Deficiency of histone variant macroH2A1.1 is associated with sexually dimorphic obesity in mice

Obesity has a major socio-economic health impact. There are profound sex differences in adipose tissue deposition and obesity-related conditions. The underlying mechanisms driving sexual dimorphism in obesity and its associated metabolic disorders remain unclear. Histone variant macroH2A1.1 is a candidate epigenetic mechanism linking environmental and dietary factors to obesity. Here, we used a mouse model genetically depleted of macroH2A1.1 to investigate its potential epigenetic role in sex dimorphic obesity, metabolic disturbances and gut dysbiosis. Whole body macroH2A1 knockout (KO) mice, generated with the Cre/loxP technology, and their control littermates were fed a high fat diet containing 60% of energy derived from fat. The diet was administered for three months starting from 10 to 12 weeks of age. We evaluated the progression in body weight, the food intake, and the tolerance to glucose by means of a glucose tolerance test. Gut microbiota composition, visceral adipose and liver tissue morphology were assessed. In addition, adipogenic gene expression patterns were evaluated in the visceral adipose tissue. Female KO mice for macroH2A1.1 had a more pronounced weight gain induced by high fat diet compared to their littermates, while the increase in body weight in male mice was similar in the two genotypes. Food intake was generally increased upon KO and decreased by high fat diet in both sexes, with the exception of KO females fed a high fat diet that displayed the same food intake of their littermates. In glucose tolerance tests, glucose levels were significantly elevated upon high fat diet in female KO compared to a standard diet, while this effect was absent in male KO. There were no differences in hepatic histology. Upon a high fat diet, in female adipocyte cross-sectional area was larger in KO compared to littermates: activation of proadipogenic genes (ACACB, AGT, ANGPT2, FASN, RETN, SLC2A4) and downregulation of antiadipogenic genes (AXIN1, E2F1, EGR2, JUN, SIRT1, SIRT2, UCP1, CCND1, CDKN1A, CDKN1B, EGR2) was detected. Gut microbiota profiling showed increase in Firmicutes and a decrease in Bacteroidetes in females, but not males, macroH2A1.1 KO mice. MacroH2A1.1 KO mice display sexual dimorphism in high fat diet-induced obesity and in gut dysbiosis, and may represent a useful model to investigate epigenetic and metabolic differences associated to the development of obesity-associated pathological conditions in males and females.

Functional Interaction between Adenosine A2A and mGlu5 Receptors Mediates STEP Phosphatase Activation and Promotes STEP/mGlu5R Binding in Mouse Hippocampus and Neuroblastoma Cell Line

(1) Background: Recently, we found that adenosine A2A receptor (A2AR) stimulation results in an increase in STEP phosphatase activity. In order to delve into the mechanism through which A2AR stimulation induced STEP activation, we investigated the involvement of mGlu5R since it is well documented that A2AR and mGlu5R physically and functionally interact in several brain areas. (2) Methods: In a neuroblastoma cell line (SH-SY5Y) and in mouse hippocampal slices, we evaluated the enzymatic activity of STEP by using a para-nitrophenyl phosphate colorimetric assay. A co-immunoprecipitation assay and a Western blot analysis were used to evaluate STEP/mGlu5R binding. (3) Results: We found that the A2AR-dependent activation of STEP was mediated by the mGlu5R. Indeed, the A2AR agonist CGS 21680 significantly increased STEP activity, and this effect was prevented not only by the A2AR antagonist ZM 241385, as expected, but also by the mGlu5R antagonist MPEP. In addition, we found that mGlu5R agonist DHPG-induced STEP activation was reversed not only by the mGlu5R antagonist MPEP but also by ZM 241385. Finally, via co-immunoprecipitation experiments, we found that mGlu5R and STEP physically interact when both receptors are activated (4) Conclusions: These results demonstrated a close functional interaction between mGlu5 and A2A receptors in the modulation of STEP activity.

Exposure to 3'Sialyllactose-Poor Milk during Lactation Impairs Cognitive Capabilities in Adulthood

Breast milk exerts pivotal regulatory functions early in development whereby it contributes to the maturation of brain and associated cognitive functions. However, the specific components of maternal milk mediating this process have remained elusive. Sialylated human milk oligosaccharides (HMOs) represent likely candidates since they constitute the principal neonatal dietary source of sialic acid, which is crucial for brain development and neuronal patterning. We hypothesize that the selective neonatal lactational deprivation of a specific sialylated HMOs, sialyl(alpha2,3)lactose (3′SL), may impair cognitive capabilities (attention, cognitive flexibility, and memory) in adulthood in a preclinical model. To operationalize this hypothesis, we cross-fostered wild-type (WT) mouse pups to B6.129-St3gal4^tm1.1Jxm/J dams, knock-out (KO) for the gene synthesizing 3′SL, thereby providing milk with approximately 80% 3′SL content reduction. We thus exposed lactating WT pups to a selective reduction of 3′SL and investigated multiple cognitive domains (including memory and attention) in adulthood. Furthermore, to account for the underlying electrophysiological correlates, we investigated hippocampal long-term potentiation (LTP). Neonatal access to 3′SL-poor milk resulted in decreased attention, spatial and working memory, and altered LTP compared to the control group. These results support the hypothesis that early-life dietary sialylated HMOs exert a long-lasting role in the development of cognitive functions.

Systemic depletion of histone macroH2A1.1 boosts hippocampal synaptic plasticity and social behavior in mice

Gene expression and epigenetic processes in several brain regions regulate physiological processes such as cognitive functions and social behavior. MacroH2A1.1 is a ubiquitous variant of histone H2A that regulates cell stemness and differentiation in various organs. Whether macroH2A1.1 has a modulatory role in emotional behavior is unknown. Here, we employed macroH2A1.1 knock-out (^-/- ) mice to perform a comprehensive battery of behavioral tests, and an assessment of hippocampal synaptic plasticity (long-term potentiation) accompanied by whole hippocampus RNA sequencing. MacroH2A1.1^-/- mice exhibit a stunningly enhancement both of sociability and of active stress-coping behavior, reflected by the increased social behavior in social activity tests and higher mobility time in the forced swim test, respectively. They also display an increased hippocampal synaptic plasticity, accompanied by significant neurotransmission transcriptional networks changes. These results suggest that systemic depletion of histone macroH2A1.1 supports an epigenetic control necessary for hippocampal function and social behavior.

Insight into the Role of the STriatal-Enriched Protein Tyrosine Phosphatase (STEP) in A2A Receptor-Mediated Effects in the Central Nervous System

The STriatal-Enriched protein tyrosine phosphatase STEP is a brain-specific tyrosine phosphatase that plays a pivotal role in the mechanisms of learning and memory, and it has been demonstrated to be involved in several neuropsychiatric diseases. Recently, we found a functional interaction between STEP and adenosine A_2A receptor (A_2AR), a subtype of the adenosine receptor family widely expressed in the central nervous system, where it regulates motor behavior and cognition, and plays a role in cell survival and neurodegeneration. Specifically, we demonstrated the involvement of STEP in A_2AR-mediated cocaine effects in the striatum and, more recently, we found that in the rat striatum and hippocampus, as well as in a neuroblastoma cell line, the overexpression of the A_2AR, or its stimulation, results in an increase in STEP activity. In the present article we will discuss the functional implication of this interaction, trying to examine the possible mechanisms involved in this relation between STEP and A_2ARs.

Sialylated human milk oligosaccharides program cognitive development through a non-genomic transmission mode

Breastmilk contains bioactive molecules essential for brain and cognitive development. While sialylated human milk oligosaccharides (HMOs) have been implicated in phenotypic programming, their selective role and underlying mechanisms remained elusive. Here, we investigated the long-term consequences of a selective lactational deprivation of a specific sialylated HMO in mice. We capitalized on a knock-out (KO) mouse model (B6.129-St6gal1^tm2Jxm/J) lacking the gene responsible for the synthesis of sialyl(alpha2,6)lactose (6'SL), one of the two sources of sialic acid (Neu5Ac) to the lactating offspring. Neu5Ac is involved in the formation of brain structures sustaining cognition. To deprive lactating offspring of 6'SL, we cross-fostered newborn wild-type (WT) pups to KO dams, which provide 6'SL-deficient milk. To test whether lactational 6'SL deprivation affects cognitive capabilities in adulthood, we assessed attention, perseveration, and memory. To detail the associated endophenotypes, we investigated hippocampal electrophysiology, plasma metabolomics, and gut microbiota composition. To investigate the underlying molecular mechanisms, we assessed gene expression (at eye-opening and in adulthood) in two brain regions mediating executive functions and memory (hippocampus and prefrontal cortex, PFC). Compared to control mice, WT offspring deprived of 6'SL during lactation exhibited consistent alterations in all cognitive functions addressed, hippocampal electrophysiology, and in pathways regulating the serotonergic system (identified through gut microbiota and plasma metabolomics). These were associated with a site- (PFC) and time-specific (eye-opening) reduced expression of genes involved in central nervous system development. Our data suggest that 6'SL in maternal milk adjusts cognitive development through a short-term upregulation of genes modulating neuronal patterning in the PFC.

The activity of the Striatal-enriched protein tyrosine phosphatase in neuronal cells is modulated by adenosine A2A receptor

We recently demonstrated that a tonic activation of adenosine A_2A receptors (A_2A Rs) is required for cocaine-induced synaptic depression and increase in the activity of STriatal-Enriched protein tyrosine Phosphatase (STEP). In this study, we elaborated on the relationship between A_2A R and STEP using genetic, pharmacological, and cellular tools. We found that the activities of protein tyrosine phosphatases (PTPs), and in particular of STEP, are significantly increased in the striatum and hippocampus of a transgenic rat strain over-expressing the neuronal A_2A R (NSEA_2A ) with respect to wild-type (WT) rats. Moreover the selective A_2A R agonist 4-[2-[[6-Amino-9-(N-ethyl-β-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride up-regulates PTPs and STEP activities in WT but not in NSEA_2A rats, while the selective A_2A R antagonist 4-(-2-[7-amino-2-{2-furyl}{1,2,4}triazolo{2,3-a} {1,3,5}triazin-5-yl-amino]ethyl)phenol restores the tyrosine phosphatase activities in NSEA_2A , having no effects in WT rats. In addition, while cocaine induced the activation of PTP and STEP in WT rats, it failed to increase phosphatase activity in NSEA_2A rats. A_2A Rs modulate STEP activity also in the SH-SY5Y neuroblastoma cell line, where a calcium-dependent calcineurin/PP1 pathway was found to play a major role. In summary, the present study identified a novel interaction between A_2A R and STEP that could have important clinical implications, since STEP has emerged as key regulator of signaling pathways involved in neurodegenerative and neuropsychiatric diseases and A_2A Rs are considered a promising target for the development of therapeutic strategies for different diseases of the central nervous system. Read the Editorial Highlight for this article on page 270.

Striatal adenosine-cannabinoid receptor interactions in rats over-expressing adenosine A2A receptors

Adenosine A2A receptors (A2 A Rs) and cannabinoid CB1 receptors (CB1 Rs) are highly expressed in the striatum, where they functionally interact and form A2A /CB1 heteroreceptor complexes. We investigated the effects of CB1 R stimulation in a transgenic rat strain over-expressing A2 A Rs under the control of the neural-specific enolase promoter (NSEA2A rats) and in age-matched wild-type (WT) animals. The effects of the CB1 R agonist WIN 55,212-2 (WIN) were significantly lower in NSEA2A rats than in WT animals, as demonstrated by i) electrophysiological recordings of synaptic transmission in corticostriatal slices; ii) the measurement of glutamate outflow from striatal synaptosomes and iii) in vivo experiments on locomotor activity. Moreover, while the effects of WIN were modulated by both A2 A R agonist (CGS 21680) and antagonists (ZM 241385, KW-6002 and SCH-442416) in WT animals, the A2 A R antagonists failed to influence WIN-mediated effects in NSEA2A rats. The present results demonstrate that in rats with genetic neuronal over-expression of A2 A Rs, the effects mediated by CB1 R activation in the striatum are significantly reduced, suggesting a change in the stoichiometry of A2A and CB1 receptors and providing a strategy to dissect the involvement of A2 A R forming or not forming heteromers in the modulation of striatal functions. These findings add additional evidence for the existence of an interaction between striatal A2 A Rs and CB1 Rs, playing a fundamental role in the regulation of striatal functions. We studied A2A -CB1 receptor interaction in transgenic rats over-expressing adenosine A2A receptors under the control of the neuron-specific enolase promoter (NSEA2A ). In these rats, we demonstrated a reduced effect of the CB1 receptor agonist WIN 55,212-2 in the modulation of corticostriatal synaptic transmission and locomotor activity, while CB1 receptor expression level did not change with respect to WT rats. A reduction in the expression of A2A -CB1 receptor heteromers is postulated.

Long-lasting beneficial effects of central serotonin receptor 7 stimulation in female mice modeling Rett syndrome

Rett syndrome (RTT) is a rare neurodevelopmental disorder, characterized by severe behavioral and physiological symptoms. Mutations in the methyl CpG binding protein 2 gene (MECP2) cause more than 95% of classic cases, and currently there is no cure for this devastating disorder. Recently we have demonstrated that specific behavioral and brain molecular alterations can be rescued in MeCP2-308 male mice, a RTT mouse model, by pharmacological stimulation of the brain serotonin receptor 7 (5-HT7R). This member of the serotonin receptor family—crucially involved in the regulation of brain structural plasticity and cognitive processes—can be stimulated by systemic repeated treatment with LP-211, a brain-penetrant selective 5-HT7R agonist. The present study extends previous findings by demonstrating that the LP-211 treatment (0.25 mg/kg, once per day for 7 days) rescues RTT-related phenotypic alterations, motor coordination (Dowel test), spatial reference memory (Barnes mazetest) and synaptic plasticity (hippocampal long-term-potentiation) in MeCP2-308 heterozygous female mice, the genetic and hormonal milieu that resembles that of RTT patients. LP-211 also restores the activation of the ribosomal protein (rp) S6, the downstream target of mTOR and S6 kinase, in the hippocampus of RTT female mice. Notably, the beneficial effects on neurobehavioral and molecular parameters of a seven-day long treatment with LP-211 were evident up to 2 months after the last injection, thus suggesting long-lasting effects on RTT-related impairments. Taken together with our previous study, these results provide compelling preclinical evidence of the potential therapeutic value for RTT of a pharmacological approach targeting the brain 5-HT7R.

Cocaine-induced changes of synaptic transmission in the striatum are modulated by adenosine A2A receptors and involve the tyrosine phosphatase STEP

The striatum is a brain area implicated in the pharmacological action of drugs of abuse. Adenosine A2A receptors (A2ARs) are highly expressed in the striatum and mediate, at least in part, cocaine-induced psychomotor effects in vivo. Here we studied the synaptic mechanisms implicated in the pharmacological action of cocaine in the striatum and investigated the influence of A2ARs. We found that synaptic transmission was depressed in corticostriatal slices after perfusion with cocaine (10 μM). This effect was reduced by the A2AR antagonist ZM241385 and almost abolished in striatal A2AR-knockout mice (mice lacking A2ARs in striatal neurons, stA2ARKO). The effect of cocaine on synaptic transmission was also prevented by the protein tyrosine phosphatases (PTPs) inhibitor sodium orthovanadate (Na3VO4). In synaptosomes prepared from striatal slices, we found that the activity of striatal-enriched protein tyrosine phosphatase (STEP) was upregulated by cocaine, prevented by ZM241385, and absent in synaptosomes from stA2ARKO. The role played by STEP in cocaine modulation of synaptic transmission was investigated in whole-cell voltage clamp recordings from medium spiny neurons of the striatum. We found that TAT-STEP, a peptide that renders STEP enzymatically inactive, prevented cocaine-induced reduction in AMPA- and NMDA-mediated excitatory post-synaptic currents, whereas the control peptide, TAT-myc, had no effect. These results demonstrate that striatal A2ARs modulate cocaine-induced synaptic depression in the striatum and highlight the potential role of PTPs and specifically STEP in the effects of cocaine.

BDNF prevents NMDA-induced toxicity in models of Huntington's disease: the effects are genotype specific and adenosine A2A receptor is involved

NMDA receptor-mediated excitotoxicity is thought to play a pivotal role in the pathogenesis of Huntington's disease (HD). The neurotrophin brain-derived neurotrophic factor (BDNF), which is also highly involved in HD and whose effects are modulated by adenosine A2 ARs, influences the activity and expression of striatal NMDA receptors. In electrophysiology experiments, we investigated the role of BDNF toward NMDA-induced effects in HD models, and the possible involvement of A2ARs. In corticostriatal slices from wild-type mice and age-matched symptomatic R6/2 mice (a model of HD), NMDA application (75 μM) induced a transient or a permanent (i.e., toxic) reduction of field potential amplitude, respectively. BDNF (10 ng/mL) potentiated NMDA effects in wild-type, while it protected from NMDA toxicity in R6/2 mice. Both effects of BDNF were prevented by A2 AR blockade. The protective effect of BDNF against NMDA-induced toxicity was reproduced in a cellular model of HD. These findings may have very important implications for the neuroprotective potential of BDNF and A2 AR ligands in HD.

Pre-synaptic adenosine A2A receptors control cannabinoid CB1 receptor-mediated inhibition of striatal glutamatergic neurotransmission

An interaction between adenosine A(2A) receptors (A(2A) Rs) and cannabinoid CB(1) receptors (CB(1) Rs) has been consistently reported to occur in the striatum, although the precise mechanisms are not completely understood. As both receptors control striatal glutamatergic transmission, we now probed the putative interaction between pre-synaptic CB(1) R and A(2A) R in the striatum. In extracellular field potentials recordings in corticostriatal slices from Wistar rats, A(2A) R activation by CGS21680 inhibited CB(1) R-mediated effects (depression of synaptic response and increase in paired-pulse facilitation). Moreover, in superfused rat striatal nerve terminals, A(2A) R activation prevented, while A(2A) R inhibition facilitated, the CB(1) R-mediated inhibition of 4-aminopyridine-evoked glutamate release. In summary, the present study provides converging neurochemical and electrophysiological support for the occurrence of a tight control of CB(1) R function by A(2A) Rs in glutamatergic terminals of the striatum. In view of the key role of glutamate to trigger the recruitment of striatal circuits, this pre-synaptic interaction between CB(1) R and A(2A) R may be of relevance for the pathogenesis and the treatment of neuropsychiatric disorders affecting the basal ganglia.

Role of adenosine A(2A) receptors in modulating synaptic functions and brain levels of BDNF: a possible key mechanism in the pathophysiology of Huntington's disease

In the last few years, accumulating evidence has shown the existence of an important cross-talk between adenosine A_2A receptors (A_2ARs) and brain-derived neurotrophic factor (BDNF). Not only are A_2ARs involved in the mechanism of transactivation of BDNF receptor TrkB, they also modulate the effect of BDNF on synaptic transmission, playing a facilitatory and permissive role. The cAMP-PKA pathway, the main transduction system operated by A_2ARs, is involved in such effects. Furthermore, a basal tonus of A_2ARs is required to allow the regulation of BDNF physiological levels in the brain, as demonstrated by the reduced protein levels measured in A_2ARs KO mice. The crucial role of adenosine A_2ARs in the maintenance of synaptic functions and BDNF levels will be reviewed here and discussed in the light of possible implications for Huntington's disease therapy, in which a joint impairment of BDNF and A_2ARs seems to play a pathogenetic role.

Influence of CGS 21680, a selective adenosine A(2A) receptor agonist, on NMDA receptor function and expression in the brain of Huntington's disease mice

The effect of chronic treatment with the selective adenosine A(2A) receptor agonist CGS 21680 on N-Methyl-d-Aspartate (NMDA) receptor function and expression has been studied in the striatum and cortex of R6/2 mice, a genetic mouse model of Huntington's disease (HD). Starting from 8weeks of age, R6/2 and wild type (WT) mice were treated daily with CGS 21680 (0.5mg/kg i.p.) for 3weeks and the expression levels of NMDA receptor subunits were then evaluated. In addition, to study CGS 21680-induced changes in NMDA receptor function, NMDA-induced toxicity in corticostriatal slices from both R6/2 and WT mice was investigated. We found that CGS 21680 increased NR2A subunit expression and the NR2A/NR2B ratio in the cortex of R6/2 mice, having no effect in WT mice. In the striatum, CGS 21680 reduced NR1 expression in both R6/2 and WT mice while the effect on NR2A and NR2/NR2B expression was genotype-dependent, reducing and increasing their expression in WT and R6/2 mice, respectively. On the contrary, NMDA-induced toxicity in corticostriatal slices was not modified by the treatment in WT or HD mice. These results demonstrate that in vivo activation of A(2A) receptors modulates the subunit composition of NMDA receptors in the brain of HD mice.

Prenatal restraint stress generates two distinct behavioral and neurochemical profiles in male and female rats

Prenatal Restraint Stress (PRS) in rats is a validated model of early stress resulting in permanent behavioral and neurobiological outcomes. Although sexual dimorphism in the effects of PRS has been hypothesized for more than 30 years, few studies in this long period have directly addressed the issue. Our group has uncovered a pronounced gender difference in the effects of PRS (stress delivered to the mothers 3 times per day during the last 10 days of pregnancy) on anxiety, spatial learning, and a series of neurobiological parameters classically associated with hippocampus-dependent behaviors. Adult male rats subjected to PRS (“PRS rats”) showed increased anxiety-like behavior in the elevated plus maze (EPM), a reduction in the survival of newborn cells in the dentate gyrus, a reduction in the activity of mGlu1/5 metabotropic glutamate receptors in the ventral hippocampus, and an increase in the levels of brain-derived neurotrophic factor (BDNF) and pro-BDNF in the hippocampus. In contrast, female PRS rats displayed reduced anxiety in the EPM, improved learning in the Morris water maze, an increase in the activity of mGlu1/5 receptors in the ventral and dorsal hippocampus, and no changes in hippocampal neurogenesis or BDNF levels. The direction of the changes in neurogenesis, BDNF levels and mGlu receptor function in PRS animals was not consistent with the behavioral changes, suggesting that PRS perturbs the interdependency of these particular parameters and their relation to hippocampus-dependent behavior. Our data suggest that the epigenetic changes in hippocampal neuroplasticity induced by early environmental challenges are critically sex-dependent and that the behavioral outcome may diverge in males and females.

Neurobehavioral assessment of rats exposed to low doses of PCB126 and methyl mercury during development

Epidemiological and laboratory studies have suggested that polychlorinated biphenyls (PCBs) and methyl mercury (MeHg) may have additive or synergistic effects on CNS function. Aim of this study was to characterize the effects of exposure to low levels of MeHg (0.5mg/kgday in drinking water) and PCB126 (100ng/kgday in food), alone and in combination, on neurobehavioral development in Wistar rats. Dams were treated from gestational day 7 to post-natal day (PND) 21. Animals were tested for developmental landmarks and reflexes (PND1-21), attention deficits (PND40), locomotor activity (PND30, 110), spatial learning (PND75), coordination and balance (PND90), object discrimination (PND80), anxiety (PND100), and conditioned learning (PND110). Parameters related to pregnancy, sex ratio at birth, and physical development (at weaning) did not differ among groups, though PCB126 decreased number of pups at birth. A slight delay in negative geotaxis was found in female rats in all treatment groups. No significant effects were seen in attention, coordination and balance, object discrimination, and spatial and conditioned learning. Increased motor activity was present in PCB126-treated male and in MeHg+PCB-treated female rats in the elevated plus maze test, and in PCB126-treated male rats in the open field test (PND110). The results do not support the hypothesis that co-exposure to MeHg and PCB126 results in additive or synergistic effects. This finding is in agreement with more recent in vitro and in vivo studies.

Maternal exposure to low levels of corticosterone during lactation protects the adult offspring against ischemic brain damage

A growing body of evidence underscores the importance of early life events as predictors of health in adulthood. Abnormalities in maternal care or other forms of early postnatal stress induce long-term changes in behavior and influence the vulnerability to illnesses throughout life. Some of these changes may be produced by the activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is invariably associated with stress. We used a model in which neonate rats are fed by mothers drinking water supplemented with 0.2 mg/ml corticosterone, the main glucocorticoid hormone in rodents. Plasma corticosterone levels increased in the dams to an extent similar to that induced by a mild stress. Corticosterone-treated dams also showed an increase in maternal care. Remarkably, adult rats that had been nursed by corticosterone-treated mothers were protected against neuronal damage and cognitive impairment produced by transient global brain ischemia. Neuroprotection was associated with a reduced HPA response to ischemia and was primarily decreased when corticosterone was injected at a dose that eliminated any difference in endogenous corticosterone levels between rats raised by mothers supplemented with corticosterone and their matched controls. These data suggest that an increased maternal care protects the offspring against ischemic neuronal damage and that at least a component of neuroprotection is mediated by a reduced response of the HPA axis to ischemia.