Why can GABA excite the neurons of a newborn's brain? · Grey Matter

GABA opens a chloride channel, and whether that inhibits depends on how much chloride is inside the cell.

Why can GABA excite the neurons of a newborn's brain?

GABA opens a chloride channel, and whether that inhibits depends on how much chloride is inside the cell. Immature neurons express the transporter NKCC1, which loads chloride in, so when GABA-A channels open chloride flows out and the membrane depolarises, sometimes enough to help fire the cell. As neurons mature they express KCC2, which pumps chloride out; internal chloride falls and GABA becomes hyperpolarising or shunting. In rodents the switch happens over the first one to two postnatal weeks, and in humans KCC2 rises steeply around full-term birth, so the newborn brain sits close to the transition.