Action de la r�serpine chez l'anguille

Quantitative changes of CRF-like immunoreactivity in eels treated with reserpine and cortisol

Immunocytochemical techniques were applied to brain and pituitary sections of European eels after experimental manipulation of the pituitary-interrenal activity. A corticotropin-releasing factor (CRF) antiserum allowed the identification of a CRF-like peptide in the preoptic nucleus (PON) and rostral and caudal neurohypophysis (NH). CRF-immunoreactivity (ir) was not affected in solvent-injected eels compared to noninjected eels. Reserpine induced a stimulation of the pituitary interrenal axis, decreased ir-CRF in the rostral NH, but did not affect hypothalamic ir-CRF. Cortisol reduced the immunostaining of hypothalamic CRF-ir perikarya and perikarya cross-sectional area. In the rostral NH, CRF-ir fibers decreased in number and almost disappeared in long-term treated eels. The immunostaining of ACTH cells with ACTH antiserum was greatly reduced. These data suggest that cortisol induces a marked reduction in the activity of the CRF-corticotrop axis. The intensity of the ir-CRF staining observed in the caudal NH, close to the intermediate lobe (IL) was not significantly affected in reserpine-treated eels, and only slightly reduced in long-term cortisol-treated eels. The intensity of ir-CRF staining in the caudal NH did not correlate with melanocorticotropic activity or plasma cortisol level. These data suggest that immunoreactive CRF fibers in the rostral and caudal NH are differently regulated.

In vivo effect of dopamine antagonists on melanocyte-stimulating hormone cells of the goldfish (Carassius auratus L.) pituitary

Young goldfish were injected with three dopaminergic antagonists, pimozide, sulpiride, and domperidone, for 5 (low dose) and 7 days (higher dose). Cytological and immunocytochemical techniques using anti-alpha-melanocyte-stimulating hormone (MSH) serum were applied to the pituitary. MSH cells in the three treated groups showed a decrease in immunoreactive cytoplasmic granules, a significant nuclear hypertrophy, and, after 7 days, a cellular enlargement. The nucleolus and the lamellar endoplasmic reticulum were more developed and some mitotic figures occurred. Erythrophores and occasional melanophores were in a stage of maximal dispersion. These changes were not apparent in the solvent-injected controls. The responses to the three blockers of dopaminergic receptors were similar. These data suggest that MSH release seems to be under a dopaminergic inhibitory control in the goldfish. The other cell type of the pars intermedia (PAS-positive and calcium-sensitive in the goldfish) was not clearly affected by the three drugs.

Effects of reserpine administration on the fine structure of the rat pars intermedia

Hormone release from the pars intermedia is under inhibitory control of the hypothalamus. Control may be mediated via dopaminergic fibers which directly contact secretory cells. Administration of reserpine in vivo to adult male rats for four consecutive days results in major alternations in pars intermedia cytology. Cells show expanded areas and whorls of rough endoplasmic reticulum, as well as extensive Golgi zones with numerous dense granules. Some nerve fibers exhibit alterations in vesicle content, while others retain a more normal appearance. Freeze-fracture of glands from reserpine-treated animals provides evidence for exocytosis of granules, although such phenomena are not observed in thin sections. The ultrastructural findings suggest that reserpine alters the content of local inhibitory neurotransmitters in the pars intermedia, leading to unrestrained hormone release, followed by renewed granule synthesis.

Effect of pimozide on the cytology of the eel pituitary. II. MSH-secreting cells

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 or 9 days in freshwater (FW) eels or eels acclimated to sea water (SW) for 10 or 30 days. The daily dose was 100 or 200 microgram/100 g. Melanophore index values increase in FW and in 1 month-SW injected eels. All the treated fish react by a total or subtotal degranulation of the lead-hematoxylin positive cells in the pars intermedia. These cells were previously identified as alpha-MSH-secreting cells. The MSH cell nuclear area is significantly increased, nucleoli are larger and the endoplasmic reticulum more developed. The intensity of the response is similar in FW and SW eels, but it does not increase with the higher dose. The rapid release of pituitary alpha-MSH is also visualized by immunofluorescence and immunoenzymologic techniques. No effect on the second cell type of the pars intermedia (PAS-positive cell) is detected. The amount of neurosecretory material is often reduced in the neurohypophysis. These results suggest that the hypothalamic inhibitory control of MSH release and synthesis is mediated through dopaminergic fibers in the eel, but other factors cannot be ignored in this regulation.