Receptor 'memory' in Tetrahymena: does it satisfy the general criteria of memory? An experimental study on induction and extinction by retroactive interference in a unicellular organism.

Diiodotyrosine induced receptor 'memory' at a concentration as low as 10(-18) M. Repeated exposure enhanced cellular responsiveness. Treatment with diiodotyrosine for 1 h, 4 times, induced receptor 'memory' more efficiently than a single uninterrupted treatment for 4 h. Immediately after induction, the receptor 'memory' is subject to retroactive interference by foreign hormonal stimuli, and can be extinguished completely by combined hormone treatment. Thus, the phenomenon of retroactive interference also takes effect at the unicellular level. The experimental observations indicate that receptor 'memory', induced in Tetrahymena by hormonal imprinting, has certain common features with the neuronal memory of higher organisms.