MODELING THE INTEGRATIVE PROPERTIES OF DENDRITES - APPLICATION TO THESTRIATAL SPINY NEURON

The role of the striatum in the control of movements and in the proces sing of cortical information has received much attention in the recent years. We set out a simple biophysical model for the medium-spiny neu ron (msn), the most abundant cell in striatum. This neuron receives tw o main kinds of inputs, namely, cortical excitatory inputs and dopamin ergic inputs coming from the substantia nigra pars compacta. The msn a xon impinges directly onto the globus pallidus and onto the substantia nigra pars reticulata neurons and onto striatal neurons through recur rent branches of the axon. The msn is characterized by spiny dendritic trees with a high density of spines (1 to 4 spines/mum) and the proba ble existence of dendritic spikes. The model predicts that the neuron can integrate excitable inputs in a linear or a nonlinear mode. In the nonlinear mode, the neuron allows the detection of simultaneous (or a lmost simultaneous) synaptic inputs; it facilitates either a slowing d own or a speeding up of the information transfer between the synaptic input location and the soma and is sensitive to inhibition-excitation pairing. Conversely, in the linear integrative mode, the somatic volta ge is determined by a weighted summation of the synaptic inputs. Sever al geometrical, electrical, or temporal factors can control the switch between these behaviors: the density of excitable dendritic elements, the dendritic radius, the resistance of the spine stem, the membrane resistance, the time between excitations, and the distance between syn aptic sites. Finally, the signification of this behavior is discussed in connection with the putative role of dopamine and with the striatal net organization. (C) 1994 Wiley-Liss, Inc.