Functional correlates of degeneration and renewal of cilia and knobs of olfactory receptor neurons in the frog

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Abstract
Changes in surface structures of the olfactory epithelium, olfactory nerve and olfactory nerve layer in the olfactory bulb following olfactory nerve section were studied, by scanning electron microscopy, in the frog. Correlative neurophysiological responses were recorded from the olfactory epithelium in response to odor stimulation. Examination of the epithelial surface showed degeneration and loss of the dense ciliary matrix and olfactory knobs by day 10, which exposed the microvillar surface of the sustentacular cells. The amplitude of slow voltage transients recorded from the epithelial surface systematically decreased through day 10. By day 40, the olfactory epithelium became responsive to odor stimulation. At this time partial renewal of the ciliary matrix on the epithelial surface and bundles of receptor cell axons in the olfactory nerve layer of the olfactory bulb were observed. There was substantial replacement of the ciliary matrix by day 100; in contrast, considerably less recovery of the slow voltage transient was evident. Recovery of odor-evoked respon sivity lagged behind recovery of the ciliary matrix. Therefore, these data imply that the reappearance of olfactory knobs and cilia is causally related to the recovery of the slow voltage transients.