Motor-coordination-dependent learning, more than others, is impaired in transgenic mice expressing pseudorabies virus immediate-early protein IE180

Disease-specific monoclonal antibodies targeting glutamate decarboxylase impair GABAergic neurotransmission and affect motor learning and behavioral functions

Autoantibodies to the smaller isoform of glutamate decarboxylase (GAD) can be found in patients with type 1 diabetes and a number of neurological disorders, including stiff-person syndrome, cerebellar ataxia and limbic encephalitis. The detection of disease-specific autoantibody epitopes led to the hypothesis that distinct GAD autoantibodies may elicit specific neurological phenotypes. We explored the in vitro/in vivo effects of well-characterized monoclonal GAD antibodies. We found that GAD autoantibodies present in patients with stiff person syndrome (n = 7) and cerebellar ataxia (n = 15) recognized an epitope distinct from that recognized by GAD autoantibodies present in patients with type 1 diabetes mellitus (n = 10) or limbic encephalitis (n = 4). We demonstrated that the administration of a monoclonal GAD antibody representing this epitope specificity; (1) disrupted in vitro the association of GAD with γ-Aminobutyric acid containing synaptic vesicles; (2) depressed the inhibitory synaptic transmission in cerebellar slices with a gradual time course and a lasting suppressive effect; (3) significantly decreased conditioned eyelid responses evoked in mice, with no modification of learning curves in the classical eyeblink-conditioning task; (4) markedly impaired the facilitatory effect exerted by the premotor cortex over the motor cortex in a paired-pulse stimulation paradigm; and (5) induced decreased exploratory behavior and impaired locomotor function in rats. These findings support the specific targeting of GAD by its autoantibodies in the pathogenesis of stiff-person syndrome and cerebellar ataxia. Therapies of these disorders based on selective removal of such GAD antibodies could be envisioned.

Characterization of a replication-incompetent pseudorabies virus mutant lacking the sole immediate early gene IE180

The alphaherpesvirus pseudorabies virus (PRV) encodes a single immediate early gene called IE180. The IE180 protein is a potent transcriptional activator of viral genes involved in DNA replication and RNA transcription. A PRV mutant with both copies of IE180 deleted was constructed 20 years ago (S. Yamada and M. Shimizu, Virology 199:366–375, 1994, doi:10.1006/viro.1994.1134), but propagation of the mutant depended on complementing cell lines that expressed the toxic IE180 protein constitutively. Recently, Oyibo et al. constructed a novel set of PRV IE180 mutants and a stable cell line with inducible IE180 expression (H. Oyibo, P. Znamenskiy, H. V. Oviedo, L. W. Enquist, A. Zador, Front. Neuroanat. 8:86, 2014, doi:10.3389/fnana.2014.00086), which we characterized further here. These mutants failed to replicate new viral genomes, synthesize immediate early, early, or late viral proteins, and assemble infectious virions. The PRV IE180-null mutant did not form plaques in epithelial cell monolayers and could not spread from primary infected neurons to second-order neurons in culture. PRV IE180-null mutants lacked the property of superinfection exclusion. When PRV IE180-null mutants infected cells first, subsequent superinfecting viruses were not blocked in cell entry and formed replication compartments in epithelial cells, fibroblasts, and neurons. Cells infected with PRV IE180-null mutants survived as long as uninfected cells in culture while expressing a fluorescent reporter gene. Transcomplementation with IE180 in epithelial cells restored all mutant phenotypes to wild type. The conditional expression of PRV IE180 protein enables the propagation of replication-incompetent PRV IE180-null mutants and will facilitate construction of long-term single-cell-infecting PRV mutants for precise neural circuit tracing and high-capacity gene delivery vectors.

Pseudorabies virus (PRV) is widely used for neural tracing in animal models. The virus replicates and spreads between synaptically connected neurons. Current tracing strains of PRV are cytotoxic and kill infected cells. Infected cells exclude superinfection with a second virus, limiting multiple virus infections in circuit tracing. By removing the only immediate early gene of PRV (called IE180), the mutant virus will not replicate or spread in epithelial cells, fibroblasts, or neurons. The wild-type phenotype can be restored by transcomplementation of infected cells with IE180. The PRV IE180-null mutant can express fluorescent reporters for weeks in cells with no toxicity; infected cells survive as long as uninfected cells. Infection with the mutant virus allows superinfection of the same cell with a second virus that can enter and replicate. The PRV IE180-null mutant will permit conditional long-term tracing in animals and is a high-capacity vector for gene delivery.

Genetic models of sensorimotor gating: relevance to neuropsychiatric disorders

Sensorimotor gating, or the ability of a sensory event to suppress a motor response, can be measured operationally via prepulse inhibition (PPI) of the startle response. PPI is deficient in schizophrenia patients as well as other neuropsychiatric disorders, can be measured across species, and has been used widely as a translational tool in preclinical neuropharmacological and genetic research. First developed to assess drug effects in pharmacological and developmental models, PPI has become one of the standard behavioral measures in genetic models of schizophrenia and other neuropsychiatric disorders that exhibit PPI deficits. In this chapter we review the literature on genetic models of sensorimotor gating and discuss the utility of PPI as a tool in phenotyping mutant mouse models. We highlight the approaches to genetic mouse models of neuropsychiatric disease, discuss some of the important caveats to these approaches, and provide a comprehensive table covering the more recent genetic models that have evaluated PPI.