Effect of pimozide on the cytology of the eel pituitary. I. Prolactin-secreting cells

Immunocytochemical studies on the pituitary gland of Anguilla anguilla L., in relation to early growth stages and diet-induced sex differentiation

Mammalian and teleost antisera against pituitary hormones were used to identify and localize pituitary cell types in the European eel (Anguilla anguilla L.). The investigation was conducted on unpigmented glass eels of 5.6-6.2 of total body length (L(T)) caught in river mouths, then on yellow eels reared from the pigmented glass eel (or elver) stage up to 12-14 cm of L(T), in an eel farm in warm freshwater. Treated elvers were fed with commercial paste food supplemented with mature carp ovaries, containing oestradiol, that induced an early ovarian differentiation and a higher growth rate. The antisera detected seven types of immunoreactive (ir) cells, six of which were already found in glass eel adenohypophysis, suggesting differentiation of these cell types during the leptocephalus stage. In 12-14 cm treated yellow eels with small ovaries, a seventh type (ir-GtH) was detected in the proximal pars distalis; in the same animals the ir-TSH cells increased in number and size. From unpigmented glass eels to 12-14 cm yellow eels, the whole pituitary volume of controls increased nearly four times, while that of treated ones increased nearly six times. The larger volume of pituitary in treated eels was mainly due to volume increase of proximal pars distalis and rostral pars distalis. The %GH, that is the potential index of GH production, was significantly higher in treated yellow eels with gonads differentiating into ovaries than in controls; no difference was detected in %PRL between treated and control eels. The above results strongly suggest that in eels the feminizing effects of oestrogen is first exerted on the pituitary, probably through the hypothalamus, and later on the gonads.

Differential effects of photoperiod and temperature on hypothalamic monoaminergic activity in the teleost Channa punctatus (Bloch)

In Channa punctatus maintained under ambient photothermal conditions (10.5L:13.5D; 13 ± 2°C) in the postspawning season, hypothalamic dopamine (DA) and norepinephrine (NE) content varied diurnally, but serotonin (5-HT) and monoamine oxidase (MAO) did not. Exposure of the fish to high temperature (25 ± 2°C), with or without altering the photopheriod, increased the NE and DA content, and NE turnover but decreased DA turnover. Increasing the photoperiod (16L:8D) alone had no significant effect on catecholaminergic (CA) content or activity. When the fish were exposed to long photoperiod, with or without altering the temperature, a day-night variation in 5-HT content and activity was induced in the postspawning season. An increase in temperature alone had no significant effect on 5-HT content or activity. Hypothalamic MAO activity was elevated in fish exposed to high temperature alone, or in combination with long photoperiod, but was not affected significantly by long photoperiod treatment. These results indicate that CA activity is influenced largely by ambient high temperature, whereas serotonergic activity is controlled primarily by photoperiod, with high temperature having an additive effect. MAO activity seems to be influenced by both temperature and photoperiod in this species.

Cytological responses of the pituitary (rostral pars distalis) and immunoreactive corticotropin-releasing factor (CRF) in the goldfish treated with dopamine antagonists

The in vivo effects of three dopamine (DA) antagonists on the cytology of the rostral pars distalis (RPD) were investigated in young goldfish (Carassius auratus L.). Pimozide, sulpiride, and domperidone were injected for 5 (low dose, Experiment I) and 7 days (higher dose, Experiment II). Cytological and immunocytochemical techniques using antisera to (1-24) ACTH and (1-39) ACTH, human beta-thyrotropin (TSH beta), and synthetic (1-41) CRF were applied to pituitary and brain sections. Cytometrical studies showed that the three drugs induced similar quantitative changes in the cells of the RPD. Prolactin (PRL)-secreting cell hypertrophy was significant in Experiment II, whereas the nuclear enlargement was significant in both experiments. The numbers of cytoplasmic granules were similar in control and treated goldfish. Thyrotropic (TSH) cells and their nuclei were significantly enlarged in both experiments; their content in immunoreactive TSH was not clearly modified. Corticotropic (ACTH) cells showed significant nuclear and cellular hypertrophy, and labeled granules were often concentrated along the cell membrane. The amount of immunoreactive CRF present in the rostral neurohypophysial ramifications was reduced in the majority of treated fish. Solvent-injected controls showed no significant changes in the RPD. These results suggest that DA inhibits PRL cell activity in goldfish. TSH and ACTH cells appear stimulated by DA-receptor blockers, although differential effects on synthesis and release cannot be evaluated in in vivo experiments. A release of corticotropin-releasing factor may be involved in the ACTH cell stimulation. These data are compared with those obtained in other vertebrates.

Immunohistochemical investigation of the pituitary of the sturgeon (Acipenser baeri, Chondrostei)

An immunohistochemical study of the sturgeon (Acipenser baeri) pituitary was undertaken using antisera directed against hormones from various classes of vertebrates, including the only pituitary hormone available from sturgeon, gonadotrophin. A positive reaction was obtained after application of antisera towards the following hormones 1-24 synthetic ACTH (1-24 ACTH), melanophore stimulating hormone (MSH), ovine prolactin (oPRL), ovine growth hormone (oGH), salmon growth hormone (sGH), carp gonadotrophin (cGTH) and its beta subunit (βcGTH), sturgeon gonadotrophin (aciGTH), carp thyrotrophin (cTSH) and β subunit of the human thyrotrophin (βhTSH). The results demonstrate that, in general, the sturgeon pituitary resembles that of teleosts as regards the distribution of the different cell types: ACTH and PRL cells in the rostral pars distalis, GTH, TSH and GH cells in the proximal pars distalis and MSH and PAS-cells in pars intermedia. In addition to the topographical organization of the sturgeon pituitary, this study provides data on the immunological relationships between sturgeon pituitary hormones and those of other vertebrates.

Responses of MSH and prolactin cells to 5-hydroxytryptophan (5-HTP) in amphibians and teleosts

Injection of 5-hydroxytryptophan (5-HTP), a precursor of serotonin, induces dispersion of melanin in the amphibians, Pleurodeles waltlii (Urodela) and Xenopus laevis (Anura), in the goldfish, Carassius auratus, and in the carp, Cyprinus carpio. It is accompanied by a dispersion of erythrophore pigments. In the pituitaries of Pleurodeles and goldfish, a stimulation of MSH cells, characterized by a significant nuclear hypertrophy, is also observed; in Carassius, MSH cells may become degranulated. Serotonin appears to exert a stimulating effect on MSH release in lower vertebrates. Swimming behavior is disturbed in the goldfish and the carp; gaseous metabolism in the swim-bladder may be affected by injection of 5-HTP, as previously reported in the eel. Prolactin (PRL) cells appear activated, but remain granulated in the treated goldfish. No clear response of PRL cells to injection of 5-HTP can be observed in Pleurodeles. A possible role of serotonin in Pleurodeles submitted to an experimental aeroionization is briefly discussed.

Serotonin and MSH secretion: effect of parachlorophenylalanine on the pituitary cytology of the eel

Parachlorophenylalanine (pCPA), an inhibitor of tryptophan hydroxylase which depletes brain serotonin in higher vertebrates, was injected into freshwater eels. After 4 or 6 injections (200 mg/kg/day) or 10 injections (100 and 140 mg/kg/day), the animals are paler, with a low melanophore index. In the pituitary gland, granules tend to accumulate in the basal part of the MSH cells and in the perinuclear area. Cells appear smaller with a decreased nuclear area (P less than 0.001). In the neurohypophysis, the amount of neurosecretory material is often reduced. Conversely, injections of 5-hydroxytryptophan induce a strong darkening, a result similar to that previously reported in some amphibian species and in one lacertilian species. These data substantiate the hypothesis of a stimulatory influence of 5-hydroxytryptamine on MSH release and possibly its synthesis in the eel and other lower vertebrates.

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.