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THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Copyright © 2002 by The American Society for Pharmacology and Experimental Therapeutics
JPET 300:138–144, 2002
Vol. 300, No. 4
4583/972756
Printed in U.S.A.
3,4-Methylenedioxymethamphetamine Produces
Glycogenolysis and Increases the Extracellular Concentration
of Glucose in the Rat Brain
ALTAF S. DARVESH, MAHALAKSHMI SHANKARAN, and GARY A. GUDELSKY
College of Pharmacy, University of Cincinnati, Cincinnati, Ohio
Received September 28, 2001; accepted December 19, 2001
This article is available online at http://jpet.aspetjournals.org
3,4-Methylenedioxymethamphetamine (MDMA), a ringsubstituted amphetamine analog, is widely abused as a recreational drug, and there is concern that the drug may damage serotonergic nerve terminals (Green et al., 1995).
MDMA-induced neurotoxicity of serotonergic nerve terminals in rodents and nonhuman primates is evidenced by
several biochemical and immunocytochemical findings such
as depletion of tissue concentration of 5-HT and its major
metabolite, 5-hydroxyindoleacetic acid (Stone et al., 1986;
Schmidt, 1987), decrease in the activity of the enzyme tryptophan hydroxylase (Schmidt and Taylor, 1987), reduction in
the [3H]paroxetine-labeled 5-HT reuptake sites (Battaglia et
al., 1987), and reduced immunostaining of 5-HT terminals
(O’Hearn et al., 1988).
Although the exact mechanism involved in MDMA-induced
5-HT neurotoxicity remains to be elucidated, oxidative stress
has been reported to play an important role in this process
(Gudelsky, 1996; Colado et al., 1997; Shankaran et al.,
This work was supported by U.S. Public Health Service Grant DA07427.
yl-1-(1-methylethyl)-ergoline-8␤-carboxylic acid 2-hydroxy-1
methylprophyl ester maleate (LY-53,857; 3 mg/kg i.p.), desipramine (10 mg/kg i.p.), and iprindole (10 mg/kg i.p.). LY-53,857
also attenuated the MDMA-induced increase in the extracellular
concentration of glucose as well as MDMA-induced hyperthermia. Amphetamine analogs (e.g., methamphetamine and parachloroamphetamine) that produce hyperthermia also produced
glycogenolysis, whereas fenfluramine, which does not produce
hyperthermia, did not alter brain glycogen content. These results support the conclusion that MDMA induces glycogenolysis and that the process involves 5-HT2 receptor activation.
These results are supportive of the view that MDMA promotes
energy dysregulation and that hyperthermia may play an important role in MDMA-induced alterations in cellular energetics.
1999a,b). MDMA increases the formation of hydroxy radicals
(Colado et al., 1997; Shankaran et al., 1999a,b) and reduces
the concentration of the endogenous antioxidants vitamin E
and ascorbic acid (Shankaran et al., 2001). Furthermore, the
administration of antioxidants prevents the MDMA-induced
depletion of brain 5-HT (Colado and Green, 1995; Gudelsky,
1996; Shankaran et al., 2001).
In addition to the potential role of oxidative stress in
MDMA neurotoxicity, there is evidence for a role of bioenergetic stress in the toxicity produced by amphetamine analogs. The concomitant administration of MDMA and the mitochondrial inhibitor malonate into the striatum has been
shown to cause a significant reduction in 5-HT tissue concentration, whereas the local administration of either drug alone
was ineffective (Nixdorf et al., 2001). Moreover, the administration of MDMA as well as methamphetamine causes a
rapid and transient inhibition of mitochondrial function
(Burrows et al., 2000). Methamphetamine also has been
shown to produce a loss of striatal ATP (Chan et al., 1994).
Finally, administration of substrates of energy metabolism,
e.g., ubiquinone and nicotinamide, has been shown to atten-
ABBREVIATIONS: MDMA, 3,4-methylenedioxymethamphetamine; PCA, parachloroamphetamine; ANOVA, analysis of variance; 5-HT, 5-hydroxytryptamine; LY-53,857, 6-methyl-1-(1-methylethyl)-ergoline-8␤-carboxylic acid 2-hydroxy-1 methylprophyl ester maleate.
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ABSTRACT
Oxidative and/or bioenergetic stress is thought to contribute
to the mechanism of neurotoxicity of amphetamine derivatives, e.g., 3,4-methylenedioxymethamphetamine (MDMA).
In the present study, the effect of MDMA on brain energy
regulation was investigated by examining the effect of
MDMA on brain glycogen and glucose. A single injection of
MDMA (10 – 40 mg/kg, s.c.) produced a dose-dependent
decrease (40%) in brain glycogen, which persisted for at
least 1 h. MDMA (10 and 40 mg/kg, s.c.) also produced a
significant and sustained increase in the extracellular concentration of glucose in the striatum. Subjecting rats to a
cool ambient temperature of 17°C significantly attenuated
MDMA-induced hyperthermia and glycogenolysis. MDMAinduced glycogenolysis also was prevented by treatment of
rats with the 5-hydroxytryptamine2 (5-HT2) antagonists 6-meth-
MDMA and Glycogenolysis
uate the neurotoxic effects of methamphetamine (Stephens
et al., 1998).
There are also several reports that amphetamine analogs
deplete brain glycogen, which is the single largest energy
reserve of the brain and is localized primarily in astrocytes
(Tsacopoulos and Magistretti, 1996). The systemic administration of amphetamine and parachloroamphetamine (PCA)
has been shown to deplete brain glycogen in mice (Hutchins
and Rogers, 1970) and rats (Heuther et al., 1997), respectively. In addition, Poblete and Azmitia (1995) have reported
that MDMA activates glycogen phosphorylase, an enzyme
responsible for the breakdown of glycogen, in astroglial-rich
primary cultures.
In the present study, the effect of MDMA to promote glycogenolysis in brain tissue and increase the extracellular
concentration of glucose in the striatum in vivo is documented. In addition, the roles of 5-HT2 receptors and hyperthermia in MDMA-induced glycogenolysis were evaluated.
Animal Procedures
Adult male rats (200 –275 g) of the Sprague-Dawley strain
(Charles River Breeding Laboratories, Portage, Canada) were used
in the studies. The animals were housed three per cage in a temperature- and humidity-controlled room with a 12-h light/dark cycle and
allowed food and water ad libitum. Animals undergoing surgery were
housed one per cage postoperatively. All procedures were in strict
adherence to the National Institutes of Health guidelines and approved by the Institutional Animal Care and Use Committee.
Chemicals, Drugs, and Drug Treatment
(⫾)-MDMA hydrochloride and (⫹)-fenfluramine hydrochloride
were provided by the National Institute on Drug Abuse. LY-53,857,
desipramine hydrochloride, (⫾)-PCA hydrochloride, and (⫹)-methamphetamine hydrochloride were obtained from Sigma-Aldrich (St.
Louis, MO). Iprindole hydrochloride was obtained from Wyeth-Ayerst Pharmaceuticals (St. Davids, PA). All the drugs were dissolved
in 0.15 M NaCl. NADP disodium salt, hexokinase, glucose-6-phosphate dehydrogenase, and amyloglycosidase were purchased from
Roche Diagnostics Corp. (Indianapolis, IN). All reagents were prepared as described previously (Nahorski and Rogers, 1972).
Brain glycogen was determined 1 h following the administration of
MDMA, methamphetamine, PCA, or fenfluramine, except in the
experiment in which the time-dependent relationship of the effect of
MDMA was determined. LY-53,857 (3 mg/kg, i.p.) was administered
30 min prior to the administration of MDMA, whereas desipramine
(10 mg/kg, i.p.) and iprindole (10 mg/kg, i.p.) were administered 1 h
prior to administration of MDMA. For the experiment in which rats
were maintained at a cool ambient temperature, the animals were
kept at 17°C for 2 h prior to and following the administration of
MDMA.
Biochemical Measurements
Assay of Tissue Glycogen. Rats were killed by decapitation, and
the brains were removed from the skull and immersed in liquid
nitrogen within 10 s. The cerebellum was removed, and the brains
were stored at ⫺80°C until analysis. Procedures for the analysis of
glycogen were similar to those described by Nahorski and Rogers
(1972). Approximately 250 mg of brain tissue were weighed and
homogenized in 3 ml of 0.03 N HCl at 0°C. The homogenate was
placed in boiling water for 5 min. Assay tubes contained 300 ␮l of
acetate buffer (pH ⫽ 4.6), 100 ␮l of the homogenate or glycogen
standard, and 10 ␮l of amyloglycosidase or water. The tubes were
vortexed and incubated at room temperature for 30 min. After incu-
bation, 1.33 ml of Tris buffer (pH ⫽ 7.8), 0.66 ml of MgCl2 (10 mM),
100 ␮l of ATP (2 mg/ml), and 10 ␮l of NADP (10 mg/ml) were added
to each tube. The tubes were vortexed and subjected to centrifugation at 10,000g for 5 min. The supernatants were transferred to other
tubes, and the fluorescence (excitation 350 nm/emission 460 nm) was
measured in a fluorescence spectrophotometer (Model F-2000; Hitachi Instruments, Inc., Naperville, IL). Ten ␮l of hexokinase (1 mg/ml)
and 10 ␮l of glucose-6-phosphate dehydrogenase (0.2 mg/ml) were
then added, and the tubes were vortexed and incubated at room
temperature for 30 min. The fluorescence was again measured. The
difference in the fluorescence values was corrected for sample, reagent, and enzyme blank. Glycogen values are reported as glucose
equivalents (micromoles per gram of tissue).
Glucose Assay. Glucose in the dialysis samples was assayed by
using a modified method of the glycogen assay (Nahorski and Rogers,
1972). Assay tubes contained 1.33 ml of Tris buffer (pH ⫽ 7.8), 0.66
ml of MgCl2(10 mM), 100 ␮l of ATP (2 mg/ml), 10 ␮l of NADP (10
mg/ml), and 20 ␮l of dialysate sample or glucose standard. The tubes
were vortexed, and fluorescence of the sample was measured as
described above. Ten ␮l of hexokinase (1 mg/ml) and 10 ␮l of glucose6-phosphate dehydrogenase (0.2 mg/ml) were added, and the tubes
were vortexed and incubated at room temperature for 30 min prior to
fluorescence determination. Glucose values were reported as millimolar concentration.
In Vivo Microdialysis Procedures. Rats were implanted with a
stainless steel guide cannula under ketamine/xylazine (70:6 mg/kg,
i.m.)-induced anesthesia 48 to 72 h prior to the insertion of the
dialysis probe. On the day of the dialysis experiment, a concentric
style dialysis probe was inserted through the guide cannula into the
striatum. The coordinates for the tip of the probe were A, 1.2 mm; L,
3.1 mm; and V, ⫺7 mm from bregma, according to the stereotaxic
atlas of Paxinos and Watson (1986). The microdialysis probes were
constructed as described previously (Yamamoto and Pehek, 1990).
The dialysis surface of the membrane (SpectraPor; 6000 molecular
weight cutoff and 210-␮m outside diameter) for the striatum was 4.5
mm in length. On the day of the dialysis experiment, the probe was
connected to an infusion pump set to deliver glucose-free Dulbecco’s
phosphate-buffered saline containing 1.2 mM CaCl2 at a rate of 1.8
␮l/min. After a 2-h equilibration period, dialysis samples were collected every 30 min. At least three baseline samples were obtained
prior to drug treatment.
Body Temperature Measurements. On the day of the experiment, the rats were allowed to acclimate at 24 or 17°C for 2 h before
body temperatures were measured. Measurements of rectal temperature were made using a telethermometer and a thermister probe.
The probe was lubricated with a small amount of petroleum jelly and
inserted 5 cm into the rectum of each rat for at least 30 s until a
stable temperature was obtained. LY-53,857 (3 mg/kg, i.p.) was
administered 30 min prior to administration of MDMA (10 mg/kg,
s.c.). Measurements were taken every 30 min for a 1-h period prior to
administration of MDMA and for a 1.5-h period following the injection of the drug. The change in body temperature was determined by
subtracting the body temperature at time 0 from the maximal body
temperature recorded after MDMA administration.
Statistical Analysis
The effect of MDMA, methamphetamine, PCA, and fenfluramine
on brain glycogen was analyzed with one-way ANOVA. The effects of
cool ambient temperature and 5-HT2 antagonists on MDMA-induced
glycogenolysis were analyzed with two-way ANOVA. Glucose data
from dialysis experiments were analyzed with two-way repeatedmeasures ANOVA. Multiple pairwise comparisons were performed
using the Student-Newman-Keuls test. Treatment differences for all
the data were considered statistically significant at p ⬍ 0.05.
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Materials and Methods
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Darvesh et al.
Fig. 2. Effect of dose of MDMA on glycogen content in brain. Rats were
administered different doses of MDMA (10, 20, and 40 mg/kg s.c.) and
killed 1 h later. The values represent the mean ⫾ S.E. of six rats and are
expressed in terms of micromoles of glucose liberated from glycogen. 多,
p ⬍ 0.05 compared with vehicle (VEH)-treated rats.
Results
A time-dependent reduction in brain glycogen was evident
following the systemic administration of MDMA (Fig. 1).
Brain glycogen concentrations were reduced by 45% following the administration of MDMA (40 mg/kg, s.c.). Significant
(p ⬍ 0.05) reductions in the brain concentration of glycogen
were observed 30 min and 1 h after an injection of MDMA.
Values for brain glycogen in rats 2 and 4 h after drug treatment did not differ significantly from those of vehicle-treated
animals.
The dose dependence of MDMA-induced glycogenolysis is
depicted in Fig. 2. Although brain glycogen concentrations
were reduced significantly (p ⬍ 0.05) following the administration of each of the doses (10, 20, and 40 mg/kg, s.c.) of
MDMA, the magnitude of the effect was greatest at 40 mg/kg
(Fig. 2).
The extent to which MDMA induced glycogenolysis was
dependent upon the ambient temperature at which the drug
was administered. Maintenance of rats at 17°C for 2 h prior
to the administration of MDMA markedly attenuated
MDMA-induced glycogenolysis. Whereas the administration
of MDMA (20 mg/kg, s.c.) resulted in a 25 to 30% reduction
(p ⬍ 0.05) in the brain concentration of glycogen in rats
maintained at 24°C, MDMA had no significant effect on brain
glycogen in rats maintained at 17°C (Fig. 3). The alteration of
ambient temperature alone did not significantly affect brain
glycogen content.
The effects of 5-HT antagonists with high affinity for 5-HT2
receptors on the reduction of brain glycogen by MDMA are
shown in Fig. 4. Treatment of rats with LY-53,857 (3 mg/kg,
i.p.), desipramine (10 mg/kg, i.p.), or iprindole (10 mg/kg, i.p.)
resulted in a significant (p ⬍ 0.05) attenuation of the MDMAinduced reduction in the brain concentration of glycogen.
Fig. 3. Effect of ambient temperature on MDMA-induced glycogen depletion. Rats were maintained at an ambient temperature of 24 and 17°C for
2 h prior to the administration of MDMA (20 mg/kg, s.c.), and the animals
were killed 1 h after drug treatment. The values represent the mean ⫾
S.E. of six rats and are expressed in terms of micromoles of glucose
liberated from glycogen. 多, p ⬍ 0.05 compared with vehicle (VEH)-treated
rats.
Although MDMA produced a significant (p ⬍ 0.05) reduction
in the brain concentration of glycogen in LY-53,857- and
iprindole-treated rats, the magnitude of the reduction was
significantly (p ⬍ 0.05) less than that produced in the vehicletreated controls. MDMA-induced glycogenolysis was com-
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Fig. 1. Effect of MDMA on glycogen content in brain. Rats were administered a single dose of MDMA (40 mg/kg, s.c.) or vehicle and killed at the
indicated time intervals. The values represent the mean ⫾ S.E. of five to
six rats and are expressed in terms of micromoles of glucose liberated
from glycogen. 多, p ⬍ 0.05 compared with vehicle (VEH)-treated rats.
MDMA and Glycogenolysis
pletely abolished in desipramine-treated rats. Treatment
with LY-53,857, iprindole, or desipramine alone did not significantly alter brain glycogen content.
Attenuation of MDMA-induced glycogenolysis by either a
cool ambient temperature (17°C) or the 5-HT2 antagonist
LY-53,857 was associated with a suppression of MDMA-induced hyperthermia. At an ambient temperature of 24°C, the
administration of 10 or 20 mg/kg of MDMA increased the
body temperature of rats by 1.1 and 1.4°C, respectively. (Table 1). Maintenance of rats at 17°C or treatment of rats with
LY-53,857 (3 mg/kg, i.p.) completely prevented MDMA-induced hyperthermia.
The brain concentration of glycogen also was quantified
following the administration of other amphetamine analogs.
Methamphetamine (10 mg/kg, i.p.) and PCA (10 mg/kg, i.p.)
produced significant (p ⬍ 0.05) reductions of 42 and 45%,
respectively, in the brain concentration of glycogen. How-
Fig. 5. Effect of amphetamine analogs on the concentration of glycogen in
brain. Rats were injected with fenfluramine (FEN) (10 mg/kg, i.p.), methamphetamine (METH) (10 mg/kg, i.p.), and PCA (10 mg/kg, i.p.) and
killed 1 h after drug treatment. The values represent the mean ⫾ S.E. of
six to eight rats and are expressed as micromoles of glucose liberated
from glycogen. 多, p ⬍ 0.05 compared with vehicle (VEH)-treated rats.
ever, the administration of fenfluramine (10 mg/kg, i.p.) did
not significantly alter brain glycogen content (Fig. 5)
In addition to the evaluation of the effects of MDMA on the
brain concentration of glycogen, the effect of MDMA on the
extracellular concentration of glucose in the striatum was
investigated using in vivo microdialysis. The systemic administration of MDMA (10 or 40 mg/kg, s.c.) resulted in an
immediate and sustained increase (p ⬍ 0.05) of 30 to 45% in
the extracellular concentration of glucose in the striatum
TABLE 1
MDMA-induced hyperthermia in rats maintained at different ambient
temperatures or treated with the 5-HT2 antagonist LY-53,857
Rats were maintained at an ambient temperature of 24°C or 17°C for 2 h prior to and
following the administration of MDMA. Body temperatures were recorded at 30-min
intervals for 90 min prior to and after MDMA administration. Other rats were
injected with either LY-53,857 (3 mg/kg, i.p.) or vehicle, 30 min prior to MDMA
administration.
Treatment/Condition
Exp. 1
24°C
17°C
Exp. 2
Vehicle ⫹ MDMA
LY-53,857 ⫹ MDMA
Dose of MDMA
⌬ Body Temperature
mg/kg
°C
20
20
1.4 ⫾ 0.2
0.0 ⫾ 0.4*
10
10
1.1 ⫾ 0.3
⫺0.3 ⫾ 0.1*
* p ⬍ 0.05 for the comparison in Experiment 1 to rats treated with MDMA at 24°C
or in Experiment 2 to rats treated with vehicle ⫹ MDMA.
Fig. 6. Effect of MDMA on the extracellular concentration of glucose in
the striatum of rats. A single injection of MDMA (10 or 40 mg/kg, s.c.) or
vehicle (VEH) was administered at time 0. The values represent the
mean ⫾ S.E. of six to eight rats. 多, p ⬍ 0.05 compared with VEH-treated
rats.
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Fig. 4. Effect of 5-HT2 antagonists on MDMA-induced glycogen depletion.
LY-53,857 (LY) (3 mg/kg, i.p.) was injected 30 min before, and desipramine (DMI) (10 mg/kg, i.p.) and iprindole (IPR) (10 mg/kg, i.p.) were
injected 1 h before, the administration of MDMA (20 mg/kg, s.c.). The rats
were killed 1 h after the MDMA injection. The values represent the
mean ⫾ S.E. of five to six rats and are expressed in terms of micromoles
of glucose liberated from glycogen. 多, p ⬍ 0.05 compared with vehicle
(VEH)-treated rats. t, p ⬍ 0.05 compared with MDMA-treated rats.
141
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Darvesh et al.
rats treated with LY-53,857 and MDMA did not differ from
that in rats treated with LY-53,857 and vehicle. Administration of LY-53,857 alone did not significantly alter the extracellular concentration of glucose.
Discussion
(Fig. 6). The extracellular concentration of glucose in the
striatum remained elevated for at least 5 h following the
administration of MDMA. In contrast, the perfusion of
MDMA (100 ␮M) by reverse dialysis through the dialysis
probe for 5 h did not significantly alter the extracellular
concentration of glucose (Fig. 7).
Treatment of rats with LY-53,857 was used to assess the
role of 5-HT2 receptors in the stimulatory effect of MDMA on
extracellular glucose. Administration of LY-53,857 (3 mg/kg,
i.p.) markedly attenuated (p ⬍ 0.05) the MDMA-induced
increase in the extracellular concentration of glucose in the
striatum (Fig. 8). The response of extracellular glucose in
Fig. 8. Effect of MDMA on the extracellular concentration of glucose in
the striatum of rats treated with LY-53,857 (LY). MDMA (20 mg/kg, s.c.)
was injected 30 min after administration of LY-53,857 (3 mg/kg, i.p.). The
values represent the mean ⫾ S.E. of 6 to 14 rats. 多, p ⬍ 0.05 compared
with vehicle (VEH)-treated rats.
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Fig. 7. Effect of perfusion of MDMA on the extracellular concentration of
glucose in the striatum of rats. MDMA (100 ␮m) was perfused through
the dialysis probe for 5 h beginning at time 0. The values represent the
mean ⫾ S.E. of 9 to 20 rats. There was no significant difference between
the vehicle (VEH)- and MDMA-perfused groups.
In the present study, treatment with MDMA resulted in a
dose- and time-dependent enhancement of glycogenolysis in
the forebrain of the rat. The induction of glycogen breakdown
elicited by MDMA is consistent with the effects of other
amphetamine analogs on brain glycogen content. Both PCA
and d-amphetamine have been reported to reduce brain glycogen content (Nahorski and Rogers, 1975; Nowak, 1988;
Heuther et al., 1997). Poblete and Azmitia (1995) have reported that under in vitro conditions MDMA increases the
activity of glycogen phosphorylase, the enzyme responsible
for the breakdown of glycogen. Inasmuch as glycogen represents the primary energy source of the brain (Tsacopoulos
and Magistretti, 1996), these results are consistent with the
view that MDMA produces an acute decrease in the energy
stores in the brain. Although much of the glycogen in the
brain is stored in glia, it is not possible to conclude on the
basis of the present results whether MDMA-induced glycogenolysis occurs in glia or neurons.
The systemic administration of MDMA also increased the
extracellular concentration of glucose in the striatum. Although the effect of MDMA on brain glycogen was transient
(i.e., less than 2 h) in nature, it is noteworthy that the
MDMA-induced increase in the extracellular concentration of
glucose was much longer in duration (i.e., greater than 5 h).
Thus, it appears that a single injection of MDMA produces a
prolonged effect on energy substrates in the brain.
It seems likely that the increase in extracellular glucose
may be the result of the breakdown of brain glycogen. Alternatively, increased brain glucose could reflect an acute action
of MDMA in the periphery to increase circulating blood glucose. However, MDMA did not increase peripheral blood glucose (data not shown).
Although MDMA produced a prolonged increase in the
extracellular concentration of glucose, it is not possible to
determine on the basis of the present data whether this
response is reflective of an increased neuronal energy demand or simply a consequence of glycogen breakdown in glia.
Amphetamine analogs have been reported to affect various
indices of energy utilization. Stephens et al. (1998) reported
that methamphetamine increases the extracellular concentration of lactate in the striatum. In addition, amphetamine
analogs have been shown to affect ATP content, lactate, and
concentrations of energy substrates (Nahorski and Rogers,
1973; LaManna et al., 1976; Sylvia et al., 1977; Chan et al.,
1994; Huang et al., 1997). The ability of MDMA to promote
glycogenolysis and increase the extracellular concentration
of glucose could be viewed as one means of facilitating increased neuronal energy utilization. However, Wilkerson and
London (1989), using 2-deoxy-[14C]glucose autoradiography,
reported that MDMA had little effect on cerebral glucose
utilization in the caudate putamen, although increases were
noted in other brain regions. Inasmuch as the extent of
2-deoxy-[14C]-glucose uptake is thought to reflect neuronal
activity, these data do not support the view that the MDMA-
MDMA and Glycogenolysis
phetamine analogs (e.g., MDMA, methamphetamine, and
PCA) that elicit hyperthermia but is unaltered by an analog
(e.g., fenfluramine) that does not alter body temperature.
Although the present data demonstrate an association between stimulant-induced hyperthermia and glycogenolysis,
the nature of the neuron-glia interactions that underlie this
interaction are not known.
The contribution of psychostimulant-induced hyperthermia to the long-term neurotoxic effects of these drugs is well
recognized. Maintenance of rats at cold ambient temperature
prevents not only MDMA-induced hyperthermia but also the
long-term neurotoxic effects of MDMA on 5-HT axon terminals (Broening et al., 1995). In addition, many pharmacological agents that prevent MDMA-induced 5-HT neurotoxicity
also attenuate the hyperthermic response to MDMA, and the
blunting of the hyperthermic response may contribute to the
mechanism of neuroprotection. However, the mechanism
whereby hyperthermia exerts a permissive role in MDMAinduced neurotoxicity has not been elucidated. On the basis
of the present results, it is tempting to speculate that
MDMA-induced hyperthermia results in a reduction in brain
energy stores that imparts a vulnerability to 5-HT neurons to
further toxicological mechanisms. Heuther et al. (1997) have
made a similar proposal.
Depletion of cellular energy stores that accompany
MDMA-induced hyperthermia could exacerbate an already
compromised cellular energetic state resulting from the continued activation of the 5-HT transporter and, subsequently,
Na⫹/K⫹-ATPase. Ultimately, MDMA-induced energy impairment may result in ionic dysregulation, the accumulation of
intracellular Ca2⫹, and, ultimately, Ca2⫹-mediated proteolytic damage to 5-HT terminals. Altered Ca2⫹ homeostasis
also may contribute to the generation of free radicals and/or
mitochondrial dysfunction. Thus, MDMA-induced hyperthermia and the accompanying disruption of cellular energetics
may contribute to the processes of oxidative and bioenergetic
stress that appear to mediate MDMA-induced 5-HT neurotoxicity.
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induced increase in the extracellular concentration of glucose
is indicative of increased glucose utilization.
In the present study, MDMA-induced glycogenolysis was
attenuated in rats treated with the 5-HT2 antagonist LY53,857. Furthermore, two other drugs, viz., desipramine and
iprindole, that exhibit affinity for 5-HT2 receptors in the 100
to 200 nM range (Palvimaki et al., 1996) also antagonized the
MDMA-induced decrease in brain glycogen content. Desipramine and iprindole were used in the present study in view of
the findings of Quach et al. (1982), who reported that 5-HT
itself induced glycogenolysis in cortical slices in vitro and
that 5-HT-induced glycogenolysis was attenuated by desipramine and iprindole. It is not possible to exclude the possibility that the actions of desipramine involve the norepinephrine transporter in the present study. However, a
commonality of LY-53,857, iprindole, and desipramine is relatively high affinity for the 5-HT2 receptor. Although MDMA
itself exhibits weak 5-HT2 agonist activity (Nash et al., 1994),
it seems reasonable to speculate that excessive 5-HT released
by MDMA is the ligand responsible for the 5-HT2 receptormediated induction of brain glycogenolysis.
It is well recognized that MDMA produces hyperthermia in
the rat (Nash et al., 1988; Schmidt et al., 1990; Dafters,
1994), and that activation of 5-HT2 receptors is thought to
mediate the increase in body temperature produced by
MDMA (Nash et al., 1988; Schmidt et al., 1990). Consistent
with these aforementioned studies, the administration of the
selective 5-HT2 antagonist LY-53,857 attenuated MDMAinduced hyperthermia. Notably, LY-53,857 also attenuated
the MDMA-induced decrease in brain glycogen and the increase in the extracellular concentration of glucose in the
striatum. Thus, the possibility exists that 5-HT2 receptors
are involved indirectly in the mechanism of MDMA-induced
glycogenolysis; 5-HT2 receptors may not directly regulate
glycogen formation/breakdown but rather modulate energy
regulation through alterations in body temperature. In further support of this view is the present finding that maintenance of rats at a modestly cool ambient temperature (i.e.,
17°C) prevented not only MDMA-induced glycogenolysis but
also MDMA-induced hyperthermia. This finding is in agreement with the work of Nowak (1988), who reported that
amphetamine-induced hyperthermia and glycogenolysis
were less at 17 than at 27°C. Also consistent with a role of
hyperthermia in the MDMA-induced alteration in energy
regulation is the finding that the administration of MDMA
via reverse dialysis into the striatum did not alter the extracellular concentration of glucose, whereas a significant increase was observed following the systemic administration of
MDMA. Although the concentration of MDMA (100 ␮M) perfused into the striatum is sufficient to evoke dopamine and
5-HT release comparable with that produced by the systemic
administration of the drug, the local perfusion of MDMA does
not produce hyperthermia (Nixdorf et al., 2001). Thus, there
appears to be an association between the propensity of
MDMA to evoke hyperthermia and induce glycogenolysis.
The association between the elicitation of hyperthermia and
the induction of glycogenolysis is strengthened further by the
finding that glycogenolysis also was enhanced by methamphetamine and PCA but not by fenfluramine. This is noteworthy inasmuch as methamphetamine and PCA, but not
fenfluramine, elicit hyperthermia (Colado et al., 1997; Wallace et al., 2001). Thus, glycogenolysis is enhanced by am-
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