Mercury is a heavy metal contaminant with
potential for global mobilization following its give off
from anthropogenic activities or natural processes1.
In nature, elemental mercury (Hg0) can be
biotransformed and converted to methylmercury
(MeHg), which is the most toxic form of mercury in
the environment2-4. The studies about MeHg toxicity
became ubiquitous and diversified since the outbreak
of environmental catastrophes such as those in
Minamata (1950s) and Niigata (1960s). In such
episodes, as a consequence of MeHg exposure, the
Methylmercury neurotoxicity & antioxidant defenses
José Luiz M. do Nascimento1, Karen Renata M. Oliveira1, Maria Elena Crespo-Lopez2, Barbarella M.
Macchi1, Luís Antônio L. Maués1, Maria da Conceição N. Pinheiro3, Luiz Carlos L. Silveira3,4 &
Anderson Manoel Herculano1,5
1Lab. Neuroquímica Molecular e Celular, Dep. Fisiologia, Instituto de Ciências Biológicas
2Lab. Farmacologia Molecular, Instituto de Ciências Biológicas, 3Núcleo de Medicina Tropical
4Lab. Neurofisiologia, Instituto de Ciências Biológicas, & 5Lab. Neuroendocrinologia Instituto de
Ciências Biológicas, Universidade Federal do Pará, Belém, PA, Brazil
Received April 21, 2008
Neurotoxicity induced by methylmercury (MeHg) increases the formation of reactive radicals and
accelerates free radical reactions. This review summarizes recent findings in the MeHg- induced
formation of free radicals and the role of oxidative stress in its neurotoxicity. Oxidative stress on
CNS can produce damage by several interacting mechanisms, including mitochondrial damage with
increase in intracellular free Ca2+, activation and inhibition of enzymes, release of excitatory amino
acids, metallothioneins expression, and microtubule disassembly. The nature of antioxidants is
discussed and it is suggested that antioxidant enzymes and others antioxidants molecules may protect
the central nervous system against neurotoxicity caused by MeHg.
Key words Anti-oxidant defenses - metallothioneins - methylmercury - microtubules network - neurotransmitters - oxidative stress
exposed individuals exhibit severe forms of
neurological disease which include a collection of
cognitive, sensory, and motor disturbance5,6.
The studies on MeHg toxicity have tried to evaluate
its impact on several ecosystems around the World,
including places in Japan, Irak, Canada, Africa,
including Brazilian Amazon, and India2,7,8, as well as to
understand its toxicological effect on biological
systems. MeHg was firstly recognized as a potent
neurotoxicant for the adult nervous system in studies
performed on exposed workers of a chemical factory in
England9,10. Later, its importance as a neurotoxicant for
Indian J Med Res 128, October 2008, pp 373-382
the nervous system during development was recognized
in the Minamata’s outbreak5,6. Since then, several studies
of exposed human populations as well as experiments
with laboratory animals demonstrated that exposure to
toxic levels of MeHg during pre- and post-natal life
causes neurological abnormalities, cognitive
impairment, and behavioural disturbance11,12. MeHg
vulnerability of the developing brain reflects the ability
of lipophylic MeHg to cross the placenta and to
concentrate in the central nervous system (CNS) once
the blood-brain barrier is not fully developed in the
The developing CNS is more affected by MeHg
exposure and exhibits different patterns of changes than
the mature CNS. In the adult brain, MeHg poisoning
damages the so-called primary areas of the cerebral
cortex, affecting the visual, auditory, somatic sensory,
and motor cortex, as well as the hippocampus and the
granule layer of the cerebellum, causing a remarkable
loss of neurones in these brain regions. On the other
hand, in the developing brain there is a widespread
neuronal loss throughout the CNS, what has been
interpreted as due to the high MeHg sensitivity of the
immature CNS11. The neural disease due to MeHg
neurotoxicity includes such symptoms as visual field
constriction, somatic sensory disturbance, hearing
disturbance, cerebellar ataxia, dysarthria, and mnemic
Membrane interactions and transporter-mediated
MeHg quickly diffuses across membranes without
significant partitioning in lipid bilayers. Thus, it has
been proposed that MeHg toxicity is mediated by MeHg
membrane leakage17. However, it has also been
suggested that the potential of MeHg to increase
oxidative events leading to cell damage is controlled
by MeHg binding to membrane transporters. MeHg
absorption, distribution, and excretion are commonly
mediated by plasma membrane protein transporters18.
In addition, it has been possible to investigate at
molecular level the mechanisms of MeHg transport
through membrane transporters with broad substrate
selectivity. These transporters are known as
“multispecific”, taking advantage of its nature to exert
their toxic effects18. The main route for MeHg
transmembrane transport seems to be the amino acid
transport system L, which transports large amino acids19.
It has been proposed that MeHg-cysteine conjugate
is the pathway whereby MeHg exerts its toxicity20. Once
the presence of such transporters is crucial for toxicity
to occur at least through this mechanism, transporter
inhibition is expected to be beneficial to prevent
disorders caused by MeHg toxicity.
Cellular mechanism to MeHg intoxication
Calcium homeostasis: Calcium ion (Ca2+) plays a critical
role in CNS cell death. Ca2+ increase beyond
physiological levels activates catabolic enzymes such
as phospholipases, proteases, and endonucleases, causes
mitochondrial dysfunction, and disturbes cytoskeletal
organization. Several lines of evidence indicate that at
low concentrations MeHg disrupts Ca2+ homeostasis,
increasing its intracellular level in a number of
experimental situations, including primary culture of
cerebellar granule cells21. This effect has all the potential
to disrupt the synaptic function and impair the neural
Ca2+ metabolism is altered through specific
pathways which affect Ca2+ regulation by some
organelles such as mitochondria and smooth
endoplasmic reticulum (SER)23. Ca2+ channel blockers
significantly delay MeHg-induced increase of Ca2+
levels in vitro24. In agreement with these data, blockers
of voltage-dependent Ca2+ channels have been shown
to prevent the appearance of neurological disorders in
rats administered with MeHg25. These observations give
support to the hypothesis that changes in Ca2+
homeostasis represent an important cellular event in the
MeHg-induced CNS toxicity.
Mitochondrial damage induced by MeHg: Mitochondria
are the main intracellular site for reactive oxygen
production and one of the most susceptible targets for
radical species to exert their actions. Importance of
mitochondria for MeHg toxicity was recognized from
studies performed both in vivo and in vitro. In vivo
exposure to MeHg causes its accumulation inside
mitochondria followed by a series of biochemical
changes in these organelles26. These effects are similar
to those observed in studies of mitochondria respiratory
Under physiological conditions, the electron
transport system of mitochondria consumes about 1-5
per cent of the oxygen that is converted to reactive
oxygen species (ROS) such as O2 and H2O2
exposed to MeHg display neurological symptoms after
a latent period and mitochondrial function is impaired
during the symptomatic period but not during the latent
phase. Although MeHg concentrations are maximal
during the latent period, the effects of MeHg on
374INDIAN J MED RES, OCTOBER 2008
mitochondria could be indirect as they are preceded by
inhibition of protein synthesis28. Rats exposed to MeHg
have reduced rates of cellular respiration and this effect
is reverted by the removal of K+, suggesting that there
is an increase in K+ permeability of the mitochondrial
membrane29. High MeHg levels cause impairment of
mitochondrial function as the organelle exhibits a
membrane permeability transition state. MeHg exposure
induces a decrease in the activity of enzymes of the
mitochondrial energy metabolism such as cytochrome
C oxidase (CCO), superoxide dismutase (SOD) and
succinate dehydrogenase (SDH)28. This is probably due
to the decrease in the respiratory rate caused by MeHg-
induced inhibition of the tricarboxylic acid cycle. This
is consistent with previous work showing that MeHg
exposure decreases succinate dehydrogenase activity30.
In vitro MeHg exposure of isolated mitochondria from
rat liver inhibits electron transport and phosphorylation,
increases K+ permeability, and dissipates the
mitochondrial membrane potential (MMP)31. Loss of
MMP results in efflux of mitochondrial Ca+2 and
inhibition of mitochondrial Ca+2 uptake32. In addition,
MeHg exposure in isolated rat brain mitochondria
causes ATP-dependent and -independent decrease in
Ca+2 uptake and increase in Ca+2 efflux from
mitochondria33. Although mitochondria participate in
Ca+2 buffering at relatively elevated Ca+2, the affinity
of the uniport carrier for Ca+2 is low, and mitochondria
may play only a minor role in buffering Ca2+ under
Increased rate of Ca+2 is not observed during
prolonged depolarization and it seems that under normal
conditions mitochondria do not contain sufficient Ca2+
to alter neurotransmitter release33. Recent evidence
suggests that increased local concentration of Ca2+ may
be required for activation of neurotransmitter release.
Thus, the relatively small changes in Ca2+ observed upon
mitochondria depolarization are likely insufficient to
alter the release of neurotransmitter via normal
physiological mechanisms. However, other mechanisms
for MeHg toxicity could be trigger by small alterations
in the internal Ca2+ concentrations.
Microtubules network: MeHg seems to interact with
cytoplasmatic cytoskeletal components, including
microtubules34. In vitro studies demonstrated that MeHg
presents high affinity for tubulin sulphydryl groups
(-SH), depolymerizing cerebral microtubules and
directly inhibiting their assembly34,35. In addition,
several works reported that MeHg promotes
microtubule disruption in a number of cell models,
including human fibroblasts34, neuroblastoma, and
Neuroblastoma cells appear to be more susceptible
to toxic effects of MeHg than either rat glioma or human
fibroblasts38, although the cell death mechanism
produced by MeHg in these cell lines has not been well
The integrity of microtubule function is critical for
the physiological development of the CNS including
cell proliferation, migration of post-mitotic neurones
to form the cortical layers of the cerebrum and
cerebellum, extension and stabilization of neuritis, and
axodendritic transport. Indeed, MeHg interference in
microtubules is consistent with neuropathologic
findings in the autoptic brains of full-term newborn
human infants from the Iraqi outbreak, who were
exposed in utero in early phases of pregnancy. These
findings included brain reduction, neuronal heterotopias
in the cerebral and cerebellar white matter, and abnormal
patterns of neuronal arrangement and alignment in the
The ability of MeHg in a concentration-dependent
way to inhibit neuronal migration from the external
granule layer towards the internal granule layer has been
demonstrated experimentally in cerebellar organotypic
cultures40. It has been suggested that the extensive
apoptotic death observed in the external granule layer
following MeHg treatment is the result and not a cause
of the impaired neuronal migration40.
Interestingly, microtubule disruption provoked by
MeHg does not only affect the neuronal migration and
development of CNS. One of the most dangerous
consequences of human exposure to relatively low
levels of MeHg is DNA damage as demonstrated by
detection of micronucleated cells and chromosomal
aberrations40,41. In recent years, microtubule disruption
was hypothesized as the origin of this genotoxic effect
of mercury42-44 and a recent report demonstrated that
very low MeHg concentrations are able to initiate
genotoxic processes in human cell lines of brain origin45.
MeHg and neurotransmitters systems: Several metal
compounds have been shown to interfere with
neurotransmission. MeHg directly affects the
mechanisms of neurotransmission, including release and
uptake of neurotransmitters, enzymatic neurotransmitter
metabolic inactivation, and post-synaptic events
associated with receptor activation46. Some
neurotransmission by interacting, for example, with
NASCIMENTO et al: METHYLMERCURY NEUROTOXICITY 375
energy metabolism, sodium channels, or ATPases.
Furthermore, changes of any parameter of
neurotransmission can be the result of neuronal death
due to cytotoxic effects of the neurotoxicants47.
The rising of extracellular glutamate levels is
responsible for the constant activation of metabotropic
and ionotropic glutamate receptors thus elevating Na+
influx and Ca2+ release from intracellular organelles that
may trigger a biochemical cascade which increases the
production of ROS47. Oxidative stress by itself inhibits
the astrocytic glutamate uptake through a direct action
on the transporter proteins48,49.
Although the toxic damage caused by MeHg might
be intrinsically prevalent in neurones, many of the
published evidences suggest that neuronal damage in
response to MeHg most likely represents aberrant
control of the extracellular milieu by the astrocytes50.
On line with this argument it should be remarked that
the neurotoxic effect of MeHg could be reverted with
antagonists of N-methyl-D-aspartate (NMDA)
Moreover, MeHg has been described to produce
increases in the spontaneous release of other
neurotransmitters such as dopamine, GABA, acetylcholine,
and serotonin from rat brain synaptosomes51-53. MeHg also
inhibits astrocytic uptake of cystine and cysteine, the key
precursor for glutathione biosynthesis50.
Methylmercury and metallothioneins: Metallothioneins
(MTs) constitute a family of proteins characterized by
an unusual cystein abundance54. Under physiological
conditions, MTs are unusually rich in multiple cysteine
residues allowing their binding to metal centers and
enabling them to serve as a heavy-metal detoxification
system55. MTs are predominantly expressed in the
central nervous system and it is important to gain new
insight into how MTs are regulated in the brain in
pathological injury, such as that produced by MeHg
Some studies have reported the potential role of
MTs in attenuating the cytotoxicity induced by
MeHg54,56. Although the interaction of MTs with MeHg
ions has long been established, elucidation of the
binding features of MeHg-MT species has been
hampered by the inherent difficulties of MeHg-thiolate
chemistry, which mainly arise from the diverse co-
ordination preferences of Hg (II) and the various ligation
modes of the thiolate ligands57. Nevertheless, the
analysis of MeHg binding to MTs has been intensively
studied. In contrast, the chemistry of MeHg-MT
complexes has attracted much less attention. Earlier
reports demonstrated the inability of MT in the
detoxification of MeHg and that it is unable to bind to
MeHg either in vivo or in vitro57,58. Subsequent attempts
to induce brain MT by exposure to MeHg+ gave
inconsistent results: MT concentrations remained
unchanged in rats, whereas MT and mRNA
concentrations increased in MeHg-treated rat neonatal
astrocyte cultures58. However, there is increasing
evidence that induction of MTs in astrocytes attenuates
and even reverses the cytotoxicity caused by MeHg,
indicating binding of MeHg by an astrocyte-specific
MT isoform, MT159.
The MT association with heavy metals has been
the subject of several studies. For example, data about
geometry of mercury and metallothionein association
have demonstrated that characteristics of MeHg-MT
species cannot be extended to Hg-MT complexes57. The
co-existence of digonal, trigonal-planar, and tetrahedral
co-ordination geometries together with the presence of
secondary mercury-sulphur interactions are common
features in the chemistry of Hg(II) thiolates57. In
contrast, MeHg shows a clear preference to form
essentially linear two-coordinate Hg(II) complexes with
thiolate ligands, even if, in some cases, secondary
interactions at the metal center are observed59,60. These
characteristics could reflect the differences in cellular
resistances or response observed against mercury
organic and inorganic toxicity57.
Methylmercury and oxidative stress
ROS are generally very small molecules and are
highly reactive due to the presence of unpaired valence
shell electrons. ROS form as a natural by-product of
the normal oxygen metabolism and have important roles
in cell signalling. These molecules are generated
continuously during oxidative metabolism and consist
of inorganic molecules, such as superoxide radical anion
(O2–), hydrogen peroxide (H2O2), hydroxyl radicals
(OH–), as well as organic molecules such as alkoxyl
and peroxyl radicals61. Some evidences suggest that the
disturbance in the balance between oxidative and
reductive cell processes is involved in the pathogenesis
of many neurodegenerative conditions such as
Alzheimer disease, amyotrophic lateral sclerosis (ALS),
and Parkinson disease. Other conditions such as
autoimmune and inflammatory diseases, cancer, and
diabetes mellitus also seemed to be related to this
376INDIAN J MED RES, OCTOBER 2008
MeHg has been thought to induce ROS and
generation of oxidative events leading to cell damage.
Previous studies have suggested that there is a
relationship between these events with dysfunction of
the cellular energetic metabolism and disruption of the
electron transport chain. These phenomena generate
oxidative stress62,63. MeHg exposure increases the rate
of ROS in the cerebellum (in vivo) and in the brain
synaptosomes as well as in the cerebellum neuronal
cultures, hypothalamic neuronal cell line, and mixed
reaggregating cell cultures64-66. The formation of these
species was critical to determine the damage and the
cell death in distinct cell types such as astrocytes and
It seems that the intensity of MeHg exposure is a
crucial factor to establish whether the neuronal death
occurs by necrosis or apoptosis67,68. However, the
mechanism of cell death induced by oxidative stress
via MeHg has not been well characterized.
Methylmercury and antioxidant defenses
Many studies have already established that MeHg
neurotoxicity evokes oxidative stress with formation
of ROS in the CNS and that the increase of ROS induces
cell damage and death in the CNS. In order to avoid the
damage caused by ROS, such as DNA strand breaks,
lipid peroxidation, and protein modification,
mechanisms have been developed during evolution
which dispose or prevent the generation of ROS69.
However, the underlying mechanisms responsible for
the protection of CNS against MeHg neurotoxicity are
still poorly understood.
It is well known that cell defences against free
radicals such as ROS include scavenger compounds
such as glutathione, cysteine, melatonin, and enzymes
with antioxidant activities as superoxide dismutase,
catalase, and glutathione peroxidase70.
It was demonstrated that MeHg induces a
concentration-dependent increase in ROS formation in
rat neonatal neuronal culture and astrocytes
culture48,71,72. It was also shown that this effect can be
reverted by the use of n-propyl gallate (PG), a free
radical scavenger, superoxide dismutase (SOD), an
antioxidant enzyme, and α-phenyl-tert-butyl nitrone
(PBN), a lipophilic hydroxyl radical spin trapping
Endogenous glutathione (GSH) is one of the most
abundant and essential thiol tripeptide present in
mammalian cells for scavenging reactive oxygen
species69. The involvement of GSH in the neurotoxicity
of MeHg was also evaluated, showing that the increased
oxidative stress is related with the depleted intracellular
GSH levels74,75. The excessive formation of ROS
induced by MeHg exposure can be reverted under
treatment with L-2-oxothiazolidine-4-carboxylic acid
(OTC), which increases the amount of intracellular
GSH, as well as the depletion of GSH by treatment with
buthionine-L-sulphoxane (BSO) can potentiate the
production of ROS induced by MeHg in rat primary
Recently, a human population study in the Amazon
correlated the MeHg exposure with the levels of
glutathione and catalase activity. Surprisingly, it was
demonstrated that high blood levels of glutathione in
woman exposed to high concentrations of MeHg may
be explained by the increase of glutathione synthesis in
response to oxidative stress or, more probably, by the
inhibition of glutathione peroxidase activity77. In the
same population the inhibition of catalase activity was
also observed. These changes likely reflect adaptive
responses of the Amazonian population to oxidative
stress induced by MeHg.
Other studies revealed that the GSH content may
vary in different regions of the CNS, demonstrating that
the GSH amount is higher in cerebral cells than in
cerebellar cells78,79. This may explain the higher
susceptibility of cerebellar cells to MeHg toxicity in
comparison with cerebral cells, but the reason why
certain areas of CNS showed different sensitivity to
MeHg toxicity, remains unclear.
In addition, MeHg poisoning can induce
sympathetic ganglia toxicity and neurite outgrowth
inhibition80,81. Compounds that possess sulphydryl (-SH)
groups attenuate MeHg neurotoxicity, once at least part
of MeHg effects occurs through interaction with -SH
groups in cellular proteins82. In this context, primary
neuronal cultures from avian sympathetic ganglion were
used to evaluate the protective role of antioxidants
agents with -SH group such as L-cysteine against MeHg
toxicity. It was reported that MeHg induces massive
cell death (neurite death) and that L-cysteine could fully
protect (nearly 100%) the sympathetic neuron against
this damage. The effect of GSH was also tested showing
the same properties of cysteine83.
The use of methionine, an antioxidant agent which
does not possess -SH groups, fails to promote cell
protection against MeHg intoxication, proving the
relevance of -SH groups to this effect83. Another
NASCIMENTO et al: METHYLMERCURY NEUROTOXICITY377
antioxidant that protects the brain against oxidative
stress is vitamin E, which maintains the integrity of
membrane by inhibiting lipid peroxidation84. Recent
findings reported the protective effect of the
antioxidants tocopherols and tocotrienols (analogs to
vitamin E) against MeHg neurotoxicity85,86. In cerebellar
granule cells (CGC), these compounds effectively
prevent cell death caused by MeHg intoxication as well
as improve cell migration87.
Evidences also suggest that the treatment with
trolox (6-hydroxy-2,5,7,8- tetramethylchroman-2-
carboxylic acid), other antioxidant derivate from
vitamin E, might provide prevention against oxidative
stress. In MeHg-treated rats, it detected many apoptotic
cells in the cerebellar granule layers and the treatment
with trolox clearly repressed the appearance of these
A number of different hypotheses have been
suggested to explain the mechanism by which the
antioxidants defences protect CNS against MeHg
neurotoxicity, which include scavenging and removal
of free radicals, reversal of glutamate uptake
impairment, inhibition of cytochrome c release, and
It has been established that MeHg inhibits glutamate
transport by astrocytes by an unknown mechanism
which leads to the increase of ROS generation88. It was
demonstrated that a variety of antioxidants can prevent
the overproduction of ROS, in this way attenuating
MeHg neurotoxicity. Some workers have focused on
the effect of antioxidant agents in the impairment of
EAA transport elicited by MeHg.
In primary cultures of astrocytes from cerebral
cortex, MeHg treatment inhibits the net uptake of 3H-
D-aspartate, a glutamate analogue, that could be
completely prevented by catalase activity suggesting
that the amount of H2O2 mediates this EAA transport
inhibition89. The mechanisms whereby H2O2 alters EAA
transport remains elusive, although it was proposed that
the excessive production of H2O2 by MeHg
intoxication involves the inhibition of plasma membrane
Na+/K+-ATPase and subsequent modification in the ratio
of intracellular/extracellular Na+ concentration
necessary for EAA transport. Interestingly, others
antioxidants that prevent ROS formation such as trolox
and PBN did not present any effect in this transport
In previous studies it was demonstrated that
intrastriatal administration of different concentrations
of MeHg produces significant increase in dopamine
release from rat striatum90. This increase is due to the
interaction of this metal with dopamine transporter
(DAT). Pre-treatment with both GSH and cysteine
significantly decreased dopamine release induced by
MeHg, with GSH being more efficient than cysteine91.
The molecular mechanisms of MeHg damage in
both adult and developing CNS is not fully understood.
Early reports have described a number of possible
cellular mechanisms to explain the neurotoxicity
induced by MeHg. Most of these studies reported the
high affinity of MeHg for thiol groups (-SH) which are
present in cytoskeletal proteins, enzymes, and peptides
that contain the amino acid cysteine78.
In accordance with these results, it is well
established that interactions between MeHg and -SH
potentially inactivate protein functions in all cellular
and subcellular compartments42,92. The mechanisms
underlying the protective role of antioxidants molecules
against CNS toxicity by MeHg will likely be related to
their thiol groups (-SH) binding capacity.
Also in line with the above results, the susceptibility
of neurones to MeHg intoxication has been associated
to the absence or limited presence of inherent protective
mechanisms such as metallothioneins, reduced
glutathione, and other stress proteins93.
This review corroborates with the major role of
ROS production in mediating MeHg toxicity in the CNS
(Fig.). MeHg-induced toxicity with an emphasis on the
generation and role of reactive oxygen and nitrogen
species is reviewed. MeHg-mediated formation of free
radicals causes many modifications to DNA bases,
enhanced lipid peroxidation, and altered calcium and
sulphydryl homeostasis. Primary route for MeHg
toxicity is depletion of glutathione and bonding to
sulphydryl groups of proteins. Various studies have
confirmed that metals activate signalling pathways and
the cytotoxic effect of MeHg has been related to
activation of mainly redoxsensitive transcription factors.
Antioxidants (both enzymatic and non enzymatic)
provide protection against deleterious metal-mediated
free radical attacks. Vitamin E and melatonin can
prevent the majority of MeHg-mediated damage both
in vitro systems and in metal loaded animals. Toxicity
produced by MeHg showed that the protective effect
of vitamin E against lipid peroxidation may be
associated rather with the level of non-enzymatic
antioxidants than the activity of enzymatic antioxidants.
378 INDIAN J MED RES, OCTOBER 2008
Molecular and cellular approaches can be a strategy
to critically examine the possibility of therapeutic
actions such as antioxidants or chelanting agents in the
treatment of neurodegeneration produced by MeHg.
This work was supported by JICA, CNPq #486351/2006-8,
#620232/2004-8, CNPq-DCR/SEDECT #015/2004, and by the
FINEP research grant “Rede Instituto Brasileiro de Neurociência
(IBN-Net)” # 01.06.0842-00. LCLS and JLMN are CNPq research
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Reprint requests: Dr José Luiz Martins do Nascimento, Universidade Federal do Pará, Instituto de Ciências Biológicas
Laboratório de Neuroquimica Molecular e Celular, 66075-900 Belém, Pará, Brazil
382 INDIAN J MED RES, OCTOBER 2008