Journal of Neuroscience, Vol 11, 287-297, Copyright © 1991 by Society for Neuroscience
Autoradiographic localization of putative nicotinic receptors in the rat brain using 125I-neuronal bungarotoxin
DW Schulz, RH Loring, E Aizenman and RE Zigmond
Department of Biological Chemistry, Harvard Medical School, Boston, Massachusetts.
Neuronal bungarotoxin (NBT), a snake venom neurotoxin, selectively blocks
nicotinic receptors in many peripheral and central neuronal preparations.
alpha-Bungarotoxin (alpha BT), on the other hand, a second toxin isolated
from the venom of the same snake, is an ineffective nicotinic antagonist in
most vertebrate neuronal preparations studied thus far. To examine central
nicotinic receptors recognized by NBT, we have characterized the binding of
125I-labeled NBT (125I-NBT) to rat brain membranes and have mapped the
distribution of 125I-NBT binding in brain sections using quantitative light
microscopic autoradiography. The binding of 125I-NBT was found to be
saturable, of high affinity, and heterogeneously distributed in the brain.
Pharmacological studies suggested that more than one population of sites is
labeled by 125I-NBT. For example, one component of 125I-NBT binding was
also recognized by alpha BT, while a second component, not recognized by
alpha BT, was recognized by the nicotinic agonist nicotine. The highest
densities of these alpha BT-insensitive, nicotine- sensitive sites were
found in the fasciculus retroflexus, the lateral geniculate nucleus, the
medial terminal nucleus of the accessory optic tract, and the olivary
pretectal nucleus. alpha BT-sensitive NBT binding sites were found in
highest density in the lateral geniculate nucleus, the subthalamic nucleus,
the dorsal tegmental nucleus, and the medial mammillary nucleus (lateral
part). The number of brain regions with a high density of 125I-NBT binding
sites, blocked either by alpha BT or by nicotine, is low when compared with
results obtained using other approaches to studying the central
distribution of nicotinic receptors, such as labeling with 3H-nicotine or
labeling with cDNA probes to mRNAs coding for putative receptor subunits.
It is proposed that 125I-NBT labels a subpopulation of nicotinic receptors
in the rat brain, and that, given its ability to block nicotinic receptors
in a variety of neuronal preparations, NBT will be a useful probe for
studying the functional properties of these sites.
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