We have used P301S human tau transgenic mice (Yoshiyama et al., 2007) to test intracerebroventricular (ICV) administration of three different C646 supplier anti-tau antibodies selected for their ability to block tau seeding activity in vitro and to block tau uptake into cells. We have previously

observed that tau aggregates, but not monomer, are up taken by cultured cells and that internalized tau aggregates trigger intracellular tau aggregation in recipient cells (Frost et al., 2009 and Kfoury et al., 2012). We characterized the HJ8 series of eight mouse monoclonal antibodies (raised against full-length human tau) and HJ9 series of five antibodies (raised against full-length mouse tau) in an adapted cellular biosensor system we have previously described (Kfoury et al., 2012) that measures cellular tau aggregation induced by the addition of brain lysates containing tau aggregates. The click here antibodies had variable effects in blocking seeding, despite the fact that all antibodies efficiently bind tau monomer and stain neurofibrillary tangles. We selected three antibodies with different potencies in blocking seeding for our studies. Prior to testing in vivo, we

determined the binding affinities and epitopes of the antibodies, which are all IgG2b isotype. We immobilized human and mouse tau on a sensor chip CM5 for surface plasmon resonance (SPR) (Figure 1). The HJ9.3 antibody, raised against mouse tau, recognizes both human (Figure 1A) and mouse (Figure 1B) tau with the same binding constant (KD = Kd/Ka = 100 pM) (Figure 1G). The association (Ka) and dissociation (Kd) rate constants were calculated by using BIAevaluation software (Biacore AB) selecting Fit kinetics simultaneous Ka/Kd (Global fitting) with 1:1 (Langmuir) interaction model. The Ka and Kd of HJ9.3 toward human (Ka = 7.5 × 104 Ms−1, Kd = 7.5 × 10−6 s−1) and mouse (Ka = 8.6 × 104 Ms−1, Kd = Thalidomide 9.1 × 10−6 s−1) indicate strong binding to both. We mapped the epitope of HJ9.3 to the repeat domain (RD) region, between amino acids 306–320. HJ9.4, raised against mouse tau, had high affinity KD (2.2

pM) toward mouse tau with a high association rate constant (Ka = 2.28 × 105 Ms−1) and very low dissociation constant (Kd = 5.1 × 10−7 s−1) ( Figures 1D and 1G). However, the same antibody had a much lower affinity (KD = 6.9 nM) toward human tau ( Figures 1C and 1G), with a similar association rate constant (Ka = 1.5 × 105 Ms−1) as mouse tau but with much faster dissociation (Kd = 1.07 × 10−3 s−1). Thus, the HJ9.4 interaction with human tau is less stable than with mouse tau. The epitope for this antibody is amino acids 7–13. HJ8.5 was raised against human tau. It binds to human tau ( Figure 1E) but not to mouse tau ( Figure 1F). The KD (0.3 pM) ( Figures 1E and 1G) and low dissociation rate (Kd = 4.38 × 10−8 s−1) indicate that HJ8.5 binds human tau with very high affinity. We mapped the epitope of HJ8.

1% of the serum levels). Thus, initial Aβ immunotherapy studies were met with some skepticism regarding how such a small amount of antibody could have robust effects on brain Aβ deposition.

Nevertheless, because Aβ is a normally secreted protein and primarily deposits outside of cells in the brain parenchyma, the concept that an anti-Aβ antibody present at low levels in the brain interstitial fluid could affect Aβ deposition was at AZD5363 manufacturer least partly accepted by the field. In contrast, when proof-of-concept studies emerged suggesting that active and passive anti-tau immunotherapy might also attenuate tau pathology in mouse models, there was substantial skepticism of how extracellular anti-tau antibodies could target intracellular tau inclusions (reviewed in Gu and Sigurdsson, 2011). Moreover, given the variance in degree of pathology in tau mouse models and the rather modest effects seen in initial studies, skepticism remained regarding the potential therapeutic utility of anti-tau immunotherapy. In the current study, Yanamandra et al. (2013) provide in vivo preclinical data in a P301S mouse model of tauopathy showing that direct chronic infusion of select anti-tau antibodies is efficacious. Not only did select tau antibodies suppress tau pathology, they also improved cognitive function. Moreover, by selecting tau antibodies based

on their empirical ability I-BET-762 cell line to block exogenous seeding of tau inclusions in cell culture, Yanamandra et al. (2013) established a method to rapidly identify potentially efficacious antibodies for in vivo testing. The most effective antibodies in vitro

Edoxaban were also the most effective at attenuating pathology in vivo. This is important as it supports Yanamandra et al. (2013)’s assertion that the most likely mechanism of action is targeting tau released from cells (see Figure 1) that is potentially capable of nucleating pathology in neighboring cells (Frost et al., 2009). As Yanamandra et al. (2013) discuss, there are other plausible mechanisms by which anti-tau antibodies could attenuate pathology and additional study will be important. For example, if an antibody-tau complex gains entry to the cell or the antibody gains entry and then binds intracellular tau, the complex could be recognized by TRIM21—a protein that contains the highest affinity IgG heavy chain (Fc) binding domain of any mammalian protein and a ubiquitin ligase domain (McEwan et al., 2011)—thus targeting the complex for degradation by the proteosome. There is also evidence that neurons have Fc receptors, which could play a role in internalization of tau antibodies (Mohamed et al., 2002). Although Yanamandra et al. (2013) did not detect intraneuronal anti-tau IgGs, others have reported the presence of tau antibodies in neurons following immunotherapy.

, 2013). As reviewed above, VCI can stem from a wide variety of cardiovascular and cerebrovascular pathologies, but it has been difficult to pin IWR-1 ic50 down the contribution of each condition to cognitive dysfunction because of the coexistence of the different lesions and overlap with neurodegenerative pathology (Gorelick et al., 2011). Reductions

in global cerebral perfusion, such as those caused by heart diseases or carotid artery stenosis/occlusion, if below a critical threshold, can impair cognition independently of brain lesions (Marshall et al., 2012). Reductions in CBF by 40%–50% are associated with suppression of brain activity and cognitive dysfunction, which are reversible upon re-establishing normal CBF levels (Marshall et al., 1999, Marshall, 2012 and Tatemichi et al., 1995). As for the other pathologies underlying VCI, there is a general correlation between the total burden of vascular pathology and cognitive deficits (Gelber et al., 2012, Gorelick et al., 2011 and Inzitari Selleck SB203580 et al., 2009). A caveat is that, due to confounding factors, such as overlap

with AD, differences in educational level (see below), and microscopic pathology not seen by in vivo imaging, the exact parameters of the relationship have been hard to define (Black et al., 2009 and Brickman et al., 2011). However, there is general consensus that cognitive impairment results from the brain dysfunction caused by cumulative tissue damage (Gorelick et al., 2011), as originally proposed by Tomlinson et al. for large cerebral infarcts

(Tomlinson et al., 1970). In addition to gray matter damage, disruption of the white matter can have profound effects on the precision and fidelity of the information transfer underlying brain function and cognitive health (Nave, 2010a). Fast-conducting myelinated white matter tracts are responsible for long-range connectivity, interhemispheric synchronization, and neurotrophic effects through spike-timing-dependent plasticity and axonal transport (Dan and Poo, 2004, Nave, 2010a and Stone and Tesche, 2013). Indeed, white matter lesions affect brain structure and function broadly and are associated with reductions in frontal lobe glucose utilization (DeCarli et al., 1995, Haight not et al., 2013 and Tullberg et al., 2004), global reduction in cortical blood flow (Appelman et al., 2008, Chen et al., 2013a, ten Dam et al., 2007 and Kobari et al., 1990), disruption of brain connectivity (Lawrence et al., 2013 and Sun et al., 2011), and cerebral atrophy (Appelman et al., 2009). In addition, since myelination of previously naked fibers participates in neuroplasticity and skilled motor learning (Fields, 2010 and Richardson et al., 2011), myelin damage could also compromise these important functions and contribute to cognitive impairment.

, 2003). Furthermore, very similar defects in synaptic development occur when presynaptic miniature

neurotransmitter release is diminished by vglut mutations. Therefore, inhibition of the production or detection of postsynaptic GSK1210151A nmr miniature events results in developmental defects consistent with a transsynaptic signal. Moreover, additionally increasing or decreasing evoked release, when miniature NT is depleted, does not further alter synaptic development. In contrast, restoring miniature NT in iGluR mutants with either Drosophila or mammalian receptors can rescue normal terminal morphology. These results indicate that it is the discrete contribution of miniature NT rather than the total quantity of vesicular NT that is the critical factor necessary for normal synapse development. Therefore, the role of small miniature events during synapse development is qualitatively rather than quantitatively different from

the function of larger evoked events. Miniature neurotransmission thus seems to act as a parallel second layer of synaptic communication with a unique and essential Ku0059436 role in promoting normal synaptic structural development. Depletion of miniature NT results in terminals with aberrantly large numbers of small boutons. Two lines of evidence suggest that these small boutons are stalled in an immature phase of a normal growth process. First, live imaging revealed that when miniature NT is depleted, new boutons form at normal frequency but then fail to subsequently expand, unlike wild-type boutons. Second, small boutons in miniature NT mutants have synapse marker and ultrastructure features that appear PAK6 identical to the small boutons of wild-type animals. These stalled boutons appear different from the aberrant small “satellite boutons” that occur when endocytosis is disrupted and have different synaptic marker and ultrastructure characteristics to normal boutons (Dickman et al., 2006). Therefore, our data support that miniature NT is critical for the normal progression of synaptic maturation. Since miniature

NT is also a component of synaptic activity, it is intriguing to speculate that miniature events could contribute activity-dependent synaptic structural plasticity. The discrete effect of altering miniature NT on individual bouton maturation coupled with the spatially restricted nature of these small events suggested a localized signaling activity. This was supported by our demonstration that miniature NT can regulate the development of individual synaptic terminals within a single neuron independently of each other. Interestingly, in cultured mammalian neurons, that activity of miniature NT on synaptic scaling also acts the levels of individual dendritic branches (Sutton et al., 2006), consistent with localized molecular signaling induced by miniature events in both paradigms.

, 2008 and Upton et al., 1999), we screened several SERT-Cre lines

to determine if any expressed Cre specifically in ipsilateral RGCs (Gong et al., 2007). Because dLGN neurons also express SERT during development (Lebrand click here et al., 1996), we sought Cre lines with no SERT-Cre expression in the dLGN. One line, ET33 SERT-Cre (see Experimental Procedures), was a promising candidate; consequently, we crossed the ET33 SERT-Cre to various Cre-dependent reporter mice to determine the spatial and temporal pattern of Cre expression. Ipsilateral-projecting RGCs reside in the ventral-temporal retina (Dräger and Olsen, 1980) (Figure 1A). We therefore examined the location of the Cre-expressing RGCs in retinal flat mounts and transverse sections (Figures 1B–1D). The spatial distribution of the Cre-expressing cells matched the predicted distribution for ipsilateral RGCs (Figures 1B and 1D), plus a thin strip of cells in the dorsal-nasal retina (Figure 1B), a pattern that closely matches SERT expression (García-Frigola and Herrera, 2010). Moreover, most of

the Cre-expressing cells were located in the RGC layer (Figure 1D) and extended axons to the optic nerve CHIR-99021 purchase head, suggesting they were RGCs (Figure 1C). Next we examined retinogeniculate projections labeled by Cre-driven expression of mGFP or tdTomato and compared them to projections labeled by intraocular injections of the anterograde tracer cholera toxin beta (CTb). If Cre expression is restricted to ipsilateral RGCs one would expect the genetically labeled axons to selectively overlap with the CTb-labeled axons very from the ipsilateral eye (Figures 1E and 1F). Indeed, that is what we observed (Figures 1I–1L). In addition, a small population of Cre reporter-labeled

axons was present in the intergeniculate leaflet (IGL), a thin nucleus that resides between the dLGN and vLGN (Figure 1G). To be certain that the genetically labeled axons arose exclusively from the ipsilateral eye, we removed one eye from an ET33-Cre::tdTomato mouse, allowed 2 weeks for the severed axons to degenerate, and then visualized the intact projections that remained. Axons from the intact eye projected ipsilaterally, whereas the contralateral dLGN was devoid of signal (Figure S1B, available online). We also noticed a small Cre-labeled projection to the contralateral IGL (Figure S1B) that probably arose from the small cohort of Cre RGCs in the dorsal-nasal retina (Figure 1B). Importantly, the enucleation experiments also confirmed that little to no Cre expression was apparent in dLGN neurons in ET33-Cre mice (Figure 1I and Figure S1B). Together these data indicate that ET33-Cre is nearly exclusively expressed in ipsilateral-projecting RGCs. ET33-Cre mice provide a powerful opportunity to selectively alter gene expression in ipsilateral-projecting RGCs.

, 1995). We are not aware of previous evidence that endocytosis augments the acute cAMP response mediated by any signaling receptor. Our study focused on cells in which D1 receptors are primarily thought to endocytose via clathrin-coated pits. There is evidence that caveolae mediate a slower component of D1 receptor endocytosis in other

cells, but this is not thought to affect the acute cAMP signal (Kong et al., 2007). As such, we believe that the presently identified role of endocytosis in supporting acute D1 receptor-mediated signaling is unique. What is the mechanism by which rapid endocytosis contributes to dopaminergic signaling? We initially favored the hypothesis that this augmentation might occur Alisertib mw by rapid cycling of receptors back to the plasma membrane. This was motivated by analogy with the resensitization paradigm established for several other GPCRs. As presently understood, however, the resensitization paradigm explains recovery of signal responsiveness after prolonged or repeated activation, and does

not affect the acute signaling response (Lefkowitz, 1998 and Pippig et al., 1995). Nevertheless, given the rapid kinetics with which D1 receptors were found to traverse Temozolomide solubility dmso the recycling pathway, we considered the hypothesis that D1 receptors might recycle so rapidly that their resensitization might have been missed by the previous paradigm. We rejected this hypothesis because genetic (EHD3 knockdown) and chemical (bafilomycin A1) inhibition of the recycling pathway did not affect D1 receptor-mediated cAMP accumulation, in contrast to the pronounced inhibition produced by various endocytic inhibitors. Our results thus support the alternative hypothesis that endocytosis augments acute dopaminergic signaling by facilitating direct D1 receptor-mediated signaling from a membrane domain in the early endocytic pathway (Figure 8E). This is supported by immunocytochemical localization data showing close proximity between D1 receptors and downstream transduction machinery upon initial entry

to the endocytic pathway. While there nearly is no doubt that the plasma membrane is a major site of GPCR signaling, there is emerging evidence that signaling can also occur from the endocytic pathway, and there is presently no compelling reason to rule out endosomal signaling via trimeric G proteins (Calebiro et al., 2010 and Sorkin and von Zastrow, 2009). Trimeric G proteins have previously been detected on endomembrane compartments in mammalian cells and tissues (Marrari et al., 2007). Further, G protein α-subunits can mediate functionally significant signaling from endosomes in yeast (Slessareva and Dohlman, 2006). Recent evidence suggests that two other mammalian GPCRs (the TSH and PTH receptors) signal via G protein-linked activation of AC directly from the endosome membrane (Calebiro et al., 2009 and Ferrandon et al., 2009).

001 ± 0.041 SEM; Vcarb/tail = 0.096 ± 0.031; Vamph = 0.031 ± 0.019; V ureth = −0.032 ± 0.09; pureth = 0.9; pcarb/tail = 0.025; pamph = 0.043; pMK = 0.7; t test). With EV, we observed significant replay after stimulation only in the amphetamine condition Adriamycin manufacturer (p < 0.05; paired t test), although EV had a tendency to have higher values than the control data (reverse EV)

for other experimental conditions (see Figures S6B–S6E). It should be noted that EV is insensitive to fine-scale temporal spiking patterns and thus provides different information from that obtained with latency measures or template matching. Memory formation is one of the most important processes in the brain, yet the neuronal dynamics underlying this process are only beginning to be understood, partly due to the technical

difficulty of recording from large neuronal populations in behaving animals. Here, we report that the hallmarks of memory formation and memory replay—stimulus-induced sequential activity patterns that reactivate spontaneously—can also be observed in urethane-anesthetized rats. In this preparation, AG-014699 mw population recordings and other brain manipulations can be more easily performed, thus providing a convenient model for electrophysiological study of mechanisms, leading to formation of sequential patterns implicated in memory processes. Furthermore, we found similar replay in both somatosensory and auditory cortices, suggesting this may be a general mechanism in the cortex. Although previous studies using voltage-sensitive dye imaging in anesthetized animals have shown that ongoing Mephenoxalone spontaneous activity can reflect stimulus-evoked spatial patterns on a coarse spatial scale (Han et al., 2008 and Kenet et al., 2003), our findings provide a major refinement of these results by demonstrating replay of fine-scale sequential spiking patterns (Figures 2 and 3) that is more analogous to sequential spiking patterns observed during memory replay in freely moving animals

(Euston et al., 2007, Hoffman and McNaughton, 2002, Kudrimoti et al., 1999, Skaggs and McNaughton, 1996 and Wilson and McNaughton, 1994). In addition, our study indicates the importance of brain state during stimulus presentation. Although multiple studies show that most memory replay occurs during synchronized states (e.g., during slow wave sleep; Battaglia et al., 2004 and Xu et al., 2012), the importance of the brain state during encoding is not clear. It is known that electrically evoked LTP is suppressed in this state ( Leonard et al., 1987), so there is a precedent for our current finding that presentation of stimuli during a desynchronized state as compared to the synchronized state is significantly more effective in inducing lasting reorganization of temporal patterns ( Figures 2 and 6), which subsequently results in stronger spontaneous replay of stimulus-induced patterns.

, 2006). Enriched on the spines of CA1 pyramidal neurons, Kv4.2 is under the regulation of synaptic activity and it in turn contributes to the regulation of synaptic plasticity (Kim et al., 2007 and Jung

et al., selleck compound 2008). Whether Kv4.2 mRNA is targeted to dendrites to present the opportunity of local regulation by synaptic activity is an open question. How Kv4.2 regulation may help neurons to stay within the dynamic range of synaptic plasticity is another open question. Whereas the rapid downregulation of Kv4.2 upon N-methyl-D-aspartate receptor (NMDAR) activation due to its internalization and degradation ( Kim et al., 2007, Lei et al., 2008 and Lei et al., 2010) provides positive feedback to enhance excitation, the dendritic potassium channel level

has to quickly recover after a barrage of synaptic activities, given that loss of Kv4.2 function causes enhanced induction of LTP ( Chen et al., 2006) while increasing Kv4.2 expression abolishes the ability to induce LTP ( Jung et al., 2008). Because alteration of Kv4.2 levels is associated with epilepsy and possibly Alzheimer’s disease ( Birnbaum et al., 2004) and the KCND2 gene coding for Kv4.2 is near rearrangement breakpoints in autism patients ( Scherer et al., 2003), better understanding of the dynamic regulation of Kv4.2 by synaptic activities will help future analyses of the contribution of this potassium channel to neuronal signaling as well as its involvement in neurological and mental disorders. The importance of local synthesis of dendritic proteins crotamiton in synaptic plasticity (Kelleher et al., 2004 and Sutton and Schuman, 2005) has stimulated recent studies on trafficking ABT-888 molecular weight of neuronal RNA granules (Kiebler and Bassell, 2006), regulation of local synthesis of synaptic proteins (Schuman et al., 2006 and Sutton and Schuman, 2005) and mRNA transport (Sossin and DesGroseillers, 2006). One of the RNA binding proteins implicated is the fragile X mental retardation protein (FMRP) linked to Fragile X syndrome (FXS), the most common

heritable mental retardation that is often associated with autism (Bagni and Greenough, 2005). Multiple symptoms of FXS patients including the altered spine morphology (Greenough et al., 2001, Hinton et al., 1991 and Irwin et al., 2001) is recapitulated in fmr1 knockout (KO) mice ( Comery et al., 1997 and Nimchinsky et al., 2001), which also display compromised learning, abnormal behavior and altered synaptic plasticity ( Penagarikano et al., 2007). This mouse model of FXS is therefore a suitable system for examining FMRP contribution to synaptic regulation of local translation. FMRP can bind to its target mRNA directly or indirectly (Bagni and Greenough, 2005). It has multiple RNA-binding domains and may regulate mRNA localization (Dictenberg et al., 2008), mRNA stability (Zalfa et al., 2007) or mRNA translation (Muddashetty et al., 2007 and Zalfa et al., 2003) in central neurons (Bassell and Warren, 2008). Because FMRP is localized to dendrites and spines (Antar et al.

He entered State University of New York (SUNY) Downstate as an

MD-PhD trainee, but as science was his passion, he completed only his PhD, focusing on the neuroanatomic analysis of visual projections. In 1978, he moved to NYU for his postdoctoral fellowship. At this time, the Department of Cell Biology at Veliparib in vivo NYU, under the leadership of David Sabatini, was in the vanguard of elucidating mechanisms of membrane protein biosynthesis and trafficking. Dave credited this fellowship and Sabatini with introducing him to myelinating glia as a spectacular model of cell polarity and membrane biogenesis. The strong cell biological perspective he acquired at NYU was a hallmark of Dave’s work throughout his career.

During this fellowship, Dave investigated the pathways of myelin protein biosynthesis. This resulted in a beautiful, foundational paper (Colman et al., 1982) that demonstrated that specific myelin proteins are synthesized on either ER-bound or free polysomes BKM120 research buy and, accordingly, follow different routes to the myelin sheath. Unexpectedly, he also found that mRNAs for the major proteins were differentially distributed in the oligodendrocyte, i.e., PLP and MBP mRNAs were enriched in the oligodendrocyte soma versus processes, respectively. This was a striking, early example of the phenomenon of local mRNA translation: a finding that helped establish that segregation and delivery of mRNAs, and their translation products, are an important general phenomenon in mammalian cells. This early work impressed many in the myelin field, including two of us (P.J.B. and J.L.S.) sufficiently that we went to NYU in 1984 in order to work with Dave, who was just starting L-NAME HCl his own laboratory. It is a testament to the happy and productive atmosphere of the fledgling Colman laboratory that, despite or perhaps because the three of us shared a 9 foot laboratory bench for the better part of a year, this

experience was the foundation of lifelong friendships and a series of coauthored publications (most recently, Tait et al., 2000). A later visit to Scotland, during one such collaboration, stimulated Dave’s interest in all matters Scotch and culminated some years later in a visit to New Jersey to acquire a sheep’s stomach in order to cook authentic haggis for Robbie Burns Night. While it took some time for the smell to clear, the good spirits survived even this. In starting his own laboratory, David set out to clone several key myelin proteins using the recently described lambda GT11 system expression cloning system (Young and Davis, 1983). This was an early, exciting era in cloning, prior to kits or PCR.

, 2009). Furthermore, numerous animal studies using toxin-induced models of PD have shown that modulating the inflammatory response can ameliorate neuronal loss (Wang et al., 2005). However, it remains unclear

how these models relate to the slowly progressive neurodegeneration that occurs in patients with idiopathic or familial forms of PD. As PD is associated with an abnormal accumulation of α-synuclein into Lewy bodies, one hypothesis is that misfolded α-synuclein induces an inflammatory response. This could occur either through the release of α-synuclein into the extracellular space, or by direct engulfment of α-synuclein as microglia participate in the regulation of synaptic membranes (Zhang et al., 2005). Interestingly, histological studies in PD patients grafted with nondiseased www.selleckchem.com/products/kpt-330.html fetal dopaminergic neurons reveal that Lewy bodies emerge in transplanted neurons (Kordower et al., 2008a and Li et al., 2008). Specifically, only patients with a robust perigraft inflammatory response were observed to have Lewy bodies in grafted neurons,

while grafted neurons survived without Lewy pathology in patients lacking evidence of perigraft microglia activation (Mendez et al., 2008). One parsimonious explanation for these findings is that an immune HDAC inhibitor review response to the graft facilitates the spread of Lewy body pathology from the host to the graft (Dawson, 2008). If this conjecture is valid, it raises the intriguing possibility that disease-associated misfolded or aggregate proteins such as α-synuclein can acquire prion-like properties and that prion-like propagation of diseased proteins from cell to

cell may be facilitated by exposure to an inflammatory milieu. The prevailing view old that neurodegenerative pathology is driven by protein misfolding and generation of toxic conformers originated in the late 1990s with the observation that disease-causing proteins such as α-synuclein and polyglutamine share common amyloidogenic properties and cascades characteristic of Alzheimer’s and prion diseases. A common theme of misfolded protein toxicity thus links prion diseases with Alzheimer’s disease, Parkinson’s disease, ALS, polyglutamine diseases, and tauopathies. However, prion diseases have been viewed as unique among the neurodegenerative proteinopathies, since prions have the capacity for cell-to-cell and organism-to-organism dissemination. The infectivity of prion protein is well established, so much so that in its prion-like state, designated as PrPSc, prion protein can induce nonpathogenic prion protein, PrPc, to undergo a conformational change into the pathogenic PrPsc state (Pan et al., 1993). In this conformational conversion, which can even occur across species barriers in certain cases (e.g.