CHRNA7 and schizophrenia: Several α7-nAChR positron emission tomography (PET) radioligands have so far been tested: 18F-ASEM was developed as an α7-nAChR antagonist with suitable binding properties (Horti et al., 2014) and tested in 21 healthy non-smoking volunteers and in 6 males with schizophrenia (Wong et al., 2014, 2018).