Differentiation of Steroidogenic Cells in the Developing Adrenal Gland of Testudo hermanni Gmelin, 1789 (Chelonian Reptiles)

The aim of this study was to investigate the development and differentiation of steroidogenic cells in the embryonic adrenal gland of Testudo hermanni using histological, histochemical, immunohistochemical and ultrastructural methods. The 26 developmental stages were divided into three periods: early (stages 1-18, up to 20days of incubation), intermediate (stages 19-22, incubation days 21-35) and advanced (stages 23-26, from incubation day 36 to hatching). A small presumptive bud of steroidogenic cells was visible at the end of the early period, protruding into the coelom from the lateral wall of intermediate mesoderm. Ultrastructural characteristics suggested that young and scarcely differentiated cells could already be able to perform steroidogenic activity: lipid droplets, large amount of SER and RER, small rounded mitochondria with variously shaped cristae and dense matrix. The cell membrane showed microvilli and coated pits. During the intermediate period, the interrenal bud deepened into the haemopoietic tissue, close to the mesonephros and the newly formed metanephros. The ultrastructural, immunohistochemical and immunocytochemical characteristics pointed to enhanced steroidogenic activity. The contact with both kidney types (mesonephros and metanephros) continued in the advanced period, and chromaffin cells were also extensively mixed with steroidogenic cells. This is a peculiar feature of chelonian adrenal gland, in comparison with that of other reptiles. The variable cytological characteristics of embryonic steroidogenic cells in the advanced period suggest a four-phase cycle of steroidogenic activity

Development and evolution of the adrenal gland and its homologs in teleosts, anurans, chelonians and birds

The morphology, histology, histochemistry and immunohistochemistry of the adrenal gland or its homolog were examined during development and in the adults of species belonging to the teleost fishes, anuran amphibians, chelonian reptiles and birds (chicken). The first objective was to clarify the ontogenetic origin of the anatomical differences observed among the adrenal glands of vertebrates. A second objective was to investigate the anatomical relationships of the gland with the renal system, which plays an important role during development. In the course of vertebrate evolution the adrenal gland emerges from the renal parenchyma and becomes more concentrated. Three main points may be stressed concerning this evolutionary process: 1- During ontogenesis, the kidneys show different patterns for controlling water loss and excreting waste through embryonic and adult life: pronephros, mesonephros and metanephros, which develop from intermediate mesoderm following a precise temporal and spatial sequence, each kidney being formed as a result of an inductive interaction with the previous form. 2- In teleosts the ontogenetic origin of the adrenocortical cells has been found in the mesoderm on the surface of the pronephros; later these cells become internal to the head kidney and make contact with the chromaffin cells deriving from the neural crests. The latter may also spread inside the kidney. In tetrapods, on the contrary, the peritoneal mesoderm gives rise to steroidogenic tissue at a more caudal level with respect to the pronephros, and chromaffin cells reach this area. The adrenal gland always retains the original position external to the mesonephric or metanephric kidney. 3- The anatomy of the adrenal gland varies independently of the renal system evolution. Teleosts and amphibians have a definitive mesonephric kidney, while they display different adrenal structural patterns. Conversely, amphibians and chelonians share the same type of gland, which is scattered over the ventral renal surface, although they do have, respectively, definitive mesonephric and metanephric kidneys. In the other reptiles, in birds and in mammals, the adrenal gland constitutes a discrete organ with little or no contact with the metanephric kidney. Structural differences among the adrenal glands can be explained by developmental modifications of the site of origin of the steroidogenic cells, the possible differentiation of connective tissue cells isolating the developing adrenal gland from the kidney and the length of the glandular blastema. Chromaffin cells migrating from neural crests also play a role in the final configuration pattern of the gland. Possible evolutionary advantages of the various structural adrenal types are suggested

The fine structure of Hamann\u27s organ in \u3cem\u3eLeptodirus hohenwarti\u3c/em\u3e, a highly specialized cave Bathysciinae (Coleoptera, Catopidae)

Hamann’s organ in Leptodirus hohenwarti a highly specialized cave Bathysciinae, has been studied under the TEM, SEM and light microscope. This receptor organ located in the 7th, 9th and 10th antennal articles and previously referred to as the “vesicule olfactive” and as the “antennal organ” or “antennal vesicle”, reaches its highest degree of structural complexity in leptodirus. This paper attempts to establish some degree of synonymy among the terms used by earlier authors in describing the various antennal parts and sensilla. Five types of sensilla to be found in the organ are described, namely cribrose-stick sensilla, cribrose-utricular sensilla, star-shaped sensilla, claviform sensilla and branching setae. Comparisons within Bathysciinae species and among the latter and other subfamilies of Catopidae reveal differences in the number of vesicles and in the number and structures of sensilla, these differences appear to depend on i) the degree of phylogenetic relationships among taxa and 2) the degree of specialization to cave environment. The considerable complexity of Hamann’s organ, unrivalled by other insects organs, apart from light receptors, suggests that it has a plurality of functions. Its hygroreceptor role, supported by recent experimental work, is discussed here