Figure 1. A typical synapse in the central nervous system.

Figure 2. The principles of radioligand-binding assays. The receptor (R) preparation and radioligand (L) are incubated to equilibrium. The bound radioactivity is then separated from the free, most frequently by rapid filtration. The bound radioactivity thus yields a measure of the receptor present. Using saturation-binding curves and Scatchard transformation, the affinity of the radioligand for the receptor can be determined.

Figure 3. Pertinent features of ligand-gated ion channel neurotransmitter receptors. (a) The key features, including the transmembrane topology of nicotinic acetylcholine, -aminobutyric acid (GABA_A), glycine and serotonin (5-HT₃) receptors. (b) The key features of the ionotropic glutamate receptors. NT, N-terminal; CT, C-terminal; I, II, III, IV are the membrane domains; the red arrows point to the sites of N-glycosylation; C-C, the cys-cys loop. (c) The arrangement of the subunits and the channel pore of the nicotinic acetylcholine receptor as viewed perpendicular to the plane of the membrane. (d) The nicotinic acetylcholine (ACh) receptor in the membrane together with the acetylcholine-binding site (drawn to scale). (d) Reproduced in part from Miyasawa A et al. (1999) Nicotinic acetylcholine receptor at 4.6Åresolution. Journal of Molecular Biology 288: 765–786, copyright © 1999 used with permission of the publisher, Academic Press.

Figure 4. Pertinent features of G protein-coupled neurotransmitter receptors. (a) The key features, including the transmembrane topology of metabotropic G protein-coupled receptors. NT, N-terminal; CT, C-terminal; the solid rectangles are the seven transmembrane domains; the red arrows point to the sites of N-glycosylation and the zig-zag line represents the palmitoylation at the C-terminus. (b) The G protein-coupled receptor as viewed through the plane of the membrane.

Figure 5. Organization of the different types of glutamate receptor at glutamatergic synapses. The diagram summarizes information that has accrued from immunochemical studies of hippocampal and cerebellar glutamatergic synapses, as indicated, using the electron microscope. Up to four different types of glutamate receptors are found in the postsynaptic membrane, including both ionotropic and metabotropic receptors. Thus it can be seen that the signalling and encoding abilities of a synapse must be defined by the complement of the receptor proteins colocalized at these synapses. AMPA, -amino-3-hydroxy-5-methylisoxazoleproprionate; NMDA, N-methyl-d-aspartate. Reproduced with permission from Takumi Y et al. (1998) Synaptic arrangement of glutamate receptors. Progress in Brain Research 116: 105–121, by permission of the publisher, Elsevier Press © 1998.