Distribution of monoaminergic, cholinergic, and GABAergic markers in the human cerebral cortex

Mapping of a number of biochemical markers for noradrenergic, dopaminergic, serotoninergic, cholinergic and GABAergic systems was undertaken in 93 samples removed from the human cerebral cortex. The right hemisphere of brains from two subjects with no known history of neurological and psychiatric diseases was examined. Neurotransmitter markers were present in all cortical samples analysed, suggesting a widespread distribution of the corresponding neurons throughout the cerebral cortex. Each marker distributed heterogeneously in a distinct pattern. Noradrenaline concentrations were highest in the frontoparietal region and lowest in prefrontal and occipital areas. Markers for dopaminergic neurons (dopamine levels, dopamine/noradrenaline ratio and homovanillic acid levels) seemed denser in the prefrontal and temporal regions. 5-Hydroxyindolacetic acid levels were particularly high in the occipital area and decreased along the caudorostral axis. Choline acetyltransferase activity was highest in temporal and frontal lobes, at variance with muscarinic receptor distribution, which was highest in occipital cortex. Glutamate decarboxylase activity, an index of GABAergic innervation, did not vary markedly among the different areas of the cerebral cortex. The different biochemical markers investigated were detected in all cerebral cortical regions; their distribution was not homogeneous. A mismatch was observed between the distribution of cholinergic neuronal systems and receptors.