Prefrontal dynamics and encoding of flexible rule switching.

Behavioral flexibility, the ability to adjust behavioral strategies in response to changing environmental contingencies and internal demands, is fundamental to cognitive functions. Despite a large body of pharmacology and lesion studies, the underlying neurophysiological correlates and mechanisms that support flexible rule switching remain elusive. To address this question, we trained mice to distinguish complex sensory cues comprising different perceptual dimensions (set shifting). Endoscopic calcium imaging revealed that medial prefrontal cortex (mPFC) neurons represented multiple task-related events and exhibited pronounced dynamic changes during rule switching. Notably, prominent encoding capacity in the mPFC was associated with switching across, but not within perceptual dimensions. We then showed the involvement of the ascending modulatory input from the locus coeruleus (LC), as inhibiting the LC impaired rule switching behavior and impeded mPFC dynamic processes and encoding. Our results highlight the pivotal role of the mPFC in set shifting processes and demonstrate the profound impact of ascending neuromodulation on shaping prefrontal neural dynamics and behavioral flexibility.

Acute Inflammation Alters Brain Energy Metabolism in Mice and Humans: Role in Suppressed Spontaneous Activity, Impaired Cognition, and Delirium.

Systemic infection triggers a spectrum of metabolic and behavioral changes, collectively termed sickness behavior, which while adaptive, can affect mood and cognition. In vulnerable individuals, acute illness can also produce profound, maladaptive, cognitive dysfunction including delirium, but our understanding of delirium pathophysiology remains limited. Here, we used bacterial lipopolysaccharide (LPS) in female C57BL/6J mice and acute hip fracture in humans to address whether disrupted energy metabolism contributes to inflammation-induced behavioral and cognitive changes. LPS (250 µg/kg) induced hypoglycemia, which was mimicked by interleukin (IL)-1ß (25 µg/kg) but not prevented in IL-1RI-/- mice, nor by IL-1 receptor antagonist (IL-1RA; 10 mg/kg). LPS suppression of locomotor activity correlated with blood glucose concentrations, was mitigated by exogenous glucose (2 g/kg), and was exacerbated by 2-deoxyglucose (2-DG) glycolytic inhibition, despite preventing IL-1ß synthesis. Using the ME7 model of chronic neurodegeneration in female mice, to examine vulnerability of the diseased brain to acute stressors, we showed that LPS (100 µg/kg) produced acute cognitive dysfunction, selectively in those animals. These acute cognitive impairments were mimicked by insulin (11.5 IU/kg) and mitigated by glucose, demonstrating that acutely reduced glucose metabolism impairs cognition selectively in the vulnerable brain. To test whether these acute changes might predict altered carbohydrate metabolism during delirium, we assessed glycolytic metabolite levels in CSF in humans during inflammatory trauma-induced delirium. Hip fracture patients showed elevated CSF lactate and pyruvate during delirium, consistent with acutely altered brain energy metabolism. Collectively, the data suggest that disruption of energy metabolism drives behavioral and cognitive consequences of acute systemic inflammation.SIGNIFICANCE STATEMENT Acute systemic inflammation alters behavior and produces disproportionate effects, such as delirium, in vulnerable individuals. Delirium has serious short and long-term sequelae but mechanisms remain unclear. Here, we show that both LPS and interleukin (IL)-1ß trigger hypoglycemia, reduce CSF glucose, and suppress spontaneous activity. Exogenous glucose mitigates these outcomes. Equivalent hypoglycemia, induced by lipopolysaccharide (LPS) or insulin, was sufficient to trigger cognitive impairment selectively in animals with existing neurodegeneration and glucose also mitigated those impairments. Patient CSF from inflammatory trauma-induced delirium also shows altered brain carbohydrate metabolism. The data suggest that the degenerating brain is exquisitely sensitive to acute behavioral and cognitive consequences of disrupted energy metabolism. Thus "bioenergetic stress" drives systemic inflammation-induced dysfunction. Elucidating this may offer routes to mitigating delirium.

Hyperammonemia compromises glutamate metabolism and reduces BDNF in the rat hippocampus.

Ammonia is putatively the major toxin associated with hepatic encephalopathy (HE), a neuropsychiatric manifestation that results in cognitive impairment, poor concentration and psychomotor alterations. The hippocampus, a brain region involved in cognitive impairment and depressive behavior, has been studied less than neocortical regions. Herein, we investigated hippocampal astrocyte parameters in a hyperammonemic model without hepatic lesion and in acute hippocampal slices exposed to ammonia. We also measured hippocampal BDNF, a neurotrophin commonly related to synaptic plasticity and cognitive deficit, and peripheral S100B protein, used as a marker for brain damage. Hyperammonemia directly impaired astrocyte function, inducing a decrease in glutamate uptake and in the activity of glutamine synthetase, in turn altering the glutamine-glutamate cycle, glutamatergic neurotransmission and ammonia detoxification itself. Hippocampal BDNF was reduced in hyperammonemic rats via a mechanism that may involve astrocyte production, since the same effect was observed in astrocyte cultures exposed to ammonia. Ammonia induced a significant increase in S100B secretion in cultured astrocytes; however, no significant changes were observed in the serum or in cerebrospinal fluid. Data demonstrating hippocampal vulnerability to ammonia toxicity, particularly due to reduced glutamate uptake activity and BDNF content, contribute to our understanding of the neuropsychiatric alterations in HE.

Enteric glial reactivity to systemic LPS administration: Changes in GFAP and S100B protein.

Lipopolysaccharide (LPS) is used to induce inflammation and promotes nervous system activation. Different regions of the brain present heterogeneous glial responses; thus, in order to verify whether systemic LPS-induced inflammation affects the enteric glia differently across the intestinal segments, we evaluated the expressions of two glial activity markers, GFAP and S100B protein, in different intestine segments, at 1h, 24h and 7days after acute systemic LPS administration (0.25 or 2.5mgkg-1) in rats. Histological inflammatory analysis indicated that the cecum was most affected when compared to the duodenum and proximal colon at the highest doses of LPS. LPS induced an increased S100B content after 24h in all three regions, which decreased at 7days after the highest dose in all regions. Moreover, at 24h, this dose of LPS increased ex-vivo S100B secretion only in the cecum. The highest dose of LPS also increased GFAP in all regions at 24h, but earlier in the cecum, where LPS-induced enteric S100B and GFAP alterations were dependent on dose, time and intestine region. No associated changes in serum S100B were observed. Our results indicate heterogeneous enteric glial responses to inflammatory insult, as observed in distinct brain areas.

Exendin-4 Reverses Biochemical and Functional Alterations in the Blood-Brain and Blood-CSF Barriers in Diabetic Rats.

Diabetes mellitus (DM) is a metabolic disorder associated with micro- and macrovascular alterations that contribute to the cognitive impairment observed in diabetic patients. Signs of breakdown of the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) have been found in patients and animal models of DM. Breakdown of the BBB and BCSFB can lead to disruptions in cerebral homeostasis and eventually neural dysfunction and degeneration. However, our understanding of the biochemistry underlying barrier protein modifications is incomplete. Herein, we evaluated changes in the levels of specific proteins in the BBB (occludin, claudin-5, ZO-1, and aquaporin-4) and BCSFB (claudin-2 and aquaporin-1) in the hippocampus of diabetic rats, and we also investigated the functional alterations in these barriers. In addition, we evaluated the ability of exendin-4 (EX-4), a glucagon-like peptide-1 agonist that can cross the BBB to reverse the functional and biochemical modifications observed in these animals. We observed a decrease in BBB proteins (except ZO-1) in diabetic rats, whereas the EX-4 treatment recovered the occludin and aquaporin-4 levels. Similarly, we observed a decrease in BCSFB proteins in diabetic rats, whereas EX-4 reversed such changes. EX-4 also reversed alterations in the permeability of the BBB and BCSFB in diabetic rats. Additionally, altered cognitive parameters in diabetic rats were improved by EX-4. These data further our understanding of the alterations in the central nervous system caused by DM, particularly changes in the proteins and permeability of the brain barriers, as well as cognitive dysfunction. Furthermore, these data suggest a role for EX-4 in therapeutic strategies for cognitive dysfunction in DM.

The effect of taurine and enriched environment on behaviour, memory and hippocampus of diabetic rats.

Diabetes mellitus (DM) has been studied recently as a major cause of cognitive deficits, memory and neurodegenerative damage. Taurine and enriched environment have stood out for presenting neuroprotective and stimulating effects that deserve further study. In this paper, we examined the effects of taurine and enriched environment in the context of diabetes, evaluating effects on behaviour, memory, death and cellular activity. Eighty-eight Wistar rats were divided into 2 groups (E=enriched environment; C=standard housing). Some animals (24/group) underwent induction of diabetes, and within each group, some animals (half of diabetics (D) and half of non-diabetics (ND)/group) were treated for 30days with taurine (T). Untreated animals received saline (S). In total, there were eight subgroups: DTC, DSC, NDTC, NDSC, DTE, DSE, NDTE and NDSE. During the experiment, short-term memory was evaluated. After 30th day of experiment, the animals were euthanized and was made removal of brains used to immunohistochemistry procedures for GFAP and cleaved caspase-3. As a result, we observed that animals treated with taurine showed better performance in behavioural and memory tasks, and the enriched environment had positive effects, especially in non-diabetic animals. Furthermore, taurine and enriched environment seemed to be able to interfere with neuronal apoptosis and loss of glial cells, and in some instances, these two factors seemed to have synergistic effects. From these data, taurine and enriched environment may have important neurostimulant and neuroprotective effects.

Striatal Injury with 6-OHDA Transiently Increases Cerebrospinal GFAP and S100B.

Both glial fibrillary acidic protein (GFAP) and S100B have been used as markers of astroglial plasticity, particularly in brain injury; however, they do not necessarily change in the same time frame or direction. Herein, we induced a Parkinson's disease (PD) model via a 6-OHDA intrastriatal injection in rats and investigated the changes in GFAP and S100B using ELISA in the substantia nigra (SN), striatum, and cerebrospinal fluid on the 1st, 7th, and 21st days following the injection. The model was validated using measurements of rotational behaviour induced by methylphenidate and tyrosine hydroxylase in the dopaminergic pathway. To our knowledge, this is the first measurement of cerebrospinal fluid S100B and GFAP in the 6-OHDA model of PD. Gliosis (based on a GFAP increase) was identified in the striatum, but not in the SN. We identified a transitory increment of cerebrospinal fluid S100B and GFAP on the 1st and 7th days, respectively. This initial change in cerebrospinal fluid S100B was apparently related to the mechanical lesion. However, the 6-OHDA-induced S100B secretion was confirmed in astrocyte cultures. Current data reinforce the idea that glial changes precede neuronal damage in PD; however, these findings also indicate that caution is necessary regarding the interpretation of data in this PD model.

Cocaine counteracts LPS-induced hypolocomotion and triggers locomotor sensitization expression.

Neuroimmune signalling underlies addiction and comorbid depression. Clinical observations indicate that infections and chronic lesions are more frequent in drug users and elevated inflammatory states are evident in cocaine dependents. Therefore, lipopolysaccharide (LPS) and inflammatory cytokines represent an important tool for the investigation of sickness, depressive illness and addiction behaviour. A major component of addiction is the progressive and persistent increase in locomotor activity after repeated drug administration and even prolonged periods of abstinence. The aim of this study was to investigate the response of locomotor sensitization when a non-sensitizing dose of cocaine is paired with a systemic inflammatory stimulus. LPS and cocaine were administered intraperitonealy in young-adult male C57bl/6 mice during a 5-day acquisition phase. After a 48-h withdrawal period all groups were challenged with cocaine to evaluate locomotor expression. During the acquisition phase, the LPS-treated groups displayed characteristic hypolocomotion related to sickness behaviour. The low dose of cocaine did not increase the distance travelled, characterizing a non-sensitization dose. Groups that received both LPS and cocaine did not display hypolocomotion, indicating that cocaine might counteract hypolocomotion sickness behaviour. Moreover, during challenge, only these animals expressed locomotor sensitization. Our results indicate that LPS could facilitate the expression of locomotor sensitization in mice and that the immune system may modulate cocaine-induced sensitization.

Effects of ß-alanine administration on selected parameters of oxidative stress and phosphoryltransfer network in cerebral cortex and cerebellum of rats.

ß-Alanine is a ß-amino acid derivative of the degradation of pyrimidine uracil and precursor of the oxidative substrate acetyl-coenzyme A (acetyl-CoA). The accumulation of ß-alanine occurs in ß-alaninemia, an inborn error of metabolism. Patients with ß-alaninemia may develop neurological abnormalities whose mechanisms are far from being understood. In this study we evaluated the effects of ß-alanine administration on some parameters of oxidative stress and on creatine kinase, pyruvate kinase, and adenylate kinase in cerebral cortex and cerebellum of 21-day-old rats. The animals received three peritoneal injections of ß-alanine (0.3 mg /g of body weight) and the controls received the same volume (10 µL/g of body weight) of saline solution (NaCl 0.85 %) at 3 h intervals. CSF levels of ß-alanine increased five times, achieving 80 µM in the rats receiving the amino acid. The results of ß-alanine administration in the parameters of oxidative stress were similar in both tissues studied: reduction of superoxide dismutase activity, increased oxidation of 2',7'-dihydrodichlorofluorescein, total content of sulfhydryl and catalase activity. However, the results of the phosphoryltransfer network enzymes were similar in all enzymes, but different in the tissues studied: the ß-alanine administration was able to inhibit the enzyme pyruvate kinase, cytosolic creatine kinase, and adenylate kinase activities in cerebral cortex, and increase in cerebellum. In case this also occurs in the patients, these results suggest that oxidative stress and alteration of the phosphoryltransfer network may be involved in the pathophysiology of ß-alaninemia. Moreover, the ingestion of ß-alanine to improve muscular performance deserves more attention in respect to possible side-effects.

Treadmill exercise induces hippocampal astroglial alterations in rats.

Physical exercise effects on brain health and cognitive performance have been described. Synaptic remodeling in hippocampus induced by physical exercise has been described in animal models, but the underlying mechanisms remain poorly understood. Changes in astrocytes, the glial cells involved in synaptic remodeling, need more characterization. We investigated the effect of moderate treadmill exercise (20 min/day) for 4 weeks on some parameters of astrocytic activity in rat hippocampal slices, namely, glial fibrillary acidic protein (GFAP), glutamate uptake and glutamine synthetase (GS) activities, glutathione content, and S100B protein content and secretion, as well as brain-derived neurotrophic factor (BDNF) levels and glucose uptake activity in this tissue. Results show that moderate treadmill exercise was able to induce a decrease in GFAP content (evaluated by ELISA and immunohistochemistry) and an increase in GS activity. These changes could be mediated by corticosterone, whose levels were elevated in serum. BDNF, another putative mediator, was not altered in hippocampal tissue. Moreover, treadmill exercise caused a decrease in NO content. Our data indicate specific changes in astrocyte markers induced by physical exercise, the importance of studying astrocytes for understanding brain plasticity, as well as reinforce the relevance of physical exercise as a neuroprotective strategy.

Non-specific inhibitors of aquaporin-4 stimulate S100B secretion in acute hippocampal slices of rats.

Aquaporin-4 (AQP-4) is the principal brain water channel and is predominantly expressed in astrocytes suggesting its dynamic involvement in water homeostasis in brain tissue. Due to the co-localization of AQP-4 and inward rectifier K(+) channels Kir 4.1, a functional coupling between these proteins has been proposed. AQP-4 has a putative role in the physiopathology of brain disorders including epilepsy and trauma. S100B is a calcium-binding protein expressed and secreted by astrocytes, and commonly used as a parameter of astroglial activation. Here, we investigate a possible link between AQP-4 activity (and Kir 4.1) and S100B secretion in hippocampal slices of rats of different ages using non-specific inhibitors of AQP-4 (AZA, acetazolamide and TEA, tetraethylammonium) and Kir 4.1 (barium chloride). We found that blockade of AQP-4 with TEA and AZA produced an increase in S100B secretion in young rats, compatible with an astroglial activation observed in many conditions of brain injury. On the other hand, BaCl(2) induced Kir 4.1 inhibition caused a decrease in S100B secretion. Both channels, AQP-4 and Kir 4.1, exhibited a similar ontogenetic profile, in spite of the functional uncoupling, in relation to S100B secretion. Moreover, we found a significant increase in the S100B secretion basal levels with the increasing of animal age and the incubation with high levels of potassium resulted in a decrease of S100B secretion in 30 and 90-day old rats. These data, together with previous observations from gap junctions and glutamate transport of astrocytes, contribute to characterize the operational system involving astroglial activation, particularly on S100B secretion, in brain disorders.

Neuroglial alterations in rats submitted to the okadaic acid-induced model of dementia.

Several types of animal models have been developed to investigate Alzheimer's disease (AD). Okadaic acid (OA), a potent inhibitor of phosphatases 1 and 2A, induces characteristics that resemble AD-like pathology. Memory impairment induced by intra-hippocampal injection of OA has been reported, accompanied by remarkable neuropathological changes including hippocampal neurodegeneration, a paired helical filament-like phosphorylation of tau protein, and formation of ß-amyloid containing plaque-like structures. Rats were submitted to bilateral intrahippocampal okadaic acid-injection (100 ng) and, 12 days after the surgery, behavioral and biochemical tests were performed. Using this model, we evaluated spatial cognitive deficit and neuroglial alterations, particularly astroglial protein markers such as glial fibrillary acidic protein (GFAP) and S100B, metabolism of glutamate, oxidative parameters and alterations in MAPKs. Our results indicate significant hippocampal changes, including increased GFAP, protein oxidation, and phosphorylation of p38(MAPK); and decreases in glutathione content, transporter EAAT2/GLT-1, and glutamine synthetase activity as well as a decrease in cerebrospinal fluid S100B. No alterations were observed in glutamate uptake activity and S100B content. In conclusion, the OA-induced model of dementia caused spatial cognitive deficit and oxidative stress in this model and, for the first time to our knowledge, specific astroglial alterations. Findings contribute to understanding diseases accompanied by cognitive deficits and the neural damage induced by AO administration.

Resveratrol protects against oxidative injury induced by H2O2 in acute hippocampal slice preparations from Wistar rats.

There is a current interest in dietary compounds (such as trans-resveratrol) that can inhibit or reverse oxidative stress, the common pathway for a variety of brain disorders, including Alzheimer's disease and stroke. The objective of the present study was to investigate the effects of resveratrol, under conditions of oxidative stress induced by H(2)O(2), on acute hippocampal slices from Wistar rats. Here, we evaluated cell viability, extracellular lactate, glutathione content, ERK(MAPK) activity, glutamate uptake and S100B secretion. Resveratrol did not change the decrease in lactate levels and in cell viability (by MTT assay) induced by 1mM H(2)O(2), but prevented the increase in cell permeability to Trypan blue induced by H(2)O(2). Moreover, resveratrol per se increased total glutathione levels and prevented the decrease in glutathione induced by 1mM H(2)O(2). The reduction of S100B secretion induced by H(2)O(2) was not changed by resveratrol. Glutamate uptake was decreased in the presence of 1mM H(2)O(2) and this effect was not prevented by resveratrol. There was also a significant activation of ERK1/2 by 1mM H(2)O(2) and resveratrol was able to completely prevent this activation, leading to activity values lower than control levels. The impairments in astrocyte activities, induced by H(2)O(2), confirmed the importance of these cells as targets for therapeutic strategy in brain disorders involving oxidative stress. This study reinforces the protective role of resveratrol and indicates some possible molecular sites of activity of this compound on glial cells, in the acute damage of brain tissue during oxidative stress.