Cocaine- and amphetamine-regulated transcript peptide and calcium binding proteins immunoreactivity in the superficial layers of the superior colliculus in the guinea pig: Implications for visual sensory processing

The purpose of this study was to investigate the distribution and colocalization of cocaine- and amphetamine-regulated transcript peptide (CART) and three calcium-binding proteins (calbindin, calretinin and parvalbumin) in the superficial layers of the superior colliculus (SCs) in the guinea pig. The CART immunoreactivity was observed exclusively in the solitary fibers and neuropil, which formed various CART-ir tiers, that corresponded partially or entirely to anatomically defined layers of the SCs. The CART-ir structures exhibited a characteristic morphology with bundles of densely intermingled neuronal fibers and terminals. This pattern of CART immunoreactivity in the visually driven SCs strongly indicates that CART peptide as a putative neurotransmitter may play an important role in processing of visual information. Double-labeling immunofluorescence showed that CART did not colocalize with either calcium binding proteins (CaBPs). Immunolabeling for CaBPs revealed the presence of different neuronal populations, which were concentrated in variously pronounced tiers. Contrary to CART, the CaBPs immunoreactivity in perikarya was relatively high and CaBPs containing neurons displayed a variety of sizes and somatodendritic morphologies. Generally, CaBPs patterns in the SCs of the guinea pig differ, to some extent, from those of other rodents. These results prove the importance of studying the neurochemical cytoarchitecture of diverse mammals.