Biomedical subjects

T Pizzorusso

Publications and source records attributed to T Pizzorusso.

At least 19 recordsLinked to original sources

PubMed2001

3,5,3'-Triiodothyronine deprivation affects phenotype and intracellular [Ca2+]i of human cardiomyocytes in culture.

OBJECTIVE: A decrease in plasma T3 concentration is a frequent finding in patients with heart failure. However, the role of this 'low T3 syndrome' on disease evolution has never been clarified. As phenotypic and functional cardiomyocyte impairments are alterations that correlate with the failing myocardium, we studied the long-term effects of T3 deprivation on human cardiomyocyte structure and calcium handling. METHODS: Atrial cardiomyocytes and myocardial tissue were cultured with or without 3 nM T3. Microscopical examination of structural features was followed by analysis of alpha-sarcomeric actinin and sarcoplasmic reticulum calcium ATP-ase (SERCA-2) content. Calcium handling was studied by [Ca2+](i) imaging. RESULTS: When stimulated with cyclopiazonic acid, a SERCA-2 inhibitor, T3-deprived cardiomyocytes showed significantly faster (P=0.03) and more transient (P=0.04) increases in [Ca(2+)](i) than T3-supplemented cells. Moreover, in the T3-free cultures a significantly lower number of cells (P=0.003) responded to caffeine, a typical activator of sarcoplasmic reticulum Ca(2+)-release channel. T3-deprived cardiomyocytes also presented altered morphology with larger dimensions than T3-supplemented cells (P < 0.0001). Additionally, in T3-deprived samples alpha-sarcomeric actinin and SERCA-2 protein levels were reduced to 65.6 +/- 3% (P < 0.0001) and 74.1 +/- 4% (P=0.005), respectively, when compared with the T3-supplemented group. CONCLUSIONS: Our data show that human cardiomyocyte calcium handling and phenotype are strongly influenced by T3 suggesting important implications of the 'low T3 syndrome' on the progression of heart failure.

Blotting, Western↗

PubMed2001

Requirement of ERK activation for visual cortical plasticity.

Experience-dependent plasticity in the developing visual cortex depends on electrical activity and molecular signals involved in stabilization or removal of inputs. Extracellular signal-regulated kinase 1,2 (also called p42/44 mitogen-activated protein kinase) activation in the cortex is regulated by both factors. We show that two different inhibitors of the ERK pathway suppress the induction of two forms of long-term potentiation (LTP) in rat cortical slices and that their intracortical administration to monocularly deprived rats prevents the shift in ocular dominance towards the nondeprived eye. These results demonstrate that the ERK pathway is necessary for experience-dependent plasticity and for LTP of synaptic transmission in the developing visual cortex.

Animals↗

PubMed2001

Requirement of the nicotinic acetylcholine receptor beta 2 subunit for the anatomical and functional development of the visual system.

In the mammalian visual system the formation of eye-specific layers at the thalamic level depends on retinal waves of spontaneous activity, which rely on nicotinic acetylcholine receptor activation. We found that in mutant mice lacking the beta2 subunit of the neuronal nicotinic receptor, but not in mice lacking the alpha4 subunit, retinofugal projections do not segregate into eye-specific areas, both in the dorso-lateral geniculate nucleus and in the superior colliculus. Moreover, beta2-/- mice show an expansion of the binocular subfield of the primary visual cortex and a decrease in visual acuity at the cortical level but not in the retina. We conclude that the beta2 subunit of the nicotinic acetylcholine receptor is necessary for the anatomical and functional development of the visual system.

Animals↗

PubMed2000

Brain-derived neurotrophic factor causes cAMP response element-binding protein phosphorylation in absence of calcium increases in slices and cultured neurons from rat visual cortex.

Neurotrophins play a crucial role in the developmental plasticity of the visual cortex, but very little is known about the cellular mechanisms involved in their action. In many models of synaptic plasticity, increases in cytosolic calcium concentration and activation of the transcription factor cAMP response element-binding protein (CREB) are crucial factors for the induction and maintenance of long-lasting changes of synaptic efficacy. Whether BDNF modulates intracellular calcium levels in visual cortical neurons and the significance of this action for BDNF signal transduction is still controversial. We investigated whether CREB phosphorylation and calcium changes are elicited by acute BDNF presentation in postnatal visual cortical slices and cultures. We found that BDNF did not cause any calcium increase, but it induced robust CREB phosphorylation in neurons from both preparations. We further analyzed signal transduction and its dependency on calcium changes in cultured neurons. CREB phosphorylation required trkB activation because treatment with the trk inhibitor k252a completely blocked CREB phosphorylation. In agreement with the imaging experiments, we verified that calcium changes were not necessary for CREB activation because preincubation with BAPTA-AM did not diminish the level of CREB phosphorylation induced by BDNF stimulation. CREB phosphorylation was accompanied by gene expression, because we observed the upregulation of c-fos expression, which was also not affected by preincubation with BAPTA-AM. Finally, BDNF caused phosphorylation of mitogen-activated protein kinase (MAPK), and because the treatment with the MAPK inhibitor U0126 completely abolished CREB activation and c-fos upregulation, it is likely that both processes depend mainly on the MAP kinase pathway. These results indicate that MAPK and CREB, but not intracellular calcium, are important mediators of neurotrophin actions in the visual cortex.

Activating Transcription Factor 2↗

PubMed2000

Effects of neurotrophins on cortical plasticity: same or different?

Neurotrophins are important regulators of visual cortical plasticity. It is still unclear, however, whether they play similar or different roles and which are their effects on the electrical activity of cortical neurons in vivo. We therefore compared the effects of all neurotrophins, nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-4 (NT-4), and neurotrophin-3 (NT-3) on visual cortical plasticity and on cell spontaneous and visually evoked activity. Rats were monocularly deprived for 1 week at the peak of the critical period, and neurotrophins were infused intracortically. The main finding is that, with the exception of NT-3, all neurotrophins affect the outcome of monocular deprivation, but there are clear differences in their mechanisms of action. In particular, NT-4 and NGF counteract monocular deprivation effects without causing detectable alterations either in spontaneous or visually evoked neuronal activity. BDNF is less effective on ocular dominance plasticity and, in addition, strongly affects spontaneous and visually evoked activity in cortical neurons.

Animals↗

PubMed2000

Role of neurotrophins in the development and plasticity of the visual system: experiments on dark rearing.

An extensive series of studies, beginning with the pioneering experiments of Wiesel and Hubel, have shown that correct visual experience is crucial for the development of the visual system. Several years ago, we put forward the hypothesis that neurotrophic factors of the neurotrophin family (NGF, BDNF, NT-3, NT-4) have a role in mediating the effects of visual experience in the developing visual system. This theory is based on the following experimental results: (a) exogenous supply of neurotrophins during the critical period prevents the effects of monocular deprivation; and (b) transplant of cells releasing NGF allows a normal development of the functional properties of visual cortical neurons in dark-reared rats.

Animals↗

PubMed2000

Critical periods during sensory development.

Recent studies have made progress in characterizing the determinants of critical periods for experience-dependent plasticity. They highlight the role of neurotrophins, NMDA receptors and GABAergic inhibition. In particular, genetic manipulation of a single molecule, brain-derived neurotrophic factor (BDNF), has been shown to alter the timing of the critical period of plasticity in mouse visual cortex, establishing a causal relation between neurotrophin action, the development of visual function, and the duration of the critical period.

Animals↗

PubMed1999

BDNF regulates the maturation of inhibition and the critical period of plasticity in mouse visual cortex.

Maturation of the visual cortex is influenced by visual experience during an early postnatal period. The factors that regulate such a critical period remain unclear. We examined the maturation and plasticity of the visual cortex in transgenic mice in which the postnatal rise of brain-derived neurotrophic factor (BDNF) was accelerated. In these mice, the maturation of GABAergic innervation and inhibition was accelerated. Furthermore, the age-dependent decline of cortical long-term potentiation induced by white matter stimulation, a form of synaptic plasticity sensitive to cortical inhibition, occurred earlier. Finally, transgenic mice showed a precocious development of visual acuity and an earlier termination of the critical period for ocular dominance plasticity. We propose that BDNF promotes the maturation of cortical inhibition during early postnatal life, thereby regulating the critical period for visual cortical plasticity.

Age Factors↗

PubMed1999

The visual physiology of the wild type mouse determined with pattern VEPs.

Genetically manipulated mice are important tools for studies on plasticity and degeneration/regeneration in the visual system. However, a description of the basic properties of the visual performance of the wild type mouse is still lacking. To characterize the visual physiology of the wild type (C57BL/6J) mouse we recorded Visual Evoked Potentials (VEPs) from the primary visual cortex. As compared to behavioral methods, VEPs may have the advantage that different aspects of vision can be screened readily and simultaneously in the same animals, including those with poor visual behavior due to motor or learning deficits. Local VEP responses to patterned visual stimuli have been recorded from the binocular visual cortex of anesthetized mice. Spatial (visual acuity, contrast threshold) and temporal (temporal function, response latency, motion sensitivity) aspects of VEPs were evaluated. The mouse VEP acuity was 0.6 c/deg, which is comparable to the behavioral visual acuity. The VEP peak contrast threshold was 5% (no behavioral data are available). Cortical representation of visual coordinates and cortical magnification factor corresponded to those previously reported using single cell recordings. Laminar analysis of VEPs indicated a dipole source in the supragranular layers of the visual cortex as a major response generator. VEPs showed contribution from both eyes, although biased strongly towards the eye contralateral to the recorded cortex. Results provide a comprehensive framework for characterizing visual phenotypes of a variety of transgenic mice.

Animals↗

PubMed1999

Monocular deprivation decreases brain-derived neurotrophic factor immunoreactivity in the rat visual cortex.

Neurotrophins play a crucial role in the development and activity-dependent plasticity of the visual cortex [Berardi N. et al. (1994) Proc. natn. Acad. Sci. U.S.A. 91, 684-688; Bonhoeffer T. (1996) Curr. Opin. Neurobiol. 6, 119-126; Cellerino A. and Maffei L. (1996) Prog. Neurobiol. 49, 53-71; Domenici L. et al. (1994) NeuroReport 5, 2041-2044; Galuske R. A. W. et al (1996) Eur. J. Neurosci. 8, 1554-1559; Katz L. C. and Shatz C. J. (1996) Science 274, 1133-1138; Maffei L. et al. (1992) J. Neurosci. 12, 4651-4662; Pizzorusso T. and Maffei L. (1996) Curr. Opin. Neurol. 9, 122-125; Thoenen H. (1995) Science 270, 593-598]. As a possible mechanism of action, it has been postulated that the activity-dependent expression of neurotrophins by cortical cells could regulate synapse stabilization during the first period of postnatal life (critical period). Indeed, brain-derived neurotrophic factor messenger RNA expression in the visual cortex is regulated by neuronal activity as well as during development [Castrén E. et al. (1992) Proc. natn. Acad. Sci. U.S.A. 89, 9444-9448]. Moreover, we showed that monocular deprivation decreases brain-derived neurotrophic factor messenger RNA levels in the visual cortex receiving input from the deprived eye [Bozzi Y. et al. (1995) Neuroscience 69, 1133-1144]. What is missing, however, is the demonstration that brain-derived neurotrophic factor protein expression follows that of brain-derived neurotrophic factor messenger RNA. The aim of the present study is to fill this important gap in order to support the hypothesis that brain-derived neurotrophic factor is fundamental in the plasticity of the visual cortex. We found that brain-derived neurotrophic factor immunoreactivity peaks during the critical period and that it is preferentially localized in layers II-III and V-VI. We also demonstrated that monocular deprivation determines a decrease of brain-derived neurotrophic factor immunoreactivity exclusively in the visual cortex contralateral to the deprived eye. Our results support the proposed role for brain-derived neurotrophic factor in the development and activity-dependent plasticity of the visual cortex [Cabelli R. J. et al. (1995) Science 267, 1662-1666].

Aging↗

PubMed1999

Expression of the transcription factor Zif268 in the visual cortex of monocularly deprived rats: effects of nerve growth factor.

Neurotrophins are known to be involved in experience-dependent plasticity of the visual cortex. Here, we have characterized in detail the effects of intraventricular nerve growth factor infusion in monocularly deprived rats by using immunostaining for the immediate-early gene product Zif268 as a marker of functional activity with cellular resolution. We have taken advantage of the rapid regulation of Zif268 by visual input to reveal the cortical units that are responsive to the deprived eye after a period of monocular deprivation. We found that responses to the deprived eye were significantly preserved in the cortex of monocularly deprived rats infused with nerve growth factor. The effects of nerve growth factor were greater for cortical cells located in deep layers and with more peripheral receptive fields. Results from Zif268 staining correlated very well with those obtained by single-cell recordings from the visual cortex. Our results demonstrate that exogenous nerve growth factor preserves the functional input from the deprived eye, enabling cortical neurons to activate immediate-early gene expression in response to stimulation of the deprived eye. Furthermore, we show that the intraventricular infusion of nerve growth factor differentially affects the ocular dominance of cells at various depths and eccentricities in the developing cortex.

Animals↗

PubMed1999

TrkA activation in the rat visual cortex by antirat trkA IgG prevents the effect of monocular deprivation.

It has been recently shown that intraventricular injections of nerve growth factor (NGF) prevent the effects of monocular deprivation in the rat. We have tested the localization and the molecular nature of the NGF receptor(s) responsible for this effect by activating cortical trkA receptors in monocularly deprived rats by cortical infusion of a specific agonist of NGF on trkA, the bivalent antirat trkA IgG (RTA-IgG). TrkA protein was detected by immunoblot in the rat visual cortex during the critical period. Rats were monocularly deprived for 1 week (P21-28) and RTA-IgG or control rabbit IgG were delivered by osmotic minipumps. The effects of monocular deprivation on the ocular dominance of visual cortical neurons were assessed by extracellular single cell recordings. We found that the shift towards the ipsilateral, non-deprived eye was largely prevented by RTA-IgG. Infusion of RTA-IgG combined with antibody that blocks p75NTR (REX), slightly reduced RTA-IgG effectiveness in preventing monocular deprivation effects. These results suggest that NGF action in visual cortical plasticity is mediated by cortical TrkA receptors with p75NTR exerting a facilitatory role.

Action Potentials↗

PubMed1999

Role of neurotrophins in neural plasticity: what we learn from the visual cortex.

A role for neurotrophins in regulating cortical developmental plasticity has clearly emerged in these last years. In this review we first present a summary of the early data on the action of NGF in visual cortical development and plasticity in the rat and of the actions of the other neurotrophins in the visual cortex of other mammals. In addition, in order to clarify the differences in the results obtained with the various neurotrophins in different animal preparations we also report new data on the action of NGF, BDNF, NT3 and NT4 in the same preparation, namely the visual cortex of the rat. We discuss old and new results in a physiological model where different neurotrophins play different roles in regulating visual cortical development and plasticity by acting on different neural targets, such as LGN afferents, intracortical circuitry and subcortical afferents and propose a tentative scheme summarizing these actions.

Journal Article↗

PubMed1998

Protection of retinal ganglion cells and preservation of function after optic nerve lesion in bcl-2 transgenic mice.

Multicellular organisms face the necessity of removing superfluous or injured cells during normal development, tissue turn-over and in response to damaging conditions. These finalised killings occur throughout a process, commonly called programmed cell death (PCD), which is placed under strict cellular control. PCD is regulated by the products of the expression of a number of genes. This fact raises the intriguing possibility of inhibiting such degenerative processes by operating on some of the controlling genes. Central neurons of transgenic mice overexpressing bcl-2, a powerful inhibitor of PCD, are remarkably resistant to degeneration induced by noxious stimuli. We have explored the ate of retinal ganglion cells and of their axons, when such transgenic animals have been challenged by a lesion of the optic nerve. These results have direct bearing on the possibility of attaining functional restoration of the injured pathway.

Animals↗

PubMed1998

Nerve growth factor and brain-derived neurotrophic factor increase neurotransmitter release in the rat visual cortex.

A number of experiments have shown that neurotrophins are involved in the development and plasticity of the visual cortex (Bonhoeffer, T., Curr. Op. Neurobiol., 6, 119, 1996). A possible mechanism underlying these effects is the neurotrophin modulation of synaptic transmission. We investigated whether nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) can modulate the release of neurotransmitter in the rat visual cortex at the peak of the critical period for plasticity (P23). The release of glutamate, acetylcholine and gamma-aminobutyric acid (GABA) from visual cortical synaptosomes was analysed in continuous perfusion conditions. We found that NGF enhances the depolarization-evoked release of glutamate (approximately 90%) and acetylcholine (approximately 35%) but not that of GABA. By contrast, BDNF enhances the depolarization-evoked release of all three neurotransmitters investigated (approximately 30%). BDNF and NGF were ineffective on basal release of neurotransmitters. The effect of NGF was not blocked by cholinergic antagonists atropine and mecamylamine. NGF and BDNF potentiation of transmitter release was strongly but not completely blocked by K252a, a tyrosine kinase inhibitor. The role of TrkA and p75NTR receptors was investigated in NGF-induced potentiation of glutamate release. Block of NGF binding to p75NTR using specific blocking antibodies (REX-IgG) slightly but significantly reduced the effect of NGF. Activation of TrkA in isolation by RTA-IgG, an antibody that specifically activates TrkA, was less effective than activation of both receptors by NGF. These results show that neurotrophin action on neurotransmitter release was mostly mediated by Trk receptors with p75NTR having a little but significant positive role. Antigen blot analysis showed the presence of TrkA, TrkB and p75NTR receptors in the visual cortex.

Animals↗

PubMed1997

Brain-derived neurotrophic factor and nerve growth factor potentiate excitatory synaptic transmission in the rat visual cortex.

1. The effect of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) on excitatory synaptic transmission in the developing visual cortex was studied by whole-cell patch-clamp recordings from rat brain slices. 2. Both neurotrophins induced a rapid increase in the amplitude of impulse-evoked excitatory postsynaptic currents (EPSCs). BDNF also increased the frequency of spontaneous EPSCs. 3. Analysis of the currents revealed that alpha-amino-3-hydroxy-5-methyl-isoxazole propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor-mediated components contributing to the EPSC peak amplitude were equally potentiated by the neurotrophins. 4. When synaptic transmission was studied by minimal stimulation of intracortical afferents, neurotrophins induced a decrease in the occurrence of release failures. 5. A number of neurones were insensitive to the effects of the neurotrophins, possibly related to the considerable heterogeneity of neuronal types and to the uneven distribution of neurotrophin receptors in the visual cortex. 6. The probability of neurotransmitter release represents a rapidly modifiable synaptic feature by which neurotrophins can potentiate the efficacy of excitatory synaptic transmission in the visual cortex.

Animals↗

PubMed1997

Temporal aspects of contrast visual evoked potentials in the pigmented rat: effect of dark rearing.

Cortical visual evoked potentials (VEPs) in response to gratings temporally modulated in counterphase were recorded in normal and dark-reared pigmented rats. Temporal modulation was either sinusoidal (0.25-15 Hz, steady state condition) or abrupt (0.5 Hz, transient condition). In normals, the amplitude spectrum of contrast VEPs has two peaks (at about 0.5 and 4 Hz) and a high temporal frequency cut-off of the order of 11 Hz. The VEP phase lags with temporal frequency, showing two different linear slopes for separate frequency ranges (0.25-1 Hz and 1-7 Hz) centred on the peaks of the curve. The different slopes correspond to apparent latencies of 500 and 136 msec, respectively. Dark rearing reduced the cut-off frequency by about 3 Hz and increased apparent latencies by about 42 msec in the low temporal frequency range and 30 msec in the high temporal frequency range. The latency of the first peak of transient VEPs was increased by about 47 msec. Results indicate that the frequency response of rat contrast VEPs is qualitatively similar to that of other mammals (including human), albeit shifted to a lower range of temporal frequencies. Dark rearing significantly alters the VEP temporal characteristics, suggesting that visual experience is necessary for their correct development.

Animals↗

PubMed1997

Transplant of polymer-encapsulated cells genetically engineered to release nerve growth factor allows a normal functional development of the visual cortex in dark-reared rats.

Visual experience is necessary for the normal development of the visual system. Dark-reared mammals show abnormal vision when reintroduced into a normal environment. The absence of visual experience during the critical period results in reduced and/or inappropriate neural responses in visual cortical neurons. The change in electrical activity induced by dark rearing is probably reflected by the modulation of specific unknown molecules. Neurotrophins are present in the developing visual cortex and their production depends on visually driven electrical activity. Recent findings support the possibility that an important link between electrical activity in the visual pathway and correct development of visual properties is represented by neurotrophins. We advance the hypothesis that the visual abnormalities present in dark-reared animals could be due to a decreased production of a neurotrophin secondary to the lack of visual stimulation. We report that some properties of visual cortical response such as receptive field size, orientation selectivity, adaptation to repeated stimulation, response latency and visual acuity are virtually normal in dark-reared rats transplanted with polymer-encapsulated baby hamster kidney cells genetically engineered to release nerve growth factor.

Adaptation, Ocular↗