Parvalbumin-immunoreactive cells in the superior colliculus in dog: Distribution, colocalization with GABA, and effect of monocular enucleation

Parvalbumin (PV) is thought to play a major role in buffering intracellular calcium. We studied the distribution, morphology of PV-immunoreactive (IR) cells, and the effect of enucleation on the PV distribution in the superior colliculus (SC) in dog (Canis familiaris) and compared PV labeling to that of calbindin D28K (CB) and GABA. These cells formed three laminar tiers in the dog SC; 1) the upper superficial gray layer (SGL), 2) the lower optic layer (OL) and the upper intermediate gray layer, and 3) the deep layer. The third tier was not very distinct when compared with the other two tiers. The distribution of PV-IR cells is thus complementary to that of CB-IR tiers. Our present data on the distribution of PV-IR cells within the superficial layers are strikingly different from those in previously studied mammals, which show PV-IR cells within the lower SGL and upper OL. However, there were no distinct differences in distribution within the deep layers compared with that of previously studied mammals. PV-IR cells in the SC varied dramatically in morphology and size, and included round/oval, vertical fusiform, stellate, horizontal and pyriform cells. Two-color immunofluorescence revealed quantitatively that 11.67% of the PV-IR cells colocalized with GABA. Monocular enucleation appeared to have no effect on the distribution of PV-IR cells in the contralateral SC. Similar to CB, these data suggest that retinal projection may not control the expression of PV in the dog SC. These results provide important information for delineating similarities and differences in the neurochemical architecture of the visual system.