra. The sensory cell has an apical specialization characterized by a recessed cilium surrounded by three rodlike stereocilia. This ciliary--stereociliary complex constitutes the receptive or dendritic pole of the sensory cell. The dense filamentous cores of the stereocilia project proximally into a narrow circumciliary cytoplasmic region connected by septate junctions to marginal processes of an enveloping epitheliomuscular cell. The central cilium has a characteristic marginal flare midway along its length and a dense filamentous substructure at its base. Pairs of branched, striated rootlets extend from the axial centriole into a mitochondria-rich region of the cell. Pigment-like granules are present in the cytoplasm around the circumciliary space. The perikaryon is characterized by an elongate nucleus surrounded by a narrow rim of cytoplasm containing prominent Golgi complexes, assorted vacuoles and dense-cored vesicles, free ribosomes, short segments of rough endoplasmic reticulum, microtubules, glycogen particles, and lipid droplets. Generally, one or two thin, naked axons extend laterally from the perikaryon into the nerve net region above the myonemes of the large epitheliomuscular cells. Within the axons are found occasional aggregates of dense-cored vesicles and en passant synapses characterized by the presence of clear or dense-cored vesicles in contact with paramembranous densities and associated intracleft cross filaments. Using these ultrastructural criteria, we demonstrated for the first time that the granule-containing sensory cells have synaptic contacts with other neurons, nematocytes, and epitheliomuscular cells hence, we considered these cells to be sensory--motor--interneurons with neurosecretory granules. We hypothesize that this unique, apparently multifunctional neuron may be a modern representative of a primitive stem cell that give rise evolutionarily to the sensory cells, motor neurons, interneurons, and neurosecretory cells of higher animals.

Effect of staphylococcal alpha-toxin on the fine structure of pancreatic acinar cells of dogs

Staphylococcal alpha-toxin induced pancreatitis in dogs was studied by electron microscopy. Pancreatic acinar cell injury was indicated by increased vesiculation of endoplasmic reticulum, loss of intracisternal granules, changes in mitochondria, membrane discontinuities and an increased number of dense complex bodies, lipid droplets and free ribosomes.

Fine Structure of the Eye of a Nudibranch Mollusc, Hermissenda Crassicornis

The eye of a nudibranch, Hermissenda crassicornis, was studied by light and electron microscopy. Three kinds of cells were observed: large sensory cells, each bearing at one end an array of microvilli (rhabdomere) and at the other end an axon which leaves the eye by the optic nerve; large pigmented supporting cells; and small epithelial cells, mostly corneal. There are five sensory cells, and the same number of nerve fibres in the optic nerve. The receptor cells contain an abundance of small vesicles, 600-800 Å in diameter. The lens is a spheroidal mass of osmiophilic, finely granular material. A basal lamina and a capsule of connective tissue enclose the eye. In some animals the eye is ‘infected’ with very small bodies, 4-5 µ in diameter, thought to be symbionts.