Selective degeneration of neurons in the olfactory bulb following prolonged odour exposure.

Abstract Rats have been exposed to a constant stream of cyclo-octanone in room air from 2 weeks of age for periods ranging from 2 weeks to 11 months. They have been compared with control litter-mates exposed to the same room air for the same periods. Consistent patterns of cell degeneration have been seen by both light and electron microscopy: in control animals, a small dorsomedial region throughout the anteroposterior extent of the bulbs; in experimental animals, in the same dorsomedial region, slightly extended, ventral and mid-lateral zones, and also throughout the anteroposterior extent, but more marked anteriorly. Cells in other regions were normal. The degeneration is very similar in type to transneuronal degeneration following olfactory nerve transection, and the effect of the odour exposure on these cells is termed ‘selective degeneration’. No morphological changes indicative of degeneration have been found in the olfactory nerve terminals. The nature of the degeneration and its functional significance is discussed and the potential value of the method is considered.

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