Changes in visual evoked potentials (VEP) induced by tricyclic antidepressants in patients with endogenous depression were studied.
VEP was recorded 3-5 times consecutively before and during the treatment. Drug-induced changes in the amplitude-ratios of P100 of VEP after loading mental tasks as well as the changes in the amplitude and latency of the baseline VEP before the tasks were studied during the treatment with amitriptyline (AMP) or imipramine (IMP).
The results were as follows :
1) The amplitude-ratios after loading the tasks increased at least once in the course of the treatment with AMP or IMP. The increase reached the level of statistical significance only when the doses of more than 75 mg per day were given.
2) With the doses of less than 75 mg per day the amplitude-ratios after the tasks scarcely showed any changes in patients treated with AMP, but showed a slight increase in patients with IMP.
3) In cases of continuous high dose administration of the drugs re-decrease of the amplituderatios sometimes occurred. The re-decrease was more often seen in patients treated with AMP than in those with IMP.
4) While amplitude of P100 of the baseline VEP before the tasks tended to decrease according to the dose increase in patients treated with AMP, no consistent changes were seen in patients with IMP regardless of the dose. No relationship was observed between P100 latency and the dose in patients treated with AMP, nor in those treated with IMP.
From these results, it is inferred that both AMP and IMP simultaneously affected stimulatory and inhibitory processes in depressive patients, and that AMP showed stronger inhibitory effects and IMP stronger stimulatory ones.