Neurons born in adulthood develop in a far different environment from those born in young animals, because the adult-born neurons must find their way through functioning brain circuits. Perhaps for this reason, the functional properties of adult-born neurons develop in a different order than that seen in young animals, reports a paper in the May issue of Nature Neuroscience.
New adult neurons migrate through mature neural tissue--first tangentially to the olfactory bulb and then radially to their final position. Pierre-Marie Lledo and colleagues used a clever technique to identify these newborn cells in living brain tissue. Patch-clamp recordings showed that tangentially migrating neurons expressed inhibitory GABAA and excitatory AMPA receptors. The plasticity-related NMDA receptors appeared later, in radially migrating neurons, in contrast to young tissue where NMDA receptors precede AMPA receptors. Spontaneous synaptic activity emerged soon after migration was completed. However, spiking activity did not occur until neurons were almost fully mature. This delayed maturation of excitability may serve to prevent the newborn cells from disrupting the function of circuitry already in place in the adult.
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