RESUMO
The saccus vasculosus is an organ present in gnathostome fishes, located ventral to the hypothalamus and posterior to the pituitary gland, whose structure is highly variable among species. In some fishes, this organ is well-developed; however, its physiological function is still under debate. Recently, it has been proposed that this organ is a seasonal regulator of reproduction. In the present work, we examined the histology, ultrastructure, and development of the saccus vasculosus in Cichlasoma dimerus. In addition, immunohistochemical studies of proteins related to reproductive function were performed. Finally, the potential response of this organ to different photoperiods was explored. C. dimerus presented a well-developed saccus vasculosus consisting of a highly folded epithelium, composed of coronet and supporting cells, closely associated with blood vessels, and a highly branched lumen connected to the third ventricle. Coronet cells showed all the major characteristics described in other fish species. In addition, some of the vesicles of the globules were positive for thyrotropin beta subunit, while luteinizing hormone beta subunit immunostaining was observed at the edge of the apical processes of some coronet cells. Furthermore, neuropeptide Y and gonadotropin inhibitory hormone innervation in the saccus vasculosus of C. dimerus were shown. Finally, animals exposed to the long photoperiod showed lower levels of thyrotropin beta and common alpha subunits expression in the saccus compared to those of animals exposed to short photoperiod. All these results support the hypothesis that the saccus vasculosus is involved in the regulation of reproductive function in fish.
RESUMO
Abstract Introduction: The digestive tract of Neotropical cichlids has not been deeply studied, and it is a fundamental topic for understanding fish physiology, nutrition, trophic associations, and evolution. Objective: To describe anatomically and histologically the digestive tract of the Neotropical cichlid fish Cichlasoma dimerus and to immunolocalize the orexigenic peptide (Npy) along the intestine. Methods: We euthanized 14 adult individuals and fixed the organs in Bouin´s solution; we stained 7 μm thick paraffin sections for general description and with Alcian Blue (pH = 2.5, AB) and Periodic acid-Schiff (PAS) to identify acid or neutral glycoconjugates, respectively. Additionally, we performed immunohistochemistry for Npy in 3 adult individuals. We manually counted PAS- and AB-positive cells, and Npy-immunoreactive cells per fold. Results: There is a short oesophagus, a sac-like stomach, and a tubular intestine with two loops. The oesophagus has a stratified epithelium with a high density of PAS- and AB-positive goblet cells and striated muscle fibers in the tunica muscularis. The stomach mucosa is formed by simple columnar epithelium. The intestine has a simple columnar epithelium, with brush border and interspersed PAS- and AB-positive goblet cells, and Npy-immunoreactive cells. There is an ileorectal valve in the transition between the posterior intestine and the rectum. This last gut portion has goblet cells and a thicker tunica muscularis. Conclusions: C. dimerus shares features with other Neotropical cichlids, but the goblet cells and gastric glands distribution seems to be unique for the species. To our understanding, this is the first work to describe Npy-immunoreactive cells distribution in the intestine of a Neotropical cichlid fish.
Resumen Introducción: El tracto digestivo de los cíclidos neotropicales no ha sido profundamente estudiado y es un tema fundamental para entender la fisiología, nutrición, asociaciones tróficas y evolución de los peces. Objetivo: Describir anatómica e histológicamente el tracto digestivo del pez cíclido neotropical Cichlasoma dimerus e inmunolocalizar el péptido orexigénico (Npy) a lo largo del intestino. Métodos: Sacrificamos 14 individuos adultos y fijamos los órganos en solución de Bouin; teñimos secciones de parafina de 7 μm de espesor para una descripción general y con azul alcián (pH = 2.5, AB) y ácido periódico-Schiff (PAS) para identificar glicoconjugados ácidos o neutros, respectivamente. Además, en 3 individuos adultos se realizaron inmunohistoquímicas contra Npy. Contamos manualmente las células PAS y AB positivas, y las células inmunorreactivas a Npy por pliegue. Resultados: Hay un esófago corto, un estómago en forma de saco y un intestino con dos vueltas. El esófago tiene un epitelio estratificado con una alta densidad de células caliciformes PAS- y AB- positivas y fibras esqueléticas estriadas en las capas musculares. La mucosa del estómago está revestida por epitelio simple cilíndrico. El epitelio intestinal es simple cilíndrico con chapa estriada y células caliciformes PAS- y AB- positivas intercaladas, y células inmunorreactivas a Npy. Hay una válvula ileorrectal en la transición entre el intestino posterior y el recto. Esta última porción intestinal tiene células caliciformes y una túnica muscular más gruesa. Conclusiones: C. dimerus comparte características con otros cíclidos neotropicales, pero la distribución de las células caliciformes y las glándulas gástricas, serían rasgos propios de esta especie. A nuestro entender, este es el primer trabajo que describe la distribución de células inmunorreactivas a Npy en el intestino de un pez cíclido neotropical.
Assuntos
Animais , Ciclídeos/anatomia & histologia , Trato Gastrointestinal , PeixesRESUMO
Morphological background adaptation is both an endocrine and a nervous response, involving changes in the amount of chromatophores and pigment concentration. However, whether this adaptation takes place at early developmental stages is largely unknown. Somatolactin (Sl) is a pituitary hormone present in fish, which has been associated to skin pigmentation. Moreover, growth hormone receptor type 1 (Ghr1) has been suggested to be the Sl receptor and was associated with background adaptation in adults. In this context, the aim of this work was to evaluate the ontogeny of morphological adaptation to background and the participation of ghr1 in this process. We found in larval stages of the cichlid Cichlasoma dimerus that the number of head melanophores and pituitary cells immunoreactive to Sl was increased in individuals reared with black backgrounds compared with that in fish grown in white tanks. In larval stages of the medaka Oryzias latipes, a similar response was observed, which was altered by ghr1 biallelic mutations using CRISPR/Cas9. Interestingly, melanophore and leucophore numbers were highly associated. Furthermore, we found that somatic growth was reduced in ghr1 biallelic mutant O. latipes, establishing the dual function of this growth hormone receptor. Taken together, these results show that morphological background adaptation is present at early stages during development and that is dependent upon ghr1 during this period.
