Figure 8.

Simulations suggest that the differences in D₁ and D₂ MSN physiology reflect the dendritic dichotomy. a, b, NEURON models constrained to anatomical reconstructions of biocytin-filled and imaged spiny projection neurons, fit with identical channel distributions and densities, display different excitability in current-clamp simulations. The D₁ MSN reconstruction model had a whole-cell capacitance of 203 pF (recorded in vitro, 209 pF) and a rheobase current of 210 pF, compared with the D₂ MSN reconstruction model with a whole-cell capacitance of 182 pF (recorded in vitro, 168 pF) and a rheobase current of 160 pA. c, d, FRED NEURON models constructed with eight or six primary dendrites to simulate a D₁ and D₂ MSN, respectively. FRED-8 (whole-cell capacitance, 213 pF) and FRED-6 (whole-cell capacitance, 173 pF) have rheobase currents of 210 and 165 pF, respectively. e, A frequency–current plot demonstrating increased firing frequency in FRED-8 for all levels of intrasomatic current injection. f, Current–voltage relationships displaying a Kir2 current of increased amplitude in the FRED-8 model. g, Somatic depolarization in FRED-6 and FRED-8 models from an AMPA-mediated PSP to a single tertiary dendrite and to five tertiary dendrites at 50 Hz with and without Kir2 channels.