The present program project centers around three independent proposals aimed at understanding the development, function and plasticity of 5HT3aR interneurons (INs) in the cerebral cortex. The impetus to create this core emerged out of the recognition that a shared molecular and transgenic resource would serve the dual purpose of cost efficiency in the production and distribution of a shared set of reagents and to foster a natural setting for collaboration between the three contributing laboratories. Indeed, the use of the same genetic tools across each of the proposals provides for a solid basis by which results garnered through diverse methods and collected at different time points from both developing and mature animals can be compared. To implement these goals we recognize that two distinct considerations need to be taken into account in assembling this core. First, (in Phase 1) we need to scale up the availability of a set of existing reagents that are broadly required for the execution of the aims of each of the constituent projects. From the judicious collection of preexisting reagents, we have assembled our preliminary data. Although lacking sufficient specificity to individually target each of the five classes of 5HT3aR INs we wish to study, we already possessed the ability to label this population in its entirety using the 5HT3aRcre driver line, as well as to selectively examine the VIP+ versus VIP- subpopulations that separate the entire 5HT3aR pool into two distinct subgroups using the VIPcre driver line in conjunction with the 5HT3aR-EGFP line. In addition, the Chatcre driver allows us to; with reasonable fidelity target the VIP+/CR+ bipolar population. In combination with a series of conditional alleles, reporters and viral effectors, with the establishment of Core A, we will have in hand the tools to at a general level address all aims in our proposal. In Phase 2 of this proposal we wish to increase the fidelity of our analysis by developing a refined set of alleles and viral reagents to more specifically label and manipulate discrete subsets of the 5HT3aR+ IN population. , Hence, having produced (or collected) such reagents during the first two years of our proposal, we wish in the second portion of the core's existence (years 3-5) to utilize these tools in a finer grained analysis of these IN subtypes.