IMMUNOHISTOCHEMICAL STUDIES ON LOCALIZATION AND DISTRIBUTION OF MONOAMINE NEURON SYSTEMS IN RAT-BRAIN .2. TYROSINE-HYDROXYLASE IN TELENCEPHALON

Abstract

Extensive plexuses of TH[tyrosine hydroxylase]-positive nerve terminals were found in many parts of the telencephalon, mainly confined to the subcortical and limbic cortical structures. Of special interest were the distinct networks of varying densities in the amygdaloid cortex, the entorhinal cortex, the prepiriform cortex, the anterior cingulate cortex and the (pre-)frontal cortex. Their distribution was identical with the patterns observed in recent studies on cortical dopamine nerve terminals using certain modifications of the Falck-Hillarp technique. The extremely dense TH innervation patterns of the caudate nucleus, nucleus accumbens, tuberculum olfactorium and the less dense basket-like innervation of the lateral septal nuclei were also demonstrated. TH-positive cell bodies in a periglomerular position could be observed in the olfactory bulb. A few TH-positive cell bodies were observed in the area around the anterior commissure and in the cingulate cortex. In 1 area, the hippocampal formation, TH-positive dotlike structures were located in the position of the mossy fibers. In all probability they do not belong to monoamine neurons, but may contain a cross-reacting protein. In general the distribution and density of TH-positive terminals agreed well with extensive regional, biochemical studies on TH activity performed by other groups. Minor discrepancies were discussed. As stated in a parallel study on the distribution of TH in the mes- and diencephalon, these findings indicated that TH activity is closely related to the amount of enzyme protein. The TH enzyme levels seem to be much higher in the DA [dopamine] than in the NA [noradrenaline; norepinephrine] nerve terminals of the forebrain, which would explain the preferential demonstration of DA terminals in the forebrain using TH antiserum and the high and low TH enzyme activity in DA and NA rich regions, respectively.