Monoamine oxidases A and B (MAO-A and MAO-B) oxidatively deaminate neurotransmitter and xenobiotic amines. Since the cellular localization of the isoenzymes in the CNS and peripheral organs determines to a large extent which substrate has access to which isoenzyme, knowledge of their tissue distribution and cellular localization is essential. Here we describe how reversible and selective inhibitors of MAO-A and MAO-B [Ro 41–1049 and Ro 19–6327 (lazabemide), respectively] can be used, as tritiated radioligands, to map the distribution and abundance of the enzymes in microscopic regions of the rat CNS and peripheral organs, and human brain by quantitative enzyme radioautography. The in vitro binding characteristics of both radiolabeled inhibitors revealed them to be selective, high-affinity ligands for the respective enzymes. KD and Bmax values for 3H-Ro 41–1049 in rat cerebral cortex were 10.7 nM and 7.38 pmol/mg protein, respectively, and for 3H-Ro 19–6327 were 18.4 nM and 3.45 pmol/mg protein, respectively. In accordance with their potencies as enzyme inhibitors, binding to MAO-A and MAO-B was competitively inhibited by clorgyline (IC50 = 1.4 nM) and L-deprenyl (selegiline; IC50 = 8.0 nM), respectively. The capacities of various rat and human tissues to bind the radioligands correlated extremely well with their corresponding enzyme activities. As revealed by the respective binding assays, the distribution and abundance of MAO-A and MAO-B in the tissues investigated differed markedly. MAO-A was most abundant in the locus coeruleus, paraventricular thalamus, bed nucleus of the stria terminalis, median habenular nucleus, ventromedial hypothalamus, raphe nuclei, solitary tract nucleus, inferior olives, interpeduncular nucleus, claustrum, and numerous peripheral tissues, including liver, vas deferens, heart, superior cervical ganglion, and exocrine and endocrine pancreas. In contrast, MAO-B was most abundant in the ependyma, circumventricular organs, olfactory nerve layer, periventricular hypothalamus, cingulum, hippocampal formation, raphe nuclei, paraventricular thalamus, mammillary nuclei, cerebellar Bergmann glia cells, liver, posterior pituitary, renal tubules, and endocrine pancreas. The cellular localization of the isoenzymes in both rat and human brain differs markedly and does not reflect the distribution of the presumed natural substrates, for example, absence of MAO-A in serotoninergic neurons. Indeed, the present evidence suggests that, whereas MAO-A is found in noradrenergic and adrenergic neurons, MAO-B occurs in astrocytes, serotoninergic neurons, as well as ventricular cells, including most circumventricular organs. The physiological roles of the enzymes are discussed in the light of these findings, some of which were unexpected.(ABSTRACT TRUNCATED AT 400 WORDS)

In this paper we describe the synthesis, structure-activity relationship (SAR), and biochemical characterization of N-(4-phenylthiazol-2-yl)benzenesulfonamides as inhibitors of kynurenine 3-hydroxylase. The compounds 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulfonamide 16 (IC50 = 37 nM, Ro-61-8048) and 4-amino-N-[4-[2-fluoro-5-(trifluoromethyl)phenyl]-thiazol-2-yl] benzenesulfonamide 20 (IC50 = 19 nM) were found to be high-affinity inhibitors of this enzyme in vitro. In addition, both compounds blocked rat and gerbil kynurenine 3-hydroxylase after oral administration, with ED50's in the 3-5 mumol/kg range in gerbil brain. In a microdialysis experiment in rats, 16 dose dependently increased kynurenic acid concentration in the extracellular hippocampal fluid. A dose of 100 mumol/kg po led to a 7.5-fold increase in kynurenic acid outflow. These new compounds should allow detailed investigation of the pathophysiological role of the kynurenine pathway after neuronal injury.

Treatment of newborn rats with 10 gg/g of nerve growth factor for 10 days enhanced not only the growth but also the differentiation of neuroblasts in superior cervical ganglia. These morphological changes were accompanied by selective induction of tyrosine hydroxylase and dopamine #-hydroxylase (EC 1.14.2.1), whereas the total and specific activities of other enzymes involved in biosynthesis or metabolic degradation of norepinephrine rose only in proportion to the increase in volume of the sympathetic ganglia. There are remarkable similarities between this effect of nerve growth factor and the induction of trans-synaptic enzymes by increased activity of the sympathetic nervous system. Ever since the discovery that a specific nerve growth factor (NGF) enhances growth and differentiative processes of sympathetic neurons (1, 2), the question has been raised whether this factor selectively stimulates metabolic pathways characteristic of this particular nerve cell type. Sympathetic neurons offer an almost ideal system to test this hypothesis, since the biochemical correlates of their function are rather well known. However, it was not until recently that sufficiently sensitive methods became available to measure the activity of enzymes involved in the synthesis and metabolic degradation of the adrenergic neurotransmitter in small tissue samples (3-6). It thus became possible to study whether the hyperplastic and hypertrophic ganglia of newborn rats treated with NGF also differ from controls in the specific activity of these enzymes.The results to be reported here show that NGF, besides its characteristic morphological effects, also produces a selective induction of tyrosine hydroxylase and dopamine ,3-hydroxylase (EC 1.14.2.1), enzymes located in adrenergic neurons (7). In contrast, the activities of Dopa decarboxylase (EC 4.1.1.26) and monoamine oxidase (EC 1.4.3.4), enzymes which are present also in other cell types (7), increase only in proportion to the rise in volume of the adrenergic neurons in the superior cervical ganglia. METHODSNewborn rats (Wistar descent) of either sex were injected subcutaneously daily for 5 and 10 days with 10 ug/g of NGF dissolved in 0.9% NaCl. The NGF was prepared according to the method of Bocchini and Angeletti (8). The animals were killed by transection of the thorax above the heart. The superior cervical ganglia were removed under the dissecting Abbreviation: NGF, nerve growth factor. microscope, fixed in Bouin's solution, and stained with toluidine blue. Ganglia of 5-and 10-day-old experimental and control littermates were then sectioned serially at 10 ,m. Cell counts were performed by inserting a micrometer disk into the ocular and counting all nerve cells in every other section of the experimental and control ganglia. For ultrastructural studies, the ganglia were fixed for 2 hr in 3% glutaraldehyde in 0.1 MI phosphate buffer (pH 7.4) with added CaCl2; the specimens were washed for 2 hr in the same buffer and postfixed in osmic hydroxide (1.33%) for 2 hr. Sections were c...

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In a shoal of four sticklebacks (Gasterosteus aculeatus) individual fish had partners with whom they repeatedly performed pairwise predator inspection visits. In six different trials, we found two reciprocal pairs per trial significantly more often than would be expected by chance. These results provide further evidence for a TIT FOR TAT like cooperation strategy in sticklebacks.