The Release of Substance P From Cultured Dorsal Root Ganglion Neurons Requires the Non-neuronal Cells Around These Neurons

Immunoreactivity of glutamine synthetase in satellite glia around various subpopulations of lumbar dorsal root ganglia neurons in adult rats treated with monosodium glutamate

Satellite glial cells (SGCs), involved inter alia in glutamate (Glu) metabolism, form a glial sheath around sensory neurons of dorsal root ganglia (DRGs). SGCs show a presence of glutamine synthetase (GS) which transform uptaken Glu into glutamine (Gln). In DRGs, this aminoacid is used mainly by small neurons which are able to synthetize substance P (SP) that play a crucial role in nociception. The aim of the study was to define the influence of monosodium glutamate (MSG) on GS immunoreactivity in satellite glia around various subpopulations of neurons including SP immunopositive cells in DRGs of adult rats. The studies were carried out on lumbar DRGs slides in rats which received subcutaneous injection of saline solution (control group) or 4 g/kg b. w. of MSG (MSG group). Immunofluorescence reactions were conducted with use of anti-GS and anti-SP antibodies. Administration of MSG to adult rats increased the GS immunoexpression in SGCs. In rats receiving MSG, a number of small neurons with GS-immunopositive glial sheath was not altered when compared to control individuals, whereas there was a statistically significant increase of GS immunoexpression in SGCs around large and medium neurons. Moreover, in these animals, a statistically significant increase in the number of small SP-positive neurons with GS-positive glial sheath was observed. SP is responsible for transmission of pain, thus the obtained results may be useful for further research concerning the roles of glia in nociceptive pathway regulation.

Involvement of mast cells and proteinase-activated receptor 2 in oxaliplatin-induced mechanical allodynia in mice

The chemotherapeutic agent oxaliplatin induces neuropathic pain, a dose-limiting side effect, but the underlying mechanisms are not fully understood. Here, we show the potential involvement of cutaneous mast cells in oxaliplatin-induced mechanical allodynia in mice. A single intraperitoneal injection of oxaliplatin induced mechanical allodynia, which peaked on day 10 after injection. Oxaliplatin-induced mechanical allodynia was almost completely prevented by congenital mast cell deficiency. The numbers of total and degranulated mast cells was significantly increased in the skin after oxaliplatin administration. Repetitive topical application of the mast cell stabilizer azelastine hydrochloride inhibited mechanical allodynia and the degranulation of mast cells without affecting the number of mast cells in oxaliplatin-treated mice. The serine protease inhibitor camostat mesilate and the proteinase-activated receptor 2 (PAR2) antagonist FSLLRY-NH2 significantly inhibited oxaliplatin-induced mechanical allodynia. However, it was not inhibited by the H1 histamine receptor antagonist terfenadine. Single oxaliplatin administration increased the activity of cutaneous serine proteases, which was attenuated by camostat and mast cell deficiency. Depletion of the capsaicin-sensitive primary afferents by neonatal capsaicin treatment almost completely prevented oxaliplatin-induced mechanical allodynia, the increase in the number of mast cells, and the activity of cutaneous serine proteases. These results suggest that serine protease(s) released from mast cells and PAR2 are involved in oxaliplatin-induced mechanical allodynia. Therefore, oxaliplatin may indirectly affect the functions of mast cells through its action on capsaicin-sensitive primary afferents.

Up-Regulation of the Biosynthesis and Release of Substance P through Wnt/β-Catenin Signaling Pathway in Rat Dorsal Root Ganglion Cells

To examine regulatory effects of β-catenin on the biosynthesis and release of substance P, a rat chronic constriction injury (CCI) model and a rat dorsal root ganglion (DRG) cell culture model were used in the present study. The CCI treatment significantly induced the overall expression of β-catenin (158 ± 6% of sham) in the ipsilateral L5 DRGs in comparison with the sham group (109 ± 4% of sham). The CCI-induced aberrant expression of β-catenin was significantly attenuated by oral administration of diclofenac (119 ± 6% of the sham value; 10 mg/kg). Importantly, aberrant nuclear accumulation of β-catenin in cultured DRG cells resulted in up-regulation of the PPT-A mRNA expression and the substance P release. The up-regulation of both the PPT-A mRNA expression and the substance P release by either a GSK-3β inhibitor TWS119 (10 μM) or a Wnt signaling agonist Wnt-3a (100 ng/ml) were significantly abolished by an inhibitor of cyclooxygenase-2 (COX-2; NS-398, 1 μM). Collectively, these data suggest that nociceptive input-activated β-catenin signaling plays an important role in regulating the biosynthesis and release of substance P, which may contribute to the inflammation responses related to chronic pain.

The role of glial cells in influencing neurite extension by dorsal root ganglion cells

When pretreated with pertussis toxin (PTX), the neurites of adult rat dorsal root ganglion (DRG) cells in mixed cell cultures retract over a period of 2 h following the initial stimulus of removal from the cell culture incubator for brief periods of observation. The purpose of this investigation was to determine whether this PTX-dependent response was specific to any one of the three subpopulations of DRG neurons. However, no neurite retraction response was observed in neuron-enriched populations of cells, or in cultures enriched in isolectin B4 (IB4)-positive neurons or in IB4-negative neurons. But, the addition of non-neuronal cells, and/or medium conditioned by non-neuronal cells, was sufficient to restore the PTX-dependent neurite retraction response, but only in large diameter IB4-negative neurons. In conclusion, we have identified a regulatory response, mediated by Gi/o-proteins, which prevents retraction of neurites in large diameter IB4-negative cells of adult rat DRG. The non-neuronal cells of adult rat DRG constitutively release factor/s that can stimulate neurite retraction of a subset of isolated DRG neurons, but this property of non-neuronal cells is only observed when the Gi/o-proteins of large diameter IB4-negative cells are inhibited.

Involvement of voltage-gated sodium channel Na(v)1.8 in the regulation of the release and synthesis of substance P in adult mouse dorsal root ganglion neurons

This study was conducted to determine whether Na(v)1.8 contributes to the release and/or synthesis of substance P (SP) in adult mice dorsal root ganglion (DRG) neurons. The SP released from cultured DRG neurons of Na(v)1.8 knock-out mice exposed to either capsaicin or KCl was significantly lower than that from wild-type (C57BL/6) mice based on a radioimmunoassay. The SP level of L6 DRG in Na(v)1.8 knock-out mice was also lower than that in wild-type mice. After chronic constriction injury (CCI) of the sciatic nerve, the level of SP decreased in the L6 ipsilateral DRG of wild-type but not Na(v)1.8 knock-out mice. The preprotachykinin-A (PPT-A) mRNAs in L4 - 6 DRGs of Na(v)1.8 knock-out mice also fell to half their normally abundant levels of expression. There were significant increases in Na(v)1.8 expression of the L6 contralateral DRG from wild-type mice and in the percentage of neurons expressing neurokinin-1 receptor in the cytosol of L6 DRGs from wild-type or Na(v)1.8 knock-out mice. These findings suggest that Na(v)1.8 is involved in the regulation of the release and synthesis of SP in the DRG neurons of wild-type mice.