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The cellular localization of monoamines in the spinal cord of the mouse and the rat has been studied with the use of a fluorescence method for histochemical demonstration of certain cate‐cholamines and tryptamines in combination with a pharmacological approach and transection experiments. Strong evidence was obtained for the view that noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) are localized in special systems of nerve tracts which from supraspinal centers descend in the lateral and anterior funiculi to terminate in the gray matter and which belong to monoaminergic neurons. The amines show a massive accumulation in the terminal part of the nerve fibres. This strongly indicates that both amines serve as synaptic transmitters in the spinal cord. Many nerve terminals containing NA or 5‐HT are present in the anterior horns. They are more scarce in the posterior horns. Terminals of both kinds are highly concentrated in the sympathetic lateral column where most—if not all—of the nerve cells are surrounded by them. They originate—at least mainly—from a tract descending in the dorsolateral funiculi. This localization of the descending fibres suggests that they arc identical with the inhibitory fibres going to the sympathetic column.

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The reaction under mild conditions between formaldehyde and phenylalanine and phenylethylamine derivatives has been studied. When the amines included in a dried protein film were exposed to formaldehyde vapour a very intense green to yellow fluorescence was give only by those that as well as being primary amines also have hydroxyl groups at the 3 and 4 positions (3,4-dihydroxyphenylalanine, dopamine, noradrenaline). The 3-OH group seems to be esssential for the reaction. The catechol amines, which are secondary amines (adrenaline, epinine), gave a much weaker fluorescence that developed more slowly. The results obtained on further examination of the reaction favour the view that the amines primarily condense with formaldehyde to 1,2,3,4-tetrahydroisoquinolines which are involved in a secondary reaction to become highly fluorescent and at the same time insoluble. This secondary reaction may be a binding to protein, and oxidation with the formation of double bonds in the heterocyclic ring, or both.

It has been shown in previous papers that catecholamines and 5-hydroxytryptamine can under certain conditions be converted to highly fluorescent 6,7 - dihydroxy - 3,4 - dihydroisoquinolines and 6-hydroxy-3,4-dihydro-β-carboline respectively, and that this can be used as a highly sensitive and specific method for the histochemical demonstration of the monoamines at the cellular level. In the present paper it is shown that the fluorescent compounds are very readily reduced by sodium borohydride to the corresponding, non-fluorescent 1,2,3,4-tetrahydro-compounds—even if they are present in a non-extractable state in dried serum albumin spots or in tissue sections—and that the fluorescence can be regenerate by renewed formaldehyde treatment. The non-specific fluorescence ( e. g. autofluorescence) in tissue sections was never observed to undergo any changes on borohydride treatment. On the basis of these findings a very simple histochemical test has been worked out to check directly in the tissue section whether or not an observed fluorescence is due to the presence of the reacting monoamines.

Dahlstrom, A., K. Fuxe, N.-& Hillarp and T. Malmfon. Adrenergic mechanism in the pupillary light-reJex path. Acta physiol. scand. 1964. 62. 11 9-1 24. -On the basis of the known effects of reserpine on the cye, the presence of monoaminergic mechanisms in the light-reflex path of the rat was studied with the use of a fluorescence method for the localization of catecholamines and 5-hydroxytryptamine at the cellular level. The nucleus of Edinger-Westphalbut not the large-celled nuclei of the oculomotor complexwas found to receive abundant nerve fibres which show a massive accumulation of a primary cateholamine, in all probability noradrenaline. There is little doubt that the nerves are adrenergic synaptic terminals. This adrenergic system is so richly developed that is must be assumed to play an important role in the regulation of the activity of the visceromotor outflow to the eye. Except this system and the adrenergic ncurons recently discovered (Malmfors 1963) in the retina, no other monoaminergic mechanisms have so far been detected with certainty in the light-reflex path. Abundant fibres of both the adrenergic and 5-hydroxytryptaminergic type terminate in other parasympathetic (e. g. the dorsal motor nucleus of the vagus) and also sympathetic nuclei (e. g. the sympathetic lateral column of the spinal cord). 5-hydroxytryptamine and noradrenaline in the central nervous system are thus not confined to action upon the parasympathetic and sympathetic systems respectively. -Current views on the central action of reserpine are discussed on the basis of the findings.

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