Olfactory tract transection reveals robust tissue-level plasticity by cellular numbers and neurotrophic factor expression in olfactory bulb.

Nervous system lesions are characterized by the loss of neuronal numbers and types. The neurotrophic factor levels in an injured tissue reflect their potential for regeneration. This hypothesis was investigated in olfactory bulb (OB), where olfactory tract was surgically transected disrupting neuronal migration and turnover. The effects were followed with quantification of mitral cells and three neurotrophic factors mRNA levels for 6 weeks. The neuronal numbers decreased by 3rd- and 4th-week in transected OBs followed by their restoration, comparable with that of controls at 5th- and 6th-week. The endogenous levels of three neurotrophic factors - (brain derived neurotrophic factor, insulin growth factor-1 and fibroblast growth factor-2) using qPCR showed increase at 2nd-week by 136-, 8- and 2-fold respectively. Also, there was a significant increase in specific neurotrophic factors at 5th-week and 6th-weeks. The results propose a temporal link between deployment of neurotrophic factors and the plausible restorative events for mitral cell numbers in OB.