Nonsynaptic glycine release is involved in the early KCC2 expression

Area of Science:

• Neuroscience
• Developmental Biology
• Cellular Physiology

Background:

• Cation-chloride transporters regulate cellular chloride homeostasis.
• Na(+) -K(+) -2Cl(-) (NKCC1) and K(+) -Cl(-) (KCC2) transporters play key roles in neuronal development and function.
• KCC2 extrudes chloride in mature neurons, mediating GABAergic/glycinergic inhibition, while NKCC1 accumulates chloride in immature neurons.

Purpose of the Study:

• To investigate the mechanisms regulating the premature expression of KCC2 in the embryonic ventral spinal cord.
• To determine the role of glycine receptors (GlyR) in KCC2 expression and spinal network maturation.

Main Methods:

• Utilized strychnine to chronically block glycine receptors (GlyR) in embryonic ventral spinal cord explants.
• Investigated effects on KCC2 and NKCC1 expression, action potential firing, and Ca(2+) -dependent PKC activity.
• Examined the role of neurotransmitter vesicular release and volume-sensitive outwardly rectifying (VSOR) chloride channels.
• Assessed the impact of GlyR blockade on rhythmic spontaneous activity.

Main Results:

• Chronic GlyR blockade with strychnine led to a loss of KCC2 expression, without affecting NKCC1 levels.
• The effect of strychnine was independent of Na(+) action potentials but mimicked by a Ca(2+) -dependent PKC blocker.
• Blocking VSOR channels reproduced the GlyR blockade effect, suggesting glycine release from progenitor radial cells regulates KCC2.
• Strychnine treatment inhibited the maturation of rhythmic spontaneous activity in spinal networks.

Conclusions:

• Glycine receptor activation is a necessary developmental process for KCC2 expression in the ventral spinal cord.
• Glycine release from progenitor radial cells appears to control KCC2 expression via a pathway involving VSOR channels and Ca(2+) -dependent PKC.
• GlyR signaling is essential for the development of functional spinal motor networks.