Carbamoylation of Brain Glutamate
Receptors by a Disulfiram Metabolite

S. Ningaraj Nagendra, Morris D. Faiman,
Kathleen Davis, Jang-Yen Wu, Xiangyue
Newby and John V. Schloss
J. Biol. Chem. This article cites 30 references, 5 of which can be accessed free at THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 272, No. 39, Issue of September 26, pp. 24247–24251, 1997 1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Printed in U.S.A. Carbamoylation of Brain Glutamate Receptors by a Disulfiram

(Received for publication, May 22, 1997) S. Ningaraj Nagendra‡, Morris D. Faiman‡§, Kathleen Davis¶, Jang-Yen Wu§¶,
Xiangyue Newby
i, and John V. Schloss§i
From the Department of Pharmacology and Toxicology, the Department of Physiology and Cell Biology, and theiDepartment of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66045 thereby limit unwanted side effects associated with excessive MeSO), a metabolite of the drug disulfiram, is a selective
antagonism (4). At present S-nitrosylation of glutamate recep- carbamoylating agent for sulfhydryl groups. Treatment
tors by an NO1 donor (e.g. nitroglycerin) is the only mechanism of glutamate receptors isolated from mouse brain with
for partially blocking receptor response in vivo that would DETC-MeSO blocks glutamate binding. In vivo, car-
achieve this effect by interaction with the redox modulatory bamoylated glutathione, administered directly to mice
sites (5, 6).
or formed by reaction of DETC-MeSO with glutathione
Disulfiram has been used in the treatment of alcoholism for in the blood, also blocks brain glutamate receptors. Car-
almost 50 years (7, 8). It has recently been demonstrated that bamoyl groups appear to be delivered to brain gluta-
disulfiram exerts its anti-alcohol effect in vivo only after bio- mate receptors or to liver aldehyde dehydrogenase in
activation to the active metabolite S-methyl-N,N-diethylthiol- vivo by a novel glutathione-mediated mechanism. Sei-
carbamate sulfoxide (DETC-MeSO)1 (9) that is a potent and zures caused by the glutamate analogs N-methyl-D-as-
selective carbamoylating agent for sulfhydryl groups (10). We partate and methionine sulfoximine, or by hyperbaric
now report that DETC-MeSO also partially blocks glutamate oxygen, are prevented by DETC-MeSO, indicating that
carbamoylation of glutamate receptors gives an antago-

binding to synaptic membrane preparations isolated from the nist effect. These observations offer an explanation for
brains of mice, and in addition, DETC-MeSO prevents seizures some of the previously reported neurological effects of
induced in mice by glutamate analogs or by exposure to hyper- disulfiram, such as its ability to prevent O -induced sei-
baric oxygen.
zures. Furthermore, some of the physiology of the disul-
MATERIALS AND METHODS firam-ethanol reaction, that could not be accounted for
Animals—Male Swiss Webster mice (20 –30 g) or male Sprague- based on the known inhibition of aldehyde dehydrogen-
Dawley rats (250 –300 g) were used in the study. All experiments that ase alone, may be explained by disulfiram's effect on
employed animals were conducted in strict compliance with the Na- tional Institutes of Health guidelines on animal use and institutionalregulations concerning animal experimentation. Animals were exposedto hyperbaric oxygen in a specially designed pressure chamber as de- Considerable effort has been devoted to discovery of gluta- scribed previously (11, 12). The time to first clonic-tonic seizure after mate antagonists (1, 2) in recent years, due to increasing evi- bringing animals to a final pressure of 5 atmospheres of 100% oxygen orafter intraperitoneal injection of convulsants was noted by criteria dence linking glutamate excitotoxicity to various neurological outlined previously (11, 12). Unless otherwise specified, the ability of disorders (3). Unfortunately, while known antagonists can pro- DETC-MeSO to prevent seizures was tested by intraperitoneal injection vide neuroprotection, excessive action of these classical block- of 5.2 mg/kg DETC-MeSO 1–2 h prior to bringing the animal to a final ing agents can obtain undesirable side effects (1, 2). To mini- pressure of 5 atmospheres of 100% oxygen or intraperitoneal injection of mize these undesirable side effects, modification of the redox N-methyl-D-aspartate (NMDA) (125 mg/kg) or L-methionine sulfoxi- modulatory sulfhydryl groups of the glutamate receptor has mine (MetSOX) (250 mg/kg). Evaluation of the statistics for wholeanimal experiments or for changes in brain glutamate binding after been suggested as a possibly superior therapeutic strategy (4).
administration of DETC-MeSO was conducted by use of the program Unlike classical antagonists, that can give complete inhibition GraphPAD InStat from GraphPAD Software (San Diego, CA).
by interaction at the glutamate receptor (e.g. CGS 19755) or Binding Studies—Synaptic membranes (100 mg of protein) were iso- directly at receptor-linked, calcium ion channels (e.g. phencyc- lated (13) from whole brain homogenate of male Swiss Webster mice lidine or MK-801) (2), inhibition via the redox modulatory sites and were incubated in 0.1 ml of 10 mM potassium phosphate, pH 7.4, are expected to give only partial inhibition of function and and DETC-MeSO (1 mM to 1 mM) or 0.5 mM L-glutamate for 30 min at25 °C. After addition of 50 nM [3H]glutamate, incubation was continuedfor an additional 45 min. Reactions were terminated by centrifugationat 4 °C to separate membrane-bound from free radioactivity. Nonspe- * This work was supported in part by grants from the Office of Naval cific binding (radioactivity bound in the presence of 0.5 mM unlabeled Research and the Naval Medical Research Institute (to J. V. S.). The glutamate) averaged 20 –30% of total radioactivity bound. The rate (k) costs of publication of this article were defrayed in part by the paymentof page charges. This article must therefore be hereby marked "adver- and maximum percent blockage of glutamate binding (M) by DETC- tisement" in accordance with 18 U.S.C. Section 1734 solely to indicate MeSO (I) during the incubation time (t) was determined by fitting the equation: % inhibition 5 M(1 2 e2kIt) to these data by use of the § Authors to whom correspondence should be addressed: Dept. of program Grafit (Erithicus Software Ltd.). This equation was derived for Medicinal Chemistry, University of Kansas, Lawrence, KS 66045. Tel.: first-order inactivation by a group-specific reagent that gives a partial 785-864-4503; Fax: 785-864-5326; E-mail: [email protected](for J. V. S.); Dept. of Physiology and Cell Biology, University of Kansas,Lawrence, KS 66045. Tel.: 785-864-4559; Fax: 785-864-5374; E-mail: 1 The abbreviations used are: DETC-MeSO, S-methyl-N,N-diethyl- [email protected] (for J.-Y. W.); Dept. of Pharmacology and thiolcarbamate sulfoxide; GSH, glutathione; GSSG, oxidized glutathi- Toxicology, University of Kansas, Lawrence, KS 66045. Tel.: 785-864- one; DETC-GS, S-(N,N-diethylcarbamoyl)glutathione; DETC-GSO, S- 4003; Fax: 785– 864-5219; E-mail: [email protected] (for M. D. F.).
aspartate; MetSOX, L-methionine sulfoximine.
This paper is available on line at
Carbamoylation of Glutamate Receptors FIG. 2. Glutamate binding to synaptic membranes isolated
FIG. 1. Inhibition of glutamate binding to brain synaptic mem-
from Swiss Webster male mice killed 2 h (A) or 24 h (B) postin-
branes in vitro by DETC-MeSO. Six determinations of the effect of
jection of a single administration of DETC-MeSO (5.2 mg/kg,
DETC-MeSO were made at each concentration tested (1, 5, 10, 50, 100, intraperitoneal) or after the last of seven daily injections. Each
200, and 1000 mM), and the average value is shown with error bars for bar represents the average of results obtained from four animals, and one standard deviation. The values for M and k obtained when a single the error bars are for one standard deviation.
exponential was fit to data were 58 6 7% and 25 6 10 respectively, and the line calculated by use of these values is shown tor blockage in vivo can be easily determined.
(solid line). A dashed line that was calculated for a double exponentialequation fit to data with nominal values of M 5 15%, M 5 43%, k 5 DETC-MeSO Effects on Brain Glutamate Receptors in Vivo— s21, and k 5 8 s21 is also shown.
Synaptic membranes were prepared from the brains of mice injected with DETC-MeSO (5.2 mg/kg, intraperitoneal). The effect. If "A" is the percent of binding activity that remains after exten- ability of synaptic membrane preparations isolated from sive exposure (t 5 ) of the receptor to excess DETC-MeSO, then M 5 DETC-MeSO-treated mice to bind glutamate was compared 100 2 A. The percent activity remaining at any time (a) would be equal with similar preparations isolated from control animals. Fig.
to: a 5 (100 2 A)e2kIt 1 A; substituting (100 2 M) for A and [100 2 % 2A illustrates the results obtained from synaptic membranes inhibition] for a in this equation gives the one employed for purposes of prepared from brains of mice killed 2 h after a single dose of data analyses. The maximum percent blockage of glutamate binding (M) observed did not depend on the concentration of glutamate em- DETC-MeSO or 2 h after the last injection of multiple consec- ployed in binding experiments, such that the modified receptors ap- utive doses (5.2 mg/kg, intraperitoneal, daily for 7 days). Either peared to be "noncompetitively" inhibited (independent of whether single or multiple dosing with DETC-MeSO reduced the capac- DETC-MeSO was still present or absent at the time that glutamate ity of synaptic membranes to bind glutamate by approximately binding was assayed). A second equation was employed in the analysis 50%, the maximum effect obtained in vitro (Fig. 2A). For brain of binding data that defines partial, irreversible inactivation of two synaptic membrane preparations isolated from mice killed 24 h distinct groups of receptors: % inhibition 5 M (1 2 e2k1It) 1 M (1 2 e2k2It), where M and M are the maximum amount of inhibition ob- after a single dose of DETC-MeSO, less inhibition of glutamate tained for complete modification of each receptor population, and k and binding was found (Fig. 2B). By contrast, for brain synaptic k are the rate constants for these modifications, respectively.
membrane preparations isolated from mice killed 24 h after the Reagents—DETC-MeSO was synthesized by the method of Hart and last dose of seven daily consecutive doses, similar inhibition of Faiman (14). Carbamoylated glutathione, S-(N,N-diethylcarbamoyl)- glutamate binding was observed to that seen 2-h postinjection glutathione (DETC-GS), was prepared essentially as described by Jin et of DETC-MeSO (Fig. 2B). The results obtained for the group al. (10). The structures and purity of DETC-MeSO and DETC-GS wereconfirmed by 300 MHz NMR and fast atom bombardment-tandem mass that received a single dose of DETC-MeSO and were sacrificed spectrometry. A QE300 NMR spectrometer (General Electric, Fremont, after 2 h were significantly different from the group that re- CA) and Autospec-Q tandem hybrid mass spectrometer (Fiscons/VG ceived a single dose and were sacrificed after 24 h (Bonferroni's Analytical Limited, Manchester, United Kingdom) were employed for p , 0.01 determined by analysis of variance). Comparison of these analyses. Liver aldehyde dehydrogenase was extracted and as- the singly dosed group that was sacrificed after 2 h with the sayed as described previously (14). MetSOX, monosodium L-glutamate, multiply dosed groups that were sacrificed after 2 h or 24 h did glycine, glutathione, and NMDA were purchased from Sigma. L-[G-3H]Glutamate (46 Ci/mmol) was obtained from Amersham Life Sci- not show statistical significance from each other by the same ence (Buckinghamshire, United Kingdom).
It is hard to reconcile the ability of DETC-MeSO to car- bamoylate brain glutamate receptors with its extreme lability DETC-MeSO Effects on Brain Glutamate Receptors in in vivo. DETC-MeSO rapidly and selectively carbamoylates the Vitro—Treatment of synaptic membrane preparations (13) sulfhydryl of glutathione (GSH) in vitro (10 from the brains of mice with DETC-MeSO resulted in a time- pH 7), and since the concentration of GSH in vivo is high (1– 6 dependent (k 5 25 6 10 21 s21), partial (M 5 58 6 7%), and mM) (15), DETC-MeSO will rapidly be converted (.95% within irreversible loss of their ability to bind glutamate (Fig. 1).
5 min) to DETC-GS, Fig. 3. DETC-GS has been detected in the Inhibition of glutamate binding appeared to depend on modi- bile of mice treated with disulfiram (10). Unlike DETC-MeSO, fication of more than one population of glutamate receptor, DETC-GS is not reactive and does not carbamoylate sulfhydryl each with distinct kinetics. Although a better fit of these data groups (10). Although DETC-GS reversibly blocked glutamate could be obtained by use of a double exponential equation (see binding to synaptic membrane preparations from mouse brain "Materials and Methods"), a unique fit of this equation to these (data not shown), a time-dependent, irreversible blockage of data could not be obtained, due to the larger number of inde- the glutamate receptor, like that observed with DETC-MeSO, pendent parameters involved. However, a nominal fit of these was not obtained.
data indicated that about one-fourth of the total inhibition (M If the effect of DETC-MeSO on glutamate receptors in vivo is 5 15%) occurs at a much faster rate (k 5 900 21 s21), than mediated by glutathione, then the carbamoylated glutathione the rate (k 5 8 21 s21) associated with inhibition of the requires activation. GSH, oxidized glutathione (GSSG), and remainder (M 5 43%) (Fig. 1). Since the effect of DETC-MeSO DETC-GS reversibly blocked glutamate binding to mouse syn- on either receptor population is irreversible, glutamate recep- aptic membrane preparations (data not shown). However, Carbamoylation of Glutamate Receptors FIG. 3. Interconversion of DETC-
the carbamoylation of glutamate re-
ceptors or aldehyde dehydrogenase.

when the membranes were washed after exposure to GSH, Effect of NMDA, MetSOX, and oxygen on mice and rats GSSG, or DETC-GS, inhibition was reversed, unlike the effectby DETC-MeSO. Oxidation of the sulfur of DETC-GS to a Mean time to seizure sulfoxide would make it reactive toward sulfhydryl groups (9), similar in chemistry to DETC-MeSO, and potentially capable of irreversible inhibition of glutamate receptors in vivo.
Carbamoylated glutathione and DETC-MeSO had the same (125 mg/kg, mice) effect in vivo, despite the fact that they had different effects on (250 mg/kg, mice) glutamate receptors in vitro. Intravenous administration of an equimolar concentration of DETC-GS or DETC-MeSO (30 (250 mg/kg, rats) mmol/kg) to mice resulted in a comparable degree of irreversi- ble brain glutamate receptor blockage (26.9 6 4.3 and 38.2 6 1.6%, respectively) or liver aldehyde dehydrogenase inhibition a The mean values for the time to the first clonic-tonic seizure are (30.1 6 1.0 or 44.9 6 1.0%, respectively). Since DETC-GS reported 6 S.E. Immediately below this value in parentheses is the reversibly blocked glutamate binding to synaptic membranes number of animals that exhibited the effect divided by the total numberof animals in that group (number of animals to which value applies/ in vitro (i.e. the inhibition can be reversed by washing the total number of animals in the group). Comparison of the means for membranes to remove DETC-GS), but in vivo both DETC- control (untreated) and DETC-MeSO-treated animals by a two-tailed t MeSO and DETC-GS irreversibly blocked glutamate binding, test gave p , 0.001. In the case of NMDA treatment, three of the eight and DETC-GS has no effect on aldehyde dehydrogenase in vitro animals in the control group failed to exhibit any seizures, even after asecond injection of NMDA. Resistance to NMDA-induced seizures ap- (reversible or irreversible), it is suggested that DETC-GS is pears to be due to P450-mediated metabolism of this glutamate analog, activated by oxidation in vivo (DETC-GSO, Fig. 3).
based on the ability of N-benzylimidazole, a P450 inhibitor, to produce Neuroprotective Effects of DETC-MeSO—To test whether sensitivity in NMDA-resistant animals. None of the animals in the carbamoylation of glutamate receptors might prevent seizures DETC-MeSO-treated group (six out of six animals) exhibited anyNMDA-induced seizures for the duration of the observation period (2 h).
caused by glutamate agonists, the effect of DETC-MeSO on In the case of MetSOX treatment, two out of eight animals in the seizures induced by glutamate analogs was examined. Treat- DETC-MeSO-treated group remained free of seizures for the period of ment of mice with DETC-MeSO prior to administration of the observation (6 h). In the case of hyperbaric oxygen exposure (5 atmos- glutamate analog NMDA (125 mg/kg, intraperitoneal) pre- pheres absolute O ), all of the animals in the DETC-MeSO-treated vented seizures that result from NMDA administration alone group (five out of five animals) remained free of seizures for the periodof observation (1 h).
(Table I). Similarly, DETC-MeSO administered to mice or rats b DETC-MeSO was administered at a dose of 5.2 mg/kg by intraperi- prior to injection of the glutamate analog MetSOX more than toneal injection 1–2 h prior to exposure to hyperbaric oxygen, NMDA, or doubled the time that the animals remain free of seizures Mice were exposed to 5 atmospheres absolute (ATA) of 100% oxygen in a pressure chamber for 60 min, then depressurized.
It has been shown that glutamate is released by rat hip- pocampal (brain) slices subjected to oxidative stress (16).
Therefore, we examined the affect of DETC-MeSO on oxygen- after 24 min in control animals (Table I).
induced seizures. Administration of DETC-MeSO (5.2 mg/kg, NMDA and Non-NMDA Subtypes of Brain Glutamate Recep- intraperitoneal) to mice two hours before exposure to 5 atmos- tors Were Inhibited to a Similar Extent by DETC-MeSO— pheres of 100% oxygen, prevented the seizures that occurred NMDA is a selective agonist for a major subtype of ionotropic Carbamoylation of Glutamate Receptors (calcium ion channel-linked) glutamate receptor (17). As deter- subtype of glutamate receptor that is associated with calcium mined in the results illustrated in Figs. 1 and 2, the effect of ion channels (17). As such, seizures induced as a consequence of DETC-MeSO on glutamate binding to synaptic membrane NMDA administration are commonly thought to be due to preparations is not a measure of DETC-MeSO's modification of interaction of NMDA with glutamate receptors. By contrast, this receptor subtype. Although up to 34% of the total gluta- MetSOX is best known as an extremely potent inhibitor of mate binding capacity of synaptic membranes is attributable to brain glutamine synthetase (20). However, inhibition of gluta- NMDA receptors (18), the effect of glutamate on these recep- mine synthetase persists long after MetSOX-induced seizures tors is dependent on glycine (19), that was not included in the have subsided (21), indicating that the cause of convulsions studies presented in Figs. 1 and 2. Under the conditions of induced by this glutamate analog is not related to glutamine these experiments, NMDA does not block glutamate binding to synthetase inhibition. It is not presently known which gluta- synaptic membrane preparations. When these binding experi- mate receptor subtypes may be affected by MetSOX or how ments were repeated in the presence of glycine (0.1 mM), re- potent these interactions may be. The discovery that glutamine versible blockage of glutamate binding to mouse brain synaptic synthetase inhibition does not correlate with the seizures in- membrane preparations by NMDA (0.5 mM, 32 6 2% blockage) duced by MetSOX (21) predates by more than a decade the and irreversible blockage by DETC-MeSO (0.1 mM, 48 6 3% discovery of glutamate receptors and their essential role in the blockage) was observed. The similar degree of inhibition ob- central nervous system (3).
served by DETC-MeSO in the presence and absence of glycine The observation that DETC-MeSO acts as a glutamate an- (48 and 58% (Fig. 1), respectively) indicates that both NMDA tagonist offers an explanation for several neurological effects of and non-NMDA glutamate receptor subtypes are affected to a the drug disulfiram. First, it is consistent with the previous similar extent by carbamoylation.
observation that disulfiram also prevents oxygen-induced sei-zures (11, 12) and requires bioactivation to DETC-MeSO (9).
Also, occasionally patients treated with disulfiram have been DETC-MeSO is effective in partially preventing glutamate reported to exhibit various neurological disorders, such as en- binding to brain synaptic membrane preparations in vitro and cephalopathy (including schizophrenic-like symptoms), parkin- in vivo. Inhibition of the glutamate receptor by DETC-MeSO in sonism, ataxia, choreoathetosis, seizures, optic neuritis, and vivo is suggested to be mediated by GSH. DETC-MeSO car- peripheral neuropathy (22–24). Patients with a clinical diagno- bamoylates GSH to form DETC-GS. DETC-GS crosses the sis of schizophrenia are thought to be especially prone to dis- blood-brain barrier and is then oxidized to DETC-GSO at the orientation, impaired memory, and hallucinations upon treat- site of action. DETC-GSO would be the ultimate carbamoylat- ment with disulfiram (24). Some of these rare side effects ing agent in vivo. The interconversion of DETC-MeSO, DETC- associated with disulfiram are consistent with those expected GS, and DETC-GSO is illustrated in Fig. 3. This novel and due to excessive blockage of glutamate function in the central efficient method for delivering the carbamoyl moiety across the nervous system (1–3). However, in a controlled clinical study of blood-brain barrier converts a small fraction of the circulating the incidence of neurological side effects associated with disul- glutathione into a carbamoyl delivery system. Reaction of the firam use (250 mg/day), there was no statistically higher inci- oxidized, reactive (sulfoxide) form of carbamoylated glutathi- dence of neurological problems than were seen in a control one (DETC-GSO) with another molecule of glutathione simply population (25). If, in humans, the normal extent of glutamate converts the carbamoyl moiety from a reactive form (DETC- antagonism by disulfiram were partial (e.g. 60% as observed for GSO) to a latent one (DETC-GS). Oxidation of the latent form mice), then the effects of excessive blockage would only be of carbamoylated glutathione (DETC-GS) would convert it once manifest in individuals with unusual response (e.g. .60%) to again to the reactive form (DETC-GSO). Thus, the carbamoyl carbamoylation of their glutamate receptors. As such, the av- moiety could cycle many times between latent and reactive erage incidence of undesirable neurological problems would be forms prior to delivery at its site of action in vivo.
quite low. In any case, since there is evidence that the density Evidence that brain glutamate receptors are carbamoylated of glutamate receptors is increased as a consequence of chronic in vivo comes from: 1) the chemistry of carbamoyl sulfoxides, alcohol consumption (26, 27), the effect on the glutamate re- that are selective carbamoylating agents for sulfhydryl groups ceptors by DETC-MeSO may actually be of positive benefit (9, 10); 2) the effect in vivo is chemically (but not biologically) during treatment of the alcoholic with disulfiram. Further- irreversible, as would be expected for carbamoylated sulfhydryl more, the physiology of the disulfiram-ethanol reaction cannot residues (9, 10); 3) the rate at which the majority of glutamate be completely explained by accumulation of acetaldehyde due binding is lost in vitro as a consequence of receptor exposure to to inactivation of aldehyde dehydrogenase (25). It is possible DETC-MeSO (8 –25 s21) is comparable with the rate at that part of the success of disulfiram in treating alcoholism which DETC-MeSO reacts with the sulfhydryl of glutathione has, in fact, relied upon its previously unrecognized effect on s21); 4) the size of the maximum effect of DETC-MeSO glutamate receptors. Much of the variability in disulfiram's in vitro (58% loss of glutamate binding capacity by synaptic effectiveness in the treatment of alcoholism can be attributed membrane preparations, Fig. 1) is approximately equal to the to variable extents of bioactivation to DETC-MeSO (9).
maximum effect observed in vivo (53% loss of glutamate bind- Not all of the adverse neurological effects of disulfiram can ing capacity after multiple serial doses of DETC-MeSO, Fig.
be attributed to modification of glutamate receptors. Disul- 2A); 5) the partial effect of other sulfhydryl modifying reagents firam is metabolized to carbon disulfide, a known neurotoxin, on the glutamate receptor (NMDA subtype) in vitro, indicating and potently inhibits copper enzymes, such as superoxide dis- that DETC-MeSO modifies the known "redox modulatory site" mutase and dopamine b-hydroxylase, through the action of of the receptor (4); 6) the protection by DETC-MeSO against another disulfiram metabolite, diethyldithiocarbamate (28, seizures induced by NMDA, MetSOX, or oxygen at high pres- 29). DETC-MeSO does not share any of these latter effects with sure. While it is possible that DETC-MeSO elicits the effect at disulfiram (carbon disulfide formation or copper enzyme inhi- the glutamate receptor by a mechanism other than carbamoy- bition),2 so it would be expected to more selectively affect glu- lation and/or prevents seizures by effects in vivo that are un- tamate receptors in vivo. In particular, DETC-MeSO is not related to modification of the glutamate receptor, these possi-bilities seem rather remote.
NMDA is recognized to be a selective agonist of a specific 2 S. N. Nagendra and M. D. Faiman, manuscript in preparation.
Carbamoylation of Glutamate Receptors likely to cause the seizures, optic neuritis, and peripheral neu- swerving support and encouragement during the early phases of this ropathy linked to higher doses (.500 mg/day) of disulfiram, that are most probably a consequence of CS formation (22–24).
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Acknowledgments—We are indebted to the Office of Naval Research 29. Eneanya, D. I., Bianchine, J. R., Duran, D. O., and Andresen, B. D. (1981) and the Naval Medical Research Institute for financial support. In Annu. Rev. Pharmacol. Toxicol. 21, 575–596
particular, we express our gratitude to Dr. Harold Bright for his un- 30. Schoepp, D. D. (1994) Neurochem. Int. 24, 439 – 449


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La disfunción eréctil (la mal llamada "impotencia") se define como la incapacidad para obtener una erección suficiente para completar una relación sexual satisfactoria. Esto incluye tanto la imposibilidad de conseguir una erección (disfunción eréctil total), como las dificultades para mantenerla durante un cierto tiempo o en determinadas posturas (disfunción eréctil parcial).