Ethanolamine O-sulphate Research Articles

Interactions between dopamine and γ-aminobutyrate in the substantia nigra: Implications for the striatonigral output hypothesis

Experiments employing a rodent circling model were conducted to test the predictive capacity of the theory which states that striatonigral γ-aminobutyrate neurones transmit striatal information influencing the animal's locomotion and orientation. In agreement with this proposal, blocking nerve conduction in one substantia nigra with procaine, or nigral γ-aminobutyrate receptors with bicuculline administered stereotaxically, frequently forced rats to move ipsiversively to systemic apomorphine, as though the treatment had impaired striatonigral transmission on that side of the brain. Attempts to reverse the direction of apomorphine circling by stimulating γ-aminobutyrate receptors with muscimol, by facilitating the amino acid's action with flurazepam, or by increasing its synaptic concentration either with a breakdown inhibitor (ethanolamine O-sulphate or 4-amino-hex-5-enoic acid) or an uptake blocker ( cis-1,3-aminocyclohexane carboxylic acid) in one nigra, proved unsuccessful. In fact, ethanolamine O-sulphate, flurazepam and muscimol all gave the appearance of hindering rather than enhancing the passage of striatal-derived motor information through the nigra. Broadly speaking, these drugs gave predictable behavioral responses from the ventromedial thalamus, suggesting they were acting in accordance with known mechanisms. The anomalous behaviour with ethanolamine O-sulphate may be attributed to its elevating γ-aminobutyrate levels in other brain areas, since similar ipsiversive rotations occurred if γ-aminobutyrate catabolism was prevented at a wide variety of extranigral sites. A simple explanation for the paradoxical ipsiversive behaviours produced by intranigral flurazepam or muscimol in combination with systemic or intracerebral injection of dopamine agonists, is that they act via presynaptic receptors to inhibit the release of endogenous γ-aminobutyrate and thereby impede striatonigral outflow ipsilaterally.

Quasi-morphine withdrawal behaviour: Indication for a specific involvement of the GABA-ergic nerve terminal compartment

Wet-dog-shaking resempling morphine withdrawal behaviour can be evoked in rats by administration of dipropylacetate (DPA). It has been postulated that DPA elicits the withdrawal like behaviour through specifically inhibiting the GABA-degradation in nerve terminals. Inhibition of GABA-transaminase (GABA-T) by aminooxyacetic acid (AOAA) in other compartments of the brain would result in an inhibition of the stimulated GABA-release via feedback on autoreceptors and therefore suppress the DPA-evoked behaviour. This hypothesis has been tested using the GABA-T inhibitors γ-acetylenic-GABA (GAG), γ-vinyl-GABA (GVG) and ethanolamine-O-sulphate (EOS). Although GAG and AOAA were found to suppress the body shakes, both GVG and EOS had no effect. Both GAG and AOAA have possibly also effect on glutamate decarboxylase (GAD) whereas GVG and EOS did not affect this enzyme, suggesting a nerve terminal-specific effect on DPA-induced behaviour. GVG stimulated DPA-evoked body shakes after 36 and 60 h, when a specific GABA-increase in nerve terminals will be present.

Evidence of a role for GABA in benzodiazepine effects on food preference in rats.

It has previously been shown that chronic treatment with the GABA-transaminase inhibitor ethanolamine-O-sulphate (EOS), which elevates brain GABA levels by around 200%, selectivity enhances novel food consumption in rats treated with chlordiazepoxide (CDP) and given a food preference test. To replicate and extend these findings, the effects of two doses of CDP with and without EOS pretreatment were compared with those of EOS or saline alone. EOS alone had no significant effects except to decrease eating rate but, in combination with 2.5 mg/kg CDP, it antagonised the increase in weight of familiar food eaten found with CDP alone and marginally increased weight eaten and duration of novel foot eating episodes. EOS magnified the effects of 5.0 mg/kg CDP to increase markedly the weight eaten and duration of episodes for novel chocolate drops. As no additive effects of EOS and CDP on rate of eating were found, the results are consistent with a facilitation of novel food consumption by an anxiolytic action of the two drugs, rather than by a rate-retarding action which might bias animals toward novel food. Finally, that EOS alone did not mimic the effects of CDP suggests that the role of GABA in the anxiolytic action of CDP may be indirect.

The reaction of ethanolamine O-sulphate with 4-aminobutyrate aminotransferase

The enzyme-induced or 'suicide' step by which the substrate analogue ethanolamine O-sulphate inactivates 4-aminobutyrate aminotransferase occurs at a rate that is one-tenth that observed for the release of the products of beta-elimination, namely ammonia, acetaldehyde and sulphate. An additional reversible reaction not leading to inactivation can be detected spectrally and this decreases the rates of both beta-elimination and inactivation. This reaction is ascribed to a step on the normal transamination path, although complete transamination does not occur significantly. The 14C moiety of radiolabelled ethanolamine O-sulphate is stably bound to the inactive enzyme in the proportion of 1 mol/mol of active site. The 35S-labelled sulphate moiety is not bound after inactivation, showing that beta-elimination must precede inactivation.

Effect of inhibitors of GABA aminotransferase on the metabolism of GABA in brain tissue and synaptosomal fractions.

Five inhibitors of the GABA degrading enzyme GABA-aminotransferase (GABA-T), viz., gabaculine, gamma-acetylenic GABA, gamma-vinyl GABA, ethanolamine O-sulphate, and aminooxyacetic acid, as well as GABA itself and the antiepileptic sodium valproate were administered to mice in doses equieffective to raise the electroconvulsive threshold by 30 V. The animals were killed at the time of maximal anticonvulsant effect of the respective drugs and GABA, GABA-T and glutamate decarboxylase (GAD) were determined in whole brain and synaptosomes, respectively. The synaptosomal fraction was prepared from brain by conventional ultracentrifugation procedures. All drugs studied brought about significant increases in both whole brain and synaptosomal GABA concentrations, and, except GABA itself, inhibited the activity of GABA-T. Furthermore, all drugs, except GABA and gamma-acetylenic GABA, activated GAD in the synaptosomal fraction. This was most pronounced with ethanolamine O-sulphate, which induced a twofold activation of this enzyme but exerted only a weak inhibitory effect on GABA-T. The results suggest that activation of GAD is an important factor in the mechanism by which several inhibitors of GABA-T and also valproate increase GABA concentrations in nerve terminals, at least in the relatively non-toxic doses as used in this study.

Correlation between alterations in brain GABA metabolism and seizure excitability following administration of GABA aminotransferase inhibitors and valproic acid—a re-evaluation

The time course of the effects of aminooxyacetic acid, ?-vinyl GABA, ?-acetylenic GABA, gabaculine, ethanolamine-O-sulphate (EOS) and valproic acid (VPA) on brain GABA content and the activities of glutamic acid decarboxylase (GAD) and GABA aminotransferase (GABA-T), the enzymes involved in biosynthesis and degradation of GABA, was re-determined and compared with the action on the electroconvulsive threshold in mice. All drugs caused significant increases in the seizure threshold, and the temporal pattern of this effect correlated rather well with the induced elevation of brain GABA. However, no clear relationship was found between the extent of GABA increase and the relative increase of seizure threshold. Except for VPA, the time course of the increment in brain GABA followed closely the inhibition of GABA-T. The activity of GAD was gradually decreased by ?-acetylenic GABA and a slow decline of GAD activity was also observed after ?-vinyl GABA. EOS and gabaculine suggesting a feedback repression of GAD synthesis by highly elevated GABA concentrations. Concomitant with significant reduction of GAD activity, a decrease in seizure threshold occurred though brain GABA levels remained markedly elevated. On the other hand, following administration of VPA the effect of GABA levels was paralleled by an increase in GAD activity indicating that the GABA-elevating action of this drug can be attributed at least in part to an activation of GABA synthesis. The data suggest that reduction of GAD activity may be an inevitable consequence of increasing brain GABA concentrations over a certain extent and this effect seems to limit the anticonvulsant efficacy of GABA-T inhibitors.

γ-Aminobutyric acid metabolism in rat brain following chronic oral administration of ethanolamine O-sulphate

Chronic, oral EOS ∗ administration resulted in a marked inhibition of rat whole-brain GABA-T activity and a significant increase in brain GABA concentrations. The maximum degree of GABA-T inhibition attained was 83 per cent, when GABA levels were 200 per cent of control values. A fixed dose of EOS produced a steady fall in GABA-T activity over the first 7 days of administration, when enzyme activity appeared to stabilize at 20–25 per cent of control values. Concurrently, GABA levels rose to a steady maximum value of approximately 240 per cent of control values. These changes were accompanied by significant reductions in whole-brain GAD activity. Chronic EOS also produced small but significant increases in brain content of alanine and taurine. No behavioural changes were seen following chronic EOS administration.

The central GABAergic system and control of food intake under different experimental conditions.

Intracerebroventricular injections of gamma-aminobutyric acid (GABA) and of the GABA-transaminase inhibitor, ethanolamine-O-sulphate (EOS), decreased the food intake of freely-fed (GABA and EOS) and food-deprived rats (EOS). The effect, still evident 24 h after treatment, was not decreased by the GABA receptor-blocker bicuculline. In contrast, intracerebroventricular injections of the GABA receptor-agonist, muscimol, caused an increase in food intake of freely-fed rats that was antagonized by bicuculline. The eating of animals receiving only bicuculline was stimulated in free-feeding and depressed in food-deprived conditions. These opposite results suggest that muscimol binds preferentially to some GABA receptors, probably those within the satiety-controlling areas (i.e. ventromedial hypothalamus), and that bicuculline influences mainly those postsynaptic neurons where GABAergic inputs prevail. These observations and the data from EOS- and GABA-treated rats provide evidence for involvement of GABA neurons in the regulation of feeding behaviour. The balance of the different effects produced in each of these areas by this modulation appears to be a decrease in feeding behaviour.

Thyrotropin-releasing rormone: hyperactivity and mesolimbic dopamine system in rats

The mechanism of stimulatory action of thyrotropin-releasing hormone (TRH) on spontaneous motor activity was investigated in rats. TRH produced a significant hyperactivity with intraperitoneal administration of 20 mg/kg or bilateral injection of 10 µg into the nucleus accumbens septi (NAS). Following bilateral injection of 6-hydroxydopamine into the mesolimbic dopamine (DA) pathway, the hyperactivity induced by TRH was not altered, whereas the response to apomorphine given intraperitoneally or DA injected into the NAS was clearly enhanced. The TRH-induced hyperactivity was remarkably suppressed by α-methyltyrosine and in contrast, augmented by pargyline. Systemic injection of aminooxyacetic acid in a dose producing behavioral depression reduced markedly the TRH-induced hyperactivity. Bilateral injection of ethanolamine O-sulphate (100 µg) into the NAS produced no behavioral depression per se, but remarkably attenuated the hyperactivity response to TRH or DA (20 µg) given intraperitoneally or into the NAS. Both TRH (10−5 and 10−24 M) and methamphetamine (10−6–10−4 M) increased the spontaneous release of 14C-DA from rat NAS slices. These findings suggest that TRH induces hyperactivity by enhancing DA release from nerve terminals in the NAS without a direct stimulation of the post-synaptic DA receptors. TRH and GABA, independently or via interaction between them, may play a reciprocal regulatory role in the activity of the mesolimbic DA system.

Effect of ethanolamine- O-sulphate on regional gaba metabolism in the mouse brain

The distribution of [ 3 H]ethanolamine-O- sulphate (EOS) and the regional changes in GABA metabolism after 160 μg (8 mg/kg) intracerebroventricularly and 2 g/kg subcutaneously have been studied in the mouse brain. Over 60 per cent of the injected radioactivity (given i.c.v.) was lost within the first hr. That remaining at 24 hr, however, after subcellular fractionation appeared to be associated with GABA-transaminase (GABA-T). The greatest binding occurred in the hypothalamus, an area with a high endogenous GABA concentration and the highest turnover rate of those areas studied. GABA turnover rates calculated over a 4 hr period for both 160 μg i.c.v. and 2 g/kg s.c. correlated (P < 0.001) with the endogenous GABA concentrations. EOS 2 g/kg s.c. was as effective as 160 μg i.c.v. in inhibiting GABA-T in the brain, but has a slower onset of action. The possibility of a larger GABA-T pool in the hypothalamus than in the other areas studied is discussed.

Regulation of nigro-striatal dopaminergic neurotransmission in the rat

Abstract The activity of the rat nigro-striatal dopaminergic system has been studied after unilateral injections of ethanolamine O-sulphate (EOS) (200 μg kg −1 ) into the substantia nigra, zone reticulata and after discrete electrolytic lesions in the same area. Twenty-four hr after EOS pretreatment, GABA-T activity was significantly reduced and the GABA concentration significantly elevated in the ipsilateral substantia nigra. At that time, apomorphine (1–8 mg kg −1 ) and (+) amphetamine (1–8 mg kg −1 ) injected intraperitoneally produced dose-dependent turning of the rats towards the injected side. There was a close temporal relationship between the increase in GABA concentration in the substantia nigra (an increase which was confined to the substantia nigra and which persisted for up to 10 days) and apomorphine-induced turning. No such behavioural changes were produced by EOS injected into the mesencephalic reticular formation or saline injections into the substantia nigra. After unilateral electrolytic lesions in the substantia nigra, similar doses of apomorphine and amphetamine produced turning towards the lesioned side and the response could still be elicited 48 days after lesioning. The dopamine concentration was reduced and the homovanillic acid concentration was increased significantly in the ipsilateral striatum 24 hr after EOS pretreatment and 14 days after electrolytic lesioning. Both dopamine and homovanillic acid concentrations returned to control levels seven days after EOS pretreatment. There was a significant increase in the firing rate of spontaneously active zona compacta neurones in the ipsilateral substantia nigra, 24 hr after EOS injection. It is concluded that the elevation of GABA concentration in the zona reticulata of the substantia nigra, or electrolytic lesions in this area, indirectly increased the activity of the ipsilateral nigro-striatal dopaminergic system. A tentative hypothesis is proposed to explain these observations.

Circling behavior in rodents following an imbalance of basal ganglia GABA concentrations

Unilateral focal injection of the GABA-transaminase inhibitor, ethanolamine O-sulphate, into one substantia nigra or globus pallidus of rats or the striatum of mice induces spontaneous and drug-induced circling behaviour. Circling parallels the imbalance of GABA concentrations between the injected and the noninjected side of the brain, being most striking on Day 1 and 3, and non-existent by Day 7. Increases in GABA concentration were demonstrated in areas distant from the injection site, on both the injected and noninjected side of the brain presumably due to diffusion of the ethanolamine O-sulphate. This diffusional effect made it impossible to define the exact site of GABA and dopamine interaction.

Monoamine and GABA metabolism and the anticonvulsant action of DI-n-propylacetate and ethanolamine-O-sulphate

The time course of changes in behaviour, seizure response and cerebral monoamine and γ-aminobutyric acid (GABA) metabolism has been studied in relation to the anticonvulsant actions of di-n-propylacetic acid (DPA) and ethanolamine-O-sulphate (EOS) on sound-induced seizures in DBA/2 mice. Changes in cerebral monoamine metabolism after EOS (75 or 150 μg, intracerebroventricularly) were not related to its anticonvulsant action. The primary effect was GABA-transaminase inhibition (by 50–70%) leading to a 2–4 fold increase in cerebral GABA concentration. Increases in brain GABA concentration (maximally 36%), 5-hydroxyindoleacetic acid (5HIAA, maximally 134%) and homovanillic acid (HVA, maximally 183%) were seen after DPA (400–600 mg/kg, i.p.). The time course of the increases in HVA and 5HIAA did not correlate with the anticonvulsant effect. Elimination of these increases by the use of inhibitors of monoamine synthesis (α-methyl-p-tyrosine and p-chlorophenylalanine) did not alter the anticonvulsant effect of DPA. Experiments using probenecid suggested that the increases in 5HIAA and HVA after DPA result from inhibition of their active transport out of the brain.

Possible GABA-mediated control of dopamine-dependent behavioural effects from the nucleus accumbens of the rat.

The effect of elevating GABA levels in the region of the nucleus accumbens on various dopamine-dependent behaviours in the rat has been studied. The GABA-transaminase inhibitor, ethanolamine O-sulphate (EOS) was injected bilaterally (through a needle angled at 45 degrees) into the nucleus accumbens. This resulted in a 4-5 fold increase in the GABA concentrations in the mesolimbic areas on day 1, a 2-fold increase on day 3, and a return to normal by day 7. Moderate increases in striatal and cortical GABA levels were also seen on days 1 and 3. At all times animals exhibited normal spontaneous activity and exploratory behaviour in a hold-board apparatus. However, on day 1, when mesolimbic GABA levels were maximal, a low dose of systematically administered amphetamine (0.5 mg/kg) did not induce the increased locomotor activity seen in a control group of animals. Similarly on day 1, the direct injection of dopamine into the nucleus accumbens of rats previously injected with EOS did not evoke the usual hyperactivity response. This response returned to normal on day 7. Apomorphine-induced stereotyped behaviour patterns observed on days 1 and 2 did not significantly differ in those rats previously injected with EOS with animals of a control group. A possible GABA-mediated control of dopaminergic mechanisms in the nucleus accumbens is suggested, and the possible site of interaction discussed.

Active-site-directed irreversible inhibition of 4-aminobutyrate aminotransferase by ethanolamine O-sulphate.

Research Article| November 01 1972 Active-site-directed irreversible inhibition of 4-aminobutyrate aminotransferase by ethanolamine O-sulphate L J Fowler; L J Fowler 1Department of Pharmacology, The School of Pharmacy, University of London, London WC1N lAX, U.K. Search for other works by this author on: This Site PubMed Google Scholar R A John R A John 2Department of Biochemistry, University College, Cathays Park, Cardiff CF1 1XL, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem J (1972) 130 (2): 80P–81P. https://doi.org/10.1042/bj1300080Pb Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation L J Fowler, R A John; Active-site-directed irreversible inhibition of 4-aminobutyrate aminotransferase by ethanolamine O-sulphate. Biochem J 1 November 1972; 130 (2): 80P–81P. doi: https://doi.org/10.1042/bj1300080Pb Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll JournalsBiochemical Journal Search Advanced Search This content is only available as a PDF. © 1972 The Biochemical Society1972 Article PDF first page preview Close Modal You do not currently have access to this content.

Active-site-directed irreversible inhibition of rat brain 4-aminobutyrate aminotransferase by ethanolamine O-sulphate in vitro and in vivo

1. Partially purified preparations of rat brain 4-aminobutyrate aminotransferase were inhibited in a time-dependent manner by ethanolamine O-sulphate. The inhibition was not reversed by dialysis. 2. The inhibitor formed an initial reversible complex with the enzyme (K(i)=4.4x10(-4)m) and the rate of inactivation followed pseudo-first-order kinetics (k=7.15x10(-4)s(-1)). The inclusion of 4-aminobutyrate markedly slowed the rate of inactivation. 3. Ethanolamine O-sulphate did not inhibit glutamate decarboxylase, alanine aminotransferase or aspartate aminotransferase. 4. Intracisternal injection of ethanolamine O-sulphate into rats led to rapid inactivation of 4-aminobutyrate aminotransferase in vivo.