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  • Author: J. C. SLOPER x
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1. A histochemical technique has been devised which demonstrates cystine or cysteine in paraffin sections.

2. This depends on the oxidation of these substances with performic acid and the demonstration of the resultant cysteic acid with a basic dye, Alcian blue 8GS, at pH 0·2.

3. The specificity of this reaction depends on excluding acidic substances already present ionized in tissues at this low pH.

4. The performic acid-Alcian blue technique selectively demonstrates material with the exact distribution of Bargmann's chrome-haematoxyphil 'neurosecretory' material in the hypothalamus and in the posterior lobe of the pituitary of man, the rat and dog.

5. This material, by reason of its content of cystine, may represent posterior pituitary hormone; severe dehydration in five rats caused the almost entire loss of this material from the posterior lobe of the pituitary.

6. The performic acid-Alcian blue reaction provides the first histochemical evidence of the hypothalamic elaboration of posterior pituitary hormone in man and rat.

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The hypothalamo-neurohypophysial systems of the dog and rat have been investigated with the electron microscope. The best preparations were obtained from anaesthetized animals cooled to about 7°.

Neuronal cell bodies in the supraoptic nuclei of the dog were characterized both by their size, by their occasional proximity to the capillary basement membranes, and by their content of electron-dense, membrane-bound inclusions measuring between 750 and 3000 å in diameter. Similar inclusions, measuring between 800 and 2400 å in diameter, characterized nerve terminals in the infundibular process. These inclusions are the same size as those found to be associated with high antidiuretic activity in samples taken from the posterior pituitary and from the hypothalamus of the dog, and could therefore be the vehicles of antidiuretic hormone. It has been calculated that in the dog these inclusions, if they contain antidiuretic hormone, are numerous enough in the neuronal cell body for the latter to constitute the only site of hormone synthesis.

Similar secretory neurones were found in the supraoptic nucleus of the rat. They were more difficult to identify than in the dog, for they contained fewer inclusions of the size which filled nerve terminals in the infundibular process.

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1. The relative radioactivity of different parts of the pituitary and hypothalamus has been assessed with a flow counter, and, more satisfactorily, both visually and by granule-counts in autoradiographs. These experiments have involved 103 rats killed between 15 sec and 97 hr after the administration of 35S dl-cysteine, dl-methionine and sodium sulphate.

2. Subarachnoid injections proved more satisfactory than intraperitoneal or intracarotid ones. They were followed by the rapid localization of radioisotope in the adenohypophysis as well as in nervous tissue.

3. The early and marked uptake of radioisotope shown by the cell bodies of neurones in various nuclear regions, and in particular in the supraoptic nuclei, has been interpreted as evidence of active protein synthesis; this pattern of uptake was observed after the injection of labelled cysteine and methionine, but not sodium sulphate.

4. A similar, early, but less marked uptake of radioisotope was noted in the pars distalis after the injection of both cysteine and methionine. Only after the injection of methionine was there a marked uptake in the pars intermedia, and this was confined to its lateral border.

5. Uptake by the infundibular process of the neurohypophysis became greater than that in pars distalis or in the superjacent hypothalamus 9½ hr and longer after injection of labelled cysteine, but not methionine. This pattern of uptake was confirmed by granule counts in twenty-five animals.

6. It is suggested that the late neurohypophysial uptake of radioisotope reflects the storage in the nerve-terminals of the gland of slowly metabolizing proteins or polypeptides synthesized in the supraoptic and paraventricular nuclear regions. These substances probably include the posterior pituitary principles, since the latter are rich in cystine, but lack methionine.