Extracellular electrophysiological recordings were used to study the firing rate of striatal neurons before and up to 4 h after intrastriatal c-fos antisense oligonucleotide injections in urethane-anesthetized rats. A four-fold increase from baseline neuronal activity was observed between 1 and 3 h upon antisense treatment, but not after control oligonucleotide injections. We conclude that, under urethane anesthesia, which here does not affect c-fos expression in the striatum by itself, neuronal activity appears to be tonically suppressed by basal striatal c-fos expression.