The term median reticular formation (RFmed) refers to one of three histologically defined longitudinal zones of the reticular formation (RFZ). Tthe zone located nearest the midline, it includes all of the serotonergic cell groups (B cell groups 1-9) ( Felten-1983 ) and all of the same nuclei as the raphe nuclei (histological) (RPHhis) except for the rostral linear nucleus of the raphe (LIRr). Updated 28 Nov 2025.