Glycine release in the substantia nigra: Interaction with glutamate and GABA.
Previous studies have reported a high number of glycine (GLY) receptors in the substantia nigra (SN) but a low number of GLY-neurons, suggesting that taurine, a partial agonist of GLY-receptors, is the natural substrate for SN GLY-receptors. By using microdialysis to quantify amino acids in the extracellular space of the SN, we observed an extracellular pool of GLY in the rat that increased after depolarizing with high-K+ in a Ca2+-dependent manner and that diffuses through the extracellular space. GLY markedly increased after blocking either the tricarboxylic cycle with fluorocitrate or the glutamine synthetase activity with MSO. Because these products act selectively on glial cells, their effects show glia as a key cell in maintaining the extracellular pool of GLY in the SN. Extracellular GLY was modified by glutamate and glutamate receptor agonists. The local administration of GLY modified the extracellular concentration of GABA. Taken together, the complex regulation of the extracellular level of GLY, its possible glial origin and interaction with glutamate and GABA suggest a volume transmitter role for GLY in the SN, a possibility which also agrees with the recent finding of GLY-transporters in this centre.
Dopico
José García
JG
Laboratory of Neurobiology and Experimental Neurology, Department of Physiology, Faculty of Medicine, University of La Laguna, La Laguna, Tenerife, Canary Islands, Spain.
González-Hernández
Tomás
T
Pérez
Ingrid Morales
IM
García
Isabel Gómez
IG
Abril
Antonio Milena
AM
Inchausti
José Obeso
JO
Rodríguez Díaz
Manuel
M
D000704:Analysis of Variance; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002951:Citrates / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D008297:Male; D017551:Microdialysis / Q000379:methods; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002951:Citrates; D018690:Excitatory Amino Acid Agonists; D014316:Tritium; C007744:fluorocitrate; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D011189:Potassium Chloride; D005998:Glycine