Morphological studies on Mn-SOD, NOS and calcium binding proteins in the rat hippocampus

The immunohistochemical localization of manganese superoxide dismutase (Mn-SOD), nitric oxide synthase (NOS) and calcium (Ca) binding proteins; calbindin-D28K (Calb) and parvalbumin (Parv), was investigated in the rat hippocampus by using a double immunostaining method and an enzyme histochemical staining method. These substances showed considerable regional immunoreactivities in the hippocampus. (1) Although Mn-SOD- and NOS-immunoreactive neurons showed a similar distribution, virtually all of the latter neurons had no or weak Mn-SOD immunoreactivity in all subfields. This finding suggests that NO-producing neurons are not directly associated with Mn-SOD scavenger system in the hippocampus. (2) The co-localization of NOS and Parv or Calb was rarely found throught the hippocampus. (3) Neurons which were intensely immunostained for Mn-SOD were frequently found to be Parv-immunoreactive non-pyramidal cells, or Calb-immunoreactive pyramidal and non-pyramidal cells. From the latter two findings, it is speculated that Ca buffering effects of Parv and Calb are required in Mn-SOD neurons, but not in NO-producing neurons. Since Parv- or Calb-containing non-pyramidal cells are known to be GABAergic, most if not all, Mn-SOD-containing non-pyramidal cells may be GABAergic inhibitory neurons in the rat hippocampus. On the other hand, NOS neurons are also known to belong to GABAergic non-pyramidal cells. Therefore, Mn-SOD and NOS neurons constitute two distinct subclasses of non-pyramidal inhibitory neurons in the hippocampus.