K. Zavitsanou et al., AUTORADIOGRAPHIC CHARACTERIZATION OF [H-3] 6-CYANO-7-NITROQUINOXALINE-2,3-DIONE BINDING-SITES IN ADULT CHICK BRAIN, Neuroscience, 62(3), 1994, pp. 955-962
The non-N-methyl-D-aspartate binding sites have been characterized in
chick brain using quantitative autoradiography, and 6-cyano-7-nitroqui
noxaline-2,3-dione (CNQX) as a radioligand. [H-3]CNQX binding sites we
re densely localized in the molecular layer of cerebellum. Other areas
of prominent binding were the superficial layers of optic tectum, one
of the isthmic nuclei, the hippocampus, the hyperstriatum accessorium
and the archistriatum ventrale. Analysis of equilibrium binding data
in the cerebellar molecular layer indicated that [H-3]CNQX bound to a
single class of sites (K-d = 78.9 +/- 11.8 nM and B-max = 41.2 +/- 3.0
pmol/mg protein). Competition experiments in six different regions of
chick brain gave the K-i and B-max values for the inhibition of [H-3]
CNQX binding by various standard compounds and indicated that: (i) [H-
3]CNQX labelled non-N-methyl-D-aspartate binding sites with high affin
ity for (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid
(AMPA) and kainate, (ii) the displacement curves for AMPA and kainate
were biphasic in all regions studied, and (iii) the potencies of AMPA
and kainate in displacing [H-3]CNQX binding were different in the reg
ions studied. Our results indicate that [H-3]CNQX labelled non N-methy
l-D-aspartate binding sites in chick brain. In the cerebellar molecula
r layer, these sites were more sensitive to kainate than AMPA, as were
the binding sites in the superficial layers of optic tectum and nucle
us isthmi magnocellularis. However, non-N-methyl-D-aspartate binding s
ites in forebrain regions such as hippocampus and hyperstriatum ventra
le appeared to be different in being equally sensitive to AMPA and kai
nate.