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Maturation of adult-generated dopaminergic neurons in the mice olfactory bulb: a functional study

By Belluzzi O and Pignatelli A


Contrary to previously held beliefs, the adult brain is in fact capable of generating new neurons that can integrate into its complex circuitry. Recent researches have demonstrated that neurogenesis constitutively occurs in two specific regions of the adult mammalian brain, olfactory bulb (OB) and hippocampus. In the OB there is a significant number of dopaminergic (DA) precursors, originated from the subventricular zone and migrated following the rostral migratory stream. The properties of these cells have been studied with the patch-clamp technique in a transgenic animal model expressing GFP under the tyrosine hydroxylase (TH) promoter. Using BrdU we have first demonstrated that, in regions not normally occupied by DA neurones (mitral and external plexiform layers, ML and EPL) there are cells in which the transcription of the TH gene occurs in the absence of significant translational activity. We have studied the functional properties of these cells, showing that they seem to refiect different degrees of maturation, acquiring gradually the traits of mature DA neurones as they become progressively closer to their final destination, the glomerular layer. ln fact, TH-GFP cells in the ML are not autorhythmic, although they can respond with trains of action potentials to sustained depolarisations. On the contrary, the cells in the EPL are autorhythmic, and their pace—maker currents are the same as in mature DA neurons in the glomerular layer. Furthermore, the cells in the EPL are synaptically connected to the olfactory nerve, whereas those in the ML are not. Our interpretation of these data is that TH-GFP+ cells in the ML would represented adult generated neuroblasts committed towards a DA phenotype, which have arrested their migration waiting for a go-ahead signal from the glomerular region, possibly consequent to the establishment of a synaptic contact with the olfactory nerve, consensus which would allow them to complete their differentiation towards the DA phenotype and let them to reach their final destination going across the EPL

Publisher: Società di Neuroscience
Year: 2007
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