Effects of Reboxetine and Desipramine on the Kinetics of the Pupillary Light Reflex

1. The aim of the study was to examine the effects of single doses of two antidepressants (desipramine and reboxetine) on three kinetic parameters (latency, amplitude, 75% recovery time) of the pupillary light reflex response. 2. Six healthy male volunteers participated in three experimental sessions at biweekly intervals. Each session was associated with one of three treatment conditions (placebo, desipramine 100 mg, reboxetine 4 mg). Subjects were allocated to sessions and treatments double-blind according to a Latin Square design. 3. Pupil diameter was measured in the dark with binocular television pupillometry. Reflex responses were evoked by 12 light stimuli (5.3 x 10(-5)-3.5 mW cm-2; 500 ms), and the kinetic parameters of each response were recorded. 4. The amplitude and 75% recovery time were positively, and latency was negatively correlated with the logarithm of light stimulus intensity. In the presence of the antidepressants the latency was prolonged, the amplitude was reduced and the 75% recovery time was shortened. There was a positive linear relationship between reflex amplitude and recovery time under all three treatment conditions; this relationship was not significantly affected by the antidepressants. 5. The effects of the antidepressants on latency and amplitude are consistent with the blockade of muscarinic cholinoceptors in the iris, whereas the shortening of the recovery time appears to be secondary to the reduction in amplitude.