Acute administration of nicotine into the higher order auditory Te2 cortex specifically decreases the fear-related charge of remote emotional memories

Nicotine elicits several behavioural effects on mood as well as on stress and anxiety processes. Recently, it was found that the higher order components of the sensory cortex, such as the secondary auditory cortex Te2, are essential for the long-term storage of remote fear memories. Therefore, in the present study, we examined the effects of acute nicotine injection into the higher order auditory cortex Te2, on the remote emotional memories of either threat or incentive experiences in rats. We found that intra-Te2 nicotine injection decreased the fear-evoked responses to a tone previously paired with footshock. This effect was cue- and dose-specific and was not due to any interference with auditory stimuli processing, innate anxiety and fear processes, or with motor responses. Nicotine acts acutely in the presence of threat stimuli but it did not determine the permanent degradation of the fear-memory trace, since memories tested one week after nicotine injection were unaffected. Remarkably, nicotine did not affect the memory of a similar tone that was paired to incentive stimuli. We conclude from our results that nicotine, when acting acutely in the auditory cortex, relieves the fear charge embedded by learned stimuli.

•

Nicotine reliefs fear memories.

•

Nicotine acts on long-term memories.

•

Nicotine modulates memory in auditory cortex.

Osteoblast-specific expression of the fibrous dysplasia (FD)-causing mutation Gsα(R201C) produces a high bone mass phenotype but does not reproduce FD in the mouse

We recently reported the generation and initial characterization of the first direct model of human fibrous dysplasia (FD; OMIM #174800), obtained through the constitutive systemic expression of one of the disease-causing mutations, Gsα(R201C) , in the mouse. To define the specific pathogenetic role(s) of individual cell types within the stromal/osteogenic system in FD, we generated mice expressing Gsα(R201C) selectively in mature osteoblasts using the 2.3kb Col1a1 promoter. We show here that this results in a striking high bone mass phenotype but not in a mimicry of human FD. The high bone mass phenotype involves specifically a deforming excess of cortical bone and prolonged and ectopic cortical bone remodeling. Expression of genes characteristic of late stages of bone cell differentiation/maturation is profoundly altered as a result of expression of Gsα(R201C) in osteoblasts, and expression of the Wnt inhibitor Sost is reduced. Although high bone mass is, in fact, a feature of some types/stages of FD lesions in humans, it is marrow fibrosis, localized loss of adipocytes and hematopoietic tissue, osteomalacia, and osteolytic changes that together represent the characteristic pathological profile of FD, as well as the sources of specific morbidity. None of these features are reproduced in mice with osteoblast-specific expression of Gsα(R201C) . We further show that hematopoietic progenitor/stem cells, as well as more mature cell compartments, and adipocyte development are normal in these mice. These data demonstrate that effects of Gsα mutations underpinning FD-defining tissue changes and morbidity do not reflect the effects of the mutations on osteoblasts proper.

Auditory cortex involvement in emotional learning and memory

Emotional memories represent the core of human and animal life and drive future choices and behaviors. Early research involving brain lesion studies in animals lead to the idea that the auditory cortex participates in emotional learning by processing the sensory features of auditory stimuli paired with emotional consequences and by transmitting this information to the amygdala. Nevertheless, electrophysiological and imaging studies revealed that, following emotional experiences, the auditory cortex undergoes learning-induced changes that are highly specific, associative and long lasting. These studies suggested that the role played by the auditory cortex goes beyond stimulus elaboration and transmission. Here, we discuss three major perspectives created by these data. In particular, we analyze the possible roles of the auditory cortex in emotional learning, we examine the recruitment of the auditory cortex during early and late memory trace encoding, and finally we consider the functional interplay between the auditory cortex and subcortical nuclei, such as the amygdala, that process affective information. We conclude that, starting from the early phase of memory encoding, the auditory cortex has a more prominent role in emotional learning, through its connections with subcortical nuclei, than is typically acknowledged.

Constitutive expression of Gsα(R201C) in mice produces a heritable, direct replica of human fibrous dysplasia bone pathology and demonstrates its natural history

Fibrous dysplasia of bone (FD) is a crippling skeletal disease associated with postzygotic mutations (R201C, R201H) of the gene encoding the α subunit of the stimulatory G protein, Gs. By causing a characteristic structural subversion of bone and bone marrow, the disease results in deformity, hypomineralization, and fracture of the affected bones, with severe morbidity arising in childhood or adolescence. Lack of inheritance of the disease in humans is thought to reflect embryonic lethality of germline-transmitted activating Gsα mutations, which would only survive through somatic mosaicism. We have generated multiple lines of mice that express Gsα(R201C) constitutively and develop an inherited, histopathologically exact replica of human FD. Robust transgene expression in neonatal and embryonic tissues and embryonic stem (ES) cells were associated with normal development of skeletal tissues and differentiation of skeletal cells. As in humans, FD lesions in mice developed only in the postnatal life; a defined spatial and temporal pattern characterized the onset and progression of lesions across the skeleton. In individual bones, lesions developed through a sequence of three distinct histopathological stages: a primary modeling phase defined by endosteal/medullary excess bone formation and normal resorption; a secondary phase, with excess, inappropriate remodeling; and a tertiary fibrous dysplastic phase, which reproduced a full-blown replica of the human bone pathology in mice of age ≥1 year. Gsα mutations are sufficient to cause FD, and are per se compatible with germline transmission and normal embryonic development in mice. Our novel murine lines constitute the first model of FD.

3D hydrogel environment rejuvenates aged pericytes for skeletal muscle tissue engineering

Skeletal muscle tissue engineering is a promising approach for the treatment of muscular disorders. However, the complex organization of muscle, combined with the difficulty in finding an appropriate source of regenerative cells and in providing an adequate blood supply to the engineered tissue, makes this a hard task to face. In the present work, we describe an innovative approach to rejuvenate adult skeletal muscle-derived pericytes (MP) based on the use of a PEG-based hydrogel scaffold. MP were isolated from young (piglet) and adult (boar) pigs to assess whether aging affects tissue regeneration efficiency. In vitro, MP from boars had similar morphology and colony forming capacity to piglet MP, but an impaired ability to form myotubes and capillary-like structures. However, the use of a PEG-based hydrogel to support adult MP significantly improved their myogenic differentiation and angiogenic potentials in vitro and in vivo. Thus, PEG-based hydrogel scaffolds may provide a progenitor cell “niche” that promotes skeletal muscle regeneration and blood vessel growth, and together with pericytes may be developed for use in regenerative applications.

Comparative analysis of multilineage properties of mesenchymal stromal cells derived from fetal sources shows an advantage of mesenchymal stromal cells isolated from cord blood in chondrogenic differentiation potential

Background aims

Cord blood (CB) and amniotic fluid (AF) could represent new and attractive mesenchymal stromal cell (MSC) sources, but their potential therapeutic applications are still limited by lack of standardized protocols for isolation and differentiation. In particular, chondrogenic differentiation has never been deeply investigated.

Methods

MSCs were obtained from CB and AF samples collected during cesarean sections at term and compared for their biological and differentiation properties, with particular interest in cartilage differentiation, in which quantitative real-time polymerase chain reaction and immunohistochemical analyses were performed to evaluate the expression of type 2 collagen, type 10 collagen, SRY-box9 and aggrecan.

Results

We were able to isolate MSCs from 12 of 30 (40%) and 5 of 20 (25%) CB and AF units, respectively. Fluorescence in situ hybridization analysis indicated the fetal origin of isolated MSC strains. Both populations expressed mesenchymal but not endothelial and hematopoietic markers, even though we observed a lower expression of human leukocyte antigen (HLA) I in CB-MSCs. No differences in proliferation rate and cell cycle analysis could be detected. After osteogenic induction, both populations showed matrix mineralization and typical marker expression. Under chondrogenic conditions, pellets derived from CB-MSCs, in contrast with AF-MSCs pellets, were significantly larger, showed cartilage-like morphology and resulted positive for chondrocyte-associated markers, such as type 2 collagen, type 10 collagen, SRY-box9 and aggrecan.

Conclusions

Our results show that CB-MSCs and AF-MSCs collected at term differ from each other in their biological and differentiation properties. In particular, only CB-MSCs showed a clear chondrogenic potential and thus could represent an ideal candidate for cartilage-tissue engineering.

A mouse bone marrow stromal cell line with skeletal stem cell characteristics to study osteogenesis in vitro and in vivo

Bone marrow stromal cells (BMSCs) are composed of progenitor and multipotent skeletal stem cells, which are able to differentiate in vitro into osteocytes, adipocytes, and chondrocytes. Mouse BMSCs (mBMSCs) are a versatile model system to investigate factors involved in BMSC differentiation in vitro and in vivo as a variety of transgenic mouse models are available. In this study, mBMSCs were isolated and osteogenic differentiation was investigated in tissue culture and in vivo. Three out of seven independent cell isolates showed the ability to differentiate into osteocytes, adipocytes, and chondrocytes in vitro. In vitro multipotency of an established mBMSC line was maintained over 45 passages. The osteogenic differentiation of this cell line was confirmed by quantitative polymerase chain reaction (qPCR) analysis of specific markers such as osteocalcin and shown to be Runx2 dependent. Notably, the cell line, when transplanted subcutaneously into mice, possesses full skeletal stem cell characteristics in vivo in early and late passages, evident from bone tissue formation, induction of vascularization, and hematopoiesis. This cell line provides, thus, a versatile tool to unravel the molecular mechanisms governing osteogenesis in vivo thereby aiding to improve current strategies in bone regenerative therapy.

Establishment of bone marrow and hematopoietic niches in vivo by reversion of chondrocyte differentiation of human bone marrow stromal cells

Human bone marrow stromal cells (BMSCs, also known as bone marrow-derived "mesenchymal stem cells") can establish the hematopoietic microenvironment within heterotopic ossicles generated by transplantation at non-skeletal sites. Here we show that non-mineralized cartilage pellets formed by hBMSCs ex vivo generate complete ossicles upon heterotopic transplantation in the absence of exogenous scaffolds. These ossicles display a remarkable degree of architectural fidelity, showing that an exogenous conductive scaffold is not an absolute requirement for bone formation by transplanted BMSCs. Marrow cavities within the ossicles include erythroid, myeloid and granulopoietic lineages, clonogenic hematopoietic progenitors and phenotypic HSCs, indicating that complete stem cell niches and hematopoiesis are established. hBMSCs (CD146(+) adventitial reticular cells) are established in the heterotopic chimeric bone marrow through a unique process of endochondral bone marrow formation, distinct from physiological endochondral bone formation. In this process, chondrocytes remain viable and proliferate within the pellet, are released from cartilage, and convert into bone marrow stromal cells. Once explanted in secondary culture, these cells retain phenotype and properties of skeletal stem cells ("MSCs"), including the ability to form secondary cartilage pellets and secondary ossicles upon serial transplantation. Ex vivo, hBMSCs initially induced to form cartilage pellets can be reestablished in adherent culture and can modulate gene expression between cartilage and stromal cell phenotypes. These data show that so-called "cartilage differentiation" of BMSCs in vitro is a reversible phenomenon, which is actually reverted, in vivo, to the effect of generating stromal cells supporting the homing of hematopoietic stem cells and progenitors.

Effects of vitamin B12 on the corneal nerve regeneration in rats

The study was designed to investigate the effects of a new ophthalmic solution containing 0.05% vitamin B12 0.05% on corneal nerve regeneration in rats after corneal injury. Eyes of anesthetized male Wistar rats were subjected to corneal injury by removing the corneal epithelium with corneal brush (Algerbrush). After the epithelial debridement, the right eye of each animal received the instillation of one drop of the ophthalmic solution containing vitamin B12 0.05% plus taurine 0.5% and sodium hyaluronate 0.5% four time per day for 10 or 30 days. Left eyes were used as control and treated with solution containing taurine 0.5% and sodium hyaluronate 0.5% alone following the same regimen. Fluorescein staining by slit-lamp and morphological analysis was used to determine corneal wound healing. Immunohistochemistry, immunoblot and confocal microscopy were used to examine corneal re-innervation. Slit-lamp and histological analyses showed that re-epithelization of the corneas was accelerated in rats treated with vitamin B12. A clear-cut difference between the two groups of rats was seen after 10 days of treatment, whereas a near-to-complete re-epithelization was observed in both groups at 30 days. Vitamin B12 treatment had also a remarkable effect on corneal re-innervation, as shown by substantial increased in the expression of neurofilament 160 and β-III tubulin at both 10 and 30 days. The presence of SV2A-positive nerve endings suggests the presence of synapse-like specialized structures in corneal epithelium of the eye treated with vitamin B12. Our findings suggest that vitamin B12 treatment represents a powerful strategy to accelerate not only re-epithelization but also corneal re-innervation after mechanical injury.

Evidence for a common progenitor of epithelial and mesenchymal components of the liver

Tissues of the adult organism maintain the homeostasis and respond to injury by means of progenitor/stem cell compartments capable to give rise to appropriate progeny. In organs composed by histotypes of different embryological origins (e.g. the liver), the tissue turnover may in theory involve different stem/precursor cells able to respond coordinately to physiological or pathological stimuli. In the liver, a progenitor cell compartment, giving rise to hepatocytes and cholangiocytes, can be activated by chronic injury inhibiting hepatocyte proliferation. The precursor compartment guaranteeing turnover of hepatic stellate cells (HSCs) (perisinusoidal cells implicated with the origin of the liver fibrosis) in adult organ is yet unveiled. We show here that epithelial and mesenchymal liver cells (hepatocytes and HSCs) may arise from a common progenitor. Sca+ murine progenitor cells were found to coexpress markers of epithelial and mesenchymal lineages and to give rise, within few generations, to cells that segregate the lineage-specific markers into two distinct subpopulations. Notably, these progenitor cells, clonally derived, when transplanted in healthy livers, were found to generate epithelial and mesenchymal liver-specific derivatives (i.e. hepatocytes and HSCs) properly integrated in the liver architecture. These evidences suggest the existence of a 'bona fide' organ-specific meso-endodermal precursor cell, thus profoundly modifying current models of adult progenitor commitment believed, so far, to be lineage-restricted. Heterotopic transplantations, which confirm the dual differentiation potentiality of those cells, indicates as tissue local cues are necessary to drive a full hepatic differentiation. These data provide first evidences for an adult stem/precursor cell capable to differentiate in both parenchymal and non-parenchymal organ-specific components and candidate the liver as the instructive site for the reservoir compartment of HSC precursors as yet non-localized in the adult.

Hurler disease bone marrow stromal cells exhibit altered ability to support osteoclast formation

Mucopolysaccharidosis type I (MPS IH; Hurler syndrome) is a rare genetic disorder that is caused by mutations in the α-L-iduronidase (IDUA) gene, resulting in the deficiency of IDUA enzyme activity and intra-cellular accumulation of glycosaminoglycans. A characteristic skeletal phenotype is one of the many clinical manifestations in Hurler disease. Since the mechanism(s) underlying these skeletal defects are not completely understood, and bone and cartilage are mesenchymal lineages, we focused on the characterization of mesenchymal cells isolated from the bone marrow (BM) of 5 Hurler patients. IDUA-mutated BM stromal cells (BMSC) derived from MPS IH patients exhibited decreased IDUA activity, consistent with the disease genotype. The expansion rate, phenotype, telomerase activity, and differentiation capacity toward adipocytes, osteoblasts, chondrocytes, and smooth muscle cells in vitro of the MPS I BMSC lines were similar to those of BMSC from age-matched normal control donors. MPS I BMSC also had a similar in vivo osteogenic capacity as normal BMSC. However, MPS I BMSC displayed an increased capacity to support osteoclastogenesis, which may correlate with the up-regulation of the RANKL/RANK/OPG molecular pathway in MPS I BMSC compared with normal BMSC.

Osteoprogenitors and the hematopoietic microenvironment

The identification of skeletal progenitor cells in the human bone marrow (so-called mesenchymal stem cells) by anatomy and phenotype (CD146-expressing, adventitial reticular cells) has coincided with the recognition that the ability to transfer the hematopoietic microenvironment is an inherent property of skeletal progenitor cells. Inasmuch as these cells generate osteoblasts, associate with sinusoids (the assembly of which they dynamically direct), and coincide with, and self-renew into, stromal reticular cells, these cells are pivotal organizers of the hematopoietic microenvironment. Their nature as osteogenic cells and sinusoidal location reconcile the dual view of endosteal surfaces and sinusoidal walls as the hematopoietic stem cell "niches", and highlight the dynamic nature of a niche/microenvironment essentially maintained by cells with properties of progenitors/stem cells for skeletal tissues. This view brings the long recognized, and somewhat mysterious, interaction between bone and bone marrow into a new perspective, where two stem cells interact with each other at the same niche.

Basolateral amygdala inactivation impairs learning-induced long-term potentiation in the cerebellar cortex

Learning to fear dangerous situations requires the participation of basolateral amygdala (BLA). In the present study, we provide evidence that BLA is necessary for the synaptic strengthening occurring during memory formation in the cerebellum in rats. In the cerebellar vermis the parallel fibers (PF) to Purkinje cell (PC) synapse is potentiated one day following fear learning. Pretraining BLA inactivation impaired such a learning-induced long-term potentiation (LTP). Similarly, cerebellar LTP is affected when BLA is blocked shortly, but not 6 h, after training. The latter result shows that the effects of BLA inactivation on cerebellar plasticity, when present, are specifically related to memory processes and not due to an interference with sensory or motor functions. These data indicate that fear memory induces cerebellar LTP provided that a heterosynaptic input coming from BLA sets the proper local conditions. Therefore, in the cerebellum, learning-induced plasticity is a heterosynaptic phenomenon that requires inputs from other regions. Studies employing the electrically-induced LTP in order to clarify the cellular mechanisms of memory should therefore take into account the inputs arriving from other brain sites, considering them as integrative units. Based on previous and the present findings, we proposed that BLA enables learning-related plasticity to be formed in the cerebellum in order to respond appropriately to new stimuli or situations.

Stem cells in skeletal physiology and endocrine diseases of bone

Self-renewing, multipotent progenitors of skeletal tissues are found within skeletal segments (skeletal stem cells) and coincide with adventitial reticular cells of bone marrow vessels in situ and with explanted clonogenic stromal cells ex vivo. These cells, which can be identified and prospectively isolated based on a minimal surface phenotype noted for expression of CD146, CD105 and alkaline phosphatase, are established during bone development through interactions with developing sinusoids. They represent a crucial crossroad of skeletal and hematopoietic physiology, as well as of endocrine regulation of bone growth and remodeling. In addition, they are central to major endocrine functions of bone itself, such as regulation of renal phosphate handling. Skeletal stem cells represent a central model system for investigating skeletal diseases, as tools for in vitro and in vivo models, for cell therapy-based strategies, or as targets for drugs.

Graft vascularization is a critical rate-limiting step in skeletal stem cell-mediated posterolateral spinal fusion

The ability of skeletal stem cells (SSCs) to direct spinal fusion (SF) upon transplantation in conjunction with osteoconductive biomaterials was investigated in a rabbit model. When tested in a mouse heterotopic transplantation assay, rabbit SSCs and Pro-Osteon 500R was osteoconductive and supported osteogenesis. When used in a SF model, the same constructs induced bone formation in periapophyseal regions (PARs). In this respect, they proved to be superior to grafts of cell-free carrier or total uncultured bone marrow-carrier constructs, used as controls. However, interapophyseal regions (IARs) remained devoid of new bone, such that true bony bridging of adjacent transverse apophyses (true SF) could not be achieved. Interestingly, this could not be predicted from high-resolution radiography. A systematic histological survey of the entire graft harvested at 6 months was essential for proper assessment of the transplantation procedure outcome. Immunohistochemical analysis of microvessel density revealed that IARs remained undervascularized, as compared to PARs, suggesting that differential vascularization could account for the absence or presence of new bone formation in the same regions. SF is an extreme model of stem cell-directed bone regeneration, requiring a combination of orthotopic (PAR) and heterotopic (IAR) bone formation. Our data show that, in this setting, graft size can be critical with respect to the necessary neovascularization, a crucial variable independent of proper osteogenic and osteoconductive competence of the cells and materials employed. Furthermore, stringent histological studies are mandatory for proper assessment of outcomes in SF studies, in which the use of mineralized materials can make radiographic assessment misleading.

Role of secondary sensory cortices in emotional memory storage and retrieval in rats

Visual, acoustic, and olfactory stimuli associated with a highly charged emotional situation take on the affective qualities of that situation. Where the emotional meaning of a given sensory experience is stored is a matter of debate. We found that excitotoxic lesions of auditory, visual, or olfactory secondary sensory cortices impaired remote, but not recent, fear memories in rats. Amnesia was modality-specific and not due to an interference with sensory or emotional processes. In these sites, memory persistence was dependent on ongoing protein kinase Mzeta activity and was associated with an increased activity of layers II-IV, thus suggesting a synaptic strengthening of corticocortical connections. Lesions of the same areas left intact the memory of sensory stimuli not associated with any emotional charge. We propose that secondary sensory cortices support memory storage and retrieval of sensory stimuli that have acquired a behavioral salience with the experience.

Cerebellum and emotional behavior

Fear conditioning involves learning that a previously neutral stimulus (CS) predicts an aversive unconditioned stimulus (US). Lesions of the cerebellar vermis may affect fear memory without altering baseline motor/autonomic responses to the frightening stimuli. Reversible inactivation of the vermis during the consolidation period impairs retention of fear memory. In patients with medial cerebellar lesions conditioned bradycardia is impaired. In humans, cerebellar areas around the vermis are activated during mental recall of emotional personal episodes, if a loved partner receives a pain stimulus, and during learning of a CS-US association. Moreover, patients with cerebellar stroke may fail to show overt emotional changes. In such patients, however, the activity of several areas, including ventromedial prefrontal cortex, anterior cingulate, pulvinar and insular cortex, is significantly increased relative to healthy subjects when exposed to frightening stimuli. Therefore, other structures may serve to maintain fear response after cerebellar damage. These data indicate that the vermis is involved in the formation of fear memory traces. We suggest that the vermis is not only involved in regulating the autonomic/motor responses, but that it also participates in forming new CS-US associations thus eliciting appropriate responses to new stimuli or situations. In other words, the cerebellum may translate an emotional state elaborated elsewhere into autonomic and motor responses.

Human maxillary tuberosity and jaw periosteum as sources of osteoprogenitor cells for tissue engineering

OBJECTIVE

Bone tissue engineering is a promising approach for bone reconstruction in oral-maxillofacial surgery. This study investigates the suitability of oral skeletal tissues as convenient and accessible sources of osteogenic progenitors as an alternative to the iliac crest bone marrow.

STUDY DESIGN

Samples of maxilla tuberosity (MT) and maxillary and mandibular periosteum (MP) were obtained during routine oral surgery, and donor site morbidity was assessed using a "split-mouth" approach. Cells isolated from MT (bone marrow stromal cells; MT-BMSCs) and from MP (periosteal cells; M-PCs), were analyzed for clonogenicity, phenotype, expression of osteogenic markers, and ability to form bone in vivo.

RESULTS

Both MT-BMSCs and M-PCs included clonogenic cells, showed comparable phenotypic profiles, and expressed early osteogenic markers. Most importantly, both cell populations formed bone upon ectopic in vivo transplantation.

CONCLUSION

MT-BMSCs and M-PCs behaved as osteoprogenitor cells in vitro and in vivo. MT and MP may be considered as suitable sources of cells for bone tissue engineering in humans.

The effects of fear conditioning on cerebellar LTP and LTD

Long-term potentiation (LTP) and depression (LTD) at parallel fibre-Purkinje cell synapses have been described in vitro in the cerebellar cortex, but the physiological roles of these two forms of plasticity have not been well defined. Here we show that, in cerebellar slices taken from rats that had undergone fear conditioning, there was a significant occlusion of electrically induced LTP at parallel fibre-Purkinje cell synapses. This effect was long-lasting and related to associative processes, as LTP was not occluded in unpaired animals. Notably, in conditioned animals the LTP-inducing protocol produced LTD in some cells instead of LTP. Conversely, synaptic depression induced by conjunctive stimulation of parallel fibers and climbing fibres was impaired in tissue taken immediately following aversive stimulation in both paired and unpaired subjects. This effect was not, however, long-lasting as the incidence and extent of LTD returned to normal levels 24 h after behavioural testing. These findings suggest that LTP takes part in the mechanisms underlying aversive associative memories in the cerebellum.

Reversible inactivation of amygdala and cerebellum but not perirhinal cortex impairs reactivated fear memories

The cerebellum, amygdala and perirhinal cortex are involved in fear learning but the different roles that these three structures play in aversive learning are not well defined. Here we show that in adult rats amygdala or cerebellar vermis blockade causes amnesia when performed immediately, but not 1 h, after the recall of fear memories. Thus, the cerebellum, as well as the amygdala, influences long-term fear memories. These effects are long lasting, as they do not recover over time, even after a reminder shock administration. However, all of the subjects were able to form new fear memories in the absence of inactivation. By increasing the strength of conditioning, we observed that stronger fear memories are affected by the combined but not independent amygdala and cerebellar blockade. These results demonstrate that the cerebellum supports the memory processes even in the absence of a crucial site for emotions like the amygdala. Furthermore, they suggest that the amygdala is only one of the neural sites underlying long-term fear memories. Finally, the inactivation of the perirhinal cortex never alters retrieved fear traces, showing important differences between the amygdala, cerebellum and perirhinal cortex in emotional memories.

Pericytes of human skeletal muscle are myogenic precursors distinct from satellite cells

Cells derived from blood vessels of human skeletal muscle can regenerate skeletal muscle, similarly to embryonic mesoangioblasts. However, adult cells do not express endothelial markers, but instead express markers of pericytes, such as NG2 proteoglycan and alkaline phosphatase (ALP), and can be prospectively isolated from freshly dissociated ALP(+) cells. Unlike canonical myogenic precursors (satellite cells), pericyte-derived cells express myogenic markers only in differentiated myotubes, which they form spontaneously with high efficiency. When transplanted into severe combined immune deficient-X-linked, mouse muscular dystrophy (scid-mdx) mice, pericyte-derived cells colonize host muscle and generate numerous fibres expressing human dystrophin. Similar cells isolated from Duchenne patients, and engineered to express human mini-dystrophin, also give rise to many dystrophin-positive fibres in vivo. These data show that myogenic precursors, distinct from satellite cells, are associated with microvascular walls in the human skeletal muscle, may represent a correlate of embryonic 'mesoangioblasts' present after birth and may be a promising candidate for future cell-therapy protocols in patients.

Lentiviral transduction of human postnatal skeletal (stromal, mesenchymal) stem cells: in vivo transplantation and gene silencing

Systems for gene transfer and silencing in human skeletal stem cells (hSSCs, also stromal or mesenchymal stem cells) are important for addressing critical issues in basic hSSC and skeletal biology and for developing gene therapy strategies for treatment of skeletal diseases. Whereas recent studies have shown the efficacy of lentiviral transduction for gene transfer in hSSCs in vitro, no study has yet proven that lentivector-transduced hSSCs retain their distinctive organogenic potential in vivo, as probed by in vivo transplantation assays. Therefore, in addition to analyzing the in vitro growth and differentiation properties of hSSCs transduced with advanced-generation lentivectors, we ectopically transplanted LV-eGFP-transduced hSSCs (along with an osteoconductive carrier) in the subcutaneous tissue of immunocompromised mice. eGFP-transduced cells formed heterotopic ossicles, generating osteoblasts, osteocytes, and stromal cells in vivo, which still expressed GFP at 2 months after transplantation. eGFP-expressing cells could be recovered from the ossicles 8 weeks posttransplantation and reestablished in culture as viable and proliferating cells. Further, we investigated the possibility of silencing individual genes in hSSCs using lentivectors encoding short hairpin precursors of RNA interfering sequences under the control of the Pol-III-dependent H1 promoter. Significant long-term silencing of both lamin A/C and GFP (an endogenous gene and a transgene, respectively) was obtained with lentivectors encoding shRNAs. These data provide the basis for analysis of the effect of gene knockdown during the organogenesis of bone in the in vivo transplantation system and for further studies on the silencing of alleles carrying dominant, disease-causing mutations.

Membrane excitability and fear conditioning in cerebellar Purkinje cell

In a previous study it has been demonstrated that fear conditioning is associated with a long-lasting potentiation of parallel fiber to Purkinje cell synaptic transmission in vermal lobules V and VI. Since modifications of intrinsic membrane properties have been suggested to mediate some forms of memory processes, we investigated possible changes of Purkinje cell intrinsic properties following the same learning paradigm and in the same cerebellar region. By means of the patch clamp technique, Purkinje cell passive and active membrane properties were evaluated in slices prepared from rats 10 min or 24 h after fear conditioning and in slices from control naïve animals. None of the evaluated parameters (input resistance, inward rectification, maximal firing frequency and the first inter-spike interval, post-burst afterhyperpolarization, action potential threshold and amplitude, action potential afterhyperpolarization) was significantly different between the three studied groups also in those cells where parallel fiber-Purkinje cell synapse was potentiated. Our results show that fear learning does not affect the intrinsic membrane properties involved in Purkinje cell firing. Therefore, at the level of Purkinje cell the plastic change associated with fear conditioning is specifically restricted to synaptic efficacy.

Involvement of the intracellular ion channel CLIC1 in microglia-mediated beta-amyloid-induced neurotoxicity

It is widely believed that the inflammatory events mediated by microglial activation contribute to several neurodegenerative processes. Alzheimer's disease, for example, is characterized by an accumulation of beta-amyloid protein (Abeta) in neuritic plaques that are infiltrated by reactive microglia and astrocytes. Although Abeta and its fragment 25-35 exert a direct toxic effect on neurons, they also activate microglia. Microglial activation is accompanied by morphological changes, cell proliferation, and release of various cytokines and growth factors. A number of scientific reports suggest that the increased proliferation of microglial cells is dependent on ionic membrane currents and in particular on chloride conductances. An unusual chloride ion channel known to be associated with macrophage activation is the chloride intracellular channel-1 (CLIC1). Here we show that Abeta stimulation of neonatal rat microglia specifically leads to the increase in CLIC1 protein and to the functional expression of CLIC1 chloride conductance, both barely detectable on the plasma membrane of quiescent cells. CLIC1 protein expression in microglia increases after 24 hr of incubation with Abeta, simultaneously with the production of reactive nitrogen intermediates and of tumor necrosis factor-alpha (TNF-alpha). We demonstrate that reducing CLIC1 chloride conductance by a specific blocker [IAA-94 (R(+)-[(6,7-dichloro-2-cyclopentyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5yl)-oxy] acetic acid)] prevents neuronal apoptosis in neurons cocultured with Abeta-treated microglia. Furthermore, we show that small interfering RNAs used to knock down CLIC1 expression prevent TNF-alpha release induced by Abeta stimulation. These results provide a direct link between Abeta-induced microglial activation and CLIC1 functional expression.