Indirect actions of bradykinin on neonatal rat dorsal root ganglion neurones: a role for non-neuronal cells as nociceptors.
(1/46)
1. In this study we have investigated the action of bradykinin (Bk) on cultured neonatal rat dorsal root ganglion (DRG) cells, with the aim of elucidating whether the neuronal response to Bk is influenced by association with non-neuronal satellite cells. 2. Bradykinin (100 nM) evoked an inward current (I(Bk)) in 51 of 58 voltage clamped DRG neurones (holding potential (V(h)) = -80 mV) that were in contact with non-neuronal satellite cells. 3. Bradykinin failed to evoke an inward current in isolated DRG neurones (V(h) = -80 mV) that were not in contact with non-neuronal satellite cells (n = 41). 4. The lack of neuronal response to Bk was not influenced by time in culture. Bradykinin failed to evoke a response in isolated neurones through 1-5 days in culture. By contrast neurones in contact with satellite cells responded to Bk throughout the same time period. 5. Failure of isolated neurones to respond to Bk was not due to the replating procedure or to selective subcellular distribution of receptors/ion channels to the processes rather than the somata of neurones. 6. Using Indo-1 AM microfluorimetry Bk (100 nM) was demonstrated to evoke an intracellular Ca(2+) increase (Ca(Bk)) in DRG neurones in contact with non-neuronal satellite cells and in isolated neurones. 7. These data suggest that the inward current response to Bk requires contact between DRG neurones and non-neuronal satellite cells. This implies an indirect mechanism of action for Bk via the non-neuronal cells, which may perform a nociceptive role. However, Bk can also act directly on the neurones, since it evokes Ca(Bk) in isolated neurones. The relationship between Ca(Bk) and the Bk-induced inward current is unknown at present. (+info)
Effects of growth factors on insulin-like growth factor binding protein (IGFBP) secretion by primary porcine satellite cell cultures.
(2/46)
Insulin-like growth factor-binding proteins (IGFBP) regulate the biological functions of insulin-like growth factors (IGF) and may affect cell growth through IGF-independent actions. Growth factors and hormones have been shown to alter IGFBP production by target cells suggesting that the effects of these factors may be partially mediated by the local production of IGFBP. Growth factors, including IGF-I, transforming growth factor-beta1 (TGF-beta1), and basic fibroblast growth factor (bFGF) have potent effects on satellite cell proliferation and differentiation, and some of these factors have been shown to alter IGFBP production in various cell types. Consequently, some of their actions on muscle satellite cells may be mediated by the local production of IGFBP. In this study, we measured the effects of IGF-I, bFGF, and TGF-beta1 on IGFBP production by primary porcine satellite cell (PSC) cultures after first determining physiologically active concentrations of these growth factors to use according to [3H]thymidine incorporation dose responses. There is little information on the effects of these growth factors on IGFBP production in primary porcine myogenic cells due to the confounding affects of contaminating nonmuscle fibroblasts. Comparative studies show that primary porcine satellite cells produce IGFBP-3 and -5 whereas porcine muscle-derived nonfusing cells (FIB) produce IGFBP-2 and -4 but not IGFBP-3 or -5. Because of this, our investigations have focused on growth factor-induced production of IGFBP-3 and -5 in primary porcine satellite cells cultures. Both IGF-I and bFGF exhibited dose-dependent increases in [3H]thymidine incorporation with increasing concentration from 1 to 50 ng/mL (P < 0.05), whereas TGF-beta1 caused a dose-dependent decrease from 0.01 to 0.5 ng/mL (P < 0.05). When 20 ng/ mL of IGF-I was added to the media, IGFBP-3 was increased approximately 65% (P < 0.05) and IGFBP-5 was increased approximately twofold (P < 0.05). The addition of 0.5 ng/mL TGF-beta1 caused more than a two-fold increase in IGFBP-3 (P < 0.05) and approximately an 80% increase in IGFBP-5 (P < 0.05), whereas 50 ng/ mL of bFGF caused approximately 40% (P < 0.05) and 70% (P < 0.05) increases in IGFBP-3 and -5, respectively. Neither IGFBP-3 nor -5 was detectable in the conditioned media from fibroblasts whether or not IGF-I, TGF- beta1 or bFGF were present. These data suggest that the effects of IGF-I, TGF- beta1 and bFGF on porcine satellite cells may in part be through the autocrine/ paracrine production of IGFBP-3 and -5 by porcine satellite cells. (+info)
There are many known growth factors/cytokines that induce skeletal muscle satellite cell proliferation. Currently, the signaling mechanisms in which these growth factors/cytokines activate satellite cell proliferation are not completely understood. Here, we sought to determine signaling mechanisms by which leukemia inhibitory factor (LIF) induces satellite cell proliferation in culture. First, we confirmed that LIF induces proliferation of C2C12 immortalized myoblasts and cultured primary rat satellite cells. In addition, we also found that this increase in proliferation can be inhibited by incubation of the cells in tyrphostin AG 490, a specific inhibitor of Janus-activated kinase (JAK) 2 activity. Furthermore, we also found that incubation of the cells at various time points with LIF (10 ng/ml) induces a significant, transient increase in JAK2 phosphorylation, signal transducers and activators of transcription (STAT3) phosphorylation, and STAT3 transcriptional activity. Increases in the STAT3-sensitive endogenous SOC3 protein followed these transient increases in STAT3 activation. In addition, AG 490 inhibited the increase in STAT3 phosphorylation. Finally, LIF did not change the phosphorylation status of extracellular signal-regulated protein kinase (ERK)1/2 or affect the phosphorylation status of Akt/protein kinase B. However, LY-294002, an inhibitor of phosphoinositide 3-kinase, blocked LIF-induced proliferation of satellite cells. These data suggest that LIF induces satellite cell proliferation by activation of the JAK2-STAT3 signaling pathway, suggesting that this may be an important pathway in muscle growth and/or hypertrophy. (+info)
Expression of glutamate transporter GLAST in the developing mouse cochlea.
(4/46)
The immunohistochemical localization of glutamate transporter GLAST in the developing mouse cochlea was studied at different ages between 0 and 30 days after birth (DAB). In the adult mouse cochlea, intense GLAST-like immunoreactivity was found in the supporting cells adjacent to the inner hair cells of the organ of Corti, the type II and suprastrial fibrocytes of the cochlear lateral wall, the fibrocytes of the spiral limbus and the satellite cells surrounding the spiral ganglion cells. At 0 DAB, weak GLAST-like immunoreactivity was found in the supporting cells around the immature inner hair cells. Immature fibrocytes in the cochlea were also positively immunostained. At 3 DAB, weak immunostaining of GLAST appeared in the immature satellite cells in the spiral ganglion. The GLAST-like immunoreactivity in the supporting cells around the inner hair cells, in the fiborocytes in the spiral ligament and the spiral limbus and in the satellite cells in the spiral ganglion increased progressively during the second postnatal week, and reached the adult level at 15 DAB. This time course correlates with the electrophysiological onset and maturation of the mouse auditory function, which is mediated by glutamatergic neurotransmission. These results suggest that the expression of GLAST may be needed for the efficient removal and metabolism of the released glutamate in the cochlea and may play important roles in the onset and maturation of the auditory system. (+info)
Selective reactions of cutaneous and muscle afferent neurons to peripheral nerve transection in rats.
(5/46)
To determine whether peripheral nerve injury has similar effects on all functional types of afferent neuron, we retrogradely labeled populations of neurons projecting to skin and to muscle with FluoroGold and lesioned various peripheral nerves in the rat. Labeled neurons were counted after different periods and related to immunohistochemically identified ectopic terminals and satellite cells in lumbar dorsal root ganglia. After 10 weeks, 30% of cutaneous afferent somata labeled from transected sural nerves had disappeared but, if all other branches of the sciatic nerve had also been cut, 60% of cutaneous neurons were lost. Small-diameter sural neurons preferentially disappeared. In contrast, the number of muscle afferent somata was not affected by transection of various nerves. p75 was downregulated in axotomized cutaneous neurons but in not axotomized muscle neurons. Conversely, p75 was upregulated in satellite cells around cutaneous but not muscle neurons. Consistent with this, perineuronal rings containing tyrosine hydroxylase, calcitonin gene-related peptide, galanin, or synaptophysin were formed preferentially around cutaneous neurons. Selective lesions of predominantly cutaneous nerves triggered the formation of rings, but none were detected after selective lesions of muscle nerves. We conclude that cutaneous neurons are both more vulnerable and more associated with ectopic nerve terminals than muscle neurons in dorsal root ganglia after transection and ligation of peripheral nerves. (+info)
Morphometric study of age-related changes in the human intracardiac ganglia.
(6/46)
The present study was performed in order to determine morphological age-related changes of the human intracardiac ganglia. Paraffin sections of 40 ganglia from infants, adult and aged human hearts were stained with Picro-Mallory method. The ganglia area, nerve cell (with clearly visible nucleolus) area, neuron soma long axis length, perimeter, area of neuronal nuclei and neuron soma form factor were measured with the aid of computer images analyzing program "Sigma Scan Pro 5.0". Also, the neuronal density and the area occupied by nerve cells per ganglion section were calculated. The relative frequency of satellite cells, in close contact with nerve cell soma, was estimated. Based on the data of this study, we concluded that the area of ganglia, neurons and their nuclei increased with age. Neuronal packing density significantly decreased, but the area occupied by nerve cells within the ganglia decreased non-significantly. Satellite cells were more numerous nearby ganglion neurons from infant hearts. Shape factor of neurons was stable between the groups. In conclusion, the present study confirms significant differences in the morphology of the intrinsic cardiac ganglia with age. (+info)
VEGF is required for the maintenance of dorsal root ganglia blood vessels but not neurons during development.
(7/46)
Vascular endothelial growth factor (VEGF) is a potent regulator of vascular function through its control of multiple endothelial cell functions. In addition to its key role in vascularization, VEGF has recently been shown to have neurotrophic activity during hypoxic stress. In the central and peripheral motor nervous system, VEGF treatment increased neuronal vascularization and perfusion, as well as having direct trophic effects on neurons and Schwann cells. However, the role of VEGF in the sensory nervous system remains unclear. To characterize the differential effects of VEGF on endothelial cells and neurons in sensory ganglia, we used explanted mouse dorsal root ganglia (DRG), a culture system containing neurons and endothelial cells in close apposition. We show that VEGF is expressed by neurons and satellite cells, but not by endothelial cells or pericytes. On the other hand, the tyrosine kinase VEGF receptor VEGFR-2 was robustly expressed by endothelial cells throughout the extensive DRG capillary network, but not found at either the transcript or protein level in sensory neurons or other nonendothelial cells of the DRG. Both soluble receptor sequestration of VEGF and small molecule kinase inhibition of VEGFR-2 signaling rapidly disrupted the connectivity, branching, and structural integrity of the capillary network of embryonic DRG; this effect was no longer evident postnatally. However, VEGF inhibition showed no detectable effect on neuronal health at any stage analyzed. These data suggest that endogenous VEGF is a strict requirement for vascular, but not neuronal, maintenance in developing sensory ganglia. (+info)
New GABAergic interneurons in the adult neocortex and striatum are generated from different precursors.
(8/46)
Ongoing neurogenesis in the adult mammalian dentate gyrus and olfactory bulb is generally accepted, but its existence in other adult brain regions is highly controversial. We labeled newly born cells in adult rats with the S-phase marker bromodeoxyuridine (BrdU) and used neuronal markers to characterize new cells at different time points after cell division. In the neocortex and striatum, we found BrdU-labeled cells that expressed each of the eight neuronal markers. Their size as well as staining for gamma-aminobutyric acid (GABA), glutamic acid decarboxylase 67, calretinin and/or calbindin, suggest that new neurons in both regions are GABAergic interneurons. BrdU and doublecortin-immunoreactive (BrdU+/DCX+) cells were seen within the striatum, suggesting migration of immature neurons from the subventricular zone. Surprisingly, no DCX+ cells were found within the neocortex. NG2 immunoreactivity in some new neocortical neurons suggested that they may instead be generated from the NG2+ precursors that reside within the cortex itself. (+info)