Targeting specific neuronal populations using adeno- and lentiviral vectors: applications for imaging and studies of cell function.

We employ viral vectors to address questions related to the function of specific types of neurones in the central control of blood pressure. Adenoviral vectors (AVVs) or lentiviral vectors (LVVs) can be used to visualize specifically living GABAergic or noradrenergic (NAergic) neurones or to interfere with intracellular signalling within these cell types. Here, we review recent in vitro, in situ and in vivo applications of these vectors in the rat brainstem as performed in our laboratories. In organotypic slice cultures prepared from defined cardiovascular brainstem areas, viral vectors were used to study the electrophysiological properties, intracellular signalling and gene expression in selected neuronal phenotypes. In vivo, vectors were microinjected into brainstem nuclei to inhibit specific aspects of cell signalling by expression of dominant negative proteins, for example. Outcomes for cardiovascular control were measured either acutely in situ or chronically in vivo with radio telemetry in freely moving rats. We showed that AVVs and LVVs have distinct properties that need to be considered prior to their application. For example, LVVs can be manufactured very quickly, have no immunogenicity and can be pseudotyped to display higher tropism for neurones than glia. However, comparatively lower production yields of LVVs may limit their use for some types of applications. In contrast, AVVs require a lengthy construction period, are easy to amplify to high yields at moderate cost but may trigger an immune response when used at high titres in vivo. These features make AVVs particularly suitable for in vitro applications. As the two vector types complement each other in several ways we generated a shuttle system that simplifies transfer of transgene cassettes between the backbones of AVVs and LVVs. Thus, AVVs and LVVs are powerful experimental tools that can be used in a variety of experimental designs in vivo, in situ and in vitro.