The glomerular network of the zebrafish olfactory bulb

Each zebrafish olfactory bulb contains ~ 140 glomeruli that are distinguishable based on size, location, neurochemistry and function. Here we examine the mitral cell innervation of differently sized glomeruli in adult zebrafish. Type 1 glomeruli had diameters of 80.9 ± 8.1 μm and were innervated by 5.9 ± 0.9 mitral cells. The Type 1 mediodorsal glomeruli (mdG) were innervated by both uniglomerular (innervating only single glomeruli) and multiglomerular mitral cells (innervating two or more glomeruli). In contrast, the Type 1 ventroposterior (vpG) and lateral glomeruli (lG) were only innervated by uniglomerular mitral cells. Type 2 ventral glomeruli were 46 ± 5.1 μm in diameter and were innervated by 3.3 ± 0.2 mitral cells. Type 2 ventromedial glomeruli (vmG) were innervated exclusively by uniglomerular mitral cells. Type 3 glomeruli had diameters of 17 ± 2.5 μm and were innervated by 1.1 ± 0.6 multiglomerular mitral cells each. Finally, Type 4 glomeruli were small, with average diameters of 4.8 ± 3.9 μm and were restricted to the lateral plexus. These glomeruli were innervated mainly by multiglomerular mitral cells with extensively branching dendrites. This study provides the first specific associations between uni- and multiglomerular mitral cells with known zebrafish glomeruli. Our results suggest that glomeruli are distinguishable based on their postsynaptic compartment and that distinct input–output computations occur in different types of zebrafish glomeruli.