A receptor in substantially pure form obtainable from rat forebrain tissue which is characterised in that: a) compound A binds to it with a Kd of 40nM for rat forebrain tissue, b) compound A binds to it with a Bmax of 220 pmol/g protein for rat forebrain tissue, c) compound B binds to it with a Kd of 2nM for rat forebrain tissue, d) compound B binds to it with a Bmax of 220pmol/g protein for rat forebrain tissue; and homologous receptors from other sources sharing at least 85 % homology with the rat forebrain tissue.
