Fluorescence-Based Monitoring of In Vivo Neural Activity Using a Circuit-Tracing Pseudorabies Virus

Department of Molecular Biology, Neuroscience Institute, Princeton University, Princeton, New Jersey, United States of America.
PLoS ONE (Impact Factor: 3.23). 02/2009; 4(9):e6923. DOI: 10.1371/journal.pone.0006923
Source: PubMed


The study of coordinated activity in neuronal circuits has been challenging without a method to simultaneously report activity and connectivity. Here we present the first use of pseudorabies virus (PRV), which spreads through synaptically connected neurons, to express a fluorescent calcium indicator protein and monitor neuronal activity in a living animal. Fluorescence signals were proportional to action potential number and could reliably detect single action potentials in vitro. With two-photon imaging in vivo, we observed both spontaneous and stimulated activity in neurons of infected murine peripheral autonomic submandibular ganglia (SMG). We optically recorded the SMG response in the salivary circuit to direct electrical stimulation of the presynaptic axons and to physiologically relevant sensory stimulation of the oral cavity. During a time window of 48 hours after inoculation, few spontaneous transients occurred. By 72 hours, we identified more frequent and prolonged spontaneous calcium transients, suggestive of neuronal or tissue responses to infection that influence calcium signaling. Our work establishes in vivo investigation of physiological neuronal circuit activity and subsequent effects of infection with single cell resolution.

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Available from: Lynn Enquist
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    • "Pseudorabies virus (PRV), an alpha-herpesvirus, and the causative agent of Aujeszky's diseases of swine [2], is a commonly used model organism for studies in pathogenesis and the molecular biology of herpesviruses. Furthermore, it is widely utilized as a neural circuit tracer [[3,4] and [5]] and has been reported to be suitable as a vector for gene delivery to various cells [6,7] and as an oncolytic agent [8]. The gene expressions of herpesviruses are currently undergoing intensive investigation in consequence of the development of new technologies allowing simultaneous analysis of the expressions of multiple genes. "
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    ABSTRACT: Herpesvirus genes are classified into distinct kinetic groups on the basis of their expression dynamics during lytic growth of the virus in cultured cells at a high, typically 10 plaque-forming units/cell multiplicity of infection (MOI). It has been shown that both the host response and the success of a pathogen are dependent on the quantity of particles infecting an organism. This work is a continuation of an earlier study 1, in which we characterized the overall expression of PRV genes following low-MOI infection. In the present study, we have addressed the question of whether viral gene expressions are dependent on the multiplicity of infection by comparing gene expressions under low and high-MOI conditions. In the present study, using a real-time RT-PCR assay, we address the question of whether the expression properties of the pseudorabies virus (PRV) genes are dependent on the number of virion particles infecting a single cell in a culture. Our analysis revealed a significant dependence of the gene expression on the MOI in most of these genes. Specifically, we found that most of the examined viral genes were expressed at a lower level at a low MOI (0.1) than at a high MOI (10) experiment in the early stage of infection; however, this trend reversed by six hour post-infection in more than half of the genes. Furthermore, in the high-MOI infection, several PRV genes substantially declined within the 4 to 6-h infection period, which was not the case in the low-MOI infection. In the low-MOI infection, the level of antisense transcript (AST), transcribed from the antiparallel DNA strand of the immediate-early 180 (ie180) gene, was comparable to that of ie180 mRNA, while in the high-MOI experiment (despite the 10 times higher copy number of the viral genome in the infected cells) the amount of AST dropped by more than two log values at the early phase of infection. Furthermore, our analysis suggests that adjacent PRV genes are under a common regulation. This is the first report on the effect of the multiplicity of infection on genome-wide gene expression of large DNA viruses, including herpesviruses. Our results show a strong dependence of the global expression of PRV genes on the MOI. Furthermore, our data indicate a strong interrelation between the expressions of ie180 mRNA and AST, which determines the expression properties of the herpesvirus genome and possibly the replication strategy (lytic or latent infection) of the virus in certain cell types.
    Full-text · Article · Dec 2010 · BMC Microbiology
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    • "However, it has been demonstrated [11] that infection by PRV152 does not interfere with normal synaptic activity in brain slices and functionally related neurons can be analyzed in the context of their local synaptic networks for up to 5 days. Finally, it has recently been shown that PRV-Bartha virus can be combined with the calcium sensitive protein G-CaMP2 to allow imaging of synaptically connected neurons [67]. "
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    ABSTRACT: The neonatal mouse has become a model system for studying the locomotor function of the lumbar spinal cord. However, information about the synaptic connectivity within the governing neural network remains scarce. A neurotropic pseudorabies virus (PRV) Bartha has been used to map neuronal connectivity in other parts of the nervous system, due to its ability to travel trans-neuronally. Its use in spinal circuits regulating locomotion has been limited and no study has defined the time course of labelling for neurons known to project monosynaptically to motoneurons. Here we investigated the ability of PRV Bartha, expressing green and/or red fluorescence, to label spinal neurons projecting monosynaptically to motoneurons of two principal hindlimb muscles, the tibialis anterior (TA) and gastrocnemius (GC). As revealed by combined immunocytochemistry and confocal microscopy, 24-32 h after the viral muscle injection the label was restricted to the motoneuron pool while at 32-40 h the fluorescence was seen in interneurons throughout the medial and lateral ventral grey matter. Two classes of ipsilateral interneurons known to project monosynaptically to motoneurons (Renshaw cells and cells of origin of C-terminals) were consistently labeled at 40 h post-injection but also a group in the ventral grey matter contralaterally. Our results suggest that the labeling of last order interneurons occurred 8-12 h after motoneuron labeling and we presume this is the time taken by the virus to cross one synapse, to travel retrogradely and to replicate in the labeled cells. The study establishes the time window for virally-labelling monosynaptic projections to lumbar motoneurons following viral injection into hindlimb muscles. Moreover, it provides a good foundation for intracellular targeting of the labeled neurons in future physiological studies and better understanding the functional organization of the lumbar neural networks.
    Full-text · Article · Jul 2010 · PLoS ONE
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    ABSTRACT: Powerful transneuronal tracing technologies exploit the ability of some neurotropic viruses to travel across neuronal pathways and to function as self-amplifying markers. Two main classes of viral transneuronal tracers are available, derived from alpha-herpesviruses (Herpes Simplex virus type 1, Pseudorabies) and rabies virus. Depending on the virus type and strain, there are major differences with regard to host range, peripheral uptake, replication mechanisms, transport direction and specificity. While alpha-herpesviruses are the tracers of choice for studying autonomic innervation, rabies virus is the ideal tool for studying motor innervation, since its peripheral uptake occurs exclusively at motor endplates. Rabies virus is the only viral tracer that is entirely specific, as it moves exclusively across chemical synapses by strictly unidirectional (retrograde) transneuronal transfer without altering neuronal metabolism, allowing for the stepwise, time-dependent, identification of neuronal networks across an unlimited number of synapses. This review will highlight and contrast the different properties of these viral tracers, and summarize the methodological issues that are critical for the appropriate execution and interpretation of transneuronal tracing studies. Combinations of viral tracing with other methodologies will be evaluated. Emerging technologies, based on genetically modified herpes and rabies tracers, will be also discussed and put in perspective.
    No preview · Article · Jan 2009 · Journal of Neuroscience Methods
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