Calcium binding protein immunoreactivity in nucleus rotundus in a reptile,Caiman crocodilus

Nucleus rotundus is a prominent nucleus in the dorsal thalamus of nonmammal ian amniotes. In one group of reptiles, Caiman crocodilus, previous studies have identified three parts of this neuronal aggregate, The central portio n, the rotundal core, which receives visual input from the midbrain and pro jects to a restricted portion of the telencephalon, contains relay cells on ly. Previous examinations using Nissl morphology indicated that neurons of the rotundal core were not a homogeneous population of cells. The present i nvestigation utilized another methodology to examine cell populations withi n the rotundal core, immunoreactivity to the calcium binding proteins, calb indin/calretinin and parvalbumin. Light microscopic observations revealed t he following features. First, calbindin/calretinin immunoreactive neurons a nd parvalbumin immunoreactive neurons were present in the rotundal core. Of these two antibodies, immunoreactivity to calbindin/calretinin was much mo re robust and calbindin/calretinin immunoreactive neurons were more numero us than parvalbumin cells. Second, neurons immunoreactive to either calbind in/calretinin or parvalbumin were not homogeneous but comprised several pop ulations based on perikaryal shape and size and neuronal process morphology . These results are compared with similar data in other amniotes.