Changes In Membrane Properties Research Articles

Deletion of the PDR16 gene influences the plasma membrane properties of the yeast Kluyveromyces lactis.

The plasma membrane is the first line of cell defense against changes in external environment, thus its integrity and functionality are of utmost importance. The plasma membrane properties depend on both its protein and lipid composition. The PDR16 gene is involved in the control of Kluyveromyces lactis susceptibility to drugs and alkali metal cations. It encodes the homologue of the major K. lactis phosphatidylinositol transfer protein Sec14p. Sec14p participates in protein secretion, regulation of lipid synthesis, and turnover in vivo. We report here that the plasma membrane of the Klpdr16Δ mutant is hyperpolarized and its fluidity is lower than that of the parental strain. In addition, protoplasts prepared from the Klpdr16Δ cells display decreased stability when subjected to hypo-osmotic conditions. These changes in membrane properties lead to an accumulation of radiolabeled fluconazole and lithium cations inside mutant cells. Our results point to the fact that the PDR16 gene of K. lactis (KlPDR16) influences the plasma membrane properties in K. lactis that lead to subsequent changes in susceptibility to a broad range of xenobiotics.

Oxidative stress induced by cumene hydroperoxide evokes changes in neuronal excitability of rat motor cortex neurons

Oxidative stress and the production of reactive oxygen radicals play a key role in neuronal cell damage. This paper describes an in vitro study that explores the neuronal responses to oxidative stress focusing on changes in neuronal excitability and functional membrane properties. This study was carried out in pyramidal cells of the motor cortex by applying whole-cell patch-clamp techniques on brain slices from young adult rats. Oxygen-derived free radical formation was induced by bath application of 10μM cumene hydroperoxide (CH) for 30min. CH produced marked changes in the electrophysiological properties of neurons (n=30). Resting membrane potential became progressively depolarized, as well as depolarization voltage, with no variations in voltage threshold. Membrane resistance showed a biphasic behavior, increasing after 5min of drug exposure and then it started to decrease, even under control values, after 15 and 30min. At the same time, changes in membrane resistance produced compensatory variations in the rheobase. The amplitude of the action potentials diminished and the duration increased progressively over time. Some of the neurons under study also lost their ability to discharge action potentials in a repetitive way. Most of the neurons, however, kept their repetitive discharge even though their maximum frequency and gain decreased. Furthermore, cancelation of the repetitive firing discharge took place at intensities that decreased with time of exposure to CH, which resulted in a narrower working range. We can conclude that oxidative stress compromises both neuronal excitability and the capability of generating action potentials, and so this type of neuronal functional failure could precede the neuronal death characteristics of many neurodegenerative diseases.

Role of Pretreatment Option for the Membrane Based Water Purification System

A serious problem regarding membrane technologies that undermines their economics is the deterioration of permeate-flux with operation time. This flux depression may be attributed to a number of factors such as membrane fouling, concentration polarization, changes in membrane properties, and changes in the properties of the feed solution. Changes in membrane properties are due to mechanical compaction or creep (caused by application of high pressures), or to chemical deterioration. The term membrane fouling refers to pore plugging and external pore blocking resulting from deposition of submicrone-sized suspended particles and colloids on the membrane surface, precipitation of relatively smaller solute species within the membrane pores and on the surface, or both. Such fouling often leads to an irreversible flux decline during various stages of the filtration, depending on the fluid and membrane characteristics. On the other hand, the concentration polarization refers to the formation of a gel layer on the membrane surface. This gel layer is formed by the deposition of larger organic molecules such as those of natural dissolved organic matter (DOM), resulting in a localized increase in organics concentration at the membrane surface.

Liposomal Entrapment of 4-Nerolidylcatechol: Impact on Phospholipid Dynamics, Drug Stability and Bioactivity

Liposomes containing 4-nerolidylcatechol (4-NC), the major metabolite isolated from Pothomorphe umbellata, were obtained and characterized. Influence of liposomal encapsulation on chemical stability of 4-NC and on cytotoxicity profile of this drug was evaluated. Soybean phosphatidylcholine liposomes were prepared by lipid film hydration followed by extrusion. Entrapment efficiency for 4-NC was approximately 92%. Mean diameter of liposomes was 100 nm with a polydispersity index below 0.13. Liposomal 4-NC (L4-NC) and free drug (F4-NC) were submitted to forced degradation assays, monitored by HPLC. Photodegradation assay followed ICH Guidelines, using a photostability chamber equipped with both UV and white light sources. Liposomal encapsulation was able to markedly reduce 4-NC degradation rates under all the conditions tested. L4-NC showed a half-live approximately 15% higher than F4-NC under light exposure. After 72 hours, acid and base hydrolysis of F4-NC lead to 13 and 16% of degradation, respectively. However, no degradation was observed in L4-NC. EPR spectra of liposomal membrane showed that greatest changes in membrane properties were obtained when 5-doxyl stearic acid was used as the spin label, indicating a marked decrease in the fluidity of the bilayer. Following incubation with K562 cells, 4-NC showed a concentration-dependent cytotoxicity profile, while L4-NC exhibited a time and concentration-dependent profile, consistent with a controlled drug release system. F4-NC induced extensive hemolysis under isotonic conditions; conversely liposomal encapsulation protected erythrocytes from 4-NC induced lysis. Liposomal 4-NC resulted in a hemocompatibility and stable formulation, representing a viable drug delivery system to further investigate in vivo performances of 4-NC in pre clinical studies.

Adaptive Mesh Refinement and Adaptive Time Integration for Electrical Wave Propagation on the Purkinje System.

A both space and time adaptive algorithm is presented for simulating electrical wave propagation in the Purkinje system of the heart. The equations governing the distribution of electric potential over the system are solved in time with the method of lines. At each timestep, by an operator splitting technique, the space-dependent but linear diffusion part and the nonlinear but space-independent reactions part in the partial differential equations are integrated separately with implicit schemes, which have better stability and allow larger timesteps than explicit ones. The linear diffusion equation on each edge of the system is spatially discretized with the continuous piecewise linear finite element method. The adaptive algorithm can automatically recognize when and where the electrical wave starts to leave or enter the computational domain due to external current/voltage stimulation, self-excitation, or local change of membrane properties. Numerical examples demonstrating efficiency and accuracy of the adaptive algorithm are presented.

Remote ischemic preconditioning of the heart: protective responses in functional and biophysical properties of cardiac mitochondria.

Remote ischemic preconditioning (RIP)-induced protection of myocardial energetics was well documented on the level of tissue, but data concerning the involvement of mitochondria were missing. We aimed at the identification of changes in membrane properties and respiratory functions induced in rat heart mitochondria by RIP. Experiments were performed on 46 male Wistar rats divided into control and RIP-treated groups of 21 animals each. Blood flow in the occluded area was recorded by MRI angiography in four animals. RIP protocol comprised of three successive 5-min occlusions each followed by 5-min reperfusions of descending branches of the right hind limb femoral artery. The efficacy of RIP was evaluated as the extent of RIP-induced protection against damage to the functions of mitochondria isolated by differential centrifugation after 30-min global ischemia followed by 40-min reperfusion of the hearts in Langendorff mode. mitochondrial membrane fluidity with a fluorescent probe DPH, CoQ(9) and CoQ(10) with HPLC, mitochondrial respiration with the Oxygraph-2k (Oroboros). Results revealed that RIP was affecting the mitochondria. The immediate protection conferred by RIP involves beneficial and prognostically significant effects: a total elimination of ischemia/reperfusion-induced depression of mitochondrial membrane fluidity and a trend for better preservation of mitochondrial state 3 respiration.

Effects of chemical sanitization using NaOH on the properties of polysulfone and polyethersulfone ultrafiltration membranes.

Membranes used in bioprocessing applications are typically sanitized before use to insure aseptic operation. However, there is almost no information in the literature on the effects of this preuse sanitization step on the properties of the membrane. Experiments were performed with commercially available hollow fiber polysulfone (PSf) and polyethersulfone (PES) membranes with different nominal molecular weight cutoffs. Data were obtained for the membrane hydraulic permeability, dextran retention coefficients, zeta potential (surface charge), and extent of protein adsorption both before and after sanitization with 0.5 N NaOH at 45°C for 30 min. Changes in chemical composition were examined using ATR-FT-IR and XPS. Sanitization caused a large increase in the net negative charge for all membranes. There was a small reduction in hydraulic permeability and a significant increase in dextran retention for the polyethersulfone membranes, consistent with a reduction in the effective pore size. Spectroscopic analyses suggest that this change is likely due to the base-catalyzed hydrolysis of the lactam ring in polyvinylpyrrolidone (PVP) that is typically is used as a wetting/pore-forming agent in PSf and PES membranes. Preuse sanitization also appeared to have a small effect on protein adsorption, although the extent of adsorption was quite low for both the virgin and sanitized membranes. The observed changes in membrane properties could have a significant impact on the ultrafiltration performance, demonstrating the importance of standardizing the sanitization procedures even in process development and scale-down validation studies.

Cell Death Parameters as Revealed by Whole-Cell Patch-Clamp and Interval Weighted Spectra Averaging: Changes in Membrane Properties and Current Frequency of Cultured Mouse Microglial Cells Induced by Glutaraldehyde

The physiological and biochemical factors that lead to cell death have not been recognized completely. To our knowledge, there are no data on the bioelectric parameters that characterize early period of cell death, as well as on the appearance of related membrane current frequencies. We studied early parameters of glutaraldehyde (GA)-induced cell death, by examining the membrane properties of mouse microglia using the whole-cell patch-clamp technique. In addition, we investigated the GA-induced changes in the membrane current frequency, to see if characteristic frequencies would appear in dying cell. For data analysis, we applied a new approach, an improved multiple moving window length analysis and interval weighted spectra averaging (IWSA). We chose GA for its ability to induce almost instantaneous cell death. The 0.6% GA did not induce changes in the bioelectric membrane properties of microglia. However, the 3% GA caused significant decrease of membrane capacitance and resistance accompanied by the prominent increase in the membrane currents and nearly ohmic current response of microglial cells. These data indicate that 3% GA caused complete loss of the membrane function consequently inducing instantaneous cell death. The membrane function loss was characterized by appearance of the 1.26-4.62 Hz frequency peak in the IWSA spectra, while no significant increase of amplitudes could be observed for cells treated with 0.6% GA. To our knowledge, this is the first record of a frequency associated with complete loss of the membrane function and thus can be considered as an early indicator of cell death.

Chemical cleaning protocols for thin film composite (TFC) polyamide forward osmosis membranes used for municipal wastewater treatment

Recently, thin film composite (TFC) polyamide forward osmosis (FO) membranes have received attention for their potential water- and energy-related applications. TFC FO membranes have been shown to achieve both higher water flux and better solute rejection than cellulose triacetate (CTA) FO membranes. One of the major obstacles in widespread membrane use is the irreversible fouling that occurs during long-term filtration processes such as wastewater treatment. The development of proper chemical cleaning protocols for TFC FO membranes holds the key to achieving sustainable operation of FO processes. In this study, virgin membrane samples were exposed to chemical cleaning agents to determine their effects on membrane properties. In Addition, the water flux recovery efficiency of selected chemical agents was investigated by measuring the change in water flux following chemical cleaning of fouled membrane samples. Exposure of TFC membranes to commercial cleaning detergents (0.8% EDTA and 1% Alconox mixture) resulted in a dramatic increase in water and solute fluxes. Alkaline soaking led to a slight increase in the relative water and solute fluxes, while acid exposure led to a decrease in these fluxes. It was also found that the changes in membrane properties caused by Alconox exposure were irreversible, while the impacts of alkaline exposure were reversible, demonstrating that the Alconox exposure caused damage to TFC membranes. Various cleaning protocols were then developed and tested on wastewater-fouled TFC membranes. Results indicate that the use of 0.1% NaOH/0.1% sodium dodecyl sulfate (SDS) mixture cleaning followed by acid cleaning with either 2% citric acid or 0.5% HCl was the most effective cleaning strategy.

Detection of IgG, IgA, and IgM antibodies against human and plant aquaporins in patients with multiple sclerosis

istration of IL-6 increases cortical excitability, culminating in epileptiform discharges in vitro and spontaneous seizures in vivo. Intracellular slice recordings from neocortical pyramidal cells obtained from IL-6treated mice prior to the appearance of spontaneous seizures in vivo show that the cells respond to repetitive orthodromic activation by generating prolonged recovery after depolarization with no change in intrinsic membrane properties. Conclusions: These data suggest that TGF-beta signaling-induced epileptogenesis results from a differential SMAD2/3 signaling in astrocyte and microglia, resulting in IL-6-mediated dysregulation of astrocyte-neuronal interactions.

Investigation of Polyvinylidene Fluoride Membranes Prepared by Using Surfactant OP-10 Alone or with a Second Component, as Additives, via the Non-Solvent-Induced Phase Separation (NIPS) Process

Polyvinylidene fluoride (PVDF) flat-sheet membranes were prepared via a non-solvent-induced phase separation (NIPS) method at 60°C using a hydrophilic surfactant OP-10 (octylphenol polyoxyethylene ether) solely (Blank) or with a second additive [H2O or lithium chloride (LiCl)] as pore-forming agents. The influence of OP-10 concentration on the surface tension, viscosity, and precipitation rate of PVDF/(H2O, LiCl, or Blank) systems were investigated, and the ultrafiltration and mechanical properties of the resultant membranes were measured. It was found that an increased demixing rate during the coagulation process was the reason for the change in membrane morphology and properties. An obviously improved flux and slightly decreased mechanical properties and rejection were found in membranes prepared using a high concentration of OP-10 and the second component as additives. SEM pictures revealed an increased porous structure on the resultant membrane surface. A hypothesis was proposed to explain these phenomena; the reoriented surfactant molecules at the interface facilitated the water diffusion channels, which finally became the porous structure on the membrane surface. The weakened mechanical properties were due to the macrovoid structure in its membrane cross-section, which developed from the micelle structure in the casting solution. This hypothesis was further confirmed in a PVDF/OP-10/polyethylene glycol (PEG) system. A consistent conclusion was obtained.

Orientational Ordering of Carotenoids in Myelin Membranes Resolved by Polarized Raman Microspectroscopy

We study orientational ordering of membrane compounds in the myelinated nerve fiber by means of polarized Raman microspectroscopy. The theory of orientational distribution functions was adapted to live-cell measurements. The obtained orientational distribution functions of carotenoids and lipid acyl chain clearly indicated a predominantly radial-like orientation in membranes of the myelin. Two-dimensional Raman images, made under optimal polarization of incident laser beam, corroborated the proposed carotenoid orientation within the bilayer. Experimental data suggested the tilted orientation of both carotenoid polyenic and lipid acyl chains. The values of maximum tilt angles were similar, with possible implication of carotenoid-induced ordering effect on lipid acyl chains, and hence change of myelin membrane properties. This study stages carotenoids of the nerve as possible mediators of excitation and leverages underlying activity-dependent membrane reordering.

Conductance modulation of charged lipid bilayer using electrolyte-gated graphene-field effect transistor.

Graphene is an attention-grabbing material in electronics, physics, chemistry, and even biology because of its unique properties such as high surface-area-to-volume ratio. Also, the ability of graphene-based materials to continuously tune charge carriers from holes to electrons makes them promising for biological applications, especially in lipid bilayer-based sensors. Furthermore, changes in charged lipid membrane properties can be electrically detected by a graphene-based electrolyte-gated graphene field effect transistor (GFET). In this paper, a monolayer graphene-based GFET with a focus on the conductance variation caused by membrane electric charges and thickness is studied. Monolayer graphene conductance as an electrical detection platform is suggested for neutral, negative, and positive electric-charged membrane. The electric charge and thickness of the lipid bilayer (QLP and LLP) as a function of carrier density are proposed, and the control parameters are defined. Finally, the proposed analytical model is compared with experimental data which indicates good overall agreement.

Risk Factors for Post-Traumatic Epilepsy in Adults

Craniocerebral trauma (CCT) is the cause of 20% ofsymptomatic and 5% of all cases of epilepsy [23]. In Russia,CCT is the main cause (27.7%) of location-dependentepilepsy in adults [1, 18].Post-traumatic epilepsy (PTE) is one of the late and mostserious complications of CCT. CCT and, hence, the possiblerisk of PTE, is most common in the age range 15–34 years,where the number of cases is about 30% [30]. The mostimportant cause of CCT consists of transport accidents (most-ly traffic accidents), as well as domestic, sporting, and indus-trial accidents, as well as military injuries.Assessment of the morbidity of PTE involves use of var-ious definitions of CCT itself and PTE [17], as well as dif-ferent durations of studies. This is because the developmentof PTE requires a stably developed focus of epileptic activityresulting from organic brain injury [1, 29]. The mechanismsof epileptogenesis are tightly linked with the course of recov-ery processes after CCT or the occurrence of aberrant plas-ticity. The most important are changes in neurotransmitterprocesses, sprouting, the various mechanisms of neurondeath, changes in membrane and receptor properties, and theformation of hyperexcitable neuronal systems [19]. Whileepileptic activity during the acute phase of traumatic braininjuries results from cortical injury and the nonspecificresponse to intense physical actions (the mechanisms of pri-mary brain damage), in the later period of trauma, the harm-ful actions of free radicals and excitotoxicity due to gluta-mate accumulation (the mechanism of delayed secondarybrain damage) are probably more important [30]. An impor-tant role here is played by impairments to cellular andhumoral immunity and disintegration of the functions ofautonomic and humoral-endocrine regulation [1]. In allcases, genetic predisposition factors are of undoubted impor-tance, though they are complex and heterogeneous [17, 21].PTE should also be discriminated from post-traumaticseizures. PTE includes repeated, late (i.e., onset more thanone week after CCT) post-traumatic seizures [15, 23, 51].Post-traumatic epileptic seizures include any epilepticseizure developing as a result of CCT [21, 34, 35]. Epilepticseizures can develop at different times after CCT. In assess-ing the periods of onset of epileptic seizures, most authorsuse the Barolin et al. classification [5], initially developedfor epileptic seizures in cerebrovascular diseases. This clas-sification identifies the following types of epileptic seizures:immediate, developing within the first 24 h; early, develop-ing at 1–7 days from onset of illness; and late, starting atseven or more days.The time of onset and the frequency of development ofepileptic seizures depend on the type, location, and volumeof the focus of brain damage and the state of the premorbidbackground of the patient (presence of cerebrovascular dis-ease, repeated CCT in the history, genetic predisposition,chronic alcoholism, etc.) [1]. The incidence of early post-traumatic seizures is 3–5%, compared with an incidence of

Pyramidal Cell Selective Ablation of N-Methyl-D-Aspartate Receptor 1 Causes Increase in Cellular and Network Excitability

BackgroundNeuronal activity at gamma frequency is impaired in schizophrenia (SZ) and is considered critical for cognitive performance. Such impairments are thought to be due to reduced N-methyl-D-aspartate receptor (NMDAR)-mediated inhibition from parvalbumin interneurons, rather than a direct role of impaired NMDAR signaling on pyramidal neurons. However, recent studies suggest a direct role of pyramidal neurons in regulating gamma oscillations. In particular, a computational model has been proposed in which phasic currents from pyramidal cells could drive synchronized feedback inhibition from interneurons. As such, impairments in pyramidal neuron activity could lead to abnormal gamma oscillations. However, this computational model has not been tested experimentally and the molecular mechanisms underlying pyramidal neuron dysfunction in SZ remain unclear. MethodsIn the present study, we tested the hypothesis that SZ-related phenotypes could arise from reduced NMDAR signaling in pyramidal neurons using forebrain pyramidal neuron specific NMDA receptor 1 knockout mice. ResultsThe mice displayed increased baseline gamma power, as well as sociocognitive impairments. These phenotypes were associated with increased pyramidal cell excitability due to changes in inherent membrane properties. Interestingly, mutant mice showed decreased expression of GIRK2 channels, which has been linked to increased neuronal excitability. ConclusionsOur data demonstrate for the first time that NMDAR hypofunction in pyramidal cells is sufficient to cause electrophysiological, molecular, neuropathological, and behavioral changes related to SZ.

Maturation of membrane properties of neurons in the rat deep cerebellar nuclei.

Patch clamp recordings of neurons in the adult rat deep cerebellar nuclei have been limited by the availability of viable brain slices. Using a new slicing technique, this study was designed to explore the maturation of membrane properties of neurons in the deep cerebellar nuclei (DCN)-an area involved in rat eyeblink conditioning. Compared to whole-cell current-clamp recordings in DCN in rat pups at postnatal day 16 (P16) to P21, recordings from weanling rats at P22-P40 revealed a number of significant changes including an increase in the amplitude of the afterhyperpolarization (AHP)-an index of membrane excitability which has been shown to be important for eyeblink conditioning-a prolonged interval between the first and second evoked action potential, and an increase in AHP amplitude for hyperpolarization-induced rebound spikes. This is the first report of developmental changes in membrane properties of DCN which may contribute to the ontogeny of eyeblink conditioning in the rat.

Delayed Effects of Corticosterone on Slow After-Hyperpolarization Potentials in Mouse Hippocampal versus Prefrontal Cortical Pyramidal Neurons

The rodent stress hormone corticosterone changes neuronal activity in a slow and persistent manner through transcriptional regulation. In the rat dorsal hippocampus, corticosterone enhances the amplitude of calcium-dependent potassium currents that cause a lingering slow after-hyperpolarization (sAHP) at the end of depolarizing events. In this study we compared the putative region-dependency of the delayed effects of corticosterone (approximately 5 hrs after treatment) on sAHP as well as other active and passive properties of layer 2/3 pyramidal neurons from three prefrontal areas, i.e. the lateral orbitofrontal, prelimbic and infralimbic cortex, with the hippocampus of adult mice. In agreement with previous studies, corticosterone increased sAHP amplitude in the dorsal hippocampus with depolarizing steps of increasing amplitude. However, in the lateral orbitofrontal, prelimbic and infralimbic cortices we did not observe any modifications of sAHP amplitude after corticosterone treatment. Properties of single action potentials or % ratio of the last spike interval with respect to the first spike interval, an indicator of accommodation in an action potential train, were not significantly affected by corticosterone in all brain regions examined. Lastly, corticosterone treatment did not induce any lasting changes in passive membrane properties of hippocampal or cortical neurons. Overall, the data indicate that corticosterone slowly and very persistently increases the sAHP amplitude in hippocampal pyramidal neurons, while this is not the case in the cortical regions examined. This implies that changes in excitability across brain regions reached by corticosterone may vary over a prolonged period of time after stress.

Osmotic stress affects the stability of freeze-dried Lactobacillus buchneri R1102 as a result of intracellular betaine accumulation and membrane characteristics

To help cells to better resist the stressful conditions associated with the freeze-drying process during starter production, we investigated the effect of various osmotic conditions on growth, survival and acidification activity of Lactobacillus buchneri R1102, after freeze-drying and during storage for 3 months at 25°C. High survival rates during freeze-drying, but not during storage, were obtained when 0·1 mol l(-1) KCl was added at the beginning of fermentation, without any change in membrane properties and betaine accumulation. This condition made it possible to maintain a high acidification rate throughout the process. In contrast, the addition of 0·6 mol l(-1) KCl concentrations at the beginning of fermentation led to a high survival rate during storage that was related to high intracellular betaine levels, low membrane fluidity and high cycC19:0 concentrations. However, these modifications induced the degradation of acidification activity during storage. When a moderate stress was applied by combining 0·1 mol l(-1) KCl at the beginning and 0·6 mol l(-1) KCl at the end of fermentation, betaine accumulated in the cells without any membrane alteration, allowing them to maintain high acidification activity and survival rate during storage. Specific osmotic conditions during fermentation induced intracellular betaine accumulation and modifications of membrane character-istics, thus affecting stress resistance of Lact. buchneri R1102. A slight osmotic stress made it possible to maintain a high acidification activity, whereas a high osmotic stress at the end of fermentation led to the preservation of cell survival during freeze-dried storage. This study revealed that the survival and preservation of acidification activity of freeze-dried Lact. buchneri R1102 during starter production can be improved by using appropriate osmotic conditions.

Striatal synaptic dysfunction and hippocampal plasticity deficits in the Hu97/18 mouse model of Huntington disease.

Huntington disease (HD) is a fatal neurodegenerative disorder caused by a CAG repeat expansion in the gene (HTT) encoding the huntingtin protein (HTT). This mutation leads to multiple cellular and synaptic alterations that are mimicked in many current HD animal models. However, the most commonly used, well-characterized HD models do not accurately reproduce the genetics of human disease. Recently, a new ‘humanized’ mouse model, termed Hu97/18, has been developed that genetically recapitulates human HD, including two human HTT alleles, no mouse Hdh alleles and heterozygosity of the HD mutation. Previously, behavioral and neuropathological testing in Hu97/18 mice revealed many features of HD, yet no electrophysiological measures were employed to investigate possible synaptic alterations. Here, we describe electrophysiological changes in the striatum and hippocampus of the Hu97/18 mice. At 9 months of age, a stage when cognitive deficits are fully developed and motor dysfunction is also evident, Hu97/18 striatal spiny projection neurons (SPNs) exhibited small changes in membrane properties and lower amplitude and frequency of spontaneous excitatory postsynaptic currents (sEPSCs); however, release probability from presynaptic terminals was unaltered. Strikingly, these mice also exhibited a profound deficiency in long-term potentiation (LTP) at CA3-to-CA1 synapses. In contrast, at 6 months of age we found only subtle alterations in SPN synaptic transmission, while 3-month old animals did not display any electrophysiologically detectable changes in the striatum and CA1 LTP was intact. Together, these data reveal robust, progressive deficits in synaptic function and plasticity in Hu97/18 mice, consistent with previously reported behavioral abnormalities, and suggest an optimal age (9 months) for future electrophysiological assessment in preclinical studies of HD.

Differential Roles of Nonsynaptic and Synaptic Plasticity in Operant Reward Learning-Induced Compulsive Behavior

Rewarding stimuli in associative learning can transform the irregularly and infrequently generated motor patterns underlying motivated behaviors into output for accelerated and stereotyped repetitive action. This transition to compulsive behavioral expression is associated with modified synaptic and membrane properties of central neurons, but establishing the causal relationships between cellular plasticity and motor adaptation has remained a challenge. We found previously that changes in the intrinsic excitability and electrical synapses of identified neurons in Aplysia's central pattern-generating network for feeding are correlated with a switch to compulsive-like motor output expression induced by in vivo operant conditioning. Here, we used specific computer-simulated ionic currents in vitro to selectively replicate or suppress the membrane and synaptic plasticity resulting from this learning. In naive in vitro preparations, such experimental manipulation of neuronal membrane properties alone increased the frequency but not the regularity of feeding motor output found in preparations from operantly trained animals. On the other hand, changes in synaptic strength alone switched the regularity but not the frequency of feeding output from naive to trained states. However, simultaneously imposed changes in both membrane and synaptic properties reproduced both major aspects of the motor plasticity. Conversely, in preparations from trained animals, experimental suppression of the membrane and synaptic plasticity abolished the increase in frequency and regularity of the learned motor output expression. These data establish direct causality for the contributions of distinct synaptic and nonsynaptic adaptive processes to complementary facets of a compulsive behavior resulting from operant reward learning.