INTERACTIONS OF GLUTAMATE AND DOPAMINE IN A COMPUTATIONAL MODEL OF THE STRIATUM

A network model of simplified striatal principal neurons with mutual i nhibition was used to investigate possible interactions between cortic al glutamatergic and nigral dopaminergic afferents in the neostriatum. Glutamatergic and dopaminergic inputs were represented by an excitato ry synaptic conductance and a slow membrane potassium conductance, res pectively. Neuronal activity in the model was characterized by episode s of increased action potential firing rates of variable duration and frequency. Autocorrelation histograms constructed from the action pote ntial activity of striatal model neurons showed that reducing peak exc itatory conductance had the effect of increasing interspike intervals. On the other hand, the maximum value of the dopamine-sensitive potass ium conductance was inversely related to the duration of firing episod es and the maximal firing rates, A smaller potassium conductance resto red normal firing rates in the most active neurons at the expense of a larger proportion of neurons showing reduced activity. Thus, a homoge neous network with mutual inhibition can produce equally complex dynam ics as have been proposed to occur in a striatal network with two neur on populations that are oppositely regulated by dopamine. Even without mutual inhibition it appears that increased dopamine concentrations c ould partially compensate for the effects of reduced glutamatergic inp ut in individual neurons.