Ornella Senatori

Monoamine oxidase expression during development and aging.

Monoamine oxidase (MAO) isoenzymes play a major role in regulating the concentration of several bioactive amines, including serotonin and catecholamines. Both in the nervous system and in peripheral organs, MAOs can potentially modulate all the processes involving these bioactive amines. In the present article, we review some of the most significant articles published so far on changes in MAOs during development and aging. The data available on development refer mainly to the mammal brain at fetal and post-fetal stages. Very little work has been done on studying MAO ontogenesis during early development, that is, at stages prior to organogenesis, and what has been done refers to non-mammal vertebrates such as fish, amphibians and birds. MAO A and MAO B changes have been measured as values of enzymatic activity, as amount of protein or, more rarely, as amount of mRNAs. A knowledge of MAO developmental changes not only provides a basis for the investigation of factors regulating MAO expression, but can also contribute to a better understanding of the possible trophic and/or morphogenetic role of monoaminergic neurotransmitters in the developing brain. Transgenic mice lacking MAO A and rodents treated with MAO inhibitors during gestation have been very useful in this second case. The investigations of changes in MAO A and MAO B during aging in the literature refer mostly to humans, mice and rats. Interest in studies on aging is stimulated, among other things, by the observation that age-related diseases leading to neurodegenerative phenomena could be accompanied by changes in MAO activity.

Some characteristics of mitochondrial monoamine oxidase activity in eggs of carp (Cyprinus Carpio) and rainbow trout (Salmo Gairdneri)

1. Monoamine oxidase (MAO) activity towards tryptamine, 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA) has been measured in mitochondria isolated from carp and trout eggs. 2. In carp eggs all the tested substrates are metabolized and the highest affinity is found with tryptamine. In trout eggs a consistent level of MAO activity is obtained using tryptamine. 3. The inhibition dose-response curves of clorgyline and deprenyl indicate that both in carp and trout eggs there is only one form of mitochondrial MAO, distinct from MAO A and B which have been described in vertebrate tissues. 4. Both in carp and trout egg mitochondria a semicarbazide-sensitive amine oxidase is not involved in the deamination of the used substrates. 5. MAO found in carp and trout eggs might be involved in metabolism of some neurotransmitter monoamines during early developmental stages.

Occurrence of type A and type B monoamine oxidase activities in toad egg mitochondria

Monoamine oxidase activity has been assayed radiochemically in mitochondria from Bufo bufo eggs. Time courses of MAO activity towards PEA and 5-HT indicate that when PEA is used as a substrate higher specific activities are obtained. The inhibition patterns by clorgyline and deprenyl demonstrate that both type A and type B MAO are present. Type A activity is more sensitive than type B to the inhibitory effect of Triton X-100. Low concentrations of 2-mercaptoethanol cause a slight stimulation of type A and B activities. Increasing concentrations result in a decrease of activity.

Monoamine oxidase activity in embryos of pike (Esox lucius)

1. Mitochondrial MAO specific activity was measured in eggs and early embryos of the teleostean fish Esox lucius using tryptamine, 5-hydroxytryptamine (5-HT) and phenylethylamine (PEA) as substrates. 2. Tryptamine is the most readily deaminated substrate in mitochondria isolated from unfertilized eggs and embryos at the stages of cleavage, blastula and gastrula. 3. Monoamine oxidase activity gradually decreases during development and at the gastrula stage it is respectively 80% (tryptamine), 70% (5-HT) and 50% (PEA) of that found in the egg using the corresponding substrate. 4. The inhibition of egg MAO activity by clorgyline and deprenyl measured in E. lucius eggs using tryptamine as substrate, indicates the presence of a single form of MAO not corresponding to the MAO A and MAO B described in terrestrial vertebrates.

Changes in monoamine oxidase activity by mitochondria isolated from late embryos of Bufo bufo

1. Monoamine oxidase activity has been assayed in mitochondria isolated from post-neural embryos (stages 14-25) of Bufo bufo, using 5-HT and PEA as substrates. 2. Mitochondria isolated from stages 19 to 25 show an increasing ability in deaminating monoamines, PEA being metabolized at a higher level with respect to 5-HT. 3. At all the examined stages 5-HT is metabolized by an enzyme corresponding to MAO A, while PEA, from stage 19, is largely deaminated by a semicarbazide-sensitive amine oxidase (SSAO). 4. The effect of Triton X-100 on MAO A activity appears remarkably different in mitochondria isolated from embryos at stages 14 and 25 respectively.

Monoamine oxidase activity in tissues of the starfish Marthasterias glacialis

1. Monoamine oxidase activity towards PEA and 5-HT has been shown radiochemically in radial nerves and pyloric caeca of the starfish Marthasterias glacialis. 2. Radial nerves show higher specific activities than pyloric caeca with both substrates and this is more evident with 5-HT. 3. Both in radial nerves and pyloric caeca MAO activity shows a higher affinity for PEA than for 5-HT. 4. Regardless of the substrate used, in both radial nerves and pyloric caeca deprenyl is a more effective inhibitor of MAO activity than clorgyline. 5. The inhibition curves obtained by either inhibitor are simple sigmoid curves, suggesting the presence of only one form of MAO.

Mitochondrial monoamine oxidase activity during preneural developmental stages of Bufo bufo.

Monoamine oxidase specific activities against PEA and 5-HT have been measured in mitochondria isolated from early embryos of Bufo bufo. During the early development up to the neural fold stage, MAO activity undergoes a continuous decrease that is more evident when PEA is used as the substrate. The inhibition patterns of deprenyl and clorgyline demonstrate that, at the neural fold stage, both type A and B MAO are present. Both in eggs and embryos MAO type A activity appears slightly more sensitive to the inhibitory effect of various concentrations (0.1-2 M) of the denaturing agent urea.

Effect of short-time exposures to nickel and lead on brain monoamine oxidase from Danio rerio and Poecilia reticulata

The aim of this work was to verify, in two small size freshwater teleosts Danio rerio and Poecilia reticulata, the effects of short‐time exposures (24 and 72 h) to a sublethal dose (500 μg/L) of nickel and lead, on brain monoamine oxidase (MAO), an important neural enzyme. The 24‐h treatment using both metals caused a strong reduction of MAO activity in D. rerio brain, whereas causing a slight MAO activity stimulation in P. reticulata brain. The same treatment in both species did not affect the brain MAO mRNA production as showed by RT‐PCR. Extending the duration of treatment as far as 72 h, partly (D. rerio) or completely (P. reticulata) reversed the metal effects on brain MAO activity suggesting that mechanisms to neutralize the metals had been activated.

Monoamine oxidase activity in hepatopancreas of Octopus vulgaris

Abstract 1. Monoamine oxidase activity has been studied in hepatopancreas of Octopus vulgaris using 5-HT and PEA as substrates. 2. Time courses of MAO activity against 5-HT and PEA show that the enzyme has higher affinity for PEA than for 5-HT. 3. MAO activity against 5-HT appears more sensitive than MAO activity against PEA, to variations of the temperature (range 17–67°C). 4. The inhibition curves obtained with clorgyline and deprenyl indicate that MAO activity is due to a single form of the enzyme, not corresponding to type A and type B MAO. 5. Semicarbazide 10−4 M does not affect the deamination of 5-HT and PEA, demonstrating that a semicarbazide-sensitive amine oxidase is not involved in this process.

Monoamine oxidase and semicarbazide sensitive amine oxidase activities in toad liver mitochondria

1. The deamination of 5-HT and PEA has been assayed by a radiochemical method in mitochondria isolated from toad liver. 2. Time courses of 5-HT and PEA deamination indicate that when PEA is used as the substrate, higher specific activities are obtained. 3. 5-HT is deaminated by MAO A and partially by a SSAO-like enzyme. 4. PEA is deaminated exclusively by SSAO and, MAO B activity, at least under the adopted experimental conditions, is not detectable.