Histogenesis of olfactory bulbs in human foetus

Authors:Sagnik Roy, Nivedita Roy
Int J Biol Med Res. 2012; 3(2): 1561 – 1564  |  PDF File

Abstract

Histogenesis of olfactory bulb was studied in 62 human foetuses. The olfactory bulbs were removed en block with the surrounding bone and fixed in 10 percent formal saline. Serial sections of paraffin embedded tissue were stained with H/E, cresyl violet and Glees Marsland’s modification of Bielschowsky’s staining method for neurites. Klüver and Barrera’s method was used for myelin and nissl granules. Sections of adult olfactory bulb stained with H/E and Klüver and Barrera’s method were used as control. Microscopic study revealed extension of lateral ventricular cavity inside the bulbs event at 15th week of development. A laminar organization was detected inside the bulbs which gradually became more distinct reaching its peak at 26 weeks of development. Thereafter, the laminar organization began to disappear and at 34 weeks laminar organization was difficult to demonstrate. Mitral cells were the largest neurons which could be detected from the earliest age groups along with the nerve fibre layer. At 24 weeks mitral cells together with tufted cells formed a distinct lamina 3 – 4 cells thick. Glomeruli were seen from 20 weeks onwards but their number and size declined after 30 weeks. The internal and external plexiform layers were well identified upto 28th week after which they gradually became obscured. Granule cells were found confined in the centre of the bulb. Myelinated nerve fibre were detected in the adult olfactory bulbs but not in any of the foetal specimen. It was concluded that myelination in the olfactory bulbs begins only after birth.