Ornithine Decarboxylase in Human Brain: Influence of Aging, Regional Distribution, and Alzheimer's Disease

Abstract: Although experimental animal data have implicated ornithine decarboxylase, a key regulatory enzyme of polyamine biosynthesis, in brain development and function, little information is available on this enzyme in normal or abnormal human brain. We examined the influence, in autopsied human brain, of postnatal development and aging, regional distribution, and Alzheimer's disease on the activity of ornithine decarboxylase. Consistent with animal data, human brain ornithine decarboxylase activity was highest in the perinatal period, declining sharply (by ∼60%) during the first year of life to values that remained generally unchanged up to senescence. In adult brain, a moderately heterogeneous regional distribution of enzyme activity was observed, with high levels in the thalamus and occipital cortex and low levels in cerebellar cortex and putamen. In the Alzheimer's disease group, mean ornithine decarboxylase activity was significantly increased in the temporal cortex (+76%), reduced in occipital cortex (−70%), and unchanged in hippocampus and putamen. In contrast, brain enzyme activity was normal in patients with the neurodegenerative disorder spinocerebellar ataxia type I. Our demonstration of ornithine decarboxylase activity in neonatal and adult human brain suggests roles for ornithine decarboxylase in both developing and mature brain function, and we provide further evidence for the involvement of abnormal polyamine system activity in Alzheimer's disease.     

ENZYMES ASSOCIATED WITH THE METABOLISM OF CATECHOLAMINES, ACETYLCHOLINE AND GABA IN HUMAN CONTROLS AND PATIENTS WITH PARKINSON''S DISEASE AND HUNTINGTON''S CHOREA

—Tyrosine hydroxylase (TH), dopa decarboxylase (DDC), glutamic acid decarboxylase (GAD), choline acetyltransferase (CAT), and acetylcholinesterase (AChE) were measured in 18–55 areas of brain from humans post mortem. Individuals meeting sudden and unexpected death (22), patients dying in hospital with non–neurological illness (6), Parkinson's disease (12), Huntington's chorea (8), terminal coma (6) or head injury (2) were included in the series. The absolute values obtained compared favourably with some previous human studies where high values for these enzymes were obtained, as well as with monkey and baboon data. The regional distributions of the enzymes were also comparable to those previously reported in human and animal studies. A number of important points with regard to human tissue seemed to emerge from the study. The mode of death was not a factor in enzyme levels in non–neurological and non-coma cases. Post mortem delay did not seem to be a major factor either even though a substantial decline in GAD, TH and DDC could be demonstrated in rats left several hours between sacrifice and removal of the brain for assay. Age had a highly significant effect in certain areas of brain. The decline typically followed a curvilinear pattern (activity = A/age + B with the sharpest drops being in the younger age groups). DDC seemed to be the enzyme most severely affected by age but all the enzymes showed declines in certain brain areas, while in other areas there was no significant decline. All the enzymes were very depressed by coma from illness except AChE. TH and DDC in the brain stem were, however, not affected in the head injury cases. The Parkinsonian cases showed a sharply decreased TH activity in the substantia nigra, caudate and putamen. There were decreases in GAD in the globus pallidus (GP) and substantia nigra with marginal decreases in the neostriatum. CAT levels in the extrapyramidal nuclei were normal. In Huntington's chorea there was a substantial decrease in GAD in all the extrapyramidal structures. There was a patchy loss of CAT in the neostriatum and locus coeruleus.     

Human Brain Cerebroside β-Galactosidase: Deficiency of Transgalactosidic Activity in Krabbe's Disease

Abstract: Under experimental conditions optimal for the assay of D-galactosyl- N -acylsphingosine galactohydrolase (EC 3.2.1.46) activity, homog-enates of neurologically normal human brain tissue could transfer galactose from galactosyl ceramide (gal-cer), lactosyl ceramide (lac-cer), 4-methylumbelliferyl- β-galactoside (4-MU-gal), or p -nitrophenyl- β-galactoside (PNP-gal) to [1-¹⁴C]oleoyl sphingosine, but homogenates of brain tissue from patients with Krabbe's disease lacked this ability. The rate of hydrolysis of ganglioside G_M1 and to a lesser extent, of PNP-gal by homogenates of Krabbe's brain tissue was also decreased. Activity of PNP- β-galactosidase in normal brain tissue, like that of cerebroside β-galactosidase from the same source, was considerably more heat-stable than the activity of either 4-MU- β-galactosidase or the predominant G_M1β-D-galactosidase (EC 3.2.1.23). Lac-cer and G_M1, as well as 4-MU-gal and PNP-gal, were competitive inhibitors of human-brain cerebroside β-galactosidase. These findings confirm the ability of mammalian cerebroside β-galactosidase to catalyze a transgalactosylation reaction and provide additional information on the substrate specificity of human brain cerebroside β-galactosidase.     

Stability of enzymes in post-mortem rat brain.

Enzyme activities were measured in rat brains kept at room temperature for various intervals after death by decapitation. Tytosine hydroxylase, monoamine oxidase, choline acetyltransferase, and acetylcholinesterase show a substantial decline in activity over 14h reaching 64, 78, 60 and 58%, respectively. of the zero-time activity. DOPA decarboxylase, glutamic acid decarboxylase, lactate dehydrogenase, Na-K-ATPase and Mg-ATPase show less than a 15% decline in activity. The activities of most of the enzymes studied show little change time period when human brain specimens are likely between the 6th and 14th hour after death, the to be obtained for biochemical studies     

Demonstration of aromatic l-amino acid decarboxylase activity in human brain with l-dopa and l-5-hydroxytryptophan as substrates by high-performance liquid chromatography with electrochemical detection

The enzymatic decarboxylations of l-DOPA and l-5-hydroxytryptophan (l-5-HTP) by aromatic l-amino acid decarboxylase (AADC) were measured with homogenates from human brain regions, caduate nucleus and hypothalamus, using our new and highly sensitive methods for l-DOPA decarboxylase and l-5-HTP decarboxylase by high-performance liquid chromatography with electrochemical detection (HPLC-ED). Dopamine formed from l-DOPA as substrate was measured for DOPA decarboxylase activity using d-DOPA for the blank. For 5-HTP decarboxylase activity, serotonin (5-HT) formed from l-5-HTP was measured, and the blank value in presence of NSD-1055 was subtracted. NSD-1055 inhibited 5-HTP decarboxylase activity completely at a concentration of 0.2 mM. In this study, the properties of l-5-HTP decarboxylase activity in human caudate nucleus were first examined. AADC activities in human brains were found to be widely variable for both l-DOPA and l-5-HTP as substrates. The ratio of the activities for l-DOPA and l-5-HTP were found to be significantly higher in hypothalamus than in caudate nucleus. AADC activity for l-DOPA in the brain was found to be linear up to 40 min of incubation, while that for l-5-HTP was found to be linear up to 240 min of incubation. The optimum pyridoxal phosphate concentration was found to be similar for both substrates and was between 0.01 and 0.1 mM. The optimum pH values were found to be 7.2 and 8.2 for l-DOPA decarboxylase and l-5-HTP decarboxylase, respectively. K_m and V_max values for a human caudate nucleus l-DOPA decarboxylase were found to be 414 μM and 482 pmol/min/g wet weight, respectively, while those for l-5-HTP decarboxylase were found to be 90 μM and 71 pmol/min/g wet weight, respectively.     

Cryptotanshinione Inhibits β-Amyloid Aggregation and Protects Damage from β-Amyloid in SH-SY5Y Cells

The deposition of amyloid β-protein (Aβ) fibrils into plaques within the brain parenchyma and along cerebral blood vessels is a hallmark of Alzheimer’s disease (AD). Aβ42 oligomers and fibrils cause the breakdown of neural circuits, neuronal death and eventually dementia. Drugs that inhibit Aβ42 aggregation may be a novel direction in AD drug discovery. Cryptotanshinone (CTS), an active component of the medicinal herb Salvia miltiorrhiza, has been shown to improve learning and memory in several pharmacological models of AD. However, the effects of CTS on the Aβ aggregation and toxicity are unclear. The current work shows the effectiveness of CTS on the inhibition of Aβ42 aggregation and toxicity to human neuroblastoma cells. In this study, we demonstrated that CTS can inhibit Aβ42 spontaneous aggregation using thioflavin T fluorescence assay and transmission electron microscopy. Furthermore, we investigated the effects of CTS on Aβ-induced oxidative cell death in cultured SH-SY5Y cells. MTT and lactate dehydrogenase assays showed that CTS reduced the cytotoxicity induced by Aβ42. CTS also dramatically reduced Aβ42-induced cellular apoptosis and increased level of reactive oxygen species in these cells. Our study suggests that CTS may be useful in the inhibition or prevention of AD development and progression.     

ACTIVITIES OF 3,4-DIHYDROXY-l-PHENYLALANINE AND 5-HYDROXY-l-TRYPTOPHAN DECARBOXYLASES IN RAT BRAIN: ASSAY CHARACTERISTICS AND DISTRIBUTION

Abstract— Optimal assay conditions for decarboxylation of 3,4-dihydroxy- l -phenylalanine (DOPA) and 5-hydroxy- l -tryptophan (5-HTP) were determined in homogenates of rat brain by use of a sensitive, precise microradiometric technique. The two activities exhibited widely different optima for pH, temperature and substrate concentrations. The activity of 5-HTP decarboxylase was stimulated 2-fold by added pyridoxal-5-phosphate and was relatively resistant to antagonists of pyridoxal-P. By contrast, the activity of DOPA decarboxylase was stimulated 20-fold by added coenzyme and could be completely inhibited by carboxyl trapping agents. DOPA decarboxylase activity in subcellular fractions of brain was associated predominately with the soluble fractions and its distribution in the various fractions closely paralleled that of lactic acid dehydrogenase. 5-HTP decarboxylase activity in brain was distributed almost equally between soluble and particulate fractions, and its distribution within the particulate fractions differed from that of succinic acid dehydrogenase. The two decarboxylases in brain exhibited a 7-fold divergence in relative specific activity when their respective distributions in subcellular fractions were compared. Similarly, the regional distributions of the two decarboxylases in rat brain did not parallel one another; e.g. there was a 4-fold difference between the ratio of the two activities in cerebellum and that found in the corpus striatum.     

Iodine levels in different regions of the human brain

BackgroundIodine is a key component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are crucial for proper growth and development of the human body. In particular, a great body of literature has been published on the link between thyroid hormones and brain development and functioning. However, there is a lack of knowledge on the iodine levels in the human brain. The aim of this work was to determine the brain iodine levels and to contribute to the establishment of “reference” levels for iodine in the different anatomical and functional regions of normal (i.e., subjects without neurological or psychiatric diseases) human brain.MethodsThe iodine levels were determined in 14 brain regions of 52 dead subjects without evidence of neurological or psychiatric disease (n = 728 samples). Iodine was extracted from brain samples using a standard procedure and determined by inductively coupled plasma – mass spectrometry (ICP-MS).ResultsFour subjects presented abnormally high brain iodine levels (26.0 ± 14.2 μg/g) and were excluded from the overall data analysis. The average brain iodine levels for the remaining 48 subjects was 0.14 ± 0.13 μg/g dry weight. Iodine showed very heterogeneous distribution across the different brain regions, with the frontal cortex, caudate nucleus and putamen showing the highest levels. Interestingly, these brain regions are closely related to cognitive function. Iodine levels also showed a tendency to increase with age. The high levels observed in four subjects seemed to be related to previous exposure to iodine-based contrast agents widely used in radiology and computed tomography exams.ConclusionsThis paper provides important data on iodine levels at different brain regions in “normal” people, which can be used to interpret eventual imbalances in subjects with mental disorders and neurodegenerative diseases.     

Neurochemical Changes in Murine Trisomy 16: Delay in Cholinergic and Catecholaminergic Systems

Abstract: Two strains of Mus musculus musculus , C57BL/6J and CD-1, and Mus musculus poschiavinus , the tobacco mouse, were used to study the effects of increased gene dosage of mouse chromosome 16 (MMU 16). A developmental delay has been found in the brains of murine trisomy 16 (Ts 16) fetuses. Both the brain weight (in all three strains) and DNA content (in CD-1) were reduced, while protein content was unchanged in Ts16 compared to normal littermates. The daily increments of weight and protein (except in M. m. poschiavinus ) were significantly greater in Ts16. The activities of choline acetyltransferase and acetylcholinesterase and nuscarinic receptor binding were reduced. Their daily increments were also reduced to less than 56% that of littermates in Ts16 brains. The rate limiting enzymes of Catecholaminergic neurons, tyrosine hydroxylase and do-pamine β-hydroxylase, and the concentration of catecholamines in the brains of Ts16 animals were lower. The activities of three other Catecholaminergic enzymes, DOPA decarboxylase, catechol O -methyltransferase, and monoamine oxidase, were generally elevated in Ts16 brain, as were their daily increments. These observations indicate a significant developmental alteration in the maturation of the trisomic brain and suggest future avenues for defining the effect of increased gene dosage of MMU 16 in the CNS.     

POLYAMINE METABOLISM IN THE BRAIN AND LIVER OF THE DEVELOPING MONKEY

Abstract— The concentrations of putrescine and the polyamines, spermidine and spermine, along with the specific activities of the enzymes involved in their biosynthesis, ornithine decarboxylase, S -adenosylmethionine decarboxylase and spermidine synthase have been measured in brain and liver of the developing Rhesus monkey from mid-gestation, through birth and neonatal life to maturity. The results suggest that it is an increased concentration of putrescine and an increased specific activity of ornithine decarboxylase which are associated with the rapid growth of fetal brain during the middle of gestation. By the end of two-thirds of gestation, both of these parameters have attained values similar to those found in mature brain. The concentration of spermidine in brain and the specific activities of S -adenosylmethionine decarboxylase and spermidine synthase are lower in fetal brain than adult brain and increase slowly after birth to reach values similar to those of the adult only after several months. These results provide additional evidence that in the mature brain spermidine serves some function other than one associated with rapid growth.
Fetal liver at mid-gestation was characterized by increased concentrations of both putrescine and spermidine and increased specific activities of the enzymes which synthesize them. By two-thirds of gestation, values similar to those found in adult liver had been attained. Liver has thus reached maturity with regard to polyamine metabolism by this time.     

THE N-ACETYL-β-d-HEXOSAMINIDASES OF CALF AND HUMAN BRAIN

Abstract— Multiple forms of calf brain N -acetyl-β-hexosaminidases (β-2-acetamido-2- deoxy- d -glucoside acetamidodeoxyglucohydrolase EC 3.2.1.30) were separated on starch gel electrophoresis at pH 5.8. The organ specific electrophoretic patterns did not depend on the cell fraction studied. Much of the activity is only separated with difficulty from particulate matter. Two major and one minor component were separated on DEAE-cellulose chromatography at pH 5.8. Each component had both N -acetyl-β-galactosaminidase and N -acetyl-β-glucosaminidase activity. The ratio of these two activities was unaffected by the presence of N -ethylmaleimide or dithiothreitol. The forms were also examined by isoelectric focusing when at least four components were recognized: isoelectric at 4.9, 6.0, 6.3 and 6.8. Interconversion of the 4.9 form to that isoelectric at pH 6.0 was noted during vacuum dialysis. Samples from normal human brain and from cases of Tay-Sachs disease were also examined and the results compared.     

The high fermentative metabolism of Kluyveromyces marxianus UFV-3 relies on the increased expression of key lactose metabolic enzymes

The aim of this work was to obtain insights about the factors that determine the lactose fermentative metabolism of Kluyveromyces marxianus UFV-3. K. marxianus UFV-3 and Kluyveromyces lactis JA6 were cultured in a minimal medium containing different lactose concentrations (ranging from 0.25 to 64 mmol l⁻¹) under aerobic and hypoxic conditions to evaluate their growth kinetics, gene expression and enzymatic activity. The increase in lactose concentration and the decrease in oxygen level favoured ethanol yield for both yeasts but in K. marxianus UFV-3 the effect was more pronounced. Under hypoxic conditions, the activities of β-galactosidase and pyruvate decarboxylase from K. marxianus UFV-3 were significantly higher than those in K. lactis JA6. The expression of the LAC4 (β-galactosidase), RAG6 (pyruvate decarboxylase), GAL7 (galactose-1-phosphate uridylyltransferase) and GAL10 (epimerase) genes in K. marxianus UFV-3 was higher under hypoxic conditions than under aerobic conditions. The high expression of genes of the Leloir pathway, LAC4 and RAG6, associated with the high activity of β-galactosidase and pyruvate decarboxylase contribute to the high fermentative flux in K. marxianus UFV-3. These data on the fermentative metabolism of K. marxianus UFV-3 will be useful for optimising the conversion of cheese whey lactose to ethanol.     

Concentrations of putrescine and polyamines and their enzymic synthesis during androgen-induced prostatic growth

1. Castration of adult rats resulted in marked decreases in the amounts of putrescine, spermidine and spermine in the ventral prostate gland. Spermidine concentrations decline rapidly over the first 11 days after androgen withdrawal, reaching a value of only 12% of normal controls. Spermine concentrations diminish more slowly, reaching 24% of normal within 11 days. The spermidine/spermine molar ratio falls from 0.9 to 0.46 under these conditions. Putrescine concentrations decrease by 70% at 7 days after castration and then remain constant for some days. 2. After daily injections of testosterone propionate to rats castrated 7 days previously, prostatic spermidine and putrescine concentrations increase significantly within 24h; normal or even greater values are observed within 8 and 4 days respectively. In contrast, the spermine concentration does not increase until 5 days after commencement of androgen treatment. 3. The activities of two enzymes involved in polyamine biosynthesis (ornithine decarboxylase and a putrescine-activated S-adenosyl-l-methionine decarboxylase system) were greatly decreased soon after castration: after 7 days the respective values were 15% of normal for ornithine decarboxylase and 7% of normal for putrescine-dependent decarboxylation of S-adenosyl-l-methionine. Injection of testosterone propionate into animals castrated 7 days previously induced a rapid increase in both enzymic activities: ornithine decarboxylase was doubled in 6h, and increased three- to four-fold within 48h, whereas the putrescine-dependent decarboxylation of S-adenosyl-l-methionine doubled in 3h and increased tenfold within 48h of commencement of daily androgen treatments. 4. The activity of these enzyme systems was very low in the ventral prostates of hypophysectomized rats and was increased by administration of testosterone in a manner similar to that found in castrated rats. 5. Alterations in the activity of two ventral-prostate enzymes involved in ornithine production (arginase) and utilization (ornithine–2-oxoglutarate transaminase) that result from changes in the androgenic status of rats are described. 6. The findings presented suggest that the activities of ornithine decarboxylase and the putrescine-dependent S-adenosyl-l-methionine decarboxylase system, rather than ornithine concentrations, are rate-limiting for the formation of putrescine and polyamines in rat ventral prostate. 7. The relation of polyamines to androgen-induced prostatic growth is discussed with particular reference to the biosynthesis of proteins and nucleic acids.     

Tryptophan is a marker of human postmortem brain tissue quality

Postmortem human brain tissue is widely used in neuroscience research, but use of tissue originating from different brain bank centers is considered inaccurate because of possible heterogeneity in sample quality. There is thus a need for well-characterized markers to assess the quality of postmortem brain tissue. Toward this aim, we determined tryptophan (TRP) concentrations, phosphofructokinase-1 and glutamate decarboxylase activities in 119 brain tissue samples. These neurochemical parameters were tested in samples from autopsied individuals, including control and pathological cases provided by 10 different brain bank centers. Parameters were assessed for correlation with agonal state, postmortem interval, age and gender, brain region, preservation and freezing methods, storage conditions and storage time, RNA integrity, and tissue pH value. TRP concentrations were elevated significantly ( p  = 0.045) with increased postmortem interval; which might indicate increased protein degradation. Therefore, TRP concentration might be one useful and convenient marker for estimating the quality of human postmortem brain tissue.     

Changes in polyamine synthesis and concentrations during chick embryo development

We have measured the activities of the two rate controlling enzymes in polyamine synthesis, L-ornithine decarboxylase (ODC) and S-adenosyl-L-methionine decarboxylase (SAMDC), and the concentrations of the polyamines, putrescine, spermidine and spermine, in the developing chick embryo from laying to hatching. The embryo exhibited major peaks in the ODC and SAMDC activities as well as in the concentrations of all three polyamines at 15 h (gastrulation), 23-30 h (early organogenesis), days 4-5 (mid-organogenesis), and days 12-17 (organ growth and maturation). In the 4 and a half-day-old embryo, ODC activity and polyamine concentrations were about twice as high in the head region as compared to the trunk region. In the 14-day-old embryo, the highest ODC and SAMDC activities were found in lung, intestine and kidney, and there was a positive correlation between the enzyme activities and the growth rates of most organs/tissues.     

Maternal diazepam exposure on brain ornithine decarboxylase and growth of offspring

The prenatal treatment of diazepam on the developmental pattern of brain ornithine decarboxylase and the general growth of offspring were studied. Diazepam (120 mg/kg/day) was administered orally to pregnant Sprague-Dawley rats from day 14 to day 20 of gestation. The activity of brain ornithine decarboxylase and body weight of the offspring were measured from the late fetal stage to the early postnatal stage. It was found that diazepam inhibited both the prenatal and 4-hour postnatal ornithine decarboxylase activities, though the general maturation pattern of the enzyme in the brain was not much altered. It may indicate that diazepam inhibits early brain development. The enzyme activity fell off as it reached maturation. Prenatal treated neonates of 6-hour or older age group had the normal activities of brain ornithine decarboxylase. The general growth of the treated offspring was substantially retarded. Their body weights were very much lower than the control offspring. The results of the present study is an additional evidence that diazepam and other benzodiazepines should be used with great care in pregnant women.     

MAXIMUM ACTIVITIES, PROPERTIES AND DISTRIBUTION OF 5''NUCLEOTIDASE, ADENOSINE KINASE AND ADENOSINE DEAMINASE IN RAT AND HUMAN BRAIN

Abstract— The maximum activities of 5'nucleotidase, adenosine kinase and adenosine deaminase have been measured in several areas of rat and human brain. There is no major difference between the activities of nucleotidase and kinase between rat and human brain, but the activity of deaminase is considerably higher in human brain. The activities of all these enzymes are similar in three areas of rat brain and nine areas of human brain, except for hind brain of the human, which has a low activity of adenosine deaminase. This variation may indicate the existence of different steady-state concentrations of adenosine in certain areas of the brain.
Subcellular fractionation of different areas of rat brain showed that, whereas adenosine kinase and deaminase activities were located mainly in the soluble fractions, 5'nucleotidase was present in all subcellular fractions (i.e. membrane, synaptosomal, mitochondrial and soluble). In particular, there was no major localisation within the synaptosomal fraction. Thus it is unlikely that the regulation of the activities of these enzymes is dependent upon changes within a specific compartment (e.g. synaptosomes) in the brain.     

DIFFERENTIAL EFFECTS OF AGONAL STATUS ON MEASUREMENTS OF GABA AND GLUTAMATE DECARBOXYLASE IN HUMAN POST-MORTEM BRAIN TISSUE FROM CONTROL AND HUNTINGTON''S CHOREA SUBJECTS

Abstract— GABA and its biosynthetic enzyme glutamic acid decarboxylase (GAD) remained remarkably stable for many hours after death in both human putamen obtained at autopsy and in mouse brain stored under conditions simulating the routine handling of human cadavers. GAD activity was profoundly influenced by agonal status in control but not in choreic subjects. Conversely, GABA concentrations were unaffected by the agonal status but showed a significant age-related decline. GAD activity and GABA concentrations were positively correlated in sudden death control cases but not in control cases suffering a protracted terminal illness or in choreic subjects. In choreic putamen there was an approximate 50% reduction in GABA concentration and GAD activity (correcting for agonal status) consistent with the hypothesis that striatal GABA-containing neurones degenerate in this disease. Since GABA concentrations are unaffected by agonal factors they may provide a reliable marker for the integrity of GABA systems provided that control and pathological groups are matched for age and delay in post-mortem sampling.     

A study of selected catecholamine metabolizing enzymes: a comparison of depressive suicides and alcoholic suicides with controls

—The regional distributions of monamine oxidase (MAO) (EC 1.4.3.4), catechol-O-methyltransferase (COMT) (EC 2.1.1.6), tyrosine hydroxylase (TH) (EC 1.14.3.2), and dopamine-β-hydroxylase (DBH) (EC 1.14.2.1) have been examined in human brains obtained at autopsy from persons who died of natural causes (controls), and from persons who committed suicide and were further categorized as suffering from affective disorder (depression) or from alcoholism. Post mortem animal studies showed no changes in MAO or COMT activities in rabbit brain or in DBH activity in rat brain when the intact bodies were left at room temperature up to 24 h. TH activity in rabbit brains, however, began to decline immediately after death and after 24 h at room temperature it was approximately 48 per cent of the fresh brain level. There was no significant variation in activity of COMT, TH and DBH in human brain attributable to age or sex. MAO activities in the 60–70 yr decade were 34 per cent higher than in the 30–40 yr decade. MAO activities were highest in the hypothalamus and substantia nigra, TH activities were highest in substantia nigra, putamen and head of caudate, and DBH activities were greatest in tegmentum of pons and hypothalamus. Only minimal regional differences in COMT activities were observed. No significant differences were found between enzyme activities in brain areas of controls and suicides with the possible exception of TH in the substantia nigra, where the depressive suicides (but not the alcoholics) showed greater activity (P < 0·02). These findings appear not to support the catecholamine hypothesis of affective disorder.