Although simple in their body plan, planarian neurons are surprisingly similar to that of vertebrates. Planaria have multiple types of neurotransmitters and neurotransmitter specific neurons. During the course of my Master's, I was hoping to understand the role of Octopamine in the complex 'behavior' of classical conditioning.
Classical conditioning is a process by which a positive (or negative) association occurs between a neutral object and an object associated with an award (or punishment). The most classic example is that of Pavlov and his dogs. In his experiments where classical conditioning was first discovered, Pavlov would ring a bell at the same time as feeding the dogs. Eventually the dogs began to associate the ringing of the bell with food and would begin to salivate extensively with just the ringing of a bell. This is a simple type of learning and I wanted to see if the species of planarian flatworm in my lab, Dugesia japonica was capable of memory at this level.
Octopamine is a neuromodulator and is often considered the 'invertebrate norepinephrine' as it is similar in effect and structure. Interestingly, some work in honeybees suggest that octopamine may play a role in memory formation. To explore this in planaria, I first demonstrated that planaria could not only be classicaly conditioned, in my case to associate red light with an electric shock, but also that their memory of the conditioning was long lasting. 'Long lasting' was 7 days, the same period of time it would take a newly decapitated planaria to regrow a functional brain. When conditioned in the presence of octopamine, planaria did not demonsrate any evidence of classical conditioning and refused to avoid the red light and subsequent shock, suggesting a potential role of octopamine in memory formation.
I was unable to have this work peer reviewed; however, contact me if you're curious to see some of my Master's thesis and or/data.
Umesono, et al., 2011. Regeneration in an evolutionary primitive brain- the planarian Dugesia japonica model. European Journal of Neuroscience 34(6): 863-9.