Distribution of calcium-binding proteins parvalbumin and calbindin in the thalamic auditory center in pigeons

Distribution of calcium-binding proteins (CaBPr) parvalbumin (PV) and calbindin (CB) in the thalamic auditory center (nucleus ovoidalis, Ov) was studied in the pigeon (Columba livia). Two parts of Ov were distinguished on the basis of their cytoarchitectonics and distribution of PV and CB immunoreactivity. The central lemniscal region (core, nCe) contains both dense PV-ir neuropil and PV-ir neurons overlapped with scant CB-ir neuropil and weaker stained CB-ir neurons. The peripheral extralemniscal region (belt), consisting of peri/paraovoidal nuclei (Ovl, Ovm, SPO), contains only CB-ir neuropil and strongly stained CB-ir neurons morphologically differing from CB-ir neurons in the nCe. A comparative analysis of our data on the distribution of PV and CB immunoreactivity in the thalamic auditory relay center in pigeons and related literature data obtained on other avian, reptilian and mammalian species indicates high evolutionary conservatism of its extralemniscal region across all sauropside amniotеs and mammals in contrast to plasticity of its central lemniscal region due to adaptive, ecologically dependent transformations during the evolution.