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Biomedical subjects

G D Pappas

Publications and source records attributed to G D Pappas.

At least 73 records · Page 4Linked to original sources
PubMed1986

Analgesia induced by isolated bovine chromaffin cells implanted in rat spinal cord.

Chromaffin cells synthesize and secrete several neuroactive substances, including catecholamines and opioid peptides, that, when injected into the spinal cord, induce analgesia. Moreover, the release of these substances from the cells can be stimulated by nicotine. Since chromaffin cells from one species have been shown to survive when transplanted to the central nervous system of another species, these cells are ideal candidates for transplantation to alter pain sensitivity. Bovine chromaffin cells were implanted into the subarachnoid space of the lumbar spinal region in adult rats. Pain sensitivity and response to nicotine stimulation was determined at various intervals following cell implantation. Low doses of nicotine were able to induce potent analgesia in implanted animals as early as one day following their introduction into the host spinal cord. This response could be elicited at least through the 4 months the animals were tested. The induction of analgesia by nicotine in implanted animals was dose related. This analgesia was blocked by the opiate antagonist naloxone and partially attenuated by the adrenergic antagonist phentolamine. These results suggest that the analgesia is due to the stimulated release of opioid peptides and catecholamines from the implanted bovine chromaffin cells and may provide a new therapeutic approach for the relief of pain.

Analgesia↗
PubMed1984

The relationship of pinocytosis and synaptic vesicles at the frog neuromuscular junction.

The fate of the extracellular marker horseradish peroxidase (HRP), following intense transmitter release was studied using identified muscle fibers from the frog sartorius nerve-muscle preparation. The muscle was stimulated indirectly via its nerve at 10 Hz or K+-depolarized for 15 min. Other preparations were also stimulated or K+-depolarized for 15 min and then rested for an additional 15 min. Endings from only identified muscle fibers were photographed with the electron microscope. It was found that in the paradigms studied above, less than 10% of the mean number of synaptic vesicle profiles per section contained the marker. Following electrical stimulation, there was a statistically significant decrease in the mean number of synaptic vesicle profiles per section. After a 15 min rest period, the vesicle profile number had returned to the control value. At this time point, the endplate potential was but 25% of the control. K+-depolarization caused no significant change in the mean number of synaptic vesicle profiles per section. Experiments were also performed to rule out any direct effect of the label on the number of coated and synaptic vesicle profiles. The mean number of labeled coated vesicle profiles increased during either electrical stimulation or K+-depolarization, and then fell during the subsequent rest period. Their numbers accounted for less than 2% of the total number vesicles/section. A suprisingly high number of coated vesicle profiles (as high as 41%) contained no label. This finding is inconsistent with the exclusive role of coated vesicles associated with synaptic vesicle membrane recycling. The low level of HRP labeling of synaptic vesicles is also inconsistent with synaptic vesicles undergoing exo- and endocytosis along the presynaptic plasma membrane.

Animals↗
PubMed1984

The fine structure of identified electrotonic synapses following increased coupling resistance.

Gap junctions exist in the septa between the segments of the lateral giant axons in the ventral nerve cord of the crayfish Procambarus. A large increase in the resistance (uncoupling) of these gap junctions was brought about by mechanical injury to the axonal segments. Both thin sections and freeze-fracture preparations were used to monitor the morphological changes which occurred up to 45 min after injury. There was no apparent change in the organization (a loose polygonal array) of the intramembrane particles which make up the junctional complex up to 45 min after injury. In some instances, however, the intramembrane particles appeared to have moved away from the junctional area. Other junctional regions were internalized and appeared similar to what have been called annular gap junctions. Also at this time (20-25 min after injury), a dense cytoplasmic plug formed in uninjured axon near the junctional region. It is concluded that the gap junctions that exhibit a loose polygonal organization of the intramembrane particles may be either in a state of low resistance (coupled) or a state of high resistance (uncoupled).

Animals↗
PubMed1984

Fine structure of squid (Loligo pealei) optic lobe synapses.

Cephalopod optic lobes are a well-known source of cholinergic nerve endings [Dowdall and Whittaker (1973) J. Neurochem, 20, 921-935]. In order to utilize this property for subsequent analyses of cholinergic mechanisms of transmission in the CNS, we describe the ultrastructure of the entire optic lobe of the squid (Loligo pealei) and relate the morphology of synaptosomes to the intact tissue. In the cortex, chemical junctions were found showing two basic forms. The first was an invaginated synapse, appearing only between presynaptic bags and spines which may originate from the trunks of amacrine cells of the outer granule layer. The second was that of a typical synapse, found in almost all layers except the upper portion of the first radial layer. Synapses in the medulla were predominantly of the second type, although a few photoreceptor endings extended to this region as well. The different types of terminals observed in the intact squid optic lobe corresponded to the different types of endings recognized in a synaptosome fraction derived from these lobes. Because of its high content of cholinergic endings and distinct synaptic types, the squid optic lobe may contribute to the elucidation of the mechanisms of cholinergic transmission in the central nervous system. In addition, electrotonic synapses were found between photoreceptor processes in the cortex, as well as other elements of the neuropil.

Animals↗
PubMed1984

Ultrastructural and physiological effects of the ionophore A23187 at identified frog neuromuscular junctions.

The physiological and morphological effects of the calcium ionophore A23187 (calimycin) at the frog neuromuscular junction in vitro were examined. Miniature endplate potentials were recorded intracellularly during exposure to the ionophore. Preparations fixed 15 or 30 min after adding the drug to the incubating medium, which exhibited a greatly increased miniature endplate potential frequency, showed no obvious morphological differences when compared to controls with regard to synaptic vesicle number or distribution of vesicles within the terminal. However, after 45-60 min of exposure to the ionophore, when miniature endplate potential frequency had declined almost to zero, most of the nerve endings appeared devoid of synaptic vesicles and other organelles while the plasma membrane was intact. It is suggested that the apparent depletion of vesicles from the terminal induced by the calcium ionophore is a consequence of irreversible changes at the terminal.

Animals↗
PubMed1983

Synaptic vesicles and the nerve-muscle preparation in resinless sections.

Resinless sections have been used to study the fine structural organization of cellular organelles and fibrous components at synapses. Presynaptic elements of the neuromuscular junction, representing the P.N.S., and of cerebral cortical synapses, representing the C.N.S., are examined and compared. Typical ultrastructural features are apparent in presynaptic and postsynaptic components and in the surrounding muscle and neuronal tissue demonstrating the reliability and usefulness of the technique.

Animals↗
PubMed1983

The cytoskeletal lattice of the neurohypophysial cells.

The cytoskeleton of rat neurohypophysial cells as seen in resinless sections is an irregular three-dimensional lattice of short strands of cytoplasmic matrix (the microtrabeculae) that interconnect parallel arrays of neurotubules, neurofilaments, abundant neurosecretory granules, and other membrane-bound organelles including the plasma membrane. This morphological finding suggests that the cytoplasmic ground substance constitutes a cytoskeletal continuum that may be the ultrastructural expression of a motile apparatus responsible for neurosecretory granule movement and hormone release in the neurohypophysis.

Animals↗
PubMed1983

Fine structure of synapses of the central nervous system in resinless sections.

The cytoskeleton has been implicated in neuronal function, particularly in axonal transport, excitability at axonal membranes, and movement of synaptic vesicles at preganglionic endings. The present study demonstrates the presence of a pre- and postsynaptic cytoskeleton in resinless sections of CNS tissue by use of the polyethylene glycol (PEG) technique of Wolosewick (1980) viewed by conventional transmission EM, scanning transmission EM, and surface scanning EM. The PEG technique permits visualization of the cytoskeletal network unobscured by the electron scattering properties of epoxy embedment. In the presynaptic process, synaptic vesicles appear to be suspended in a filamentous network that is contiguous with the synaptic vesicle membrane and with the presynaptic plasma membrane and its dense material. In the postsynaptic process, the postsynaptic density (PSD) is seen in intimate contact with the postsynaptic membrane. En face images of the PSD in some synapses appear as a torus. Emanating from the filamentous web of the PSD are filaments which extend to the adjacent plasma membrane. We conclude that membranous synaptic elements are contiguous with a three-dimensional lattice network that is similar to that described in whole unembedded cells (Wolosewick and Porter, 1976). Moreover, the synaptic densities represent a specialized elaboration of the cytoskeleton.

Animals↗
PubMed1983

The electromotor system of the stargazer: a model for integrative actions at electrotonic synapses.

The electric organs of Astroscopus are modified from extraocular muscles and innervated by the enlarged oculomotor nuclei. The electromotor neuron somata are contacted by fine processes with which they form gap junctions. Presynaptic vesicles and active zones are also present, although physiological data give no indication of chemically mediated transmission. Antidromic stimulation produces long lasting graded depolarizations in the electromotor neurons. The latency is sufficiently short to indicate that the cells are electrotonically coupled, which was confirmed by direct measurement. Antidromic invasion may normally fail and is easily blocked by hyperpolarization revealing initial segment and axon spikes. Spinal stimulation evokes postsynaptic potentials (PSPs) and orthodromic impulses; the PSPs are not smoothly graded in amplitude. A medullary nucleus innervates the electromotor nucleus; the medullary cells also show short latency graded antidromic depolarizations and presumably are electrotonically coupled. Their coupling accounts for the variability in PSPs evoked by spinal stimulation. Apparent time constants differ greatly for direct stimulation of a single cell, decay of afterhyperpolarization, electrotonic spread from one cell to a neighbor, and decay of PSPs and graded antidromic depolarizations. The differences can be accounted for in terms of a highly interconnected network of electrotonically coupled cells, which was simulated computationally. Because of the long membrane time constant graded antidromic depolarizations summate. Because antidromic invasion is facilitated by depolarization, the antidromic depolarizations can show pronounced facilitation. The observed "plasticity" within this electrotonically coupled system provides a model for integrative actions at other sites of coupling.

Afferent Pathways↗
PubMed1981

The effect of postsynaptic deprivation on the presynaptic chief cell in the rat carotid body.

After the surgical removal of the postsynaptic sensory sinus nerve, the presynaptic specializations in the chief cell of the rat carotid body chemoreceptor rapidly disappear. When the sinus nerve is allowed to regenerate, the presynaptic specializations reappear almost simultaneously with the re-establishment of apposition of the nerve to chief cells and the number of the synapses is restored to a normal range by the third week after deafferentation. This finding indicates that the maintenance of the presynaptic specializations in the chief cell depends on the persistence of the postsynaptic element, and further suggest the neurotrophic maintenance of the presynaptic specializations may be exerted by the postsynaptic sinus nerve. The sustentacular cells may play a role in governing the specificity of reinnervation by the sinus nerve.

Animals↗
PubMed1980

A light and electron microscopic study of the rat superior cervical ganglion cells by intracellular HRP-labeling.

Horseradish peroxidase (HRP) was injected intracellularly into single neurons of the isolated rat superior cervical ganglia. Intracellular iontophoresis of HRP did not seem to damage the sympatheticneurons or to affect synaptic transmission. Under the light microscope, 9 of the 27 HRP-labeled sympathetic neurons exhibited varicosities in their dendrites, but not in their axons; the varicose dendrites came into close contacts with adjacent non-labeled neurons. With the electron microscope, the varicose dendrites of 3 separate neurons lightly stained with HRP, morphological features of synapses could be identified at the contact site: clusters of vesicles in the varicose dendrites, intercellular space of about 20 nm separating the apposed membranes, and an intermediate density on the postjunctional membrane. These findings suggest at the ultrastructural level the occurrence of dendrodendritic and dendro-somatic synapses in mammalian sympathetic ganglia.

Animals↗
PubMed1980

Coordinated micropinocytotic activity of adjacent neuronal membranes in mammalian central nervous system.

Neuropil from a number of sites in both mammalian and inframammalian species were examined by electron microscopy. Complex micropinocytotic invaginations in which a tongue of cytoplasm extended into the endocytotic indentation of the cell membrane, were observed in all tissues. These complex membrane infoldings occurred at both chemical and electrotonic synapses. Coated invaginations of apposed membranes, at which infoldings occurred directly opposite each other, were also observed at the interfaces between neighboring dendrites. These observations indicate that micropinocytotic membrane infoldings involving the coordinated activity of adjacent neuronal membranes occur in a wide variety of tissues. Coordinated exocytosis/endocytosis may provide a mechanism for interneuronal bulk transport of material, both at synapses and at non-synaptic sites, in the central nervous system.

Animals↗
PubMed1979

Ultrastructure of synapses and cellular relationships in the oculomotor nucleus of the rhesus monkey.

The fine structure of synapses and of cellular relations was examined in the somatic efferent portion of the oculomotor nucleus of the adult rhesus monkey. Axosomatic and axodendritic synapses are characterized by distinct synaptic clefts which usually measure 20-30 nm between pre- and postsynaptic membranes. Cytoplasmic "thickenings" of pre- and postsynaptic membranes are often observed. Subjunctional bodies are present at both axosomatic and axodendritic synapses. Somatic and dendritic spine synapses are present. Serial synapses are also found, suggesting the operation of presynaptic inhibition in this nucleus. At some synapses the extracellular gap between pre- and postsynpatic membranes is reduced to 5-9 nm. However, junctions similar to the latter are also present between neurons and glia, and at the junctions between adjacent glial elements. The present results provide no evidence for a clear morphological substrate for electrotonic transmission in the somatic efferent portion of the primate oculomotor nucleus.

Animals↗
PubMed1979

Phosphorylation of specific, distinct proteins in synaptosomes and axons from squid nervous system.

Synaptosomes and axons from squid were incubated with [gamma-(32)P]ATP or [(32)P]orthophosphate and specific, distinct proteins were found to be labeled in each preparation. In axoplasm, only the major 200,000 M(r) neurofilament protein and a specific protein of approximately 400,000 M(r) were labeled, as reported previously [Pant, H. C., Shecket, G., Gainer, H. & Lasek, R. J. (1978) J. Cell Biol. 78, R23-R27]. These results were independent of whether the cosubstrates were (32)PO(4) (2-) or [gamma-(32)P]ATP. However, synaptosomes lacked the 200,000 M(r) neurofilament protein and several lower molecular weight proteins were labeled instead, the most prominent being a 47,000 M(r) species. [gamma-(32)P]ATP was much more effective in labeling the 47,000 M(r) species than (32)PO(4) (2-). Synaptosomes also contained a distinct 250,000 M(r) protein species which, however, was not labeled. The protein kinase activity in synaptosomes was sensitive to various pharmacological agents, depending on whether the labeled phosphate came directly from ATP or orthophosphate. Carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, a mitochondrial H(+) uncoupler, almost completely inhibited incorporation of (32)P into protein with (32)PO(4) (2-) as cosubstrate, as expected, but produced only 32% inhibition with [gamma-(32)P]ATP as cosubstrate. The activity could be augmented by incubating synaptosomes in a calcium-free medium and could be suppressed by increasing intrasynaptosomal Ca(2+) with A23187, a Ca(2+) ionophore. The latter effect was more prominent with (32)PO(4) (2-) than with [gamma-(32)P]ATP as cosubstrate. Depolarizing agents such as veratridine and high K(+) also suppressed activity, and the veratridine effect was completely reversed by tetrodotoxin or by omission of Ca(2+) when [gamma-(32)P]ATP was used, and partially reversed when (32)PO(4) (2-) was used. We conclude that the morphological transformation of an axon into a terminal is accompanied by significant changes in protein and phospho-protein composition that may be related to synaptic transmission.

Animals↗