Distribution of betaine/gaba transporter BGT-1 in excitotoxic brain injury and its role in osmoregulation in the brain

Abstract

The present study aims to dissect the betaine/GABA transporter BGT-1 in the brain. BGT-1 is found in the cell bodies and dendrites of pyramidal neurons, and is localized in peri-extrasynaptic region of asymmetric synapse. BGT-1 expression decreases in pyramidal neurons but increases in astrocytes after kainate-induced neuronal injury. Treatment of human U373 MG astrocytoma cells for 12 hours with 1-100 mM of betaine results in increased BGT-1 immunointensity and increased [14C] betaine transport into the cells. In contrast to rats received intracerebroventricular injection with kainate plus saline, which show loss of BGT-1 immunoreactivity in neurons and little induction of BGT-1 in astrocytes, a marked increase in BGT-1 immunoreactivity is shown in astrocytes in the degenerating CA fields and fimbria, in rats injected with kainate and betaine. These astrocytes have swollen mitochondria at electron microscopy. The study elucidates an important role of BGT-1 in osmoregulation in the brain.