Types of cholecystokinin-containing periglomerular cells in the mouse olfactory bulb

The periglomerular cells (PG) of the olfactory bulb (OB) are involved in the primary processing and the refinement of sensory information from the olfactory epithelium. The neurochemical composition of these neurons has been studied in depth in many species, and over the last decades such studies have focused mainly on the rat. The increasing use of genetic models for research into olfactory function demands a profound characterization of the mouse olfactory bulb, including the chemical composition of bulbar interneurons. Regarding both their connectivity with the olfactory nerve and their neurochemical fate, recently, two different types of PG have been identified in the mouse. In the present report, we analyze both the synaptology and the chemical composition of specific PG populations in the murine olfactory bulb, in particular, those containing the neuropeptide cholecystokinin. Our results demonstrate the existence in the mouse of non-GABAergic PG and that these establish synaptic contacts with the olfactory nerve within the glomeruli. Based on previous classifications, we propose that this population would constitute a new subtype of type 1 mouse PG. In addition, we demonstrate the partial coexistence of cholecystokinin with the calcium-binding proteins neurocalcin and parvalbumin. All these findings add further data to our knowledge of the synaptology and neurochemistry of mouse PG. The differences observed from other rodents reflect the neurochemical heterogeneity of PG in the mammalian OB.