Cellular and Synaptic Organization of the Human Olfactory Bulb

The distribution of cell types and synapses is well characterized in the rodent olfactory bulb (OB), and from that plausible models of odor processing have been constructed. Individual olfactory sensory neurons (OSNs) express only 1 of ~1000 odorant receptors (ORs) and send their axons to specific synaptic targets in the OB glomerular neuropil. Each glomerulus is innervated exclusively by OSN axons expressing the same OR. The distribution of these glomeruli is conserved across animals, as is the numerical relationship between number of expressed ORs and number of glomeruli in the OB. Our objective is to extend such results to the level of the human OB to determine how its cellular and synaptic organization, and more specifically how the number and distribution of its glomeruli, compare to what has been elucidated in mice. As there are ~2,000 glomeruli for ~1,000 ORs in mice, we predicted ~700 glomeruli in humans based on the ~350 intact OR genes identified in the human through genomic studies. Using immunohistochemistry, the organization of cells and synapses in human OBs was evaluated and quantified. While the laminar structure of the OB is broadly conserved between species, in the human OB the laminar organization as well as additional structural features suggest a less rigorously organized OB than in rodents, perhaps suggesting that odor processing in the human OB may be less efficient than in mice. Of particular note, the total number of glomeruli in the human OB differs significantly from predicted and demonstrates a high degree of variability amongst specimens, thus far ranging from approximately 3000 - 9000/OB. These results indicate that the principles of OR-homotypic axon convergence developed from mouse studies may not be readily applicable to the human, and that central processing of odor signals in the human may differ from those characterized in the mouse

Principles of Glomerular Organization in the Human Olfactory Bulb – Implications for Odor Processing

Olfactory sensory neurons (OSN) in mice express only 1 of a possible 1,100 odor receptors (OR) and axons from OSNs expressing the same odor receptor converge into ,2 of the 1,800 glomeruli in each olfactory bulb (OB) in mice; this yields a convergence ratio that approximates 2:1, 2 glomeruli/OR. Because humans express only 350 intact ORs, we examined human OBs to determine if the glomerular convergence ratio of 2:1 established in mice was applicable to humans. Unexpectedly, the average number of human OB glomeruli is .5,500 yielding a convergence ratio of ,16:1. The data suggest that the initial coding of odor information in the human OB may differ from the models developed for rodents and that recruitment of additional glomeruli for subpopulations of ORs may contribute to more robust odor representation

Principles of Glomerular Organization in the Human Olfactory Bulb – Implications for Odor Processing

Olfactory sensory neurons (OSN) in mice express only 1 of a possible 1,100 odor receptors (OR) and axons from OSNs expressing the same odor receptor converge into ∼2 of the 1,800 glomeruli in each olfactory bulb (OB) in mice; this yields a convergence ratio that approximates 2∶1, 2 glomeruli/OR. Because humans express only 350 intact ORs, we examined human OBs to determine if the glomerular convergence ratio of 2∶1 established in mice was applicable to humans. Unexpectedly, the average number of human OB glomeruli is >5,500 yielding a convergence ratio of ∼16∶1. The data suggest that the initial coding of odor information in the human OB may differ from the models developed for rodents and that recruitment of additional glomeruli for subpopulations of ORs may contribute to more robust odor representation

A minimum data set approach to post-mortem computed tomography reporting for anthropological biological profiling

Anthropological examination of bones is routinely undertaken in medico-legal investigations to establish an individual’s biological profile, particularly their age. This often requires the removal of soft tissue from bone (de-fleshing), which, especially when dealing with the recently deceased, is a time consuming and invasive procedure. Recent advances in multi-detector computed tomography have made it practical to rapidly acquire high-resolution morphological skeletal information from images of “fleshed” remains. The aim of this study was to develop a short standard form, created from post-mortem computed tomography images, that contains the minimum image-set required to anthropologically assess an individual. The proposed standard forms were created for 31 juvenile forensic cases with known age-at-death, spanning the full age range of the developing human. Five observers independently used this form to estimate age-at-death. All observers estimated age in all cases, and all estimations were within the accepted ranges for traditional anthropological and odontological assessment. This study supports the implementation of this approach in forensic radiological practice