The non-hallucinogenic LSD analog 2-Br-LSD acts as a partial agonist at several aminergic G protein-coupled receptors, including 5-HT2A, but does not induce the head-twitch response in mice, indicating it lacks hallucinogenic effects. Unlike LSD, 2-Br-LSD does not activate 5-HT2B, avoiding a risk of cardiac valvulopathy. It produces weak 5-HT2A β-arrestin recruitment and internalization in vitro and does not cause tolerance after repeated dosing. In cultured rat cortical neurons, 2-Br-LSD promotes dendritogenesis and spinogenesis, and in mice it increases active coping behavior—an effect blocked by a 5-HT2A antagonist—and reverses behavioral effects of chronic stress. These findings suggest 2-Br-LSD has an improved pharmacological profile over LSD and potential therapeutic value for mood disorders.
The ketamine metabolite (2R,6R)-hydroxynorketamine (HNK) activates signaling pathways (ERK1/2, mTOR, S6K1) in the hippocampus, rescuing long-term potentiation and memory deficits in two mouse models of Alzheimer's disease: mice infused with amyloid-β oligomers and aged APP/PS1 mice. The rescue depends on ERK signaling. HNK also corrects aberrant transcription in APP/PS1 mice. These results suggest HNK could be a therapeutic approach for Alzheimer's disease.