title: Time-course of apoptosis in the olfactory epithelium of rainbow trout exposed to a low copper level.
abstract: Copper at low doses is known to specifically induce olfactory neuron death in fish olfactory epithelium. Using light and electron transmission microscopy, we have investigated the features and the time-course of receptor cell death in rainbow trout exposed for 15 days to 20 mug Cu(2+)/l. Ultrastructural observations demonstrate that degenerating cells, which included both mature and immature neurons, exhibited morphological changes characteristic of a cell death by apoptosis. Quantitative analysis shows that the number of apoptotic cells increased significantly already after 1 day of exposure, reaching a peak at day 5. From this timepoint of exposure, no more mature neuron was noted in the olfactory epithelium. Following a significant decrease in the number of apoptotic cells at day 10, a second wave of neuron death was noted at day 15. These findings argue for the occurrence of a neurogenesis process to balance the receptor cell death, despite continued copper exposure, and for a higher vulnerability to the metal of olfactory neurons presenting more advanced stages of cell differentiation. The molecular mechanisms by which copper may induce olfactory neuron apoptosis are discussed.
authors.affiliation: Laboratoire de Physiologie Neurosensorielle, Université Claude Bernard/Lyon 1, 69622 Villeurbanne, Cedex, France.
authors.forename: A K
authors.initials: AK
authors.lastname: Julliard
authors.forename: D
authors.initials: D
authors.lastname: Saucier
authors.forename: L
authors.initials: L
authors.lastname: Astic