Ammonia inhibits long-term potentiation via neurosteroid synthesis in hippocampal pyramidal neurons

► Ammonia inhibits LTP, a cellular model of memory, via neurosteroid production. ► Ammonia enhances neurosteroid immunostaining in pyramidal neurons. ► Finasteride is used to antagonize 5α-reductase, an enzyme for neurosteroidgenesis. ► Finasteride overcomes ammonia-mediated LTP inhibition. ► Enhanced neurosteroid immunostaining by ammonia is blocked by finasteride.