The distribution of monoamine oxidase and acetylcholinesterase in the hypothalamus and its relation to the hypothalamo-hypophysial neurosecretory system in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary The distribution of monoamine-oxidase and acetylcholinesterase activities in the hypothalamus of the White-crowned Sparrow has been studied in relation to the hypothalamohypophysial neurosecretory system. The enzyme activities, as revealed by the methods employed, are unaffected during photoperiodically induced testicular growth. Monoamine oxidase has a distribution distinctly different from that of the aldehyde-fuchsin positive neurosecretory material in that there is high activity in the peripheral palisade layers of both the anterior and posterior divisions of the median eminence. Intimate contact is made between these areas with the primary vessels of the hypophysial portal system. A second concentration of activity lies in a layer between the ependymal cells and the neurosecretory material of the fiber tract. In general, monoamine oxidase appears to be associated with glial elements and non-neurosecretory axons. The pars nervosa has little or no monoamine-oxidase activity. The distribution of acetylcholinesterase activity in the anterior division of the median eminence is very similar to that of the aldehyde-fuchsin positive neurosecretory neurons; however, acetylcholinesterase also occurs in the posterior division without associated neurosecretory fibers. These distribution of enzyme activities are considered in relation to possible adrenergic and cholinergic mechanisms in the median eminence.Dedicated to Professor Berta Scharrer in honor of her 60th birthday.Supported by grant NB-01353 from the National Institutes of Health to Professor Farner. This investigation was conducted while Doctor Kobayashi was a National Science Foundation Senior Foreign Scientist at Washington State University. We are indebted to Doctor Christian Da Lage, Laboratoire de Histologie, Falculté de Médecine de Paris, for the preliminary development of some of the techniques used in these investigations.     

Histochemical characterization of monoamine oxidase in ependyma of rat hypothalamus

Sunopsis Monoamine oxidase (MAO) activity has been demonstrated histochemically in rat hypothalamic ependyma using the sulphate-tetrazolium and coupled peroxidatic techniques with tryptamine, tyramine, 5-hydroxytryptamine and benzylamine as substrates. Both methods were applied to cryostat sections with and without exposure to selective amine oxidase inhibitors, including the selective A-MAO inhibitor clorgyline, and the B-MAO inhibitor deprenyl. Our results show that both cuboidal-columnar and tanycyte ependyma contain one or more forms of MAO not generally present in the hypothalamus. It is suggested that ependymal MAO may form an amine-barrier system modulating the movement and effect within the hypothalamus of specific cerebrospinal fluid or blood monoamines.     

Histochemical study of monoamine oxidase latency in the liver of the rat

Summary In a histochemical test system with adrenaline as substrate and nitroblue tetrazolium (NBT) as electron acceptor, an increase of NBT reduction in rat liver sections was found microspectrophotometrically following short hypotonic treatment. Investigations with iproniazide, a monoamine oxidase inhibitor, and non-enzymatic NBT reduction showed that the increased formazan formation was related to the presence of monoamine oxidase. It is suggested that the reason for the observed increase of formazan formation is due to increased permeability of the inner mitochondrial membrane to NBT. Consequently, the increase of monoamine oxidase observed in the histochemical test system does not represent mobilization of a latent activity, but rather complete assessment of activity that is normally present.     

Histochemical study of monoamine oxidase latency in the liver of the rat.

In a histochemical test system with adrenaline as substrate and nitroblue tetrazolium (NBT) as electron acceptor, an increase of NBT reduction in rat liver sections was found microspectrophotometrically following short hypotonic treatment. Investigations with iproniazide, a monoamine oxidase inhibitor, and non-enzymatic NBT reduction showed that the increased formazan formation was related to the presence of monoamine oxidase. It is suggested that the reason for the observed increase of formazan formation is due to increased permeability of the inner mitochondrial membrane to NBT. Consequently, the increase of monoamine oxidase observed in the histochemical test system does not represent mobilization of a latent activity, but rather complete assessment of activity that is normally present.     

Histochemical studies of monoamine oxidase of the brain of rodents

Summary MAO of the brain was investigated histochemically in mice, rats, guinea pigs and rabbits. Fresh frozen sections were subjected to the tryptamine-tetrazolium method by Glenner, Burtner and Brown (1957).MAO activity of the brain of 4 animal species is generally similar with respect to its pattern of distribution. However, the intensity of enzyme action of the brain as a whole differs somewhat in animal species, being highest in guinea pigs, intermediate in rats and lowest in mice and rabbits. The enzyme action occurs mainly in the neuropil of the cerebral grey matter, while weak or negative activity is generally observed in the white matter excepting the tractus retroflexus of Meynert.The marked activity is encountered in the interpeduncular nucleus, locus coeruleus, area postrema, dorsal nucleus of the vagus nerve, hypothalamus, habenular nuclei and midline nuclear group of the thalamus, nucleus of the brachium conjunctivum, and central grey matter. The enzyme activity is weak or negative in the neocortex, striatum, mamillary body, thalamic nuclei (excepting the habenula and midline nuclear group), subthalamic nucleus, substantia nigra, red nucleus and nuclei of the somatic cranial nerves.The possible function and significance of MAO in the brain were discussed particularly by comparing the sites of this enzyme with those of succinic dehydrogenase and cytochrome oxidase, and the inverse relation between these enzymes was suggested.     

Immunocytochemical demonstration of the hypothalamo-hypophysial vasotocinergic system of Lampetra fluviatilis

Summary With the use of the unlabeled antibody peroxidase-antiperoxidase (PAP) technique at the light microscopic level, it was shown that the preoptico-hypophysial neurosecretory system of the adult migrating Lampetra fluviatilis is a vasotocinergic system. It does not synthesize vasopressin. The results are entirely consistent with earlier chromatographic and pharmacological indications that it produces little or no oxytocin-like peptide hormone. In the adenohypophysis, immunoreactive neurohypophysial peptidergic fibres are absent.This investigation was supported by a grant from the Belgian Nationaal Fonds voor Geneeskundig Wetenschappelijk Onderzoek     

Histochemical localization of monoamine oxidase types A and B in the adrenal gland

Summary The distribution of monoamine oxidase types A and B within the adrenal galdn was studied in several mammals by histochemical methods. Controls showed that the methods were valid. The bovine adrenal medulla contained mostly the B type enzyme, distributed heterogeneously, with some A type associated with endothelium, nerves, and cells surrounding the nerves. The bovine adrenal cortex showed a marked zonation of the two types of monoamine oxidase. The zona glomerulosa contained the B type enzyme and the zona fasciculata and zona reticularis contained the type A enzyme. The adrenal medulla of the dog, cat, and rat demonstrated relatively little enzyme activity and it appeared to be both type A and B. The adrenal cortex of these animals appeared to contain mostly the B type enzyme, except the canine zona reticularis, which contained some A type monoamine oxidase as well.     

Histochemical evidence of monoamine oxidase activity in rats of different ages

Summary The histochemically detectable monoamine oxidase activity in certain organs of young and old rats is compared. Regardless of age, the activity is strong in the liver, faint in the skeletal muscle, and absent in the kidney. In the myocardium, however, the quantity of monoamine oxidase increases strongly with age. Its activity is manifest in the form of granular and diffuse formazan precipitates; both disappear after a preliminary treatment of the animals with a monoamine oxidase inhibitor. This finding indicates that the diffuse as well as the previously identified granular precipitates represent monoamine oxidase.     

Histochemical localization of monoamine oxidase in whole-body, freeze-dried sections of mice

Summary Monoamine oxidase was investigated histochemically in tissues of the mouse by incubating freeze-dried, whole-body sections with tryptamine, serotonin, tyramine, -phenylethylamine, or benzylamine as substrate and Nitroblue tetrazolium as the final electron acceptor. The most intense staining with tryptamine was exhibited by intestinal epithelium and adrenal cortex; moderate staining was noted in the epithelium of the nose, bronchi, oesophagus, and upper stomach and in preputial gland, pancreas, nerve, spinal cord and brain. Weak staining was seen in the lung, spleen, liver and kidney. The distribution of the formazan deposition was similar, but much less intense, when serotonin and tyramine were used as the substrates. Only very weak staining was observed when -phenylethylamine was the substrate; no staining was seen with benzylamine. Monoamine oxidase activities with tryptamine were greatly inhibited by pretreatment with clorgyline (10 m), while deprenyl (10 m) slightly inhibited activities in all tissues except liver. This staining technique should be useful in further studies on the identification of the multiple forms of monoamine oxidase in tissues of the mouse. Nicotine and nitrosonornicotine were not substrates in any of the tissues; consequently, this enzyme system does not appear to produce the proximal carcinogen from this nitrosamine.     

Histochemical demonstration of copper in LEC rat liver

Livers of LEC rats were histochemically stained for copper according to the modified Timm's method, which includes trichloroacetic acid (TCA) treatment. TCA pretreatment was effective in removing zinc and iron, leaving copper as the major metal in the liver. Hepatocytes in 3-month-old rats were stained intensely by the modified Timm's method, both in frozen sections and in paraffin-embedded specimens. The centrilobular hepatocytes were usually stained, but positive cells were also randomly distributed in the hepatic lobes, showing a mosaic pattern. The staining was intensified in 8- compared to 3-month-old LEC rats. In contrast hepatocytes from LEA rats, the normal counterpart of LEC rats, were faintly stained for copper. Proliferating cholangioles found in older LEC rats were shown to lack copper deposition, and hepatocellular carcinoma showed less copper deposits than the hepatocytes surrounding the tumor. The copper staining was augmented in livers of LEC rats subjected to copper-loading, but was less intense in the livers treated with d-penicillamine. The staining intensity under the various experimental conditions showed good correlation with the copper concentration. Lysosomal deposition of copper in hepatocytes was demonstrated by electron microscopic analysis for copper. Thus the modified Timm's method was shown to produce valuable results in demonstrating copper in LEC rat livers, providing important information for an understanding of the mechanism of copper deposition and hepatic disease of the animal.