Catecholamine microfluorometry of nigral perikarya and tyrosine hydroxylase assay in some telencephalic structures of rats exposed to different behavioral situations.

In an earlier attempt to detect biochemical changes in the prefrontal system of rats performing a task sensitive to prefrontal damage, significant changes in amount of synaptic proteins were found only in the prefrontal cortex and only in the yoked control group. In a similar experimental paradigm, we measured presently activity of tyrosine hydroxylase in several telencephalic formations and intensity of dopamine fluorescence in neurons of the substantia nigra. The neurons in the medial and anterior portion of the substantia nigra of all experimental groups fluoresced significantly stronger than those in the lateral and posterior portions. The activity of tyrosine hydroxylase was 3-4 times higher in the medial prefrontal area than in the occipital cortex. No significant behavior-induced changes were detected in either of these variables. These results-in turn (1) demonstrate an unexpectedly strong dopamine concentration in the nigral neurons which innervate the prefrontal target of the neostriatum; (2) support the evidence of a strong dopaminergic innervation of the prefrontal cortex; and (3) indicate that the dopaminergic transmission in the prefrontal system was not affected by presumed activation of the system to a degree detectable by the presently used methods.