Identification and quantification of monoaminergic neuromodulators in the sub-cortical region of cat visual cortex by microbore HPLC-ED and protein assay

Removal of retinal input from a restricted region of adult visual cortex leads to a substantial reorganisation of the retinotopy within the deprived zone. To investigate the role of the total (intra- and extracellular) concentration of the monoaminergic neuromodulators in the sub-cortical region of cat visual cortex, which is possibly involved in this reorganisation mechanism, a method for identification and quantification of noradrenaline, dopamine, serotonin, and their major metabolites, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylacetic acid, 5-hydroxyindole-3-acetic acid in small amounts of brain extracts has been developed and validated. Control or retinal lesion cats were killed with pentobarbital; the brains were quickly frozen, and 200 μm cryostat sections were cut. Under visual control through a surgical microscope, the cortical tissue was first separated from the underlying white matter. Three pieces of tissue measuring 2 × 4 mm2, containing the six cortical layers, were sampled out...