TBOA-sensitive uptake limits glutamate penetration into brain slices to a few micrometers.
Removal of neurotransmitter from the extracellular space is crucial for normal functioning of the central nervous system. In this study, we have used high-affinity metabotropic glutamate receptors (mGluRs) expressed by hippocampal CA1 pyramidal cells to test how far bath-applied glutamate penetrates into slice tissue before being removed by uptake mechanisms. Activation of group I mGluRs by 100 microM DHPG produced an inward current of -48+/-10pA (I(mGluR)), which was blocked by application of group I mGluR antagonists. In contrast, bath application of 100 microM glutamate in the presence of a ionotropic glutamate receptor antagonist and TTX did not activate I(mGluR) in CA1 cells patch-clamped at a depth of approximately 30 microm. Similarly, sole inhibition of glutamate transporters by the broad-spectrum glutamate transporter antagonist TBOA did not induce I(mGluR) under the same conditions. Only if glutamate was co-applied with TBOA an I(mGluR) of -39+/-8pA was recorded which was also blocked by group I antagonists. The data suggest that TBOA-sensitive uptake mechanisms are able to maintain a steep concentration gradient of glutamate to such a degree that a CA1 neuron at a depth of 30 microm is exposed to low extracellular glutamate levels that are not sufficient to induce a detectable activation of group I mGluRs (< 2 microM).
Gueler
Nevzat
N
University Clinic Bonn, Department of Neurosurgery, Experimental Neurophysiology, NCH U1 R035, Sigmund-Freud-Str. 25, 53105 Bonn, Germany.
Kukley
Maria
M
Dietrich
Dirk
D
D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques
C120673:benzyloxyaspartate; D001224:Aspartic Acid; D018698:Glutamic Acid