The recently isolated Corticotropin Releasing Factor (CRF) related peptide, urocortin, has been reported to elicit a different behavioral profile than that of CRF. CRF is a potent anxiogenic agent and stimulant of motor activity whereas under similar conditions urocortin is a potent anorectic and mild locomotor stimulant. The neurophysiological effects of this newly synthesized peptide have not yet been examined. The present study evaluated the effects of intracerebroventricular administration of 3 doses of urocortin on the electroencephalogram (EEG) and on Event-Related Potentials (ERPs) in rats. Twenty male Wistar rats were implanted with electrodes in the amygdala and dorsal hippocampus, a cannula into the lateral ventricle, and skull surface electrodes over the frontal and parietal cortices. Following recovery from surgery, urocortin (0.01-1.0 microg) was infused into the lateral ventricle 5 min prior to the recording of EEG (10 min) and ERPs (10 min). Urocortin at any of the doses, did not produce any electrographic or behavioral signs of seizure activity. The predominant effect of urocortin infusion on EEG spectral activity was an increase in mean power in the 4-16 Hz range in the frontal cortex and a decrease in EEG stability in the frontal cortex and amygdala. Urocortin administration also decreased the latency of the P3 component of the ERP in the amygdala and hippocampus. These neurophysiological effects, that only partially overlap with those of CRF, are consistent with the behavioral profile described following urocortin administration in rats. Overall, these data further support the assertion that urocortin functions as a mild CNS stimulant enhancing arousal, as measured by EEG, and modulating the speed of stimulus evaluation as measured by ERPs.