On the 48÷80-induced secretion of tissue mast cells and its mitogenic effect on nearby cells in the intact rat

Histamine release from tissue-bound mast cells and cell proliferation in the proper mesentery in the intact rat was quantitated following in intraperitoneal injection of graded doses of compound 48/80. The dose-response curves were sigmoid-like in linear-log plots. ED50 for histamine release was 0.035-0.040 and for increased cell proliferation 0.040-0.048 microgram per g BW. The proliferative response following mast-cell secretion ceased after a period of between 48-72 h, irrespective of whether a high or a low dose of 48/80 was used. Basal on the net rate of histamine synthesis (ca. 0.45 microgram/g mesentery wet weight/h) after an initial injection of 48/80, on the extent of histamine release and the proliferative response after a repeated injection of 48/80, it is concluded that there is a lag period of at least 3 days before proliferation can be re-stimulated by renewed 48/80-induced mast-cell secretion.     

Regulation of EphA 4 kinase activity is required for a subset of axon guidance decisions suggesting a key role for receptor clustering in Eph function

Signaling by receptor tyrosine kinases (RTKs) is mediated by their intrinsic kinase activity. Typically, kinase-activating mutations result in ligand-independent signaling and gain-of-function phenotypes. Like other RTKs, Ephs require kinase activity to signal, but signaling by Ephs in vitro also requires clustering by their membrane bound ephrin ligands. The relative importance of Eph kinase activity and clustering for in vivo functions is unknown. We find that knockin mice expressing a mutant form of EphA4 (EphA4(EE)), whose kinase is constitutively activated in the absence of ephrinB ligands, are deficient in the development of thalamocortical projections and some aspects of central pattern generator rhythmicity. Surprisingly, other functions of EphA4 were regulated normally by EphA4(EE), including midline axon guidance, hindlimb locomotion, in vitro growth cone collapse, and phosphorylation of ephexin1. These results suggest that signaling of Eph RTKs follows a multistep process of induced kinase activity and higher-order clustering different from RTKs responding to soluble ligands.     

Nitrosylation precedes caspase-3 activation and translocation of apoptosis-inducing factor in neonatal rat cerebral hypoxia-ischaemia

Excessive nitric oxide (NO) production after cerebral hypoxia-ischaemia (HI) may induce cellular injury in various ways, including reaction with superoxide to form the highly reactive peroxynitrite. We characterized the spatial and temporal formation of peroxynitrite through immunohistochemical detection of nitrosylated proteins. Nitrotyrosine immunoreactivity peaked around 3 h post-HI and was detected in areas of injury, as judged by the loss of microtubule-associated protein-2 (MAP-2) staining, in neurones, glia and endothelial cells. Nitrotyrosine staining co-localized with three other cellular markers of injury, active caspase-3, nuclear translocation of apoptosis-inducing factor (AIF) and an oligonucleotide hairpin probe detecting specific DNA strand breaks. The number of nitrotyrosine-positive cells at early time points outnumbered the cells positive for the other three markers of injury, indicating that nitrosylation preceded caspase-3 activation. Pharmacological inhibition of neuronal and inducible nitric oxide synthase (nNOS and iNOS) using 2-iminobiotin, which has been demonstrated earlier to be neuroprotective, significantly reduced nitrotyrosine formation and caspase-3 activation, but not nuclear translocation of AIF, in cortex and striatum of the ipsilatral hemisphere. In summary, nitrotyrosine is an early marker of cellular injury and inhibition of nNOS and iNOS is a promising strategy for neuroprotection after perinatal HI.     

Fluorescence Time-lapse Imaging of the Complete S. venezuelae Life Cycle Using a Microfluidic Device

Live-cell imaging of biological processes at the single cell level has been instrumental to our current understanding of the subcellular organization of bacterial cells. However, the application of time-lapse microscopy to study the cell biological processes underpinning development in the sporulating filamentous bacteria Streptomyces has been hampered by technical difficulties. Here we present a protocol to overcome these limitations by growing the new model species, Streptomyces venezuelae, in a commercially available microfluidic device which is connected to an inverted fluorescence widefield microscope. Unlike the classical model species, Streptomyces coelicolor, S. venezuelae sporulates in liquid, allowing the application of microfluidic growth chambers to cultivate and microscopically monitor the cellular development and differentiation of S. venezuelae over long time periods. In addition to monitoring morphological changes, the spatio-temporal distribution of fluorescently labeled target proteins can also be visualized by time-lapse microscopy. Moreover, the microfluidic platform offers the experimental flexibility to exchange the culture medium, which is used in the detailed protocol to stimulate sporulation of S. venezuelae in the microfluidic chamber. Images of the entire S. venezuelae life cycle are acquired at specific intervals and processed in the open-source software Fiji to produce movies of the recorded time-series.     

VGLUT2 controls heat and punctuate hyperalgesia associated with nerve injury via TRPV1-Cre primary afferents

Nerve injury induces a state of prolonged thermal and mechanical hypersensitivity in the innervated area, causing distress in affected individuals. Nerve injury-induced hypersensitivity is partially due to increased activity and thereby sustained release of neurotransmitters from the injured fibers. Glutamate, a prominent neurotransmitter in primary afferents, plays a major role in development of hypersensitivity. Glutamate is packed in vesicles by vesicular glutamate transporters (VGLUTs) to enable controlled release upon depolarization. While a role for peripheral VGLUTs in nerve injury-induced pain is established, their contribution in specific peripheral neuronal populations is unresolved. We investigated the role of VGLUT2, expressed by transient receptor potential vanilloid (TRPV1) fibers, in nerve injury-induced hypersensitivity. Our data shows that removal of Vglut2 from Trpv1-Cre neurons using transgenic mice abolished both heat and punctuate hyperalgesia associated with nerve injury. In contrast, the development of cold hypersensitivity after nerve injury was unaltered. Here, we show that, VGLUT2-mediated glutamatergic transmission from Trpv1-Cre neurons selectively mediates heat and mechanical hypersensitivity associated with nerve injury. Our data clarifies the role of the Trpv1-Cre population and the dependence of VGLUT2-mediated glutamatergic transmission in nerve injury-induced hyperalgesia.     

Role of glutamate in locomotor rhythm generating neuronal circuitry

Central pattern generators (CPGs) are defined as neuronal circuits capable of producing a rhythmic and coordinated output without the influence of sensory input. The locomotor and respiratory neuronal circuits are two of the better-characterized CPGs, although much work remains to fully understand how these networks operate. Glutamatergic neurons are involved in most neuronal circuits of the nervous system and considerable efforts have been made to study glutamate receptors in nervous system signaling using a variety of approaches. Because of the complexity of glutamate-mediated signaling and the variety of receptors triggered by glutamate, it has been difficult to pinpoint the role of glutamatergic neurons in neuronal circuits. In addition, glutamate is an amino acid used by every cell, which has hampered identification of glutamatergic neurons. Glutamatergic excitatory neurotransmission is dependent on the release from glutamate-filled presynaptic vesicles loaded by three members of the solute carrier family, Slc17a6-8, which function as vesicular glutamate transporters (VGLUTs). Recent data describe that Vglut2 (Slc17a6) null mutant mice die immediately after birth due to a complete loss of the stable autonomous respiratory rhythm generated by the pre-B?tzinger complex. Surprisingly, we found that basal rhythmic locomotor activity is not affected in Vglut2 null mutant embryos. With this perspective, we discuss data regarding presence of VGLUT1, VGLUT2 and VGLUT3 positive neuronal populations in the spinal cord.