Ethanolamine O-sulphate Research Articles

289-LB: Hepatic Gamma-Amino Butyric Acid Release Drives Hyperinsulinemia and Insulin Resistance

The degree of hepatic lipid accumulation in obesity directly correlates with the severity of hyperinsulinemia and systemic insulin resistance. Here, we propose a mechanism that explains this associative link, whereby, hepatic steatosis dysregulates glucose and insulin homeostasis. Obesity-induced lipid accumulation results in hepatocyte depolarization. We have established that hepatocyte depolarization depresses hepatic vagal afferent nerve (HVAN) firing (22.9 ± 7.6%; P < 0.05). The HVAN plays a key role in regulating whole-body glucose homeostasis. Accordingly, we propose that dysregulated hepatocyte-vagal communication underlies the metabolic dysfunction in obesity. Using an ex vivo explant liver slice model, we showed that diet induced obesity nearly triples hepatic GABA release/mg DNA in mice (P < 0.05). We hypothesize that hepatic GABA release decreases HVAN activity to stimulate insulin release and decrease peripheral insulin sensitivity. To establish that hepatocyte depolarization encourages GABA export in obesity, we virally induced expression of Kir2.1, a hyperpolarizing channel, in hepatocytes. Kir2.1 expression decreased hepatic slice GABA release to half of that observed in control obese mice, while protecting against hyperinsulinemia and insulin resistance on a high fat diet. Hepatic GABA is synthesized by GABA-Transaminase (GABA-T). To determine the role of hepatic GABA production in diet induced metabolic dysfunction, we treated obese mice with the irreversible GABA-T inhibitors, ethanolamine-O-sulphate (EOS) or vigabatrin (8mg/day; IP). Within 5 days, GABA-T inhibition ameliorated the hyperinsulinemia and insulin resistance of obesity (P < 0.05). These improvements in glucose homeostasis are dependent on an intact HVAN, as EOS did not affect serum insulin or insulin sensitivity in obese hepatic vagotomized mice. This work establishes that limiting hepatocyte GABA production or release can mute the glucoregulatory dysfunction common to obesity. Disclosure C. Geisler: None. S. Ghimire: None. B.J. Renquist: None. Funding Arizona Biomedical Research Commission (ADHS14-082986, ADHS18-201472 to B.J.R.); American Heart Association (15BGIA25090300 to B.J.R.)

GABA-mediated effects of some taurine derivatives injected i.c.v. on rabbit rectal temperature and gross motor behavior

Some synthetic taurine analogues, namely ethanolamine-O-sulphate (EOS), N,N-dimethyltaurine (DMT), N,N,N-trimethyltaurine (TMT) and 2-aminoethylphosphonic acid (AEP) were shown to interact with rabbit brain GABA(A)- or GABA(B)-receptors, while (+/-)piperidine-3-sulfonic acid (PSA) inhibited the activity of rabbit brain 4-aminobutyrate transaminase. This suggests that they behave like direct/indirect GABA agonists or GABA antagonists and affect thermoregulation and gross motor behaviour (GMB) which are under GABA control. In the present study micromole (1.2-48) amounts of these compounds were i.c.v. injected in conscious, restrained rabbits while monitoring rectal temperature (RT), ear skin temperature (EST) and GMB. AEP, EOS, DMT and TMT induced a dose-related hyperthermia, ear vasoconstriction and excitation of GMB, while PSA induced a dose-related hypothermia, ear vasodilation and inhibition of GMB. EOS antagonized in a dose-related fashion hypothermia induced by 60 nmol THIP, a GABA(A) agonist, while AEP, DMT and TMT counteracted that induced by 8 nmol R(-)Baclofen, a GABA(B) agonist. In conclusion, EOS and AEP, DMT, TMT seem to act as GABA(A) and GABA(B) antagonists, respectively, while PSA behaves like an indirect GABA agonist, all affecting the central mechanisms which drive rabbit thermoregulation.

GABA release and uptake measured in crude synaptosomes from Genetic Absence Epilepsy Rats from Strasbourg (GAERS)

GABA release and uptake were examined in Genetic Absence Epilepsy Rats from Strasbourg and in non-epileptic control animals, using crude synaptosomes prepared from the cerebral cortex and thalamus. Uptake of [ 3H]GABA over time was reduced in thalamic synaptosomes from epileptic rats, compared to controls. The affinity of the uptake process in thalamic synaptosomes was lower in epileptic animals. NNC-711, a ligand for the GAT-1 uptake protein, reduced synaptosomal uptake by more than 95%; β-alanine, an inhibitor selective for the uptake proteins GAT-2 and -3, did not significantly reduce synaptosomal uptake. Autoradiography studies using [ 3H]tiagabine, a ligand selective for GAT-1, revealed no differences between the strains in either affinity or levels of binding. Ethanolamine O-sulphate (100 μM), a selective inhibitor of GABA-transaminase, did not affect uptake levels. Aminooxyacetic acid (10–100 μM), an inhibitor of GABA-transaminase and, to a lesser extent, glutamate decarboxylase, caused an increase in measured uptake in both thalamic and cortical synaptosomes, in both strains. We found no difference in in vitro basal or KCl-stimulated endogenous GABA release between epileptic and control rats. These results indicate that GABA uptake in the thalamus of Genetic Absence Epilepsy Rats from Strasbourg was reduced, compared to control animals. The lower uptake affinity in the epileptic animals probably contributed to the reduction in uptake over time. Uptake appeared to be mediated primarily by the ‘neuronal’ transporter GAT-1. Autoradiography studies revealed no differences in the number or affinity of this uptake protein. It is therefore possible that altered functional modulation of GAT-1 caused the decrease in uptake shown in the epileptic animals. Inhibition of GABA-transaminase activity had no effect on measured GABA uptake, whereas a reduction in glutamate decarboxylase activity may have affected measured uptake levels.

Effect of chronic treatment with the GABA transaminase inhibitors gamma-vinyl GABA and ethanolamine O-sulphate on the in vitro GABA release from rat hippocampus.

1. The effects of 2, 8 and 21 day oral treatment with the specific gamma-aminobutyric acid transaminase (GABA-T) inhibitors gamma-vinyl GABA (GVG) and ethanolamine O-sulphate (EOS) on brain GABA levels, GABA-T activity, and basal and stimulated GABA release from rat cross-chopped brain hippocampal slices was investigated. 2. Treatment with GABA-T inhibitors lead to a reduction in brain GABA-T activity by 65-80% compared with control values, with a concomitant increase in brain GABA content of 40-100%. 3. Basal hippocampal GABA release was increased to 250-450% of control levels following inhibition of GABA-T activity. No Ca2+ dependence was observed in either control or treated tissues. 4. GVG and EOS administration led to a significant elevation in the potassium stimulated release of GABA from cross-chopped hippocampal slices compared with that of controls. Although stimulated GABA release from control tissues was decreased in the presence of a low Ca2+ medium, GVG and EOS treatment abolished this Ca2+ dependency. 5. GABA compartmentalization, Na+ and Cl- coupled GABA uptake carriers and glial release may provide explanations for the loss of the Ca2+ dependency of stimulated GABA release observed following GVG and EOS treatment. 6. Administration of GABA-T inhibitors led to increases in both basal and stimulated hippocampal GABA release. However, it is not clear which is the most important factor in the anticonvulsant activity of these drugs, the increased GABA content 'leaking' out of neurones and glia leading to widespread inhibition, or the increase in stimulated GABA release which may occur following depolarization caused by an epileptic discharge.

Unforgettable tetanus

Unforgettable tetanus

Effects of chronic oral treatment with GABA-transaminase inhibitors on the GABA system in brain, liver, kidney, and plasma of the rat

The inhibitory neurotransmitter γ-aminobutyric acid (GABA) is not solely located in the CNS, it and the enzymes responsible for its synthesis (glutamic acid decarboxylase, GAD, EC 4.1.1.15) and catabolism (GABA-transaminase, GABA-T, EC 2.6.1.19) are also present in non-neuronal organs. Following 2, 8 and 21 day oral administration of ethanolamine-O-sulphate (EOS) and γ-vinyl GABA (GVG), two irreversible inhibitors of GABA-T, the GABA content and activities of GAD and GABA-T in rat brain, liver and kidney, and the GABA content of plasma were determined. GABA-T activity was significantly decreased (over 80%) in liver, brain and kidney, although there was 2–3 times the residual activity left in the brain compared with the peripheral organs. GABA content was subsequently significantly elevated in the liver (300–1500%), plasma (200–300%) and brain (200–300%), although, surprisingly, the kidney GABA content was reduced (by 60–70%) compared with control. GAD activity was decreased following 8 day treatment in liver and brain. Kidney GAD was reduced at all time points. These two compounds are anticonvulsant, GVG is used clinically for the treatment of epilepsy but it seems that these drugs have significant peripheral effects.

The Effect of Chronic Treatment with the GABA Transaminase Inhibitors γ‐Vinyl‐GABA and Ethanolamine‐O‐Sulphate on the In Vivo Release of GABA from Rat Hippocampus

The effects of chronic treatment with the specific, mechanism-based, irreversible inhibitors of 4-aminobutyrate aminotransferase (EC 2.6.1.19; GABA transaminase), ethanolamine O-sulphate (EOS), and 4-aminohexenoate [vigabatrin; gamma-vinyl-GABA (GVG)] on the extracellular concentrations of GABA in the hippocampus have been studied using in vivo microdialysis in conscious animals. Oral dosing [3 mg/ml of drinking water, giving doses of GVG of 194 +/- 38 mg/kg/day and of EOS of 303 +/- 42 mg/kg/day (mean +/- SD)] was followed by microdialysis at 2, 8, and 21 days. The basal outflow of GABA (in the range of approximately 1-2 pmol/30 microliters/30-min sample) after 2 and 8 days of treatment was not significantly different from that in control animals, but the 21-day treatment gave significant rises in the extracellular GABA concentration (up to approximately 6-8 pmol/30 microliters/30-min sample). Both inhibitors gave similar results. Depolarisation with 100 mM K+ gave large increases in GABA release in control (approximately 20-60 pmol/30 microliters/30-min sample) and treated animals. The 8- and 21-day-treated animals showed significant increases in the stimulated release compared with control animals (approximately 80-100 pmol/30 microliters/30-min sample). Excluding Ca2+ had no significant effect on either basal or stimulated release. The significant increases in K(+)-evoked release of GABA show that the increased intracellular pool of GABA is available for release, and this may be related to the anticonvulsant action of these compounds.

Neonatal administration of a GABA-T inhibitor alters central GABAA receptor mechanisms and alcohol drinking in adult rats.

Long-term effects of chronic treatment with a GABA-T (GABA-transaminase) inhibitor, ethanolamine O-sulphate (EOS) (200 mg/kg/day for the postnatal days 3-21) on the binding parameters of GABAA receptors, hypothalamic monoamines and subsequent behavior were studied in Wistar rats. At the age of 1 month, EOS-treated rats showed reduced activity in the open-field and, at the age of 4 months, their voluntary alcohol consumption was increased. No changes were seen in Porsolt's swim test or in the plus-maze test. Weight gain was significantly retarded in EOS-treated rats. Maximal stimulation of [3H] flunitrazepam binding by GABA was decreased in the cerebral cortex and the EC50-value for the GABA stimulation increased in the hippocampus in the EOS rats at the age of 4 months. EOS treatment did not alter the cerebellar diazepam sensitive and insensitive binding components of the imidazobenzodiazepine [3H]Ro 15-4513. No changes were observed in the hypothalamic monoamine concentrations. The results are in agreement with the idea that GABA-T inhibitor treatment permanently alters GABAA mechanisms. Moreover, altering the CNS GABA level during development increases adult alcohol intake in rat.

GABAergic regulation of striatal opioid gene expression

Peptides derived from prodynorphin and preproenkephalin are located in GABAergic striatal projection neurons. We have used nucleic acid hybridization techniques to investigate the role of GABA in the regulation of striatal opioid peptide gene expression. Rats were treated with the GABA-transaminase inhibitors aminooxy acetic acid, ethanolamine O-sulphate and γ-vinyl-GABA for one week. The GABA levels in the striatum were significantly elevated after each treatment. The GABA-transaminase-inhibitors decreased the striatal levels of the opioid peptides met-enkephalin and dynorphin(1–8) and concomitantly decreased the concentrations of the mRNAs coding for proenkephalin and prodynorphin. These findings indicate that GABA exerts an inhibitory influence on prodynorphin and proenkephalin gene expression in the striatum. The mechanisms underlying these inhibitions are discussed.

Behavioural and biochemical effects of muscimol in ethanolamine O-sulphate-treated rats

A behavioural model, accompanied by biochemical analysis, was used to study the effects of the GABA-A receptor agonist muscimol on untreated and ethanolamine O- sulphate (EOS)-treated male rats. The most pronounced effect of muscimol was a lengthening of the duration of investigating behaviour. Pretreatment with EOS for 29 days potentiated this effect. Muscimol decreased the accumulation of GABA in the substantia nigra after 8 days but not after 30 days of EOS treatment, indicating that receptor adaptation might have occurred. We conclude that muscimol influences investigating behaviour and that chronic elevated brain GABA levels potentiate this effect.

The behavioural effects of chronic elevation of rat brain GABA by ethanolamine O-sulphate

This study examined the functional effects of long-term elevated brain GABA concentrations. The increase in GABA was achieved by use of the GABA-aminotransferase (GABA-T) inhibitor, ethanolamine O-sulphate (EOS). Forms of exploratory behaviour pre viously demonstrated to be sensitive to GABAergic receptor stimulation were measured over a 4 week period of EOS treatment. The most pronounced behavioural effect was an increased duration of investigating behaviour following 2-21 days of EOS treatment. This effect was accompanied by an accumulation of GABA in the substantia nigra and the corpus striatum. After 28-30 days of EOS treatment the GABA concentration was still significantly elevated, whereas the investigating behaviour was no longer different from controls.

Adaptation of the GABAA-receptor complex in rat brain during chronic elevation of GABA by ethanolamine O-sulphate.

Slice preparations of rat cuneate nucleus were used for studies on the gamma-aminobutyric acid GABAA-receptor complex following chronic and acute pretreatment with GABA-alpha-ketoglutarate aminotransferase (GABA-T) inhibitors. The whole brain GABA concentration was significantly increased 2.9 fold and 2.6 fold following treatment with ethanolamine O-sulphate (EOS, orally) for 15-30 days and 56-64 days, respectively. One hour after a single injection of gamma-acetylenic GABA (GAG) i.p., there was a significant 2.1 fold increase in whole brain GABA. Superfusion of a slice with muscimol or the GABA uptake inhibitor nipecotic acid depolarized the afferent nerve fibres. These effects were potentiated by flurazepam (1 microM) and pentobarbitone (10 microM) and antagonized by picrotoxin (3 microM, 30 microM). Following 15-30 days of EOS-treatment, the depolarization response to muscimol was decreased and that to nipecotic acid increased. These changes were no longer significant by 56-64 days of pretreatment. The acute dose of GAG did not affect the depolarization response to muscimol but increased that to nipecotic acid. The potentiations of muscimol by flurazepam (1 microM) and pentobarbitone (10 microM) were enhanced following chronic EOS treatment (15-64 days). The enhancement of flurazepam was less after 56-64 days than after 15-30 days pretreatment whereas the enhancement of pentobarbitone was similar at both times. Acute GAG treatment had no effect. The potency of picrotoxin as an antagonist of muscimol was reduced following chronic EOS treatment; the enhancement was less after 56-64 days than after 15-30 days pretreatment. Acute GAG treatment caused only a very small reduction in picrotoxin potency. Possible adaptations in the GABAA-receptor complex and its modulation during chronic elevation of brain GABA are discussed.

Behavioural and pharmacological dissociation of chlordiazepoxide effects on discrimination and punished responding.

Effects of chlordiazepoxide (CDP) and ethanolamine-O-sulphate (EOS) alone and in combination were tested on the acquisition and performance of continuous reinforcement - time out (CR-TO) and variable interval reinforcement - time out (VI-TO) operant discriminations in rats. CDP disrupted acquisition of CR-TO discrimination; effects were short lived, and neither CR-TO performance nor its reversal were impaired. Acquisition of VI-TO discrimination was increasingly impaired, and performance disrupted in pre-trained animals. EOS alone was inactive, and with CDP exerted only slight interactive effects. When a conflict component was added to the VI-TO schedule, however, EOS showed substantial additive effects with CDP on punished responding. The results suggest that CDP-induced increases in non-rewarded (TO) responding were related to task difficulty, pointing to a discrimination impairment rather than an anxiolytic effect. In addition, the specificity of EOS potentiation may reflect a pharmacological dissociation between CDP effects on discrimination and on punished responding, and suggest that GABA is selectively involved in resistance to punishment.

Development of the gamma-aminobutyric acid neurotransmitter system in the rat cerebral cortex during repeated administration of the GABA-transaminase inhibitor ethanolamine O-sulphate.

Ethanolamine O-sulphate (400 mg/kg, i.p.) was administered to rat pups at 9 days of age and on alternate days up to 17 days of age. At 18 days of age, gamma-aminobutyric acid (GABA) concentration was increased (three- to fourfold), glutamic acid decarboxylase (GAD) activity reduced to 55% of control, and the number of GABAA and GABAB binding sites increased in the cerebral cortex. This is the same pattern of change as seen previously with oral administration of ethanolamine O-sulphate to the adult rat but the changes occur more rapidly in the developing rat. A lower dose of ethanolamine O-sulphate (100 mg/kg, i.p.), administered according to the same schedule, caused a twofold increase in cortical GABA at 18 days of age whereas GAD activity and GABAA binding were not significantly altered.

The modulation of cortical acetylcholine release by GABA, GABA-like drugs and benzodiazepines in freely moving guinea-pigs

In order to define the modulatory role played by γ-aminobutyric acid (GABA) in corticopetal cholinergic projections, the effect of this amino acid and related drugs on gross behaviour, the EEG and the release of acetylcholine (ACh) from the cerebral cortex in freely moving guinea-pigs was studied. (1) γ Aminobutyric acid, injected intracerebroventricularly (20–50 μmol) induced a three-phase picture: first (5–15 min) behavioural activation and increased release of ACh, then (30–90 min) depression, EEG synchronization and reduced release of ACh, and finally “rebound” stimulation. 1. (2) Ethanolamine- O-sulphate (EOS) injected intraventricularly (28 μmol/kg) or intraperitoneally (14 mmol/kg) reproduced the first two phases of the effects of GABA (i.e. stimulation followed by inhibition), while diazepam (0.7 and 3.5 μmol/kg, i.p.) and flurazepam (32 μmol/kg, i.p.) caused, at first, only depression. 2. (3) Muscimol and 4,5,6,7-tetrahydroisoxazolo(4,5-c)pyridine-3-ol (THIP) injected intraventricularly (in the nmol range) or intraperitoneally (in the μmol range) produced behavioural activation and increased release of ACh; the depressant signs appeared only after very large, toxic doses. 3. (4) Picrotoxin and bicuculline, at sub-convulsive doses, reduced the symptomatology caused by GABA and antagonized the sedation produced by diazepam. 4. (5) Methysergide (8–16 μmol/kg, i.p.) prevented the behavioural activation and the increased release of ACh by GABA, unmasked the depression due to subthreshold doses of diazepam (i.c.v., 7–70 nmol) and reversed the stimulation induced by muscimol into sedation and reduced the outflow of ACh. Pretreatment with 5,7-HT also dampened and shortened the stimulation by muscimol. These findings suggest that compounds related to GABA interact sequentially and/or preferably with two subtypes of conventional GABA receptors, differing in their functional role. Benzodiazepines mainly facilitate GABA-mediated inhibitory mechanisms, also involving cholinergic neurones, while muscimol and THIP, interact with GABA recognition sites, which restrain tryptaminergic neurones, thus determining behavioural and cholinergic disinhibition. The interrelationship of these opposite effects explains the complex pattern of effects of exogenous GABA and ethanolamine- O-sulphate and accounts for the different influences exerted by GABA-like compounds in the physiological dispositon of ACh in various animal species and areas of the brain.

Chronic administration of the GABA-transaminase inhibitor ethanolamine O-sulphate leads to up-regulation of GABA binding sites

In rats receiving the γ-aminobutyric acid (GABA)-transaminase inhibitor ethanolamine O-sulphate (EOS) in their drinking water for up to 28 days, the number of GABA A and GABA B binding sites was increased compared to controls. There was no change in binding affinity at GABA A or GABA B sites. One week after EOS withdrawal, the number of GABA A and GABA B sites in previously treated EOS rats did not differ from controls. There was no difference in the number or affinity of benzodiazepine binding sites between EOS-treated and control rats during EOS administration or withdrawal. There was no difference in the stimulation of benzodiazepine binding by GABA (alone or in the presence of NaCl) during EOS administration. Cortical and cerebellar GABA concentration was increased 3.2- to 4.6-fold and cortical glutamate decarboxylase (GAD) activity reduced 30–42%. The current required to induce electroshock convulsions did not differ between EOS-treated rats and control rats during EOS administration. We speculate that the stimulus for the increased number of GABA A and GABA B binding sites is a reduction in GABA release subsequent to a reduction in GAD activity.

Prolactin control by the tubero-infundibular gabaergic system: role of anterior pituitary GABA receptors

Anterior pituitary (AP) GABA receptors have been shown to play a functional role in the inhibitory control of prolactin (PRL) secretion by this amino acid. However, the physiological significance and the pharmacological characteristics of these receptors have yet to be determined. In normal male rat AP's incubated in vitro, GABA (10 −6M) is effective in decreasing PRL release only when incubated in the presence of ethanolamine-O-sulphate (EOS), a potent GABA-transaminase (GABA-T) blocker. The failure of GABA alone to inhibit PRL release in vitro could be explained by the rapid degradation of the amino acid when added to the medium by AP-GABA-T. Central nervous system (CNS)- and AP-GABA receptors present similar affinity constants when evaluated by Scatchard analysis. However, displacement studies show that AP-GABA receptors have 10- and 100-times less affinity for muscimol (M), a GABA agonist, and for bicuculline, a GABA antagonist, respectively, than have CNS GABA receptors. The low affinity of the agonist towards the AP receptors could also account for the relatively poor sensitivity of lactotrophs to GABA-mimetic compounds. Failure of chronic treatment with aminooxyacetic acid, a GABA-T inhibitor, to modify the PRL-lowering effect of GABA-mimetic compounds, despite the decrease in the number of AP-GABA receptors, indicates that in normal conditions only a reduced number of receptors are operative. These studies of AP-GABA receptors provide insight for a better understanding of the mechanisms involved in the regulation of PRL secretion by the hypothalamic GABAergic system.

Effect of 2-aminoethanol on the synthesis, binding, uptake and metabolism of GABA

2-Aminoethanol (ethanolamine) was studied for effects on neurochemical assays for GABA synthesis, receptor binding, uptake and metabolism in rat brain preparations. The effects of ethanolamine were compared with those of ethanolamine O-sulphate (EOS), an inhibitor of GABA degradation. Furthermore, the effect of both compounds was compared on GABA metabolism in rat brain in vivo. In vitro, ethanolamine and EOS had no significant effect on the GABA synthesizing enzyme glutamic decarboxylase (GAD) and GABA uptake, but both drugs proved virtually equipotent to inhibit the GABA degrading enzyme GABA aminotransferase (GABA-T). EOS was a relatively potent inhibitor of GABA receptor binding, whereas ethanolamine was not effective in this regard. Following systemic administration in rats, 50% inhibition of GABA-T in the brain was achieved by 500 mg/kg ethanolamine or 2000 mg/kg EOS, respectively. As a consequence of GABA-T inhibition, GABA levels increased significantly. GAD activity remained unchanged after both treatments. The present results suggest that the recently reported enhancement of functional effects of GABA by ethanolamine may relate, at least in part, to the inhibitory effect of the compound on GABA catabolism.

Diazepam antagonizes GABA- and muscimol-induced changes of acetylcholine release in slices of guinea-pig cerebral cortex.

The acetylcholine (ACh) release was studied in superfused, electrically-stimulated slices of guinea-pig cerebral cortex. Muscimol and 4,5,6,7-tetrahydroisoxazolo (5-4-c)-pyridin-3-ol (THIP), as well as exogenous GABA, reduced the electrically-evoked ACh release and enhanced its spontaneous outflow. Picrotoxin antagonized these effects. In addition, picrotoxin and ethanolamine-O-sulphate (EOS) caused opposite changes in transmitter outflow, suggesting the existence of an exogenous GABAergic control on the cholinergic nerve endings. Neither flurazepam 6.6 X 10(-6)--3.3 X10(-5) mol/l nor diazepam 3.3 X 10(-6)--3.3 X 10(-5) mol/l by themselves affected ACh release. Diazepam prevented GABA-, muscimol- and EOS-induced changes in spontaneous and 1 Hz-evoked outflow. Ro 15-1788 3.3 X 10(*-6) mol/l abolished diazepam antagonism vs exogenous GABA. The ineffectiveness of flurazepam and diazepam on normal release (i.e. the lack of potentiation vs the endogenous GABAergic control) supports the view that "synaptic" GABA receptors acting upon the cholinergic nerve endings are not coupled with Benzodiazepine receptors. The unexpected diazepam antagonism vs exogenous GABA and GABA-like compounds can be explained with an unusual Diazepam negative cooperation with "extrasynaptic" GABA receptors, possibly present on the cholinergic terminals. Thus, the rule of benzodiazepine-GABA synergism does not seem always tenable, at least at certain pre-synaptic sites.

The reactions of aminobutyrate aminotransferase and ornithine aminotransferase with analogues of ethanolamine O-sulphate

The reactions of aminobutyrate aminotransferase and ornithine aminotransferase with analogues of ethanolamine O-sulphate