Many discoveries in neurosciences revealed the interconnections between epigenetic, synaptic and circuit modifications to sensory experience and behaviour. In contrast, very little is known about how neuronal activity and sensory experience influence the structure and function of dendritic trees.
To study whether mechanosensory stimulation affects behaviour and the dendritic tree architecture, we used natural mechanical stimulation with signals that are generated by physical contacts between worms. We first compared grouped to single isolated embryos to test the influence of mechanosensory experience on behaviour using a paradigm established by the Rankin lab (Rose et al. 2005). We found that worm isolation affected two behaviours: First, it altered the sinusoidal waveforms produced during worm movement. Second, it decreased the number of responses generated by the adult following harsh mechanical stimulation.
We then asked whether the morphology of the polymodal mechanosensory PVD is affected by mechanical isolation, focusing on the number and geometry of its repetitive dendritic trees that are similar to “menorahs” (Oren-Suissa et al. 2010). We found that isolation of both larvae and adult worms significantly affected two parameters of PVD structure: First, it increased the number of dendritic branches. Second, it modified the straight geometry of the “candles” of the menorahs (quaternary branches), into wavy structures. Moreover, when we isolated worms with glass beads, that function as static mechanical stimulators in the plate, the reduction in the number of straight quaternary branches following isolation was rescued. In contrast, isolation of worms following chemical stimulation (with plates previously exposed to worms) resulted in similar effect on the PVD, as without chemical stimulation.
In conclusion, our observations indicate that mechanical isolation induces changes in dendritic branching architecture of the PVD. We found that the menorahs structural plasticity is accompanied by altered behavioural output in functions that are mediated, at least in part, by the PVD. Thus, we propose that mechanical isolation during development and adulthood affects PVD dendritic arbors and these structural changes influence worm behaviour. The genetic basis of these structural and behavioural modifications is currently being characterized.
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