The present study showed that many neurons in the adult rat brain possessed a perineuronal sulfated proteoglycan surface coat which reacted to cationic iron colloid and aldehyde fuchsin. This surface coat was stained supravitally with Ehrlich's methylene blue and doubly stained with Ehrlich's methylene blue and aldehyde fuchsin. The surface coat was also stained with Gomori's ammoniacal silver and doubly stained with Gomori's ammoniacal silver and cationic iron colloid. The surface coat was usually expressed together with a nerve cell surface glycoprotein net detectable with lectin Wisteria floribunda agglutinin. These findings indicate that the perineuronal proteoglycan surface coat is identical to Cajal's superficial reticulum and contains some collagenous elements. It was further demonstrated that collagenase digestion erased Gomori's ammoniacal silver impregnation within the perineuronal proteoglycan surface coat.</p
