Transaminase reactions and glutamate dehydrogenase in gastropod hepatopancreas

Summary In toads,Bufo bufo L., ACTH (1 I.U.) causes a retardation of extinction compared with Ringer administration irrespective of whether the animals have received the ACTH injection before or at the end of acquisition. Treatment with ACTH 20 min prior to acquisition lowers the starting activity. Therefore, habituation is completed earlier than in Ringer controls. The effect of ACTH treatment is stimulus-specific, as toads habituated to a wormlike stripe show normal turning activity to a triangle even under the influence of ACTH.The conformity of these results with the ACTH effect on complex learning behaviour especially in rats may indicate an underlying common principle. It is concluded that ACTH and, possibly, related peptides elicite neuronal events which favour learning and memory processes even in lower vertebrates.We thank Prof. Dr. W. Hanke, Karlsruhe, for fruitful discussions.