sentences:  Much is known about the binding affinity of hundreds of synthetic compounds to the σ1 receptor.An endogenous ligand for the σ1 receptor has yet to be conclusively identified, but tryptaminergic trace amines, as well as neuroactive steroids such as dehydroepiandrosterone (DHEA) and pregnenolone all activate the receptor.The σ1 receptor is defined by its unique pharmacological profile.