Location and function of serotonin in the central and peripheral nervous system of the Colorado potato beetle

In this thesis we have localized serotoninergic neurons in the central and peripheral nervous system of the Colorado potato beetle, Leptinotarsa decemlineata by means of immunohistochemistry with a specific antiserurn to serotonin and assessed the possible role of these neurons in feeding physiology. Emphasis was laid on the location of serotoninergic neurons involved in: (1) channelling of sensory information from antennal and gustatory sensory systems to the central nervous system; (2) the central organization of the serotoninergic neuron system providing information on possible central processing of this information; and the routes of innervation of possible target organs.We have shown that about 200 serotoninergic neurons are present in the cerebral ganglion complex of the beetle, representing interneurons serving short- and long range communication. These neurons were grouped according to their location, number, and distribution of their processes. Clusters of paired protocerebral neurons appeared to be responsible for left-right communication within the brain and are the sole source of immunoreactivity in the central complex and the corpora pedunculata. Other neurons in the optic lobes and the deutocerebrum are likely to play an important role in the processing of visual and olfactory information respectively. This serotoninergic network in the brain does not project to other parts of the central nervous system and has the appearance of an individual serotoninergic neural unit. No neurons with a secretory function are present in the cerebral ganglion complex, nor are there structural indications that serotoninergic neurons are involved with the control of peptidergic neurosecretory neurons in the protocerebrum ( Chapter 2 )In the remainder of the central nervous system, the ventral nerve cord, altogether 74 serotoninergic neurons were found and their organization pattern enabled us to group them into five neuron classes. Two paired segmental twin interneurons are present in each ganglion or neuromere. These neurons have extensive dendritic arborizations in the contralateral hemisphere of the ganglion, and small arborization close to the perikaryon. Their axons take a contra- and ipsilateral course to more frontally and/ or caudally located ganglia. The distribution of processes is indicative of a division of labour among these neurons. The intersegmental projection are indicative of a function in interganglionic communication, whereas the dendritic projections suggest a function in the coordination of left-right neural activity within the ganglia. Four large frontal secretory neurons are present in the suboesophageal ganglion with axons projecting to a diffuse neurohemal system on oesophageal nerves. A pair of large caudal efferent neurons in the terminal ganglion send their processes in the proctodaeal nerves and innervate the proximal part of the hindgut. The function of miniature and terminal neurons is unknown. The distribution pattern of serotonin-like immunoreactivity enabled us to distinguish three separate putative functional units. The function of the caudal functional unit might be the synaptic control of caudal neurons innervating the alimentary canal, the function of the other two units is unknown ( Chapter 3 ).The presence of serotoninergic axons in the proctodaeal nerves indicated that the gut might be under serotoninergic control. By means of immunohistochemistry, it was shown that the alimentary canal of the beetle receives innnervation from two separate sources. Large efferent neurons in both the stomatogastric and central nervous system innervate the gut. Four neurons in the frontal ganglion have axons which run via the recurrent nerve to the circular and longitudinal muscles of the fore- and anterior midgut and supply the surface of these muscles with neurohemal axon swellings. The posterior midgut is devoid of immunoreactivity. The longitudinal muscles of the hindgut are supplied by the two caudal neurons described in Chapter 3 . Electron-microscopical inspections of the axon swellings showed that exocytosis of immunolabelled vesicles occurs at some distance from the muscles fibres, indicating that the gut muscles might be under neurohormonal control. No serotoninergic synapses are observed on muscle fibres. A possible serotoninergic neurohormonal control of gut muscles, was confirmed in a bioassay. It appeared that administration of graded dosages of serotonin to the incubation medium has a clear inhibitory effect on spontaneous contractions of hindguts in vitro at concentrations of 10 -8-10 -8M. This effect was dose-dependent ( Chapter 4 ).Other organs might be under serotoninergic control as well. Two diffuse neurohemal systems for serotonin are present in the head of the beetle. Axons of four secretory neurons in the suboesophageal ganglion, described in Chapter 3 , enter the ipsilateral mandibular nerve and cover the surface with a dense network of immunoreactive swellings. Two efferent neurons in the frontal ganglion have processes that run into the frontal connectives. Here, the axons emerge and form a similar network of axon swellings on the surface of the labro-frontal, pharyngeal, and antennal nerves, and on the frontal ganglion. Electron microscopy showed that these axon swellings are located outside the impermeable neural sheath, surrounding the nerves, and hence in close contact with the hemolymph. Next to this neurohemal release, a targeted release of serotonin occurs near the muscles of labrum, mandibles, pharynx, and salivary glands, indicating that these organs are under serotoninergic control ( Chapter 5 ).We have investigated the presence of serotoninergic sensory neuronal cell bodies in sensilla on labial and maxillary palps, galea, ventral labrum, tarsi, and compound eyes. It appeared that no afferent serotoninergic neurons are present in the peripheral nervous system of the beetle ( Chapter 6 ).The studies presented in this thesis show that the biogenic amine serotonin (5- hydroxytryptamine) is a ubiquitous and versatile neuroactive substance in both the central and peripheral nervous system of the Colorado potato beetle. In the central nervous system it is present in interneurons serving intra- and interganglionic communication. Here, it probably functions as a neurotransmitter and/or neuromodulator. A small number of serotoninergic neurons release serotonin, via elaborate ways, as a neurohormone into the hemolymph and/or close to their target organs.In this thesis we have provided evidence that serotoninergic neurons are involved in the regulation of some aspects of feeding physiology at both the central and peripheral level. In the central nervous system, several serotoninergic interneurons, i.e. those in the cerebral ganglion complex, participate in the channelling and the central processing of antennal and optic information, whereas other interneurons, i.e. those in the ventral nerve cord, are part of functional neural units which are proposed to control efferent neurons, e.g. the caudal neurons innervating the hindgut. Serotoninergic neurosecretory neurons are involved in control of gut functioning, as shown in immunohistochemical and bioassay studies. Another class of efferent neurosecretory neurons were shown to innervate salivary glands and muscles of labrum, mandibles, and anterior pharynx, indicating that these organs might also be under serotoninergic control

GABAergic presubicular projections to the medial entorhinal cortex of the rat

We characterized presubicular neurons giving rise to bilateral projections to the medial entorhinal cortex (MEA) of the rat. Retrograde labeling of presubiculo–entorhinal projections with horseradish peroxidase and subsequent GABA immunocytochemistry revealed that 20–30 % of the ipsilaterally projecting neurons are GABAergic. No GABAergic projections to the contralateral MEA were observed. GABAergic projection neurons were observed only in the dorsal part of the presubiculum, which, when taking into account the topography of presubicular projections to MEA, indicates that only the dorsal part of MEA receives GABAergic input. The GABAergic projection neurons constitute �30-40 % of all GABAergic neurons present in the superficial layers of the dorsal presubiculum. Using doublelabel fluorescent retrograde tracing, we found that the ipsilateral and contralateral presubiculo–entorhinal projections originat

Genetic factors and insulin secretion: gene variants in the IGF genes

IGFs are important regulators of pancreatic beta-cell development, growth, and maintenance. Mutations in the IGF genes have been found to be associated with type 2 diabetes, myocardial infarction, birth weight, and obesity. These associations could result from changes in insulin secretion. We have analyzed glucose-stimulated insulin secretion using hyperglycemic clamps in carriers of a CA repeat in the IGF-I promoter and an ApaI polymorphism in the IGF-II gene. Normal and impaired glucose-tolerant subjects (n = 237) were independently recruited from three different populations in the Netherlands and Germany to allow independent replication of associations. Both first- and second-phase insulin secretion were not significantly different between the various IGF-I or IGF-II genotypes. Remarkably, noncarriers of the IGF-I CA repeat allele had both a reduced insulin sensitivity index (ISI) and disposition index (DI), suggesting an altered balance between insulin secretion and insulin action. Other diabetes-related parameters were not significantly different for both the IGF-I and IGF-II gene variant. We conclude that gene variants in the IGF-I and IGF-II genes are not associated with detectable variations in glucose-stimulated insulin secretion in these three independent populations. Further studies are needed to examine the exact contributions of the IGF-I CA repeat alleles to variations in ISI and DI

Gene Variants in the Novel Type 2 Diabetes Loci CDC123/CAMK1D, THADA, ADAMTS9, BCL11A, and MTNR1B Affect Different Aspects of Pancreatic β-Cell Function

OBJECTIVE - Recently, results from a meta-analysis of genome-wide association studies have yielded a number of novel type 2 diabetes loci. However, conflicting results have been published regarding their effects on insulin secretion and insulin sensitivity. In this study we used hyperglycemic clamps with three different stimuli to test associations between these novel loci and various measures of β-cell function. RESEARCH DESIGN AND METHODS - For this study, 336 participants, 180 normal glucose tolerant and 156 impaired glucose tolerant, underwent a 2-h hyperglycemic clamp. In a subset we also assessed the response to glucagon-like peptide (GLP)-1 and arginine during an extended clamp (n = 123). All subjects were genotyped for gene variants in JAZF1, CDC123/CAMK1D, TSPAN8/LGR5, THADA, ADAMTS9, NOTCH2/ADAMS30, DCD, VEGFA, BCL11A, HNF1B, WFS1, and MTNR1B. RESULTS - Gene variants in CDC123/CAMK1D, ADAMTS9, BCL11A, and MTNR1B affected various aspects of the insulin response to glucose (all P < 6.9 × 10-3). The THADA gene variant was associated with lower β-cell response to GLP-1 and arginine (both P < 1.6 × 1

Discrimination of Methionine Sulfoxide and Sulfone by Human Neutrophil Elastase

Human neutrophil elastase (HNE) is a uniquely destructive serine protease with the ability to unleash a wave of proteolytic activity by destroying the inhibitors of other proteases. Although this phenomenon forms an important part of the innate immune response to invading pathogens, it is responsible for the collateral host tissue damage observed in chronic conditions such as chronic obstructive pulmonary disease (COPD), and in more acute disorders such as the lung injuries associated with COVID-19 infection. Previously, a combinatorially selected activity-based probe revealed an unexpected substrate preference for oxidised methionine, which suggests a link to oxida-tive pathogen clearance by neutrophils. Here we use oxidised model substrates and inhibitors to confirm this observation and to show that neutrophil elastase is specifically selective for the di-oxygenated methionine sulfone rather than the mono-oxygenated methionine sulfoxide. We also posit a critical role for ordered solvent in the mechanism of HNE discrimination between the two oxidised forms methionine residue. Preference for the sulfone form of oxidised methionine is especially significant. While both host and pathogens have the ability to reduce methionine sulfoxide back to methionine, a biological pathway to reduce methionine sulfone is not known. Taken to-gether, these data suggest that the oxidative activity of neutrophils may create rapidly cleaved elas-tase “super substrates” that directly damage tissue, while initiating a cycle of neutrophil oxidation that increases elastase tissue damage and further neutrophil recruitment

Twitteren over grondrechten in tijden van de pandemie: Startpunt voor discussie of stok om mee te slaan?

The Legitimacy and Effectiveness of Law & Governance in a World of Multilevel Jurisdiction

Combined Risk Allele Score of Eight Type 2 Diabetes Genes Is Associated With Reduced First-Phase Glucose-Stimulated Insulin Secretion During Hyperglycemic Clamps

OBJECTIVE - At least 20 type 2 diabetes loci have now been identified, and several of these are associated with altered β-cell function. In this study, we have investigated the combined effects of eight known β-cell loci on insulin secretion stimulated by three different secretagogues during hyperglycemic clamps. RESEARCH DESIGN AND METHODS - A total of 447 subjects originating from four independent studies in the Netherlands and Germany (256 with normal glucose tolerance [NGT]/ 191 with impaired glucose tolerance [IGT]) underwent a hyperglycemic clamp. A subset had an extended clamp with additional glucagon-like peptide (GLP)-1 and arginine (n = 224). We next genotyped single nucleotide polymorphisms in TCF7L2, KCNJ11, CDKAL1, IGF2BP2, HHEX/IDE, CDKN2A/B, SLC30A8, and MTNR1B and calculated a risk allele score by risk allele counting. RESULTS - The risk allele score was associated with lower first-phase glucose-stimulated insulin secretion (GSIS) (P = 7.1 × 1