Intraneuronal dopamine in the primate substantia nigra

The substantia nigra (SN) area compacta (AC) of primates was studied at various microscopic levels following treatment for the histo/cytochemical localization of dopamine (DA) in an effort to establish the intraneuronal loci of DA in neuron cell bodies. The method utilizes treatment of brain tissue slices in 4% glutaraldehyde in F12 buffer (pH 7.2) followed by 3% K2Cr2O7 (DC) in F12 buffer at pH 4.1. In this manner the glutaraldehyde (Glut)-DA product selectively reacts with DC to deposit chromium (Cr) at DA loci resulting in light and electron microscopic identification of DA in the perikarya of the AC. This selective technique has been analytically confirmed by in vitro model systems. The Cr accumulation within the tissues produces electron densities seen with the ordinary electron microscope whether viewed stained or unstained or with or without OsO4; however, the reactive areas are better studied without additional contrast chemicals. Examination of the densities with an energy dispersive x-ray analytical system (EDS) presents significant Cr readings and the degree of density can be correlated with the height of the Cr peak. Non-dense areas show either no Cr counts of only low background Cr values. Endogenous elements with higher than background values identified along with the exogenous Cr are chlorine (Cl) and sulfur (S) and phosphorous (P). Only particular neurons of the AC possess the Cr positive DA reactivity. It is apparent that the Cr positive organelles differ structurally from organelles in non-DA neurons. There appear to be DA organelles specific to particular SN neurons.(ABSTRACT TRUNCATED AT 250 WORDS)