Differential expression patterns of K super(+)/Cl super(-) cotransporter 2 in neurons within the superficial spinal dorsal horn of rats

• Published in: Journal of comparative neurology (1911) 2015-09, Vol.523 (13), p.1967-1983
• Main Authors: Javdani, Fariba, Hollo, Krisztina, Hegeds, Krisztina, Kis, Greta, Hegyi, Zoltan, Docs, Klaudia, Kasugai, Yu, Fukazawa, Yugo, Shigemoto, Ryuichi, Antal, Miklos
• Format: Article
• Language: English
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23774

gamma -Aminobutyric acid (GABA)- and glycine-mediated hyperpolarizing inhibition is associated with a chloride influx that depends on the inwardly directed chloride electrochemical gradient. In neurons, the extrusion of chloride from the cytosol primarily depends on the expression of an isoform of potassium-chloride cotransporters (KCC2s). KCC2 is crucial in the regulation of the inhibitory tone of neural circuits, including pain processing neural assemblies. Thus we investigated the cellular distribution of KCC2 in neurons underlying pain processing in the superficial spinal dorsal horn of rats by using high-resolution immunocytochemical methods. We demonstrated that perikarya and dendrites widely expressed KCC2, but axon terminals proved to be negative for KCC2. In single ultrathin sections, silver deposits labeling KCC2 molecules showed different densities on the surface of dendritic profiles, some of which were negative for KCC2. In freeze fracture replicas and tissue sections double stained for the beta 3-subunit of GABA sub(A) receptors and KCC2, GABA sub(A) receptors were revealed on dendritic segments with high and also with low KCC2 densities. By measuring the distances between spots immunoreactive for gephyrin (a scaffolding protein of GABA sub(A) and glycine receptors) and KCC2 on the surface of neurokinin 1 (NK1) receptor-immunoreactive dendrites, we found that gephyrin-immunoreactive spots were located at various distances from KCC2 cotransporters; 5.7 % of them were recovered in the middle of 4-10- mu m-long dendritic segments that were free of KCC2 immunostaining. The variable local densities of KCC2 may result in variable postsynaptic potentials evoked by the activation of GABA sub(A) and glycine receptors along the dendrites of spinal neurons. J. Comp. Neurol. 523:1967-1983, 2015 Investigation of the cellular distribution of KCC2 in the spinal dorsal horn of rats revealed that KCC2 molecules were inhomogeneously distributed on the surface of dendrites. GABAergic and glycinergic synapses were revealed on dendritic segments with high and low KCC2 densities, and also on those that were free of KCC2.