Sunflower seed-derived bioactive peptides show antioxidant and anti-inflammatory activity: From in silico simulation to the animal model

The evolving field of food technology is increasingly dedicated to developing functional foods. This study explored bioactive peptides from sunflower protein isolate (SPI), obtained from defatted flour, a by-product of the oil processing industry. SPI underwent simulated gastrointestinal digestion and the obtained peptide-enriched fraction (PEF) showed antioxidant properties in vivo, in zebrafish. Among the peptides present in PEF identified by mass spectrometry analysis, we selected those with antioxidant properties by in silico evaluation, considering their capability to interact with Keap1, key protein in the regulation of antioxidant response. The selected peptides were synthesized and evaluated in a cellular model. As a result, DVAMPVPK, VETGVIKPG, TTHTNPPPEAE, LTHPQHQQQGPSTG and PADVTPEEKPEV activated Keap1/Nrf2 pathway leading to Antioxidant Response Element-regulated enzymes upregulation. Since the crosstalk between Nrf2 and NF-κB is well known, the potential anti-inflammatory activity of the peptides was assessed and principally PADVTPEEKPEV showed good features both as antioxidant and anti-inflammatory molecule.

Male violence disrupts estrogen receptor β signaling in the female hippocampus

Women are the main target of intimate partner violence (IPV), which is escalating worldwide. Mechanisms subtending IPV-related disorders, such as anxiety, depression and PTSD, remain unclear. We employed a mouse model molded on an IPV scenario (male vs. female prolonged violent interaction) to unearth the neuroendocrine alterations triggered by an aggressive male mouse on the female murine brain. Experimental IPV (EIPV) prompted marked anxiety-like behavior in young female mice, coincident with high circulating/cerebral corticosterone levels. The hippocampus of EIPV-inflicted female animals displayed neuronal loss, reduced BrdU-DCX-positive nuclei, decreased mature DCX-positive cells, and diminished dendritic arborization level in the dentate gyrus (DG), features denoting impaired neurogenesis and neuronal differentiation. These hallmarks were associated with marked down-regulation of estrogen receptor β (ERβ) density in the hippocampus, especially in the DG and dependent prosurvival ERK signaling. Conversely, ERα expression was unchanged. After EIPV, the DG harbored lowered local BDNF pools, diminished TrkB phosphorylation, and elevated glucocorticoid receptor phosphorylation. In unison, ERβ KO mice had heightened anxiety-like behavior and curtailed BDNF levels at baseline, despite enhanced circulating estradiol levels, while dying prematurely during EIPV. Thus, reiterated male-to-female violence jeopardizes hippocampal homeostasis in the female brain, perturbing ERβ/BDNF signaling, thus instigating anxiety and chronic stress.

Control of circadian rhythm on cortical excitability and synaptic plasticity

Living organisms navigate through a cyclic world: activity, feeding, social interactions are all organized along the periodic succession of night and day. At the cellular level, periodic activity is controlled by the molecular machinery driving the circadian regulation of cellular homeostasis. This mechanism adapts cell function to the external environment and its crucial importance is underlined by its robustness and redundancy. The cell autonomous clock regulates cell function by the circadian modulation of mTOR, a master controller of protein synthesis. Importantly, mTOR integrates the circadian modulation with synaptic activity and extracellular signals through a complex signaling network that includes the RAS-ERK pathway. The relationship between mTOR and the circadian clock is bidirectional, since mTOR can feedback on the cellular clock to shift the cycle to maintain the alignment with the environmental conditions. The mTOR and ERK pathways are crucial determinants of synaptic plasticity and function and thus it is not surprising that alterations of the circadian clock cause defective responses to environmental challenges, as witnessed by the bi-directional relationship between brain disorders and impaired circadian regulation. In physiological conditions, the feedback between the intrinsic clock and the mTOR pathway suggests that also synaptic plasticity should undergo circadian regulation.

Cranial Window for Acute and Chronic Optical Access to Record Neuronal Network Dynamics in the Olfactory Bulb

Cranial window implant is the preparation of choice for acute and chronic optical access to a given brain area. The cranial window provides a stable preparation, which can last for months. This window allows to follow the activity of distinct population of neurons expressing genetically encoded fluorescent reporters of activity in awake, behaving, head-fixed animals. The optical access can also be exploited for acute imaging, in anesthetized animals. Here we provide a detailed protocol for acute and chronic cranial window implantations in the olfactory bulb. We also provide the procedure to perform injections of adeno-associated viruses expressing genetically encoded fluorescent sensors in the same area.

Optogenetic Methods to Investigate Brain Alterations in Preclinical Models

Investigating the neuronal dynamics supporting brain functions and understanding how the alterations in these mechanisms result in pathological conditions represents a fundamental challenge. Preclinical research on model organisms allows for a multiscale and multiparametric analysis in vivo of the neuronal mechanisms and holds the potential for better linking the symptoms of a neurological disorder to the underlying cellular and circuit alterations, eventually leading to the identification of therapeutic/rescue strategies. In recent years, brain research in model organisms has taken advantage, along with other techniques, of the development and continuous refinement of methods that use light and optical approaches to reconstruct the activity of brain circuits at the cellular and system levels, and to probe the impact of the different neuronal components in the observed dynamics. These tools, combining low-invasiveness of optical approaches with the power of genetic engineering, are currently revolutionizing the way, the scale and the perspective of investigating brain diseases. The aim of this review is to describe how brain functions can be investigated with optical approaches currently available and to illustrate how these techniques have been adopted to study pathological alterations of brain physiology.

Genetically encoded sensors for Chloride concentration

Insights into chloride regulation in neurons have come slowly, but they are likely to be critical for our understanding of how the brain works. The reason is that the intracellular Cl^- level ([Cl^-]_i) is the key determinant of synaptic inhibitory function, and this in turn dictates all manner of neuronal network function. The true impact on the network will only be apparent, however, if Cl^- is measured at many locations at once (multiple neurons, and also across the subcellular compartments of single neurons), which realistically, can only be achieved using imaging. The development of genetically-encoded anion biosensors (GABs) brings the additional benefit that Cl^- imaging may be done in identified cell-classes and hopefully in subcellular compartments. Here, we describe the historical background and motivation behind the development of these sensors and how they have been used so far. There are, however, still major limitations for their use, the most important being the fact that all GABs are sensitive to both pH and Cl^-. Disambiguating the two signals has proved a major challenge, but there are potential solutions; notable among these is ClopHensor, which has now been developed for in vivo measurements of both ion species. We also speculate on how these biosensors may yet be improved, and how this could advance our understanding of Cl^- regulation and its impact on brain function.

Aberrant Patterns of Sensory-Evoked Activity in the Olfactory Bulb of LRRK2 Knockout Mice

The LRRK2 gene is the major genetic determinant of familiar Parkinson's disease (PD). Leucine-rich repeat kinase 2 (LRRK2) is a multidomain protein involved in several intracellular signaling pathways. A wealth of evidence indicates that LRRK2 is enriched at the presynaptic compartment where it regulates vesicle trafficking and neurotransmitter release. However, whether the role of LRRK2 affects neuronal networks dynamic at systems level remains unknown. Addressing this question is critical to unravel the impact of LRRK2 on brain function. Here, combining behavioral tests, electrophysiological recordings, and functional imaging, we investigated neuronal network dynamics, in vivo, in the olfactory bulb of mice carrying a null mutation in LRRK2 gene (LRRK2 knockout, LRRK2 KO, mice). We found that LRRK2 KO mice exhibit olfactory behavioral deficits. At the circuit level, the lack of LRRK2 expression results in altered gamma rhythms and odorant-evoked activity with significant impairments, while the spontaneous activity exhibited limited alterations. Overall, our data in the olfactory bulb suggest that the multifaced role of LRRK2 has a strong impact at system level when the network is engaged in active sensory processing.

The role of the odorant receptors in the formation of the sensory map

In the olfactory system, odorant receptors (ORs) expressed at the cell membrane of olfactory sensory neurons detect odorants and direct sensory axons toward precise target locations in the brain, reflected in the presence of olfactory sensory maps. This dual role of ORs is corroborated by their subcellular expression both in cilia, where they bind odorants, and at axon terminals, a location suitable for axon guidance cues. Here, we provide an overview and discuss previous work on the role of ORs in establishing the topographic organization of the olfactory system and recent findings on the mechanisms of activation and function of axonal ORs.

Whole brain functional recordings at cellular resolution in zebrafish larvae with 3D scanning multiphoton microscopy

Optical recordings of neuronal activity at cellular resolution represent an invaluable tool to investigate brain mechanisms. Zebrafish larvae is one of the few model organisms where, using fluorescence-based reporters of the cell activity, it is possible to optically reconstruct the neuronal dynamics across the whole brain. Typically, leveraging the reduced light scattering, methods like lightsheet, structured illumination, and light-field microscopy use spatially extended excitation profiles to detect in parallel activity signals from multiple cells. Here, we present an alternative design for whole brain imaging based on sequential 3D point-scanning excitation. Our approach relies on a multiphoton microscope integrating an electrically tunable lens. We first apply our approach, adopting the GCaMP6s activity reporter, to detect functional responses from retinal ganglion cells (RGC) arborization fields at different depths within the zebrafish larva midbrain. Then, in larvae expressing a nuclear localized GCaMP6s, we recorded whole brain activity with cellular resolution. Adopting a semi-automatic cell segmentation, this allowed reconstructing the activity from up to 52,000 individual neurons across the brain. In conclusion, this design can easily retrofit existing imaging systems and represents a compact, versatile and reliable tool to investigate neuronal activity across the larva brain at high resolution.

Spontaneous Afferent Activity Carves Olfactory Circuits

Electrical activity has a key role in shaping neuronal circuits during development. In most sensory modalities, early in development, internally generated spontaneous activity sculpts the initial layout of neuronal wiring. With the maturation of the sense organs, the system relies more on sensory-evoked electrical activity. Stimuli-driven neuronal discharge is required for the transformation of immature circuits in the specific patterns of neuronal connectivity that subserve normal brain function. The olfactory system (OS) differs from this organizational plan. Despite the important role of odorant receptors (ORs) in shaping olfactory topography, odor-evoked activity does not have a prominent role in refining neuronal wiring. On the contrary, afferent spontaneous discharge is required to achieve and maintain the specific diagram of connectivity that defines the topography of the olfactory bulb (OB). Here, we provide an overview of the development of olfactory topography, with a focus on the role of afferent spontaneous discharge in the formation and maintenance of the specific synaptic contacts that result in the topographic organization of the OB.

Topographic organization in the olfactory bulb

The ability of the olfactory system to detect and discriminate a broad spectrum of odor molecules with extraordinary sensitivity relies on a wide range of odorant receptors and on the distinct architecture of neuronal circuits in olfactory brain areas. More than 1000 odorant receptors, distributed almost randomly in the olfactory epithelium, are plotted out in two mirror-symmetric maps of glomeruli in the olfactory bulb, the first relay station of the olfactory system. How does such a precise spatial arrangement of glomeruli emerge from a random distribution of receptor neurons? Remarkably, the identity of odorant receptors defines not only the molecular receptive range of sensory neurons but also their glomerular target. Despite their key role, odorant receptors are not the only determinant, since the specificity of neuronal connections emerges from a complex interplay between several molecular cues and electrical activity. This review provides an overview of the mechanisms underlying olfactory circuit formation. In particular, recent findings on the role of odorant receptors in regulating axon targeting and of spontaneous activity in the development and maintenance of synaptic connections are discussed.

Modelling genetic mosaicism of neurodevelopmental disorders in vivo by a Cre-amplifying fluorescent reporter

Genetic mosaicism, a condition in which an organ includes cells with different genotypes, is frequently present in monogenic diseases of the central nervous system caused by the random inactivation of the X-chromosome, in the case of X-linked pathologies, or by somatic mutations affecting a subset of neurons. The comprehension of the mechanisms of these diseases and of the cell-autonomous effects of specific mutations requires the generation of sparse mosaic models, in which the genotype of each neuron is univocally identified by the expression of a fluorescent protein in vivo. Here, we show a dual-color reporter system that, when expressed in a floxed mouse line for a target gene, leads to the creation of mosaics with tunable degree. We demonstrate the generation of a knockout mosaic of the autism/epilepsy related gene PTEN in which the genotype of each neuron is reliably identified, and the neuronal phenotype is accurately characterized by two-photon microscopy.

Role of Axonal Odorant Receptors in Olfactory Topography

A unique feature in the organization of the olfactory system is the dual role of the odorant receptors: they detect odors in the nasal epithelium and they play an instructive role in the convergence of olfactory sensory neuron axons in specific loci, ie, glomeruli, in the olfactory bulb. The dual role is corroborated by the expression of the odorant receptors in 2 specific locations of the olfactory sensory neurons: the cilia that protrude in the nostril, where the odorant receptors interact with odors, and the axon terminal, a suitable location for a potential axon guidance molecule. The mechanism of activation and function of the odorant receptors expressed at the axon terminal remained unknown for almost 20 years. A recent study identified the first putative ligand of the axonal odorant receptors, phosphatidylethanolamine-binding protein1, a molecule expressed in the olfactory bulb. The distinctive mechanisms of activation of the odorant receptors expressed at the opposite locations in sensory neurons, by odors, at the cilia, and by molecules expressed in the olfactory bulb, at the axon terminal, explain the dual role of the odorant receptors and link the specificity of odor perception with its internal representation, in the topographic map.

Oligophrenin-1 regulates number, morphology and synaptic properties of adult-born inhibitory interneurons in the olfactory bulb

Among the X-linked genes associated with intellectual disability, Oligophrenin-1 (OPHN1) encodes for a Rho GTPase-activating protein, a key regulator of several developmental processes, such as dendrite and spine formation and synaptic activity. Inhibitory interneurons play a key role in the development and function of neuronal circuits. Whether a mutation of OPHN1 can affect morphology and synaptic properties of inhibitory interneurons remains poorly understood. To address these open questions, we studied in a well-established mouse model of X-linked intellectual disability, i.e. a line of mice carrying a null mutation of OPHN1, the development and function of adult generated inhibitory interneurons in the olfactory bulb. Combining quantitative morphological analysis and electrophysiological recordings we found that the adult generated inhibitory interneurons were dramatically reduced in number and exhibited a higher proportion of filopodia-like spines, with the consequences on their synaptic function, in OPHN1 ko mice. Furthermore, we found that olfactory behaviour was perturbed in OPHN1 ko mice. Chronic treatment with a Rho kinase inhibitor rescued most of the defects of the newly generated neurons. Altogether, our data indicated that OPHN1 plays a key role in regulating the number, morphology and function of adult-born inhibitory interneurons and contributed to identify potential therapeutic targets.

Role of the odorant receptor in neuronal connectivity in the olfactory bulb

Olfaction is a highly sophisticated sensory modality able to detect and discriminate thousands of different odours, even at very low concentration. How such a challenging task is achieved remains to be fully understood. A unique feature of the olfactory system is the dual role of the odorant receptor: it does detect odours in the olfactory epithelium but it also contributes to neuronal circuit formation in the olfactory bulb. The odorant receptors are indeed expressed on the cilia that protrude in the nasal cavity, where they bind odorants, and at the axon termini, where they could act as axon guidance molecules. In this review we discuss findings that show how the odorant receptor contributes in regulating neuronal connectivity.

Mesencephalic dopaminergic neurons express a repertoire of olfactory receptors and respond to odorant-like molecules

Background

The mesencephalic dopaminergic (mDA) cell system is composed of two major groups of projecting cells in the Substantia Nigra (SN) (A9 neurons) and the Ventral Tegmental Area (VTA) (A10 cells). Selective degeneration of A9 neurons occurs in Parkinson’s disease (PD) while abnormal function of A10 cells has been linked to schizophrenia, attention deficit and addiction. The molecular basis that underlies selective vulnerability of A9 and A10 neurons is presently unknown.

Results

By taking advantage of transgenic labeling, laser capture microdissection coupled to nano Cap-Analysis of Gene Expression (nanoCAGE) technology on isolated A9 and A10 cells, we found that a subset of Olfactory Receptors (OR)s is expressed in mDA neurons. Gene expression analysis was integrated with the FANTOM5 Helicos CAGE sequencing datasets, showing the presence of these ORs in selected tissues and brain areas outside of the olfactory epithelium. OR expression in the mesencephalon was validated by RT-PCR and in situ hybridization. By screening 16 potential ligands on 5 mDA ORs recombinantly expressed in an heterologous in vitro system, we identified carvone enantiomers as agonists at Olfr287 and able to evoke an intracellular Ca²⁺ increase in solitary mDA neurons. ORs were found expressed in human SN and down-regulated in PD post mortem brains.

Conclusions

Our study indicates that mDA neurons express ORs and respond to odor-like molecules providing new opportunities for pharmacological intervention in disease.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-729) contains supplementary material, which is available to authorized users.

Odorant receptors in the formation of the olfactory bulb circuitry

In mammals, smell is mediated by odorant receptors expressed by sensory neurons in the nose. These specialized receptors are found both on olfactory sensory neurons' cilia and axon terminals. Although the primary function of ciliary odorant receptors is to detect odorants, their axonal role remains unclear but is thought to involve axon guidance. This review discusses findings that show axonal odorant receptors are indeed functional and capable of modulating neural connectivity.

A cell-penetrating ratiometric nanoprobe for intracellular chloride

NanoChlor, a nanoparticle-based fluorescent probe for chloride that is both ratiometric and capable of spontaneously penetrating neuronal cells at submillimolar concentrations, was designed and studied. NanoChlor is built on silica nanoparticles grafted with 6-methoxyquinolinium as the chloride-sensitive component and fluorescein as the reference dye. A Stern-Volmer constant of 50 M(-1) was measured in Ringer's buffer at pH 7.2, and the response to chemically induced chloride currents was recorded in real time in hippocampal cells.

Genetic modulation of BDNF signaling affects the outcome of axonal competition in vivo

BACKGROUND

Activity-dependent competition that operates on branch stability or formation plays a critical role in shaping the pattern and complexity of axonal terminal arbors. In the mammalian central nervous system (CNS), the effect of activity-dependent competition on axon arborization and on the assembly of sensory maps is well established. However, the molecular pathways that modulate axonal-branch stability or formation in competitive environments remain unknown.

RESULTS

We establish an in vivo axonal-competition paradigm in the mouse olfactory system by employing a genetic strategy that permits suppression of neurosecretory activity in random subsets of olfactory sensory neurons (OSNs). Long-term follow up confirmed that this genetic manipulation triggers competition by revealing a bias toward selective stabilization of active arbors and local degeneration of synaptically silent ones. By using a battery of genetically modified mouse models, we demonstrate that a decrease either in the total levels or the levels of activity-dependent secreted BDNF (due to a val66met substitution), rescues silent arbors from withering. We show that this effect may be mediated, at least in part, by p75(NTR).

CONCLUSIONS

We establish and experimentally validate a genetic in vivo axonal-competition paradigm in the mammalian CNS. By using this paradigm, we provide evidence for a specific effect of BDNF signaling on terminal-arbor pruning under competition in vivo. Our results have implications for the formation and refinement of the olfactory and other sensory maps, as well as for neuropsychiatric diseases and traits modulated by the BDNF val66met variant.

Functional topography of connections linking mirror-symmetric maps in the mouse olfactory bulb

In rodents, each main olfactory bulb contains two mirror-symmetric glomerular maps, a feature not found in the initial topographic maps of other sensory systems. Targeting tracer injections to identified glomeruli revealed that isofunctional odor columns-translaminar assemblies connected to a given glomerulus-were specifically and reciprocally interconnected through a mutually inhibitory circuit with exquisite topographic specificity. Thus, instead of containing two mirror-symmetric maps, we propose that the olfactory bulb contains a single integrated map in which isofunctional odor columns are connected through an intrabulbar link, analogous to the specific horizontal connections linking iso-orientation columns in primary visual cortex.

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.

Odorant receptors instruct functional circuitry in the mouse olfactory bulb

The mammalian olfactory system detects and discriminates thousands of odorants using many different receptors expressed by sensory neurons in the nasal epithelium. Axonal projections from these neurons to the main olfactory bulbs form reproducible patterns of glomeruli in two widely separated regions of each bulb, creating two mirror-symmetric maps of odorant receptor projections. To investigate whether odorant receptors organize neural circuitry in the olfactory bulb, we have examined a genetically modified mouse line, rI7 --> M71, in which a functionally characterized receptor, rI7, has been substituted into the M71 receptor locus. Here we show that despite their ectopic location the resulting glomeruli are responsive to known ligands of the rI7 receptor, attract postsynaptic innervation by mitral/tufted cell dendrites, and endow these cells with responses that are characteristic of the rI7 receptor. External tufted cells receiving input from rI7 --> M71 glomeruli form precise intrabulbar projections that link medial and lateral rI7 --> M71 glomeruli anatomically, thus providing a substrate for coordinating isofunctional glomeruli. We conclude that odorant receptor identity in epithelial neurons determines not only glomerular convergence and function, but also functional circuitry in the olfactory bulb.

Bcl-2 overexpression per se does not promote regeneration of neonatal crushed optic fibers

We have explored whether overexpression of the bcl-2 gene 'per se' can promote regeneration of retinal ganglion cells (RGCs) after optic nerve axotomy in developing transgenic mice. We have used newborn mice (postnatal day 5) because at this age the central nervous system environment is more permissive for regeneration than in adults, thus, maximizing the probability to detect a regeneration-promoting role of bcl-2. Thirty days postsurgery we found that in mice overexpressing bcl-2, a high proportion of retinal ganglion cells survived and also that some fibers in the proximal stump of the optic nerve were preserved. However, the optic nerve of transgenic mice does not show signs of regeneration. On the contrary, in the presence of Schwann cell transplants, there are signs of fiber regrowth. Indeed, many axonal terminals cross the crush site and reach the chiasm in both wild type and transgenic mice nerves. These results suggest that bcl-2 overexpression is not sufficient 'per se' to increase the regenerative potentiality of axotomized RGCs.

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.

Effects of nerve growth factor on visual cortical plasticity require afferent electrical activity

It is known that administration of nerve growth factor (NGF) prevents the ocular dominance shift induced by monocular deprivation in the rat. To determine whether electrical activity in the visual afferent pathway is required for NGF effects on ocular dominance, we infused NGF into the cortex of animals subjected to complete monocular blockade of retinal discharges. Rats at the peak of the critical period received intravitreal tetrodotoxin (TTX) injections to silence activity in one eye for a period of 6-7 days; NGF was concurrently delivered into the visual cortex by means of osmotic minipumps. At the end of the treatment period, the ocular dominance distribution of cortical neurons was assessed by single-cell recordings. The results demonstrate that while infusion of NGF is effective in preventing the ocular dominance shift in lid-sutured rats, virtually no rescue can be observed in TTX-injected animals. Identical results were obtained when a specific agonist of the NGF receptor TrkA, the bivalent anti-rat TrkA IgG (RTA), was infused into the cortex in place of NGF. We conclude that NGF signalling via the TrkA receptor must be coupled to afferent electrical activity to produce its effects on the eye preference of cortical neurons. This suggests a generalized mechanism in which high-affinity neurotrophin receptor activation and afferent discharge interact to modulate neuronal plasticity in the developing visual cortex.

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.