The ERK phosphorylation levels in the amygdala predict anxiety symptoms in humans and MEK/ERK inhibition dissociates innate and learned defensive behaviors in rats.

We demonstrate that the rate of extracellular signal-related kinase phosphorylation (P-ERK1,2/Total-ERK1,2) in the amygdala is negatively and independently associated with anxiety symptoms in 23 consecutive patients with drug-resistant mesial temporal lobe epilepsy that was surgically treated. In naive Wistar rats, the P-ERK1,2/Total-ERK1,2 ratio in the amygdala correlates negatively with innate anxiety-related behavior on the elevated plus maze (n = 20) but positively with expression of defensive-learned behavior (i.e., freezing) on Pavlovian aversive (fear) conditioning (n = 29). The microinfusion of ERK1/2 inhibitor (FR180204, n = 8-13/group) or MEK inhibitor (U0126, n = 8-9/group) into the basolateral amygdala did not affect anxiety-related behavior but impaired the evocation (anticipation) of conditioned-defensive behavior (n = 9-11/group). In conclusion, the P-ERK1,2/Total-ERK1,2 ratio in the amygdala predicts anxiety in humans and the innate anxiety- and conditioned freezing behaviors in rats. However, the ERK1/2 in the basolateral AMY is only required for the expression of defensive-learned behavior. These results support a dissociate ERK-dependent mechanism in the amygdala between innate anxiety-like responses and the anticipation of learned-defensive behavior. These findings have implications for understanding highly prevalent psychiatric disorders related to the defensive circuit manifested by anxiety and fear. HIGHLIGHTS: The P-ERK1,2/Total-ERK1,2 ratio in the amygdala (AMY) correlates negatively with anxiety symptoms in patients with mesial temporal lobe epilepsy. The P-ERK1,2/Total-ERK1,2 in the amygdala correlates negatively with the anxiety-like behavior and positively with freezing-learned behavior in naive rats. ERK1,2 in the basolateral amygdala is required for learned-defensive but not for the anxiety-like behavior expression in rats.

Functional interplay between adenosine A2A receptor and NMDA preconditioning in fear memory and glutamate uptake in the mice hippocampus.

N-methyl D-aspartate (NMDA) administered at subtoxic dose plays a protective role against neuronal excitotoxicity, a mechanism described as preconditioning. Since the activation of adenosinergic receptors influences the achievement of NMDA preconditioning in the hippocampus, we evaluated the potential functional interplay between adenosine A1 and A2A receptors (A1R and A2AR) activities and NMDA preconditioning. Adult male Swiss mice received saline (NaCl 0.9 g%, i.p.) or a nonconvulsant dose of NMDA (75 mg/kg, i.p.) and 24 h later they were treated with the one of the ligands: A1R agonist (CCPA, 0.2 mg/kg, i.p.) or antagonist (DPCPX, 3 mg/kg, i.p.), A2AR agonist (CGS21680, 0.05 mg/kg, i.p.) or antagonist (ZM241385, 0.1 mg/kg, i.p.) and subjected to contextual fear conditioning task. Binding properties and content of A2AR and glutamate uptake were assessed in the hippocampus of mice subjected to NMDA preconditioning. Treatment with CGS21680 increased the time of freezing during the exposure of animals to the new environment. NMDA preconditioning did not affect the freezing time of mice per se, but it prevented the response observed after the activation of A2AR. Furthermore, the activation of A2AR by CGS21680 after the preconditioning blocked the increase of glutamate uptake induced by NMDA preconditioning. The immunodetection of A2AR in total hippocampal homogenates showed no significant differences evoked by NMDA preconditioning and did not alter A2AR maximum binding for the selective ligand [3H]CGS21680. These results demonstrate changes in A2AR functionality in mice following NMDA preconditioning.

Adenosine and NMDA Receptors Modulate Neuroprotection-Induced NMDA Preconditioning in Mice.

The severity score of quinolinic acid (QA)-induced seizures was investigated after N-methyl-D-aspartate (NMDA) preconditioning associated with adenosine receptors. Also, the levels of adenosine A1 and A2A receptors and subunits of NMDA receptors in the hippocampi of mice were determined to define components of the resistance mechanism. Adult CF-1 mice were treated intraperitoneally with saline or NMDA (75 mg/kg), and some mice were treated intracerebroventricularly (i.c.v.) with 0.1 pmol of adenosine receptor antagonists 8-cyclopentyltheophylline (CPT; receptor A1) or ZM241385 (receptor A2A) 0, 1, or 6 h after NMDA administration. These adenosine receptor antagonists were administered to block NMDA's protective effect. Seizures and their severity scores were evaluated during convulsions induced by QA (36.8 nmol) that was administered i.c.v. 24 h after NMDA. The cell viability and content of subunits of the NMDA receptors were analyzed 24 h after QA administration. NMDA preconditioning reduced the maximal severity 6 displayed in QA-administered mice, inducing protection in 47.6% of mice after QA-induced seizures. CPT increased the latency of seizures when administered 0 or 6 h, and ZM241385 generated the same effect when administered 6 h after NMDA administration. The GluN1 content was lower in the hippocampi of the QA mice and the NMDA-preconditioned animals without seizures. GluN2A content was unaltered in all groups. The results demonstrated the components of resistance evoked by NMDA, in which adenosine receptors participate in a time-dependent mode. Similarly, the reduction on GluN1 expression in the hippocampus may contribute to this effect during the preconditioning period.

Role of Phosphatidylinositol-3 Kinase Pathway in NMDA Preconditioning: Different Mechanisms for Seizures and Hippocampal Neuronal Degeneration Induced by Quinolinic Acid.

N-methyl D-aspartate (NMDA) preconditioning is evoked by the administration of a subtoxic dose of NMDA and is protective against neuronal excitotoxicity. This effect may involve a diversity of targets and cell signaling cascades associated to neuroprotection. Phosphatidylinositol-3 kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinases (MAPKs) such as extracellular regulated protein kinase 1/2 (ERK1/2) and p38MAPK pathways play a major role in neuroprotective mechanisms. However, their involvement in NMDA preconditioning was not yet fully investigated. The present study aimed to evaluate the effect of NMDA preconditioning on PI3K/Akt, ERK1/2, and p38MAPK pathways in the hippocampus of mice and characterize the involvement of PI3K on NMDA preconditioning-evoked prevention of seizures and hippocampal cell damage induced by quinolinic acid (QA). Thus, mice received wortmannin (a PI3K inhibitor) and 15 min later a subconvulsant dose of NMDA (preconditioning) or saline. After 24 h of this treatment, an intracerebroventricular QA infusion was administered. Phosphorylation levels and total content of Akt, glycogen synthase protein kinase-3ß (GSK-3ß), ERK1/2, and p38MAPK were not altered after 24 h of NMDA preconditioning with or without wortmmanin pretreatment. Moreover, after QA administration, behavioral seizures, hippocampal neuronal degeneration, and Akt activation were evaluated. Inhibition of PI3K pathway was effective in abolishing the protective effect of NMDA preconditioning against QA-induced seizures, but did not modify neuronal protection promoted by preconditioning as evaluated by Fluoro-Jade B staining. The study confirms that PI3K participates in the mechanism of protection induced by NMDA preconditioning against QA-induced seizures. Conversely, NMDA preconditioning-evoked protection against neuronal degeneration is not altered by PI3K signaling pathway inhibition. These results point to differential mechanisms regarding protection against a behavioral and cellular manifestation of neural damage.

Atorvastatin Protects from Aß1-40-Induced Cell Damage and Depressive-Like Behavior via ProBDNF Cleavage.

Intracerebroventricular (icv) amyloid-beta (Aß)1-40 infusion to mice has been demonstrated to cause neurotoxicty and depressive-like behavior and it can be used to evaluate antidepressant and neuroprotective effect of drugs. Atorvastatin is a widely used statin that has demonstrated antidepressant-like effect in predictable animal behavioral models and neuroprotective effect against Aß1-40 infusion. The purpose of this study was to determine the effect of in vivo atorvastatin treatment against Aß1-40-induced changes in mood-related behaviors and biochemical parameters in ex vivo hippocampal slices from mice. Atorvastatin treatment (10 mg/kg, p.o., once a day for seven consecutive days) abolished depressive-like and anhedonic-like behaviors induced by Aß1-40 (400 pmol/site, icv) infusion. Aß1-40-induced hippocampal cell damage was reversed by atorvastatin treatment. Aß1-40 infusion decreased glutamate uptake in hippocampal slices, and atorvastatin did not altered it. Glutamine synthetase activity was not altered by any treatment. Atorvastatin also increased hippocampal mature brain-derived neurotrophic factor (mBDNF)/precursor BDNF (proBDNF) ratio, suggesting an increase of proBDNF to mBDNF cleavage. Accordingly, increased tissue-type plasminogen activator (tPA) and p11 genic expression were observed in hippocampus of atorvastatin-treated mice. Atorvastatin displays antidepressant-like and neuroprotective effects against Aß1-40-induced toxicity, and these effects may involve tPA- and p11-mediated cleavage of proBDNF to mBDNF.

Adenosine A1 receptor activation modulates N-methyl-d-aspartate (NMDA) preconditioning phenotype in the brain.

N-methyl-d-aspartate (NMDA) preconditioning is induced by subtoxic doses of NMDA and it promotes a transient state of resistance against subsequent lethal insults. Interestingly, this mechanism of neuroprotection depends on adenosine A1 receptors (A1R), since blockade of A1R precludes this phenomenon. In this study we evaluated the consequences of NMDA preconditioning on the hippocampal A1R biology (i.e. expression, binding properties and functionality). Accordingly, we measured A1R expression in NMDA preconditioned mice (75mg/kg, i.p.; 24h) and showed that neither the total amount of receptor, nor the A1R levels in the synaptic fraction was altered. In addition, the A1R binding affinity to the antagonist [(3)H] DPCPX was slightly increased in total membrane extracts of hippocampus from preconditioned mice. Next, we evaluated the impact of NMDA preconditioning on A1R functioning by measuring the A1R-mediated regulation of glutamate uptake into hippocampal slices and on behavioral responses in the open field and hot plate tests. NMDA preconditioning increased glutamate uptake into hippocampal slices without altering the expression of glutamate transporter GLT-1. Interestingly, NMDA preconditioning also induced antinociception in the hot plate test and both effects were reversed by post-activation of A1R with the agonist CCPA (0.2mg/kg, i.p.). NMDA preconditioning or A1R modulation did not alter locomotor activity in the open field. Overall, the results described herein provide new evidence that post-activation of A1R modulates NMDA preconditioning-mediated responses, pointing to the importance of the cross-talk between glutamatergic and adenosinergic systems to neuroprotection.

Mitochondrial respiratory chain and creatine kinase activities following trauma brain injury in brain of mice preconditioned with N-methyl-D-aspartate.

Traumatic brain injury (TBI) induces glutamatergic excitotoxicity through N-methyl-D-aspartate (NMDA) receptors, affecting the integrity of the mitochondrial membrane. Studies have pointed to mitochondria as the master organelle in the preconditioning-triggered endogenous neuroprotective response. The present study is aimed at understanding energy metabolism in the brains of mice after preconditioning with NMDA and TBI. For this purpose, male albino CF-1 mice were pre-treated with NMDA (75 mg/kg) and subjected to brain trauma. Mitochondrial respiratory chain and creatine kinase activities were assessed at 6 or 24 h after trauma. The mice preconditioned and subjected to TBI exhibited augmented activities of complexes II and IV in the cerebral cortex and/or cerebellum. Creatine kinase activity was also augmented in the cerebral cortex after 24 h. We suggest that even though NMDA preconditioning and TBI have similar effects on enzyme activities, each manage their response via opposite mechanisms because the protective effects of preconditioning are unambiguous. In conclusion, NMDA preconditioning induces protection via an increase of enzymes in the mitochondria.

N-methyl-D-aspartate glutamate receptor blockade attenuates lung injury associated with experimental sepsis.

BACKGROUND: The aim of this study was to examine the effects of the N-methyl-D-aspartate receptor (NMDAR) channel blocker dizocilpine (MK-801) on lung injury in rats submitted to experimental sepsis induced by cecal ligation and perforation (CLP). METHODS: Adult male Wistar rats submitted to CLP were given a single systemic injection of MK-801 (subcutaneously at 0.3 mg/kg) administered 4 or 7 h after CLP induction. Twelve hours after CLP BAL was performed to determine total cell count, protein content, and inflammatory parameters. In addition, lung was excised for histopathologic analyses and determination of NMDAR subunits content. In a separate cohort of animals mortality was recorded for 5 days. RESULTS: Animals submitted to sepsis induced by CLP showed an increase in the content of NMDAR subunits NR1 and NR2A in the lung. Administration of MK-801 4 h after CLP induction resulted in a decrease in BAL fluid cellular content and decreased levels of proinflammatory cytokines. In addition, MK-801 decreased lung oxidative stress markers and histopathologic alterations and improved survival. CONCLUSIONS: These findings indicate that NMDAR blockade might represent a promising novel therapeutic strategy for the treatment of sepsis and inflammatory disorders.

N-methyl-D-aspartate preconditioning improves short-term motor deficits outcome after mild traumatic brain injury in mice.

Traumatic brain injury (TBI) causes impairment of fine motor functions in humans and nonhuman mammals that often persists for months after the injury occurs. Neuroprotective strategies for prevention of the sequelae of TBI and understanding the molecular mechanisms and cellular pathways are related to the glutamatergic system. It has been suggested that cellular damage subsequent to TBI is mediated by the excitatory neurotransmitters, glutamate and aspartate, through the excessive activation of the N-methyl-D-aspartate (NMDA) receptors. Thus, preconditioning with a low dose of NMDA was used as a strategy for protection against locomotor deficits observed after TBI in mice. Male adult mice CF-1 were preconditioned with NMDA (75 mg/kg) 24 hr before the TBI induction. Under anesthesia with O(2)/N(2)O (33%: 66%) inhalation, the animals were subjected to the experimental model of trauma that occurs by the impact of a 25 g weight on the skull. Sensorimotor gating was evaluated at 1.5, 6, or 24 hr after TBI induction by using footprint and rotarod tests. Cellular damage also was assessed 24 hr after occurrence of cortical trauma. Mice preconditioned with NMDA were protected against all motor deficits revealed by footprint tests, but not those observed in rotarod tasks. Although mice showed motor deficits after TBI, no cellular damage was observed. These data corroborate the hypothesis that glutamatergic excitotoxicity, especially via NMDA receptors, contributes to severity of trauma. They also point to a putative neuroprotective mechanism induced by a sublethal dose of NMDA to improve motor behavioral deficits after TBI.

Depressive-like parameters in sepsis survivor rats.

The inflammatory and immune responses evoked in sepsis may create not only an acute brain dysfunction, which occurs in the majority of septic patients, but also long-term deficits such as memory impairment. In this context, we evaluated depressive-like parameters in sepsis survivor rats. For this purpose, male Wistar rats, weighing 300-350 g, underwent cecal ligation and perforation (CLP) (sepsis group) followed by "basic support", or were sham-operated (control group). After 3 days of the sepsis procedure, the animals were treated with imipramine at 10 mg/kg or saline during 14 days (days 3-17). The consumption of sweet food was measured for 7 days (days 10-17) and the body weight was measured before CLP, 10, and 17 days after CLP. Seventeen days after sepsis (immediately after sweet food consumption measurement), the animals were anesthetized and blood was withdrawn for the analyses of corticosterone and adrenocorticotropic hormone (ACTH) levels, and immediately killed by decapitation. The adrenal gland and hippocampus were immediately isolated and weighed, and the hippocampus was utilized for determining brain-derived neurotrophic factor (BDNF) levels. It was observed that animals subjected to CLP presented decreased sucrose intake. Septic rats did not increase body weight and presented an increase in the weight of adrenal gland. Both corticosterone and ACTH levels were increased, while hippocampus weight and BDNF levels in the hippocampus decreased. The treatment with imipramine reversed all the parameters described above. Our results supported the hypothesis that rats that survive sepsis show depressive-like behavior, alterations in the hypothalamus-pituitary-adrenal axis, and decreased BDNF levels in the hippocampus.

Oxidative variables and antioxidant enzymes activities in the mdx mouse brain.

Dystrophin is a protein found at the plasmatic membrane in muscle and postsynaptic membrane of some neurons, where it plays an important role on synaptic transmission and plasticity. Its absence is associated with Duchenne's muscular dystrophy (DMD), in which cognitive impairment is found. Oxidative stress appears to be involved in the physiopathology of DMD and its cognitive dysfunction. In this regard, the present study investigated oxidative parameters (lipid and protein peroxidation) and antioxidant enzymes activities (superoxide dismutase and catalase) in prefrontal cortex, cerebellum, hippocampus, striatum and cortex tissues from male dystrophic mdx and normal C57BL10 mice. We observed (1) reduced lipid peroxidation in striatum and protein peroxidation in cerebellum and prefrontal cortex; (2) increased superoxide dismutase activity in cerebellum, prefrontal cortex, hippocampus and striatum; and (3) reduced catalase activity in striatum. It seems by our results, that the superoxide dismutase antioxidant mechanism is playing a protective role against lipid and protein peroxidation in mdx mouse brain.

Early long-term exposure with caffeine induces cross-sensitization to methylphenidate with involvement of DARPP-32 in adulthood of rats.

Chronic ingestion of caffeine causes dependence and sleep disturbance in children and adolescents. In rodents, the administration of caffeine may produce behavioral cross-sensitization to some psychostimulants, such as dopaminergic psychoactive drugs. Methylphenidate (MPH; Ritalin) is a psychostimulant used in pediatric- and adult human populations to manage the symptoms associated with attention-deficit hyperactivity disorder (ADHD). Previous studies have suggested that dopamine- and cAMP-regulated phosphoproteins of 32 kDa (DARPP-32) participate in the manifestation of behavioral activity following ingestion of caffeine or MPH. The aim of the present study was to evaluate whether long-term administration of low doses of caffeine in rodents during their adolescence induces cross-sensitization to MPH challenge in their adulthood and investigate the involvement of DARPP-32 in this model. Young rats (P25) consumed water or caffeine (0.3 g/L; mean consumption was 7.5 mg/day/kg) for 28 days. The caffeine consumption was then suspended for 14 days (washout period) when the animals received saline solution or MPH (1, 2, or 10 mg/kg) (P67) intraperitoneally. The locomotor activity of these rats was assessed using the open-field test, following which the immunocontent of DARPP-32 was evaluated in samples of their prefrontal cortex, striatum, or hippocampus. Rats chronically exposed to caffeine in their adolescent period and to inactive doses of MPH (1mg/kg) in adulthood showed augmented locomotor activity. The behavioral effect observed was accompanied by increased levels of DARPP-32 in the striatum and prefrontal cortex compared to control groups (saline or caffeine). However, no alteration caused by these treatments was noted in the hippocampus. In conclusion, chronic caffeine exposure induces likely long-term cross-sensitization to MPH in a DARPP-32-dependent pathway.

Cognitive impairment in the septic brain.

Sepsis is a major disease entity with important clinical implications. It is associated with a high mortality rate in humans. Recently, several studies have demonstrated that Intensive Care Unit survivors present long-term cognitive impairment, including alterations in memory, attention, concentration and/or global loss of cognitive function. The pathogenesis of septic encephalopathy and cognitive impairment are still poorly known and further understanding of these processes is necessary for the development of effective preventive and therapeutic interventions. Here we discuss the clinical presentation and underlying pathophysiology of the encephalopathy and neurobiology of the cognitive impairment associated with sepsis.