Communication between two neurogenic zones in the adult mouse nervous system
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There is ongoing neurogenesis in the subventricular zone (SVZ) of the adult brain which supplies interneurons to the olfactory bulb. There is also continuous neurogenesis in the olfactory epithelium (OE) supplying new olfactory sensory neurons whose axons terminate in the olfactory bulb. These axons synapse with tyrosine hydroxylase-positive periglomerular neurons within the olfactory bulb, which are the product of subventricular zone neurogenesis. We hypothesize that focal denervation of the olfactory sensory neurons and thereby lesioning of the presynaptic input to the Type 1 neurons would result in their degeneration, and a subsequent upregulation of subventricular zone neurogenesis. Adult mice (n=26) were treated with methimazole causing the ablation of the OE, and the tissues examined at multiple time-points after treatment. The survival of the olfactory sensory neurons within the OE was assessed together with their terminals within glomeruli of the olfactory bulb. The loss of tyrosine hydroxylase periglomerular neurons was quantified. Cell proliferation in the SVZ was also quantified using an antibody to Ki67, a marker of proliferating cells, and EdU, a thymidine analogue to track DNA synthesis. Methimazole treatment led to loss of olfactory sensory neurons in the OE, loss of their terminals in the glomeruli and loss of tyrosine-hydroxylase-positive periglomerular neurons in the olfactory bulb 14-18 days later (p=0.05). Cell proliferation in the SVZ was increased 14 days post methimazole treatment (p=0.02). The results are consistent with our hypothesis that neurogenesis in the brain has a common neurogenic axis with the olfactory neuroepithelium. We propose the presence of a signalling pathway between these two neurogenic zones, which remains to be elucidated.
Proceedings of the Australian Neuroscience Society
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Central Nervous System