Localization of Calbindin-D28k and Calretinin in the Brain of Dermophis Mexicanus (Amphibia: Gymnophiona) and Its Bearing on the Interpretation of Newly Recognized Neuroanatomical Regions

The analysis of the distribution of the calbindin-D28k and calretinin immunoreactive (CBir and CRir) systems recently described in the brain of anuran and urodele amphibians was very useful for the interpretation of many otherwise indistinct brain regions and cell masses. In the present study we have followed a similar approach to investigate the distribution of CBir and CRir cell bodies and fibers in the brain of Dermophis mexicanus, a member of the much neglected third amphibian order of gymnophionans. The pattern of distribution obtained showed particular characteristics in Dermophis, such as the existence of abundant CRir elements in the olfactory bulbs and CBir and CRir cell populations in pallial areas. The distinct distribution of the two proteins allowed the tentative identification of currently described subregions, mainly in the amygdaloid complex and hypothalamic areas. The analysis of the diencephalon and brainstem distribution framed in the neuromeric model highlighted common traits with other amphibians but also specific features. Therefore, the immunohistochemical detection of calcium-binding proteins has served to discern cell populations and has helped to demonstrate neuronal heterogeneity. However, it should be pointed out that a straightforward comparison based only on the presence of these proteins should not be made due to the great variability observed in well-established homologous regions in the brain of different vertebrates, as evidenced within the class Amphibia.