Studies on uptake of intraventricularly administered tritiated noradrenaline and 5-hydroxytryptamine with combined fluorescence histochemical and autoradiographic techniques

Summary

Tritiated noradrenaline (NA) and 5-hydroxytryptamine (5-HT) (1.5–30 μC) have been injected intraventricularly into normal or reserpine-nialamide pretreated rats 1/2 to 2 hours before the killing. Various parts of the brains were freeze-dried, reacted with formaldehyde gas and embedded in paraffin or Araldite. Before application of the stripping film emulsion many sections were photographed in the fluorescence microscope in order to perform a combined histochemical and autoradiographic study of the monoamine neurons. By such an approach it was possible to demonstrate 1. that the accumulation of radioactivity in cell bodies after ³H-NA and ³H-5-HT injection is localized to catecholamine (CA) and 5-HT cell bodies respectively; 2. that injected ³H-NA and ³H-5-HT in the doses used relatively selectively are taken up into the NA and 5-HT nerve terminals respectively, since the distribution of grains in the sections follow that of the fluorescent terminals; 3. that the accumulation of silver grains only reaches the zone (200–400 μ) close to the ventricles and the ventral part of the subarachnoidal space. By grain counting it was possible to estimate that the degree of concentration of radioactivity in the monoamine cell bodies was up to 4 times that in the immediate surroundings. — The Araldite sections consistently gave a better resolution in the autoradiographic picture than the paraffin sections. It is postulated that freeze-drying and plastic embedding for autoradiography will be a valuable method for the cellular demonstration of certain biogenic amines which are not easily demonstrated by the histochemical fluorescence method and of other biologically active water-soluble compounds, since diffusion will be restricted to a minimum.