Localization of Catechol Amines in Visceral Organs and Ganglia of the Rat, Guinea‐pig and Rabbit

This method allows accurate localization of certain catechol amines and tryptamines in completely dry tissue.These substances are condensed with formaldehyde to form intensely fluorescent and relatively stable products.The fluorescence can be excited in ultraviolet light and a fluorescence of characteristic wavelength observed in structures containing these mono- amines with a microscope equipped for fluorescence work.The method has been exten- sively used to study the distribution of catechol amines in various tissues of different animal species (Falck, 1962; Carlsson et al., 1962; Falck et al., 1962; Dahlstr6m & Fuxe, 1964; Norberg & Hamberger, 1964).We have used the method to study the localization of catechol amines in some visceral organs and ganglia of the rat, guinea-pig and rabbit.METHODS Animals and freeze-drying procedure.The tissues studied were obtained from four female Wistar rats, four male guinea-pigs and three female rabbits.All animals were adult and kept on standard laboratory diets; they were killed by a blow on the head and were bled.Small pieces of tissue were rapidly excised for freeze-drying.These were mounted on to paper identification slips and rapidly frozen by immersion in dichlorodifluoromethane (Arcton 12, I.C.I.; Bell, 1952) which had been previously cooled in liquid nitrogen.The frozen tissues were dried in a Canalco tissue freeze-drying apparatus as follows: they were kept for 5 to 7 days at a temperature of -35°C; 12 hr before termination of drying, the temperature was increased to -20°C, and, finally, before breaking the vacuum the temperature was raised to 50°C to prevent condensation of water on the tissues.The specimens were transferred into a desiccator and cooled to room temperature.A vacuum better than 0.001 mm Hg was maintained throughout the drying period.Treatment with formaldehyde.The freeze-dried specimens, other than those intended as controls, were exposed to formaldehyde vapour at a temperature of 800 C for a period of 1 hr.Paraformaldehyde powder (Merck) was used which had been previously equilibrated to a constant relative humidity of 25% by standing over a 57% v/v sulphuric acid solution.Paraffin infiltration, embedding and microtomy.The formaldehyde-treated and the untreated control specimens were infiltrated with paraffin wax (560 C melting point) for 10 to 15 min under reduced pressure