Lithium reduces ocular dominance plasticity in kitten visual cortex.

Activity-dependent processes within the visual pathway play a crucial role in the expression of ocular dominance plasticity in immature visual cortex. The necessity of non-retinal, modulatory afferents to the regulation of ocular dominance plasticity has been recognized. Among a few chemically defined signaling systems, the noradrenaline-activated beta-adrenoreceptors seem to have a prime role in this matter. The involvement of acetylcholine afferents was also proven. We looked for plausible molecular mechanisms which integrate the contribution of the two neuromodulator systems to ocular dominance plasticity. At the first step, based on the rich literature on psychotropic action of lithium and the recent advancement in understanding of its molecular mechanisms, we physiologically studied visual cortex of kittens which had been repeatedly injected with the lithium solution intraperitoneally or the cortex directly infused with it. We found (1) that ocular dominance plasticity was significantly reduced in lithium-injected kittens, (2) that the decrease was directly correlated with plasma concentrations of lithium (i.e. the higher the lithium concentration, the lower the plasticity), and (3) that the comparable decrease in the plasticity was obtained from kitten visual cortex which had been directly infused with the lithium solution. The present results suggest that lithium-sensitive processes, through most likely reduced production of second messengers, underlie the regulation of ocular dominance plasticity.