How is firing activity of substantia nigra cells regulated? Relevance of pattern-code in the basal ganglia.

The current model of the basal ganglia (BG) assumes that neurons use a firing rate renewal code for movement computing under normal and pathological conditions. Here, we report nonrenewal firing (neuronal firing is influenced by its own previous activity) in cells of the anesthetized rat's substantia nigra (SN). Both compensatory (short interspike intervals (ISIs) are followed by long ISIs and vice versa) and persistent (short and long ISIs cluster for long time periods) nonrenewal activity was found in 52.6% and 33.8% of SN cells, respectively. A compensatory pattern was found in 77.7% of DA cells, but in only 9.8% of GABA-cells. Conversely, a persistent pattern was observed in 74.6% of GABAergic cells and in only 9.9% of DA cells. These findings indicate two types of nonrenewal firing pattern codes specifically present in SN dopaminergic and GABAergic neurons. Disruption of these patterns may play a role in the pathophysiology of basal ganglia disorders such as Parkinson's disease and dyskinesias. Copyright 2003 Wiley-Liss, Inc.