Converting bile acids into mitocans.

Cholic acid (1, CD), deoxycholic (3, DCA), chenodeoxycholic acid (5, CDCA), ursodeoxycholic acid (7, UDCA), and lithocholic acid (9, LCA) were acetylated and converted into their piperazinyl spacered rhodamine B conjugates 16-20. While the parent bile acids showed almost no cytotoxic effects for several human tumor cell lines, the piperazinyl amides were cytostatic but an even superior effect was observed for the rhodamine B conjugates. Extra staining experiments showed these compounds as mitocans; they led to a cell arrest in the G1 phase.

Sensory input drives rapid homeostatic scaling of the axon initial segment in mouse barrel cortex.

The axon initial segment (AIS) is a critical microdomain for action potential initiation and implicated in the regulation of neuronal excitability during activity-dependent plasticity. While structural AIS plasticity has been suggested to fine-tune neuronal activity when network states change, whether it acts in vivo as a homeostatic regulatory mechanism in behaviorally relevant contexts remains poorly understood. Using the mouse whisker-to-barrel pathway as a model system in combination with immunofluorescence, confocal analysis and electrophysiological recordings, we observed bidirectional AIS plasticity in cortical pyramidal neurons. Furthermore, we find that structural and functional AIS remodeling occurs in distinct temporal domains: Long-term sensory deprivation elicits an AIS length increase, accompanied with an increase in neuronal excitability, while sensory enrichment results in a rapid AIS shortening, accompanied by a decrease in action potential generation. Our findings highlight a central role of the AIS in the homeostatic regulation of neuronal input-output relations.

Cerebellar and hepatic alterations in ACBD5-deficient mice are associated with unexpected, distinct alterations in cellular lipid homeostasis.

ACBD5 deficiency is a novel peroxisome disorder with a largely uncharacterized pathology. ACBD5 was recently identified in a tethering complex mediating membrane contacts between peroxisomes and the endoplasmic reticulum (ER). An ACBD5-deficient mouse was analyzed to correlate ACBD5 tethering functions with the disease phenotype. ACBD5-deficient mice exhibit elevated very long-chain fatty acid levels and a progressive cerebellar pathology. Liver did not exhibit pathologic changes but increased peroxisome abundance and drastically reduced peroxisome-ER contacts. Lipidomics of liver and cerebellum revealed tissue-specific alterations in distinct lipid classes and subspecies. In line with the neurological pathology, unusual ultra-long chain fatty acids (C > 32) were elevated in phosphocholines from cerebelli but not liver indicating an organ-specific imbalance in fatty acid degradation and elongation pathways. By contrast, ether lipid formation was perturbed in liver towards an accumulation of alkyldiacylglycerols. The alterations in several lipid classes suggest that ACBD5, in addition to its acyl-CoA binding function, might maintain peroxisome-ER contacts in order to contribute to the regulation of anabolic and catabolic cellular lipid pathways.

Implant Retention or Removal for Management of Surgical Site Infection After Spinal Surgery.

STUDY DESIGN: A literature review. OBJECTIVE: To summarize the implant removal rate, common bacterial organisms found, time of onset, ratio of superficial to deep infection, and regurgitating the prevalence among all the retrospective and prospective studies on management and characterization of surgical site infections (SSIs). METHODS: PubMed was searched for articles published between 2000 and 2018 on the management or characterization of SSIs after spinal surgery. Only prospective and retrospective studies were included. RESULTS: A total of 49 articles were found relevant to the objective. These studies highlighted the importance of implant removal to avoid recurrence of SSI. The common organisms detected were methicillin-resistant Staphylococcus aureus, methicillin-resistant Staphylococcus epidermis, Staphylococcus epidermis, Staphylococcus aureus, and Propionibacterium acnes, with prevalence of 1% to 15%. A major proportion of all were deep SSI, with minority reporting on late-onset SSI. CONCLUSION: Long-term antibiotics administration, and continuous irrigation and debridement were common suggestion among the authors; however, the key measure undertaken or implied by most authors to avoid risk of recurrence was removal or replacement of implants for late-onset SSI.

Updates on Evidence-Based Practices to Reduce Preoperative and Intraoperative Contamination of Implants in Spine Surgery: A Narrative Review.

The current communication seeks to provide an updated narrative review on latest methods of reducing implant contaminations used during spine surgery. Recent literature review has shown that both preoperative reprocessing and intraoperative handling of implants seem to contaminate implants. In brief, during preoperative phase, the implants undergo repeated bulk cleaning with dirty instruments from the OR, leading to residue buildup at the interfaces and possibly on the surfaces too. This, due to its concealed nature, remains unnoticed by the SPD (sterile processing department) or other hospital staff. Nevertheless, these can be avoided by using individually prepackaged presterilized implants. In the intraoperative phase, the implants (in the sterile field) are directly touched by the scrub tech with soiled (assisting the surgeon dispose the tissues from the instruments in use) gloves for loading onto an insertion device. It is then kept exposed on the working table (either separately or next to the used instruments as the pedicles hole are being prepared). Latest investigation has shown that by the time it is implanted in the patient, it can harbor up to 10e7 bacterial colony-forming units. The same implants were devoid of such colony-forming units, when sheathed by an impermeable sterile sheath around the sterile implant.

A Multicenter Trial Demonstrating Presence or Absence of Bacterial Contamination at the Screw-Bone Interface Owing to Absence or Presence of Pedicle Screw Guard, Respectively, During Spinal Fusion.

STUDY DESIGN: A prospective multicenter study. OBJECTIVE: The objective of this study was to assess bacterial contamination in current practices of pedicle screw handling and comparing it to a novel method of using an intraoperative, sterile implant guard for screws. SUMMARY OF BACKGROUND DATA: Postoperative infections occur at the higher end of 2%-13%, as cited in the literature, and are underestimated due to various reasons in such publications. Despite concerns associated with vancomycin application immediately before closure, it is theoretically impossible to irrigate the screw-bone interface postimplantation. Consequently, any contamination of pedicle screw before implantation is permanent, and has the potential to cause deep-bone infection, or hardware loosening due to encapsulation of biofilm between the bone and the screw. Therefore, continued vigilance and effective preventive measures should be undertaken if available. MATERIALS AND METHODS: Two groups of presterile individually-packaged pedicle screws, one incased in a sterile, protective guard (group 1: G) and the other without such a guard (group 2: NG), 31 samples in each group were distributed over 28 spinal fusion surgeries at 5 independent hospitals groups. Each were loaded onto the insertion device by the scrub tech and left on the sterile table. Twenty minutes later, the lead surgeon who had just finished preparing the surgical site, handles the pedicle screw, to check the fit with the insertion device. Then, instead of implantation, it was transferred to a sterile container using fresh sterile gloves for bacterial analysis. RESULTS: The standard unguarded pedicle screws presented bioburden in the range of 10 to 10 colonies forming units per screw, whereas the guarded pedicle screws showed no bioburden. CONCLUSION: Standard, current, handling of pedicle screws leads to bacterial contamination, which can be avoided if the screws are sterilely prepackaged with an intraoperative guard (preinstalled).

Dynamic Regulation of Synaptopodin and the Axon Initial Segment in Retinal Ganglion Cells During Postnatal Development.

A key component allowing a neuron to function properly within its dynamic environment is the axon initial segment (AIS), the site of action potential generation. In visual cortex, AIS of pyramidal neurons undergo periods of activity-dependent structural plasticity during development. However, it remains unknown how AIS morphology is organized during development for downstream cells in the visual pathway (retinal ganglion cells; RGCs) and whether AIS retain the ability to dynamically adjust to changes in network state. Here, we investigated the maturation of AIS in RGCs during mouse retinal development, and tested putative activity-dependent mechanisms by applying visual deprivation with a focus on the AIS-specific cisternal organelle (CO), a presumed Ca2+-store. Whole-mount retinae from wildtype and Thy1-GFP transgenic mice were processed for multi-channel immunofluorescence using antibodies against AIS scaffolding proteins ankyrin-G, ßIV-spectrin and the CO marker synaptopodin (synpo). Confocal microscopy in combination with morphometrical analysis of AIS length and position as well as synpo cluster size was performed. Data indicated that a subset of RGC AIS contains synpo clusters and that these show significant dynamic regulation in size during development as well as after visual deprivation. Using super resolution microscopy, we addressed the subcellular localization of synpo in RGC axons. Similar to cortical neurons, RGCs show a periodic distribution of AIS scaffolding proteins. A previously reported scaffold-deficient nanodomain correlating with synpo localization is not evident in all RGC AIS. In summary, our work demonstrates a dynamic regulation of both the AIS and synpo in RGCs during retinal development and after visual deprivation, providing first evidence that the AIS and CO in RGCs can undergo structural plasticity in response to changes in network activity.

Harboring Contaminants in Repeatedly Reprocessed Pedicle Screws.

STUDY DESIGN: It consisted of evaluation of the pedicle screws for presence of residual nonmicrobial contaminants and tabulation of the minimum steps and time required for reprocessing implants as per guidelines and its comparison with actual practice. OBJECTIVE: An evaluation of the nonmicrobial contaminants prevalent on the pedicle screws used for spine surgery and the underlying practice cause behind the source. METHODS: The first component consisted of a random selection of 6 pedicle screws and its assessment using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The second component consisted of review of implant reprocessing guidelines and its applicability. RESULTS: Three types of contaminants were identified: corrosion, saccharide of unknown origin, and soap residue mixed with and were mostly present at the interfaces with low permeability. In addition, manufacturer's guideline recommends 19 hours of reprocessing, whereas the real-time observation revealed a turnaround time of 1 hour 17 minutes. CONCLUSION: Repeatedly reprocessed pedicle screws host corrosion, carbohydrate, fat, and soap, which could be a cause of surgical site infection and inflammatory responses postsurgery. The cause behind it is the impracticality of repeated cleaning and inspection of such devices.

Efficacy of Intraoperative Implant Prophylaxis in Reducing Intraoperative Microbial Contamination.

STUDY DESIGN: A prospective single-center study. OBJECTIVES: Assess to what degree contamination of pedicle screws occur in standard intraoperative practice and if use of an impermeable guard could mitigate or reduce such an occurrence. METHODS: Two groups of sterile prepackaged pedicle screws, one with an intraoperative guard (group 1) and the other without such a guard (group 2), each consisting of 5 samples distributed over 3 time points, were loaded onto the insertion device by the scrub tech and left on the sterile table. Approximately 20 minutes later, the lead surgeon who had just finished preparing the surgical site touches the pedicle screw. Then instead of implantation it was transferred to a sterile container using fresh clean gloves for bacterial and gene analysis. Guarded screw implies that even after unwrapping from the package, the screw carries an impermeable barrier along its entire length, which is only removed seconds prior to implantation. RESULTS: The standard unguarded pedicle screws presented bioburden in the range of 105 to 107 (colony forming units/implant) with bacterial genus mostly consisting of Staphylococcus and Micrococcus, the 2 most common genera found in surgical site infection reports. The common species among them were Staphylococcus epidermis, Staphylococcus aureus, Micrococcus luteus, and Staphylococcus pettenkoferi, whereas the guarded pedicle screws showed no bioburden. CONCLUSIONS: Shielding the pedicle screws intraoperatively using a guard provides a superior level of asepsis than currently practiced. All unshielded pedicles screws were carrying bioburden of virulent bacterial species, which provides an opportunity for the development of postoperative infections.

Intracellular redistribution of neuronal peroxisomes in response to ACBD5 expression.

Peroxisomes can be frequently found in proximity to other subcellular organelles such as the endoplasmic reticulum (ER), mitochondria or lysosomes. The tail-anchored protein ACBD5 was recently identified as part of a tethering complex at peroxisome-ER contact sites, interacting with the ER resident protein VAPB. Contact site disruption was found to significantly increase peroxisome motility, apparently interfering with intracellular positioning systems. Unlike other somatic cells, neurons have to distribute organelles across relatively long distances in order to maintain their extraordinary cellular polarity. Using confocal live imaging microscopy in cultured hippocampal neurons we observed that peroxisomes and mitochondria show a strikingly similar motility with approximately 10% performing microtubule-driven long range movements. In order to investigate if ER contacts influence overall peroxisome motility and cellular distribution patterns, hippocampal neurons were transfected with plasmids encoding ACBD5 to stimulate peroxisome-ER interactions. Overexpression of ACBD5 reduced peroxisomal long range movements in the neurites of the hippocampal cells by 70%, implying that ER attachment counteracts microtubule-driven peroxisome transport, while mitochondrial motility was unaffected. Moreover, the analyses of peroxisome distribution in fixed neurons unveiled a significant redistribution of peroxisomes towards the periphery of the perikaryon underneath the plasma membrane and into neurites, where peroxisomes are frequently found in close proximity to mitochondria. Surprisingly, further analysis of peroxisome and VAPB distribution upon ACBD5 expression did not reveal a substantial colocalization, implying this effect may be independent of VAPB. In line with these findings, expression of an ACBD5 variant unable to bind to VAPB still altered the localization of peroxisomes in the same way as the wild-type ACBD5. Thus, we conclude, that the VAPB-ACBD5 facilitated peroxisome-ER interaction is not responsible for the observed organelle redistribution in neurons. Rather, we suggest that additional ACBD5-binding proteins in neurons may tether peroxisomes to contact sites at or near the plasma membrane of neurons.

Implant Prophylaxis: The Next Best Practice Toward Asepsis in Spine Surgery.

STUDY DESIGN: A literature review. OBJECTIVES: An evaluation of the contaminants prevalent on implants used for surgery and the aseptic methods being employed against them. METHODS: PubMed was searched for articles published between 2000 and 2017 for studies evaluating the contaminants present on spine implants, and associated pre- and intraoperative implant processing and handling methodology suggested to avoid them. Systematic reviews, observational studies, bench-top studies, and expert opinions were included. RESULTS: Eleven studies were identified whose major focus was the asepsis of implants to reduce the incidence of surgical site infection incidences during surgery. These studies measured the colony forming units of bacteria on sterilized implants and/or gloves from the surgeon, scrub nurse, and assistants, as well as reductions of surgical site infection rates in spine surgery due to changes in implant handling techniques. Additionally, the search included assessments of endotoxins and carbohydrates present on reprocessed implants. The suggested changes to surgical practice based on these studies included handling implants with only fresh gloves, keeping implants covered until the immediate time of use, reducing operating room traffic, avoiding reprocessing of implants (ie, providing terminally sterilized implants), and avoiding touching the implants altogether. CONCLUSIONS: Both reprocessing (preoperative) and handling (intraoperative) of implants seem to lead to contamination of sterilized implants. Using a terminally sterilized device may mitigate reprocessing (preoperative implant prophylaxis), whereas the use of fresh gloves for handling each implant and/or a permanent shielding technique (intraoperative implant prophylaxis) could potentially avoid recontamination at the theatre.

Heterogeneity of the Axon Initial Segment in Interneurons and Pyramidal Cells of Rodent Visual Cortex.

The microdomain that orchestrates action potential initiation in neurons is the axon initial segment (AIS). It has long been considered to be a rather homogeneous domain at the very proximal axon hillock with relatively stable length, particularly in cortical pyramidal cells. However, studies in other brain regions paint a different picture. In hippocampal CA1, up to 50% of axons emerge from basal dendrites. Further, in about 30% of thick-tufted layer V pyramidal neurons in rat somatosensory cortex, axons have a dendritic origin. Consequently, the AIS is separated from the soma. Recent in vitro and in vivo studies have shown that cellular excitability is a function of AIS length/position and somatodendritic morphology, undermining a potentially significant impact of AIS heterogeneity for neuronal function. We therefore investigated neocortical axon morphology and AIS composition, hypothesizing that the initial observation of seemingly homogeneous AIS is inadequate and needs to take into account neuronal cell types. Here, we biolistically transfected cortical neurons in organotypic cultures to visualize the entire neuron and classify cell types in combination with immunolabeling against AIS markers. Using confocal microscopy and morphometric analysis, we investigated axon origin, AIS position, length, diameter as well as distance to the soma. We find a substantial AIS heterogeneity in visual cortical neurons, classified into three groups: (I) axons with somatic origin with proximal AIS at the axon hillock; (II) axons with somatic origin with distal AIS, with a discernible gap between the AIS and the soma; and (III) axons with dendritic origin (axon-carrying dendrite cell, AcD cell) and an AIS either starting directly at the axon origin or more distal to that point. Pyramidal cells have significantly longer AIS than interneurons. Interneurons with vertical columnar axonal projections have significantly more distal AIS locations than all other cells with their prevailing phenotype as an AcD cell. In contrast, neurons with perisomatic terminations display most often an axon originating from the soma. Our data contribute to the emerging understanding that AIS morphology is highly variable, and potentially a function of the cell type.

Structural Plasticity of Synaptopodin in the Axon Initial Segment during Visual Cortex Development.

The axon initial segment (AIS) is essential for action potential generation. Recently, the AIS was identified as a site of neuronal plasticity. A subpopulation of AIS in cortical principal neurons contains stacks of endoplasmic reticulum (ER) forming the cisternal organelle (CO). The function of this organelle is poorly understood, but roles in local Ca2+-trafficking and AIS plasticity are discussed. To investigate whether the presence and/or the size of COs are linked to the development and maturation of AIS of cortical neurons, we analyzed the relationship between COs and the AIS during visual cortex development under control and visual deprivation conditions. In wildtype mice, immunolabeling for synaptopodin, ankyrin-G, and ßIV-spectrin were employed to label COs and the AIS, respectively. Dark rearing resulted in an increase in synaptopodin cluster sizes, suggesting a homeostatic function of the CO in this cellular compartment. In line with this observation, synaptopodin-deficient mice lacking the CO showed AIS shortening in the dark. Collectively, these data demonstrate that the CO is an essential part of the AIS machinery required for AIS plasticity during a critical developmental period of the visual cortex.

Multisite Assessment of Aging-Related Tau Astrogliopathy (ARTAG).

Aging-related tau astrogliopathy (ARTAG) is a recently introduced terminology. To facilitate the consistent identification of ARTAG and to distinguish it from astroglial tau pathologies observed in the primary frontotemporal lobar degeneration tauopathies we evaluated how consistently neuropathologists recognize (1) different astroglial tau immunoreactivities, including those of ARTAG and those associated with primary tauopathies (Study 1); (2) ARTAG types (Study 2A); and (3) ARTAG severity (Study 2B). Microphotographs and scanned sections immunostained for phosphorylated tau (AT8) were made available for download and preview. Percentage of agreement and kappa values with 95% confidence interval (CI) were calculated for each evaluation. The overall agreement for Study 1 was >60% with a kappa value of 0.55 (95% CI 0.433-0.645). Moderate agreement (>90%, kappa 0.48, 95% CI 0.457-0.900) was reached in Study 2A for the identification of ARTAG pathology for each ARTAG subtype (kappa 0.37-0.72), whereas fair agreement (kappa 0.40, 95% CI 0.341-0.445) was reached for the evaluation of ARTAG severity. The overall assessment of ARTAG showed moderate agreement (kappa 0.60, 95% CI 0.534-0.653) among raters. Our study supports the application of the current harmonized evaluation strategy for ARTAG with a slight modification of the evaluation of its severity.

The HIV-derived protein Vpr52-96 has anti-glioma activity in vitro and in vivo.

Patients with actively replicating human immunodeficiency virus (HIV) exhibit adverse reactions even to low irradiation doses. High levels of the virus-encoded viral protein R (Vpr) are believed to be one of the major underlying causes for increased radiosensitivity. As Vpr efficiently crosses the blood-brain barrier and accumulates in astrocytes, we examined its efficacy as a drug for treatment of glioblastoma multiforme (GBM).In vitro, four glioblastoma-derived cell lines with and without methylguanine-DNA methyltransferase (MGMT) overexpression (U251, U87, U251-MGMT, U87-MGMT) were exposed to Vpr, temozolomide (TMZ), conventional photon irradiation (2 to 6 Gy) or to combinations thereof. Vpr showed high rates of acute toxicities with median effective doses of 4.0±1.1 µM and 15.7±7.5 µM for U251 and U87 cells, respectively. Caspase assays revealed Vpr-induced apoptosis in U251, but not in U87 cells. Vpr also efficiently inhibited clonogenic survival in both U251 and U87 cells and acted additively with irradiation. In contrast to TMZ, Vpr acted independently of MGMT expression.Dose escalation in mice (n=12) was feasible and resulted in no evident renal or liver toxicity. Both, irradiation with 3x5 Gy (n=8) and treatment with Vpr (n=5) delayed intracerebral tumor growth and prolonged overall survival compared to untreated animals (n=5; p3x5 Gy<0.001 and pVpr=0.04; log-rank test).Our data show that the HIV-encoded peptide Vpr exhibits all properties of an effective chemotherapeutic drug and may be a useful agent in the treatment of GBM.

Association among pain, masticatory performance, and proinflammatory cytokines in crevicular fluid during orthodontic treatment.

INTRODUCTION: Orthodontic patients usually complain about masticatory limitations associated with the activation of fixed appliances. The aim of this investigation was to evaluate whether orthodontic pain reflects differences in the objective evaluation of mastication and in the levels of proinflammatory cytokines in the crevicular fluid of patients undergoing orthodontic treatment. METHODS: Twenty patients with malocclusions requiring orthodontic treatment were included in this prospective study. Their pain experience, masticatory performance, and levels of interleukin 1-beta and prostaglandin E2 in crevicular fluid were evaluated at 3 times: before bracket placement, 24 hours after archwire placement, and 30 days after the initial appointment. All variables were compared with those of a control group of 25 subjects with normal occlusion. RESULTS: The masticatory performance of the patients was significantly reduced at 24 hours after bracket placement, the period in which they reported higher values of pain and had higher levels of interleukin 1-beta. The levels of prostaglandin E2 did not change in the periods evaluated, and there were no correlations between the levels of cytokines and the functional limitations observed. The only significant correlation was between pain and decreased masticatory performance. CONCLUSIONS: The masticatory performance of orthodontic patients is significantly reduced only during the period of greatest pain. However, these alterations did not correlate with any measurement of interleukin 1-beta or prostaglandin E2 in the crevicular fluid, suggesting that these solitary measurements are inadequate to predict the temporary pain and masticatory limitations experienced by patients undergoing orthodontic treatment.

Axon-carrying dendrites convey privileged synaptic input in hippocampal neurons.

Neuronal processing is classically conceptualized as dendritic input, somatic integration, and axonal output. The axon initial segment, the proposed site of action potential generation, usually emanates directly from the soma. However, we found that axons of hippocampal pyramidal cells frequently derive from a basal dendrite rather than from the soma. This morphology is particularly enriched in central CA1, the principal hippocampal output area. Multiphoton glutamate uncaging revealed that input onto the axon-carrying dendrites (AcDs) was more efficient in eliciting action potential output than input onto regular basal dendrites. First, synaptic input onto AcDs generates action potentials with lower activation thresholds compared with regular dendrites. Second, AcDs are intrinsically more excitable, generating dendritic spikes with higher probability and greater strength. Thus, axon-carrying dendrites constitute a privileged channel for excitatory synaptic input in a subset of cortical pyramidal cells.

Anatomy of the hippocampal formation.

The hippocampus is one of several brain regions that together comprise the hippocampal formation. The hippocampal formation is a prominent C-shaped structure bulging in the floor of the temporal horn of the lateral ventricle. The hippocampus proper consists of three major subfields (CA1-CA3). The other regions that together comprise the hippocampal formation consist of the dentate gyrus, the subicular complex, and the entorhinal cortex. Based on its extrinsic connectivity, the hippocampal formation receives a vast amount of highly processed multimodal sensory information that is funneled into the hippocampal formation mainly by the entorhinal cortex. The entorhinal cortex is connected to associational neocortical areas in a reciprocal manner. Extensive hippocampal integration of sensory information is established by a largely unidirectional chain of intrinsic hippocampal projections. Our current knowledge on hippocampal connectivity and function is largely based on studies of rodents and monkeys. It still remains to be determined to which extent such neuroanatomical data of experimental animals is applicable to the human hippocampal formation.

A period of structural plasticity at the axon initial segment in developing visual cortex.

Cortical networks are shaped by sensory experience and are most susceptible to modifications during critical periods characterized by enhanced plasticity at the structural and functional level. A system particularly well-studied in this context is the mammalian visual system. Plasticity has been documented for the somatodendritic compartment of neurons in detail. A neuronal microdomain not yet studied in this context is the axon initial segment (AIS) located at the proximal axon segment. It is a specific electrogenic axonal domain and the site of action potential (AP) generation. Recent studies showed that structure and function of the AIS can be dynamically regulated. Here we hypothesize that the AIS shows a dynamic regulation during maturation of the visual cortex. We therefore analyzed AIS length development from embryonic day (E) 12.5 to adulthood in mice. A tri-phasic time course of AIS length remodeling during development was observed. AIS first appeared at E14.5 and increased in length throughout the postnatal period to a peak between postnatal day (P) 10 to P15 (eyes open P13-14). Then, AIS length was reduced significantly around the beginning of the critical period for ocular dominance plasticity (CP, P21). Shortest AIS were observed at the peak of the CP (P28), followed by a moderate elongation toward the end of the CP (P35). To test if the dynamic maturation of the AIS is influenced by eye opening (onset of activity), animals were deprived of visual input before and during the CP. Deprivation for 1 week prior to eye opening did not affect AIS length development. However, deprivation from P0 to 28 and P14 to 28 resulted in AIS length distribution similar to the peak at P15. In other words, deprivation from birth prevents the transient shortening of the AIS and maintains an immature AIS length. These results are the first to suggest a dynamic maturation of the AIS in cortical neurons and point to novel mechanisms in the development of neuronal excitability.

Nerve growth factor induces sensitization of nociceptors without evidence for increased intraepidermal nerve fiber density.

Nerve growth factor (NGF) is involved in the long-term sensitization of nociceptive processing linked to chronic pain. Functional and structural ("sprouting") changes can contribute. Thus, humans report long-lasting hyperalgesia to mechanical and electrical stimulation after intradermal NGF injection and NGF-induced sprouting has been reported to underlie cancer bone pain and visceral pain. Using a human-like animal model we investigated the relationship between the structure and function of unmyelinated porcine nociceptors 3 weeks after intradermal NGF treatment. Axonal and sensory characteristics were studied by in vivo single-fiber electrophysiology and immunohistochemistry. C fibers recorded extracellularly were classified based on mechanical response and activity-dependent slowing (ADS) of conduction velocity. Intraepidermal nerve fiber (IENF) densities were assessed by immunohistochemistry in pigs and in human volunteers using the same NGF model. NGF increased conduction velocity and reduced ADS and propagation failure in mechano-insensitive nociceptors. The proportion of mechano-sensitive C nociceptors within NGF-treated skin areas increased from 45.1% (control) to 71% and their median mechanical thresholds decreased from 40 to 20 mN. After NGF application, the mechanical receptive fields of nociceptors increased from 25 to 43 mm(2). At the structural level, however, IENF density was not increased by NGF. In conclusion, intradermal NGF induces long-lasting axonal and mechanical sensitization in porcine C nociceptors that corresponds to hyperalgesia observed in humans. Sensitization is not accompanied by increased IENF density, suggesting that NGF-induced hyperalgesia might not depend on changes in nerve fiber density but could be linked to the recruitment of previously silent nociceptors.