Cs. Toomim et Wr. Millington, Regional and laminar specificity of kainate-stimulated cobalt uptake in the rat hippocampal formation, J COMP NEUR, 402(2), 1998, pp. 141-154
Kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA
) receptors were initially found to be impermeable to calcium, but cloning
and expression studies subsequently revealed that certain kainate and AMPA
receptor subunit combinations display substantial divalent cation permeabil
ity. The regional and cellular distribution of calcium-permeable kainate/AM
PA receptors has not been extensively investigated, however. In this study,
we used a histochemical technique, the kainate-stimulated cobalt uptake as
say, to localize calcium-permeable kainate responsive receptors in the rat
hippocampal formation. In the presence of cobalt, kainate produced a highly
localized, dark granular precipitate in dendrites, perikarya, or both, of
hippocampal neurons. Kainate-stimulated cobalt uptake was time- and concent
ration-dependent (1 mu M-1 mM) and was blocked by the glutamate receptor an
tagonist, kynurenate. The specific cellular location of cobalt labeling var
ied regionally within the hippocampal formation, switching from selective l
abeling of only apical dendrites in Ammon's horn subregion 1a (CA1a) to a d
iffuse band of punctate labeling in CA1c to labeling of cell bodies along w
ith their proximal dendrites in CA3. Furthermore, increasing the kainate co
ncentration not only enhanced the intensity of cobalt labeling, but also ch
anged the pattern of cellular staining from exclusively dendritic labeling
to extensive staining of both cell bodies and dendrites in CA1a pyramidal n
eurons. High kainate concentrations or prolonged incubation times produced
a diffuse cellular labeling suggestive of neurotoxicity. These data are con
sistent with evidence that specific kainate and AMPA receptor subunit combi
nations are targeted to specific synapses in hippocampal pyramidal neurons.
J. Comp. Neurol. 402:141-154, 1998. (C) 1998 Wiley-Liss, Inc.