Unsuccessful Attempts to Transfer Morphine Tolerance and Passive Avoidance by Brain Extracts

Abstract

SEVERAL positive and negative reports have been reviewed recently^1,2 on the possibility of transferring acquired behaviour from animal to animal by injecting brain extract from a trained donor into an untrained recipient. We were interested in the possibility of transferring morphine tolerance from rats to mice, as reported by Ungar and Galvan³. We failed to replicate this finding, as had other investigators^4,5. Nevertheless, we felt it worthwhile to search for the appropriate conditions and chose Ungar's simpler system of “fear transfer” as a model^6,7. Here rats are overtrained (by means of foot shock) to avoid entering a black box; recipient mice are then tested in the same box. To enable us to follow accurately the published procedures one of us (A. G.) spent a few days in Ungar's laboratory. In the next 3 months we carried out eighteen unsuccessful experiments with 125 donor rats and 383 recipient and saline control mice. We then did a blind test in our mice using control and trained donor extracts provided by Dr Ungar. Next, we sent 100 of our mice to Houston, for testing as recipients concurrently with the local strain. Finally, we selected, from all our experiments, those mice (of both sexes) which seemed to avoid the black box more often after receiving the extracts. These animals were bred and the offspring were tested as recipients. We hoped to select for recipient capability that might be under genetic influence. The results of all these experiments were negative or equivocal.