Characterization of newborn interneurons in the mouse olfactory bulb using postnatal electroporation

Sensory experience regulates the development of various brain structures, including the cortex, hippocampus, and olfactory bulb (OB). In the OB, the regulation of the neuronal development by sensory experience is well-studied in mitral and tufted cells, but little is known about how morphological changes depending on a neuronal activity occur in OB interneurons, such as granule cells and periglomerular cells. OB interneurons are a useful model for studying the modification of neural circuits by sensory inputs from the external world during postnatal stages. Interestingly, OB interneurons are generated and integrated into preexisting neural circuits in rodents even at the adult stage. Thus, an efficient method of gene transfer into newborn neurons would allow a better understanding of adult neurogenesis in the OB. In this chapter, we describe a basic method for in vivo electroporation of DNA into OB interneurons in postnatal mice, without the need for complex surgery. Delivery of electric pulses following microinjection of plasmid DNA into the lateral ventricle enabled efficient gene transfer into newborn OB interneurons. Utilizing a fluorescent protein gene, labeling appears in various classes of OB interneurons and persists into adulthood with no adverse side effects. Collectively, postnatal electroporation is a powerful tool to understand adult neurogenesis, and compares favorably in terms of time and cost to other genetic manipulation techniques.