Chronological study of the appearance of adenohypophysial cells in the ayu ( Plecoglossus altivelis )

Abstract

We previously reported the chronological appearance of adenohypophysial cells in freshwater teleosts using an immunocytochemical technique. The present study investigated the chronological appearance of adenohypophysial cells in the ayu, which is spawned and has its early development in brackish water, and the results were compared with those obtained in freshwater and seawater teleosts, as well as in other vertebrates. In the adult teleostean adenohypophysis, seven or eight types of secretory cells have been distinguished, each of which produce different hormones: prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), gonadotropic hormones (GTH I and GTH II), adrenocorticotropic hormone (ACTH), melanophore stimulating hormone (MSH) and somatolactin (SL). In the pituitary of adult ayu, seven distinct types of glandular cells (PRL, GH, TSH, GTH, ACTH, MSH and SL cells) were identified. Chronologically, a few immunoreactive (ir)-PRL and ir-GH cells appeared in the ventral side of the pituitary one day before hatching. Then, just after hatching, ir-GTH cells were observed in the central to dorsal portion; ir-ACTH cells were found distributed in the anterior portion and some ir-MSH and a few ir-SL cells were seen in the posterior portion of the pituitary. Finally, a small number of ir-TSH cells were identified 50 days after hatching. These results differed from those obtained in other fishes previously reported with regard to the times of appearance of the PRL and GH cells. PRL cells appeared first, followed by GH cells in the freshwater teleosts, PRL and GH cells appeared at the same time in the brackishwater teleosts, while GH cells appeared first and PRL cells appeared last in the seawater teleosts. These results reflect the fact that PRL plays a major role in osmoregulation among freshwater teleosts, as compared with GH, which plays a similar role in seawater teleosts. It seems that both PRL and GH may play important roles in osmoregulation in brackishwater fish.

Developmental tracing of luteinizing hormone β‐subunit gene expression using green fluorescent protein transgenic medaka (Oryzias latipes) reveals a putative novel developmental function

“…Thus, LH gonadotropes could require hypothalamic inputs for final gonadotrope activation similar to in sheep (Brooks et al, 1992;Szarek et al, 2008) and rat (Aubert et al, 1985) gonadotrope maturation. This is further supported by the observation that gonadotropin expression starts later than other anterior pituitary hormones in multiple fish and mammal species (Asa et al, 1988;Saga et al, 1993Saga et al, , 1999Japon et al, 1994;Laiz-Carrion et al, 2003). However, zebrafish, one of the species with the best characterized adenohypophysis development, provides partially conflicting results.…”

“…Gonadotropes and thyrotropes are present in the developing adenohypophysis anlage of zebrafish by 32 hours post fertilization (hpf) as determined by gpa gene expression (Nica et al, 2006); however, fshb is first detected later at 4 days postfertilization (dpf) and lhb is not detected until around 25 dpf by in situ hybridization (ISH; Chen and Ge, 2012). The ontogeny of pituitary cell types has also been followed in rainbow trout (Saga et al, 1993), American shad (Laiz-Carrion et al, 2003), and Ayu (Saga et al, 1999) by immunohistochemistry.…”

Thyroid and pituitary gland development from hatching through metamorphosis of a teleost flatfish, the Atlantic halibut

“…Despite their differing larval ontogeny, endocrine cells have been reported to first arise in the post-hatch larvae of sea bass, coho salmon (Oncorhynchus kisutch), chum salmon, sea bream, ayu and Japanese eel (Cambre et al 1990;Power and Canario 1992;Naito et al 1993;Saga et al 1999). In a study carried out on several marine species, somatotrophs and lactotrophs have been detected shortly before the end of yolk sack absorption, in species with small pelagic eggs and at hatching, in species with larger demersal eggs and/or ovoviviparous species (Tanaka et al 1995).…”

“…Studies on the ontogeny of thyrotrophs in teleost fish are scarce, but indicate that the first appearance of thyrotrophs varies considerably among the teleost species. Thyrotrophs are detected before hatching in salmonids (Naito et al 1993;Saga et al 1993), at hatching in sea bream (Sparus aurata) (Ayala et al 2003), and shortly after hatching in Japanese flounder and sea bass (Dicentrarchus labrax) (Miwa and Inui 1987b;Cambre et al 1990) whereas, in the ayu (Plecoglossus altivelis), thyrotrophs appear as late as 50 days after hatching (Saga et al 1999). Unexpectedly, in Japanese eel (Anguilla japonica), Anguilla obscura and Anguilla bicolor TSH immunoreactive cells are first seen just prior to the onset of metamorphosis, the transition from leptocephalus to glass eel, while active T 4 producing cells are earlier observed in the leptocephalus stage.…”

“…However, in many fish species, somatotrophs, lactotrophs and somatolactotrophs are confined to the same structural area of the pituitary. Accordingly, in striped bass (Morone saxatilis), African catfish (Clarias gariepinus), European eel (A. anguilla), sea bream, sea bass, chum salmon, rainbow trout, ayu, American shad (Alosa sapidissima) and the cichlid fish (Cichlasoma dimerus), somatotrophs are localized in the PPD and lactotrophs in the RPD (Cambre et al 1990;Power and Canario 1992;Naito et al 1993;Saga et al 1993Saga et al , 1999Huang and Specker 1994;Volckaert et al 1999;Pandolfi et al 2001;Grandi et al 2003;Laiz-Carrion et al 2003), and in sea bream, European eel, ayu and American shad, somatolactotrophs are located in the PI (Villaplana et al 1997;Saga et al 1999;Grandi et al 2003;Laiz-Carrion et al 2003). The spatial distribution of immunoreactive endocrine cells in a chondrostean species (Acipenser naccarii) follows the same pattern as in teleost fishes, indicating a similar course of development (Grandi and Chicca 2004).…”