Opioids and testicular activity in the frog, Rana esculenta

ABSTRACT The presence and activity of brain, pituitary and testicular β-endorphin (β-EP)-like material have been studied in the frog, Rana esculenta, using reverse-phase high-pressure liquid chromatography, coupled with radioimmunoassay and immunocytochemistry. In-vivo and in-vitro treatments with naltrexone were carried out to assess the putative physiological activity of opioid peptides. β(1–31) and (1–27), together with their acetylated forms, have been identified in brain, pituitary and testis. In particular, β-EP(1–31) concentrations peaked during July in the brain and pituitary, whilst in testes maximum concentrations were found in April and November. β-EP immunoreactivity was present in the brain within the nucleus preopticus and nucleus infundibularis ventralis while positive fibres in the retrochiasmatic regions projected to the median eminence. In the testis, interstitial cells, canaliculi of the efferent system, spermatogonia and spermatocytes showed positive immunostaining for β-EP. In intact animals, naltrexone treatment increased plasma and testicular androgen levels and this effect was confirmed in in-vitro incubations of minced testes. Naltrexone also induced a significant increase in germ cell degeneration. Our results indicated that an opioid system modulates the hypothalamus-pituitary-gonadal axis in the frog, Rana esculenta and, for the first time, we have shown that the testicular activity of a non-mammalian species may be regulated by opiates locally. Journal of Endocrinology (1993) 137, 49–57

The pituitary adrenocorticotropes originate from neural ridge tissue in Xenopus laevis

A series of grafting experiments was conducted to determine pituitary origins prior to brain tube closure in Xenopus laevis. Extirpation experiments indicated that the ventral neural ridge (VNR) tissue of stage-18+ embryos was essential for pituitary development. Bolton–Hunter reagent was used to label stage-18+ VNR tissue with 125I, and this tissue was then returned to the donor and its subsequent ontogenesis followed. Labelled tissue was ultimately found in the ventral hypothalamus, the ventral retina, and the anterior pituitary. Using immunocytochemical techniques with antisera to adrenocorticotropin (ACTH), it was found that some of the VNR-derived cells were corticotropes. A region of the nucleus infundibularis which was radioactive labelled also gave ACTH-positive immunoreaction. This might indicate that some ACTH containing neurones of the hypothalamus are VNR in origin. We suggest that stage-18+ VNR is the site of attachment of brain and anterior pituitary ectoderm. Part of this adherence point is eventually incorporated into the anterior pituitary and will form corticotropes. It is concluded that the ventral retina, the preoptic region of the hypothalamus, some hypothalamic ACTH-immunoreactive cells, and the most anterior portion of the adenohypophysis are all ventral neural ridge in origin.