The Journal of comparative neurology
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N-methyl-D-aspartate (NMDA) receptors in sensory afferents participate in chronic pain by mediating peripheral and central sensitization. We studied the presence of NMDA receptor subunits in different types of primary afferents. Western blots indicated that rat dorsal root ganglia (DRG) contain NR1, NR2B, NR2C, and NR2D but not NR2A. ⋯ The intracellular distribution of the NR2 subunits was strikingly different: Whereas NR2A/NR2B immunoreactivity was found in the Golgi apparatus and occasionally at the plasma membrane, NR2C/NR2D immunoreactivity was found in the cytoplasm but not in the Golgi. The NR1 subunit was present throughout the cytoplasm and was more intense in the Golgi. These findings indicate that DRG neurons have two different NMDA receptors, one containing the NR1, NR2D, and possibly the NR2C subunits, found only in C-fibers, and the diheteromer NR1/NR2B, present in the Golgi apparatus of both A- and C-fibers.
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Antibodies directed against choline acetyltransferase (ChAT), the synthesizing enzyme for acetylcholine (ACh) and a specific marker of cholinergic neurons, were used to label axons and nerve terminals of efferent fibers that innervate the chick basilar papilla (BP). Two morphologically distinct populations of cholinergic fibers were labeled and classified according to the region of the BP they innervated. The inferior efferent system was composed of thick fibers that coursed radially across the basilar membrane in small fascicles, gave off small branches that innervated short hair cells with large cup-like endings, and continued past the inferior edge of the BP to ramify extensively in the hyaline cell area. ⋯ The distribution of ChAT-positive efferent endings appeared very similar to the population of efferent endings that labeled with synapsin antisera. Double labeling with ChAT and synapsin antibodies showed that the two markers colocalized in all nerve terminals that were identified in BP whole-mounts and frozen sections. These results strongly suggest that all of the efferent fibers that innervate the chick BP are cholinergic.
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Inhibitory synapses with large and gephyrin-rich postsynaptic receptor areas are likely indicative of higher synaptic strength. We investigated the presynaptic inhibitory neurotransmitter content (GABA, glycine, or both) and the presence and subunit composition of GABA(A) and glycine postsynaptic receptors in one example of gephyrin-rich synapses to determine neurochemical characteristics that could also contribute to enhance synaptic strength. Hence, we analyzed subunit receptor expression in gephyrin patches located on Renshaw cells, a type of spinal interneuron that receives powerful excitatory and inhibitory inputs and displays many large gephyrin patches on its surface. ⋯ Significantly, 40% of GABA(A) receptor clusters were opposed to presynaptic boutons that contained only glycinergic markers. We postulate that GABA and glycine corelease, and the presence of alpha3-containing GABA(A) receptors can enhance the postsynaptic current and contribute to strengthen inhibitory input on Renshaw cells. In addition, a certain degree of imprecision in the localization of postsynaptic GABA(A) receptors in regard to GABA release sites onto adult Renshaw cells was also found.
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After spinal cord injury (SCI), white matter tracts are characterized by demyelination and increased sensitivity to the K(+) channel blocker 4-aminopyridine (4-AP). These effects appear to contribute to neurological impairment after SCI, although the molecular changes in K(+) channel subunit expression remain poorly understood. We examined changes in gene expression of the 4-AP-sensitive voltage-gated K(+) channel Kv 1.4 after chronic SCI in the rat. ⋯ Finally, quantitative in situ hybridization showed that Kv 1.4 mRNA was significantly upregulated in spinal cord white matter, but not gray matter, after SCI. In summary, we show that Kv 1.4 is expressed in glial cells and not in axons in the rat spinal cord white matter and that its expression is markedly increased in cells of the oligodendrocyte lineage after chronic SCI. Given that K(+) channels play a role in glial cell proliferation, cells exhibiting changes in Kv 1.4 expression may represent proliferating oligodendroglia in the chronically injured spinal cord.
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Nerve fibers immunoreactive for enzymes synthesizing catecholamines were examined in the central autonomic nucleus, a column of sympathetic preganglionic neurons, in the filefish Stephanolepis cirrhifer. Varicose nerve fibers immunoreactive for tyrosine hydroxylase were densely distributed in the rostral part, sometimes in contact with perikarya but were sparse in the caudal part of this nucleus. Fluorescent double labeling distinguished noradrenergic nerve fibers immunoreactive for both tyrosine hydroxylase and dopamine beta hydroxylase, and dopaminergic fibers immunoreactive only for tyrosine hydroxylase. ⋯ After application of DiI to the central autonomic nucleus, retrogradely labeled neurons were seen in the caudal dorsomedial medulla but not in the locus coeruleus or the area postrema. These findings suggest that the sympathetic preganglionic neurons of the filefish may receive noradrenergic axonal projections from neurons in the caudal dorsomedial medulla. In the light of previous studies, inputs of these catecholaminergic fibers to the central autonomic nucleus may be involved in regulation of sympathetic activity of peripheral organs, together with serotoninergic and peptidergic inputs to this nucleus.