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C Konradi

Publications and source records attributed to C Konradi.

45 records · Page 3Linked to original sources
PubMed1989

Neurochemical perspectives to the function of monoamine oxidase.

Dopamine (DA) is degraded in part by MAO, an intraneuronal and glial enzyme localized at the outer mitochondrial membrane. DA is a good substrate for MAO-B and selegiline enhances DA-transmission and improves akinesia of Parkinson's disease (PD) by selective MAO-B blockade. Immunocytochemistry (ICC) and histochemistry (HC) demonstrate that neurons of substantia nigra (SN) lack MAO near totally (but see Moll et al 1988). Consequently, inhibition of MAO-B in this brain area occurs mainly in glial cells. Therefore an increase of DA in glia seems to be of long-lasting therapeutic benefit in PD. In addition, synthesis of hydrogen peroxide generated via MAO-B is blocked by selegiline. By this toxicity by endogenous free radicals is diminished. Furthermore, exogenous neurotoxicity by MAO-B substrates can be prevented by inhibition of MAO-B, while such MAO-A substrates are metabolized at the level of the MAO-A containing endothelium of capillaries. As conclusion, selegiline is a safe inhibitor of MAO-B that reduces neurotoxicity possibly triggering PD. (Table: see text).

Brain↗
PubMed1989

[Neurochemical perspectives of the function of monoamine oxidases].

Monoamine oxidase (MAO) and its subtypes MAO-A and MAO-B show different distribution in post mortem human brain areas. While MAO-B is the predominant type in glial tissue, intraneuronal MAO is either of type A (locus coeruleus, only 10% of substantia nigra neurons stain MAO-A), while raphe neurons contain entirely MAO-B. Inhibition of MAO-subtypes leads to accumulation of biogenic amines in glial tissue while there is a selective intraneuronal influence differing between various brain areas. Generation of toxic end-products (eg. aldehydes, hydrogen peroxide, ammonia) may contribute to trigger or at least to progress Parkinson's disease.

Animals↗
PubMed1988

Topographic immunocytochemical mapping of monoamine oxidase-A, monoamine oxidase-B and tyrosine hydroxylase in human post mortem brain stem.

Immunocytochemical demonstration of monoamine oxidase-A, monoamine oxidase-B and tyrosine hydroxylase was performed in the human brain stem using monoclonal antibodies to monoamine oxidase-A and monoamine oxidase-B and polyclonal antibodies to tyrosine hydroxylase. In most of the brain areas examined, except the serotonergic dorsal nucleus of raphe, the noradrenergic locus coeruleus and the dorsal efferent nucleus of vagus, tyrosine hydroxylase-positive neurons were in greater number than monoamine oxidase-A-stained or monoamine oxidase-B-stained neurons. The dorsal nucleus of raphe showed no tyrosine hydroxylase immunoreactivity, but reacted positively to serotonin- and monoamine oxidase-B antibodies, while monoamine oxidase-A staining was moderate. In none of the investigated brain areas did neurons exclusively react with monoamine oxidase-B antibodies without expressing monoamine oxidase-A in a few neurons, while in some areas neurons expressed both monoamine oxidase-A and tyrosine hydroxylase (locus coeruleus; dorsal efferent nucleus of vagus). The oculomotor nucleus stained only with monoamine oxidase-A antibodies, substantia nigra neurons reacted only with tyrosine hydroxylase antibodies. Glial staining in most of the brain areas examined seemed, with slight differences, to have the same intensity with monoamine oxidase-A and monoamine oxidase-B antibodies used. No glial staining was obtained with tyrosine hydroxylase antibodies.

Aged↗
PubMed1988

Platelet MAO-B activity and the psychopathology of Parkinson's disease, senile dementia and multi-infarct dementia.

Monoamine oxidase-B (MAO-B) activity of platelets of an age- and sex-matched group of controls was compared with several groups of inpatients having non-familial dementia of Alzheimer type (DAT), Parkinson's disease (PD), multi-infarct dementia (MID), mixed types of these 3 diseases and a group of other central nervous system (CNS) organic disorders. All patients were subjected to several psychometric tests, including the Sandoz Clinical Assessment--Geriatric Scale, Hamilton Rating Scale for Depression, Mini-Mental State Examination and the Organic mental Disorder Scale (OMDS). A statistically significant enhancement of MAO-B activity could be observed in DAT patients and in PD patients, whereas the MID group showed a mean activity similar to that of the control group and the group with other organic CNS disorders. In DAT patients the degree of dementia in the OMDS test and the enhancement of MAO activity were positively correlated, but PD did not show such a correlation. It is concluded that the increase of MAO activity in PD and in DAT might be due to a disease-related enhanced affinity to oxygen and to such oxygen-derived radicals as superoxide or hydroxyl radicals. However, a possible drug-induced enhancement of MAO activity in PD cannot be excluded. Furthermore, the MAO-B activity values in platelets of individual patients or controls are not indicative of diagnosis or prognosis of any of these diseases and are of no disease-related specificity.

Adult↗
PubMed1987

Histochemistry of MAO-A and MAO-B in the locus coeruleus of the Mongolian gerbil.

A coupled peroxidation technique for localization of monoamine oxidase (MAO-A and MAO-B), applied to post-mortem fixed tissue of the locus coeruleus of the Mongolian gerbil is demonstrated. Tyramine hydrochloride, beta-phenylethylamine and 5-hydroxytryptamine creatinine sulphate were used as substrates, 1-deprenyl and clorgyline served as specific inhibitors. All three substrates stained the neurons of locus coeruleus in the absence of inhibitor. In the presence of 1-deprenyl, tyramine hydrochloride and 5-hydroxytryptamine creatinine sulphate were metabolized, whereas in the presence of clorgyline no reaction with either substrate could be observed. Immunocytochemical staining of tyrosine hydroxylase (TH) was employed as comparison.

Animals↗
PubMed1987

Localization of MAO-A and MAO-B in human brain: a step in understanding the therapeutic action of L-deprenyl.

The discovery that MAO can be differentiated biochemically and pharmacologically into two forms, types A and B, with different substrate specificities and inhibitor sensitivities has renewed the interest in MAO inhibiting as a therapeutic agent. L-Deprenyl, a selective inhibitor of MAO-B, was introduced by us into clinical use as an adjunct to L-DOPA some years ago. This drug has found therapeutic importance in that it can potentiate the pharmacological action of L-DOPA. The mechanism underlying the action of L-deprenyl is thought to be related to its inhibition of MAO-B and thus increased levels of PEA and DA, as measured in the striatal and limbic region of human brain. Animal studies have indicated the MAO-A is mainly, but not exclusively, located in brain neurons, while MAO-B is preferentially placed in glia and astrocytes. In general human and primate brain studies show similar MAO distribution. The observation that MAO-B activity could not be located in the catecholaminergic neurons of human brain by the use of monoclonal antibody studies seriously questions the validity of this technique. The exact locations of MAO-A and -B in human brain are important to understand the mechanism of L-deprenyl action as an antiparkinson drug. If there is an absence of MAO-B from dopaminergic neurons, one may now consider that MAO-B activity within glia plays a far more important role than hitherto considered. This, however, is questionable.

Animals↗
PubMed1987

Cellular action of MAO inhibitors.

Sites of action of monoamine oxidase (MAO) inhibitors in the human brain were analyzed by studying the distribution of the respective MAO subtype, MAO-A or -B. Blood brain barrier (BBB), glial cells and neurons of several brain areas were examined with biochemical and immunocytochemical methods. Whereas MAO-A was localized in microvessels and neurons of locus ceruleus, MAO-B was present predominantly in neuronal cells of dorsal raphe nucleus. The neurons of substantia nigra revealed no immunohistochemically detectable MAO. Astrocytes expressed both subtypes and were observed in all cortical areas examined and all over the brain stem including medulla reticular formation, pontine reticular formation, reticular formation of mesencephalon, midbrain reticular formation, red nucleus, substantia nigra, caudate nucleus and putamen (sections according to DeArmond et al., 1976). MAO activity in several brain areas seems mostly to be due to astrocytes rather than to neuronal cells. As MAO inhibitors have beneficial effects in the treatment of malfunctions of aminergic transmitter systems (Johnstone and Marsh, 1973; Robinson et al., 1973; Birkmayer et al., 1977; Knoll, 1981; Zarifian, 1984; Riederer and Youdim, 1986) and a large amount of MAO activity seems to be localized in brain astrocytes, the function of glial cells especially with regard to their neuromodulating capacity should be focused in more detailed research in future.

Aged↗
PubMed1986

Hydrogen peroxide enhances the activity of monoamine oxidase type-B but not of type-A: a pilot study.

The effect of hydrogen peroxide on monoamine oxidase (MAO) activity has been determined in homogenates of human brain areas taken postmortem. It could be shown that hydrogen peroxide enhances significantly the activity of MAO-B after short-term incubation (2 min), while no changes have been noted after long-term preincubation (60 min) indicating reversibility of this effect. MAO-A activity was not changed or decreased after preincubation with hydrogen peroxide. Freezing and thawing procedures did not change hydrogen peroxide stimulation of MAO in the caudate nucleus, while MAO-A activity dose dependently decreased. Inhibition of hydrogen peroxide stimulated MAO-B activity in human cortex by (-)deprenyl was found to be of similar potency compared to hydrogen peroxide free estimations. Glutathione, ascorbic acid and mannitol did not block MAO stimulation by hydrogen peroxide, while sodium azide led to a complete inhibition of hydrogen peroxide derived MAO activitation. Interorgan comparison showed increase of MAO-B activity in crude mitochondrial fractions of rat liver after preincubation with hydrogen peroxide, while with rat heart a reduction of MAO activity was detectable. As a conclusion these data indicate a possible role of hydrogen peroxide in the age-dependent increase of MAO-B in platelets and brain. Furthermore, increase of cytotoxic hydrogen peroxide via combined L-dopa therapy cannot be excluded to be of importance in the appearance of adverse reactions after long-term treatment with high doses. To reduce hydrogen peroxide production due to MAO activity, a combined treatment of L-dopa plus a selective MAO inhibitor and eventually additional administration of radical scavengers (ascorbic acid, vitamin E etc.) seems to be indicated.

Adult↗