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Vanderbilt Addiction Center

Consequences of In Vivo Neocortical GAD67 Downregulation

Glutamic acid decarboxylase 67kDa (GAD67) transcript reduction in the postmortem prefrontal cortex is the most robust and consistently replicated finding across different cohorts of subjects with schizophrenia. This critical, brain-specific GABA synthesis enzyme is shows expression deficit in distinct interneuronal populations of the human cortex. As a result, we expect that a directed cortical downregulation of GAD67 in these distinct interneuronal subphenotypes will 1) mimic the human postmortem findings in schizophrenia 2) have distinct consequences on cortical functioning and 3) lead to a better understanding of cortical inhibition. In this proposal, we hypothesize that in vivo downregulation of GAD67 in SST, NPY, CCK and PARV-containing cortical interneurons will result in distinct anatomical, neurochemical, molecular and behavioral changes that will share common features with human schizophrenia. To test our central hypothesis we propose 4 specific Aims which will focus on the generation and characterization of four transgenic mouse lines. In Aim 1 we will generate four distinct, GFP-labeled, GAD67 hypomorphic mice under the control of SST, NPY, CCK and PARV promoters. We will achieve this using a mouse bacterial artificial chromosome (BAC) containing SST, NPY, CCK and PARV promoter/enhancer regions modified to express both GFP and an intron-encoded microRNA (miRNA) specific to GAD67. In Aim 2 we will perform an anatomical/neurochemical assessment of the newly generated transgenic mice strains. We will assess each mouse line by gross anatomical measurements, general microanatomy and neurochemical methods. Aim 3 will focus on behavioral assessment of the four GAD67 knockdown mice strains. Beyond the basic behavioral characterization of the mice (neurological exam and sensorymotor assessments) we will assess prepulse inhibition, spatial working memory and social behaviors. Aim 4 will establish the neocortical gene expression changes that are shared between GAD67 KO mice and expression alterations in the PFC of schizophrenia. Downregulation of GAD67 transcripts in specific interneuronal subpopulations will likely lead to expression changes in both interneurons and pyramidal cells, and we believe that some of these expression changes will mimic the expression changes seen in human postmortem brain of subjects with schizophrenia. To test this, for each of the knockdown animals showing a behavioral/anatomical phenotype, we will the expression of genes known to be altered in human schizophrenia (e.g. SYN2, RGS4, MOG, SST, NPY, GAD67, HSP70, AMPA etc). The first transgenic mouse line, with GAD67 downregulation in the PARV+ interneuronal subpopulation has been successfully generated and awaits characterization.

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