Mossy cells in the mouse dentate gyrus: identification in the dorsal hilusand their distribution along the dorsoventral axis

Previously we showed that large multipolar cells immunoreactive for calreti nin and subunits 2 and 3 of amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) type glutamate receptors (GluR2/3) clustered in the ventral hilus of the mouse dentate gyrus and revealed that they were mossy cells. Although such large calretinin immunoreactive cells were not seen in the dorsal hilu s, our Golgi study revealed the presence of mossy cells in the dorsal hilus . As we observed large intensely GluR2/3 immunoreactive cells in the dorsal hilus, we suggested that these calretinin negative but intensely GluR2/3 p ositive large cells in the dorsal hilus were also mossy cells. In the prese nt study we confirmed this identification with several methods. The extrace llular tracer labeling studies revealed that all of 47 mossy cells identifi ed morphologically were intensely GluR2/3 positive but calretinin negative, whereas none of 22 non-messy hilar neurons were intensely GluR2/3 positive . Electron microscopically most of intensely GluR2/3 positive somata and de ndritic processes showed the characteristic ultrastructural features of mos sy cells. Furthermore, the fimbria-fornix-hippocampal commissure transectio n procedures induced the calretinin expression in some of these dorsal GluR 2/3 immunoreactive cells. On the basis of these observations, we concluded that the vast majority of intensely GluR2/3 immunoreactive large cells in t he mouse dorsal hilus were mossy. cells. Then we evaluated the presumed dif ference in the distribution of mossy cells along the dorsoventral axis by t he disector. The numerical density of mossy cells was about 1.4 times large r at the ventral level than at the dorsal level, indicating that the dorsov entral difference in the distribution of mossy cells in the mouse hilus was far smaller than that previously speculated. (C) 1999 Elsevier Science B.V . All rights reserved.