Current projects
In Drosophila, dopamine and octopamine have been implicated in punishment and reward signaling, respectively (Schroll et al. 2006). We have identified the entire circuitry of the larval dopaminergic system and have analyzed for the first time the role of specific dopamine cells in the processes involved in associative learning (Selcho et al. 2009) (Fig. 1). Our studies show that MB Kenyon cells are targets of dopaminergic neurons and suggest that different types of these neurons are involved in different types of signaling required for the formation or retrieval of aversive and appetitive memory.
Fig 1: Dopaminergic neurons (green) of the Drosophila larva shown on background staining (magenta).
Our future projects will continue to focus on the mechanisms of chemosensory learning in the fly larva, from the cellular level to behavior. We attempt to dissect the entire circuitry from the sensory neurons which signal the to-be-associated stimuli up to the memory centers in the higher brain and down to the motor areasthat trigger the relevant behavioral outputs. A special focus will be on the dopamine and octopamine reinforcing system and on the MBs, in which associations of odors with positive or negative reinforcement are thought to be formed. Also, we want to uncover the neural substrate of the reported persistence of larval olfactory memory through metamorphosis (Tully et al. 1994).
Figure 2: Anatomy and function of the larval mushroom body. A) By crossing to UAS-shi'ts to a set of different MB specific GAL4 driver lines to conditionally block synaptic output, 201y and NP1131 showed a learning phenotype after appetitive olfactory conditioning. B) Anatomical inspection revealed overlapping expression of both lines in a set of embryonic-born MB Kenyon cells. C) 3D-reconstruction of the larval mushroom body visualizes the detailed morphology in at least 10 further subdivisions (use this link to download a full-size image).
In detail, we were able to show that, similar to adult flies and other insects, the larval MB forms an olfactory memory centre. Interestingly, we identified the approximately 200 embryonic-born Kenyon cells as being necessary and sufficient to form appetitive olfactory associations in the larva (Pauls et al., submitted). The participation of larval-born Kenyon cells in this task is unlikely, i.e. neurons that become gradually integrated in the developing mushroom body during larval life. Taken together a basic understanding of the neuronal pathways underlying olfactory learning has emerged, which will be refined in the future.
Schroll C et al. (2006) Current Biology 16: 1741-1747.
Selcho M, Pauls D, Han KA, Stocker RF & Thum AS (2009) PLoS ONE 4(6): e5897.
Tully T, Cambiazo V & Cruse L (1994) J Neuroscience 14: 68-74.
