THE PLASMA-CONCENTRATION OF GABA SHOWS NO EVIDENCE OF A CIRCADIAN-RHYTHM AND IS STABLE OVER WEEKS IN NORMAL MALES

The concentration of free GABA was measured in the plasma of 18 normal young men, in three separate studies. Overall, it varied by a factor of about 4-fold in normal subjects, from values of 0.10 nmol/ml to 0.4 0 nmol/ml. Day-to-day stability was found to be very high (r=0.94, n=8 subjects, p<0.002). Free GABA concentration was stable over more than 2 weeks (r=0.95, n=5 subjects, p<0.02). A study of circadian rhythms was carried out (n=5 subjects) comparing a condition with no food and partial light deprivation in a supine position during 34 hr. (''rest'' condition'') with a condition of normal daily activities (''activity' ' condition). No circadian rhythm was found in the ''rest'' condition. In the ''activity'' condition, there was a mid-day rise in GABA conce ntrations in 3 out of 5 subjects. The significance of these changes wa s explored using different statistical tests.