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M O'Shea

Publications and source records attributed to M O'Shea.

At least 73 records · Page 4Linked to original sources
PubMed1987

Identification and purification of two precursors of the insect neuropeptide adipokinetic hormone.

Our objective was to establish a system for the investigation of neuropeptide biosynthesis in an insect. To achieve this we developed an in vitro organ culture system for the corpora cardiaca (CC) of the locust (Schistocerca gregaria). The CC are the neurosecretory structures containing the adipokinetic hormones AKH I and AKH II. Tritiated amino acids were added to the glands, and we studied the development of label in newly made proteins using size-exclusion and reverse-phase liquid chromatography. We performed pulse-chase and pulse-translation block experiments using 3H-tryptophan as tracer. We also raised an antiserum to a synthetic AKH analog and used this in combination with liquid chromatography to identify 2 precursor polypeptides, P1 and P2. Size-exclusion chromatography indicated the presence of a major component of the CC of about 8 kDa that incorporates 3H-tryptophan before AKH I and II. Moreover, in both pulse-chase and pulse-translation block experiments we showed that label is transferred from this 8 kDa component into AKH I. We call this component proAKH; it is recognized by anti-AKH serum in a radioimmunoassay (RIA). Further fractionation of tritium-labeled proAKH by reverse-phase chromatography yielded 2 polypeptides, P1 and P2. Both are AKH-immunoreactive and contain 3H-tryptophan after in vitro pulse labeling, and both are proposed precursors of AKH I. The in vitro system we have developed may be a model system for the study of the processes of neuropeptide biosynthesis and its regulation in an intact neurosecretory tissue of an insect.

Animals↗
PubMed1985

Peptidergic innervation of insect skeletal muscle: immunochemical observations.

Proctolin (Arg-Tyr-Leu-Pro-Thr) is a pentapeptide present in the hindgut or proctodeum of the cockroach Periplaneta americana where it may be a transmitter. Its widespread distribution among peripherally projecting neurons in the CNS (Bishop and O'Shea, '82) suggested that proctolin's motor function is not restricted to the hindgut, but has a variety of peripheral targets. This idea was further supported when proctolin was localized to an identified skeletal motoneuron, the slow coxal depressor, where it acts as a cotransmitter (O'Shea and Bishop, '82; Adams and O'Shea, '83). Our objective was to investigate the proctolinergic innervation of a variety of skeletal muscles of the cockroach Periplaneta americana. We used immunohistochemical and radioimmunochemical methods to map the distribution of proctolin immunoreactivity. This survey revealed that a subpopulation of skeletal muscles are innervated by proctolinergic motoneurons. The anatomical features of the peptidergic innervation and the levels of proctolinlike immunoreactivity of one muscle group, the coxal depressor system, are here described in detail. The source of the proctolin innervation to the metathoracic coxal depressor group is identified as the slow coxal depressor motoneuron. The results of a survey of fast and slow skeletal muscles revealed that proctolin is associated with slow motor function. The functional implications of the association of a peptide with motoneurons are discussed in relationship to the organization of the insect motor pool.

Animals↗
PubMed1985

Model peptidergic systems at the insect neuromuscular junction.

The emergence of neuropeptides as a prominent neurotransmitter class raises fundamental new questions about modes of chemical signaling in the nervous system. These relate to the large number of peptides, their co-localization in neurons and to novel actions at innervated targets. Synaptic preparations in insects offer excellent experimental models for studies of multiple transmitters and their joint actions at uniquely identified nerve-muscle junctions. Peptidergic systems in insects are reviewed with particular reference to two identified neuromuscular preparations which demonstrate cotransmitter actions of peptides and "classical" neurotransmitter substances.

Animals↗
PubMed1985

Neuropeptide function: the invertebrate contribution.

The following is a list of generalizations that arise from considering the present state of knowledge concerning the functions of invertebrate peptides. Some of these clearly also apply to vertebrates. Invertebrate peptides can be classified into structurally related groups. Structural similarity of peptides may represent true evolutionary homology by selection acting on an original gene. Alternatively, independent evolution of similar genes may have occurred because certain amino acid sequences represent optimal solutions to complex functional problems. Invertebrate neuropeptides have multiple functions. Thus, proctolin is a cardioactive peptide, a skeletal neuromuscular transmitter, a hindgut neuropeptide, a peptide of CNS interneurons (Keshishian & O'Shea 1984) and may have humoral roles. Invertebrate peptides act through a variety of molecular mechanisms. Generalizations about the mechanism cannot yet be made. Thus, proctolin's action on crustacean skeletal muscle is not associated with stimulation of cyclic-AMP or protein phosphorylation, but the action of SCPB on molluscan skeletal muscle involves elevation of cAMP. Invertebrate peptide inactivation can be caused by proteolysis that can also function to enhance peptide bioactivity. Proctolin is made virtually biologically inactive by any proteolysis, but alpha-BCP bioactivity is enhanced by two steps of carboxy peptidase digestion before being functionally inactivated. Protease action on released peptides is not necessarily a "simple" form of transmitter inactivation. Protease action also involves functional processing whereby the temporal and spatial parameters of a peptide's action may be shaped. Invertebrate neuropeptides are frequently co-localized with other neuroeffectors. Peptides may be co-localized and released with other active peptides as in the bag-cell example, or may be coactive with more conventional transmitters, as in the Ds motoneuron example. In such circumstances there is no reason to view either transmitter as primary or secondary. Invertebrate neuropeptides are widely involved in the control of muscle contraction. These effects may be locally and directly mediated as in the Ds motoneuron example or may be humoral. The peptide may act directly on the muscle contractile system or function to modulate the muscles' response to other motor input. Muscle contraction may be induced by a neuropeptide without depolarization of the muscle cells, for example see proctolin. Invertebrate neuropeptides are frequently involved in the control of oscillatory functions. In several examples peptides activate rhythmic myogenic contractions of cardiac and skeletal muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1985

The acquisition and expression of a peptidergic phenotype in the grasshopper embryo.

We have examined the developmental acquisition and regional expression of the neurotransmitter proctolin in neurons of the grasshopper embryo, using both assay and immunocytochemistry. There are four stages in the acquisition and accumulation of proctolin in the embryo. The first stage (50 to 60% embryogenesis) consists of a slow accumulation of proctolin prior to the onset of central nervous system (CNS) staining. During the second stage proctolin levels increase at a 5-fold faster rate. During this stage, which ends at 70% of development, a stable pattern of staining is established in the ganglia. The third stage (70 to 95% embryogenesis) consists of a rapid accumulation of peripheral proctolin levels that occurs principally in motor endings, without a significant increase in the CNS. This stage also correlates with the onset of peripheral staining. During the fourth stage, over the final 5% of embryogenesis, there is a 20% loss of proctolin in the periphery. We have attempted to relate these changes to developmental events occurring in identified clusters of neurons, by examining the development of neuromuscular connections made by embryonic terminal ganglion motoneurons to the intrinsic muscles of the hindgut. Of the 30 hindgut motoneurons, only six anterior medial (AM) efferents are proctolin immunoreactive in the embryo. Their axons establish a dense proctolin-staining arborization over the intrinsic muscles. The peptide accumulates in the endings as staining appears in the terminal ganglion. Hindgut proctolin levels increase substantially and then decline in a manner similar to that found for total peripheral proctolin. By the end of embryogenesis the endings will release proctolin, in a calcium-dependent manner, when depolarized. The six proctolin-staining AM neurons constitute a simple model system for studying the determination and expression of neurotransmitters in identified embryonic cells.

Animals↗
PubMed1985

The distribution of a peptide neurotransmitter in the postembryonic grasshopper central nervous system.

Proctolin is a peptide neurotransmitter, discovered in the visceral muscles of the cockroach. The peptide has recently been identified in the nervous systems of many invertebrates. Using reverse phase high pressure liquid chromatography together with a sensitive bioassay, we analyzed the distribution of proctolin in the central nervous system of the grasshopper Schistocerca nitens. We also used immunocytochemistry to identify about 70 diverse proctolin-staining neurons in the postembryonic ventral nerve cord. Proctolin immunoreactivity is rare, being found in only about 0.6% of the ganglionic neurons. Among the cells we stained for proctolin were thoracic skeletal motoneurons, a cluster of efferents to the intrinsic muscles of the hindgut, and both inter- and intraganglionic thoracic interneurons, as well as several interspecies homologues to proctolin-staining neurons in the cockroach. The map of proctolin expression within the central nervous system is not extensively altered during postembryonic life. It is the product of embryonic development, which is the subject of the following paper (Keshishian, H., and M. O'Shea (1985) J. Neurosci. 5: 1005-1015).

Abdomen↗
PubMed1984

Structures of two cockroach neuropeptides assigned by fast atom bombardment mass spectrometry.

Amino acid sequences have been assigned to two cockroach neuropeptides (greater than Glu-Val-Asn-Phe-Ser-Pro-Asn-Trp-NH2, M I, and greater than Glu-Leu-Thr-Phe-Thr-Pro-Asn-Trp-NH2, M II) by application of fast atom bombardment mass spectrometry, including high resolution and linked scan (metastable) studies. The peptides show considerable homology with two other invertebrate neuropeptides, adipokinetic hormone (AKH, from a locust) and red pigment concentrating hormone (RPCH, from a prawn), whose fast atom bombardment spectra were also studied. M I and M II are thus members of a family of structurally-related invertebrate neuropeptides.

Amino Acid Sequence↗
PubMed1984

Discontinued use of intrauterine contraceptive device and pregnancy loss.

To evaluate the risk of spontaneous abortion among former intrauterine contraceptive device (IUD) users, we compared the contraceptive history of 328 women with a spontaneous abortion up to 28 weeks' gestation with that of 1715 women having a term delivery. A similar percentage of case and comparison subjects reported prior IUD use as well as IUD use within the year before pregnancy. However, IUD use lasting more than 12 months was associated with a 1.5-fold increase in the crude risk of spontaneous abortion up to 28 weeks' gestation (p less than 0.05), a 1.8-fold increased risk of first-trimester spontaneous abortion, and a 1.7-fold increased risk of incomplete abortion (p less than 0.01). The results were not altered by control of individual confounding factors. When confounding factors were controlled simultaneously in a multiple logistic regression analysis, the relative risks were 1.4, 1.7 and 1.6, respectively; however, they were no longer statistically significant. The results suggest that prolonged IUD use may be associated with a modest increase in risk of subsequent spontaneous abortion.

Abortion, Incomplete↗
PubMed1984

Neuropeptide proctolin in postural motoneurons of the crayfish.

The neuropeptide transmitter candidate proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) was associated with three of the five excitatory motoneurons innervating the tonic flexor muscles of the crayfish abdomen. Proctolin immunohistochemical staining occurred in cell bodies and axons of these three identified neurons. Stained axon terminals were detected across the entire tonic flexor muscle. Bioassay of extracts of the tonic flexor muscles indicated the presence of 370 fmol of proctolin/muscle or 670 fmol/mg dry weight. Bioactivity was eliminated in muscles in which the tonic flexor motor root was cut 2 months prior to extraction and in muscle extracts pre-incubated with proctolin antiserum. High pressure liquid chromatography purification of tissue extract indicated that all bioactivity in the crude extract was due to authentic proctolin. Our findings suggest that these three cells function as peptidergic motoneurons. A precedent for this is the proctolin-containing postural motoneuron of the cockroach.

Abdomen↗
PubMed1984

Isolation and characterization of two myoactive neuropeptides: further evidence of an invertebrate peptide family.

The neuropeptide proctolin acts as a neuromuscular co-transmitter in insect skeletal muscle. As a prelude to determining whether other peptides may function in a similar way, we are attempting to isolate and characterize the chemical nature of new myoactive neuropeptides in insects. We examined the corpus cardiacum, a major insect neurosecretory structure of the American cockroach (Periplaneta americana), using a skeletal muscle bioassay and high pressure liquid chromatography fractionation and identified two myoactive factors, MI and MII. They are synthesized in the corpus cardiacum and released from it into the blood by a calcium-dependent mechanism. Amino acid and fast atom bombardment-mass spectroscopy analysis show that MI and MII are structurally related octapeptides representing the major secreted products of the cockroach corpus cardiacum. Both MI and MII are also present in the CNS and in the gut, indicating transmitter as well as hormonal functions in the cockroach. A survey in other species indicates MI may be present in invertebrates other than insects, but neither was found in the rat. The MI and MII peptides have clear chemical affinities to two previously described invertebrate peptides, locust adipokinetic hormone and crustacean red pigment concentrating hormone, as well as sharing biological activity with these peptides. Our results provide further evidence for the existence of a large family of structurally related peptides with divergent functions in a variety of invertebrate types.

Animals↗
PubMed1983

Peptide cotransmitter at a neuromuscular junction.

The neuropeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) is present in the nerve terminals of an identified slow skeletal motoneuron in the cockroach. Proctolin is released onto the target muscle, a coxal depressor, by neuron stimulation and by depolarization with potassium. The physiological action of the motoneuron suggests that proctolin acts as a cotransmitter. Proctolin and neural stimulation produce delayed and sustained contractile effects without muscle depolarization.

Action Potentials↗
PubMed1983

Serotonin immunoreactive neurons in the central nervous system of an insect (Periplaneta americana).

Serotonin-like immunoreactivity was mapped in the central nervous system (CNS) of the cockroach, Periplaneta americana. Immunoreactive staining occurred in every ganglion of the CNS. The largest numbers of immunoreactive somata were detected in the optic lobes and the brain, and lowest numbers in the first and second thoracic ganglia. Dense stained fibers, ramifications, and varicosities were found in all ganglia, and numerous axon like processes occurred in all interganglionic connectives. Immunoreactive processes were not, however, detected in most of the peripherally projecting nerve roots. Processes were found only in roots of the suboesophageal ganglion and the tritocerebral lobes of the brain. A comparison of the map for serotonin immunoreactivity with one generated for the pentapeptide transmitter proctolin suggests that the two systems overlap only in the suboesophageal ganglion and the tritocerebrum. The amine and peptide may co-occur in neurons in these regions. The serotonin immunoreactive system appeared significantly different from the octopaminergic system of the ventral nerve cord. Seventy-two potentially identifiable immunoreactive cells were located in the cockroach CNS. Some of these may be suitable for physiological study of the functional role of serotonin.

Animals↗
PubMed1982

Neuropeptide proctolin (H-Arg-Try-Leu-Pro-Thr-OH): immunocytochemical mapping of neurons in the central nervous system of the cockroach.

Proctolinlike immunoreactivity was mapped in the central nervous system of the cockroach, Periplaneta americana, by using whole-ganglion immunoreacted preparations. The procedure for this immunohistochemical staining of whole-mounts is described. Immunoreactivity was confined to neuronal cell bodies and and processes. These were found in all ganglia of the CNS. The cells varied in the consistency and intensity of their staining. The occurrence and variability of staining is described in detail. Cell bodies were found in the dorsal, ventral, and lateral regions of the ganglia. The highest number of cell bodies was found in the terminal ganglion and the lowest number in the cerebral ganglion. Those in the cerebral ganglion occurred mainly in the tritocerebral lobes. The distribution of immunoreactive cell bodies correlated with results previously obtained by radioimmunoassay. Immunoreactive processes were detected in all interganglionic connectives and many ganglionic nerve roots. Dense ramifications of immunoreactive processes and variocosities were detected in many of the ganglia. The widespread presence of immunoreactivity suggests that proctolin has diverse central and peripheral functions. The mapping immunoreactive neuronal somata provides a valuable step in the identification of putative proctolin-containing neurons suitable for further biochemical, anatomical, and physiological analysis.

Animals↗
PubMed1982

Neuropeptide proctolin associated with an identified skeletal motoneuron.

Our objective was to find large and identifiable peptide-containing neurons and their postsynaptic targets. For this, a whole mount immunohistochemical method was used to locate cell bodies of neurons in the cockroach central nervous system immunoreactive to antibodies raised against the pentapeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH). The morphology and projections of the immunoreactive neurons were investigated by combining intracellular dye injection and electrophysiological and immunochemical procedures. The presence of proctolin in specific immunoreactive neurons was check by high pressure liquid chromatography combined with bioassay applied to extracts made from individually identified and isolated cell bodies. Using these approaches, we have identified a large proctolin-containing motoneuron which innervates muscles in a proximal segment of the cockroach leg. This study establishes a well characterized cellular preparation in which the physiological actions and functions of a peptide-containing neuron can be studied in vivo.

Animals↗
PubMed1982

Identification of proctolin-containing neurons.

Proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH), a highly bioactive peptide found first in insects, is shown to be localized to specific neurons in the central nervous system (CNS) of the cockroach Periplaneta americana. Application of an antiproctolin serum to whole ganglia in a whole-mount immunohistochemical technique reveals the presence of proctolin immunoreactive neurons throughout the CNS. These neurons can be mapped and appear in consistent positions in different individuals. Some have been uniquely identified by intracellular dye injection combined with immunological localization. The presence of proctolin in individually identified neurons has been determined by high-pressure liquid chromatography combined with proctolin bioassay detection performed on extracts made from single identified cells. Some proctolin-containing neurons contain large vacuolelike inclusions in their cell bodies. These vacuoles appear to be the greatly enlarged lumena of the rough endoplasmic reticulum and may be part of the morphological substrate for the manufacture of proctolin. Electrophysiological studies suggest that some proctolin-containing neurons in different segmental ganglia, although not all, are normally recruited together as a functional unit by shared presynaptic input. This characterization of individual proctolin neurons is a prelude to a cellular study of the physiological role of a neuropeptide.

Animals↗
PubMed1981

Pentapeptide (proctolin) associated with an identified neuron.

Individual neurons can be recognized and identified anatomically, physiologically, and biochemically in the insect central nervous system. Biochemical analyses of extracts prepared from one such identified neuron show it to be associated with a bioactive pentapeptide called proctolin. This peptide may be a neurotransmitter, and a preparation is established in which its physiological action can be studied at the cellular level.

Animals↗