SECTION I V

Several ways of obtaining sensitive histochemical methods for catechol- amines have been investigated in these laboratories. The most promising method so far is based on the principle that the primary amines can be transformed into intensely fluorescent products by condensation with formaldehyde. The chief problem has been to prevent extraction or diffusion of the amines during the treatment of the tissues. Since the fluorescent products were found to be insoluble in hot paraffin or xylene, condensation was attempted under near dry conditions by exposing freeze-dried tissue to water-poor formaldehyde vapour before embedding in paraffin. Experiments with models and adrenal medulla showed that a condensation, accompanied by the development of an extremely intense fluorescence without significant diffusion, took place under these cir- cumstances.

This method has been applied to several tissues from different mam- mals. I n all tissues where adrenergic nerves are known to be present. the formaldehyde treatment developed a strong yellow-green fluorescence in a network of fine fibres having the same morphology and topography as those of the axons running in the autonomic ground plexus. It seems possible that, by modifications of the conditions for the formaldehyde condensation, the fluorescence method may also make possible the cellular localization of 5-hydroxytryptamine, dopamine, and adrenaline.

REFERENCES

Carlsson, A., Falck, B. , Hillarp, N.-A . , Thieme, G. & Torp, A. (1961). Med. Exp. 4, 113. Falck, B., Hillarp, N.-A. , Thieme, 0. & Torp, -4. (1962). J. Histochem. Cytochem. (in

FaZck, B. & Torp, A. (1962). Med. Exp. (in press). press).

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THE DISTRIBUTION OF MONOAMINE OXIDASE I N THE BRAIN AND PITUITARY GLAND O F THE ALBINO RAT

bY

BARBARA SMITH The Maida Vale Hospital for Nervous Diseases, London, Engltmd

Monoamine oxidase acts on a number of substrates, but in the brain its most important function is probably the inactivation of noradrenaline and 5-hydroxytryptamine (serotonin). Considerable quantities of the enzyme and the two substrates can be found biochemically, particularly in the hypothalamus and mid-brain.

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SECTION IV

In this work the localization of monoamine oxidase activity was stu- died in the brain and pituitary gland of the rat using the tetrazolium technique, with Nitro-B.T. and M.T.T. as the tetrazolium salts.

The detectable activity has been arbitrarily divided into three grades. There was background activity, which could be seen to be perivascular. The greater activity of the grey matter, compared to the white matter, observed biochemically, may be related to the greater vascular density of the former. There was a much higher activity in the posterior lobe and neural stalk of the pituitary gland, in certain nuclei of the hypo- thalamus, especially the supra-optic and paraventricular, and in parts of the brain stem, especially the peri-ventricular grey matter. There was very high activity in the habenular nucleus, the fasciculus retroflexus, the interpeduncular nucleus, the dorsal tegmental nucleus and part of the mesencephalic root of the trigeminal nucleus. These structures form an anatomical system connected by the stria medullaris to the olfactory centres. These structures are more prominent in macrosomatic animals, but are well-defined, though small in man.

Animals were given a monoamine oxidase inhibitor, and histochemical methods for noradrenaline and 5-hydroxytryptamine were applied to sections of the brains. The increase in concentration of the substrates within the brain did not reach detectable levels with the methods avail- able. There was possibly an increase of peri-vascular 5-hydroxytrypta- mine in the blood-vessels of the meninges.

The relationship between enzyme activity in the three sites, in the blood-vessels, in the hypothalamo-hypophyseal system and in the habe- nular system, will be discussed in relation to their physiology, and to the action of monoamine oxidase inhibitors or tranquillizers.

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AKTIVITATSANSTIEG VON ENZYMEN DER OXYDOREDUK- TION I N AXONEN DES ZENTRALEN UND PERIPHEREN

NERVENSYSTEMS NACH DURCHSCHNEIDUNG

von

G. KREUTZBERG Deutsche Forschungsanstalt fur Psychiatrie, (Max-Planck-Institiit)

Kraepelinstrasse 4, Miinrhen 23, Germany

Bei Durchschneidung von Fasersystemen in Gehirn und Ruckeninark von Ratten liess sich in den Axonstiimpfen ein erheblicher Aktirit.%ts-

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