Role and Characterization of Dopaminergic Interneurons in Mouse Olfactory Bulbs

The olfactory system enables us to perceive and discriminate odors, and these important sensory activities allow us to interact with the external environment in our daily lives. The reception of odors occurs in the olfactory epithelium, but the primary center for processing olfactory information is the olfactory bulb (OB). Within this structure, in addition to projection neurons, interneurons play an essential role in sensory activity; among these, we find periglomerular (PG) dopaminergic (DA) neurons. These cells are strategically located at the entrance of the bulbar circuit, directly contacting the olfactory nerve terminals, and play a key role in odor processing and the adaptation of the bulbar network to external conditions. Moreover, likely due to their activity, they are an exception compared to other parts of the brain; in fact, like other interneurons in the OB, they are continuously generated in the postnatal and adult period and play an important role in OB physiology. Here, we describe some of the properties related to DA-PG cells present in the OB. First, we examine the electrophysiological profile of mature DA interneurons and how this differs in the immature stage. We also describe how it is possible, using cell sorting techniques and semiquantitative real-time PCR on enzymatically dissociated cells of the OB, to detect the different levels of gene expression related to the degree of maturation of DA neurons. Furthermore, we present some effects of brain-derived neurotrophic factor (BDNF) on the excitability of PG-DA cells. Finally, we present some data on the deleterious effects of ozone (O3) on these cells and how O3 reduces the rate of spontaneous spike firing in PG-DA cells of the OB, thereby compromising olfactory perception of odors.