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Zentrum fur Molekulare Biologie Universitat Heidelberg 1m Neuenheimer Feld 282 6900 Heidelberg, FRG Signal transmission at chemical synapses involves specific receptors that transduce neurotransmitter binding into alterations of membrane potential. Receptors containing integral ion channels mediate rapid (in the ~ msec range) transduction events, whereas receptors activating G-protein coupled channels operate at slower time scales (in the msec to sec range). At resting membrane potential, excitation is generated by cation influx, but inhibition of neuronal firing results from increased chloride permeability.The nicotinic acetylcholine receptor at the neuromuscular junction initiates muscle contraction. Due to its abundance in the electric organ of certain fish species, it is the best characterized ion channel protein known (reviewed in Changeux et al., 1984). The primary structures of its subunits have been determined in different species, and homologous cDNAs have been isolated from vertebrate and Drosophila brain. The major inhibitory neurotra1).smitters at central synapses, glycine and ~-aminobutyric acid (GABA), gate chloride channel-forming receptors of similar conductance properties (Bormann et al., 1987), but dis tinc t pharmacology . For example, the convulsive alkaloid strychnine antagonizes postsynaptic inhibition by glycine, the predominant inhibitory neurotransmitter in brain stem and spinal cord, whereas benzodiazepines and barbiturates modify inhibitory GABAA receptor responses in many regions of the central nervous system.

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