Conditioning of the microcirculation in the rat

The serotonin-catecholamine balancing mechanism maintains normal vascular tonus and permeability of the microcirculation. Serotonin provokes local vasodilatation and increases capillary permeability in the skin of rats. Released or injected catecholamines inhibit the serotonin-induced peripheral hemodynamic alterations. Following eleotroconvulsive treatment (ECT) (US), there is a catecholamine release and the microcirculatory response to serotonin does not occur. When the administration of a visual stimulus (in six consecutive occasions) proceedingly coincided with the administration of the ECT, it was noted that the light became an effective stimulus for this system. Light alone is an indifferent stimulus to catecholamine release. Thus, the inhibition of the serotonin-induced vasodilatation by ECT (via catecholamine release) became conditioned to the visual-conditional stimulus. Since the net effect of extrinsic serotonin depends on free catecholamines at the vascular bed, the intensity of the serotonin-induced vascular response reflects alterations in the chemical balancing mechanism. This mechanism can be conditioned with the present technique. The result indicates that there is central nervous system mediation.