Figure 5.
Computer simulation of IPSC generation on striatal spiny neurons. a, Voltage-clamp results applying a -10 mV pulse to a spiny neuron recorded using Cs+ replacement of K+ and loading with Cl- as used in postsynaptic neurons in paired recordings. The gray line is the clamp current; the black line is a best fit for model parameters given in the figures. b, Morphological model of the spiny neuron used in the curve fit and the simulations. Dendritictips are 220 μm from the soma, and a single synapse was placed on a single dendrite (black) at various distances from the soma. c, The relationship between somatic input resistance and membrane conductivity for the model neuron with other parameters as determined in the curve fit. The value of gm associated with the configuration used for voltage-clamped postsynaptic neurons is shown, as is the value estimated from typical measurements of the input resistance of the spiny neuron in the up state in vivo (Wilson and Kawaguchi, 1996). d, Amplitude of simulated IPSCs for synaptic conductances with decay time constant of 12.5 msec (as measured in the experiments), and amplitudes of 1 nS, in a spiny neuron at a membrane potential of -50 mV. The effect of the change in membrane conductance on IPSC amplitude is apparent at all of the places along the dendrite but gets increasingly pronounced on the distal dendrites. Vm, Membrane voltage; gsyn, synaptic conductivity. e, A comparison of IPSC amplitudes expected for identical IPSCs evoked by dendritic synapses using the Cs+ replacement value of membrane conductance and the value expected from in vivo recording. Note that the IPSC in the in vivo case is <0.05 mV in amplitude. Increasing the membrane conductance to the range seen in slice recordings (30-70 MΩ) produced IPSCs of ∼0.1 mV, as reported in current-clamp papers cited (data not shown).