Brain biogenic amines and altered thyroid function.

Evidence has been presented that alterations in thyroidal status produce marked changes in the metabolism of several biogenic amines in developing brain. Neonatal hypothyroidism induced either by ¹³¹I or by an anti-thyroid agent, methimazole, markedly decreased the concentrations of norepinephrine, dopamine and 5-hydroxytryptamine and the activity of their rate-limiting enzymes, tyrosine hydroxylase and tryptophan hydroxylase. However, the levels of 5-hydroxyindoleacetic acid, the chief metabolite of 5-hydroxytryptamine were elevated in several regions of the brain. Whereas thyroid deficiency in early life produced no appreciable change in whole brain monoamine oxidase activity, it was increased in mid brain and decreased in the hypothalamus. Brain acetylcholine levels were significantly elevated and the activity of acetylcholinesterase remained unchanged in rats made hypothyroid at 1 day of age. Delaying thyroidectomy for 20 days after birth produced less appreciable changes in norepinephrine and 5-hydroxytryptamine metabolism. Thyroid deficiency suppressed the ontogenesis of behavioural arousal and spontaneous locomotor activity. The administration of L-triiodothyronine to hypothyroid animals in early life restored the metabolism of various neurohumors virtually to the normal limits. However, when the replacement therapy was postponed until adulthood, L-triiodothyronine failed to produce any restorative effects, suggesting that a critical period exists in early life during which thyroid hormone must be present to permit normal developmental pattern of central amines. Data also have been obtained demonstrating that neonatal hyperthyroidism induced by daily administration of L-triiodothyronine results in an increased turnover of norepinephrine and 5-hydroxytryptamine. These amine changes were accompanied by a marked rise in the spontaneous locomotor activity in hyperthyroid rats. Finally, chronic treatment with lithium, an antimanic drug, also known to suppress thyroid hormone production, significantly decreased not only the spontaneous locomotor activity, but also changes in the turnover of 5-hydroxytryptamine and norepinephrine in neonatally hyperthyroid rats.     

Changes of Acetylcholinesterase Activity in Brain Areas and Liver of Sucrose- and Ethanol-Fed Rats

The effects of chronic ethanol or sucrose administration to rats on acetylcholinesterase from brain and liver were investigated. Membrane-bound and soluble acetylcholinesterase activities were determined in fractions prepared by centrifugation. The thermal stability and the effects of temperature and different types of alcohols on acetylcholinesterase activity were also studied. Membrane-bound acetylcholinesterase activity increased (p < 0.01) in the liver after chronic ethanol administration, whereas no differences among groups in the encephalic areas, except in the brain stem soluble form, were found. Membrane-bound acetylcholinesterase from the ethanol- and sucrose-treated groups was more stable at the different temperatures assayed between 10 and 50°C than that corresponding to the control group. Non-linear Arrhenius plots were obtained with preparations of membrane-bound acetylcholinesterase from rat liver, with discontinuities at 30°C (control or sucrose groups) or 34–35°C (alcohol group). Assays made with membrane-bound or soluble enzyme from brain showed linear Arrhenius plots in all groups studied. The inhibitory effects of increasing concentrations of ethanol, n-propanol and n-butanol on acetylcholinesterase preparations from forebrain, cerebellum, brain stem and liver of the three experimental groups (control, sucrose-fed and ethanol-fed) were very similar. However, n-butanol displayed a biphasic action on particulate or soluble preparations of rat forebrain. n-butanol inhibited (competitive inhibition) at higher concentrations (250–500 mM), while at lower concentrations (10–25 mM), the alcohol inhibited at low substrate concentrations but activated at high substrate concentration. These results suggest that the liver is more affected by ethanol than the brain. Moreover, the lipid composition of membranes is probably modified by ethanol or sucrose ingestion and this would affect membrane fluidity and consecuently the behaviour of acetylcholinesterase.     

Intracellular distribution of molecular forms of acetylcholinesterase in rat brain and changes after diisopropylfluorophosphate treatment

The subcellular distribution of acetylcholinesterase activities was studied in the striatum and cerebellum of rat brain. The highest percentage of the enzyme activity was found in the crude synaptosomal (P₂) fraction, with striatum much higher than cerebellum. On sucrose density gradient centrifugation analyses all the particulate fractions (P₁, P₂, and P₃) showed a major peak of the 10 S form of acetylcholinesterase activity with very little activity of the 4 S form of the enzyme. The 10 S/4 S ratio was much higher in striatum than in cerebellum. In the soluble fraction (100,000g supernatant) the 10 S form was less than the 4 S form in the adult rat brain, but this was reversed in the 6-day-old rat brain. After diisopropylfluorophosphate administration the recovery of acetylcholinesterase molecular forms in various subcellular fractions differed at different recovery periods. These results indicate that the distribution of molecular forms of acetylcholinesterase in rat brain differs in various subcellular fractions, and also the pattern of distribution differs in different regions of the brain as well as in adult and developing brains.     

Tryptophan force-feeding: Changes in the activities of acetylcholinesterase in various tissues of well-fed normal and adrenalectomized rats

The activity of acetylcholinesterase in the liver, heart, spleen, lungs and kidneys of well-fed normal and adrenalectomized rats was measured following a single tube-feeding of tryptophan. In well-fed normal rats, 30 min after tryptophan force-feeding, the enzyme activity in the heart and lungs was stimulated by 28 and 25% as compared to the water-fed control while in well-fed adrenalectomized rats acetylcholinesterase acticity in the heart, liver spleen and lungs was 40, 31, 22 and 15% increased, respectively over that of the corresponding control. In both groups of rats the enzyme activity in the kidney was unaffected by tryptophan. In the liver, spleen and heart of well-fed adrenalectomized rats the pattern of response for acetylcholinesterase to a tryptophan dose, over a period of 24-hr. was found to be biphasic. In well-fed adrenalectomized rats the tryptophan-mediated stimulation of acetylcholinesterase activity in the heart was found to be insensitive to actinomycin-D. The tryptophan-mediated stimulation of acetylcholinesterase activity in the heart of well-fed normal and adrenalectomized rats could not be related to the presence of an activator.     

Lamprey brain contains globular and asymmetric forms of acetylcholinesterase

To obtain more information about the evolution of acetylcholinesterase in the vertebrates, we studied the cholinesterase activity from the brain of the lamprey Petromyzon marinus. We found that the enzyme is true acetylcholinesterase and that 98% of it is present in the G₄ globular form. Only 1% of the enzyme was found distributed among the asymmetric forms A₄, A₈ and A₁₂; an additional 1% of the activity could not be extracted from the brain. The identity of the asymmetric forms was confirmed by collagenase digestion. These data demonstrate that asymmetric acetylcholinesterase is present in the CNS of organisms representing all classes of vertebrates. However, our results are inconsistent with an evolutionary trend that has been observed for vertebrate brain acetylcholinesterase.     

High-performance liquid chromatographic analysis of monoamines and some of theirγ-glutamyl conjugates produced by the brain and other tissues ofHelix aspersa (gastropoda)

1. Earlier reports from this and other laboratories have indicated that wide variations exist in estimates of the concentrations of norepinephrine in the brain and heart of the snail Helix aspersa. This is a report on investigations of norepinephrine concentrations in Helix aspersa tissues using high-performance liquid chromatography with electrochemical detection. In addition, the effects of treatment with some amino acid precursors or enzyme inhibitors on the concentrations of norepinephrine, dopamine, 5-hydroxytryptamine, and some of their metabolites were investigated. 2. The levels of norepinephrine in the brain were low (46 ng/g) in comparison to dopamine (2.1) micrograms/g) and 5-hydroxytryptamine (2.6 micrograms/g). Epinephrine was not observed in either snail heart of snail nervous tissue. 3. Administration of L-3,4-dihydroxyphenylalanine resulted in elevated snail brain dopamine, while 3,4-dihydroxyphenylserine treatment increased norepinephrine. Treatment with blockers of tyrosine hydroxylase and aromatic-L-amino acid decarboxylase reduced dopamine concentrations without affecting 5-hydroxytryptamine. 4. The dopamine metabolite 3,4-dihydroxyphenylacetic acid was observed only after administration of L-3,4-dihydroxyphenylalanine or dopamine and then only in very small amounts. At no time was the dopamine metabolite homovanillic acid or the 5-hydroxytryptamine metabolite 5-hydroxyindoleacetic acid observed in brain, heart, or whole-body extracts of the snail. 5. Incubation of nervous tissue with either dopamine or 5-hydroxytryptamine resulted in the production of electrochemically active metabolites which were identified by oxidation characteristics and cochromatography with synthesized standards as the gamma-glutamyl conjugates of the amines. Treatment of snails with 5-hydroxytryptamine or dopamine also resulted in the production of gamma-glutamyl conjugates. 6. The present experiments show that great care must be exercised when measuring monoamines and their metabolites in gastropod tissues by high-performance liquid chromatography with electrochemical detection.     

Inactivation of rat brain acetylcholinesterase by pyridoxal 5'-phosphate

Effects of pyridoxal 5'-phosphate on the activity of crude and purified acetylcholinesterase from cerebral hemispheres of adult rat brain were examined. Acetylcholinesterase was completely inactivated by incubation with 0.5 mM pyridoxal 5'-phosphate. The enzyme activity remained unaltered in the presence of analogs of pyridoxal 5'-phosphate, pyridoxal, pyridoxamine and pyridoxamine 5'-phosphate. The inhibition of acetylcholinesterase activity by pyridoxal 5'-phosphate appeared to be of a noncompetitive nature, as determined by Lineweaver-Burk analysis. The inhibitory effect of pyridoxal 5'-phosphate on acetylcholinesterase appeared to be a general one, as the activity of the enzyme from the brains of immature chick and egg-laying hen, and from different tissues of the adult male rats, exhibited a similar pattern in the presence of the inhibitor. The inhibitory effects of pyridoxal 5'-phosphate could be reversed upon exhaustive dialysis of the pyridoxal 5'-phosphate-treated acetylcholinesterase preparations. We propose that the effects of pyridoxal 5'-phosphate are due to its interaction with acetylcholinesterase, and that it can be employed as a useful tool for studying biochemical aspects of this important brain enzyme.     

Alterations in lipid composition and neuronal injury in primates following chronic aluminium exposure

The effect of chronic aluminium exposure (25 mg/kg b.wt.) was studied on the lipid composition and various membrane-bound enzymes in different regions of monkey brain. Aluminium (Al) administration caused a significant decrease in the total lipid, glycolipid, and phospholipid content of primate brain. Cholesterol levels and the phospholipid to cholesterol ratio were, however, markedly increased as a consequence of Al administration, thereby indicating a loss of membrane integrity. This was further confirmed when Al treatment was found to have a significant effect on the various membrane-bound enzymes in terms of decreased activities of Na⁺ K⁺ ATPase and acetylcholinesterase along with a decrease in the activity of the myelin-specific enzyme, 2′ 3′-cyclic nucleotide phosphohydrolase.     

Inactivation of rat brain acetylcholinesterase by pyridoxal 5′-phosphate

Effects of pyridoxal 5′-phosphate on the activity of crude and purified acetylcholinesterase from cerebral hemispheres of adult rat brain were examined. Acetylcholinesterase was completely inactivated by incubation with 0.5 mM pyridoxal 5′-phosphate. The enzyme activity remained unaltered in the presence of analogs of pyridoxal 5′-phosphate, pyridoxal, pyridoxamine and pyridoxamine 5′-phosphate. The inhibition of acetylcholinesterase activity by pyridoxal 5′-phosphate appeared to be of a noncompetitive nature, as determined by Lineweaver-Burk analysis. The inhibitory effect of pyridoxal 5′-phosphate on acetylcholinesterase appeared to be a general one, as the activity of the enzyme from the brains of immature chick and egg-laying hen, and from different tissues of the adult male rats, exhibited a similar pattern in the presence of the inhibitor. The inhibitory effects of pyridoxal 5′-phosphate could be reversed upon exhaustive dialysis of the pyridoxan 5′-phosphate-treated acetylcholinesterase preparations. We propose that the effects of pyridoxal 5′-phosphate are due to its interaction with acetylcholinesterase, and that it can be employed as a useful tool for studying biochemical aspects of this important brain enzyme.     

Modification by physostigmine of the cardiovascular responses to intracerebroventricular administration of 5-hydroxytryptamine in rats

In rats the effect of inhibition of the brain cholinesterase activity on the pressor and heart rate responses to 5-hydroxytryptamine (5-HT), administered into the lateral cerebral ventricle (l.c.v.) was examined. After administration of physostigmine (twice in a small dose of 2.5 micrograms l.c.v., 20 and 15 min before the second injection of 5-HT), the pressor effect of 5-HT (5 micrograms) was strongly reduced or almost abolished, its pure tachycardia was reduced or reversed into a bradycardia and its pure bradycardia was diminished or reversed into a tachycardia. The type of the cardiovascular response to ACh (5 micrograms l.c.v., 20 min after the second administration of 5-HT) indicates that the modification of the cardiovascular response to 5-HT was accompanied by inhibition of the brain cholinesterase activity. Thus, it seems that a functionally competent cholinesterase in the brain is necessary for the generation of the 5-HT-induced pressor response. The present experiments provide further evidence that there is a cholinergic link in the pathway by which serotonergic mechanisms in the preoptic-anterior hypothalamic area rise blood pressure and support the idea that the same link exists in the pathway(s) mediating the heart rate responses to intracerebroventricular administration of 5-HT.     

Chlorimipramine,fenfluramine and quipazine decrease 5-hydroxytryptamine synthesis in discrete rat brain nuclei

A procedure for studying 5-hydroxytryptamine synthesis by determining the rate of accumulation of 5-hydroxytryptophan after administering m-hydroxybenzylhydrazine, an inhibitor of aromatic-l-amino acid decarboxylase, and large doses of l-tryptophan was characterized. The utility of this method as an index of 5-hydroxytryptamine neuronal activity was studied by determining the effects on 5-hydroxytryptophan accumulation of direct and indirect 5-hydroxytryptamine agonists; viz, chlorimipramine-a 5-hydroxytryptamine uptake inhibitor, fenfluramine-a 5-hydroxytryptamine releaser, and quipazine-a 5-hydroxytryptamine receptor agonist. In the absence of m-hydroxybenzylhydrazine pretreatment 5-hydroxytryptophan and the dopamine precursor 3,4-dihydroxyphenylalanine were not readily detectable in any brain region studied. They both accumulated after m-hydroxybenzylhydrazine treatment in a time-dependent manner with the 30 min time point being on the linear portion of the curve. Administration of l-tryptophan 60 min before sacrifice increased 5-hydroxytryptophan, but not 3,4-dihydroxyphenylalanine, in a dose-related manner with the peak effect occurring after 100–300 mg/kg. Chlorimipramine, fenfluramine and quipazine all decreased 5-hydroxytryptophan, but not 3,4-dihydroxyphenylalanine, in m-hydroxybenzylhydrazine and l-tryptophan-treated animals. Chlorimipramine produced these effects in a dose-related manner only after l-tryptophan loading and without affecting brain concentrations of l-tryptophan. These results suggest that the measurement of 5-hydroxytryptophan after l-tryptophan administration and aromatic-l-amino acid decarboxylase inhibition might serve as a useful index of 5-hydroxytryptamine synthesis.     

5,5''-Dihydroxy-4,4''-Bitryptamine: A Potentially Aberrant, Neurotoxic Metabolite of Serotonin

Previous investigators have detected unknown oxidized forms of 5-hydroxytryptamine (5-HT) in the CSF of Alzheimer's disease (AD) patients. Furthermore, an unidentified autoxidation product of this neurotransmitter is an inhibitor of acetylcholinesterase (AChE), an enzyme compromised in the Alzheimer brain. In this study it is demonstrated that the major product of autoxidation of 5-HT is 5,5'-dihydroxy-4,4'-bitryptamine (DHBT). Central administration of DHBT to mice at a dose of 40 micrograms (free base) evokes profound behavioral responses, which persist until the animals die (approximately 24 h). One hour after central administration of DHBT, the levels of norepinephrine, dopamine, 5-HT, and acetylcholine and their metabolites in whole brain are greatly elevated. Disturbances to the catecholaminergic and serotonergic systems were still evident shortly before the death of animals. DHBT is also shown to be a noncompetitive inhibitor of AChE in vitro. These observations suggest that if DHBT is formed as an aberrant metabolite of 5-HT in the human brain, it could potentially be neurotoxic and contribute to the neuronal degeneration and other neurochemical and neurobiochemical changes associated with AD or perhaps other neurodegenerative diseases.     

Immunochemical differences among molecular forms of acetylcholinesterase in brain and blood

Molecular forms of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) differ in their solubility properties as well as in the number of their catalytic subunits. We used monoclonal antibodies to investigate the structure of acetylcholinesterase forms in brain, erythrocytes and serum of rats, rabbits and other mammals. Two antibodies were found to bind tetrameric acetylcholinesterase in preference to the monomeric enzyme. These antibodies also displayed lower affinity for certain forms of 'soluble' brain acetylcholinesterase than for the 'membrane-associated' counterparts. Furthermore, one of them was virtually lacking in affinity for the membrane-associated enzyme of erythrocytes. The basis for the antibody specificity was not fully determined. However, the immunochemical results were supported by measurements of enzyme thermolability, which showed that the catalytic activity of 'soluble' acetylcholinesterase was comparatively heat-resistant. These observations point toward structural differences among the solubility classes of acetylcholinesterase.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

Effect of propranolol on electrophysiologic features of the heart in patients with hyperthyroidism]

The effect of increasing doses of intravenously administered propranolol on electrophysiological features of heart was studied in 17 patients with untreated hyperthyroidism by using the transesophageal stimulation method. A positive and dose-dependent effect of propranolol on the studied parameters was found with the normalization of the majority of disturbances taking place after the administration of 6 mg of propranolol. This dose was safe and well tolerated by the patients. The sensitivity of the auriculo-ventricular junction to propranolol was less pronounced during the stimulated rhythm than during the sinus rhythm.     

Evidence for the role of brain biogenic amines in depressed motor activity seen in chemically thyroidectomized rats.

Abstract— The effects of exposure to an antithyroid drug, methimazole, on brain tyrosine hydroxylase and tryptophan hydroxylase activity, as well as the levels of norepinephrine, dopamine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid have been investigated in maturing brain. Daily treatment of neonatal rats with methimazole for 30 days induced chemical thyroidectomy as evidenced by significant impairment of body and brain growth. The activities or brain tyrosine hydroxylase and tryptophan hydroxylase and the levels of norepinephrine, dopamine and 5-hydroxytryptamine were markedly altered in a dose- and time-dependent manner in methimazole-treated rats. Conversely, the concentration of brain 5-hydroxyindoleacetic acid was elevated (46%) by methimazole administration. Treatment with the antithyroid drug failed to exert any significant effect on the endogenous levels of brain tryptophan, as well as on the activity of the deaminating enzyme, monoamine oxidase. Administration of triiodothyronine (25 or 100 μg/100 g) to hypothyroid rats for 30 days did not produce any appreciable effect upon the neurochemical parameters related to either norepinephrine or 5-hydroxytryptamine mctabolism. However, increasing the dose of triiodothyronine to 250 μg/100 g significantly elevated the levels of norepinephrine and 5-hydroxytryplamine as well as the activities of the two synthesizing enzymes, tyrosine hydroxylase and tryptophan hydroxylase. Brain 5-hydroxyindoleacetic acid levels were restored to normal values in thyroid hormone-deficient rats treated with this higher dose of triiodothyronine. Evidencc also was obtained to show that chemical thyroidectomy suppressed the spontancous locomotor activity in neonatal rats; the changes being apparent at 15 days of age. Our data support the view that thyroid hormone in neonatal life displays an important regulatory effect on the metabolism of norepinephrine, dopamine and 5-hydroxytryptamine. Since certain amines have been known to be implicated as the neurochemical substrates for behavioural arousal, it is conceivable that the observed hypoactivity in methimazolc-treated rats may, at least in part, be related to impaired maturation of norepinephrine and dopamine-synthesizing systems in brains of cretinous rats.     

USE OF ARRHENIUS PLOTS OF Na-K ATPase and ACETYLCHOLINESTERASE AS A TOOL FOR STUDYING CHANGES IN LIPID-PROTEIN INTERACTIONS IN NEURONAL MEMBRANES DURING BRAIN DEVELOPMENT

Abstract— The activities of Na-K ATPase and acetylcholinesterase in the rat brain cortex were measured at different postnatal ages as a function of temperature. It was found that compared to acetylcholinesterase, Na-K ATPase is more strongly affected by the rise in temperature and that this response is further enhanced with age. Arrhenius plots of the data were prepared and the apparent energies of activation were computed for each plot. It was observed that all plots were biphasic except that for Na-K ATPase of the immature (5-day-old) brain which showed no transition temperature, with an apparent energy of activation of 15.5 kcal/mol. The enzyme from the mature brain (25-day-old) showed an average transition temperature of 22.6°C, with average apparent energies of activation of 15.3 and 27.2 kcal/mol above and below the transition temperature respectively. The cortex of 1-day-old rat showed no Na-K ATPase activity. Arrhenius plots of acetylcholinesterase studied at ages 1, 5 and 25 days postnatally all showed transition temperatures which increased from an average of 16.1°C for 1-day-old to 17 and 21.5°C for 5- and 25-day-old animals respectively. The average apparent energies of activation for acetylcholinesterase below the transition temperature changed from 8.3 kcal/mole at day 1 to 8.7 and 7.2 kcal/mol at days 5 and 25, while above the transition temperature they were 4.3, 5.2 and 4.1 at days 1, 5 and 25 respectively. The results are discussed in terms of the differences and changes in the interactions of Na-K ATPase and acetylcholinesterase with membrane lipids during the postnatal phase of brain development.     

The role of liver tryptophan pyrrolase in the opposite effects of chronic administration and subsequent withdrawal of drugs of dependence on rat brain tryptophan metabolism.

1. Chronic administration of morphine, nicotine or phenobarbitone has previously been shown to inhibit rat liver tryptophan pyrrolase activity by increasing hepatic [NADPH], whereas subsequent withdrawal enhances pyrrolase activity by a hormonal-type mechanism. 2. It is now shown that this enhancement is associated with an increase in the concentration of serum corticosterone. 3. Chronic administration of the above drugs enhances, whereas subsequent withdrawal inhibits, brain 5-hydroxytryptamine synthesis. Under both conditions, tryptophan availability to the brain is altered in the appropriate direction. 4. The chronic drug-induced enhancement of brain tryptophan metabolism is reversed by phenazine methosulphate, whereas the withdrawal-induced inhibition is prevented by nicotinamide. 5. The chronic morphine-induced changes in liver [NADPH], pyrrolase activity, tryptophan availability to the brain and brain 5-hydroxytryptamine synthesis are all reversed by the opiate antagonist naloxone. 6. It is suggested that the opposite effects on brain tryptophan metabolism of chronic administration and subsequent withdrawal of the above drugs of dependence are mediated by the changes in liver tryptophan pyrrolase activity. 6. Similar conclusions based on similar findings have previously been made in relation to chronic administration and subsequent withdrawal of ethanol. These findings with all four drugs are briefly discussed in relation to previous work and the mechanism(s) of drug dependence.     

Effect of thiamine and its derivatives on acetylcholinesterase activity of the blood and brain of albino mice

Thiamine, thiaminepyrophosphate and 4-methyl-5-beta-oxyethylthiazole are studied for their effect on the acetylcholinesterase activity in the brain, blood plasma and cells. The activity of acetylcholinesterase in blood cells is shown to be inhibited most of all by thiamine and thiazole. Acetylcholinesterase of the brain has been efficiently inhibited only by thiamine pyrophosphate.     

GABA agonists and neurotransmitters metabolizing enzymes in steroid-primed OVX rats

The effect of intraventricular (IVT) administration of GABAA receptor agonist muscimol and GABAB receptor agonist, baclofen was examined on the activity of acetylcholinesterase (AChE), monoamine oxidase (MAO) and Na+, K+-ATPase in discrete areas of brain from estrogen-progesterone primed ovariectomized rats. AChE enzyme activity was increased in two subcellular fractions (soluble and total particulate) studied, with statistically significant changes in cerebral hemispheres (CH), cerebellum (CB), thalamus (TH) and hypothalamus (HT), Na+, K+-ATPase enzyme activity was decreased in both these fractions. MAO activity increased significantly in CH, TH and HT. The presented results suggest a functional relationship between GABAergic (inhibitory), cholinergic and monoaminergic (excitatory) systems by affecting the rate of degradation of the excitatory neurotransmitters and Na+, K+-ATPase. (Mol Cell Biochem 167: 107-111, 1997)