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.