La Carta Del Restauro del Contemporaneo. Uno strumento utile?

There is an urgent need for renovation in the field of contemporary art restoration that cannot be provided by the 1972 and 1987 Restoration Charters. What is required, however, is not a new Charter, which would risk becoming obsolete within a few years, but a series of commonly shared guidelines to help manage the heterogeneity of contemporary artwork. Compared to previous centuries, in fact, modern artists have been able to experiment with new chemical products and materials that can deteriorate quickly. This gives rise to several questions, one of which is: can traditional restoration principles still be considered valid? The answer is, yes, in part. For example, some concepts of preventive maintenance, retractability, and minor intervention still seem relevant. Another important issue is the possibility of rebuilding the creative process underlying these new works of art to identify any common aspects. Interviewing the artist and examining any existing archival sources about an artwork\u2019s exhibition and ownership history, would be very helpful. Concerning restorations, it would be inadvisable to have artists carry them out themselves, because this would restart the creative process, resulting in entirely new works of art. This paper will highlight these and other issues and provide some useful suggestions to help guide us through this new artistic landscape in an attempt to preserve the different types of cultural heritage for future generations

Paired-pulse depression at photoreceptor synapses.

Synaptic depression produced by repetitive stimulation is likely to be particularly important in shaping responses of second-order retinal neurons at the tonically active photoreceptor synapse. We analyzed the time course and mechanisms of synaptic depression at rod and cone synapses using paired-pulse protocols involving two complementary measurements of exocytosis: (1) paired whole-cell recordings of the postsynaptic current (PSC) in second-order retinal neurons and (2) capacitance measurements of vesicular membrane fusion in rods and cones. PSCs in ON bipolar, OFF bipolar, and horizontal cells evoked by stimulation of either rods or cones recovered from paired-pulse depression (PPD) at rates similar to the recovery of exocytotic capacitance changes in rods and cones. Correlation between presynaptic and postsynaptic measures of recovery from PPD suggests that 80-90% of the depression at these synapses is presynaptic in origin. Consistent with a predominantly presynaptic mechanism, inhibiting desensitization of postsynaptic glutamate receptors had little effect on PPD. The depression of exocytotic capacitance changes exceeded depression of the presynaptic calcium current, suggesting that it is primarily caused by a depletion of synaptic vesicles. In support of this idea, limiting Ca2+ influx by using weaker depolarizing stimuli promoted faster recovery from PPD. Although cones exhibit much faster exocytotic kinetics than rods, exocytotic capacitance changes recovered from PPD at similar rates in both cell types. Thus, depression of release is not likely to contribute to differences in the kinetics of transmission from rods and cones

Kinetics of exocytosis is faster in cones than in rods.

Cone-driven responses of second-order retinal neurons are considerably faster than rod-driven responses. We examined whether differences in the kinetics of synaptic transmitter release from rods and cones may contribute to differences in postsynaptic response kinetics. Exocytosis from rods and cones was triggered by membrane depolarization and monitored in two ways: (1) by measuring EPSCs evoked in second-order neurons by depolarizing steps applied to presynaptic rods or cones during simultaneous paired whole-cell recordings or (2) by direct measurements of exocytotic increases in membrane capacitance. The kinetics of release was assessed by varying the length of the depolarizing test step. Both measures of release revealed two kinetic components to the increase in exocytosis as a function of the duration of a step depolarization. In addition to slow sustained components in both cell types, the initial fast component of exocytosis had a time constant ofcones, \u3e10-fold faster than that of rods. Rod/cone differences in the kinetics of release were substantiated by a linear correlation between depolarization-evoked capacitance increases and EPSC charge transfer. Experiments on isolated rods indicate that the slower kinetics of exocytosis from rods was not a result of rod-rod coupling. The initial rapid release of vesicles from cones can shape the postsynaptic response and may contribute to the faster responses of cone-driven cells observed at light offset

Le Archeidi di Giulio Turcato problematiche conservative e proposte di intervento

Le Archeidi, gruppo scultoreo composto da cinque elementi realizzati con laminati di ferro a struttura tubolare assemblati artigianalmente, sono alte circa quattro metri e il loro ingombro varia tra gli ottanta e i novanta centimetri. Vennero realizzate da Giulio Turcato nel 1989 per la citt\ue0 di Salerno, in occasione della prima edizione di \u201cSalerno Incontri d\u2019Arte\u201d, parallelamente alla mostra \u201cGiulio Turcato per/Corso\u201d, tenutasi in tre gallerie della citt\ue0 \u201cLa Bottegaccia\u201d, \u201cIl Catalogo\u201d e \u201cLa Seggiola\u201d. Il gruppo scultoreo era composto da quattro elementi che erano stati scherzosamente definiti dal maestro \u201caculei\u201d e da un quinto che ricordava le sembianze di un \u201cfiore\u201d. Purtroppo, appena le opere vennero collocate lungo il percorso cittadino, una sub\uec un atto vandalico mentre un\u2019altra venne trafugata. Le cinque sculture furono realizzate, seguendo il progetto dell\u2019artista, nella bottega di un fabbro salernitano e successivamente trattate cromaticamente. Le ragioni principali del degrado delle Archeidi sono legate alla collocazione in ambiente esterno e al fatto che l\u2019aspettativa di vita dei materiali utilizzati non garantisce la durabilit\ue0 del gruppo scultoreo. Quattro strutture, di propriet\ue0 del Comune di Salerno, si presentano oggi in un precario stato di conservazione, aggravato dall\u2019umidit\ue0 dello spazio dove sono conservate. Ad un\u2019osservazione preliminare si riscontra un viraggio completo dei colori e la presenza diffusa di ruggine. Le opere, dopo un accurato intervento di restauro, attendono di trovare una nuova collocazione che risponda alle necessit\ue0 di una buona conservazione e al tempo stesso alla natura di \u201copera ambientale\u201d cos\uec come ideata dall\u2019artista

Il Grano di Pietro Gaudenzi. Stato di conservazione e problematiche di intervento

L\u2019opera Il grano (\u201cdipinto murale su intonaco applicato a masonite\u201d, cm 249x434, Pinacoteca del Museo Civico \u201cAla Ponzone\u201d di Cremona) viene realizzata da Pietro Gaudenzi nel 1940 per la seconda edizione del Premio Cremona istituito da Roberto Farinacci nel 1939, a seguito della necessit\ue0 di rafforzare il mercato e le quotazioni d\u2019arte attraverso mostre e premi che richiamassero i valori dell\u2019ideologia fascista in campo artistico. I cartoni preparatori degli affreschi eseguiti da Gaudenzi a Rodi, raccolti nella recente mostra (2015) Pietro Gaudenzi: gli affreschi perduti del Castello dei Cavalieri a Rodi [1], ritenuti l\u2019ultima testimonianza rimasta delle pitture murali che occupavano la Sala del pane e la Sala della famiglia del Castello - ricostruito dagli italiani dal 1936 al 1940 - evocano il trittico che vincer\ue0 il premio Cremona nel 1940. Diversamente dalle tecniche sperimentali che hanno caratterizzato molte delle opere del ritorno alla tradizione decorativa murale, Gaudenzi dipinge il trittico su un intonaco composto da un aggregato silicatico e calce. Il disegno \ue8 stato eseguito tramite incisioni dirette da cartoni preparatori, successivamente ripassate con un tratto bruno, i colori sono stati scelti tra quelli tradizionalmente usati per questo tipo di pittura, unitamente a pigmenti inorganici minerali sintetici in uso a partire dal XIX secolo. L\u2019opera, realizzata su pannelli rigidi (masonite), risulta \u2013 sul fondo \u2013 impermeabile al vapore acqueo che, in situazioni di variazione dei parametri microclimatici ambientali e a causa delle frequenti movimentazioni del dipinto, provoca sollevamenti localizzati di forme tondeggianti (a bolla). La pellicola pittorica, resa leggermente plastica dalla vernice, si rigonfia distaccandosi dal supporto in quantit\ue0 talvolta, estese. I conseguenti necessari interventi di manutenzione, mirati al consolidamento dei sollevamenti, risultano particolarmente complessi per l\u2019impossibilit\ue0 di intervenire dal retro: la necessit\ue0 di attraversare il film protettivo e penetrare la pellicola pittorica in assenza di crettature ha evidenziato l\u2019estrema fragilit\ue0 sia del film pittorico che della materia sottostante. Lo studio presenta alcune metodologie di intervento utilizzate, nel tempo, per consolidare il trittico. La possibilit\ue0 di poter analizzare alcuni microframmenti ha richiesto l\u2019applicazione di una strategia analitica basata sull\u2019uso di microscopi e microsonde. La successione degli strati tecnici \ue8 stata definita in microscopia ottica (OM) ed elettronica a scansione (SEM), su \u201ccross section\u201d. Le tessiture e la composizione chimica dei leganti e dei pigmenti dei singoli strati sono state determinate utilizzando un sistema di microanalisi in dispersione di energia (EDS) e in spettrofotometria FT-IR. Questi dati integrano le informazioni ottenute con le tecniche non invasive d\u2019immagine (luminescenza UV, riflettografia IR e riprese IR in falso colore) e puntuali (XRF) realizzate in situ

Differential expression of microRNAs in mouse pain models

<p>Abstract</p> <p>Background</p> <p>MicroRNAs (miRNAs) are short non-coding RNAs that inhibit translation of target genes by binding to their mRNAs. The expression of numerous brain-specific miRNAs with a high degree of temporal and spatial specificity suggests that miRNAs play an important role in gene regulation in health and disease. Here we investigate the time course gene expression profile of miR-1, -16, and -206 in mouse dorsal root ganglion (DRG), and spinal cord dorsal horn under inflammatory and neuropathic pain conditions as well as following acute noxious stimulation.</p> <p>Results</p> <p>Quantitative real-time polymerase chain reaction analyses showed that the mature form of miR-1, -16 and -206, is expressed in DRG and the dorsal horn of the spinal cord. Moreover, CFA-induced inflammation significantly reduced miRs-1 and -16 expression in DRG whereas miR-206 was downregulated in a time dependent manner. Conversely, in the spinal dorsal horn all three miRNAs monitored were upregulated. After sciatic nerve partial ligation, miR-1 and -206 were downregulated in DRG with no change in the spinal dorsal horn. On the other hand, axotomy increases the relative expression of miR-1, -16, and 206 in a time-dependent fashion while in the dorsal horn there was a significant downregulation of miR-1. Acute noxious stimulation with capsaicin also increased the expression of miR-1 and -16 in DRG cells but, on the other hand, in the spinal dorsal horn only a high dose of capsaicin was able to downregulate miR-206 expression.</p> <p>Conclusions</p> <p>Our results indicate that miRNAs may participate in the regulatory mechanisms of genes associated with the pathophysiology of chronic pain as well as the nociceptive processing following acute noxious stimulation. We found substantial evidence that miRNAs are differentially regulated in DRG and the dorsal horn of the spinal cord under different pain states. Therefore, miRNA expression in the nociceptive system shows not only temporal and spatial specificity but is also stimulus-dependent.</p

Calcium Homeostasis and Cone Signaling Are Regulated by Interactions between Calcium Stores and Plasma Membrane Ion Channels

Calcium is a messenger ion that controls all aspects of cone photoreceptor function, including synaptic release. The dynamic range of the cone output extends beyond the activation threshold for voltage-operated calcium entry, suggesting another calcium influx mechanism operates in cones hyperpolarized by light. We have used optical imaging and whole-cell voltage clamp to measure the contribution of store-operated Ca2+ entry (SOCE) to Ca2+ homeostasis and its role in regulation of neurotransmission at cone synapses. Mn2+ quenching of Fura-2 revealed sustained divalent cation entry in hyperpolarized cones. Ca2+ influx into cone inner segments was potentiated by hyperpolarization, facilitated by depletion of intracellular Ca2+ stores, unaffected by pharmacological manipulation of voltage-operated or cyclic nucleotide-gated Ca2+ channels and suppressed by lanthanides, 2-APB, MRS 1845 and SKF 96365. However, cation influx through store-operated channels crossed the threshold for activation of voltage-operated Ca2+ entry in a subset of cones, indicating that the operating range of inner segment signals is set by interactions between store- and voltage-operated Ca2+ channels. Exposure to MRS 1845 resulted in ∼40% reduction of light-evoked postsynaptic currents in photopic horizontal cells without affecting the light responses or voltage-operated Ca2+ currents in simultaneously recorded cones. The spatial pattern of store-operated calcium entry in cones matched immunolocalization of the store-operated sensor STIM1. These findings show that store-operated channels regulate spatial and temporal properties of Ca2+ homeostasis in vertebrate cones and demonstrate their role in generation of sustained excitatory signals across the first retinal synapse

Synaptic Transmission from Horizontal Cells to Cones Is Impaired by Loss of Connexin Hemichannels

In the vertebrate retina, horizontal cells generate the inhibitory surround of bipolar cells, an essential step in contrast enhancement. For the last decades, the mechanism involved in this inhibitory synaptic pathway has been a major controversy in retinal research. One hypothesis suggests that connexin hemichannels mediate this negative feedback signal; another suggests that feedback is mediated by protons. Mutant zebrafish were generated that lack connexin 55.5 hemichannels in horizontal cells. Whole cell voltage clamp recordings were made from isolated horizontal cells and cones in flat mount retinas. Light-induced feedback from horizontal cells to cones was reduced in mutants. A reduction of feedback was also found when horizontal cells were pharmacologically hyperpolarized but was absent when they were pharmacologically depolarized. Hemichannel currents in isolated horizontal cells showed a similar behavior. The hyperpolarization-induced hemichannel current was strongly reduced in the mutants while the depolarization-induced hemichannel current was not. Intracellular recordings were made from horizontal cells. Consistent with impaired feedback in the mutant, spectral opponent responses in horizontal cells were diminished in these animals. A behavioral assay revealed a lower contrast-sensitivity, illustrating the role of the horizontal cell to cone feedback pathway in contrast enhancement. Model simulations showed that the observed modifications of feedback can be accounted for by an ephaptic mechanism. A model for feedback, in which the number of connexin hemichannels is reduced to about 40%, fully predicts the specific asymmetric modification of feedback. To our knowledge, this is the first successful genetic interference in the feedback pathway from horizontal cells to cones. It provides direct evidence for an unconventional role of connexin hemichannels in the inhibitory synapse between horizontal cells and cones. This is an important step in resolving a long-standing debate about the unusual form of (ephaptic) synaptic transmission between horizontal cells and cones in the vertebrate retina

A Positive Feedback Synapse from Retinal Horizontal Cells to Cone Photoreceptors

Cone photoreceptors and horizontal cells (HCs) have a reciprocal synapse that underlies lateral inhibition and establishes the antagonistic center-surround organization of the visual system. Cones transmit to HCs through an excitatory synapse and HCs feed back to cones through an inhibitory synapse. Here we report that HCs also transmit to cone terminals a positive feedback signal that elevates intracellular Ca2+ and accelerates neurotransmitter release. Positive and negative feedback are both initiated by AMPA receptors on HCs, but positive feedback appears to be mediated by a change in HC Ca2+, whereas negative feedback is mediated by a change in HC membrane potential. Local uncaging of AMPA receptor agonists suggests that positive feedback is spatially constrained to active HC-cone synapses, whereas the negative feedback signal spreads through HCs to affect release from surrounding cones. By locally offsetting the effects of negative feedback, positive feedback may amplify photoreceptor synaptic release without sacrificing HC-mediated contrast enhancement