INTRAHIPPOCAMPAL, BUT NOT INTRAAMYGDALA, INFUSION OF AN INHIBITOR OF HEME OXYGENASE CAUSES RETROGRADE-AMNESIA IN THE RAT

Zinc protoporhyrin-9 (ZnPP) is an inhibitor of heme oxygenase, the enz yme involved in the biosynthesis of carbon monoxide (CO). CO regulates the activity of glutamatergic synapses and has been proposed to play a role in the early phases of long-term potentiation. The present pape r reports on the effect of ZnPP on memory of inhibitory avoidance and of habituation to a novel environment. The bilateral infusion of ZnPP (2 mu g/side) into the dorsal hippocampus caused amnesia for the inhib itory avoidance task when given before training or 0 or 30 min, but no t 60 or 100 min, after training. The immediate post-training intrahipp ocampal infusion of ZnPP also caused amnesia for the habituation task. The immediate post-training intra-amygdala infusion of ZnPP had no ef fect on retention of the avoidance task. The data are consistent with the hypotheses that memory involves long-term potentiation initiated a t the time of training in the hippocampus, and that hippocampal but no t amygdala long-term potentiation may be regulated by CO.