Changes in hypothalamic catecholamine levels in relation to season, ovariectomy, and 17 beta-estradiol replacement in the catfish, Clarias batrachus (L.)

Targeted metabolomics revealed the seasonal plasticity of skin color and pigment metabolites in ornamental koi carp

The koi carp is an ornamental fish that was obtained through artificial selection from the common carp (Cyprinus carpio L.). The most economically important traits of koi are their beautiful skin patterns in bright colors. As seasonality is an important factor in the biology and ecology of fish, we thus assumed that seasonal changes are involved in regulating the formation of skin color and patterns of koi carp. The white, red, cyan, and black skin colors from four varieties of scaleless koi carp (Doitsu Shiromuji (W), Doitsu Kohaku (WR), Doitsu Showa Sanke (WRI), and Kumonryu (WI)) were evaluated using the CIELab color space (lightness, redness, and yellowness) in different seasons. Compared to winter, the yellowness of the white color in all koi varieties decreased in summer and autumn. The black skin color areas in WRI and WI koi increased in summer and autumn compared to winter. The yellowness of the red color decreased only in WRI koi, while no changes were observed in WR koi. Targeted metabolomics analysis revealed that the levels of the structural pigment guanine of all koi varieties showed significant seasonal variation. Of seven detected carotenoids, the zeaxanthin and tunaxanthin contents in W, WI, and WRI koi changed with the seasons, while none of the carotenoids in WR koi were altered. Of the seven potential regulatory metabolites, epinephrine, melatonin, and cyclic adenosine monophosphate (cAMP) in all four koi varieties showed the highest levels in winter. A correlation analysis suggested that the seasonal changes in white skin color occurred through the epinephrine-cAMP pathway; melanin-dependent and carotenoid-dependent skin color changes occurred through melatonin in koi carp. This study demonstrated the seasonal plasticity of skin color in koi carp regulated by melatonin and epinephrine, associating with variety and color specificity.

Comparative study of 17 β-estradiol on endocrine disruption and biotransformation in fingerlings and juveniles of Japanese sea bass Lateolabrax japonicus

Estrogenic contaminants in the aquatic environment are associated with endocrine disruption and feminization in fish. The effects of endocrine disrupting chemicals (EDCs) on fish have been well documented. However, very few studies have focused on 17 β-estradiol (E2) and its effects on endocrine system and biotransformation in a single prolonged exposure. This study investigated changes in the levels of serotonin (5-hydroxytryptamine) and acetyl choline esterase (AchE) in brain, cortisol in plasma and Ethoxyresorufin-O-deethylase (EROD) activity in gill of two different size groups (fingerlings and juveniles) of Japanese sea bass (Lateolabrax japonicus) upon exposure to two sub-lethal concentrations (200 and 2000 ng L(-1)) of E2 for 30 d. The results indicate that cortisol level and EROD activity significantly increased in both groups, whereas serotonin level increased in juveniles and decreased in fingerlings due to E2 exposure. The correlation analysis revealed that E2 significantly affected the endocrine and biotransformation systems in both age groups.

Estradiol-17β modulates dose-dependently hypothalamic tyrosine hydroxylase activity inhibited by α-methylparatyrosine in the catfish Heteropneustes fossilis

The brain is a target for organizational and activational effects of oestrogens synthesized de novo or transported from the peripheral organs. A neuroprotective role of oestrogens has been documented in a variety of vertebrates. In the present study in the catfish Heteropneustes fossilis, we have demonstrated that estradiol-17β (E(2)), the major circulating oestrogen at low dosages (0.05 and 0.1 μg/g body weight of fish for 3 days) stimulated hypothalamic tyrosine hydroxylase (TH) activity, and countered the negative effects of ovariectomy (3-week) or α-methylparatyrosine (α-MPT: 250 μg/g body weight, a competitive inhibitor of TH). In contrast, high dosages of E(2) (1 and 2 μg/g body weight of fish for 3 days) were inhibitory and further amplified the inhibitory effects of ovariectomy and α-MPT. The inhibiting role of E(2) was higher in gonad-active (prespawning) phase than gonad-inactive (resting phase) phase. The dual roles of E(2) may ensure a tight regulation of catecholaminergic activity, activating and inhibiting the system against wide fluctuations that are characteristic of seasonally breeding animals.

Intracerebroventricular Injections of Noradrenaline Affect Brain Energy Metabolism of Rainbow Trout

To assess the role of noradrenaline (NA) as a possible regulator of brain energy metabolism in teleost fish, the impact of increased noradrenaline levels within the brain on several parameters of energy metabolism was assessed in rainbow trout brain. Accordingly, two different doses of noradrenaline, producing increases in brain NA levels comparable to those occurring in several physiological processes in nature, were selected. In a subsequent set of three different experiments, fish were intracerebroventricularly injected with 1 microL 100 g(-1) body weight of Cortland saline alone (control) or containing NA (5 nmol NA and 10 nmol NA); after 30 min, brain and plasma samples were taken to assess changes in parameters of energy metabolism due to NA treatment. The results obtained clearly show dose-dependent changes in NA-treated fish in several parameters, including decreased glycogen and ATP levels, increased lactate and pyruvate levels, decreased fructose 1,6-bisphosphatase activity, and increased pyruvate kinase and lactate dehydrogenase activities. Altogether, the present experiments show for the first time in a teleost fish evidence supporting that increased noradrenaline levels in the brain elicit metabolic changes in the brain (enhanced glycogenolysis and glycolysis), resulting in an increased energy demand. These metabolic changes may be related to those occurring under several physiological conditions in nature such as hypoxia, in which increased energy demand and increased noradrenaline levels occur in the brain simultaneously.

Brain tyrosine hydroxylase in the catfish Heteropneustes fossilis: annual and circadian variations, and sex and regional differences in enzyme activity and some kinetic properties

Dynamics of tyrosine hydroxylase (TH) was studied in various brain regions and pituitary in relation to annual/seasonal and circadian variations in either sex of the catfish Heteropneustes fossilis. alpha-Methylparatyrosine inhibited TH activity significantly in a time-(in vivo study) and concentration-(in vitro study) dependent manner. The inhibition was higher in resting phase than preparatory phase and in females than males (time-course study). The apparent kinetic constant of inhibition (K(i)) varied both seasonally and regionally. The values were higher in resting phase and in the forebrain regions (telencephalon and hypothalamus) than medulla oblongata. No significant sex difference was noticed in the K(i) values in the same season. TH activity showed significant annual/seasonal variations with telencephalon and hypothalamus showing higher activity than medulla oblongata. The females showed significantly higher enzyme activity than males with a distinct activity peak in June (prespawning phase). Such an activity peak was apparently absent in males. TH activity showed significant circadian/diurnal variations, the highest activity was noticed at 12 h and the lowest at 24 h. The apparent Michaelis-Menten constant (K(m)) values (hypothalamic TH) for substrate (L-tyrosine) and cofactor (DMPH(4)) showed seasonal variations with the highest values in the resting phase, decreasing through preparatory and prespawning phases, to the lowest values in spawning phase. V(max) was the lowest in the resting phase and highest in the spawning phase. TH activity was low in the pituitary and could be detected in pooled samples from March (preparatory phase) to July (spawning phase). Activity showed significant variations, which could be correlated with the gonadosomatic index. The results show that TH activity could be positively correlated with the annual reproductive cycle. The enzyme activity could be also correlated with seasonal, sex, and regional variations in the apparent K(m) and V(max) values suggesting apparent differences in the affinity of the enzyme towards substrate and cofactor.

Effects of altered photoperiod and temperature, serotonin-affecting drugs, and melatonin on brain tyrosine hydroxylase activity in female catfish, Heteropneustes fossilis: a study correlating ovarian activity changes

Exposure of female catfish, Heteropneustes fossilis to 30-day regimes of long photoperiod (16L), elevated temperature (28 +/- 2 degrees C), or a combination of both stimulated brain tyrosine hydroxylase (TH) activity significantly over that of control fish held in natural conditions in gonad resting (10.5L:13.5D, 10 +/- 2 degrees C) and preparatory (12.5L:11.5D,18 +/- 2 degrees C) phases. The response was high in the combination group in both phases. The increase in TH activity was higher in forebrain regions (telencephalon and hypothalamus) than medulla oblongata. Exposure of the fish to short photoperiod (8L:16D) and total darkness decreased the enzyme activity significantly in both resting and preparatory phases regardless of the temperature. The inhibition was high in fish held under total darkness. Gonadosomatic index (GSI) was significantly elevated in long photoperiod and high temperature groups, alone or in combination, and decreased significantly in short photoperiod (only in preparatory phase) and total darkness groups. Administration of the serotonin precursor 5-hydroxytryptophan (5-HTP; 5mg/100g body weight [BW], three daily intraperitoneal [i.p.] injections prior to sacrificing) stimulated TH activity in fish held under long and normal photoperiods in both phases. Three daily injections of the serotonin blocker parachlorophenylalanine (p-CPA; 10mg/100g BW) and melatonin (75 microg/100g BW) prior to sacrificing inhibited brain TH activity significantly in both phases. GSI was significantly stimulated by 5-HTP, and inhibited by both p-CPA and melatonin injections. Changes in TH activity and GSI can be correlated and explained on the basis of previous reports on changes in catecholamine activity that modulates gonadotropin secretion in the catfish. Further, the photoperiod and temperature-induced changes in TH activity may be modulated by alterations in serotonergic activity.

Seasonal changes in beta-endorphin-like immunoreactivity in the olfactory system of the female catfish, Clarias batrachus (Linn)

In the olfactory system of the catfish Clarias batrachus, beta-endorphin-like immunoreactivity was seen in several olfactory receptor neurons (ORN) and their fiber projections extending caudally over the olfactory nerve to the olfactory bulb (OB). With beta-endorphin-like immunoreactivity as a cellular marker, the olfactory system in the female fish was investigated at different stages of its annual reproductive cycle. The reproductive cycle of the fish is divisible into four distinct phases: preparatory (February-April), prespawning (May-June), spawning (July-August), and postspawning (September-January). The gonosomatic index and the immunocytochemical profile of beta-endorphin-like immunoreactivity showed distinct changes as the fish progressed from one phase to another. In the preparatory phase, limited immunoreactivity was seen in the periphery of the bulb. However, the immunoreactivity showed a robust increase as the immunolabeled fibers extended progressively deeper into the bulb toward the mitral cell layer during the prespawning and spawning phases. Significant reduction in the immunoreactivity was noticed in the olfactory nerve layer of the fish in the postspawning phase. Several granule cells showed poor to moderate immunoreactivity during the spawning phase, although no immunoreactivity was seen in the inner cell layer during the rest of the year. The beta-endorphin-like immunoreactivity in the ORN also showed season-related changes, although these were less distinct. Whereas weak immunoreactivity confined to a few ORN was noticed in the fish collected in the preparatory phase, those in the prespawning phase showed conspicuous augmentation in immunoreactivity. During the spawning phase, the sensory layer of the olfactory epithelium showed reduced, homogenous immunoreactivity. In the postspawning phase, several ORN revealed distinct granular immunoreactivity, suggesting possibilities of de novo synthesis. These annual cyclic changes in the beta-endorphin-like immunoreactivity were consistently observed over a 30-month study period that spanned three consecutive spawning phases. The results suggest that the beta-endorphin-containing ORN, their fiber projections to the OB, and several granule cells in the inner cell layer may be involved in the processing of reproduction/reproductive behavior-related signals.

Changes in the pituitary metabolism of monoamines (dopamine, norepinephrine, and serotonin) in female and male rainbow trout (Oncorhynchus mykiss) during gonadal recrudescence

The dynamics of the levels and metabolism of dopamine, norepinephrine, and serotonin were studied in pituitaries of male and female rainbow trout at different stages of gonadal development. In female rainbow trout, the turnover of dopamine (calculated using the inhibitor of tyrosine hydroxylase alpha-methyl-p-tyrosine methyl-ester HCl), serotonin metabolism, and norepinephrine levels decreased in the advanced stage of exogenous vitellogenesis with respect to the initial stage. However, data obtained in males did not show changes in either serotonergic or noradrenergic metabolism during the last stages of gonadal development. However, an increase of dopaminergic turnover was noticed in the male fish at the end of spermiation. Finally, pituitary dopaminergic activity was significantly higher in immature (prepubescent stage) than in adult fish.

Annual and diurnal variations in, and effects of altered photoperiod and temperature, ovariectomy, and estradiol-17 beta replacement on catechol-O-methyltransferase level in brain regions of the catfish, Heteropneustes fossilis

The annual data show that catechol-O-methyltransferase (COMT) content increases with the progress of ovarian recrudescence in all the brain regions (telencephalon, hypothalamus, thalamus + tegmentum, and medulla oblongata) and declines after spawning to low values in quiescent phase. Diurnal variation in enzyme concentration with peak values at 24 hr was noticed in the hypothalamus throughout the reproductive cycle; in other brain regions, it was observed only in February and March. The stimulatory response of the enzyme to photoperiod and temperature alterations was differential and region-specific; an effect of photoperiod change was noticed only in the hypothalamus and was less in magnitude compared to the temperature effect. The response of the enzyme to ovariectomy (OVX) and E2 supplementation was region-specific (hypothalamus only), season-specific (prespawning phase), and varied:inhibitory at 3 and 4 weeks, stimulatory at 6-week of OVX and after 0.05, 0.1, 5, and 10 micrograms/g doses of E2, and none at week 2 and 5 of OVX and after 0.5 and 1 microgram/g doses of E2. The season-specific changes in hypothalamic COMT may be indicative of its involvement in catecholamine (and possibly catecholestrogen)-mediated neuroendocrine control of gonadotropin.

Influence of 17- alpha-estradiol on catecholamine secretion from the perfused rat adrenal gland

OBJECTIVES

It has been known that adrenal corticosteroids influence the expression of adrenomedullary catecholamine-synthetizing enzymes and also suppress the emission of axonal-like processes in cultured chromaffin cells. In the present study, it was attempted to investigate the effect of 17-alpha-estradiol on catecholamine (CA) secretion evoked by acetylcholine (ACh). DMPP. McN-A-343, excess K+ and Bay-K-8644 from the isolated perfused rat adrenal gland.

METHODS

Mature male Sprague-Dawley rats were anesthetized with ether. The adrenal gland was isolated by the method of WaKade. A cannula used for perfusion of the adrenal gland was inserted into the distal end of the renal vein. The adrenal gland, along with ligated blood vessels and the cannula, was carefully removed from the animal and placed on a platform of a leucite chamber.

RESULTS

The perfusion of 17-alpha-estradiol (1-100 uM) into an adrenal vein for 20 min produced relatively dose-dependent inhibition in CA secretion evoked by ACh (5.32 mM). DMPP (100 uM for 2 min). McN-A-343 (100 uM for 2 min) and Bay-K-8644 (10 uM for 4 min), while it did not affect the CA secretory effect of high K+ (56 mM). Also, in the presence of 17-beta-estradiol. CA secretion of ACh. DMPP and McN-A-343, without any effect on excess K(+)-evoked CA sectretion was depressed. However, in adrenal glands pre-loaded with 17-alpha-estradiol (10 uM) plus tamoxifen (2 uM), which is known to be a selective antagonist of estrogen receptors (for 20 min). CA secretory responses evoked by ACh. DMPP and McN-A-343 were condiderably recovered as compared to that of 17-alpha-estradiol only, but excess K(+)-induced CA secretion was not affected. However, pre-treatment with 17-alpha-estradiol in the presence of meclopramide (dopaminergic antagonist) did not affect the secretory effect of CA evoked by ACh. DMPP, McN-A-343 and high potassium.

CONCLUSIONS

These results suggest that 17-alpha-estradiol causes the marked inhibition of CA secretion evoked by cholinergic receptor stimulation, but not that by excess K+, indicating strongly that this effect may be mediated by inhibiting the influx of extracellular calcium into the rat adrenomedullary chromaffin cells through the activation of inhibitory estrogen receptors, and it also plays a modulatory role in regulating CA secretion.

Effects of photoperiod alterations on day-night variations in hypothalamic serotonin content and turnover, and monoamine oxidase activity in the female catfish, Heteropneustes fossilis (Bloch)

The effects of different photoperiod regimes, and total darkness on day-night variations in hypothalamic serotonin (5-HT) content and turnover index (TI), and monoamine oxidase (MAO) activity that occur exclusively during the gonadal preparatory phase (February-March) were investigated in female Heteropneustes fossilis. Exposure of the fish to long photoperiods (16L:8D; light between 06.00-22.00h, for 40 days elevated both the midphotophase and midscotophase values of 5-HT content and MAO, and abolished their day-night differences. The daily variations of 5-HT-TI was further intensified by the treatment. Under short photoperiods (4L:20D; light between 18.00-22.00h for 40 days), there was a significant decrease in both 5-HT content and TI, a reversal of the day-night variations of 5-HT content and MAO activity, and loss of the 5-HT-TI pattern. In fish maintained in total darkness the day-night variations were not found and there was a significant inhibition of 5-HT. Exposure of the fish to continuous light abolished the day-night variations of these correlates and elevated their values at both intervals. When the LD cycle was reversed, there was a corresponding shift in the day-night patterns. The gonadosomatic index (GSI) was significantly elevated in the long photoperiod and continuous illumination groups, significantly decreased in the short photoperiod and total darkness groups, and unchanged in the reversed LD cycle regime. The results indicate that the day-night variations of 5-HT and MAO are photoperiod-dependent and are controlled by the prevailing LD cycle during the gonadal preparatory phase of the annual reproductive cycle. The photoperiod effects on the gonadal activity may be mediated through the hypothalamic serotonergic system.

Central dopaminergic neurons in tilapia: effects of gonadectomy and hypothalamic lesion

The effects of gonadectomy, testosterone and estrogen on the dopamine (DA) neurons were examined by measuring the concentrations of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) in the brain and pituitary of male tilapia. The tuberal area and the pituitary had significantly high levels of DA and low levels of DOPAC, indicating the existence of a rich dopaminergic innervation in these areas. Gonadectomy and sex steroid replacement had no effect on DA and DOPAC levels. Preoptic lesions (14 days survival period) significantly increased DA levels of the pituitary, indicating a possible existence of a preoptico-hypophysial neural system that inhibits pituitary DA synthesis in tilapia. The lack of effect by preoptic (4 days survival period) and posterior hypothalamic lesions on the DA content of the pituitary indicates the absence of dopaminergic innervation of the pituitary by the preoptic and the posterior hypothalamus. Instead, the overall results do suggest the anterior periventricular area as a possible source of pituitary dopaminergic innervation.

Effects of estradiol on brain aminergic turnover of the female rainbow trout (Oncorhynchus mykiss) at the beginning of vitellogenesis

Brain serotonin and dopamine (DA) turnovers in the female rainbow trout were studied at the beginning of the vitellogenesis and related to blood estradiol (E2) levels; pituitary and plasma gonadotropin (GtH) were also assayed. Ovariectomy did not modify brain aminergic turnover. E2 replacement on ovariectomized fish increased hypothalamic DA turnover (increased DA and increased DA metabolites). E2 stimulated GtH synthesis (positive feedback) but did not enhance GtH release; hypothalamic E2-mediated aminergic inhibition upon release was suspected. Individual relations between blood E2 levels and catecholaminergic neurotransmitters were determined. A linear positive correlation (r = 0.82) was found for the hypothalamus, but not for the pituitary, the preoptic area, or the telencephalon. These data suggest that an activation of hypothalamic tyrosine hydroxylase (the limiting step of catecholamines synthesis) by E2 could develop as vitellogenesis proceeds.

Serotonin and dopamine turnover in the female rainbow trout (Oncorhynchus mykiss) brain and pituitary: changes during the annual reproductive cycle

Brain serotonin (5HT) and dopamine (DA) turnover were studied at various stages of the reproductive cycle of the female rainbow trout by simultaneous determination by HPLC of neurotransmitters and major related metabolites. An increase of 5HT turnover in telencephalon and hypothalamus and a decrease of DA turnover in pituitary and hypothalamus were observed during the periovulatory period. Some changes also occurred during vitellogenesis: decreased 5HT metabolite in telencephalon and preoptic area and increased DA content in preoptic area. These data suggest that physiological fluctuations of biogenic amines could be involved in both ovarian recrudescence and ovulation, with major effects on the hypothalamo-hypophysial complex during the periovulatory period.