Biomedical subjects

Gerd Bicker

Publications and source records attributed to Gerd Bicker.

10 recordsLinked to original sources

PubMed2007

Embryonic differentiation of serotonin-containing neurons in the enteric nervous system of the locust (Locusta migratoria).

The enteric nervous system (ENS) of the locust consists of four ganglia (frontal and hypocerebral ganglion, and the paired ingluvial ganglia) located on the foregut, and nerve plexus innervating fore- and midgut. One of the major neurotransmitters of the ENS, serotonin, is known to play a vital role in gut motility and feeding. We followed the anatomy of the serotonergic system throughout embryonic development. Serotonergic neurons are generated in the anterior neurogenic zones of the foregut and migrate rostrally along the developing recurrent nerve to contribute to the frontal ganglion. They grow descending neurites, which arborize in all enteric ganglia and both nerve plexus. On the midgut, the neurites closely follow the leading migrating midgut neurons. The onset of serotonin synthesis occurs around halfway through development-the time of the beginning of midgut closure. Cells developing to serotonergic phenotype express the serotonin uptake transporter (SERT) significantly earlier, beginning at 40% of development. The neurons begin SERT expression during migration along the recurrent nerve, indicating that they are committed to a serotonergic phenotype before reaching their final destination. After completion of the layout of the enteric ganglia (at 60%) a maturational phase follows, during which serotonin-immunoreactive cell bodies increase in size and the fine arborizations in the nerve plexus develop varicosities, putative sites of serotonin release (at 80%). This study provides the initial step for future investigation of potential morphoregulatory functions of serotonin during ENS development.

Animals↗

PubMed2007

Pharmacological approaches to nitric oxide signalling during neural development of locusts and other model insects.

A novel aspect of cellular signalling during the formation of the nervous system is the involvement of the messenger molecule nitric oxide (NO), which has been discovered in the mammalian vascular system as mediator of smooth muscle relaxation. NO is a membrane-permeant molecule, which activates soluble guanylyl cyclase (sGC) and leads to the formation of cyclic GMP (cGMP) in target cells. The analysis of specific cell types in model insects such as Locusta, Schistocerca, Acheta, Manduca, and Drosophila shows that the NO/cGMP pathway is required for the stabilization of photoreceptor growth cones at the start of synaptic assembly in the optic lobe, for regulation of cell proliferation, and for correct outgrowth of pioneer neurons. Inhibition of the NOS and sGC enzymes combined with rescue experiments show that NO, and potentially also another atypical messenger, carbon monoxide (CO), orchestrate cell migration of enteric neurons. Cultured insect embryos are accessible model systems in which the molecular pathways linking cytoskeletal rearrangement to directed cell movements can be analyzed in natural settings. Based on the results obtained from the insect models, I discuss current evidence for NO and cGMP as essential signalling molecules for the development of vertebrate brains.

Animals↗

PubMed2006

Diltiazem protects human NT-2 neurons against excitotoxic damage in a model of simulated ischemia.

In vitro models are often used to investigate pathophysiological mechanisms of brain cell injury as they occur for instance during cerebral ischemia. To analyze the efficacy of potential neuroprotective compounds, cell physiological experiments were performed in a recently improved culture system of human model neurons. The postmitotic neurons were generated from the human NT-2 teratocarcinoma cell line, using a cell sphere culture method to facilitate rapid terminal differentiation. We simulated ischemic conditions in cultures of purified NT-2 neurons and found that low doses of the antihypertensive drug diltiazem protected against excitotoxic neuronal damage in vitro. Experiments with primary cortical mouse neuron cultures demonstrated a similar response to simulated ischemia and confirmed the neuroprotective effect of diltiazem. Calcium imaging experiments showed that diltiazem reduced both NMDA- and glutamate-induced calcium influxes in NT-2 neurons suggesting that its neuroprotective effect is based on the inhibition of voltage-gated calcium channels. These results indicate that diltiazem is an effective blocker of glutamate-induced excitotoxicity. Moreover, we suggest that cell cultures of human model neurons can provide an important initial test system for drug development in stroke therapy.

Animals↗

PubMed2005

STOP and GO with NO: nitric oxide as a regulator of cell motility in simple brains.

During the formation of the brain, neuronal cell migration and neurite extension are controlled by extracellular guidance cues. Here, I discuss experiments showing that the messenger nitric oxide (NO) is an additional regulator of cell motility. NO is a membrane permeant molecule, which activates soluble guanylyl cyclase (sGC) and leads to the formation of cyclic GMP (cGMP) in target cells. The analysis of specific cells types in invertebrate models such as molluscs, insects and the medicinal leech provides insight how NO and cyclic nucleotides affect the wiring of nervous systems by regulating cell and growth-cone motility. Inhibition of the NOS and sGC enzymes combined with rescue experiments show that NO signalling orchestrates neurite outgrowth and filopodial dynamics, cell migration of enteric neurons, glial migration and axonogenesis of pioneer fibers. Cultured insect embryos are accessible model systems in which cellular mechanisms of NO-induced cytoskeletal reorganizations can be analyzed in natural settings. Finally, I will outline some indications that NO may also regulate cell motility in the developing and regenerating vertebrate nervous system.

Animals↗

PubMed2004

Cellular expression patterns of acetylcholinesterase activity during grasshopper development.

We examined the expression of acetylcholinesterase (AChE) in the nervous system and epidermal body structures during embryonic and larval development of two grasshopper species: Locusta migratoria and Schistocerca americana. Histochemical labelling was blocked by the enzyme inhibitors eserine and BW284c51, but not by iso-OMPA, showing that the staining reflected true AChE activity. The majority of staining was localized on the cell surface but granular intracellular staining was also visible in many cell bodies. In both species, the cellular expression of AChE followed a similar but complex spatiotemporal staining pattern. Initially, mainly epidermal tissue structures were stained in the various body appendages (stages 25%-30%). Labelling subsequently appeared in outgrowing neurons of the central nervous system (CNS) and in the nerves innervating the limbs and dorsal body wall (stages 30%-40%). The latter staining originated in motoneurons of the ventral nerve cord. In a third phase (after 45%), the somata of certain identified mechanosensory neurons started to express AChE activity, presumably reflecting cholinergic differentiation. Staining was also found in repo-positive glial cells of the CNS, longitudinal glia of connectives, glia of the stomatogastric nervous system and glial cells ensheathing peripheral nerves. Glial cells remained AChE-positive during larval to adult development, whereas motoneurons lost their AChE expression. The expression pattern in non-neuronal cells and glutamatergic motoneurons and the developmental appearance of AChE prior to synaptogenesis in the CNS suggest non-cholinergic functions of AChE during grasshopper embryogenesis.

Acetylcholinesterase↗

PubMed2004

Hypoxic/ischaemic cell damage in cultured human NT-2 neurons.

Postmitotic neurons were generated from the human NT-2 teratocarcinoma cell line in a novel rapid differentiation procedure. These neurons were used to establish an in vitro assay system that allows the investigation of hypoxic/ischaemic cell damage and the development of neuroprotective strategies. In experiments of simulated ischaemia, the neurons were subjected to anoxia and hypoglycaemia. The viability of NT-2 neuronal cells was significantly reduced by anoxia especially in the presence of glutamate, reflecting the cellular vulnerability to excitotoxic conditions. The addition of the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 reduced glutamate-induced neuronal damage. Calcium imaging showed that NT-2 neurons increased cytosolic calcium levels in response to stimulation with glutamate or NMDA, an effect that was abolished in calcium free medium and at low pH values. The NMDA receptor antagonists MK-801, AP 5 and ketamine reduced the NMDA-induced response, suggesting the presence of functional NMDA receptors in the human neuronal cells. The mitochondrial potential of neurons was estimated using the fluorescent dye rhodamine 123 (R123). The fluorescence imaging experiments indicated an energetic collapse of mitochondrial functions during anoxia, suggesting that the human NT-2 neurons can be used to investigate subcellular processes during the excitotoxic cascade.

Aging↗

PubMed2004

Axonal regeneration of proctolinergic neurons in the central nervous system of the locust.

We provide evidence for axonal regeneration in the central nervous system (CNS) of the locust (Locusta migratoria). We followed the morphology of a small set of proctolin-immunoreactive neurons in the ventral nerve cord before and after crushing one cervical connective in the third instar. The proximal segments started sprouting within 3 days post lesion and grew into the suboesophageal ganglion within 9 days, covering a distance of approximately 2 mm. Within the suboesophageal ganglion, the regenerated neurites formed arborisations in the appropriate region which closely resemble the original shape. These findings will allow us to compare regeneration to the well-described embryonic development of axonal connectivity in this animal.

Animals↗

PubMed2003

Turning teratocarcinoma cells into neurons: rapid differentiation of NT-2 cells in floating spheres.

Cells from the human teratocarcinoma line NTera-2 can be induced to terminally differentiate into postmitotic neurons when treated with retinoic acid. However, this differentiation process is rather time consuming as it takes between 42 and 54 days. Here, we propose a modified differentiation protocol which reduces the time needed for differentiation considerably without compromising the quantity of the neurons obtained. The introduction of a proliferation step as free floating cell spheres cuts the total time needed to obtain high yields of purified NT-2 neurons to about 24-28 days. The cells obtained show neuronal morphology and migrate to form ganglion-like cell conglomerates. Differentiated cells express neuronal polarity markers such as the cytoskeleton associated proteins MAP2 and Tau. Moreover, the generation of neurons in sphere cultures induced immunoreactivity to the ELAV-like neuronal RNA-binding proteins HuC/D, which have been implicated in mechanisms of nerve cell differentiation.

Biomarkers↗

PubMed2003

Nitric oxide and cyclic nucleotides are regulators of neuronal migration in an insect embryo.

The dynamic regulation of nitric oxide synthase (NOS) activity and cGMP levels suggests a functional role in the development of nervous systems. We report evidence for a key role of the NO/cGMP signalling cascade on migration of postmitotic neurons in the enteric nervous system of the embryonic grasshopper. During embryonic development, a population of enteric neurons migrates several hundred micrometers on the surface of the midgut. These midgut neurons (MG neurons) exhibit nitric oxide-induced cGMP-immunoreactivity coinciding with the migratory phase. Using a histochemical marker for NOS, we identified potential sources of NO in subsets of the midgut cells below the migrating MG neurons. Pharmacological inhibition of endogenous NOS, soluble guanylyl cyclase (sGC) and protein kinase G (PKG) activity in whole embryo culture significantly blocks MG neuron migration. This pharmacological inhibition can be rescued by supplementing with protoporphyrin IX free acid, an activator of sGC, and membrane-permeant cGMP, indicating that NO/cGMP signalling is essential for MG neuron migration. Conversely, the stimulation of the cAMP/protein kinase A signalling cascade results in an inhibition of cell migration. Activation of either the cGMP or the cAMP cascade influences the cellular distribution of F-actin in neuronal somata in a complementary fashion. The cytochemical stainings and experimental manipulations of cyclic nucleotide levels provide clear evidence that NO/cGMP/PKG signalling is permissive for MG neuron migration, whereas the cAMP/PKA cascade may be a negative regulator. These findings reveal an accessible invertebrate model in which the role of the NO and cyclic nucleotide signalling in neuronal migration can be analyzed in a natural setting.

Actins↗

PubMed2002

Developmental expression of nitric oxide/cyclic GMP signaling pathways in the brain of the embryonic grasshopper.

Biochemical, cytochemical, and physiological investigations have demonstrated the presence of the nitric oxide/cyclic GMP signaling system in the brain of the adult locust, Schistocerca gregaria. Here, we characterize nitric oxide (NO) releasing neurons and neurons that synthesize cyclic GMP (cGMP) in response to a NO stimulus in the brain of the embryonic grasshopper. Using NADPH-diaphorase histochemistry to detect NO synthesizing cells we describe the appearance of several individually identifiable neurons. At embryonic stage 50% four NADPH-diaphorase positive neurons can be detected in each brain hemisphere. In addition to the labeling of differentiating neurons, NADPH-diaphorase staining appears also in distinct proliferative cell clusters. At embryonic stage 70% the general organization of NADPH-diaphorase activity starts to resemble the adult brain. The immunocytochemical detection of NO-induced accumulation of cGMP starts at embryonic stage 45% resulting in the staining of large neuronal populations in all brain areas. During embryonic stages 50-70%, the number of cGMP-immunoreactive cells increases from 200 to several hundred in each brain hemisphere. Since all NADPH-diaphorase positive local interneurons of the adult antennal lobe express GABA-immunoreactivity, we also report on the earliest appearance of GABA-immunoreactivity in the embryonic antennal lobe. Thus, we present a first developmental investigation of nitrergic and GABAergic transmitter phenotypes in the brain of the embryonic grasshopper.

Animals↗