Effects of systemic clonidine on auditory event-related potentials in squirrel monkeys.

Event-related potential (ERP), electroencephalographic (EEG), and behavioral data were collected from squirrel monkeys (Saimiri sciureus) in a 90-10 auditory oddball paradigm. Background or target tones were presented once every 2 s, and responses to the targets were rewarded. ERPs were recorded from epidural electrodes following systemic administration of clonidine (0.1 mg/kg) or a saline placebo. EEG power spectral and behavioral performance were assessed simultaneously as indices of behavioral state. Clonidine significantly decreased the area and increased the latency of a P300-like potential. The amplitude and areas of the earlier P1, N1, and P2 components and a later slow wave-like potential were not reduced, nor were ther latencies altered. Clonidine produced increased EEG power in the alpha range (7.5-12 Hz) and decreased power in the upper beta range (20-40 Hz) but did not affect performance in the oddball task. Because two major effects of clonidine are to substantially reduce activity in the noradrenergic nucleus locus coeruleus (LC) and to reduce norepinephrine (NE) release from axons, the present results support the hypothesis that the LC and its efferent projection system are important in modulating the activity of P300-like potentials.