Autoradiographic localization of putative nicotinic receptors in the rat brain using 125I-neuronal bungarotoxin

Abstract

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.

Alpha-bungarotoxin binding to hippocampal interneurons: immunocytochemical characterization and effects on growth factor expression

“…These data are supported by the prominent binding of the neuromuscular-type antagonist oc-bungarotoxin (a-BT) in the CA3 field of the hippocampus (Hunt and Schmidt, 1978;Segal et al, 1978;Clarke et al, 1985;Harfstrand et al, 1988;Pauly et al, 1989). The ganglionic antagonist called neuronal or K-BT also binds in CA3, but the binding is fully displaced by a-BT (Schulz et al, 1991). In most other brain areas, there is no such displacement.…”

Neuroimaging - Clinical Applications

“…In general, regions with high-to moderate-density of α7 nAChR gene expression and [ 125 I]α-BGT binding are related to learning and memory such as thalamic and hippocampal structures, the horizontal limb of the diagonal band of Broca, and the nucleus basalis of Meynert (Alkondon et al, 2007;Breese et al, 1997;FabianFine et al, 2001;Hellström-Lindahl et al, 1999;Schulz et al, 1991;Spurden et al, 1997). However, species differences exist regarding the total number of binding sites of α7 nAChR specific radioligands (Han et al, 2003) with for example a lower amount of [ 125 I]α-BGT binding in the monkey hippocampus or the human thalamus and cortex compared with the same regions of rat brain ) (Tab.…”

Tobacco Smoking and Nicotine Neuropsychopharmacology: Some Future Research Directions

“…CHOLINERGIC RECEPTORS Schwartz et al (1982), Clarke andPert (1984, 1985), Clarke et al (1985b), London et al (1985), Schwartz and Kellar (1985), and Schulz et al (1991) described the autoradiographic distribution of nAChRs in rat brain using H-ACh binding is highest in the interpeduncular nucleus, most thalamic nuclei, superior colliculus, medial habenula, presubiculum, layers I, III, and IV of the cerebral cortex, substantia nigra pars compacta, and the ventral tegmental area. Deutch et al (1987) and Swanson et al (1987) used monoclonal antibodies generated against purified AChR from Torpedo electric organ, or chicken and rat brain, to determine the immunohistochemical localization of nAChR in rat and mouse brain.…”