Calretinin expression in hilar mossy cells of the hippocampal dentate gyrus of nonhuman primates and humans

Mossy cells, the major excitatory neurons of the hilus of the dentate gyrus constitutively express calretinin in several rodent species, including mouse and hamster, but not in rats. Several studies suggest that mossy cells of the monkey dentate gyrus are calretinin-positive, but others have reported mossy cells in monkeys to be devoid of detectable calretinin-like immunoreactivity. In the present study, the hilar region was investigated throughout the entire longitudinal extent of the hippocampal dentate gyrus in both Old World and New World monkeys, as well as in humans. In the examined four monkey species, mossy cells were found to be calretinin-positive at the uncal pole and at variable length within the main body of the dentate gyrus but not in the tail part. The associational pathway, formed by axons of mossy cells in the inner dentate molecular layer was calretinin-positive in more caudal sections, suggesting that mossy cell axon terminals may contain calretinin, whereas mossy cell somata may contain calretinin in a concentration too low to be detected by immunocytochemistry. In contrast, human mossy cells appear to be devoid of calretinin immunoreactivity in both their somata and their axon terminals. Taken together, mossy cells of nonhuman primates and humans exhibit different expression pattern for calretinin whereas they show similarities in neurochemical content, such as the cocaine and amphetamine-related transcript peptide. (C) 2008 Wiley-Liss, Inc.