Morphological and immunohistochemical comparison of the pituitary gland between a tropical Paracheirodon axelrodi and a subtropical Aphyocharax anisitsi characids (Characiformes: Characidae)

Abstract

Cardinal tetra Paracheirodon axelrodi and bloodfin tetra Aphyocharax anisitsi are two species of characids with high trade value as ornamental fish in South America. Although both species inhabit middle water layers, cardinal neon exhibits a tropical distribution and bloodfin tetra a subtropical one. Generally, these species are difficult to grow, so it becomes essential to know some key components of the neuroendocrine system to achieve their reproduction in captivity. Considering the importance of deepening the knowledge of the reproductive physiology through functional morphology, for the first time in this work we performed an anatomical, morphological and immunohistochemical analysis of the pituitary gland of these two species. In both species, a leptobasic type pituitary is found in the ventral zone of the hypothalamus and it is characterized by a neurohypophysis which has a well-developed pituitary stalk and a globular adenohypophysis. The pituitary components, characterized by histochemistry and immunohistochemistry, shows a distribution pattern of cells types similar to other teleost species, with only slight differences in the distribution of βFSH and βLH for P. axelrodi.

3D atlas of the pituitary gland of the model fish medaka

“…We also found cells coexpressing fshb-tshba and sl-lhb. Although previous immunohistochemtry studies on the pituitary of several teleost species showed cross-reaction between Tsh and Lh/Fsh (43,53) and between Lh and Sl antibodies (16,53,74,75), we show specific labeling of tshb, fshb, lhb, and sl in the current study confirming the specificity of the probes. Therefore, the observation of colocalization of fshb-tshba and sl-lhb supports that these bi-hormonal cells exist in the medaka pituitary.…”

“…However, these cells were found only in some fish and not always at the same location, which makes them difficult to map. We found Lh gonadotropes in the PI, in addition to in the PPD, but only in adults, and we did not observe Lh cells in RPD as reported by some studies (16,17,(46)(47)(48). The extra-PPD localization of Lh gonadotropes might be due to PPD extension (20) or Lh cell migration to other zones during the ontogeny of the adenohypophysis (49).…”

“…The extra-PPD localization of Lh gonadotropes might be due to PPD extension (20) or Lh cell migration to other zones during the ontogeny of the adenohypophysis (49). Meanwhile, several studies reported somatotropes in the RPD (45,50) and PI (51,52), and somatolactotropes and melanotropes in the PPD (13,(16)(17)(18)51). However, we did not observe this in medaka.…”

“…However, we did not observe this in medaka. The wide localization of Gh, Sl, and α-Msh cells in these studies might also be explained by antigenic similarities as suggested in (13,16,53).…”

“…However, our scRNA-seq data exhibit only a few cells co-expressing prl and gh. While antigenic similarities could be the reason of costaining between these cell types (13,16,53), their low occurrence in the medaka pituitary might be the reason of being unable to observe them with FISH.…”