Protection by cholesterol-extracting cyclodextrins: a role for N-methyl-d-aspartate receptor redistribution

Unveiling enigmatic essence of Sphingolipids: A promising avenue for glaucoma treatment

Treatment of glaucoma, the leading cause of irreversible blindness, remains challenging. The apoptotic loss of retinal ganglion cells (RGCs) in glaucoma is the pathological hallmark. Current treatments often remain suboptimal as they aim to halt RGC loss secondary to reduction of intraocular pressure. The pathophysiological targets for exploring direct neuroprotective approaches, therefore are highly relevant. Sphingolipids have emerged as significant target molecules as they are not only the structural components of various cell constituents, but they also serve as signaling molecules that regulate molecular pathways involved in cell survival and death. Investigations have shown that a critical balance among various sphingolipid species, particularly the ceramide and sphingosine-1-phosphate play a role in deciding the fate of the cell. In this review we briefly discuss the metabolic interconversion of sphingolipid species to get an insight into "sphingolipid rheostat", the dynamic balance among metabolites. Further we highlight the role of sphingolipids in the key pathophysiological mechanisms that lead to glaucomatous loss of RGCs. Lastly, we summarize the potential drug candidates that have been investigated for their neuroprotective effects in glaucoma via their effects on sphingolipid axis.

Are There Lipid Membrane-Domain Subtypes in Neurons with Different Roles in Calcium Signaling?

Lipid membrane nanodomains or lipid rafts are 10-200 nm diameter size cholesterol- and sphingolipid-enriched domains of the plasma membrane, gathering many proteins with different roles. Isolation and characterization of plasma membrane proteins by differential centrifugation and proteomic studies have revealed a remarkable diversity of proteins in these domains. The limited size of the lipid membrane nanodomain challenges the simple possibility that all of them can coexist within the same lipid membrane domain. As caveolin-1, flotillin isoforms and gangliosides are currently used as neuronal lipid membrane nanodomain markers, we first analyzed the structural features of these components forming nanodomains at the plasma membrane since they are relevant for building supramolecular complexes constituted by these molecular signatures. Among the proteins associated with neuronal lipid membrane nanodomains, there are a large number of proteins that play major roles in calcium signaling, such as ionotropic and metabotropic receptors for neurotransmitters, calcium channels, and calcium pumps. This review highlights a large variation between the calcium signaling proteins that have been reported to be associated with isolated caveolin-1 and flotillin-lipid membrane nanodomains. Since these calcium signaling proteins are scattered in different locations of the neuronal plasma membrane, i.e., in presynapses, postsynapses, axonal or dendritic trees, or in the neuronal soma, our analysis suggests that different lipid membrane-domain subtypes should exist in neurons. Furthermore, we conclude that classification of lipid membrane domains by their content in calcium signaling proteins sheds light on the roles of these domains for neuronal activities that are dependent upon the intracellular calcium concentration. Some examples described in this review include the synaptic and metabolic activity, secretion of neurotransmitters and neuromodulators, neuronal excitability (long-term potentiation and long-term depression), axonal and dendritic growth but also neuronal cell survival and death.

Unveiling the Role of Cholesterol in Subnanomolar Ouabain Rescue of Cortical Neurons from Calcium Overload Caused by Excitotoxic Insults

Na/K-ATPase maintains transmembrane ionic gradients and acts as a signal transducer when bound to endogenous cardiotonic steroids. At subnanomolar concentrations, ouabain induces neuroprotection against calcium overload and apoptosis of neurons during excitotoxic stress. Here, the role of lipid rafts in interactions between Na/K-ATPase, sodium-calcium exchanger (NCX), and N-methy-D-aspartate receptors (NMDARs) was investigated. We analyzed 0.5-1-nanometer ouabain's effects on calcium responses and miniature post-synaptic current (mEPSCs) frequencies of cortical neurons during the action of NMDA in rat primary culture and brain slices. In both objects, ouabain attenuated NMDA-evoked calcium responses and prevented an increase in mEPSC frequency, while the cholesterol extraction by methyl-β-cyclodextrin prevented the effects. The data support the conclusions that (i) ouabain-induced inhibition of NMDA-elicited calcium response involves both pre- and post-synapse, (ii) the presence of astrocytes in the tripartite synapse is not critical for the ouabain effects, which are found to be similar in cell cultures and brain slices, and (iii) ouabain action requires the integrity of cholesterol-rich membrane microdomains in which the colocalization and functional interaction of NMDAR-transferred calcium influx, calcium extrusion by NCX, and Na/K-ATPase modulation of the exchanger occur. This regulation of the molecules by cardiotonic steroids may influence synaptic transmission, prevent excitotoxic neuronal death, and interfere with the pharmacological actions of neurological medicines.

Molecular Mind Games: The Medicinal Action of Cyclodextrins in Neurodegenerative Diseases

Cyclodextrins are often used as molecular carriers for small active ingredients in medicine. Recently, the intrinsic medicinal activity of some of these compounds has been under investigation, mainly related to their ability to interfere with cholesterol and, therefore, prevent and treat cholesterol-related diseases such as cardiovascular disease and neuronal diseases arising from altered cholesterol and lipid metabolism. One of the most promising compounds within the cyclodextrin family is 2-hydroxypropyl-β-cyclodextrin (HPβCD), owing to its superior biocompatibility profile. This work presents the most recent advances in the research and clinical use of HPβCD against Niemann-Pick disease, a congenital condition involving cholesterol accumulation inside lysosomes in brain cells, Alzheimer's and Parkinson's. HPβCD plays a complex role in each of these ailments, going beyond the mere sequestering of cholesterol molecules and involving an overall regulation of protein expression that helps restore the normal functioning of the organism.

The Interplay Between Cholesterol and Amyloid-β on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling

BACKGROUND

There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-β (Aβ) pathology, but these therapeutics have generally failed in clinical trials. Aβ is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined.

OBJECTIVE

This work elucidates some of the interplay between membrane cholesterol and Aβ42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways.

METHODS

The effects of cholesterol depletion by methyl-β-cyclodextrin followed by treatment with Aβ and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy.

RESULTS

Cell viability studies show that cholesterol depletion was mildly protective against Aβ toxicity. Together cholesterol reduction and Aβ42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aβ42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion.

CONCLUSIONS

Cholesterol depletion impacted the effects of Aβ42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Evaluation of Neuroprotective Effects of Sugammadex Following a Head Trauma in an Experimental Study

ABSTRACT

To compare the efficacy of mannitol, the first choice of treatment in daily clinical practice for head trauma, and sugammadex, a frequently used neuroanesthesia in recent years. A total of 35 male rats were randomly selected and were divided into 5 groups, each comprising 7 rats. The groups were divided into Group I, sham (n = 7); Group II, control (head trauma, n = 7); Group III, treated with mannitol (head trauma, mannitol 20% 1 g/kg, n = 7); Group IV, treated with sugammadex (head trauma, sugammadex 100 mg/kg, n = 7); and Group V, treated with mannitol and sugammadex (head trauma, mannitol 20% 1 g/kg and sugammadex 100 mg/kg, n = 7). After the sacrification, histological examination and immunohistochemical staining were performed in the brain of all subjects. Mann-Whitney U test was used to evaluate the significance between neuronal density, neuronal nuclei, and activated caspase-3 immunohistochemistry results measured from the prefrontal cortex. Neuronal density showing neuronal viability was observed to significantly increase in Group III compared to Group IV. However, neuronal nuclei immunohistochemistry showing apoptotic neurons also significantly increased. The present study has shown that sugammadex, an agent reversing the effects of neuromuscular blocking agents, has neuroprotective effects and is as effective as mannitol.

Nephroprotective Efficacy of Sugammadex in Ischemia-Reperfusion Injury: An Experimental Study in a Rat Model

Background: It is known that ischemia-reperfusion damage in the kidney is one of the most common causes of acute kidney failure. It is also known that reduced renal damage has a nephroprotective effect by reducing the release of inflammatory and vasoactive peptides that cause tissue damage. Therefore, we think that reperfusion caused by ischemia in kidney damage may be an important focus for clinical research.

Methods: A total of 21 healthy 230-250 g female rats were used in our experimental study. During the experiment, animals were randomly divided into three groups, each containing seven rats. Group 1: The group that underwent left nephrectomy with a sham operation. Group 2: Left renal ischemia for 60 minutes, then left nephrectomy followed by 45 minutes of reperfusion. Group 3: Left renal ischemia for 60 minutes, then reperfusion for 45 minutes, followed by left nephrectomy. In this group, sugammadex was given intravenously at a dose of 100 mg/kg at the beginning of reperfusion. In the histomorphological examination, damage findings of tubules atrophy, dilation and cast formation, tubular epithelial brush border loss and vacuolization, presence of fibrosis as interstitial structural change, capillary vasodilatation/congestion and neutrophilic cell infiltrates in interstitial spaces, and morphological changes in glomeruli were evaluated.

Results: When evaluated based on tubular brush border, there were no significant differences between Group 2 and Group 1 (P = 0.454), while the damage in Group 3 was less significant than Group 2 (P = 0.017). When evaluated in terms of tubular vacuolization, there was no significant difference between Group 2 and Group 1 (P = 0.902), while the damage in Group 3 was less significant than Group 2 (P = 0.017).

Conclusion: We believe that 100 mg/kg sugammadex given at the beginning of reperfusion after one hour of ischemic condition on rats has a histochemically detectable nephroprotective effect.

Cholesterol modulates presynaptic and postsynaptic properties of excitatory synaptic transmission

Cholesterol is a structural component of cellular membranes particularly enriched in synapses but its role in synaptic transmission remains poorly understood. We used rat hippocampal cultures and their acute cholesterol depletion by methyl-β-cyclodextrin as a tool to describe the physiological role of cholesterol in glutamatergic synaptic transmission. Cholesterol proved to be a key molecule for the function of synapses as its depletion resulted in a significant reduction of both NMDA receptor (NMDAR) and AMPA/kainate receptor-mediated evoked excitatory postsynaptic currents (eEPSCs), by 94% and 72%, respectively. We identified two presynaptic and two postsynaptic steps of synaptic transmission which are modulated by cholesterol and explain together the above-mentioned reduction of eEPSCs. In the postsynapse, we show that physiological levels of cholesterol are important for maintaining the normal probability of opening of NMDARs and for keeping NMDARs localized in synapses. In the presynapse, our results favour the hypothesis of a role of cholesterol in the propagation of axonal action potentials. Finally, cholesterol is a negative modulator of spontaneous presynaptic glutamate release. Our study identifies cholesterol as an important endogenous regulator of synaptic transmission and provides insight into molecular mechanisms underlying the neurological manifestation of diseases associated with impaired cholesterol synthesis or decomposition.

Defining parameters of specificity for bioluminescent optogenetic activation of neurons using in vitro multi electrode arrays (MEA)

In Bioluminescent Optogenetics (BL-OG) a biological, rather than a physical, light source is used to activate light-sensing opsins, such as channelrhodopsins or pumps. This is commonly achieved by utilizing a luminopsin (LMO), a fusion protein of a light-emitting luciferase tethered to a light-sensing opsin. Light of the wavelength matching the activation peak of the opsin is emitted by the luciferase upon application of its small molecule luciferin, resulting in activation of the fused opsin and subsequent effects on membrane potential. Using optimized protocols for culturing, transforming, and testing primary neurons in multi electrode arrays, we systematically defined parameters under which changes in neuronal activity are specific to bioluminescent activation of opsins, rather than due to off-target effects of either the luciferin or its solvent on neurons directly, or on opsins directly. We further tested if there is a direct effect of bioluminescence on neurons. Critical for assuring specific BL-OG effects are testing the concentration and formulation of the luciferin against proper controls, including testing effects of vehicle on LMO expressing and of luciferin on nonLMO expressing targets.

Recovery from Anesthesia after Robotic-Assisted Radical Cystectomy: Two Different Reversals of Neuromuscular Blockade

During robot-assisted radical cystectomy (RARC), specific surgical conditions (a steep Trendelenburg position, prolonged pneumoperitoneum, effective myoresolution until the final stages of surgery) can seriously impair the outcomes. The aim of the study was to evaluate the incidence of postoperative nausea and vomiting (PONV) and ileus and the quality of cognitive function at the awakening in two groups of patients undergoing different reversals. In this randomized trial, patients that were American Society of Anesthesiologists physical status (ASA) ≤III candidates for RARC for bladder cancer were randomized into two groups: In the sugammadex (S) group, patients received 2 mg/kg of sugammadex as reversal of neuromuscolar blockade; in the neostigmine (N) group, antagonization was obtained with neostigmine 0.04 mg/kg + atropine 0.02 mg/kg. PONV was evaluated at 30 min, 6 and 24 h after anesthesia. Postoperative cognitive functions and time to resumption of intestinal transit were also investigated. A total of 109 patients were analyzed (54 in the S group and 55 in the N group). The incidence of early PONV was lower in the S group but not statistically significant (S group 25.9% vs. N group 29%; p = 0.711). The Mini-Mental State test mean value was higher in the S group vs. the N group (1 h after surgery: 29.3 (29; 30) vs. 27.6 (27; 30), p = 0.007; 4 h after surgery: 29.5 (30; 30) vs. 28.4 (28; 30), p = 0.05). We did not observe a significant decrease of the PONV after sugammadex administration versus neostigmine use. The Mini-Mental State test mean value was greater in the S group.

Calcium-Dependent Desensitization of NMDA Receptors

Glutamate receptors play the key role in excitatory synaptic transmission in the central nervous system (CNS). N-methyl-D-aspartate-activated glutamate receptors (NMDARs) are ion channels permeable to sodium, potassium, and calcium ions that localize to the pre- and postsynaptic membranes, as well as extrasynaptic neuronal membrane. Calcium entry into dendritic spines is essential for long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission. Both LTP and LTD represent morphological and functional changes occurring in the process of memory formation. NMDAR dysfunction is associated with epilepsy, schizophrenia, migraine, dementia, and neurodegenerative diseases. Prolonged activation of extrasynaptic NMDARs causes calcium overload and apoptosis of neurons. Here, we review recent findings on the molecular mechanisms of calcium-dependent NMDAR desensitization that ensures fast modulation of NMDAR conductance in the CNS and limits calcium entry into the cells under pathological conditions. We present the data on molecular determinants related to calcium-dependent NMDAR desensitization and functional interaction of NMDARs with other ion channels and transporters. We also describe association of NMDARs with lipid membrane microdomains.

State-dependent alterations of lipid profiles in patients with bipolar disorder

Objective Serum lipid levels may be associated with the affective severity of bipolar disorder, but data on lipid profiles in Asian patients with bipolar disorder and the lipid alterations in different states of opposite polarities are scant. We investigated the lipid profiles of patients in the acute affective, partial, and full remission state in bipolar mania and depression. Methods The physically healthy patients aged between 18 and 45 years with bipolar I disorder, as well as age-matched healthy normal controls were enrolled. We compared the fasting blood levels of glucose, cholesterol, triglyceride, low-density lipoprotein, and high-density lipoprotein of manic or depressed patients in the acute phase and subsequent partial and full remission with those of their normal controls. Results A total of 32 bipolar manic patients (12 women and 20 men), 32 bipolar depressed participants (18 women and 14 men), and 64 healthy control participants took part in this study. The mean cholesterol level in acute mania was significantly lower than that in acute depression (p < 0.025). The lowest rate of dyslipidemia (hypertriglyceridemia or low high-density lipoprotein cholesterol) was observed in acute bipolar mania. Conclusion Circulating lipid profiles may be easily affected by affective states. The acute manic state may be accompanied by state-dependent lower cholesterol and triglyceride levels relative to that in other mood states.

Membrane cholesterol depletion in cortical neurons highlights altered NMDA receptor functionality in a mouse model of amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a chronic neurodegenerative disease affecting upper and lower motor neurons, with unknown aetiology. Lipid rafts, cholesterol enriched microdomains of the plasma membrane, have been linked to neurodegenerative disorders like ALS. The NMDA-receptor subcellular localization in lipid rafts is known to play many roles, from modulating memory strength to neurotoxicity. In this study, performed on the widely used G93A mouse model of ALS, we have shown an equal content of total membrane cholesterol in Control and G93A cortical cultures. Moreover, by electrophysiological studies, we have recorded NMDA- and AMPA-evoked currents which were not significantly different between the two neuronal populations. To study the role of membrane cholesterol on glutamate receptor functionality, we have analysed NMDA and AMPA receptors following cholesterol membrane depletion by methyl-β-cyclodextrin (MβCD). Interestingly, MβCD chronic treatment has provoked a significant reduction of NMDA-evoked currents in both cellular populations which was dose- and time-dependent but significantly higher in ALS neurons compared to Control. The different MβCD effect on NMDA-evoked currents was not due to a different membrane receptor subunit composition but seemed to cause in both neuronal populations a NMDA receptor membrane redistribution. MβCD treatment effect was receptor-specific since no alterations in the two neuronal populations were detected on AMPA receptors. These results lead us to speculate for an altered proteomic composition of lipid rafts in cortical mutated neurons and suggest the need for further studies on the lipid rafts composition and on their interaction with membrane receptors in ALS cortices.

Neurotoxin-Induced Catecholaminergic Loss in the Colonic Myenteric Plexus of Rhesus Monkeys

OBJECTIVE

Constipation is a common non-motor symptom of Parkinson's disease (PD). Although pathology of the enteric nervous system (ENS) has been associated with constipation in PD, the contribution of catecholaminergic neurodegeneration to this symptom is currently debated. The goal of this study was to assess the effects of the neurotoxin 6-hydroxydopamine (6-OHDA) on the colonic myenteric plexus and shed light on the role of catecholaminergic innervation in gastrointestinal (GI) function.

METHODS

Proximal colon tissue from 6-OHDA-treated (n=5) and age-matched control (n=5) rhesus monkeys was immunostained and quantified using ImageJ software. All animals underwent routine daily feces monitoring to assess for constipation or other GI dysfunction.

RESULTS

Quantification of tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC)-immunoreactivity (-ir) revealed significant reduction in myenteric ganglia of 6-OHDA-treated animals compared to controls (TH-ir: 87.8%, P<0.0001; AADC-ir: 61.7% P=0.0034). Analysis of pan-neuronal markers (PGP9.5, HuC/D), other neurochemical phenotypes (VIP, nNOS), PD-associated pathology proteins (α-synuclein, phosphorylated α-synuclein), glial marker GFAP and neuroinflammation and oxidative stress (HLA-DR, CD45, Nitrotyrosine) did not show significant differences. Monitoring of feces revealed frequent (>30% days) soft stool or diarrhea in 2 of the 5 6-OHDA-treated animals and 0 of the 5 control animals during the 2 months prior to necropsy, with no animals exhibiting signs of constipation.

CONCLUSION

Systemic administration of 6-OHDA to rhesus monkeys significantly reduced catecholaminergic expression in the colonic myenteric plexus without inducing constipation. These findings support the concept that ENS catecholaminergic loss is not responsible for constipation in PD.

Neuroprotective Effects of Engineered Polymeric Nasal Microspheres Containing Hydroxypropyl-β-cyclodextrin on β-Amyloid (1-42)-Induced Toxicity

β-Amyloid (Aβ) plaques are the key neurotoxic assemblies in Alzheimer disease. It has been suggested that an interaction occurs between membrane cholesterol and Aβ aggregation in the brain. Cyclodextrins can remove cholesterol from cell membranes and change receptor function. This study aimed to investigate the effect of hydroxypropyl-β-cyclodextrin (HP-CD) polymeric microspheres, based on chitosan or sodium alginate, on the levels of lipid peroxidation, reactive oxygen species production, and mitochondrial function in brain synaptosomes. The effect of microspheres on DNA fragmentation, the expression of Bcl-2, Bax, and Apex1 mRNAs in rat hippocampus after Aβ(1-42) peptide-induced neurotoxicity was also evaluated. Comparison with HP-CD raw material was performed. Aβ(1-42) treatment significantly decreased the mitochondrial activity of Apex1 and Bcl-2 mRNAs, induced DNA fragmentation, and increased mRNA levels of Bax. Treatment with HP-CD microspheres against Aβ(1-42) significantly reduced DNA fragmentation and increased the Bcl-2/Bax mRNA ratio and mitochondrial function. In addition, HP-CD microspheres used against Aβ(1-42) decreased the levels of lipid peroxidation and reactive oxygen species production. These results indicate that nasally administered spray-dried HP-CD microspheres are able to provide protection against Aβ(1-42)-induced neurotoxicity, due to the suppressed levels of oxidative stress and apoptotic signals in the rat hippocampus.

Effectiveness of sugammadex for cerebral ischemia/reperfusion injury

Cerebral ischemia may cause permanent brain damage and behavioral dysfunction. The efficacy and mechanisms of pharmacological treatments administered immediately after cerebral damage are not fully known. Sugammadex is a licensed medication. As other cyclodextrins have not passed the necessary phase tests, trade preparations are not available, whereas sugammadex is frequently used in clinical anesthetic practice. Previous studies have not clearly described the effects of the cyclodextrin family on cerebral ischemia/reperfusion (I/R) damage. The aim of this study was to determine whether sugammadex had a neuroprotective effect against transient global cerebral ischemia. Animals were assigned to control, sham-operated, S 16 and S 100 groups. Transient global cerebral ischemia was induced by 10-minute occlusion of the bilateral common carotid artery, followed by 24-hour reperfusion. At the end of the experiment, neurological behavior scoring was performed on the rats, followed by evaluation of histomorphological and biochemical measurements. Sugammadex 16 mg/kg and 100 mg/kg improved neurological outcome, which was associated with reductions in both histological and neurological scores. The hippocampus TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) and caspase results in the S 16 and S 100 treatment groups were significantly lower than those of the I/R group. Neurological scores in the treated groups were significantly higher than those of the I/R group. The study showed that treatment with 16 mg/kg and 100 mg/kg sugammadex had a neuroprotective effect in a transient global cerebral I/R rat model. However, 100 mg/kg sugammadex was more neuroprotective in rats.

Raised Intracellular Calcium Contributes to Ischemia-Induced Depression of Evoked Synaptic Transmission

Oxygen-glucose deprivation (OGD) leads to depression of evoked synaptic transmission, for which the mechanisms remain unclear. We hypothesized that increased presynaptic [Ca²⁺]_i during transient OGD contributes to the depression of evoked field excitatory postsynaptic potentials (fEPSPs). Additionally, we hypothesized that increased buffering of intracellular calcium would shorten electrophysiological recovery after transient ischemia. Mouse hippocampal slices were exposed to 2 to 8 min of OGD. fEPSPs evoked by Schaffer collateral stimulation were recorded in the stratum radiatum, and whole cell current or voltage clamp recordings were performed in CA1 neurons. Transient ischemia led to increased presynaptic [Ca²⁺]_i, (shown by calcium imaging), increased spontaneous miniature EPSP/Cs, and depressed evoked fEPSPs, partially mediated by adenosine. Buffering of intracellular Ca²⁺ during OGD by membrane-permeant chelators (BAPTA-AM or EGTA-AM) partially prevented fEPSP depression and promoted faster electrophysiological recovery when the OGD challenge was stopped. The blocker of BK channels, charybdotoxin (ChTX), also prevented fEPSP depression, but did not accelerate post-ischemic recovery. These results suggest that OGD leads to elevated presynaptic [Ca²⁺]_i, which reduces evoked transmitter release; this effect can be reversed by increased intracellular Ca²⁺ buffering which also speeds recovery.

Cyclodextrin Alters GABAergic Input to CA1 Pyramidal Cells in Wild-Type But Not in NPC1-Deficient Mice

Niemann–Pick type C1 disease (NPC1) is a neurodegenerative disorder caused by mutations in the NPC1 gene. Actual, no causative treatment for NPC1 is available, although some drugs have been proven to be beneficial to patients, for example, 2-hydroxypropyl-β-cyclodextrin (CDX). In this study, we used the BALB/c_Nctr-Npc1m1N/-J mouse strain to study the effect of CDX, which is described to prolong the life span and to alleviate the pathogenic phenotype. By means of patch clamp recordings, we measured inhibitory postsynaptic currents (IPSCs) of CA1 pyramidal cells of CDX-treated and -untreated animals to elucidate the influence of CDX on the synaptic transmission. Surprisingly, CDX induced a significantly higher GABAergic IPSC frequency in wild-type mice than in NPC1^−/− mice. Although the IPSCs were mainly GABAergic, we observed a significant reduction of the IPSC frequency in the presence of the glycine receptor antagonist strychnine. The effect of strychnine did not differ in untreated and treated animals, indicating that the effect of CDX was most likely not based on an interaction with glycinergic transmission machinery. However, the unexpected effect of CDX on the GABAergic synaptic transmission is of special interest as a disturbance plays, for example, a crucial role in epilepsy and, moreover, as CDX is currently under investigation as a treatment for NPC1 in humans.

Cholesterol modulates open probability and desensitization of NMDA receptors

NMDA receptors (NMDARs) are glutamate-gated ion channels that mediate excitatory neurotransmission in the CNS. Although these receptors are in direct contact with plasma membrane, lipid-NMDAR interactions are little understood. In the present study, we aimed at characterizing the effect of cholesterol on the ionotropic glutamate receptors. Whole-cell current responses induced by fast application of NMDA in cultured rat cerebellar granule cells (CGCs) were almost abolished (reduced to 3%) and the relative degree of receptor desensitization was increased (by seven-fold) after acute cholesterol depletion by methyl-β-cyclodextrin. Both of these effects were fully reversible by cholesterol repletion. By contrast, the responses mediated by AMPA/kainate receptors were not affected by cholesterol depletion. Similar results were obtained in CGCs after chronic inhibition of cholesterol biosynthesis by simvastatin and acute enzymatic cholesterol degradation to 4-cholesten-3-one by cholesterol oxidase. Fluorescence anisotropy measurements showed that membrane fluidity increased after methyl-β-cyclodextrin pretreatment. However, no change in fluidity was observed after cholesterol enzymatic degradation, suggesting that the effect of cholesterol on NMDARs is not mediated by changes in membrane fluidity. Our data show that diminution of NMDAR responses by cholesterol depletion is the result of a reduction of the open probability, whereas the increase in receptor desensitization is the result of an increase in the rate constant of entry into the desensitized state. Surface NMDAR population, agonist affinity, single-channel conductance and open time were not altered in cholesterol-depleted CGCs. The results of our experiments show that cholesterol is a strong endogenous modulator of NMDARs.

Low levels of methyl β-cyclodextrin disrupt GluA1-dependent synaptic potentiation but not synaptic depression

Methyl-β-cyclodextrin (MβCD) is a reagent that depletes cholesterol and disrupts lipid rafts, a type of cholesterol-enriched cell membrane microdomain. Lipid rafts are essential for neuronal functions such as synaptic transmission and plasticity, which are sensitive to even low doses of MβCD. However, how MβCD changes synaptic function, such as N-methyl-d-aspartate receptor (NMDA-R) activity, remains unclear. We monitored changes in synaptic transmission and plasticity after disrupting lipid rafts with MβCD. At low concentrations (0.5 mg/mL), MβCD decreased basal synaptic transmission and miniature excitatory post-synaptic current without changing NMDA-R-mediated synaptic transmission and the paired-pulse facilitation ratio. Interestingly, low doses of MβCD failed to deplete cholesterol or affect α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R) and NMDA-R levels, while clearly reducing GluA1 levels selectively in the synaptosomal fraction. Low doses of MβCD decreased the inhibitory effects of NASPM, an inhibitor for GluA2-lacking AMPA-R. MβCD successfully decreased NMDA-R-mediated long-term potentiation but did not affect the formation of either NMDA-R-mediated or group I metabotropic glutamate receptor-dependent long-term depression. MβCD inhibited de-depression without affecting de-potentiation. These results suggest that MβCD regulates GluA1-dependent synaptic potentiation but not synaptic depression in a cholesterol-independent manner.

Cyclodextrins, blood-brain barrier, and treatment of neurological diseases

Biological barriers are the main defense systems of the homeostasis of the organism and protected organs. The blood-brain barrier (BBB), formed by the endothelial cells of brain capillaries, not only provides nutrients and protection to the central nervous system but also restricts the entry of drugs, emphasizing its importance in the treatment of neurological diseases. Cyclodextrins are increasingly used in human pharmacotherapy. Due to their favorable profile to form hydrophilic inclusion complexes with poorly soluble active pharmaceutical ingredients, they are present as excipients in many marketed drugs. Application of cyclodextrins is widespread in formulations for oral, parenteral, nasal, pulmonary, and skin delivery of drugs. Experimental and clinical data suggest that cyclodextrins can be used not only as excipients for centrally acting marketed drugs like antiepileptics, but also as active pharmaceutical ingredients to treat neurological diseases. Hydroxypropyl-β-cyclodextrin received orphan drug designation for the treatment of Niemann-Pick type C disease. In addition to this rare lysosomal storage disease with neurological symptoms, experimental research revealed the potential therapeutic use of cyclodextrins and cyclodextrin nanoparticles in neurodegenerative diseases, stroke, neuroinfections and brain tumors. In this context, the biological effects of cyclodextrins, their interaction with plasma membranes and extraction of different lipids are highly relevant at the level of the BBB.

Lipid dynamics at dendritic spines

Dynamic changes in the structure and composition of the membrane protrusions forming dendritic spines underlie memory and learning processes. In recent years a great effort has been made to characterize in detail the protein machinery that controls spine plasticity. However, we know much less about the involvement of lipids, despite being major membrane components and structure determinants. Moreover, protein complexes that regulate spine plasticity depend on specific interactions with membrane lipids for proper function and accurate intracellular signaling. In this review we gather information available on the lipid composition at dendritic spine membranes and on its dynamics. We pay particular attention to the influence that spine lipid dynamism has on glutamate receptors, which are key regulators of synaptic plasticity.

Simvastatin treatment enhances NMDAR-mediated synaptic transmission by upregulating the surface distribution of the GluN2B subunit

The ramifications of statins on plasma cholesterol and coronary heart disease have been well documented. However, there is increasing evidence that inhibition of the mevalonate pathway may provide independent neuroprotective and procognitive pleiotropic effects, most likely via inhibition of isoprenoids, mainly farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP). FPP and GGPP are the major donors of prenyl groups for protein prenylation. Modulation of isoprenoid availability impacts a slew of cellular processes including synaptic plasticity in the hippocampus. Our previous work has demonstrated that simvastatin (SV) administration improves hippocampus-dependent spatial memory, rescuing memory deficits in a mouse model of Alzheimer's disease. Treatment of hippocampal slices with SV enhances long-term potentiation (LTP), and this effect is dependent on the activation of Akt (protein kinase B). Further studies showed that SV-induced enhancement of hippocampal LTP is driven by depletion of FPP and inhibition of farnesylation. In the present study, we report the functional consequences of exposure to SV at cellular/synaptic and molecular levels. While application of SV has no effect on intrinsic membrane properties of CA1 pyramidal neurons, including hyperpolarization-activated cyclic-nucleotide channel-mediated sag potentials, the afterhyperpolarization (AHP), and excitability, SV application potentiates the N-methyl D-aspartate receptor (NMDAR)-mediated contribution to synaptic transmission. In mouse hippocampal slices and human neuronal cells, SV treatment increases the surface distribution of the GluN2B subunit of the NMDAR without affecting cellular cholesterol content. We conclude that SV-induced enhancement of synaptic plasticity in the hippocampus is likely mediated by augmentation of synaptic NMDAR components that are largely responsible for driving synaptic plasticity in the CA1 region.

Cholesterol-independent effects of methyl-β-cyclodextrin on chemical synapses

The cholesterol chelating agent, methyl-β-cyclodextrin (MβCD), alters synaptic function in many systems. At crayfish neuromuscular junctions, MβCD is reported to reduce excitatory junctional potentials (EJPs) by impairing impulse propagation to synaptic terminals, and to have no postsynaptic effects. We examined the degree to which physiological effects of MβCD correlate with its ability to reduce cholesterol, and used thermal acclimatization as an alternative method to modify cholesterol levels. MβCD impaired impulse propagation and decreased EJP amplitude by 40% (P<0.05) in preparations from crayfish acclimatized to 14 °C but not from those acclimatized to 21 °C. The reduction in EJP amplitude in the cold-acclimatized group was associated with a 49% reduction in quantal content (P<0.05). MβCD had no effect on input resistance in muscle fibers but decreased sensitivity to the neurotransmitter L-glutamate in both warm- and cold-acclimatized groups. This effect was less pronounced and reversible in the warm-acclimatized group (90% reduction in cold, P<0.05; 50% reduction in warm, P<0.05). MβCD reduced cholesterol in isolated nerve and muscle from cold- and warm-acclimatized groups by comparable amounts (nerve: 29% cold, 25% warm; muscle: 20% cold, 18% warm; P<0.05). This effect was reversed by cholesterol loading, but only in the warm-acclimatized group. Thus, effects of MβCD on glutamate-sensitivity correlated with its ability to reduce cholesterol, but effects on impulse propagation and resulting EJP amplitude did not. Our results indicate that MβCD can affect both presynaptic and postsynaptic properties, and that some effects of MβCD are unrelated to cholesterol chelation.

Cerebroside-A provides potent neuroprotection after cerebral ischaemia through reducing glutamate release and Ca²⁺ influx of NMDA receptors

Excessive presynaptic glutamate release after cerebral ischaemia leads to neuronal death mainly through excessive calcium entry of N-methyl-D-aspartate receptors (NMDARs). Our recent study reported that cerebroside can open large-conductance Ca²⁺-activated K⁺ (BKCa) channels. The present study evaluated the effects of cerebroside-A (CS-A), a single molecule isolated from an edible mushroom, on brain injury after focal or global ischaemia in adult male mice and rats. We herein report that treatment with CS-A after 60-min middle cerebral artery occlusion dose-dependently reduced the cerebral infarction with at least a 6-h efficacious time-window, which was partially blocked by the BKCa channel blocker charybdotoxin (CTX). Treatment with CS-A after 20 min global cerebral ischaemia (four-vessel occlusion) significantly attenuated the death of pyramidal cells in hippocampal CA1 area, which was also sensitive to CTX. CS-A, by opening the BKCa channel, could prevent excessive glutamate release after oxygen-glucose deprivation (OGD). In addition, CS-A could inhibit NMDAR Ca²⁺ influx, which did not require the activation of the BKCa channel. Furthermore, CS-A blocked the OGD-induced NMDAR-dependent long-term potentiation in hippocampal CA1 region. These findings indicate that treatment with CS-A after stroke exerts potent neuroprotection through prevention of excessive glutamate release and reduction of Ca²⁺ influx through NMDARs.

Indinavir inhibits the expression of cytoplasmic aromatase and nuclear SREBP in the hippocampus of reperfusion injury-induced ischemic rats

Ischemic brain injury due to insults, such as stroke, is a leading cause of severe neurological and neurobehavioral deficits and death. Neurodegeneration can be prevented by local aromatase expression, and estrogen synthesis can be neuroprotective in ischemia/reperfusion. Therefore, aromatase, the enzyme that transforms androgens to estrogens, may be a potential target for the study of reperfusion injury after brain ischemia. We investigated the expression of aromatase and sterol regulatory element binding protein (SREBP) using Western blotting in the rat hippocampus after transient global ischemia plus hypotension. After 10 min of ischemia, aromatase and SREBP expression was observed in cytosolic extracts after 1, 4 and 10 weeks of reperfusion. Previous immunoblot analysis demonstrated that the highest aromatase expression appeared in damaged hippocampi after 1 week. In this study, SREBP expression was increased at 1 week in the nuclear extracts of damaged hippocampi. The aromatase inhibitor megestrol acetate (20 mg/kg/day; 21 days) and the SREBP inhibitor indinavir (15 mg/kg/day; 30 days) suppressed aromatase levels in ischemic hippocampi. Our findings indicate that ischemia, as well as chronic neurodegenerative processes, leads to an increase in cytoplasmic aromatase and nuclear SREBP. Thus, it is possible to hypothesize that an interaction between this enzyme gene and the transcription factor exists.

Regulation of presynaptic strength by controlling Ca2+ channel mobility: effects of cholesterol depletion on release at the cone ribbon synapse

Synaptic communication requires proper coupling between voltage-gated Ca(2+) (Ca(V)) channels and synaptic vesicles. In photoreceptors, L-type Ca(V) channels are clustered close to synaptic ribbon release sites. Although clustered, Ca(V) channels move continuously within a confined domain slightly larger than the base of the ribbon. We hypothesized that expanding Ca(V) channel confinement domains should increase the number of channel openings needed to trigger vesicle release. Using single-particle tracking techniques, we measured the expansion of Ca(V) channel confinement domains caused by depletion of membrane cholesterol with cholesterol oxidase or methyl-β-cyclodextrin. With paired whole cell recordings from cones and horizontal cells, we then determined the number of Ca(V) channel openings contributing to cone Ca(V) currents (I(Ca)) and the number of vesicle fusion events contributing to horizontal cell excitatory postsynaptic currents (EPSCs) following cholesterol depletion. Expansion of Ca(V) channel confinement domains reduced the peak efficiency of release, decreasing the number of vesicle fusion events accompanying opening of each Ca(V) channel. Cholesterol depletion also inhibited exocytotic capacitance increases evoked by brief depolarizing steps. Changes in efficiency were not due to changes in I(Ca) amplitude or glutamate receptor properties. Replenishing cholesterol restored Ca(V) channel domain size and release efficiency to control levels. These results indicate that cholesterol is important for organizing the cone active zone. Furthermore, the finding that cholesterol depletion impairs coupling between channel opening and vesicle release by allowing Ca(V) channels to move further from release sites shows that changes in presynaptic Ca(V) channel mobility can be a mechanism for adjusting synaptic strength.

Inhibition of neutral sphingomyelinase-2 perturbs brain sphingolipid balance and spatial memory in mice

The sphingolipid ceramide is a bioactive signaling lipid that is thought to play important roles in modulating synaptic activity, in part by regulating the function of excitatory postsynaptic receptors. However, the molecular mechanisms by which ceramide exerts its effects on synaptic activity remain largely unknown. We recently demonstrated that a rapid generation of ceramide by neutral sphingomyelinase-2 (nSMase2; also known as "sphingomyelin phosphodiesterase-3") played a key role in modulating excitatory postsynaptic currents by controlling the insertion and clustering of NMDA receptors (Wheeler et al. [2009] J. Neurochem. 109:1237-1249). We now demonstrate that nSMase2 plays a role in memory. Inhibition of nSMase2 impaired spatial and episodic-like memory in mice. At the molecular level, inhibition of nSMase2 decreased ceramide, increased PSD-95, increased the number of AMPA receptors, and altered the subunit composition of NMDA receptors. Our study identifies nSMase2 as an important component for efficient memory formation and underscores the importance of ceramide in regulating synaptic events related to learning and memory.

Membrane cholesterol modulates {beta}-amyloid-dependent tau cleavage by inducing changes in the membrane content and localization of N-methyl-D-aspartic acid receptors

We have previously shown that β-amyloid (Aβ) treatment resulted in an age-dependent calpain activation leading to Tau cleavage into a neurotoxic 17-kDa fragment in a cellular model of Alzheimer disease. This detrimental cellular response was mediated by a developmentally regulated increase in membrane cholesterol levels. In this study, we assessed the molecular mechanisms by which cholesterol modulated Aβ-induced Tau cleavage in cultured hippocampal neurons. Our results indicated that these mechanisms did not involve the regulation of the binding of Aβ aggregates to the plasma membrane. On the other hand, experiments using N-methyl-d-aspartic acid receptor inhibitors suggested that these receptors played an essential role in cholesterol-mediated Aβ-dependent calpain activity and 17-kDa Tau production. Biochemical and immunocytochemical analyses demonstrated that decreasing membrane cholesterol levels in mature neurons resulted in a significant reduction of the NR1 subunit at the membrane as well as an increase in the number of large NR1, NR2A, and NR2B subunit clusters. Moreover, the majority of these larger N-methyl-d-aspartic acid receptor subunit immunoreactive spots was not juxtaposed to presynaptic sites in cholesterol-reduced neurons. These data suggested that changes at the synaptic level underlie the mechanism by which membrane cholesterol modulates developmental changes in the susceptibility of hippocampal neurons to Aβ-induced toxicity.

Sphingolipids in neurodegeneration

Although the brain contains a high content of sphingolipids, we know relatively little about the roles that sphingolipids play in regulating neural functions. Once regarded only for their structural roles in maintaining the integrity of cellular and sub-cellular compartments, it is now apparent that many sphingolipid species are biologically active and play important roles in regulating signaling events. Recent technological and scientific advances are rapidly increasing our knowledge of the roles that sphingolipids play in regulating normal neural activity. Likewise, we are beginning to understand how perturbations in sphingolipid metabolism contribute to the pathogenesis of a variety of neurodegenerative conditions. In this special issue of NeuroMolecular Medicine, we present a series of review articles that summarize new and emerging technologies for the analysis of sphingolipids, sphingolipid metabolic pathways, and how dysfunctions in sphingolipid metabolism contribute to neurodegeneration in lysosomal storage disorders, Alzheimer's disease and Multiple Sclerosis.

The effect of simvastatin on the proteome of detergent-resistant membrane domains: decreases of specific proteins previously related to cytoskeleton regulation, calcium homeostasis and cell fate

Cell death induced by over-activation of glutamate receptors occurs in different neuropathologies. Cholesterol depletors protect from neurotoxic over-activation of glutamate receptors, and we have recently reported that this neuroprotection is associated with a reduction of the N-methyl-D-aspartate subtype of glutamate receptors in detergent-resistant membrane domains (DRM). In the present study we used comparative proteomics to further identify which proteins, besides the N-methyl-D-aspartate receptor, change its percentage of association to DRM after treatment of neurons with simvastatin. We detected 338 spots in neuronal DRM subjected to 2-DE; eleven of these spots changed its intensity after treatment with simvastatin. All 11 differential spots showed reduced intensity in simvastatin-treated samples and were identified as adipocyte plasma membrane associated protein, enolase, calretinin, coronin 1a, f-actin capping protein alpha1, f-actin capping protein alpha2, heat shock cognate protein 71, malate dehydrogenase, n-myc downregulated gene 1, prohibitin 2, Rab GDP dissociation inhibitor, translationally controlled tumor protein and voltage dependent anion selective channel protein 1. The proteins tested colocalized with the lipid raft marker caveolin-1. Interestingly, the proteins we have identified in the present study had been previously reported to play a role in cell fate and, thus, they might represent novel targets for neuroprotection.

Ferulic acid inhibits nitric oxide-induced apoptosis by enhancing GABA(B1) receptor expression in transient focal cerebral ischemia in rats

AIM

Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) provides neuroprotection against apoptosis in a transient middle cerebral artery occlusion (MCAo) model. This study was to further investigate the anti-apoptotic effect of FA during reperfusion after cerebral ischemia.

METHODS

Rats were subjected to 90 min of cerebral ischemia followed by 3 or 24 h of reperfusion after which they were sacrificed.

RESULTS

Intravenous FA (100 mg/kg) administered immediately after middle cerebral artery occlusion (MCAo) or 2 h after reperfusion effectively abrogated the elevation of postsynaptic density-95 (PSD-95), neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), nitrotyrosine, and cleaved caspase-3 levels as well as apoptosis in the ischemic cortex at 24 h of reperfusion. FA further inhibited Bax translocation, cytochrome c release, and p38 mitogen-activated protein (MAP) kinase phosphorylation. Moreover, FA enhanced the expression of gamma-aminobutyric acid type B receptor subunit 1 (GABA(B1)) in the ischemic cortex at 3 and 24 h of reperfusion. In addition, nitrotyrosine-positive cells colocalized with cleaved caspase-3-positive cells, and phospho-p38 MAP kinase-positive cells colocalized with nitrotyrosine- and Bax-positive cells, indicating a positive relationship among the expression of nitrotyrosine, phospho-p38 MAP kinase, Bax, and cleaved caspase-3. The mutually exclusive expression of GABA(B1) and nitrotyrosine revealed that there is a negative correlation between GABA(B1) and nitrotyrosine expression profiles. Additionally, pretreatment with saclofen, a GABA(B) receptor antagonist, abolished the neuroprotection of FA against nitric oxide (NO)-induced apoptosis.

CONCLUSION

FA significantly enhances GABA(B1) receptor expression at early reperfusion and thereby provides neuroprotection against p38 MAP kinase-mediated NO-induced apoptosis at 24 h of reperfusion.

Quantification of brain endocannabinoid levels: methods, interpretations and pitfalls

Endocannabinoids play an important role in a diverse range of neurophysiological processes including neural development, neuroimmune function, synaptic plasticity, pain, reward and affective state. This breadth of influence and evidence for altered endocannabinoid signalling in a variety of neuropathologies has fuelled interest in the accurate quantification of these lipids in brain tissue. Established methods for endocannabinoid quantification primarily employ solvent-based lipid extraction with further sample purification by solid phase extraction. In recent years in vivo microdialysis methods have also been developed for endocannabinoid sampling from the brain interstitial space. However, considerable variability in estimates of endocannabinoid content has led to debate regarding the physiological range of concentrations present in various brain regions. This paper provides a critical review of factors that influence the quantification of brain endocannabinoid content as determined by lipid extraction from bulk tissue and by in vivo microdialysis. A variety of methodological issues are discussed including analytical approaches, endocannabinoid extraction and purification, post-mortem changes in brain endocannabinoid content, cellular reactions to microdialysis probe implantation and caveats related to lipid sampling from the extracellular space. The application of these methods for estimating brain endocannabinoid content and the effects of endocannabinoid clearance inhibition are discussed. The benefits, limitations and pitfalls associated with each approach are emphasized, with an eye toward the appropriate interpretation of data gathered by each method.

Roles for dysfunctional sphingolipid metabolism in Alzheimer's disease neuropathogenesis

Sphingolipids in the membranes of neurons play important roles in signal transduction, either by modulating the localization and activation of membrane-associated receptors or by acting as precursors of bioactive lipid mediators. Activation of cytokine and neurotrophic factor receptors coupled to sphingomyelinases results in the generation of ceramides and gangliosides, which in turn, modify the structural and functional plasticity of neurons. In aging and neurodegenerative conditions such as Alzheimer's disease (AD), there are increased membrane-associated oxidative stress and excessive production and accumulation of ceramides. Studies of brain tissue samples from human subjects, and of experimental models of the diseases, suggest that perturbed sphingomyelin metabolism is a pivotal event in the dysfunction and degeneration of neurons that occurs in AD and HIV dementia. Dietary and pharmacological interventions that target sphingolipid metabolism should be pursued for the prevention and treatment of neurodegenerative disorders.

Cholesterol and affective morbidity

Depression and mania have been linked with low cholesterol though there has been limited prospective study of cholesterol and subsequent course of affective illness. We studied the relationship between fasting total cholesterol and subsequent depressive and manic symptoms. A total of 131 participants from a prospective cohort study were identified as having had a fasting total cholesterol evaluation at intake. Participants were predominantly inpatients at index visit and were followed for a median of 20 and up to 25 years. Cholesterol was modeled with age, gender, and index use of a mood stabilizer in linear regression to assess its influence on subsequent depressive symptom burden in participants with unipolar disorder as well as depressive and manic symptom burden in participants with bipolar disorder. Among bipolar participants (N=65), low cholesterol predicted a higher proportion of follow-up weeks with manic, but not depressive symptoms. Cholesterol did not appear to predict depressive symptom burden among participants with unipolar depression (N=66). Lower cholesterol levels may predispose individuals with bipolar disorder to a greater burden of manic symptomatology and may provide some insight into the underlying neurobiology.

Hippocampal N-methyl-D-aspartate receptor subunit expression profiles in a mouse model of prenatal alcohol exposure

BACKGROUND

Although several reports have been published showing prenatal ethanol exposure is associated with alterations in N-methyl-D-aspartate (NMDA) receptor subunit levels and, in a few cases, subcellular distribution, results of these studies are conflicting.

METHODS

We used semi-quantitative immunoblotting techniques to analyze NMDA receptor NR1, NR2A, and NR2B subunit levels in the adult mouse hippocampal formation isolated from offspring of dams who consumed moderate amounts of ethanol throughout pregnancy. We employed subcellular fractionation and immunoprecipitation techniques to isolate synaptosomal membrane- and postsynaptic density protein-95 (PSD-95)-associated pools of receptor subunits.

RESULTS

We found that, compared to control animals, fetal alcohol-exposed (FAE) adult mice had: (i) increased synaptosomal membrane NR1 levels with no change in association of this subunit with PSD-95 and no difference in total NR1 expression in tissue homogenates; (ii) decreased NR2A subunit levels in hippocampal homogenates, but no alterations in synaptosomal membrane NR2A levels and no change in NR2A-PSD-95 association; and (iii) no change in tissue homogenate or synaptosomal membrane NR2B levels but a reduction in PSD-95-associated NR2B subunits. No alterations were found in mRNA levels of NMDA receptor subunits suggesting that prenatal alcohol-associated differences in subunit protein levels are the result of differences in post-transcriptional regulation of subunit localization.

CONCLUSIONS

Our results demonstrate that prenatal alcohol exposure induces selective changes in NMDA receptor subunit levels in specific subcellular locations in the adult mouse hippocampal formation. Of particular interest is the finding of decreased PSD-95-associated NR2B levels, suggesting that synaptic NR2B-containing NMDA receptor concentrations are reduced in FAE animals. This result is consistent with various biochemical, physiological, and behavioral findings that have been linked with prenatal alcohol exposure.

Cholesterol depletion inhibits electrophysiological changes induced by anoxia in CA1 region of rat hippocampal slices

The hyper-activation of glutamate receptors is a key event in the degenerative processes triggered by ischemia in the brain. Several types of these receptors reside in cholesterol-sphingomyelin rich domains of post-synaptic plasma membranes and have been described to be sensitive to cholesterol depletion. Hence we investigated, by extracellular recordings, the effect of cholesterol depletion on population spikes (PS) during ischemia-like conditions in the CA1 region of rat hippocampal slices using the cholesterol-depleting agent methyl-beta-cyclodextrin (MbetaCD). Results obtained demonstrate that MbetaCD prevents the changes induced by anoxic insult, i.e., depression of the population spike amplitude and insurgence of ischemic long-term potentiation. Furthermore cholesterol depletion prevents the disappearance of population spike induced by anoxia/aglycemia during kainate perfusion. Our data suggest a possible role of MbetaCD in preventing the pathological changes in synaptic activity induced by ischemia and indicate that manipulation of lipid components of membrane rafts might provide a new approach for the treatment of ischemia.

Neuroprotective actions of brain aromatase

The steroidal regulation of vertebrate neuroanatomy and neurophysiology includes a seemingly unending list of brain areas, cellular structures and behaviors modulated by these hormones. Estrogens, in particular have emerged as potent neuromodulators, exerting a range of effects including neuroprotection and perhaps neural repair. In songbirds and mammals, the brain itself appears to be the site of injury-induced estrogen synthesis via the rapid transcription and translation of aromatase (estrogen synthase) in astroglia. This induction seems to occur regardless of the nature and location of primary brain damage. The induced expression of aromatase apparently elevates local estrogen levels enough to interfere with apoptotic pathways, thereby decreasing secondary degeneration and ultimately lessening the extent of damage. There is even evidence suggesting that aromatization may affect injury-induced cytogenesis. Thus, aromatization in the brain appears to confer neuroprotection by an array of mechanisms that involve the deceleration and acceleration of degeneration and repair, respectively. We are only beginning to understand the factors responsible for the injury-induced transcription of aromatase in astroglia. In contrast, much of the manner in which local and circulating estrogens may achieve their neuroprotective effects has been elucidated. However, gaps in our knowledge include issues about the cell-specific regulation of aromatase expression, steroidal influences of aromatization distinct from estrogen formation, and questions about the role of constitutive aromatase in neuroprotection. Here we describe the considerable consensus and some interesting differences in knowledge gained from studies conducted on diverse animal models, experimental paradigms and preparations towards understanding the neuroprotective actions of brain aromatase.

A novel protein complex in membrane rafts linking the NR2B glutamate receptor and autophagy is disrupted following traumatic brain injury

Hyperactivation of N-methyl-D-aspartate receptors (NRs) is associated with neuronal cell death induced by traumatic brain injury (TBI) and many neurodegenerative conditions. NR signaling efficiency is dependent on receptor localization in membrane raft microdomains. Recently, excitotoxicity has been linked to autophagy, but mechanisms governing signal transduction remain unclear. Here we have identified protein interactions between NR2B signaling intermediates and the autophagic protein Beclin-1 in membrane rafts of the normal rat cerebral cortex. Moderate TBI induced rapid recruitment and association of NR2B and pCaMKII to membrane rafts, and translocation of Beclin-1 out of membrane microdomains. Furthermore, TBI caused significant increases in expression of key autophagic proteins and morphological hallmarks of autophagy that were significantly attenuated by treatment with the NR2B antagonist Ro 25-6981. Thus, stimulation of autophagy by NR2B signaling may be regulated by redistribution of Beclin-1 in membrane rafts after TBI.

Neuronal nitric oxide synthase: structure, subcellular localization, regulation, and clinical implications

Nitric oxide (NO), a free gaseous signaling molecule, is involved in the regulation of the cardiovascular, nervous and immune system. The neurotransmitter function of nitric oxide is dependent on dynamic regulation of its biosynthetic enzyme, nitric oxide synthase (NOS). There are three types of NOS, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS). Of the three NOS, we focus on nNOS in the present review. Brain nNOS exists in particulate and soluble forms and the differential subcellular localization of nNOS may contribute to its diverse functions. Proteins bearing PDZ domains can interact directly with the PDZ domain of nNOS, influencing the subcellular distribution and/or activity of the enzyme. During the past several years, an increasing number of reports have demonstrated the importance of nNOS in a variety of synaptic signaling events. nNOS has been implicated in modulating physiological functions such as learning, memory, and neurogenesis, as well as being involved in a number of human diseases. In this review we concentrate on recent findings regarding the structural features, subcellular localization and factors regulating nNOS function. In particular, we conclude with a section discussing the role of nNOS in a wide range of physiological and pathological conditions.

Tumor necrosis factor-alpha-induced neutral sphingomyelinase-2 modulates synaptic plasticity by controlling the membrane insertion of NMDA receptors

The insertion and removal of NMDA receptors from the synapse are critical events that modulate synaptic plasticity. While a great deal of progress has been made on understanding the mechanisms that modulate trafficking of NMDA receptors, we do not currently understand the molecular events required for the fusion of receptor containing vesicles with the plasma membrane. Here, we show that sphingomyelin phosphodiesterase 3 (also known as neutral sphingomyelinase-2) is critical for tumor necrosis factor (TNF) alpha-induced trafficking of NMDA receptors and synaptic plasticity. TNFalpha initiated a rapid increase in ceramide that was associated with increased surface localization of NMDA receptor NR1 subunits and a specific clustering of NR1 phosphorylated on serines 896 and 897 into lipid rafts. Brief applications of TNFalpha increased the rate and amplitude of NMDA-evoked calcium bursts and enhanced excitatory post-synaptic currents. Pharmacological inhibition or genetic mutation of neutral sphingomyelinase-2 prevented TNFalpha-induced generation of ceramide, phosphorylation of NR1 subunits, clustering of NR1, enhancement of NMDA-evoked calcium flux and excitatory post-synaptic currents.

Near-field scanning optical microscopy detects nanoscale glycolipid domains in the plasma membrane

The localization of asialo-GM1 in ordered membrane raft domains in HeLa cells has been examined using a combination of membrane fractionation and fluorescence imaging. The glycolipid is enriched in Triton X-100 insoluble membrane fractions that contain high concentrations of cholesterol and caveolin-1 but is also found in detergent soluble membrane fractions. Near-field fluorescence microscopy shows that a fraction of the asialo-GM1 is localized in small nanoscale clusters that have an upper limit for the average diameter of approximately 90 nm and are partially colocalized with caveolae membrane domains. In addition to clusters, a diffuse, non-clustered population of asialo-GM1 is observed and is hypothesized to correspond to glycolipid isolated in detergent soluble membrane fractions.

Simvastatin reduces the association of NMDA receptors to lipid rafts: a cholesterol-mediated effect in neuroprotection

BACKGROUND AND PURPOSE

Excess brain extracellular glutamate induced by cerebral ischemia leads to neuronal death, mainly through overactivation of N-methyl-D-aspartate (NMDA) receptors. The cholesterol-lowering drugs statins have been reported to protect from NMDA-induced neuronal death but, so far, the mechanism underlying this protection remains unclear. Because NMDA receptors have been reported to be associated with the cholesterol-rich membrane domains known as lipid rafts, we have investigated the effect of treatments that deplete cholesterol levels on excitotoxicity and on association of NMDA receptors to lipid rafts.

METHODS

Primary neuronal cultures were pretreated with inhibitors of cholesterol synthesis and cholesterol, and NMDA-induced cell death was determined by measuring release of lactate dehydrogenase. Lipid raft fractions were isolated and Western blots were performed.

RESULTS

Treatment with the inhibitors of cholesterol synthesis simvastatin, which inhibits the first step of cholesterol synthesis, or AY9944, which inhibits the last step of cholesterol synthesis, protected neurons from NMDA-induced neuronal death by 70% and 54%, respectively. Treatment with these compounds reduced neuronal cholesterol levels by 35% and 13%, respectively. Simvastatin and AY9944 reduced the association of the subunit 1 of NMDA receptors (NMDAR1) to lipid rafts by 42% and 21%, respectively, and did not change total expression of NMDAR1. Addition of cholesterol reduced neuroprotection by statins and AY9944, and partially reverted the effect of simvastatin on the association of NMDAR1 to lipid rafts.

CONCLUSIONS

These data demonstrate that reduction of cholesterol levels protects from NMDA-induced neuronal damage probably by reducing the association of NMDA receptors to lipid rafts.