Ethanol challenge alters amino acid neurotransmitter release from frontal cortex of the aged rat

In two groups of male rats having an average age of either 90 days or two years, guide cannulae for bilateral push-pull perfusion were implanted stereotaxically to rest upon the superficial frontal cerebral cortex. On post-operative recovery, either 1.5 or 3.0 g/kg 20% ethanol (V/V) was given by intragastric gavage to each unrestrained rat. Sequential samples of venous blood were obtained from the tail and analyzed for alcohol levels by gas chromatography. A set of push-pull perfusions of the cortical sites was carried out with an artificial CSF before gavage and at 25, 50 and 150 min after the administration of ethanol. An individual perfusion was continued for 5.0 min at a rate of 25 microliters/min. Using high performance liquid chromatography with electrochemical detection (HPLC-EC) each sample of perfusate was then assayed for its content of glutamate (Glu), aspartate (Asp), glutamine (Gln), glycine (Gly), taurine (Tau) and GABA with homoserine used as the internal standard. The results showed that the 3.0 g/kg dose of ethanol resulted in a higher level of blood ethanol in the older animals, which persisted over the 150 min time interval. Further, the 1.5 g/kg dose of ethanol administered to the older rats reduced the cortical activity of Glu and Gln relative to the younger animals. In addition, the 3.0 g/kg dose augmented the cortical efflux of Tau in the aged rats. Neither dose of ethanol affected the efflux of Asp or Gly from the perfused frontal cortex of either the young or old group, nor was the release of GABA detectable under either the control condition or following treatment with ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)