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Biomedical subjects

G D Pappas

Publications and source records attributed to G D Pappas.

At least 55 records · Page 3Linked to original sources
PubMed1990

Morphological, physiological and biochemical observations on skate electric organ.

The electric organs of two species of skate have been examined morphologically, physiologically and biochemically. They can be easily dissociated into innervated or denervated component electrocytes by a Torpedo Ringer's solution containing 1% collagenase. Collagenase treatment did not, however, separate the Schwann cell cover capping the synaptosomes. Isolated electrocytes generate normal MEPP frequencies and show evoked responses for two days in Torpedo Ringer's. The nerve terminals retain excitability and transmitter release properties up to the time of separation. Since isolated terminals and denervated electrocytes show normal ultrastructural characteristics for up to 12 h, the skate electric organ provides several preparations which are not attainable with Torpedo tissue. Acetylcholine (ACh) content of supernatant fractions containing the synaptosomes was comparable to that found in Torpedo (sps.). Collagenase specifically eliminates the basal lamina associated with the synaptic junctional region. Neuronal cell death and synaptic terminal degeneration were also noted in the adult organs of both species. The skate electric organ is ideally suited for the study of cholinergic development and transmission.

Acetylcholine↗
PubMed1990

Host-graft relationships of isolated bovine chromaffin cells in rat periaqueductal grey.

The transplantation of chromaffin cells from the adrenal medulla into pain modulatory regions of the CNS has previously been shown to reduce pain sensitivity, most likely via local release of neuroactive substances from the transplanted cells. The ready availability of bovine adrenal glands, as well as the high levels of opioid peptides produced by their chromaffin cells, make these glands a potentially valuable donor source for antinociception studies. However, the success of these xenografts depends on their ability to survive and integrate within the host CNS. The aim of the present study was to assess host-graft relationships of bovine chromaffin cells transplanted to the rat CNS. We have found that isolated bovine chromaffin cells survive for at least three months in the rat periaqueductal grey, with no evidence of immunological response following a short-term course of immunosuppressant treatment. In the early stages following transplantation, only minor pathology is found at the injection site, which apparently recovers completely at later stages. The host-graft borders are not well demarcated, in contrast to solid tissue grafts. Neuronal processes of host origin, forming numerous synapses with the transplanted bovine chromaffin cells, are apparent by three weeks following transplantation. Migration also occurs from the graft into the host parenchyma, as evidenced by individual chromaffin cells found near host parenchymal blood vessels. The clusters of chromaffin cells found in the graft itself are generally not very vascular, in contrast to solid tissue grafts. The chromaffin cell clusters are surrounded by blood vessels of the non-fenestrated CNS type at the host-graft border. It is likely that the small size of the graft does not require extensive angiogenesis. The lack of fenestrated peripheral-type endothelial capillaries, normally seen in adrenal medullary tissue grafts, may contribute to the survival of these xenografts in the rat brain.

Adrenal Medulla↗
PubMed1990

Ultrastructural, biochemical, and immunologic evidence of receptor-mediated endocytosis in the crystalline lens.

The lens epithelium is essentially the basal layer of the crystalline lens of the eye, an uncommon stratified epithelium. Ions and metabolites present in the aqueous humor gain access to the lens epithelium by diffusion through the lens capsule (the basement membrane of the lens epithelium). Then, it is presumed, the underlying lens fiber cells obtain necessary ions, metabolites, and nutrients through gap junctions conjoining the apical surfaces of the lens epithelial cells from the basal layer with the apical surfaces of elongating fiber cells from upper strata. In this report, correlative morphologic, biochemical, and immunochemical evidence is presented that both lens epithelial and fiber cells use endocytotic and/or transcytotic processes rather than being solely dependent on gap junctions for metabolic cooperation. Freeze-fracture analysis of the apicoapical interface between lens epithelial and elongating fiber cells (epithelial-fiber cell interface [EFI]) revealed protrusions and pits of two distinct sizes (average diameters, 46 and 126 nm). Gap junctions with tight particle packing were only rarely observed at the EFI. Gap junctions with loose particle packing were never observed at the EFI. "Orthogonal arrays" of intramembrane particles (OAPs) were not uncommon at the EFI. Thin-sections taken perpendicular to the EFI confirmed the existence of micropinocytotic and clathrin-coated vesicles in both lens epithelial and elongating fiber cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of separate preparations of lens epithelial and fiber cells, specifically enriched for clathrin-coated vesicles, showed a 180-kD protein. Western blot analysis of this protein revealed selective cross-reactivity with polyclonal anticlathrin antibodies. These results strongly suggest that transcytotic processes provide a primary route for the entry and egress of macromolecules in the lens.

Animals↗
PubMed1990

Endocytosis of serum albumin-gold conjugates by microvascular endothelial cells in rat adrenal gland: regional differences between cortex and medulla.

We investigated the distribution of serum albumin (bovine) modified by adsorption to 15 nm diameter colloidal gold (Au15BSA) in rat adrenal vasculature after perfusion of Au15BSA in situ for 6-20 min. A striking difference in permeability to and uptake of Au15BSA by adrenal cortical and medullary endothelial cells was found. The fenestrated capillary endothelial cells in the cortex were permeable to Au15BSA particles, but showed no significant endocytosis of these conjugates. Endothelial cells of the medullary capillaries and venous tributaries of the central vein were markedly less fenestrated than cortical capillaries, and resembled morphologically the sinusoidal endothelial cells of bone marrow. These endothelial cells, unlike those in the cortex, were not permeable to the perfused Au15BSA, and showed endocytosis of the gold-conjugated protein by means of coated pits and vesicles. No evidence of transcytosis of Au15BSA by means of non-coated, plasmalemmal vesicles was found. Uptake of Au15BSA by medullary endothelia was not appreciably diminished by the presence of one hundred-fold excess, unmodified, monomeric BSA. One hundred-fold excess of serum albumin which was modified by treatment with formaldehyde (FmBSA), on the other hand, did effectively compete for uptake of Au15BSA. These results indicate that adrenal medullary endothelial cells, in contrast to those of the cortex, selectively take up serum albumin modified by adsorption to colloidal gold beads, or modified by treatment with formaldehyde. The endocytosis appears to involve selective adsorption of the Au-modified albumin to sites, perhaps receptors, at coated regions of the luminal endothelial surface.

Adrenal Cortex↗
PubMed1988

Immunocytochemical localization of alpha-actinin in frog muscle treated with the ionophore A23187.

Incubation of frog skeletal muscle with the ionophore A23187 induces severe damage in the muscle. At the level of the Z line, the ionophore induces redistribution and release of the protein alpha-actinin, as shown by immunocytochemical techniques. The ionophore does not induce damage in denervated preparations or in preparations pretreated with d-tubocurarine, which indicates that the effect is indirect and neurally mediated. It is concluded that the increase in spontaneous transmitter release produced by the ionophore induces Ca2+ influx through the acetylcholine receptor. Calcium ions activate neutral proteases which release alpha-actinin from the Z line.

Actinin↗
PubMed1988

Fine structural localization of Ca2+-ATPase activity at the frog neuromuscular junction.

Ca2+-ATPase activity has been shown to be associated with the nerve terminal plasma membrane at the frog neuromuscular junction. Using a modification of the Wachstein-Meisel procedure for localization of phosphatases, a dense reaction product forms at the neuronal plasma membrane/Schwann cell interface. It has been determined that this reaction product is associated with the plasma membrane of the nerve terminal and not the plasma membrane of the Schwann cell. No ATPase activity is demonstrated at the presynaptic portion of the plasma membrane facing the synaptic gap. When a preparation is denervated, a Schwann cell process moves into the space previously occupied by the nerve. There is no ATPase activity associated with the Schwann cell plasma membrane. Conversely, when the Schwann cell is selectively injured, dense reaction product continues to be associated with the nerve terminal plasma membrane. There is some indication that this ATPase activity is dependent on the presence of Ca2+ and Mg2+. Incubation in the calmodulin inhibitor, R24571, shows little inhibition of labelling.

Animals↗
PubMed1988

Fine structural correlates of vascular permeability of chromaffin cell transplants in CNS pain modulatory regions.

Adrenal medullary tissue, bovine chromaffin cells, and PC12 cells were transplanted into the pain modulatory regions of the rat midbrain periaqueductal gray (PAG) or dorsal spinal cord. Fine structural studies of vascular permeability of these grafts revealed that in all three cases, the capillary endothelium of the graft vasculature was attenuated and fenestrated, unlike that of the surrounding host CNS tissue. The intravascular injection of the protein marker, horseradish peroxidase (HRP), enters the grafted tissue parenchyma and is found in the extracellular space of the surrounding host CNS. In contrast, control gelfoam transplants, which become vascularized, do not contain vessels with fenestrated endothelium and do not leak HRP. Since cell suspension implants do not contain endothelial cells, the vasculature of the grafts must be derived from the host. However, as their morphological characteristics are similar to those of the in situ adrenal medulla, it appears that the tissue environment of the graft influences the permeability properties of the vascular bed. The increased permeability to HRP is apparently permanent and most likely is due to the passage through endothelial cell fenestrae.

Adrenal Medulla↗
PubMed1988

Pharmacologic consequences of the vascular permeability of chromaffin cell transplants in CNS pain modulatory regions.

The transplantation of peripheral neural tissue into the CNS has been shown to alter blood-brain barrier (BBB) permeability to intravascularly injected proteins such as horseradish peroxidase. The pharmacological consequences of such BBB alterations following the transplantation of adrenal medullary tissue, isolated bovine chromaffin cell suspensions, or PC12 cell suspensions into the pain modulatory regions of the periaqueductal gray (PAG) or subarachnoid space of the lumbar spinal cord were studied using agents that normally do or do not readily pass the BBB. The injection of nicotine in animals with adrenal medullary or chromaffin cell transplants produces potent analgesia, most likely due to the stimulated release of opioid peptides and catecholamines from the transplanted cells. This analgesia could be blocked by nicotinic antagonist mecamylamine, which normally passes the BBB, but not by nicotinic antagonist hexamethonium, which normally does not readily pass the BBB. Furthermore, quaternary nicotinic agonists tetramethylammonium and 1,1-dimethyl-phenyl-piperazinium had no effect on pain sensitivity in animals with adrenal medullary implants. The Met-enkephalin peptide analog, D-Ala-Met-enkephalinamide, which normally does not alter pain sensitivity when injected systemically due to limited penetration to the CNS, produced analgesia in animals with adrenal medullary, bovine chromaffin cell, and PC12 cell implants in the PAG, but not in control gelfoam-implanted animals. This analgesia, as well as analgesia induced by nicotine, was completely blocked by naloxone pretreatment, but not by naloxone methobromide, a quaternary derivative of naloxone that does not normally pass the BBB.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1988

Fine structure of neuronal spherical arginine-rich bodies of substantia nigra and locus coeruleus in the human brain.

Neuronal spherical bodies, rich in arginine, of catecholamine neurons in man display staining reactions of mitotic chromosomes and myelin basic protein. They show a unique fine structure and density in the EM after phosphotungstic acid hematoxylin block-staining. With an electron-lucent core, a dense rim and a limiting double membrane they stand out and are differentiated from all other neuronal inclusions, especially melanin. Protein bodies were found inside mitochondria, where they apparently originate as small globules in the matrix. They later enlarge into spheres by obliterating the cristae, but retaining the outer membranes of the parent mitochondrion. The arginine-rich basic protein of the spherical bodies, it is argued, may be involved in the modulation of excitability of the catecholamine neurons in man.

Adult↗
PubMed1987

Alterations in nociception following adrenal medullary transplants into the rat periaqueductal gray.

Adrenal medullary chromaffin cells were transplanted to the midbrain periaqueductal gray, a region known to play a primary role in the modulation of nociception. Chromaffin cells were chosen for transplantation since they contain several neuroactive substances (e.g. catecholamines, opioid peptides, other neuropeptides) whose release can be stimulated by pharmacological agents such as nicotine. Both dissected adult rat adrenal medullary tissue and bovine chromaffin cells served as graft tissue in the periaqueductal gray region of adult rats. When stimulated with a low dose of nicotine, potent analgesia was induced in these animals as assessed by tail flick, paw pinch and hot plate tests. The bovine chromaffin cell implants were more effective in inducing this response. The analgesia induced by nicotine stimulation in rats with adrenal medullary implants was partially attenuated by both opiate antagonist naloxone, and adrenergic antagonist phentolamine. These results suggest that the implantation of cells which release neuroactive substances can produce reductions in pain sensitivity.

Adrenal Medulla↗
PubMed1987

Fine structure of adrenal medullary grafts in the pain modulatory regions of the rat periaqueductal gray.

Recent findings in our laboratory indicate that adrenal medullary grafts produce significant alterations in pain sensitivity. Electron microscopic studies were undertaken to correlate these behavioral changes with the neural interactions of the host and graft tissue in the periaqueductal gray. A striking change found 8 weeks after transplantation is that pronounced myelination has taken place both in the graft and in the host tissue. The new myelin formation in the graft has the typical appearance of PNS myelination and, in the host the appearance of CNS myelination. The endothelial cells of the capillaries in the grafted tissue are attenuated and fenestrated in contrast to those of the surrounding parenchymal tissue of the host. By 8 weeks, the graft becomes heavily encapsulated with collagen, while the host CNS tissue develops layers of glial processes outlining the graft. However, collagen and glial layers apparently do not form an absolute barrier to either cellular or humoral interaction between the host and graft tissue. Chromaffin cells can be found protruding into the host CNS tissue and sometimes forming synapses with presumably the host neuronal processes. Grafted chromaffin cells may participate as both postsynaptic and, less often, as presynaptic components of synaptic junctions. The behavioral relevance of these synaptic contacts is unclear, since similar implants of adrenal medullary tissue into the dorsal spinal cord subarachnoid space, which also induce potent analgesia, do not contain synapses. Thus, it is more likely that behavioral changes are brought about by diffusion of neuroactive substances from grafted chromaffin cells to host receptors.

Adrenal Medulla↗
PubMed1987

Two classes of spontaneous miniature excitatory junction potentials and one synaptic vesicle class are present in the ray electrocyte.

Cross sections (1-2 mm thick) of the ray (Raja) tail were secured to a dish and immersed in elasmobranch saline. Spontaneous miniature excitatory junction potentials (MEJPs) were recorded by advancing a 50 k omega, KCl filled electrode into the electric organ (20 microV peak-to-peak baseline noise). Data were filmed, and/or recorded on magnetic tape for computer analyses. Intracellularly recorded MEJP amplitude histograms showed a peak at 60 microV and had a right-hand skew with MEJPs up to 0.5 mV. The small peak amplitude and the skewed amplitude distribution of intracellularly recorded MEJPs result from the relatively low input resistance and the short space constant of the electrocyte coupled with the dispersed synapses on the electrocyte. At 23 degrees C the intracellularly recorded MEJP frequency ranged from 1-10 MEJPs/s. The MEJPs became larger and became focally recorded as the electrode was advanced against the intracellular surface of the innervated membrane of the electrocyte. Focal extracellular MEJPs (reversed polarity) were also recorded with the electrode positioned against the outside surface of the innervated side of the electrocyte. The frequency of focally recorded intracellular MEJPs was increased (up to 40/s) when the electrode was pushed against the membrane. Focal MEJP frequencies decreased to a few/min within 5-10 min but the mean amplitude of 3-5 mV remained constant. Decreases in amplitude and frequency in focally recorded intracellular MEJPs are attributed to changes in electrode pressure against the membrane. Amplitude histograms were constructed from focally recorded intracellular or extracellular MEJPs which showed the same time characteristics. The focal MEJP amplitude histograms have two distinct classes, each forming a bell-shaped distribution. It is concluded that both classes are generated at the electrode tip. The smaller class of MEJPs has a mean 1/10th that of the larger class and composes about 2% of the MEJPs. The small class is analogous to the sub-MEPP class found in the frog sartorius (Kriebel and Gross 1974) and mouse diaphragm (Kriebel et al. 1976, 1982). Distributions of synaptic vesicle diameters are slightly log normal (right hand skew) such that the mean diameter (57 nm) is slightly larger than the modal value (52 nm). Vesicles touching the membrane were of the same size and diameter distribution as the entire vesicle population. The profiles of the distributions are smooth and suggest only 1 class of synaptic vesicle based on diameter.

Action Potentials↗
PubMed1987

Effect of hypertonic saline on quantal size and synaptic vesicles in identified neuromuscular junction of the frog.

Miniature endplate potential amplitude distributions, miniature endplate potential frequencies and the percentage of sub-miniature endplate potentials were studied during treatment with hypertonic saline (with sucrose) during the initial high frequencies of release and after fatigue. Small muscle fibers were selected which had normal miniature endplate potential frequencies of 0.1/s to 1/s so that the miniature endplate potential amplitude distributions could be determined at the height of the hypertonic effect (first 5-15 min) at which time the miniature endplate potential frequency increased two-hundredfold. During the first few minutes of the effect, there was little change in miniature endplate potential amplitude or in the profiles of their amplitude histograms. Subsequently, after the occurrence of as few as 10(4) miniature endplate potentials, the size of the mean bell-miniature endplate potentials decreased. Later (25 min) the amplitude profiles became uniform, and finally (45 min) the percentage of sub-miniature endplate potentials and smaller miniature endplate potentials increased until many miniature endplate potentials (30-70%) were of the sub-miniature endplate potential class and the overall distributions were skewed. The mean sub-miniature endplate potential amplitude did not appear to change. After the initial high frequency of release, many miniature endplate potentials showed a definite break on the rising phase and the amplitude of the break was usually that of the sub-miniature endplate potential. The rapid decrease in miniature endplate potential size, change in miniature endplate potential amplitude profile and breaks on the miniature endplate potential rising phase can be explained with the subunit hypothesis. The edge fibers of the sartorius muscle were used so that physiologically studied edge junctions that were producing various miniature endplate potential histograms could be identified for electron microscopy. Synaptic vesicle diameters and the coefficient of variation of vesicle diameters were not changed either during high miniature endplate potential frequencies or in those junctions that generated mainly sub-miniature endplate potentials. Thus, the quantal class (i.e. sub-miniature endplate potential or bell-miniature endplate potential) cannot be determined from the vesicle diameter.

Action Potentials↗
PubMed1986

Adrenal medullary tissue transplants in the rat spinal cord reduce pain sensitivity.

Adrenal chromaffin cells contain and release several neuroactive substances which induce analgesia when injected directly into the spinal cord (e.g. opioid peptides and catecholamines). Furthermore, the release of these substances can be induced by nicotine. In order to determine whether adrenal medullary tissue transplanted to the spinal cord can produce alterations in pain sensitivity, pieces of dissected rat adrenal medulla were placed in the subarachnoid space of rat spinal cords. Stimulation by a low dose of nicotine induced potent analgesia in animals with adrenal medullary transplants, but not in animals with control transplants. Furthermore, this analgesia was reversed to pre-nicotine levels by the opiate antagonist naloxone. Thus adrenal medullary transplants in the spinal cord may provide a permanent and locally available source of opioid peptides for the relief of intractable pain.

Adrenal Medulla↗
PubMed1986

Fine structure of PC12 cell implants in the rat spinal cord.

PC12 cells, a clonal cell line established from a rat pheochromocytoma, were injected into the subarachnoid space in the lumbar spinal cord of adult rats. These cells invaded the spinal cord as a metastatic tumor and, after 2 weeks, displaced one-third of the cord parenchyma, causing hind limb paralysis. The tumor consisted of densely packed cube-like polygonal cells containing dense core granules. At the tumor-host margins there were no astrocytic or other intervening glial processes. In spite of the destruction and invasion of the spinal cord tissue parenchyma that occurred, no glial reaction could be seen. The endothelial cells of the capillaries in the vascularized tumor are of the attenuated, fenestrated type in contrast to the non-fenestrated type of the host tissue from which they were derived.

Adrenal Gland Neoplasms↗
PubMed1986

Serotonin metabolism and the nature of monoamine oxidase in squid central nervous system.

Monoamine oxidase activity, using type A and type B substrates and inhibitors, was investigated in the central brain and synaptosomes prepared from the optic lobe of squid. Although substantial MAO activity towards serotonin (5-HT), phenylethylamine and tyramine was present, the enzyme could not be differentiated into the two subtypes previously described in the vertebrate central nervous system. However, this enzyme is functional since 5-HT levels, as identified by immunocytochemical procedures, are low in the squid nervous system and show significant increases in pargyline treated squids.

Animals↗