Neuroepithelial bodies in the lung of Basiliscus vittatus (Reptilia, Iguanidae).

Abstract

Neuro-epithelial bodies (NEB) are corpuscles of currently equivocal function which are present in the lungs of vertebrates. Comparative studies may help to elucidate their role. The NEB of Basiliscus vittatus (Reptilia, Iguanidae), a terrestrial lower vertebrate able to dive, are for the first time examined by electron microscopy, immunocytochemistry, and for argyrophilia. Most NEB contain both immunoreactive calcitonin and serotonin but are not labelled with argyrophilia or immunocytochemistry against calcitonin gene-related peptide (CGRP), protein gene product 9.5 (PGP 9.5), or the Leu-7 epitope (Leu-7). Therefore, in NEB of this species, the transcription of the calcitonin/CGRP gene exclusively favors the expression of calcitonin and this is in contrast to the intrapulmonary small neurons. Also, a physiologic difference is expected in the metabolism of ubiquitin in NEB of B. vittatus vs. mammalian NEB and neurons. In addition, the NEB cells are always covered by at least a thin cytoplasmic extension of a neighbouring cell, indicating that luminal contact is not required. Stronger still, it appears that in some lower vertebrates contact to the airspace is avoided. Finally, we provide ultrastructural evidence for the basket-like innervation of NEB in some reptiles. This way of innervation possibly represents an evolutionarily different concept for interaction between NEB corpuscular cells and nerve fibers. Beyond the confirmation that morphology, content of biologically active substances such as serotonin and calcitonin, and innervation are evolutionary well preserved features of NEB, the results reveal some intriguing features of B. vittatus NEB: strict separation of calcitonin and CGRP, reduced need for the de-ubiquitinating enzyme PGP 9.5, lack of luminal contact, and the basket-like innervation. The latter two properties possibly refer to a mechanoreceptor function of NEB in this species.