THE RE-INNERVATION OF OLFACTORY GLOMERULI FOLLOWING TRANSECTION OF PRIMARY OLFACTORY AXONS IN THE CENTRAL OR PERIPHERAL NERVOUS-SYSTEM

  • 1 January 1983
    • journal article
    • research article
    • Vol. 137  (AUG) , 1-19
Abstract
The re-innervation of the olfactory bulb was studied in rats in which the primary afferent axons were transected either in the peripheral nervous system, on the intracranial side of the cribriform plate, in the CNS or in the nerve fibers layer of the bulb. Both procedures resulted in denervation of glomeruli on the dorsal surface of the olfactory bulb. Re-innervation of these glomeruli was 1st seen approximately 3 wk after operation and was largely completed by the 6th wk, irrespective of the site of the lesion. The similarity of the timing of reinnervation following the 2 procedures indicates that the cut fibers did not regenerate from their sites of transection. It is more probable that the re-innervating axons were those of neurons newly generated in the olfactory epithelium. This view is supported by the results of other investigations, in which retrograde degeneration and subsequent replacement of the neurons have been found to follow transection of the olfactory nerves. After transection of the olfactory nerves, the new axons entering the bulb grew through the site of the lesion, across the interface between peripheral and central nervous tissue, through the nerve fiber layer and into the glomeruli. They followed the same course as normally growing primary olfactory axons. After the afferent fibers had been cut within the olfactory bulb, the site of transection was transformed into a scar composed largely of astrocytes. No olfactory axons grew through the scar and none passed beneath it in the deeper layers of the bulb. By tracing the anterograde axonal transport of horseradish peroxidase, it was shown that axons immediately rostral to the lesion terminated in the re-innervated glomeruli. These denervated glomeruli were probably re-innervated by axons that grew through the intact central nervous tissue of the nerve fiber layer on either side of the lesion.