elav regulatory sequences drives expression of 'nlgSNTG4', an engineered receptor that can be used to monitor synaptic contacts between neurons in vivo. The nlgSNTG4 protein is a fusion of 1. a single-chain antibody domain (SCAD) that recognizes the extracellular domain of Mmus\Cd19, 2. N amino acid residues 1460-1767, encoding the NRR (Notch regulatory region, a fragment of the extracellular domain) and TMD (transmembrane domain), 3. the Tag:TS(Nlg2) tag (which results in the protein being targeted to postsynaptic sites) and 4. the GAL4(esn) driver. When nlgSNTG4 is expressed postsynaptically in one neuron type, and an appropriate ligand protein (containing the extracellular domain of Mmus\Cd19, the binding partner of SCAD) is expressed presynaptically on a neuron that forms a synaptic contact with the nlgSNTG4-expressing neuron, then upon binding of nlgSNTG4 and the Mmus\Cd19 fragment, components of the endogenous Notch/Delta signaling pathway cleave the N sequences in the NRR and TMD, releasing the GAL4(esn) driver, which can then enter the nucleus and activate transcription of a UAS-driven construct.