Age-related changes in CNS-sensitivity to hexobarbital and thiopental in the rat.

CNS-sensitivity to hexobarbital and thiopental was determined with an EEG-threshold method in rats of different ages. The results show that the threshold dose decreases by 15% for both barbiturates when the rats are between 50 and 150 days of age. Brain concentrations of hexobarbital also decreased with increasing age and show that the changes in threshold doses are due to changes in CNS-sensitivity. Anesthesia times after threshold determinations decrease with increasing age for thiopental, but there was no change in anesthesia times after hexobarbital thresholds. At 90-100 days of age there was a significant increase in EEG-threshold for hexobarbital, and brain concentrations in the same age interval indicate a decreased CNS-sensitivity.