CALBINDIN(D28K)-IMMUNOREACTIVE AND PARVALBUMIN-IMMUNOREACTIVE NEURONSFORM COMPLEMENTARY SUBLAMINAE IN THE RAT SUPERIOR COLLICULUS

By using light microscopic immunocytochemistry and computer analysis, we have mapped the distributions of two calcium-binding proteins (CaBP s), calbindin(D28k) (CB) and parvalbumin (PV), in the rat superior col liculus (SC). The patterns of CaBP expression were complementary. A ba nd of heavily labeled, medium-sized CB-immunoreactive cells (CB-cells) was centered in the optic layer (OL), whereas PV-immunoreactive cells (PV-cells) were found predominantly in the intermediate gray layer (I GL), where they were clustered within patches of PV-labeled fibers. Th e superficial gray layer (SGL) could be divided into two sublaminae. C B-cells were found mostly in the dorsal half of the SGL, whereas PV-ce lls were scattered throughout the ventral SGL and the dorsal OL. Most of the CaBP-immunoreactive cells in the SGL were small bipolar cells w ith vertically oriented dendrites; however, there were also some PV-ce lls with horizontally oriented dendrites. Quantitative analysis of the CaBP distributions reinforced our observations that these cells are d istributed in complementary tiers that are not restricted to the tradi tional laminae. The size and shape of some of these tiers were determi ned from a three-dimensional reconstruction of serial sections. The co mplementarity of the CaBP-immunoreactive tiers was also confirmed by f luorescence microscopy of double-labeled sections, in which few if any double-labeled neurons were observed. Complementary tiers of CB-cells and PV-cells have been observed previously in the SC of the cat. The present results demonstrate them in another species and further sugges t that there are functional sublaminae in the SC that can be distingui shed by CaBP content. (C) 1998 Wiley-Liss, Inc.