Extracellular levels of brain aspartate, glutamate and GABA during an inhibitory avoidance response in the rat.
The extracellular levels of aspartate, glutamate and GABA were measured by microdialysis, coupled with an HPLC method, in rat prefrontal cortex (mPFC) and ventral hippocampus (VH) before and during the performance of a step-down inhibitory task. The basal levels of glutamate were about 50% higher than those of aspartate, and GABA levels were about 20-folds smaller than those of the excitatory amino acids. There were no significant differences in the basal levels of any of the three amino acids between the two brain regions. The extracellular levels of aspartate increased during acquisition and recall trials in both VH and mPFC, whereas those of glutamate increased in the VH during acquisition only. A significant increase in GABA levels was also detected during acquisition but only in the mPFC. The neuronal origin of the increased extracellular levels of aspartate, glutamate and GABA was demonstrated by administering tetrodotoxin directly into the mPFC or VH by reverse dialysis. These findings, together with previous evidence from our and other laboratories, indicate a differential release of aspartate and glutamate from excitatory neurons during the performance of behavioral responses, and therefore, distinct roles for the two excitatory amino acids should be envisaged.
Ballini
Chiara
C
Dipartimento di Farmacologia Preclinica e Clinica M. Aiazzi Mancini, Università degli Studi di Firenze, Viale G. Pieraccini, Firenze, Italia.
Corte
Laura Della
LD
Pazzagli
Marta
M
Colivicchi
Maria Alessandra
MA
Pepeu
Giancarlo
G
Tipton
Keith F
KF
Giovannini
Maria Grazia
MG
D000818:Animals; D001224:Aspartic Acid / Q000032:analysis / Q000378:metabolism*; D001362:Avoidance Learning / Q000502:physiology*; D005110:Extracellular Space / Q000737:chemistry / Q000378:metabolism*; D018698:Glutamic Acid / Q000032:analysis / Q000378:metabolism*; D008297:Male; D009433:Neural Inhibition / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D005680:gamma-Aminobutyric Acid / Q000032:analysis / Q000378:metabolism*
D001224:Aspartic Acid; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid