Sección Biología Celular

Glomeruli are cell-free neuropil structures that emerge during prenatal and postnatal development. Within glomeruli, the axons of olfactory sensory neurons form glutamatergic synapses with the dendrites of mitral and tufted cells, the second-order neurons in the olfactory pathway. The neuroanatomist Camillo Golgi, using his newly developed silver impregnation technique, was the first to report olfactory bulb glomeruli, in the year 1875. Santiago Ramón y Cajal described in 1890 their shape as “de forma de pera ó bota de vino”. Apparently, glomeruli represented an anatomical unit and, most likely, a functional unit as well. However, their definitive characteristic and the key determinant responsible for the formation of glomeruli during development remained elusive for more than a century. The precise nature of the glomerulus as a unit was elucidated through molecular and genetic studies in the wake of the discovery of odorant receptor genes in 1991. We have developed a genetic technique, based on an internal ribosome entry site and an axonal marker, to specifically label individual olfactory sensory neurons that express one of the 1141 inact odorant receptor genes in mouse. Our technique enables the direct observation, on whole mounts or in histological sections, of the coalescence of axons of olfactory sensory neurons expressing the same odorant receptor gene into two (sometimes three) glomeruli per olfactory bulb – one located in the medial half and the other in the lateral half. The exact number of glomeruli per olfactory bulb has remained unclear, a century and a half after their discovery. Recently we have devised a methodology for quantifying the number, size, and shape of the glomeruli, by imaging olfactory bulbs labeled immunohistochemically as whole mounts with serial two-photon tomography. We counted a median of 2851 glomeruli per olfactory bulb at postnatal day 56, corresponding to 2.50 glomeruli per intact odorant receptor gene per olfactory bulb. By quantifying glomerular shape with aspect-length ratios and sphericity, we demonstrate that glomeruli do not conform to spherical shapes. We propose the descriptor “tuberiform” to encompass the diversity of glomerular shapes. 

Información relacionada: https://onlinelibrary.wiley.com/doi/10.1111/ejn.70327?af=R