Neuroscience
-
Comparative Study
Expression of pannexin1 in the CNS of adult mouse: cellular localization and effect of 4-aminopyridine-induced seizures.
The expression pattern of pannexin1, a gene coding for a protein that forms gap junction channels, was studied as both mRNA and protein in the CNS of adult mouse. Pannexin1 was widely expressed in the CNS by neuronal cell types but not glial cells, except for Bergmann glial cells of the cerebellar cortex. Cells positive to Ca-binding proteins, principally parvalbumin, but also calbindin and calretinin, as well as glutamate decarboxylase 67 kDa isoform, were pannexin1-positive. ⋯ Since connexin36 expression levels change after seizures, we examined the expression of both pannexin1 and connexin36 in cerebral cortex, hippocampus, cerebellum and brain stem at different time intervals (2, 4 and 8 h) after i.p. injection of 4-aminopyridine, which resulted in systemic seizures. The only modification of the expression levels observed in this study concerned the progressive decrement of the connexin36 in the hippocampus, while pannexin1 expression was unchanged. This finding suggested that pannexin1 and connexin36 are involved in different functional roles or that they are expressed in different cell types and that only those expressing the Cx36 are induced to apoptosis by epileptic seizures.
-
Comparative Study
The tyrosine receptor kinase B ligand, neurotrophin-4, is not required for either epileptogenesis or tyrosine receptor kinase B activation in the kindling model.
The kindling model of epilepsy is a form of neuronal plasticity induced by repeated induction of pathological activity in the form of focal seizures. A causal role for the neurotrophin receptor, tyrosine receptor kinase B, in epileptogenesis is supported by multiple studies of the kindling model. Not only is tyrosine receptor kinase B required for epileptogenesis in this model but enhanced activation of tyrosine receptor kinase B has been identified in the hippocampus in multiple models of limbic epileptogenesis. ⋯ No differences were found between +/+ and -/- mice with respect to any facet of the development or persistence of kindling. Despite the absence of NT4, activation of the tyrosine receptor kinase B receptor in the mossy fiber pathway as assessed by phospho-trk immunohistochemistry was equivalent to that of +/+ mice. Together these findings demonstrate that NT4 is not required for limbic epileptogenesis nor is it required for activation of tyrosine receptor kinase B in hippocampus during limbic epileptogenesis.
-
Two cold-sensitive transient receptor potential (TRP) channels, TRPA1 and TRPM8, have been identified and considered interesting because of their possible roles in thermosensation, nociception and other functions. Recently, we have reported that the phosphorylation of extracellular signal-regulated protein kinase and p38 mitogen-activated protein kinase occurred in primary afferent neurons in response to noxious heat stimulation of the peripheral tissue, i.e. activity-dependent activation of extracellular signal-regulated protein kinase and p38 in dorsal root ganglion neurons. In the present study, we investigated the phosphorylation of extracellular signal-regulated protein kinase, p38, and c-Jun N-terminal kinase in the rat dorsal root ganglion by cold stimulation using immunohistochemistry. ⋯ We then performed double-labeling experiments for TRPA1 and TRPM8 mRNA and phosphorylation of mitogen-activated protein kinase. The majority of phosphorylated-extracellular signal-regulated protein kinase-positive neurons also expressed TRPM8 mRNA, whereas phosphorylated-p38 heavily colocalized with TRPA1 mRNA after noxious cold stimulation. Our data suggest that the noxious, but not innocuous, cold stimulation in vivo induced differential activation of extracellular signal-regulated protein kinase and p38 pathways in each subpopulation containing TRPA1 or TRPM8 in dorsal root ganglion.
-
This study evaluated the plastic changes of c-jun and c-fos in the right sixth lumbar dorsal root ganglion (L6 DRG), Rexed's lamina II in representative spinal segments L3, L5, and L6 and in the nucleus dorsalis (ND) at L3 segments after electro-acupuncture (EA) in cats subjected to removal of L1-L5 and L7-S2 DRG. Following dorsal root ganglionectomy, there was a significant increase in the density of c-jun immunoreactivity in the neurons and glia in spinal lamina II and in the ND; there was also marked elevation in the expression of c-fos in ND. In both cases there was no change in the c-jun and c-fos immunoreactivity in the DRG. ⋯ Following partial deafferentation, there was a significant increase in the protein level of both c-jun and c-fos in the dorsal horn, while, in both cases there was no change in c-jun and c-fos protein and mRNA in the DRG. After EA in the operated animals, both c-jun protein and its mRNA in the L6 DRG as well as the associated dorsal horn of L6 spinal segment were upregulated, but increased c-fos protein and its mRNA was observed only in the L6 DRG. These findings suggested that c-jun and c-fos might be related to the acupuncture promoted spinal cord plasticity as reported previously.
-
In vitro studies have demonstrated that prolonged N-methyl-D-aspartate receptor (NMDAR) blockade triggers a homeostatic up-regulation of NMDARs at synapses. Such upregulation can also be seen within 30 min in vivo in adult rats, implicating trafficking of reserve pools of NMDARs. Here, we evaluated the involvement of filamentous actin (F-actin), the major cytoskeletal component in spines, in this rapid in vivo homeostatic response, using biotinylated phalloidin as its probe. ⋯ However, the average postsynaptic density length was reduced by 25 nm among the fewer, drebrin A immuno-negative spines, indicating that drebrin A confers stability to synapse size. We propose that, in a homeostatic in vivo response, increases of drebrin A and F-actin within spines can enhance NMDAR trafficking by reducing cytoskeletal rigidity within the spine cytoplasm without changing the overt morphology of axo-spinous synapses. Alternatively or in addition, the cytoskeletal redistribution within spine cytoplasm may be triggered by the D-APV-induced, homeostatic up-regulation of NMDAR.