Giant depolarizing potentials
Giant depolarizing potentials (GDP) are the first type of electrical activity of developing
brain. These patterns of activity differ a lot from the adult brain activity patterns: they do not carry encoded information, they are generalized, they are relatively slow (with typical time of .1 s), they are repetitive (with typical time of 1s). They are, however, very different from epileptiform activity.
GDPs are slowly spreading in brain structures with a speed of approximately 1 mm/s. They use
neuron's connection ( axons) for this, using these connections they can develop in connected structures as well (from example from retinato geniculate nucleus).
GDPs are observed only in early stages of brain development. In
humans they exist only on prenatalstages, in rats they last for approximately P6.
According to current point of view, slow developing GDPs are essential for
neural nets of immature brain development. It's supposed that GDPs take the closest part in synaptogenesys, modification of synaptic connections and synapses maturation. But the precise role of GDPs in development, and the primary regulatory mechanisms are yet to be uncovered.
Origin and properties
One of the main conditions for GDPs development (that are met in premature brain and that don't take place in adult one) is that
GABAaction on these stages should be excitatoryrather than inhibitory. This is caused by a much higher concentration of Cl- concentration in neonatal neurons cytoplasm. Further, the expression of the chloride transporter, KCC2, is less in immature neurons, as a result of which there is the above mentioned high intracellular chloride. On receiving a GABAergic stimulus, there is an efflux of Chloride from the cell, resulting in depolarization of the cell. This causes the GDPs. Once the KCC2 expression is relatively high, as in the adult, mature neurons, the GDPs almost simultaneously disappear. Though it must be remembered that the increased level of KCC2 expression in adult, mature neurons alone is not the reason for the disappearance of the GDPs.
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