ANALYSIS OF SYNAPTIC TRANSMISSION AT SINGLE IDENTIFIED BOUTONS ON RATSPINAL NEURONS IN CULTURE

The spatial organization of receptor channels has a major influence on the speed and possible plasticity of synaptic signal transmission. We have studied glutamatergic synapses on neurons in organotypic culture s of rat spinal cord. In order to avoid the problems related to the an alysis of currents of unknown origin within a neuron, we chose to exam ine the functional properties of single identified synapses. Iontophor etic mapping of the cell surface revealed hot spots of high glutamate sensitivity coincident with presynaptic boutons stained with the dye F M 1-43. Local application of KCl to these sites caused bursts of synap tic release. Hot spots typically consisted of 330 receptors with an av erage single-channel conductance of 8.3 pS. Evoked synaptic currents i nvolved only about 40-50 receptors and nevertheless showed characteris tics of saturation. This suggests that glutamate receptor clusters at sites of presynaptic terminals are organized into well separated subcl usters opposite release sites.