Addiction-Related Memory Transfer and Retention in Planaria

Abstract

Memory retention and transfer in organisms happen at either the neural or genetic level. In humans, addictive behavior is known to pass from parents to offspring. In flatworm planaria (Dugesia tigrina), memory transfer has been claimed to be horizontal, i.e., through cannibalism. Our study is a preliminary step to understand the mechanisms underlying the transfer of addictive behavior to offspring. Since the neural and neurochemical responses of planaria share similarities with humans, it is possible to induce addictions and get predictable behavioral responses. Addiction can be induced in planaria, and decapitation will reveal if the addictive memories are solely stored in the brain. The primary objective was to test the hypothesis that addictive memory is also retained in the brainless posterior region of planaria. The surface preference of the planaria was first determined between smooth and rough surfaces. Through Pavlovian conditioning, the preferred surface was paired with water and the unpreferred surface with sucrose. After the planaria were trained and addicted, their surface preference shifted as a conditioned place preference (CPP) was established. When decapitated, the regenerated segment from the anterior part containing the brain retained the addiction, thus maintaining a shift in the surface preference. Importantly, we observed that the posterior part preserved this CPP as well, suggesting that memory retention is not attributed exclusively to the brain but might also occur at the genetic level. As a secondary objective, the effects of neurotransmitter blocking agents in preventing addiction were studied by administering a D1 dopamine antagonist to planaria, which could provide pointers to treat addictions in humans.