Neurotransmitter systems in the visual cortex of the cat: possible involvement in plastic phenomena

The aim of this paper is to review some of the investigations on neurotransmitter systems suggesting their possible role in visual information processing and their putative involvement in the plastic phenomena observed in the primary visual cortex of the cat. The neurotransmitters discussed include excitatory amino acids, ?-amino-butyric acid, acetylcholine, noradrenaline and serotonin. The following problems are discussed: (i) the occurrence and localization of the various neurotransmitter system components, (ii) the developmental changes of the components of a given neurotransmitter system, particularly in the critical period, (iii) the effects of manipulating the visual input on neurotransmitter system markers. It seems that especially during the critical period there exists a peculiar pattern of interactions between numerous neurotransmitters and neuromodulators. This may create unique conditions, which enable the visual cortical neurons to change their properties as a results of alterations of the visual input.