Distribution of norepinephrine and dopamine in cerebral cortical areas of the rat.

Concentrations of norepinephrine and dopamine were determined using enzyme isotope assay in 27 microdissected cerebral cortical areas of the rat. A detailed map is presented for microdissection of rat cerebral cortex. Norepinephrine was found in low but still measurable quantities throughout the cortex. Differences between cortical areas are also low. Relatively highest levels were demonstrated in the pyriform, insular and entorhinal cortices. The distribution of dopamine was found to be uneven with a maximal regional difference of 1:24. Concentration of dopamine was in all areas lower than that of norepinephrine. The highest dopamine concentration (2,4 ng/mg protein) was measured in the rostral pyriform cortex but other mesocortical (cingulate, frontal, insular and entorhinal) dopaminergic areas also contained relatively high amounts. Except for the caudal occipital and caudal entorhinal cortices all regions studied contained measurable quantities of dopamine. Its low concentration relative to norepinephrine (below 15%) suggests that in the cortical areas studied dopamine is present as the precursor of norepinephrine.