Ontogeny of the endocrine pancreatic cells of the gilthead sea bream, Sparus aurata (Teleost)

Histopathological effects of long-term exposure to realistic concentrations of cadmium in the hepatopancreas of Sparus aurata juveniles

In recent decades, cadmium has emerged as an environmental stressor in aquatic ecosystems due to its persistence and toxicity. It can enter water bodies from various natural and anthropogenic sources and, once introduced into aquatic systems, can accumulate in sediments and biota, leading to bioaccumulation and biomagnification in the food chain. For this reason, the effects of cadmium on aquatic life remain an area of ongoing research and concern. In this paper, a multidisciplinary approach was used to assess the effects of long-term exposure to an environmental concentration on the hepatopancreas of farmed juveniles of sea bream, Sparus aurata. After determining metal uptake, metallothionein production was assessed to gain insight into the organism's defence response. The effects were also assessed by histological and ultrastructural analyses. The results indicate that cadmium accumulates in the hepatopancreas at significant concentrations, inducing structural and functional damage. Despite the parallel increase in metallothioneins, fibrosis, alterations in carbohydrate distribution and endocrine disruption were also observed. These effects would decrease animal fitness although it did not translate into high mortality or reduced growth. This could depend on the fact that the animals were farmed, protected from the pressure deriving from having to search for food or escape from predators. Not to be underestimated is the return to humans, as this species is edible. Understanding the behaviour of cadmium in aquatic systems, its effects at different trophic levels and the potential risks to human health from the consumption of contaminated seafood would therefore be essential for informed environmental management and policy decisions.

Immunohistochemical study of the principal pancreatic islet of the toadfish, Halobatrachus didactylus (Pisces: Batrachoididae)

The endocrine pancreas of the toadfish, Halobatrachus didactylus, consists of one large circular principal islet (Brockman body) located in the dorsal side or neck region of the gallbladder, along with various accessory islets of variable sizes and shapes, embedded in the exocrine tissue located within the digestive organs connecting mesenteries. Islet cells showed variable shapes, angular or fusiform, with long cytoplasmic processes, granular cytoplasm, and a large eccentric nucleus. Cells were found scattered or as aggregates or cords. Four primary endocrine cell types immunoreactive for glucagon (α cells), insulin (β cells), somatostatin (δ cells), and pancreatic polypeptide (F cells) were identified within the toadfish principal islet. The α, δ, and F cells were located both at the periphery and in the central regions, while β cells, which were the predominant type, were present only in the central core. α and δ cells were found in moderate frequencies, while F cells were the least abundant. Macroscopically, the Brockman body of H. didactylus is visible as a milky white nodule separated from the exocrine tissue. Its size, location, and ease of extraction suggest that H. didactylus is suitable as experimental subject for biochemical, immunological, and physiological studies of the endocrine pancreas including in vitro investigations of hormone production, storage, and release.

The comparative anatomy of islets

In the past 20 years, numerous publications on a variety of mammalian and non-mammalian species have appeared in the literature to supplement the excellent comparative work performed in the 70s and 80s by the Falkmer, Epple, and Youson groups. What emerges is that islets are much more complex than once thought and show a lot of similarities in rodents and higher primates. The diversity of lifestyles, metabolic demands, and diets has most likely influenced the great diversity in both structure and cell-type content of islets in lower vertebrate species. In this chapter, I try to provide an overview of the evolution from endocrine cell types in invertebrates to the higher mammals and focus on what has been reported in the literature and some of our own experiences and also include a description of other hormones reported to be found in islets.