Since we designed the device to function as a screening system for therapeutic development, we tested a specific receptor-ligand interaction. We purposefully chose a receptor that would be present in neurons on only one side of the device in order to measure a purely post-synaptic response. To control the cells we were stimulating, we utilized DREADDs, specifically the combination of hM3Dq/CNO. Only excitatory neurons infected with mCherry-hM3Dq showed the presence of mCherry throughout the compartment, indicating successful cloning of the hM3Dq-mCherry sequence, as well as the ability to co-culture infected excitatory iNs with non-infected inhibitory iNs in the same microwell. DREADD-positive neurons demonstrate a robust response to high concentrations of CNO, but little to no reaction to doses lower than 100 nM (Fig. 7). These results reveal the utility of the system as a screening platform for neuroactive compound screening. Neuronal circuits can be parallelized in the microplate and several different conditions (in this case, drug concentrations) can be tested in distinct wells. Expansion of this approach to multiple plates can further extend the opportunity to screen different drugs and different cell lines in a micro-circuit context.
