Immunohistochemical localization of laminin, fibronectin and collagen type IV in the nerve fiber layer of the olfactory bulb.

When the olfactory nerve is injured in adult mammals, the axons grow across the PNS-CNS transitional zone and re-innervate their synaptic contacts within the olfactory bulb. Some years ago, Liesi [Liesi P. (1985) Laminin-immunoreactive glia distinguish regenerative adult CNS systems from non-regenerative ones. EMBO J. 4, 2505-2511] reported the presence of laminin in non-basal lamina locations within the nerve fiber layer (NFL) of the olfactory bulb of adult rats and suggested that this molecule may facilitate olfactory axonal growth into and within the CNS. The purpose of the present study was to compare the expression of laminin, fibronectin, and collagen type IV in: (a) the NFL of developing and adult rats; and (b) the NFL rostral and caudal to a stab wound in the olfactory bulb of adult rats. Numerous punctate deposits of immunofluorescence were seen in the NFL of the E18 (Theiler stage 23) bulb when antisera to laminin, fibronectin or collagen type IV were used. There was a dramatic drop-off in staining at the border between the NFL and the presumptive glomerular layer. The staining pattern was similar in the newborn bulb, although the immunofluorescence was not as strong. In the unoperated adult rats, only laminin was present consistently as punctate deposits within the NFL, whereas all three antisera stained numerous punctate deposits within the NFL during the first week after a stab wound. Although there was a partial recapitulation of the expression pattern for laminin, fibronectin and collagen type IV in the lesioned adult NFL, it never reached the extent found in the E18 or newborn bulbs and its expression returned to normal levels prior to the re-innervation of the bulb during the second and third weeks after surgery. The results suggest that the molecular requirements for the successful growth of olfactory axons may differ during development to growth in adult animals.