Neurogenesis and neuron regeneration in the olfactory system of mammals. III. Deafferentation and reinnervation of the olfactory bulb following section of the fila olfactoria in rat.

Axotomy at the level of the lamina cribrosa in rat induces rapid degeneration of the olfactory sensory axons in the bulb. The phenomenon, which is limited to the layer of olfactory fibres and to the glomeruli of the bulb, can be observed as early as 15-24 h after surgery, and peaks at 3-4 days. The glomeruli located in the rostro-ventral portion of the bulb are affected first, and the process extends to the dorso-caudal portion with a delay of 12-24 h. Reactive hypertrophy of the glia coincides with removal of the degenerating terminals, and is maximal 48 h after axotomy. Axotomy does not preclude reinnervation of the bulb by axons originating from new, reconstituted neurons in the olfactory neuroepithelium. These new axons begin to reach the periphery of the bulk approximately at the 20th day post-operative and then reinnervate the glomeruli. The rostro-ventral portion of the bulb is the first to be reinvaded by the new axons. The glomeruli reacquire a morphological pattern similar to controls between 20 to 30 days.