Rat developmental fluoride exposure affects retention memory, leads to a depressive-like behavior, and induces biochemical changes in offspring rat brains.

Water is the principal source of human exposure to fluoride (F). The high permeability of the placenta and blood-brain barrier to F during the intrauterine life up to the end of lactation may be crucial to neurological fetus development. Therefore, this study explores the effects of 5 and 10 mg/l F exposure during entire gestation and lactation periods, through neurobehavioral and biochemical tests performed on 90-day-old male offspring rats. The present study shows that pre and peri-natal exposure to F doses that are in the range of those found in groundwater sources in Argentina affects long-term memory and leads to a depressive-like behavior in 90-day-old male pup. Furthermore, the purpose of the investigation was to find out the possible biochemical changes through which the pre and peri-natal F-administration could generate such behavioral variations. We found alterations in transaminases, acetylcholinesterase, and alkaline phosphatase enzymes activity in specific brain areas (the prefrontal cortex, the striatum, and the hippocampus), together with findings regarding misbalanced oxidative stress. In conclusion, F exposure during the early stages of rat development alters brain-oxidative stress markers as well as the activity of enzymes implicated in cholinergic and glutamatergic systems. These molecular changes could contribute to the neurobehavioral alterations described in the present investigation.

Impairment of glutamate homeostasis in the nucleus accumbens core underpins cross-sensitization to cocaine following chronic restraint stress.

Though the facilitating influence of stress on drug abuse is well documented, the mechanisms underlying this interaction have yet to be fully elucidated. The present study explores the neurobiological mechanisms underpinning the sensitized response to the psychomotor-stimulating effects of cocaine following chronic restraint stress (CRS), emphasizing the differential contribution of both subcompartments of the nucleus accumbens (NA), the core (NAcore) and shell (NAshell), to this phenomenon. Adult male Wistar rats were restrained for 2 h/day for 7 days and, 2 weeks after the last stress exposure (day 21), all animals were randomly assigned to behavioral, biochemical or neurochemical tests. Our results demonstrated that the enduring CRS-induced increase in psychostimulant response to cocaine was paralleled by an increase of extracellular dopamine levels in the NAcore, but not the NAshell, greater than that observed in the non-stress group. Furthermore, we found that CRS induced an impairment of glutamate homeostasis in the NAcore, but not the NAshell. Its hallmarks were increased basal extracellular glutamate concentrations driven by a CRS-induced downregulation of GLT-1, blunted glutamate levels in response to cocaine and postsynaptic structural remodeling in pre-stressed animals. In addition, ceftriaxone, a known GLT-1 enhancer, prevented the CRS-induced GLT-1 downregulation, increased basal extracellular glutamate concentrations and changes in structural plasticity in the NAcore as well as behavioral cross-sensitization to cocaine, emphasizing the biological importance of GLT-1 in the comorbidity between chronic stress exposure and drug abuse. A future perspective concerning the paramount relevance of the stress-induced disruption of glutamate homeostasis as a vulnerability factor to the development of stress and substance use disorders during early life or adulthood of descendants is provided.

CB1R activation in nucleus accumbens core promotes stress-induced reinstatement of cocaine seeking by elevating extracellular glutamate in a drug-paired context.

Preclinical models of stress-induced relapse to drug use have shown that the dysregulation of glutamatergic transmission within the nucleus accumbens (NA) contributes notably to the reinstatement of cocaine-seeking behavior in rodents. In this sense, there has been increasing interest in the cannabinoid type-1 receptor (CB1R), due to its crucial role in modulating glutamatergic neurotransmission within brain areas involved in drug-related behaviors. This study explored the involvement of CB1R within the NA subregions in the restraint stress-induced reinstatement of cocaine-conditioned place preference (CPP), as well as in the regulation of glutamatergic transmission, by using a pharmacological approach and the in vivo microdialysis sampling technique in freely moving rats. CB1R blockade by the antagonist/inverse agonist AM251 (5 nmol/0.5 µl/side) or CB1R activation by the agonist ACEA (0.01 fmol/0.5 µl/side), prevented or potentiated restraint stress-induced reinstatement of cocaine-CPP, respectively, after local administration into NAcore, but not NAshell. In addition, microdialysis experiments demonstrated that restraint stress elicited a significant increase in extracellular glutamate in NAcore under reinstatement conditions, with the local administration of AM251 or ACEA inhibiting or potentiating this, respectively. Interestingly, this rise specifically corresponded to the cocaine-associated CPP compartment. We also showed that this context-dependent change in glutamate paralleled the expression of cocaine-CPP, and disappeared after the extinction of this response. Taken together, these findings demonstrated the key role played by CB1R in mediating reinstatement of cocaine-CPP after restraint stress, through modulation of the context-specific glutamate release within NAcore. Additionally, CB1R regulation of basal extracellular glutamate was demonstrated and proposed as the underlying mechanism.

Stress-induced vulnerability to develop cocaine addiction depends on cofilin modulation.

Actin dynamics in dendritic spines can be associated with the neurobiological mechanisms supporting the comorbidity between stress exposure and cocaine increase rewards. The actin cytoskeleton remodeling in the nucleus accumbens (NA) has been implicated in the expression of stress-induced cross-sensitization with cocaine. The present study evaluates the involvement of cofilin, a direct regulator of actin dynamics, in the impact of stress on vulnerability to cocaine addiction. We assess whether the neurobiological mechanisms that modulate repeated-cocaine administration also occur in a chronic restraint stress-induced cocaine self-administration model. We also determine if chronic stress induces alterations in dendritic spines through dysregulation of cofilin activity in the NA core. Here, we show that the inhibition of cofilin expression in the NA core using viral short-hairpin RNA is sufficient to prevent the cocaine sensitization induced by chronic stress. The reduced cofilin levels also impede a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor surface expression enhancement and promote the reduction of head diameter in animals pre-exposed to stress after a cocaine challenge in the NA core. Moreover, downregulation of cofilin expression prevents facilitation of the acquisition of cocaine self-administration (SA) in male rats pre-exposed to chronic stress without modifying performance in sucrose SA. These findings reveal a novel, crucial role for cofilin in the neurobiological mechanisms underpinning the comorbidity between stress exposure and addiction-related disorders.

Endogenous enkephalin is necessary for cocaine-induced alteration in glutamate transmission within the nucleus accumbens.

Altered glutamate transmission within the nucleus accumbens (NAc) has been proposed as a central mechanism underlying behavioural sensitisation associated with repeated cocaine exposure. In addition to glutamate, enkephalin, an endogenous opioid peptide derived from proenkephalin, is necessary for the neuroadaptations associated with chronic cocaine. However, the influence of enkephalin on long-term changes in glutamate transmission within the NAc associated with cocaine-induced sensitisation has not been described. This study used knockout proenkephalin mice (KO) to study the influence of endogenous enkephalin on the adaptations in glutamate neurotransmission associated with repeated cocaine treatment. Wild-type (WT) and KO mice were treated with daily cocaine injections for 9 days to induce sensitisation. On days 15 and 21, the animals received a cocaine challenge and locomotor sensitisation was evaluated, and microdialysis was performed to determine accumbens glutamate content on day 21. No expression of behavioural sensitisation to cocaine was evidenced in the KO mice. Consistently, these showed no changes in glutamate transmission in the NAc associated with repeated cocaine. This study reveals the central role of enkephalin in regulating the glutamate mechanisms associated with cocaine sensitisation.

Effects of Perinatal Fluoride Exposure on Short- and Long-Term Memory, Brain Antioxidant Status, and Glutamate Metabolism of Young Rat Pups.

Exposure to fluoride (F) during the development affects central nervous system of the offspring rats which results in the impairment of cognitive functions. However, the exact mechanisms of F neurotoxicity are not clearly defined. To investigate the effects of perinatal F exposure on memory ability of young rat offspring, dams were exposed to 5 and 10 mg/L F during gestation and lactation. Additionally, we evaluated the possible underlying neurotoxic mechanisms implicated. The results showed that the memory ability declined in 45-day-old offspring, together with a decrease of catalase and glutamate transaminases activity in specific brain areas. The present study reveals that exposure to F in early stages of rat development leads to impairment of memory in young offspring, highlighting the alterations of oxidative stress markers as well as the activity of enzymes involved in the glutamatergic system as a possible mechanisms of neurotoxicity.

Alterations in the memory of rat offspring exposed to low levels of fluoride during gestation and lactation: Involvement of the α7 nicotinic receptor and oxidative stress.

Daily exposure to fluoride (F) depends mainly on the intake of this element with drinking water. When administered during gestation and lactation, F has been associated with cognitive deficits in the offspring. However, the mechanisms underlying the neurotoxicity of F remain obscure. In the current study, we investigated the effects of oral exposure to low levels of F during the gestational and lactation periods, on the memory of adult female rat offspring. We also considered a possible underlying neurotoxic mechanism. Our results showed that this exposure reduced step-down latency in the inhibitory avoidance task, and decreased both mRNA expression of the α7 nicotinic receptor (nAChR) and catalase activity in hippocampus. Our data indicates that low F concentrations administrated during gestation and lactation decrease the memory of 90-day-old female offspring. This suggests that the mechanism might be connected with an α7 nAChR deficit in the hippocampus, induced by oxidative stress.

Enkephalin as a Pivotal Player in Neuroadaptations Related to Psychostimulant Addiction.

Enkephalin expression is high in mesocorticolimbic areas associated with psychostimulant-induced behavioral and neurobiological effects, and may also modulate local neurotransmission in this circuit network. Psychostimulant drugs, like amphetamine and cocaine, significantly increase the content of enkephalin in these brain structures, but we do not yet understand the specific significance of this drug-induced adaptation. In this review, we summarize the neurochemical and molecular mechanism of psychostimulant-induced enkephalin activation in mesocorticolimbic brain areas, and the contribution of this opioid peptide in the pivotal neuroadaptations and long-term behavioral changes underlying psychostimulant addiction. There is evidence suggesting that adaptive changes in enkephalin content in the mesocorticolimbic circuit, induced by acute and chronic psychostimulant administration, may represent a key initial step in the long-term behavioral and neuronal plasticity induced by these drugs.

Phosphatidyl-Inositol-3 Kinase Inhibitors Regulate Peptidoglycan-Induced Myeloid Leukocyte Recruitment, Inflammation, and Neurotoxicity in Mouse Brain.

Acute brain injury leads to the recruitment and activation of immune cells including resident microglia and infiltrating peripheral myeloid cells (MC), which contribute to the inflammatory response involved in neuronal damage. We previously reported that TLR2 stimulation by peptidoglycan (PGN) from Staphylococcus aureus, in vitro and in vivo, induced microglial cell activation followed by autophagy induction. In this report, we evaluated if phosphatidyl-inositol-3 kinase (PI3K) pharmacological inhibitors LY294200 and 3-methyladenine (3-MA) can modulate the innate immune response to PGN in the central nervous system. We found that injection of PGN into the mouse brain parenchyma (caudate putamen) triggered an inflammatory reaction, which involved activation of microglial cells, recruitment of infiltrating MC to injection site, production of pro-inflammatory mediators, and neuronal injury. In addition, we observed the accumulation of LC3B+ CD45+ cells and colocalization of LC3B and lysosomal-associated membrane protein 1 in brain cells. Besides, we found that pharmacological inhibitors of PI3K, including the classical autophagy inhibitor 3-MA, reduced the recruitment of MC, microglial cell activation, and neurotoxicity induced by brain PGN injection. Collectively, our results suggest that PI3K pathways and autophagic response may participate in the PGN-induced microglial activation and MC recruitment to the brain. Thus, inhibition of these pathways could be therapeutically targeted to control acute brain inflammatory conditions.

Modulation of Ethanol-Metabolizing Enzymes by Developmental Lead Exposure: Effects in Voluntary Ethanol Consumption.

This review article provides evidence of the impact of the environmental contaminant lead (Pb) on the pattern of the motivational effects of ethanol (EtOH). To find a mechanism that explains this interaction, the focus of this review article is on central EtOH metabolism and the participating enzymes, as key factors in the modulation of brain acetaldehyde (ACD) accumulation and resulting effect on EtOH intake. Catalase (CAT) seems a good candidate for the shared mechanism between Pb and EtOH due to both its antioxidant and its brain EtOH-metabolizing properties. CAT overactivation was reported to increase EtOH consumption, while CAT blockade reduced it, and both scenarios were modified by Pb exposure, probably as the result of elevated brain and blood CAT activity. Likewise, the motivational effects of EtOH were enhanced when brain ACD metabolism was prevented by ALDH2 inhibition, even in the Pb animals that evidenced reduced brain ALDH2 activity after chronic EtOH intake. Overall, these results suggest that brain EtOH metabolizing enzymes are modulated by Pb exposure with resultant central ACD accumulation and a prevalence of the reinforcing effects of the metabolite in brain against the aversive peripheral ACD accumulation. They also support the idea that early exposure to an environmental contaminant, even at low doses, predisposes at a later age to differential reactivity to challenging events, increasing, in this case, vulnerability to acquiring addictive behaviors, including excessive EtOH intake.

NMDA antagonist MK 801 in nucleus accumbens core but not shell disrupts the restraint stress-induced reinstatement of extinguished cocaine-conditioned place preference in rats.

Relapse is a common feature of cocaine addiction. In rodents, it can be elicited by cues, stress or the drug. Restraint stress-induced reinstatement of cocaine-conditioned place preference (CPP) is a useful model to study the mechanisms involved in stress-induced relapse of drug-seeking behavior. There is evidence that the glutamate NMDA receptors are critically involved in drug- and cue-induced reinstatement of seeking behavior and drug-CPP responses. The aim of this study was to investigate the contribution of NMDA receptors within core vs. shell nucleus accumbens (NAc) subregions to restraint stress-induced reinstatement of extinguished cocaine-CPP. After extinction of cocaine-conditioned preference, animals were administered MK 801 systemically or directly into intra-core or intra-shell, and restrained for 30min or left undisturbed in their home-cages. First, we demonstrated that restraint stress-induced reinstatement of extinguished cocaine-CPP depends on the duration of restraint as well as on the context in which it is applied. Second, this effect was blocked by systemic MK 801 administration either before or after restraint. Third, intra-core but not intra-shell administration abrogated the restraint stress-induced reinstatement. These findings show that NMDA receptors within NAc core, but not shell, play a critical role in restraint stress-induced reinstatement of cocaine-CPP.

Enkephalin is essential for the molecular and behavioral expression of cocaine sensitization.

Behavioral sensitization to cocaine is associated to neuroadaptations that contribute to addiction. Enkephalin is highly expressed in mesocorticolimbic areas associated with cocaine-induced sensitization; however, their influence on cocaine-dependent behavioral and neuronal plasticity has not been explained. In this study, we employed a knockout (KO) model to investigate the contribution of enkephalin in cocaine-induced behavioral sensitization. Wild-type (WT) and proenkephalin KO mice were treated with cocaine once daily for 9 days to induce sensitization. Additionally, to clarify the observations in KO mice, the same procedure was applied in C57BL/6 mice, except that naloxone was administered before each cocaine injection. All animals received a cocaine challenge on days 15 and 21 of the treatment to evaluate the expression of locomotor sensitization. On day 21, microdialysis measures of accumbal extracellular dopamine, Western blotting for GluR1 AMPA receptor (AMPAR), phosphorylated ERK2 (pERK2), CREB (pCREB), TrKB (pTrkB) were performed in brain areas relevant for sensitization from KO and WT and/or naloxone- and vehicle pre-treated animals. We found that KO mice do not develop sensitization to the stimulating properties of cocaine on locomotor activity and on dopamine release in the nucleus accumbens (NAc). Furthermore, pivotal neuroadaptations such as the increase in pTrkB receptor, pERK/CREB and AMPAR related to sensitized responses were absent in the NAc from KO mice. Consistently, full abrogation of cocaine-induced behavioral and neuronal plasticity after naloxone pre-treatment was observed. We show for first time that the proenkephalin system is essential in regulating long-lasting pivotal neuroadaptations in the NAc underlying behavioral sensitization to cocaine.

Neurobehavioural effects of exposure to fluoride in the earliest stages of rat development.

It is known that exposure to high concentrations of Fluoride (F) produces deleterious health effects in human population. However, in the last years it has been concluded that low concentrations of F may have adverse health effects as well. Transplacental passage of F and its incorporation into foetal tissues has been demonstrated. Therefore, the purpose of the present work was to study the effects of the exposure to low levels of F during pregnancy and lactation on the central nervous system functionality. Wistar rats were exposed to low F concentrations (5 and 10 mg/l) during pregnancy and lactation. Sensorimotor reflexes in the each pup were analysed and the postnatal day on which both eyes and auditory canals were opened was recorded. Locomotor activity and anxiety were subsequently analysed in 45- and 90-day-old offspring by an open field test and plus maze test, respectively. A significant delay in the development of eye opening was observed in all offspring whose mothers had been exposed to the two F concentrations tested. Exposure to 5 and 10 mg/l F was also found to significantly decrease locomotor activity only in 90-day-old male and female offspring. A low index of anxiety in the young females and in all adult offspring exposed to the two F concentrations tested was also detected. Taken together, findings from the present study show that exposure to low F concentrations during pregnancy and lactation produces dysfunction in the central nervous system mechanisms which regulate motor and sensitive development, locomotor activity and anxiety

Angiotensin II AT1 receptors are involved in neuronal activation induced by amphetamine in a two-injection protocol.

It was already found that Ang II AT1 receptors are involved in the neuroadaptative changes induced by a single exposure to amphetamine, and such changes are related to the development of behavioral and neurochemical sensitization. The induction of the immediately early gene c-fos has been used to define brain activated areas by amphetamine. Our aim was to evaluate the participation of AT1 receptors in the neuronal activation induced by amphetamine sensitization. The study examined the c-fos expression in mesocorticolimbic areas induced by amphetamine challenge (0.5 mg/kg i.p) in animals pretreated with candesartan, a selective AT1 receptor blocker (3 mg/kg p.o × 5 days), and amphetamine (5 mg/kg i.p) 3 weeks before the challenge. Increased c-fos immunoreactivity was found in response to the amphetamine challenge in the dorsomedial caudate-putamen and nucleus accumbens, and both responses were blunted by the AT1 receptor blocker pretreatment. In the infralimbic prefrontal cortex, increased c-fos immunoreactivity was found in response to amphetamine and saline challenge, and both were prevented by the AT1 receptor blocker. No differences were found neither in ventral tegmental area nor prelimbic cortex between groups. Our results indicate an important role for brain Ang II in the behavioral and neuronal sensitization induced by amphetamine.

Participation of catalase in voluntary ethanol consumption in perinatally low-level lead-exposed rats.

BACKGROUND: Environmental lead (Pb) exposure and alcohol abuse pose significant public health problems for our society. One of the proposed mechanisms of action of the developmental neurotoxicant Pb is related to its ability to affect antioxidant enzymes, including catalase (CAT). Ethanol's (EtOH) motivational effects are postulated to be mediated by the CAT-dependent acetaldehyde generated in the brain. The current study sought to investigate the role of this enzyme in the elevated EtOH intake previously reported in perinatally Pb-exposed rats. METHODS: Thirty-five-day-old male Wistar rats exposed to 220 ppm Pb during gestation and lactation were offered escalating EtOH solutions (2 to 10%) or water, 2 h/d for 28 days. Once baseline 10% EtOH intake was achieved, they were injected with (i) saline (SAL), (ii) 3-amino 1,2,4 triazole (aminotriazole [AT], a CAT inhibitor, 250 mg/kg intraperitoneally [i.p.], 5 hours before the last 8 EtOH intake sessions), or (iii) 3-nitropropionic acid (3NPA; a CAT activator, 20 mg/kg subcutaneously [s.c.], 45 minutes before the last 4 EtOH intake sessions). Rats were then sacrificed, blood collected, and brain regions harvested for CAT activity determination. Additional studies evaluated EtOH intake and CAT activity in response to 10 and 30 mg/kg 3NPA. Both 3NPA and AT were evaluated for striatal cytotoxicity. RESULTS: We observed that AT pretreatment blunted the increased EtOH intake, as well as the elevated CAT activity in blood, cerebellum, and hippocampus evidenced in the developmentally Pb-exposed rats that have consumed EtOH. Conversely, 20 mg/kg 3NPA further increased voluntary EtOH intake in these animals as compared with controls, concomitantly with a slight elevation in CAT activity both in blood and in the striatum, associated with no changes in striatal cytotoxicity. CONCLUSIONS: These results suggest a participation of CAT, and possibly acetaldehyde, in Pb-induced high EtOH intake, and open up new avenues to elucidate the mechanism that underlies the Pb and EtOH interaction.

Toll-like receptor 2 ligands promote microglial cell death by inducing autophagy.

Microglial cells are phagocytes in the central nervous system (CNS) and become activated in pathological conditions, resulting in microgliosis, manifested by increased cell numbers and inflammation in the affected regions. Thus, controlling microgliosis is important to prevent pathological damage to the brain. Here, we evaluated the contribution of Toll-like receptor 2 (TLR2) to microglial survival. We observed that activation of microglial cells with peptidoglycan (PGN) from Staphylococcus aureus and other TLR2 ligands results in cell activation followed by the induction of autophagy and autophagy-dependent cell death. In C57BL/6J mice, intracerebral injection of PGN increased the autophagy of microglial cells and reduced the microglial/macrophage cell number in brain parenchyma. Our results demonstrate a novel role of TLRs in the regulation of microglial cell activation and survival, which are important for the control of microgliosis and associated inflammatory responses in the CNS.

Stress-induced sensitization to cocaine: actin cytoskeleton remodeling within mesocorticolimbic nuclei.

This study investigated the consequence of repeated stress on actin cytoskeleton remodeling in the nucleus accumbens (NAc) and prefrontal cortex (Pfc), and the involvement of this remodeling in the expression of stress-induced motor cross-sensitization with cocaine. Wistar rats were restrained daily (2 h) for 7 days and, 3 weeks later, their NAc and Pfc were dissected 45 min after acute saline or cocaine (30 mg/kg i.p.). F-actin, actin-binding proteins (ABP) and GluR1 were quantified by Western blotting, and dendritic spines and postsynaptic density (PSD) size measured by electron microscopy. In the NAc from the stress plus cocaine group we observed a decrease in the phosphorylation of two ABPs, cofilin and cortactin, and an increase in the PSD size and the surface expression of GluR1, consistent with a more highly branched actin cytoskeleton. The Pfc also showed evidence of increased actin polymerization after stress as an increase was observed in Arp2, and in the number of spines. Inhibiting actin cycling and polymerization with latrunculin A into the NAc, but not the Pfc, inhibited the expression of cross-sensitization to cocaine (15 mg/kg i.p.) and restored the expression of GluR1 to control levels. This study shows that a history of repeated stress alters the ability of a subsequent cocaine injection to modulate dendritic spine morphology, actin dynamics and GluR1 expression in the NAc. Furthermore, by regulating GluR1 expression in the NAc, elevated actin cycling contributes to the expression of cross-sensitization between stress and cocaine, while stress-induced changes in the Pfc were not associated with cross-sensitization.

The AT1 angiotensin II receptor blockade attenuates the development of amphetamine-induced behavioral sensitization in a two-injection protocol.

It has been shown that a single exposure to amphetamine is sufficient to induce long-term behavioral, neurochemical, and neuroendocrine sensitization in rats. Dopaminergic neurotransmission in the nucleus accumbens and the caudate-putamen plays a critical role in the addictive properties of drugs of abuse. Angiotensin (Ang) II receptors are found on the soma and terminals of mesolimbic dopaminergic neurons and it has been shown that Ang II acting through its AT1 receptors facilitates dopamine release. The hypothesis was tested that Ang II AT1 receptors are involved in the neuroadaptative changes induced by a single exposure to amphetamine and that such changes are related to the development of behavioral and neurochemical sensitization. For this purpose, the study examined the expression of amphetamine-enhanced (0.5 mg kg⁻¹ i.p.) locomotor activity in animals pretreated with candesartan, an AT1 blocker, (3 mg kg⁻¹ p.o. x 5 days), 3 weeks after an amphetamine injection (5 mg kg⁻¹ i.p.). Dopaminergic hyperreactivity was tested by measuring the 3H-DA release in vitro from caudate-putamen and nucleus accumbens slices, induced by K+ stimulus. It was confirmed the behavioral sensitization in the two-injection protocol and candesartan pretreatment attenuate this response. It was also found that AT1 blockade pretreatment did not affect the locomotor response to dopamine agonists. In respect to the neurochemical sensitization tested using ex vivo 3H-DA release experiments it was found that AT1 receptor pretreatment blunted the enhanced response induced by K+ stimulus. The results support the idea that the development of neuroadaptive changes induced by amphetamine involves brain AT1 Ang II receptor activation.

A glutamate-dopamine interaction in the persistent enhanced response to amphetamine in nucleus accumbens core but not shell following a single restraint stress.

The administration of psychostimulant drugs or stress can elicit a sensitized response to the stimulating and reinforcing properties of the drug. We previously demonstrated that a single restraint stress session enhanced d-amphetamine (d-AMPH)-induced locomotion the day after the stress session, which lasted up to 8 days. The present experiments were designed to identify the contribution of major dopamine (DA) brain areas in the short- and long-lasting enhancement of d-AMPH-induced locomotion following a single stress, and to test the involvement of N-methyl-D-aspartate (NMDA) receptors in that phenomena. To achieve our goal, 24 h and 8 days after a 2-h restraint stress session either with or without a NMDA receptor blockade, we measured locomotor activity and DA overflow in nucleus accumbens (NAcc) core and shell and caudate putamen (CPu) following a d-AMPH injection (0.5 mg/kg i.p.). The stimulant effect of d-AMPH on DA overflow was enhanced in all nuclei at 24 h after a single stress, while at 8 days the enhanced responsiveness was maintained only in the NAcc core. When the rats were administered with MK-801 (0.1 mg/kg i.p.) 30 min before restraint stress, the d-AMPH-induced enhancement on locomotor activity and DA neurotransmission was prevented in all studied brain areas at both times. These findings show that a glutamate-dopamine link is underlying the short- and long- term d-AMPH-induced enhancement on DA and locomotor activity following stress. The persistent glutamate-dependent DA enhancement in NAcc core highlights the relevance of this region in the long-term proactive effects of stress on vulnerability to drug abuse.