PREGNENOLONE SULFATE ENHANCES POST-TRAINING MEMORY PROCESSES WHEN INJECTED IN VERY-LOW DOSES INTO LIMBIC SYSTEM STRUCTURES - THE AMYGDALA IS BY FAR THE MOST SENSITIVE

Immediate post-training, stereotactically guided, intraparenchymal adm inistration of pregnenolone sulfate (PS) into the amygdala, septum, ma mmillary bodies, or caudate nucleus and of PS, dehydroepiandrosterone sulfate, and corticosterone into the hippocampus was performed in mice that had been weakly trained in a foot-shock active avoidance paradig m. Intrahippocampal injection of PS resulted in memory enhancement (ME ) at a lower dose than was found with dehydroepiandrosterone sulfate a nd corticosterone, Intraamygdally administered PS was approximately 10 (4) times more potent on a molar basis in producing ME than when PS wa s injected into the hippocampus and approximately 10(5) times more pot ent than when injected into the septum or mammillary bodies. ME did no t occur on injection of PS into the caudate nucleus over the range of doses tested in the other brain structures, The finding that fewer tha n 150 molecules of PS significantly enhanced post-training memory proc esses when injected into the amygdala establishes PS as the most poten t memory enhancer yet reported and the amygdala as the most sensitive brain region for ME by any substance yet tested.