Changes in brain monoamine metabolism and carbon dioxide induced amnesia in the rat

The effect of treatment with carbon dioxide (CO2) on the performance of rats 24 hr after receiving a foot shock in a passive avoidance task was studied. Foot shock induced avoidance. Carbon dioxide produced retrograde amnesia for the foot shock induced avoidance response. Changes in brain monoamine metabolism were studied in groups of rats which had been treated with CO2, foot shock or foot shock +CO2. The rats were killed 24 hr after treatment. Changes mainly occurred in the brain stem and hippocampus. In the rats which had received foot shock alone, brain stem and hippocampal serotonin concentration were raised. This rise was not observed when the foot shock was followed by CO2 treatment. Furthermore, it was found that there was an increased release of noradrenaline in those rats subjected to foot shock alone but a decreased release of this amine in the group which received foot shock followed by CO2. It is suggested that the amnesic effect of CO2 parallels changes in brain serotonin and noradrenaline metabolism.