[Monoaminergic activity acts on the visual evoked potentials]

Animal experiments show that pyramidal cells obtain strong noradrenergic innervation in the primary visual cortex. Its neurotransmitter, norepinephrine, has strong inhibitory-hyperpolarizing effect on these cells. Because pyramidal cells are known to be the main generator of cortical bioelectrical activity, we supposed correlation between monoaminergic activity and evoked potential. In the present study this hypothesis was tested using 31 healthy volunteers. As pyramidal cells possess contrast and orientation specificity in the visual cortex, a checkerboard pattern was used for stimulation, at four light intensities. For statistical analysis, the relative peak amplitudes (CI-CII, CII-CIII) and peak latencies (L1, L2, L3) of VEP components were used. To characterise noradrenergic activity, platelet monoamine oxidase and plasma dopamine-beta-hydroxylase were determined from blood samples. We also measured the plasma cortisol level, which is also a good marker of vegetative activity. We found a significant negative correlation between MAO activity and the amplitude of VEP; a strong negative correlation between CS level and L1 latency, and a significant positive correlation between DBH level and L1 latency. Our results prove not only the close correlation between the MAO activity and the bioelectrical characteristics of the visual cortex, but also suggest that VEP could be a good noninvasive tool for the characterisation of central monoaminergic activity.