Clonidine-induced antagonism of norepinephrine modulates the attentional processes involved in peak-interval timing

The effects of the alpha(2)-agonist clonidine and the alpha(2)-antagonist idazoxan were studied with emphasis on the attentional mechanisms subserving interval-timing behavior. Administration of clonidine (0.015 mg/kg IF) to rats trained on a 20-s peak-interval (PI) timing procedure caused a rightward shift in peak functions, whereas idazoxan (0.15 mg/kg IF) caused a leftward shift. Rats were also trained on 10-s and 30-s baseline PI timing procedures in combination with the prior-entry and prior-entry reversal versions of this task that produced leftward shifts and rightward shifts relative to baseline training, respectively. Clonidine (0.025 mg/kg IF) produced a rightward shift in peak functions for all of these behavioral procedures. Taken together, these horizontal shifts in the peak functions indicate a decrease (leftward shift) or an increase (rightward shift) in the latency to start the internal clock that is influenced both by the attentional demands of the task and the effective level of brain norepinephrine.