Abstract

Increases in the concentration of brain 5HT induced by intracarotid injection of 5HTP (a total of 22 or 44 mg per animal) caused a biphasic variation of synchronized and desynchronized EEG patterns of the brain. The mechanism by which 5HT produced these changes is not clear; however, the two effects bear a positive correlation with the extent of increase of 5HT in the mesodiencephalon thus suggesting that 5HT acts directly upon some region of the reticular formation.

Divergent biochemical changes in the brain were produced by different MAO inhibitors which may partly explain the diverse electrical effects induced by these compounds. Intravenous injection of 2 mg/kg of either JB 516 or SKF 385 induced a persistent desynchronization of the EEG and evoked a rapid rise in brain 5HT within a few hours, during which time minimal changes in NE took place. In contrast, intravenous injection of IPZ (25 mg/kg) did not modify the EEG and produced a slow increase of both 5HT and NE over a 4-day period.

These findings suggest that the relative amounts of NE and 5HT and their rate of formation in the brain are important factors involved in determining the nature of the electrical activity of the brain following injection of MAO inhibitors.