PHARMACOLOGY OF SACCADIC EYE-MOVEMENTS IN MAN .2. EFFECTS OF THE ALPHA-2-ADRENOCEPTOR LIGANDS IDAZOXAN AND CLONIDINE

The effects of alpha-2-adrenoceptor agonists and antagonists on saccadic eye movements were studied in normal volunteers using the agonist clonidine and the antagonist idazoxan. Changes in blood pressure, heart rate, and several psychological self-ratings were also recorded. Clonidine produced marked slowing of peak saccade velocity, acceleration and deceleration, with deceleration affected more than acceleration, but had no effect on saccade error or latency measurements. In contrast, most saccade parameters were not altered by idazoxan, although fatigue effects were eliminated. Blood pressure, heart rate, and self ratings of alertness were increased by idazoxan and reduced by clonidine, with opposite effects noted on sedation self-ratings. There were no correlations between the clonidine-induced changes in saccade parameters and changes in self-ratings. Although the slowing of some saccade parameters by clonidine may imply that alpha-2-adrenoceptors are involved in control of saccades, it may also be due to sedation. Although alpha-2-adrenoceptor antagonists may abolish fatigue effects, they cannot increase them over baseline values.