The Regulation of Endogenous Glutamate and GABA Release from In Vitro Preparations of Rat Striatum
Abstract
The release of the major excitatory and inhibitory neurotransmitters, glutamate and GABA from rat caudate-putamen (CP) tissue slices and GABA release from fetal rat primary striatal cultures were studied to ascertain key mechanisms underlying the regulation of their release. An improved, highly sensitive method of high performance liquid chromatography and electrochemical detection (LCED) was developed to enable the reliable measurement of these endogenous amino acids from tissue release extracts.The assay permits detection of endogenous amino acids from one milligram of CP tissue in vitro. Release of both amino acids from CP tissue was evoked by elevated levels of potassium while the potassium channel blocker, 4-aminopyridine (4-AP) selectively released GABA. Glu was selectively released by the excitatory amino acid (EAA) receptor agonist N-methyl-D-aspartate (NMDA) independently of external Ca2+ concentration. Ca2+-dependent release of Glu and GABA by potassium- and 4-AP evoked depolarization was shown to be solely dependent on external Ca2+ influx through the P-type Ca2+ channel (P<O.OO5); blockade of L- and N- types of Ca2+ channels did not reduce release of either amino acid. Potassium and 4-AP also evoked Ca2+-dependent release of GABA from the striatal cultures: GABA was also released by Glu through aCa2+-independent process. Activation of DI dopamine receptors elicited a significant stimulation of GABA release from striatal cultures (P<O.O 1), but no dopaminergic effects were observed on release of either amino acid in CP tissue slices. Potassium (50 IlLM:KCI) stimulated release of GABA from the cultures was shown to be significantly increased by bicuculline (P<O.05), the GABA(A) receptor antagonist. These studies suggest that NMDA or Glu stimulation of in vitro Glu and GABA release is most likely mediated through depolarization-evoked reversal of the plasma membrane amino acid transporters.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 19, 1997
- Accession Number
- AD1011742
Entities
People
- James Jr B. Phillips
Organizations
- Uniformed Services University of the Health Sciences